JP7797481B2 - Silicon-carbon composites containing very low Z - Google Patents

Description

Embodiments of the present invention generally relate to silicon-carbon composites with properties that overcome the challenges of providing amorphous nano-sized silicon incorporated within porous carbon. The silicon-carbon composites are produced by impregnating amorphous nano-sized silicon into the pores of a porous scaffold via chemical vapor infiltration. Suitable porous scaffolds include, but are not limited to, porous carbon scaffolds, such as carbons having a pore volume containing micropores (less than 2 nm), mesopores (2-50 nm), and/or macropores (greater than 50 nm). Precursors for suitable carbon scaffolds include, but are not limited to, sugars and polyols, organic acids, phenolic compounds, crosslinkers, and amine compounds. Suitable composite materials include, but are not limited to, silicon materials. Precursors for silicon include, but are not limited to, silicon-containing gases, such as silane, higher silanes (such as di-, tri-, and/or tetrasilane), and/or chlorosilanes (such as mono-, di-, tri-, and tetrachlorosilane), and mixtures thereof. Chemical vapor infiltration (CVI) of silicon into the pores of the porous scaffold material is achieved by exposing the porous scaffold to a silicon-containing gas (e.g., silane) at elevated temperatures. The porous carbon scaffold can be particulate porous carbon.

A key achievement in this regard is achieving the desired morphology of silicon, i.e., amorphous nanosized silicon. Furthermore, another key achievement in this regard is achieving the impregnation of silicon into the pores of porous carbon. Such materials, such as silicon-carbon composites, have utility as anode materials for energy storage devices (e.g., lithium-ion batteries).

2. Description of the Related Art: CVI is a process in which a gaseous substrate is reacted within a porous scaffold material. This approach, which can be used to produce composite materials (e.g., silicon-carbon composites), involves decomposing a silicon-containing gas within a porous carbon scaffold at high temperatures. This approach can be used to manufacture a variety of composite materials, with particular interest in silicon-carbon (Si-C) composites. Such Si-C composites have utility, for example, as energy storage materials (e.g., anode materials in lithium-ion batteries (LIBs)). LIBs have the potential to replace many applications used today. For example, today's automotive lead-acid batteries are unsuitable for next-generation all-electric and hybrid electric vehicles due to the irreversible and stable formation of sulfates during discharge. Lithium-ion batteries could replace today's lead-based systems due to their capacity and other considerations.

To this end, there has been strong interest in developing new LIB anode materials, especially silicon, which has a gravimetric capacity ten times greater than that of conventional graphite. However, silicon exhibits large volume changes during cycling, resulting in electrode degradation and destabilization of the solid-electrolyte interface (SEI). The most common improvement approach is to reduce the grain size of silicon, either as individual particles or within the matrix (e.g., D _V < 150 nm, e.g., D _V < 100 nm, e.g., D V < ₅₀ nm, e.g., D _V < 20 nm, e.g., D _{V < 10} nm, e.g., D _V < 5 nm, e.g., D _V < 2 nm). To date, nanoscale silicon fabrication techniques have involved high-temperature reduction of silicon oxide, extensive grain reduction, multiple toxic etching steps, and/or other costly processes. Similarly, common matrix approaches involve expensive materials such as graphene or nanographite and/or require complex processes and coatings.

Non-graphitizable (hard) carbons are known from the scientific literature to be useful as LIB anode materials (Liu Y, Xue JS, Zheng T, Dahn JR. Carbon 1996, 34:193-200; Wu YP, Fang SB, Jiang YY. 1998, 75:201-206; Buiel E, Dahn JR. Electrochim Acta 1999, 45:121-130). The basis for this improved performance stems from the disordered nature of the graphene layers, which allows Li ions to intercalate on both sides of the graphene, theoretically doubling the stoichiometric Li content relative to crystalline graphite. Furthermore, in contrast to graphite, where lithiation proceeds only parallel to the graphene stack plane, the disordered structure allows Li ions to intercalate isotropically, thereby increasing the rated capacity of the material. Despite these desirable electrochemical properties, amorphous carbon has not seen widespread deployment in commercial Li-ion batteries, primarily due to its low FCE and low bulk density (<1 g/cc). Instead, amorphous carbon is more commonly used as a low-mass additive and coating for the battery's other active material components to improve electrical conductivity and inhibit surface-side reactions.

In recent years, amorphous carbon as a LIB battery material has attracted considerable attention as a coating for silicon anode materials. This silicon-carbon core-shell structure not only improves electrical conductivity but also mitigates expansion during silicon lithiation, thereby stabilizing cycling stability and minimizing problems related to particle pulverization, segregation, and SEI integrity (Jung, Y, Lee K, Oh, S. Electrochim Acta 2007 52:7061-7067; Zuo P, Yin G, Ma Y. Electrochim Acta 2007 52:4878-4883; Ng SH, Wang J, Wexler D, Chew SY, Liu HK. J Phys Chem C 2007 111:11131-11138). Problems associated with this method include the lack of suitable silicon starting materials suitable for the coating process and the inherent lack of engineered voids within the carbon-coated silicon core-shell composite particles to accommodate the expansion of silicon during lithiation. This inevitably leads to a lack of cycling stability due to the destruction of the core-shell structure and SEI layer. (Beattie SD, Larcher D, Morcrette M, Simon B, Tarascon J-M. J Electrochem Soc 2008 155:A158-A163)

U.S. Patent Application No. 7,723,262 U.S. Patent Application No. 8,293,818 U.S. Patent Application No. 8,404,384 U.S. Patent Application No. 8,654,507 U.S. Patent Application No. 8,916,296 U.S. Patent Application No. 9,269,502 U.S. Patent Application No. 10,590,277 US Patent Application Publication No. 2016/745197 U.S. Provisional Patent Application No. 63/075566 US Patent Application Publication No. 2017/336104 US Patent Application Publication No. 2017/336085

Liu Y, Xue, JS, Zheng T, Dahn, JR. Carbon 1996, 34:193-200; Wu, YP, Fang, SB, Jiang, YY. 1998, 75:201-206 Buiel E, Dahn JR. Electrochim Acta 1999 45:121-130 Jung, Y, Lee K, Oh, S. Electrochim Acta 2007 52:7061-706 Zuo P, Yin G, Ma Y.. Electrochim Acta 2007 52:4878-4883 Ng SH, Wang J, Wexler D, Chew SY, Liu HK. J Phys Chem C 2007 111:11131-11138 Beattie SD, Larcher D, Morcrette M, Simon B, Tarascon, J-M. J Electrochem Soc 2008 155:A158-A163 The Chemistry and Applications of Metal-Organic Frameworks, Hiroyasu Furukawa et al. Science 341, (2013); DOI: 10.1126/science.1230444

An alternative to the core-shell structure is one in which amorphous nano-sized silicon is uniformly distributed within the void spaces of a porous carbon scaffold. Porous carbon has desirable properties:
(i) the porosity of the carbon provides void volume to accommodate the expansion of silicon during lithiation, thus reducing the net composite particle expansion at the electrode level;
(ii) the disordered graphene network enhances electrical conductivity to silicon, thus enabling faster charge/discharge rates; and
(iii) the nano-porous structure acts as a template for the synthesis of silicon, thus defining its size, distribution, and morphology;
Give.

To this end, the desired inverse hierarchical structure can be achieved by using CVI, where silicon-containing gases can fully infiltrate the nanoporous carbon and decompose into nanosized silicon there. The CVI approach offers several advantages in terms of silicon structure. One advantage is that the nanoporous carbon provides nucleation sites for silicon growth while defining maximum particle shape and size. Confining silicon growth within the nanoporous structure reduces susceptibility to cracking or pulverization and reduces contacts caused by expansion. Furthermore, this structure promotes nanosized silicon to remain in the amorphous phase. This property, especially in combination with the proximity of silicon within the conductive carbon scaffold, offers the opportunity for high charge/discharge rates. This system provides a fast-acting, solid-state lithium diffusion pathway for lithium ions, which directly delivers lithium ions to the nanoscale silicon interface. Another advantage of silicon provided by CVI within the carbon scaffold is the inhibition of the formation of the undesired crystallized Li ₁₅ Si ₄ layer. Yet another advantage is that the CVI process provides voids within the particles.

Thermogravimetric analysis (TGA) may be used to measure the relative amount of silicon impregnated into the pores of porous carbon. TGA can be used to assess the fraction of silicon present within the pores of the porous carbon relative to the total silicon present, i.e., the sum of silicon within the pores and on the particle surface. When a silicon-carbon composite is heated under air, the sample exhibits a mass increase between 300°C and 500°C, reflecting the onset of oxidation of silicon to _SiO2 . The sample then exhibits a mass loss as the carbon burns out. The sample then exhibits a mass increase, reflecting the resumption of the conversion of silicon to _SiO2 , which increases until silicon oxidation is complete, i.e., toward an asymptotic value of 1100°C. For the purposes of this analysis, the minimum mass recorded for the sample heated from 800°C to 1100°C is assumed to represent the point at which carbon combustion is complete. Any further mass increase beyond this point corresponds to the oxidation of silicon to _SiO2 , and the total mass at the end of oxidation is _SiO2 . Thus, the percentage of partially or non-oxidized silicon after carbon burnout relative to the total weight of silicon is calculated using the following formula:
Z=1.875×[(M1100-M)/M1100]×100%
where M is the mass of the sample after oxidation is complete at 1100°C, and M is the minimum mass recorded for the sample heated between 800°C and 1100°C.
It can be calculated by:

Without being bound by theory, the temperature at which silicon oxidizes under TGA conditions is related to the length scale of the oxide coating on the silicon due to the diffusion of oxygen atoms through the oxide layer. Thus, silicon present within the carbon pores will oxidize at a lower temperature than silicon deposits on the particle surface, due to the necessarily thinner coating at the particle surface. Thus, the calculation of Z can be used to quantitatively assess the fraction of silicon not impregnated within the pores of a porous carbon scaffold.

BRIEF SUMMARY Silicon-carbon composite materials and related processes are disclosed that solve the problem of providing amorphous nanosized silicon impregnated within porous carbon. Compared to other inferior materials and processes described in the prior art, the materials and processes disclosed herein find utility in a variety of applications, including energy storage devices such as lithium-ion batteries.

An embodiment is a composite containing group 14 elements such as silicon and carbon, with the preferred mode: silicon incorporated within amorphous, nano-sized, and porous carbon;
The present invention provides novel anode materials for lithium-silicon batteries (including composites containing Group 14 elements such as silicon and carbon), comprising a composite comprising: (a) a silicon-carbon composite (a) containing a group 14 element (e.g., silicon-carbon composite) (B) (c) (d) (e) (e) (f) (g) (g) (h) (i) (i) (i) (i) (i) (ii) (ii) (iii) (iii) (iv) (v ... Precursors for silicon include, but are not limited to, silicon-containing gases, such as silane, higher silanes (such as di-, tri-, and/or tetrasilane), and/or chlorosilanes (such as mono-, di-, tri-, and tetrachlorosilane), and mixtures thereof. CVI, which produces silicon within the pores of a porous scaffold material, is achieved by exposing the porous scaffold to a silicon-containing gas (e.g., silane) at elevated temperatures. The porous carbon scaffold can be particulate porous carbon.

A key achievement in this regard is achieving the desired morphology of silicon, i.e., amorphous nanosized silicon. Yet another key achievement is achieving silicon impregnation into the pores of porous carbon. Such materials, such as silicon-carbon composites, have utility as anode materials for energy storage devices (e.g., lithium-ion batteries).

Relationship between Z and average Coulombic efficiency for various silicon-carbon composites. Differential capacity vs. voltage plot for silicon-carbon composite 3 at 2 cycles using a half cell. Differential capacity vs. voltage plot for silicon-carbon composite 3 at cycles 2-5 using a half cell. Plot of dQ/dV vs V for various silicon-carbon composites. Example of calculation of φ in silicon-carbon composite 3. Z vs φ plot for various silicon-carbon composites.

DETAILED DESCRIPTION In the following description, specific details are set forth to provide a thorough understanding of various embodiments. However, those skilled in the art will understand that the present invention may be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless otherwise noted, in the following specification and claims, the term "comprise" and its derivatives, such as "comprises" and "comprising," are to be interpreted in an open and inclusive sense, i.e., "including, but not limited to." Furthermore, headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention.

Throughout this specification, a reference to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment. Moreover, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Also, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless otherwise indicated. Please also note that the term "or" is generally used to include "and/or" unless otherwise indicated.

A. Porous Scaffold Materials
For purposes of embodiments of the present invention, a porous scaffold impregnated with silicon may be used. In this aspect, the porous scaffold can comprise a variety of materials. In some embodiments, the porous scaffold comprises primarily carbon, such as hard carbon. Other carbon allotropes, such as graphite, amorphous carbon, diamond, C60, carbon nanotubes (e.g., single-walled and/or multi-walled), graphene, and/or carbon fibers, are also contemplated in other embodiments. The introduction of pores into carbon materials can be achieved by various techniques. For example, pores in carbon materials can be achieved by the modulation of polymer precursors and/or processing conditions during the fabrication of the porous carbon materials, as described in more detail in the following sections.

In other embodiments, the porous scaffold comprises a polymeric material. For this purpose, various embodiments contemplate a wide range of polymers having utility, including, but not limited to, inorganic polymers, organic polymers, and addition polymers. Inorganic polymers of the present invention include, but are not limited to, silicon-silicon homochain polymers, such as polysilanes, silicon carbides, polygermanes, and polystannanes. Further examples of inorganic polymers include, but are not limited to, heterochain polymers, such as polyborazylenes, polysiloxanes, such as polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), and polydiphenylsiloxane, polysilazanes, such as perhydridopolysilazane (PHPS), polyphosphazenes, and poly(dichlorophosphazenes), polyphosphates, polythiazyls, and polysulfides. Examples of organic polymers include, but are not limited to, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon, nylon 6, nylon 6,6, Teflon (polytetrafluoroethylene), thermoplastic polyurethane (TPU), polyurea, polylactic acid, polyglycolide, and combinations thereof, phenolic resins, polyamides, polyaramids, polyethylene terephthalate, polychloroprene, polyacrylonitrile, polyaniline, polyimides, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PDOT:PSS), and other organic polymers known in the art. Organic polymers can be synthetic or natural. In some embodiments, the polymer is a polysaccharide, such as starch, cellulose, cellobiose, amylose, amylopectin, gum arabic, lignin, and the like. In some embodiments, the polysaccharides are derived from the caramelization of monosaccharides or oligosaccharides, such as fructose, glucose, sucrose, maltose, and raffinose.

In certain embodiments, the porous scaffold polymer material includes a coordination polymer. Coordination polymers in this embodiment include, but are not limited to, metal-organic frameworks (MOFs). Techniques for producing MOFs, as well as exemplary MOF species, are known in the art and are described in the following literature (The Chemistry and Applications of Metal-Organic Frameworks, Hiroyasu Furukawa et al. Science 341, (2013); DOI: 10.1126/science.1230444). Examples of MOFs in the present invention include, but are not limited to, Basolite™ materials and zeolitic imidazolate frameworks (ZIFs).

With the vast number of polymers envisioned as having the potential to provide porous matrices, various processing approaches are envisioned in various embodiments for achieving the above-mentioned pores. In this regard, numerous general methods exist for imparting pores to various materials, including those known in the art (e.g., emulsification, micelle formation, gasification, dissolution followed by solvent removal (e.g., freeze-drying), axial compaction and sintering, gravity sintering, powder rolling and sintering, metal spraying, metal coating and sintering, metal injection molding and sintering, etc.). Other approaches to creating porous polymeric materials are also envisioned, including, for example, the creation of porous gels, such as freeze-dried gels and aerogels.

In certain embodiments, the porous scaffold material comprises a porous ceramic material. In certain embodiments, the porous scaffold material comprises a porous ceramic foam. In this aspect, general methods for imparting pores to ceramic materials are varied and include, but are not limited to, fabrication of pores as known in the art. In this aspect, general methods and materials suitable for containing porous ceramic include, but are not limited to, porous aluminum oxide, porous zirconia-toughened alumina, porous partially stabilized zirconia, porous alumina, porous sintered silicon carbide, sintered silicon nitride, porous cordierite, porous zirconium oxide, and clay-bonded silicon carbide.

In certain embodiments, the porous scaffold comprises porous silica or other oxygen-containing silicon materials. The preparation of sol-gels and other silicon gels, including porous silica materials, is known in the art.

In certain embodiments, the porous material comprises a porous metal. Suitable metals in this regard include, but are not limited to, porous aluminum, porous steel, porous nickel, porous Inconcel, porous Hastelloy, porous titanium, porous copper, porous brass, porous gold, porous silver, porous germanium, and other metals known in the art that can form porous structures. In some embodiments, the porous scaffold material comprises a porous metal foam. Relevant metal types and manufacturing methods are known in the art. Such methods include, but are not limited to, casting (including foaming, infiltration, and lost-foam casting), sublimation (chemical and physical), gas eutectic formation, powder metallurgy techniques (such as powder sintering, compaction in the presence of foaming agents, and fiber metallurgy).

B. Porous Carbon Scaffolds Methods for preparing porous carbon materials from polymer precursors are known in the art. For example, methods for preparing carbon materials are described in U.S. Patent Application Nos. 7,723,262, 8,293,818, 8,404,384, 8,654,507, 8,916,296, 9,269,502, 10,590,277, and U.S. Patent Application Publication No. 2016/745197, the disclosures of all of which are incorporated herein by reference in their entireties for all purposes.

Therefore, in one embodiment, the present disclosure provides a method for preparing any of the carbon materials or polymer gels described above. The carbon material may be synthesized by pyrolysis of any single precursor, such as a sugar material (sucrose, fructose, glucose, dextrin, maltodextrin, starch, amylopectin, amylose, lignin, gum arabic, and other sugars known in the art, and combinations thereof). Alternatively, the carbon material may be synthesized by pyrolysis of a composite resin. The composite resin is formed, for example, by a sol-gel process using a polymer precursor in a suitable solvent with a crosslinker. The polymer precursor may be, for example, phenol, resorcinol, bisphenol A, urea, melamine, and other suitable compounds known in the art, and combinations thereof. The suitable solvent may be, for example, water, ethanol, methanol, and other solvents known in the art, and combinations thereof. Examples of crosslinking agents include formaldehyde, hexamethylenetetramine, furfural, and other crosslinking agents known in the art, as well as combinations thereof. The resins may be acidic or basic and may contain a catalyst. The catalyst may be volatile or nonvolatile. Pyrolysis temperatures and reaction times may vary as known in the art.

In some embodiments, the method involves preparing a polymer gel by a sol-gel process, a condensation process, or a crosslinking process (where the process involves a monomer precursor and a crosslinker, two polymers in a system and a crosslinker, or a single polymer and a crosslinker), followed by pyrolysis of the polymer gel. The polymer gel may be dried (e.g., lyophilized) prior to pyrolysis; however, drying is not necessary.

Where the polymerization reaction produces a resin/polymer with the required carbon backbone, the carbon properties of interest can be derived from a variety of polymer chemistries. Various polymer species include novolacs, resoles, acrylates, styrenes, urethanes, rubbers (neoprene, styrene-butadiene, etc.), nylons, etc. Preparation of any of the above polymer resins can occur through a variety of processes (e.g., sol-gel, emulsion/suspension, solid-state, liquid-state, melt-state, etc.) involving polymerization and crosslinking processes.

In some embodiments, the electrochemical modifier is introduced into the material as a polymer. For example, an organic or carbon-containing polymer (e.g., RF) is copolymerized with the polymer and contains the electrochemical modifier. In one embodiment, the electrochemical modifier-containing polymer contains silicon. In one embodiment, the polymer is tetraethylorthosilane (TEOS). In one embodiment, a TEOS solution is added to the RF solution before or during polymerization. In other embodiments, the polymer is a polysilane having side groups. In some examples, these side groups are methyl groups, and in other examples, these side groups are phenyl groups. In some examples, the side chains contain a Group 14 element (silicon, germanium, tin, or lead). In other examples, the side chains contain a Group 13 element (boron, aluminum, boron, gallium, indium). In other examples, the side chains contain a Group 15 element (nitrogen, phosphorus, arsenic). In other examples, the side chains contain a Group 16 element (oxygen, sulfur, selenium).

In other embodiments, the electrochemical modifier comprises a silole. In some examples, it is a phenol-silole or a silafluorene. In other examples, it is a poly-silole or a poly-silafluorene. In some examples, the silicon is replaced with germanium (germole or germafluorene), tin (stannole or stannafluorene), nitrogen (carbazole), or phosphorus (phosphole, phosphafluorene). In all examples, the heteroatom-containing material can be a small molecule, oligomer, or polymer. The phosphorus atom may or may not be bonded to oxygen.

In some embodiments, the reactant comprises phosphorus. In certain other embodiments, the phosphorus is in the form of phosphate. In certain other embodiments, the phosphorus can be in the form of a salt, the anion of which comprises one or more phosphate, phosphorous, phosphide, hydrogen phosphate, dihydrogen phosphate, hexafluorophosphate, hypophosphorous acid, polyphosphate, or pyrophosphate ions, or a combination thereof. In other embodiments, the phosphorus can be in the form of a salt, the cation of which comprises one or more phosphonium ions. Non-phosphate salts comprising any of the anions or cation pairs of the above embodiments can be selected from those known and described in the art. In this aspect, exemplary cations that pair with the phosphate-containing anions include, but are not limited to, ammonium, tetraethylammonium, and tetramethylammonium ions. In this aspect, exemplary anions that pair with the phosphate-containing cations include, but are not limited to, carbonate, dicarbonate, and acetate ions.

In some embodiments, the catalyst comprises a volatile base catalyst. For example, in one embodiment, the volatile base catalyst comprises ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium hydroxide, or a combination thereof. In yet another embodiment, the volatile base catalyst is ammonium carbonate. In another embodiment, the volatile base catalyst is ammonium acetate.

In yet other embodiments, the method includes mixing an acid. In certain embodiments, the acid is a solid at room temperature and pressure. In some embodiments, the acid is a liquid at room temperature and pressure. In some embodiments, the acid is a liquid at room temperature and pressure and does not dissolve one or more other polymer precursors.

The acid may be selected from a number of acids suitable for the polymerization process. For example, in some embodiments, the acid is acetic acid, and in other embodiments, the acid is oxalic acid. In further embodiments, the acid is mixed with the first or second solvent in an acid to solvent ratio of 99:1, 90:10, 75:25, 50:50, 25:75, 20:80, 10:90, or 1:90. In other embodiments, the acid is acetic acid and the first or second solvent is water. In other embodiments, the acidification is achieved by the addition of a solid acid.

The total amount of acid in the mixture can be varied to alter the properties of the final product. In some embodiments, the acid is present in the mixture at about 1% to about 50% by weight. In other embodiments, the acid is present at about 5% to about 25% by weight. In other embodiments, the acid is present at about 10% to about 20% by weight (e.g., about 10%, about 15%, about 20%).

In certain embodiments, the polymer precursor components are blended together and then maintained at a temperature and time sufficient to complete polymerization. One or more of the polymer precursor components may have a particle size of less than 20 mm (e.g., less than 10 mm, e.g., less than 7 mm, e.g., less than 5 mm, e.g., less than 2 mm, e.g., less than 1 mm, e.g., less than 100 microns, e.g., less than 10 microns). In some embodiments, the particle size of one or more of the polymer precursor components decreases during the blending process.

Blending of one or more polymer precursor components in the absence of a solvent can be accomplished by methods known in the art, such as ball milling, jet milling, Fritsch milling, planetary mixing, and other mixing methods involving mixing or blending solid particles while controlling process conditions (e.g., temperature). The mixing or blending process can be accomplished before, during, and/or after (or a combination of these) incubation at the reaction temperature.

Reaction parameters include aging the blended mixture at room temperature for a time sufficient to allow the one or more polymer precursors to react with each other and form a polymer. In this regard, suitable aging temperatures range from about room temperature to a temperature at or near the melting point of the one or more polymer precursors. In some embodiments, suitable aging temperatures range from about room temperature to a temperature at or near the glass transition temperature of the one or more polymer precursors. For example, in some embodiments, the solvent-free mixture is aged at about 20°C to about 600°C (e.g., about 20°C to about 500°C, e.g., about 20°C to about 400°C, e.g., about 20°C to about 300°C, e.g., about 20°C to about 200°C). In certain embodiments, the solvent-free mixture is aged at about 50°C to about 250°C.

The reaction time is generally sufficient to allow the polymer precursors to react and produce the polymer; for example, the mixture may be aged anywhere from 1 hour to 48 hours, or more or less depending on the desired results. Typical embodiments include aging for about 2 hours to about 48 hours, such as about 12 hours in some embodiments, and about 4 to 8 hours (e.g., 6 hours) in other embodiments.

In certain embodiments, an electrochemical modifier is introduced during the polymerization process described above. For example, in some embodiments, an electrochemical modifier in the form of metal particles, metal paste, metal salt, metal oxide, or molten metal may be dissolved or suspended in the mixture from which the gel resin is formed.

Exemplary electrochemical modifiers for producing composite materials may fall into one or more chemical classes. In some embodiments, the electrochemical modifier is a lithium salt, including, but not limited to, lithium fluoride, lithium chloride, lithium carbonate, lithium hydroxide, lithium benzoate, lithium bromide, lithium formate, lithium hexafluorophosphate, lithium iodate, lithium iodide, lithium perchlorate, lithium phosphate, lithium sulfate, lithium tetraborate, lithium tetrafluoroborate, and combinations thereof.

In certain embodiments, the electrochemical modifier comprises a metal, and typical species include, but are not limited to, aluminum isopropoxide, manganese acetate, nickel acetate, iron acetate, tin chloride, silicon chloride, and combinations thereof. In certain embodiments, the electrochemical modifier is a phosphate compound, and typical species include, but are not limited to, phytic acid, phosphoric acid, ammonium dihydrogen phosphate, and combinations thereof. In certain embodiments, the electrochemical modifier comprises silicon, and typical species include, but are not limited to, silicon powder, silicon nanotubes, polycrystalline silicon, nanocrystalline silicon, amorphous silicon, porous silicon, nanosized silicon, nanofeatured silicon, nanosized and nanofeatured silicon, silicyne, black silicon, and combinations thereof.

Electrochemical modifiers can be coupled to various polymer systems either by physical mixing or chemical reaction with latent (or secondary) polymer functional groups. Examples of latent polymer functional groups include, but are not limited to, epoxide groups, unsaturation (double or triple bonds), acid groups, alcohol groups, and base groups. Crosslinking with latent functional groups can occur through reaction with heteroatoms (e.g., vulcanization reactions with sulfur and acid/base/ring-opening reactions with phosphoric acid), reaction with organic acids or bases (as described above), coordination to transition metals (e.g., titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, silver, gold, etc.), or ring-opening or ring-closing reactions (e.g., rotaxanes, spiro compounds, etc.).

Electrochemical modifiers can also be added to polymer systems by physical blending. Physical blending can include, but is not limited to, melt blending of polymers and/or copolymers, inclusion of discrete particles, vapor-phase chemical deposition of the electrochemical modifier, and co-precipitation of the electrochemical modifier and the base polymer material.

In some examples, the electrochemical modifier may be added via a metal salt solid, solution, or suspension. The metal salt solid, solution, or suspension may contain an acid and/or alcohol to enhance the solubility of the metal salt. In other further variations, the polymer gel (either before or after any drying step) is contacted with a paste containing the electrochemical modifier. In yet other variations, the polymer gel (either before or after any drying step) is contacted with a metal or metal oxide containing the desired electrochemical modifier.

In addition to the electrochemical modifiers exemplified above, the composite material may also include one or more additional forms (i.e., allotropes) of carbon. In this regard, the inclusion of various allotropes of carbon (e.g., graphite, amorphous carbon, conductive carbon, carbon black, diamond, C60, carbon nanotubes (e.g., single-walled and/or multi-walled), graphene, and/or carbon fiber, etc.) in the composite material has been found to be effective for optimizing the electrochemical performance of the composite material. Various allotropes of carbon can be introduced into the carbon material at any stage of the preparation process described herein (e.g., during the dissolution phase, gelation phase, curing phase, pyrolysis phase, milling phase, or post-milling). In some embodiments, a second carbon foam is introduced into the composite material by adding the second carbon foam during or before polymerization of the polymer gel, as described in more detail herein. The polymerized polymer gel containing the second carbon foam is processed according to the general methods described herein to obtain a carbon material containing the second allotrope of carbon.

In a preferred embodiment, carbon is produced from precursors that require little or no solvent for processing. The structure of polymer precursors suitable for use in low-solvent or essentially solvent-free reaction mixtures is not particularly limited, provided that the polymer precursors can be reacted with other polymer precursors or a second polymer precursor to produce a polymer. Polymer precursors include amine-containing compounds, alcohol-containing compounds, and carbonyl-containing compounds. For example, in some embodiments, the polymer precursor is selected from alcohols, phenols, polyalcohols, sugars, alkylamines, aromatic amines, aldehydes, ketones, carboxylic acids, esters, ureas, acid halides, and isocyanates.

In one embodiment using a low-solvent or essentially solvent-free reaction mixture, the method includes the use of first and second polymer precursors, and in some embodiments, one of the first or second polymer precursors is a carbonyl-containing compound and the other is an alcohol-containing compound. In some embodiments, the first polymer precursor is a phenolic compound and the second polymer precursor is an aldehyde compound (e.g., formaldehyde). In one embodiment, the phenolic compound of the method is phenol, resorcinol, catechol, hydroquinone, phloroglucinol, or a combination thereof; and the aldehyde compound is formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, cinnamaldehyde, or a combination thereof. In a further embodiment, the phenolic compound is resorcinol, phenol, or a combination thereof, and the aldehyde compound is formaldehyde. In further embodiments, the phenolic compound is resorcinol and the aldehyde compound is formaldehyde. In some embodiments, the polymer precursors are an alcohol and a carbonyl compound (e.g., resorcinol and an aldehyde), which are present in a ratio of about 0.5:1.0, respectively.

Suitable polymer precursor materials for the low-solvent or essentially solvent-free reaction mixtures described herein include (a) alcohols, phenolic compounds, and other mono- or polyhydroxy compounds, and (b) aldehydes, ketones, and combinations thereof. Exemplary alcohols in this embodiment include linear and branched, saturated, and unsaturated alcohols. Suitable phenolic compounds include polyhydroxybenzenes (such as dihydroxy or trihydroxybenzenes). Exemplary polyhydroxybenzenes include resorcinol (i.e., 1,3-dihydroxybenzene), catechol, hydroquinone, and phloroglucinol. Other suitable compounds in this regard are bisphenols (e.g., bisphenol A). Mixtures of two or more polyhydroxybenzenes can also be used. Phenols (monohydroxybenzenes) can also be used. Exemplary polyhydroxy compounds include sugars (e.g., glucose, sucrose, fructose, chitin, and other polyols such as mannitol). Aldehydes in this embodiment include the following:
straight-chain saturated aldehydes, such as methanal (formaldehyde), ethanal (acetaldehyde), propanal (propionaldehyde), butanal (butyraldehyde), etc.;
Straight-chain unsaturated aldehydes, such as ethenone and other ketenes, as well as 2-propenal (acrylaldehyde), 2-butenal (crotonaldehyde), and 3-butenal;
Branched-chain saturated and unsaturated aldehydes; and aromatic type aldehydes such as benzaldehyde, salicylic aldehyde, hydrocinnamaldehyde, etc. Suitable ketones include:
linear saturated ketones, such as propanone and 2-butanone;
straight-chain unsaturated ketones, such as propenone, 2-butenone, and 3-butenone (methyl vinyl ketone);
branched chain saturated and unsaturated ketones; and aromatic type ketones, such as methyl benzyl ketone (phenylacetone), ethyl benzyl ketone, etc. The polymer precursor material may also be a combination of the precursors listed above.

In some embodiments, one polymer precursor in the solvent-poor or essentially solvent-free reaction mixture is an alcohol-containing species, and the other polymer precursor is a carbonyl-containing species. The relative amounts of alcohol-containing species (e.g., alcohols, phenolic compounds, and mono- or poly-hydroxy compounds, or combinations thereof) reacted with the carbonyl-containing species (e.g., aldehydes, ketones, or combinations thereof) can vary substantially. In some embodiments, the ratio of alcohol-containing species to aldehyde species is selected so that the total moles of reactive alcohol groups in the alcohol-containing species are approximately equal to the total moles of reactive carbonyl groups in the aldehyde-containing species. Similarly, the ratio of alcohol-containing species to ketone species may be selected so that the total moles of reactive alcohol groups in the alcohol-containing species are approximately equal to the total moles of reactive carbonyl groups in the ketone-containing species. The same general 1:1 molar ratio remains true when the carbonyl-containing species includes a combination of aldehyde and ketone species.

In other embodiments, the polymer precursor in the low-solvent or essentially solvent-free reaction mixture is a urea or amine-containing compound. For example, in some embodiments, the polymer precursor is urea, melamine, hexamethylenetetramine (HMT), or a combination thereof. Other embodiments include polymer precursors selected from isocyanates or other activated carbonyl compounds (e.g., acid halides, etc.).

Some embodiments of the disclosed method involve the preparation of solvent-poor or solvent-free polymer gels (and carbon materials) containing electrochemical modifiers. Examples of such electrochemical modifiers include, but are not limited to, nitrogen, silicon, and sulfur. In other embodiments, the electrochemical modifiers include fluorine, iron, tin, silicon, nickel, aluminum, zinc, or manganese. The electrochemical modifiers can be included at any stage during the preparation process. For example, some electrochemical modifiers are mixed with the mixture, the polymer phase, or a subsequent phase.

Blending of one or more polymer precursor components in the absence of a solvent can be accomplished by methods described in the art, such as ball milling, jet milling, Fritsch milling, planetary mixing, and other mixing methods involving mixing or blending solid particles while controlling process conditions (e.g., temperature). The mixing or blending process can be accomplished before, during, and/or after (or a combination of these) incubation at the reaction temperature.

Reaction parameters include aging the blend mixture at a temperature and for a time sufficient to cause one or more polymer precursors to react with one another and form a polymer. In this regard, suitable aging temperatures range from about room temperature to a temperature at or near the melting point of one or more polymer precursors. In some embodiments, suitable aging temperatures range from about room temperature to a temperature at or near the glass transition temperature of one or more polymer precursors. For example, in some embodiments, the solvent-free mixture is aged at about 20°C to about 600°C, e.g., about 20°C to about 500°C, e.g., about 20°C to about 400°C, e.g., about 20°C to about 300°C, e.g., about 20°C to about 200°C. In certain embodiments, the solvent-free mixture is aged at about 50°C to 250°C.

Porous carbon materials can be achieved by pyrolysis of polymers produced from the precursor materials described above. In some embodiments, the porous carbon material comprises amorphous activated carbon, which is produced by pyrolysis, physical or chemical activation, or a combination thereof, either in a single process step or in a series of process steps.

The pyrolysis temperature and treatment time can vary, for example, from 1 minute to 10 minutes, 10 minutes to 30 minutes, 30 minutes to 1 hour, 1 hour to 2 hours, 2 hours to 4 hours, 4 hours to 24 hours, etc. The temperature can also vary, for example, pyrolysis temperatures can be from 200°C to 300°C, 250°C to 350°C, 350°C to 450°C, 450°C to 550°C, 540°C to 650°C, 650°C to 750°C, 750°C to 850°C, 850°C to 950°C, 950°C to 1050°C, 1050°C to 1150°C, 1150°C to 1250°C, etc. Pyrolysis can be accomplished in an inert gas (e.g., nitrogen or argon).

In some embodiments, alternative gases are used to achieve further carbon activation. In certain embodiments, pyrolysis and activation are performed simultaneously. Suitable gases for achieving carbon activation include, but are not limited to, carbon dioxide, carbon monoxide, water (water vapor), air, oxygen, and further combinations thereof. Activation temperatures and treatment times can vary, including, for example, treatment times of 1 minute to 10 minutes, 10 minutes to 30 minutes, 30 minutes to 1 hour, 1 hour to 2 hours, 2 hours to 4 hours, 4 hours to 24 hours, etc. The temperature can vary, for example, pyrolysis temperatures can be 200°C to 300°C, 250°C to 350°C, 350°C to 450°C, 450°C to 550°C, 540°C to 650°C, 650°C to 750°C, 750°C to 850°C, 850°C to 950°C, 950°C to 1050°C, 1050°C to 1150°C, 1150°C to 1250°C, etc.

The particle size of the carbon may be reduced before pyrolysis, and/or after pyrolysis, and/or after activation. Particle size reduction can be achieved by various methods known in the art, such as jet milling in the presence of various gases, including air, nitrogen, argon, helium, supercritical steam, and other gases known in the art. Other particle size reduction methods are contemplated, including grinding, ball milling, jet milling, water jet milling, and other approaches known in the art.

The porous carbon scaffold may be in the form of particles. Particle size and particle size distribution can be measured by various methods known in the art and expressed based on volume fraction. In this regard, the Dv,50 of the carbon scaffold may be between 10 nm and 10 mm, e.g., between 100 nm and 1 mm, e.g., between 1 μm and 100 μm, e.g., between 2 μm and 50 μm, e.g., between 3 μm and 30 μm, e.g., between 4 μm and 20 μm, e.g., between 5 μm and 10 μm, etc. In certain embodiments, the Dv,50 is less than 1 mm, e.g., less than 100 μm, e.g., less than 50 μm, e.g., less than 30 μm, e.g., less than 20 μm, e.g., less than 10 μm, e.g., less than 8 μm, e.g., less than 5 μm, e.g., less than 3 μm, e.g., less than 1 μm, etc. In certain embodiments, Dv,100 is less than 1 mm, such as less than 100 μm, for example less than 50 μm, for example less than 30 μm, for example less than 20 μm, for example less than 10 μm, for example less than 8 μm, for example less than 5 μm, for example less than 3 μm, for example less than 1 μm, etc. In certain embodiments, Dv,99 is less than 1 mm, such as less than 100 μm, for example less than 50 μm, for example less than 30 μm, for example less than 20 μm, for example less than 10 μm, for example less than 8 μm, for example less than 5 μm, for example less than 3 μm, for example less than 1 μm, etc. In certain embodiments, Dv,90 is less than 1 mm, such as less than 100 μm, for example less than 50 μm, for example less than 30 μm, for example less than 20 μm, for example less than 10 μm, for example less than 8 μm, for example less than 5 μm, for example less than 3 μm, for example less than 1 μm, etc. In certain embodiments, Dv,0 is greater than 10 nm, such as greater than 100 nm, such as greater than 500 nm, such as greater than 1 μm, such as greater than 2 μm, such as greater than 5 μm, such as greater than 10 μm. In certain embodiments, Dv,1 is greater than 10 nm, such as greater than 100 nm, such as greater than 500 nm, such as greater than 1 μm, such as greater than 2 μm, such as greater than 5 μm, such as greater than 10 μm. In certain embodiments, Dv,10 is greater than 10 nm, such as greater than 100 nm, such as greater than 500 nm, such as greater than 1 μm, such as greater than 2 μm, such as greater than 5 μm, such as greater than 10 μm.

In some embodiments, the porous carbon scaffold can include a surface area of greater than 400 m ² /g, such as greater than 500 m ² /g, such as greater than 750 m ² /g, such as greater than 1000 m ² /g, such as greater than 1250 m ² /g, such as greater than 1500 m ² /g, such as ^{greater than 1750 m 2 /} g, such as greater than 2000 m ² /g, such as greater than 2500 m ² /g, such as greater than 3000 m ² /g, etc. In other embodiments, the surface area of the porous carbon scaffold can be less than 500 m ² /g. In some embodiments, the surface area of the porous carbon scaffold is between 200 m 2 /g and 500 ^{m 2} /g. In some embodiments, the surface area of the porous carbon scaffold is between 100 m ² /g and 200 m ² /g. In some embodiments, the surface area of the porous carbon scaffold is between 50 m ² /g and 100 m ² /g. In some embodiments, the surface area of the porous carbon scaffold is between 10 m ² /g and 50 m ² /g. In some embodiments, the surface area of the porous carbon scaffold can be less than 10 m ² /g.

In some embodiments, the pore volume of the porous carbon scaffold is greater than 0.4 cm ³ /g, such as greater than 0.5 cm ³ /g, for example greater than 0.6 cm ³ /g, for example greater than 0.7 cm ³ /g, for example greater than 0.8 cm ³ /g, for example greater than 0.9 cm ³ /g, for example greater than 1.0 cm ³ /g, for example greater than 1.1 cm ³ /g, for example greater than 1.2 cm ³ /g, for example greater than 1.4 cm ³ /g, for example greater than 1.6 cm ³ /g, for example greater than 1.8 cm ³ /g, for example greater than 2.0 cm ³ /g, etc. In other embodiments, the pore volume of the porous silicon scaffold is less than 0.5 cm ³ , for example between 0.1 cm ³ /g and 0.5 cm ³ /g. In certain embodiments, the pore volume of the porous silicon scaffold is between 0.01 cm ³ /g and 0.1 cm ³ /g.

In some embodiments, the porous carbon scaffold is an amorphous activated carbon having a pore volume of 0.2-2.0 cm ³ /g. In certain embodiments, the carbon is an amorphous activated carbon having a pore volume of 0.4-1.5 cm ³ /g. In certain embodiments, the carbon is an amorphous activated carbon having a pore volume of 0.5-1.2 cm ³ /g. In certain embodiments, the carbon is an amorphous activated carbon having a pore volume of 0.6-1.0 cm ³ /g.

In other embodiments, the porous carbon scaffold comprises a tap density of less than 1.0 g/ ^cm3 , such as less than 0.8 g/ ^cm3 , such as less than 0.6 g/ ^cm3 , such as less than 0.5 g/ ^cm3 , such as less than 0.4 g/ ^cm3 , such as less than 0.3 g/ ^cm3 , such as less than 0.2 g/ ^cm3 , such as less than 0.1 g/ ^cm3 , etc.

The surface functionality of porous carbon scaffolds can vary. One property that can predict surface functionality is the pH of the porous carbon scaffold. The porous carbon scaffolds disclosed herein include pH values ranging from less than 1 to about 14, such as less than 5, 5-8, or greater than 8. In some embodiments, the pH of the porous carbon is less than 4, less than 3, less than 2, or less than 1. In other embodiments, the pH of the porous carbon is between about 5-6, about 6-7, about 7-8, 8-9, or 9-10. In still other embodiments, the pH of the porous carbon is high, such as greater than 8, greater than 9, greater than 10, greater than 11, greater than 12, or greater than 13.

The pore volume distribution of the porous carbon scaffold can vary. For example, the micropore percentage can include less than 30%, such as less than 20%, such as less than 10%, such as less than 5%, such as less than 4%, such as less than 3%, such as less than 2%, such as less than 1%, such as less than 0.5%, such as less than 0.2%, such as less than 0.1%, etc. In certain embodiments, there is no detectable micropore volume in the porous carbon scaffold.

The mesopores contained in the porous carbon scaffold can vary. For example, the mesopore percentage can be less than 30%, such as less than 20%, such as less than 10%, such as less than 5%, such as less than 4%, such as less than 3%, such as less than 2%, such as less than 1%, such as less than 0.5%, such as less than 0.2%, such as less than 0.1%, etc. In certain embodiments, there is no detectable mesopore volume in the porous carbon scaffold.

In some embodiments, the pore volume distribution of the porous carbon scaffold comprises greater than 50% macropores, such as greater than 60% macropores, such as greater than 70% macropores, such as greater than 80% macropores, such as greater than 90% macropores, such as greater than 95% macropores, such as greater than 98% macropores, such as greater than 99% macropores, such as greater than 99.5% macropores, such as greater than 99.9% macropores, etc.

In certain preferred embodiments, the pore volume of the porous carbon scaffold comprises a blend of micropores, mesopores, and macropores. Thus, in certain embodiments, the porous carbon scaffold comprises 0-20% micropores, 30-70% mesopores, and less than 10% macropores. In other specific embodiments, the porous carbon scaffold comprises 0-20% micropores, 0-20% mesopores, and 70-95% macropores. In other specific embodiments, the porous carbon scaffold comprises 20-50% micropores, 50-80% mesopores, and 0-10% macropores. In other specific embodiments, the porous carbon scaffold comprises 40-60% micropores, 40-60% mesopores, and 0-10% macropores. In certain other embodiments, the porous carbon scaffold comprises 80-95% micropores, 0-10% mesopores, and 0-10% macropores. In certain other embodiments, the porous carbon scaffold comprises 0-10% micropores, 30-50% mesopores, and 50-70% macropores. In certain other embodiments, the porous carbon scaffold comprises 0-10% micropores, 70-80% mesopores, and 0-20% macropores. In certain other embodiments, the porous carbon scaffold comprises 0-20% micropores, 70-95% mesopores, and 0-10% macropores. In certain other embodiments, the porous carbon scaffold comprises 0-10% micropores, 70-95% mesopores, and 0-20% macropores.

In certain embodiments, the percentage of pore volume representing 100-1000 A (10-100 nm) pores in the porous carbon scaffold comprises more than 30% of the total pore volume, such as more than 40% of the total pore volume, such as more than 50% of the total pore volume, such as more than 60% of the total pore volume, such as more than 70% of the total pore volume, such as more than 80% of the total pore volume, such as more than 90% of the total pore volume, such as more than 95% of the total pore volume, such as more than 98% of the total pore volume, such as more than 99% of the total pore volume, such as more than 99.5% of the total pore volume, for example more than 99.9% of the total pore volume.

In certain embodiments, the pycnometry density of the porous carbon scaffold ranges from about 1 g/cc to about 3 g/cc, for example, from about 1.5 g/cc to about 2.3 g/cc. In other embodiments, the skeletal density is in the range of about 1.5 g/cc to about 1.6 g/cc, about 1.6 g/cc to about 1.7 g/cc, about 1.7 g/cc to about 1.8 g/cc, about 1.8 g/cc to about 1.9 g/cc, about 1.9 g/cc to about 2.0 g/cc, about 2.0 g/cc to about 2.1 g/cc, about 2.1 g/cc to about 2.2 g/cc, about 2.2 g/cc to about 2.3 g/cc, about 2.3 g/cc to about 2.4 g/cc, or about 2.4 g/cc to about 2.5 g/cc.

C. Fabrication of Silicon by Chemical Vapor Infiltration (CVI) Chemical vapor deposition (CVD) is a process in which a substrate provides a first component of a composite, and a gas thermally decomposes on the solid surface of the first component to provide a second component of the composite. Such a CVD approach may be used, for example, to create Si—C composite materials in which silicon is coated on the outer surfaces of silicon particles. Alternatively, chemical vapor infiltration (CVI) is a process in which a substrate provides a porous scaffold containing a first component of a composite, and a gas thermally decomposes within the porosity of the porous scaffold material to provide a second component of the composite.

In one embodiment, silicon is produced within the pores of the porous carbon scaffold by exposing the porous carbon particles to a silicon-containing precursor gas, preferably silane, at an elevated temperature in the presence of a silicon-containing gas to decompose the silicon-containing gas into silicon. The silicon-containing precursor gas may be mixed with other inert gases, such as nitrogen gas. The treatment temperature and time may vary, for example, from 200°C to 900°C, e.g., from 200°C to 250°C, e.g., from 250°C to 300°C, e.g., from 300°C to 350°C, e.g., from 300°C to 400°C, e.g., from 350°C to 450°C, e.g., from 350°C to 400°C, e.g., from 400°C to 500°C, e.g., from 500°C to 600°C, e.g., from 600°C to 700°C, e.g., from 700°C to 800°C, e.g., from 800°C to 900°C, e.g., from 600°C to 1100°C, etc.

The gas mixture may include 0.1-1% silane and the remaining inert gas. Alternatively, the gas mixture may include 1-10% silane and the remaining inert gas. Alternatively, the gas mixture may include 10-20% silane and the remaining inert gas. Alternatively, the gas mixture may include 20-50% silane and the remaining inert gas. Alternatively, the gas mixture may include more than 50% silane and the remaining inert gas. Alternatively, the gas may include essentially 100% silane gas. Suitable inert gases include, but are not limited to, hydrogen, nitrogen, argon, and combinations thereof.

The pressure in the CVI process can vary. In some embodiments, the pressure is atmospheric. In some embodiments, the pressure is less than atmospheric. In some embodiments, the pressure is greater than atmospheric.

D. Physicochemical and Electrochemical Properties of Silicon-Carbon Composites Without wishing to be bound by theory, it is believed that the nanosized silicon results from loading the porous carbon scaffold with the desired pore volume structure (e.g., silicon-filled pores in the range of 5 nm to 1000 nm, or other ranges disclosed elsewhere herein), which, along with the advantageous properties of the other components of the composite (including low surface area, low pycnometric density), results in a composite with a variety of advantageous properties (e.g., electrochemical performance) when the composite comprises an anode for a lithium ion energy storage device.

In certain embodiments, the silicon particles embedded within the composite have nanosized features. Nanosized features may have a characteristic length scale of preferably less than 1 μm, preferably less than 300 nm, preferably less than 150 nm, preferably less than 100 nm, preferably less than 50 nm, preferably less than 30 nm, preferably less than 15 nm, preferably less than 10 nm, and preferably less than 5 nm.

In certain embodiments, the silicon embedded within the composite is spherical in shape. In other specific embodiments, the porous silicon particles are non-spherical, e.g., rod-like or fibrous in structure. In some embodiments, the silicon is present as a layer coating the inside of the pores within the porous carbon scaffold. The depth of this silicon layer can vary, for example, from 5 nm to 10 nm, e.g., from 5 nm to 20 nm, e.g., from 5 nm to 30 nm, e.g., from 5 nm to 33 nm, e.g., from 10 nm to 30 nm, e.g., from 10 nm to 50 nm, e.g., from 10 nm to 100 nm, e.g., from 10 nm to 150 nm, e.g., from 50 nm to 150 nm, e.g., from 100 nm to 300 nm, e.g., from 300 nm to 1000 nm, etc.

In some embodiments, the embedded silicon in the composite is nanosized and resides within the pores of a porous carbon scaffold. For example, the embedded silicon can be impregnated and deposited by CVI or other suitable process into pores within porous carbon particles (wherein the pores have diameters of 5-1000 nm, e.g., 10-500 nm, e.g., 10-200 nm, e.g., 10-100 nm, e.g., 33-150 nm, e.g., 20-100 nm, etc.). Other ranges of carbon pore size in terms of fractional pore volume are similarly contemplated, whether micropores, mesopores, or macropores.

In some embodiments, the pore volume distribution of a carbon scaffold can be described as the number of pores or the volume distribution of pores, as determined by gas adsorption analysis (e.g., nitrogen gas adsorption analysis) as known in the art. In some embodiments, the pore size distribution can be expressed in terms of the pore size at which pores account for less than a certain percentage of the total pore volume. For example, the pore size at which 10% or less pores are present can be expressed as DPv10.

The DPv10 of the porous carbon scaffold may vary, for example, the DPv10 may be 0.01 nm to 100 nm, such as 0.1 nm to 100 nm, such as 1 nm to 100 nm, such as 1 nm to 50 nm, such as 1 nm to 40 nm, such as 1 nm to 30 nm, such as 1 nm to 10 nm, such as 1 nm to 5 nm, etc.

The DPv50 of the porous carbon scaffold may vary, for example, the DPv50 may be 0.01 nm to 100 nm, such as 0.1 nm to 100 nm, for example, 1 nm to 100 nm, for example, 1 nm to 50 nm, for example, 1 nm to 40 nm, for example, 1 nm to 30 nm, for example, 1 nm to 10 nm, for example, 1 nm to 5 nm, etc. In other embodiments, the DPv50 may be 2 to 100, for example, 2 to 50, for example, 2 to 30, for example, 2 to 20, for example, 2 to 15, for example, 2 to 10, etc.

The DPv90 of the porous carbon scaffold may vary, for example, the DPv90 may be 0.01 nm to 100 nm, such as 0.1 nm to 100 nm, for example, 1 nm to 100 nm, for example, 1 nm to 50 nm, for example, 1 nm to 50 nm, for example, 1 nm to 40 nm, for example, 1 nm to 30 nm, for example, 1 nm to 10 nm, for example, 1 nm to 5 nm, etc. In other embodiments, the DPv50 may be 2 nm to 100 nm, for example, 2 nm to 50 nm, for example, 2 nm to 30 nm, for example, 2 nm to 20 nm, for example, 2 nm to 15 nm, for example, 2 nm to 10 nm, etc.

In some embodiments, the DPv90 is less than 100 nm, such as less than 50 nm, such as less than 40 nm, such as less than 30 nm, such as less than 20 nm, such as less than 15 nm, such as less than 10 nm. In some embodiments, the carbon scaffold comprises more than 70% micropores and a DPv90 less than 100 nm, such as a DPv90 less than 50 nm, such as a DPv90 less than 40 nm, such as a DPv90 less than 30 nm, such as a DPv90 less than 20 nm, such as a DPv90 less than 15 nm, such as a DPv90 less than 10 nm, such as a DPv90 less than 5 nm, such as a DPv90 less than 4 nm, such as a DPv90 less than 3 nm, etc.

The DPv99 of the porous carbon scaffold may vary, for example, the DPv99 may be 0.01 nm to 1000 nm, such as 0.1 nm to 1000 nm, for example, 1 nm to 500 nm, for example, 1 nm to 200 nm, for example, 1 nm to 150 nm, for example, 1 nm to 100 nm, for example, 1 nm to 50 nm, for example, 1 nm to 20 nm, etc. In other embodiments, the DPv99 may be 2 nm to 500 nm, for example, 2 nm to 200 nm, for example, 2 nm to 150 nm, for example, 2 nm to 100 nm, for example, 2 nm to 50 nm, for example, 2 nm to 20 nm, for example, 2 nm to 15 nm, for example, 2 nm to 10 nm, etc.

Embodiments of the highly durable lithium intercalation composites disclosed herein improve numerous properties of electrical energy storage devices, such as lithium-ion batteries. In some embodiments, the silicon-carbon composites disclosed herein exhibit a Z of less than 10, e.g., a Z of less than 5, e.g., a Z of less than 4, e.g., a Z of less than 3, e.g., a Z of less than 2, e.g., a Z of less than 1, e.g., a Z of less than 0.1, e.g., a Z of less than 0.01, e.g., a Z of less than 0.001, etc. In certain embodiments, Z is 0.

In certain preferred embodiments, the silicon-carbon composites comprise a combination of a desirably low Z and multiple desired physicochemical and/or electrochemical properties, or multiple other desired physicochemical and/or electrochemical properties. Table 1 describes certain embodiments of silicon-carbon composite property combinations, including reversible capacity. Surface area can be measured, for example, by nitrogen gas adsorption analysis, as known in the art. Silicon content can be measured, for example, by TGA, as known in the art. The property value Z is determined by TGA in accordance with the present disclosure. First cycle efficiency can be determined, for example, by calculation based on the first cycle charge and discharge capacity of a full cell or half cell, as known in the art. For example, first cycle efficiency can be measured in a half cell for a voltage window of 5 mV to 0.8 V, or alternatively, 5 mV to 1.5 V. Reversible capacity can be described as maximum reversible capacity or maximum capacity and can be measured in a half cell for a voltage window of, for example, 5 mV to 0.8 V, alternatively, 5 mV to 1.5 V, as known in the art.

Specific Property Values for Silicon-Carbon Composite Embodiments

According to Table 1, silicon-carbon composites can include various combinations of properties. For example, a silicon-carbon composite can include a Z of less than 10, a surface area of less than 100 m ² /g, a first cycle efficiency of greater than 80%, and a reversible capacity of 1300 mAh/g or greater. For example, a silicon-carbon composite can include a Z of less than 10, a surface area of less than 100 m ² /g, a first cycle efficiency of greater than 80%, and a reversible capacity of 1600 mAh/g or greater. For example, a silicon-carbon composite can include a Z of less than 10, a surface area of less than 20 m ² /g, a first cycle efficiency of greater than 85%, and a reversible capacity of 1600 mAh/g or greater. For example, a silicon-carbon composite can include a Z of less than 10, a surface area of less than 10 m ² /g, a first cycle efficiency of greater than 85%, and a reversible capacity of 1600 mAh/g or greater. For example, the silicon-carbon composite may include a Z less than 10, a surface area less than 10 m ² /g, a first cycle efficiency greater than 90%, and a reversible capacity greater than or equal to 1600 mAh/g. For example, the silicon-carbon composite may include a Z less than 10, a surface area less than 10 m ² /g, a first cycle efficiency greater than 90%, and a reversible capacity greater than or equal to 1800 mAh/g.

The silicon-carbon composite can include a combination of the above properties, and the carbon scaffold can also include properties described herein. Accordingly, a description of specific embodiments of combinations of property values for silicon-carbon composites is provided in Table 2 below.

Specific Property Values for Silicon-Carbon Composite Embodiments

As used herein, the percentages "microporosity," "mesoporosity," and "macroporosity" refer to the percentage of micropores, mesopores, and macropores, respectively, relative to the total pore volume. For example, a carbon scaffold having 90% microporosity is a carbon scaffold in which 90% of the total pore volume of the carbon scaffold is formed by micropores.

According to Table 2, silicon-carbon composites can include various combinations of properties. For example, a silicon-carbon composite may include a Z less than 10, a surface area less than 100 m ² /g, a first cycle efficiency greater than 80%, a reversible capacity equal to or greater than 1600 mAh/g, a silicon content between 15% and 85%, and a carbon scaffold with a total pore volume of 0.2-1.2 cm ³ /g, where the pore volume of the scaffold includes greater than 80% micropores, less than 20% mesopores, and less than 10% macropores. For example, a silicon-carbon composite may include a carbon scaffold having a Z less than 10, a surface area less than 20 ^m /g, a first cycle efficiency greater than 85%, a reversible capacity equal to or greater than 1600 mAh/g, a silicon content of 15% to 85%, and a total pore volume of 0.2-1.2 ^cm /g, wherein the pore volume of the scaffold is greater than 80% micropores, less than 20% mesopores, and less than 10% macropores. For example, a silicon-carbon composite may include a carbon scaffold having a Z less than 10, a surface area less than 10 ^m /g, a first cycle efficiency greater than 85%, a reversible capacity equal to or greater than 1600 mAh/g, a silicon content of 15% to 85%, and a total pore volume of 0.2-1.2 ^cm /g, wherein the pore volume of the scaffold is greater than 80% micropores, less than 20% mesopores, and less than 10% macropores. For example, a silicon-carbon composite may comprise a carbon scaffold with a Z less than 10, a surface area less than 10 m ² /g, a first cycle efficiency greater than 90%, a reversible capacity equal to or greater than 1600 mAh/g, a silicon content between 15% and 85%, and a total pore volume of 0.2-1.2 cm ³ /g, the pore volume of the scaffold comprising greater than 80% micropores, less than 20% mesopores, and less than 10% macropores. For example, a silicon-carbon composite may comprise a carbon scaffold with a Z less than 10, a surface area less than 10 m ² /g, a first cycle efficiency greater than 90%, a reversible capacity equal to or greater than 1800 mAh/g, a silicon content between 15% and 85%, and a total pore volume of 0.2-1.2 cm ³ /g, wherein the pore volume of the scaffold comprises greater than 80% micropores, less than 20% mesopores, and less than 10% macropores.

Also, according to Table 2, the silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9969 or greater, and a Z of less than 10. For example, the silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9970 or greater, and a Z of less than 10. For example, the silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9970 or greater, and a Z of less than 10. For example, the silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9975 or greater, and a Z of less than 10. For example, a silicon-carbon composite can comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9980 or greater, and a Z of less than 10. For example, a silicon-carbon composite can comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9985 or greater, and a Z of less than 10. For example, a silicon-carbon composite can comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9990 or greater, and a Z of less than 10. For example, a silicon-carbon composite can comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9995 or greater, and a Z of less than 10. For example, a silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9970 or greater, and a Z of less than 10. For example, a silicon-carbon composite may comprise a carbon scaffold with greater than 80% micropores, a silicon content of 30-60%, an average Coulombic efficiency of 0.9999 or greater, and a Z of less than 10.

Without being bound by theory, it is believed that the loading of silicon into the pores of the porous carbon traps the pores within the porous carbon scaffold particles, creating inaccessible volumes, such as volumes that are inaccessible to nitrogen gas. Thus, the silicon-carbon composite exhibits a pycnometric density of less than 2.1 g/cm ³ , such as less than 2.0 g/cm ³ , for example, less than 1.9 g/cm ³ , for example, less than 1.8 g/cm ³ , for example, less than 1.7 g/cm ³ , for example, less than 1.6 g/cm ³ , for example, less than 1.4 g/cm ³ , for example, less than 1.2 g/cm ³ , for example, less than 1.0 g/cm ³ .

In some embodiments, the silicon-carbon composite material may exhibit a pycnometric density of 1.7 g/cm ^to 2.1 g/ ^cm , such as ^1.7 g/cm to 1.8 g/ ^cm , such as 1.8 g/ ^cm to 1.9 g/ ^cm , such as 1.9 g/cm ^to 2.0 g/ ^cm , such as ^2.0 g/cm to ^2.1 g/cm, etc. In some embodiments, the silicon-carbon composite material may exhibit a pycnometric density of ^1.8 g/cm to 2.1 g/ ^cm . In some embodiments, the silicon-carbon composite material may exhibit a pycnometric density of 1.8 ^g /cm to 2.0 g/ ^cm . In some embodiments, the silicon-carbon composite material may exhibit a pycnometric density ^of 1.9 g/cm ^to 2.1 g/cm.

The pore volume of composite materials that exhibit very durable lithium intercalation can be from 0.01 cm ³ /g to 0.2 cm ³ /g. In certain embodiments, the pore volume of the composite material can range from 0.01 cm ³ /g to 0.15 cm ³ /g, such as from 0.01 cm ³ /g to 0.1 cm ³ /g, for example, from 0.01 cm ³ /g to 0.05 cm ³ /g.

The particle size distribution of composites exhibiting very durable lithium intercalation is equally important for both power performance and volumetric capacity. Increased packing may also increase volumetric capacity. In one embodiment, the distribution is either Gaussian with a sharp peak, bimodal, or polymodal (more than two distinct peaks, e.g., trimodal). The particle size characteristics of the composite may be described by D0 (smallest particle in the distribution), Dv50 (average particle size), and Dv100 (maximum size of the largest particle). The optimal combination of particle packing and performance may be a combination of the following size ranges: Particle size reduction in such embodiments can be achieved, for example, by jet milling in the presence of various gases, as known in the art. Examples of such gases include air, nitrogen, argon, helium, supercritical steam, and others known in the art.

In one embodiment, the Dv0 of the composite material may be in the range of 1 nm to 5 μm. In other embodiments, the Dv0 of the composite is in the range of 5 nm to 1 μm, e.g., 5 to 500 nm, e.g., 5 to 100 nm, e.g., 10 to 50 nm. In other embodiments, the Dv0 of the composite is in the range of 500 nm to 2 μm, e.g., 750 nm to 1 μm, or 1 to 2 μm. In other embodiments, the Dv0 of the composite is 2 to 5 μm, or greater than 5 μm.

In one embodiment, the Dv1 of the composite material may be in the range of 1 nm to 5 μm. In other embodiments, the Dv1 of the composite is in the range of 5 nm to 1 μm, e.g., 5 to 500 nm, e.g., 5 to 100 nm, e.g., 10 to 50 nm. In other embodiments, the Dv1 of the composite is in the range of 100 nm to 10 μm, 200 nm to 5 μm, 500 nm to 2 μm, 750 nm to 1 μm, or 1 to 2 μm. In other embodiments, the Dv1 of the composite is 2 to 5 μm, or greater than 5 μm.

In one embodiment, the Dv10 of the composite material may be in the range of 1 nm to 10 μm. In another embodiment, the Dv10 of the composite is in the range of 5 nm to 1 μm, e.g., 5 to 500 nm, e.g., 5 to 100 nm, e.g., 10 to 50 nm. In another embodiment, the Dv10 of the composite is in the range of 100 nm to 10 μm, 500 nm to 10 μm, 500 nm to 5 μm, 750 nm to 1 μm, or 1 to 2 μm. In other embodiments, the Dv10 of the composite is 2 to 5 μm, or greater than 5 μm.

In some embodiments, the Dv50 of the composite material is in the range of 5 nm to 20 μm. In other embodiments, the Dv50 of the composite is in the range of 5 nm to 1 μm, e.g., 5 to 500 nm, e.g., 5 to 100 nm, e.g., 10 to 50 nm. In other embodiments, the Dv50 of the composite is in the range of 500 nm to 2 μm, 750 nm to 1 μm, or 1 to 2 μm. In further embodiments, the Dv50 of the composite is in the range of 1 to 1000 μm, e.g., 1 to 100 μm, e.g., 1 to 10 μm, e.g., 2 to 20 μm, e.g., 3 to 15 μm, e.g., 4 to 8 μm. In certain embodiments, the Dv50 is greater than 20 μm, e.g., greater than 50 μm, e.g., greater than 100 μm.

The span is given by:
(Dv50)/(Dv90-Dv10)
[where Dv10, Dv50, and Dv90 represent particle sizes at 10%, 50%, and 90% of the volume distribution, respectively]
The span can vary, for example, from 100 to 10, from 10 to 5, from 5 to 2, or from 2 to 1. In some embodiments, the span can be less than 1. In certain embodiments, the particle size distribution of the composite comprising carbon and porous silicon materials can be multimodal (e.g., bimodal, or trimodal).

The surface functionality of the composite materials disclosed herein, which exhibit highly durable lithium intercalation, can be modified to achieve desired electrochemical properties. One property that can predict surface functionality is the pH of the composite material. The composite materials disclosed herein include pHs ranging from less than 1 to about 14, such as less than 5, 5-8, or greater than 8. In some embodiments, the pH of the composite material is less than 4, less than 3, less than 2, or less than 1. In other embodiments, the pH of the composite material is about 5-6, about 6-7, about 7-8, 8-9, or 9-10. In still further embodiments, the pH of the composite material is high, such as greater than 8, greater than 9, greater than 10, greater than 11, greater than 12, or greater than 13.

Silicon-carbon composites can contain varying amounts of carbon, oxygen, hydrogen, and nitrogen, as determined by gas chromatography CHNO analysis. In one embodiment, the carbon content of the composite is greater than 98% by weight, or greater than 99.9% by weight, as determined by CHNO analysis. In another embodiment, the carbon content of the silicon-carbon composite ranges from 10 to 90% by weight, such as 20 to 80% by weight, such as 30 to 70% by weight, or 40 to 60% by weight.

In some embodiments, the silicon-carbon composite material has a nitrogen content in the range of 0-90%, e.g., 0.1-1%, e.g., 1-3%, e.g., 1-5%, e.g., 1-10%, e.g., 10-20%, e.g., 20-30%, e.g., 30-90%.

In some embodiments, the oxygen content ranges from 0 to 90%, for example, 0.1 to 1%, for example, 1 to 3%, for example, 1 to 5%, for example, 1 to 10%, for example, 10 to 20%, for example, 20 to 30%, for example, 30 to 90%, etc.

Silicon-carbon composites may incorporate electrochemical modifiers selected to optimize the electrochemical performance of the native composite. The electrochemical modifiers may be introduced into the pore structure and/or on the surface of the porous carbon scaffold, into embedded silicon, into the final layer of carbon, or via a conductive polymer, coating, or any number of other methods. For example, in some embodiments, the composite comprises a coating of an electrochemical modifier (e.g., silicon or Al ₂ O ₃ ) on the surface of the carbon material. In some embodiments, the composite comprises greater than about 100 ppm of the electrochemical modifier. In certain embodiments, the electrochemical modifier is selected from iron, tin, silicon, nickel, aluminum, and manganese.

In certain embodiments, the electrochemical modifier includes an element capable of lithiation between 3 and 0 V relative to lithium metal (e.g., silicon, tin, sulfur). In other embodiments, the electrochemical modifier includes a metal oxide capable of lithiation between 3 and 0 V relative to lithium metal (e.g., iron oxide, molybdenum oxide, titanium oxide). In still further embodiments, the electrochemical modifier includes an element that does not lithiate between 3 and 0 V relative to lithium metal (e.g., aluminum, manganese, nickel, metal phosphates). In still further embodiments, the electrochemical modifier includes a non-metal element (e.g., fluorine, nitrogen, hydrogen, boron, phosphorus). In still further embodiments, the electrochemical modifier includes any of the electrochemical modifiers described above, or any combination thereof (e.g., tin-silicon, nickel-titanium oxide).

The electrochemical modifier may be provided in a number of forms. For example, in some embodiments, the electrochemical modifier comprises a salt. In other embodiments, the electrochemical modifier comprises one or more elements in elemental form, such as iron, tin, silicon, nickel, or manganese. In other embodiments, the electrochemical modifier comprises one or more elements in oxide form, such as iron oxide, tin oxide, silicon oxide, nickel oxide, aluminum oxide, or manganese oxide.

The electrochemical properties of the composite material can be modified, at least in part, by the amount of electrochemical modifier in the material, where the electrochemical modifier is an alloy material such as silicon, tin, indium, aluminum, germanium, or gallium. Thus, in some embodiments, the composite material comprises 0.10% or more, 0.25% or more, 0.50% or more, 1.0% or more, 5.0% or more, 10% or more, 25% or more, 50% or more, 75% or more, 90% or more, 95% or more, 99% or more, or 99.5% or more of the electrochemical modifier.

The particle size of the composite material may expand upon lithiation compared to the unlithiated state. For example, the expansion coefficient is defined as the ratio of the average particle size of the composite material containing the porous silicon material upon lithiation divided by the average particle size under non-lithiated conditions. As described in the art, the expansion coefficient is relatively large for known, non-optimal silicon-containing materials, e.g., about 4X (corresponding to a 400% volume expansion upon lithiation). The inventors have discovered composite materials containing porous silicon material that can exhibit lower expansion coefficients, e.g., expansion coefficients that can vary from 3.5 to 4.0, 3.0 to 3.5, 2.5 to 3.0, 2.0 to 2.5, 1.5 to 2.0, or 1.0 to 1.5.

In certain embodiments, the composite material is contemplated to include a portion of trapped pore volume, i.e., a portion of void volume that is inaccessible to nitrogen gas, where the void volume can be measured by nitrogen gas adsorption measurements. Without being bound by theory, this trapped pore volume is important in that it provides a volume into which silicon expands upon lithiation.

In certain embodiments, the ratio of trapped void volume to silicon volume containing the composite particles is between 0.1:1 and 10:1. For example, the ratio of trapped void volume to silicon volume containing the composite particles is between 1:1 and 5:1, or between 5:1 and 10:1. In some embodiments, the ratio of trapped void volume to silicon volume containing the composite particles is between 2:1 and 5:1, or about 3:1, which can efficiently accommodate the maximum expansion of silicon upon lithiation.

In certain embodiments, the electrochemical performance of the composites disclosed herein is tested in half cells; alternatively, the performance of the highly durable lithium intercalation composites disclosed herein is tested in full cells (e.g., a full cell coin cell, a full cell pouch cell, a prismatic cell, or other battery configurations known in the art). Additionally, anode configurations of the highly durable lithium intercalation composites disclosed herein may include various species, as known in the art. Additional formulation components include, but are not limited to, conductive additives, such as conductive carbon (e.g., Super C45, Super P, and Ketjenblack carbon), conductive polymers, and binders (e.g., styrene-butadiene rubber sodium carboxymethylcellulose (SBR-Na-CMC), polyvinylidene fluoride (PVDF), polyimide (PI), polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyamideimide (PAI)), and combinations thereof. In certain embodiments, the binder may include lithium ions as counterions.

Other species, including electrodes, are known in the art. The weight percent of active material in the electrode can vary, such as 1-5 wt %, such as 5-15 wt %, such as 15-25 wt %, such as 25-35 wt %, such as 35-45 wt %, such as 45-55 wt %, such as 55-65 wt %, such as 65-75 wt %, such as 75-85 wt %, such as 85-95 wt %, etc. In some embodiments, the active material comprises 80-95% of the electrode. In certain embodiments, the amount of conductive additive in the electrode can vary, such as 1-5 wt %, such as 5-15 wt %, such as 15-25 wt %, such as 25-35 wt %, etc. In certain embodiments, the amount of binder can vary, such as 1-5 wt %, such as 5-15 wt %, such as 15-25 wt %, such as 25-35 wt %, etc. In certain embodiments, the amount of conductive additive in the electrode is 5 to 25% by weight.

The silicon-carbon composite material is pre-lithiated as known in the art. In certain embodiments, pre-lithiation is accomplished electrochemically, e.g., in a half-cell prior to construction of a lithiated anode comprising the porous silicon material in a full-cell lithium-ion battery. In certain embodiments, pre-lithiation is achieved by doping the cathode with a lithium-containing compound (e.g., a lithium-containing salt). Suitable lithium salts in this embodiment include, but are not limited to, dilithium tetrabromonickel(II), dilithium tetrachlorocuprate(II), lithium azide, lithium benzoate, lithium bromide, lithium carbonate, lithium chloride, lithium cyclohexanebutyrate, lithium fluoride, lithium formate, lithium hexafluoroarsenate(V), lithium hexafluorophosphate, lithium hydroxide, lithium iodate, lithium metaborate, lithium perchlorate, lithium phosphate, lithium sulfate, lithium tetraborate, lithium tetrachloroaluminate, lithium tetrafluoroborate, lithium thiocyanate, lithium trifluoromethanesulfonate, and combinations thereof.

Anodes comprising silicon-carbon composites can be paired with a variety of cathode materials to produce full-cell lithium-ion batteries. Examples of suitable cathode materials are known in the art, including _, but not limited to, _LiCoO2 (LCO), _{LiNi0.8Co0.15Al0.05O2} (NCA), LiNi1 _{/ 3Co1 /3Mn1/ 3O2 ( NMC} ), _LiMn2O4 and its variants ( _LMO ), and _LiFePO4 (LFP).

For full-cell lithium-ion batteries including an anode further comprising a silicon-carbon composite material, the cathode and anode pairing may vary. For example, the cathode to anode capacity ratio may vary from 0.7 to 1.3. In certain embodiments, the cathode to anode capacity ratio may vary from 0.7 to 1.0, such as from 0.8 to 1.0, such as from 0.85 to 1.0, such as from 0.9 to 1.0, such as from 0.95 to 1.0. In other embodiments, the cathode to anode capacity ratio may vary from 1.0 to 1.3, such as from 1.0 to 1.2, such as from 1.0 to 1.15, such as from 1.0 to 1.1, such as from 1.0 to 1.05, etc. In yet other embodiments, the ratio of the cathode to anode capacities may vary from 0.8 to 1.2, such as from 0.9 to 1.1, e.g., from 0.95 to 1.05.

For full-cell lithium-ion batteries including an anode further comprising a silicon-carbon composite material, the voltage window for charging and discharging can vary. In this regard, the voltage window can vary depending on various characteristics of the lithium-ion battery, as is known in the art. For example, as is known in the art, the selection of the cathode plays a role in the selected voltage window. The voltage window can vary, for example, from 2.0 V to 5.0 V relative to the potential of Li/Li+, including, for example, 2.5 V to 4.5 V, 2.5 V to 4.2 V, etc.

For full-cell lithium-ion batteries that include an anode further comprising a silicon-carbon composite material, methods for conditioning the battery can vary, as is known in the art. For example, conditioning can be achieved by performing multiple charge and discharge cycles at various rates, e.g., at a rate slower than the desired cycle rate. As is known in the art, the conditioning process may further include opening the lithium-ion battery, venting any gases generated during the conditioning process, and then resealing the lithium-ion battery.

For full-cell lithium-ion batteries including an anode further comprising a silicon-carbon composite material, the cycle rate may vary as known in the art, for example, the rate may be C/20 to 20C, e.g., C/10 to 10C, e.g., C/5 to 5C, etc. In certain embodiments, the cycle rate is C/10. In certain embodiments, the cycle rate is C/5. In certain embodiments, the cycle rate is C/2. In certain embodiments, the cycle rate is 1C. In certain embodiments, the cycle rate is 1C, with periodic reductions to slower rates (e.g., applying a C/10 rate reduction every 20 cycles). In certain embodiments, the cycle rate is 2C. In certain embodiments, the cycle rate is 4C. In certain embodiments, the cycle rate is 5C. In certain embodiments, the cycle rate is 10C. In certain embodiments, the cycle rate is 20C.

The first cycle efficiency of the highly durable lithium intercalation composites disclosed herein is measured by comparing the lithium inserted into the anode during the first cycle, prior to prior lithiation, with the lithium extracted from the anode during the first cycle. When insertion and extraction are equal, the efficiency is 100%. As is known in the art, anode materials can be tested in half-cells, where the counter electrode is lithium metal, the electrolyte is 1 M LiPF ₆ , and 1:1 ethylene carbonate:diethyl carbonate (EC:DEC), and a commercially available polypropylene separator is used. In certain embodiments, the electrolyte can contain various additives known to enhance performance, such as fluoroethylene carbonate (FEC) or other related fluorinated carbonate compounds, or ester cosolvents (e.g., methyl butanoate, vinylene carbonate, etc.), and other additives known to enhance the electrochemical performance of silicon-containing anode materials. In certain embodiments, the first cycle efficiency of the half-cell can be measured over a voltage window of 5 mV to 0.8 V. In other embodiments, the first cycle efficiency of the half-cell can be measured over a voltage window of 5 mV to 1.0 V. In other embodiments, the first cycle efficiency of the half-cell can be measured over a voltage window of 5 mV to 1.5 V. In other embodiments, the first cycle efficiency of the half-cell can be measured over a voltage window of 5 mV to 2.0 V. In other embodiments, the first cycle efficiency was measured on a full-cell battery, for example, over a voltage window of 2.0 V to 4.5 V, 2.3 V to 4.5 V, 2.5 V to 4.2 V, or 3.0 V to 4.2 V, etc.

The coulombic efficiency can be averaged, for example, over cycles 7 through 25 in half-cell testing. The coulombic efficiency can be averaged, for example, over cycles 7 through 20 in half-cell testing. In certain embodiments, composites with highly durable lithium intercalation have an average efficiency greater than 0.9%, or greater than 90%. In certain embodiments, the average efficiency is greater than 0.95%, or greater than 95%. In certain embodiments, the average efficiency is 0.99 or greater, such as 0.991 or greater, such as 0.992 or greater, such as 0.993 or greater, such as 0.994 or greater, such as 0.995 or greater, such as 0.996 or greater, such as 0.997 or greater, such as 0.998 or greater, such as 0.999 or greater, such as 0.9991 or greater, such as 0.9992 or greater, such as 0.9993 or greater, such as 0.9994 or greater, such as 0.9995 or greater, such as 0.9996 or greater, such as 0.9997 or greater, such as 0.9998 or greater, such as 0.9999 or greater, etc.

In yet other embodiments, the present disclosure provides composite materials that exhibit highly durable lithium intercalation, wherein the composite materials, when incorporated into an electrode of a lithium-based energy storage device, have a volumetric capacity that is at least 10% higher than when incorporated into an electrode of a lithium-based energy storage device that includes a graphite electrode. In some embodiments, the lithium-based energy storage device is a lithium-ion battery. In some embodiments, the composite materials have a volumetric capacity in a lithium-based energy storage device that is at least 5%, at least 10%, or at least 15% higher than a similar electrical energy storage device with a graphite electrode. In still other embodiments, the composite materials have a volumetric capacity in a lithium-based energy storage device that is at least 20%, at least 30%, at least 40%, at least 50%, at least 200%, at least 100%, at least 150%, or at least 200% higher than a similar electrical energy storage device with a graphite electrode.

The composite material may be pre-lithiated as known in the art. The lithium atoms may or may not be separated from the carbon. The number of lithium atoms per six carbon atoms is determined by the following formula, which is a method known to those skilled in the art:
#Li=Q×3.6×MM/(C%×F)
[where Q is the lithium extraction capacity (mAh/g) measured at voltages between 5 mV and 2.0 V versus lithium metal, M is the molecular mass of 72 or 6 carbon, F is Faraday's constant (96500), and C% is the weight percent of carbon present in the structure as measured by CHNO or XPS.]
It can be calculated by:

The composite material can be characterized by the ratio of lithium atoms to carbon atoms (Li:C), which can be between about 0:6 and 2:6. In some embodiments, the Li:C is between about 0.05:6 and 1.9:6. In other embodiments, the lithium is in ionic and not metallic form, and the maximum Li:C ratio is 2.2:6. In certain other embodiments, the Li:C ratio is between about 1.2:6 and about 2:6, between about 1.3:6 and about 1.9:6, between about 1.4:6 and about 1.9:6, between about 1.6:6 and about 1.8:6, or between about 1.7:6 and about 1.8:6. In other embodiments, the Li:C ratio is greater than 1:6, greater than 1.2:6, greater than 1.4:6, greater than 1.6:6, or greater than 1.8:6. In still other embodiments, the Li:C ratio is about 1.4:6, about 1.5:6, about 1.6:6, about 1.7:6, about 1.8:6, or about 2:6. In certain embodiments, the Li:C ratio is about 1.78:6.

In certain embodiments, the composite material comprises a Li:C ratio ranging from about 1:6 to about 2.5:6, from about 1.4:6 to about 2.2:6, or from about 1.4:6 to about 2:6. In yet other embodiments, the composite material does not necessarily contain lithium, but instead possesses lithium uptake capacity, i.e., the ability to absorb a certain amount of lithium, for example, during cycling of the material between two voltage conditions (in this case, a lithium-ion half cell, a typical voltage window is 0-3 V, e.g., 0.005-2.7 V, e.g., 0.005-1 V, e.g., 0.005-0.8 V, etc.). Without wishing to be bound by theory, the lithium uptake capacity of the composite material contributes to its superior performance in lithium-based energy storage devices. Lithium uptake capacity is expressed as the ratio of lithium atoms replaced by the composite. In other specific embodiments, composite materials exhibiting highly durable lithium intercalation include lithium uptake capacities ranging from about 1:6 to about 2.5:6, from about 1.4:6 to about 2.2:6, or from about 1.4:6 to about 2:6, etc.

In certain other embodiments, the lithium uptake capacity ranges from about 1.2:6 to about 2:6, from about 1.3:6 to about 1.9:6, from about 1.4:6 to about 1.9:6, from about 1.6:6 to about 1.8:6, or from about 1.7:6 to about 1.8:6, etc. In other embodiments, the lithium uptake capacity is greater than 1:6, greater than 1.2:6, greater than 1.4:6, greater than 1.6:6, or greater than 1.8:6. In still other embodiments, the Li:C ratio is about 1.4:6, about 1.5:6, about 1.6:6, about 1.6:6, about 1.7:6, about 1.8:6, or about 2:6. In one particular embodiment, the Li:C ratio is about 1.78:6.

EXAMPLES Example 1. Fabrication of Silicon-Carbon Composite by CVI. The properties of the carbon scaffold (Carbon Scaffold 1) used to fabricate the silicon-carbon composite are shown in Table 3 below. A silicon-carbon composite (Silicon-Carbon Composite 1) was fabricated by CVI using Carbon Scaffold 1 as follows: A 0.2 gram mass of amorphous porous carbon was placed in a 2-inch by 2-inch ceramic crucible and placed in the center of a horizontal tube furnace. The furnace was sealed and purged with nitrogen gas at 500 cubic centimeters per minute (ccm). The furnace temperature was increased at 20°C per minute to a peak temperature of 450°C and maintained for 30 minutes. At this point, the nitrogen was turned off, and subsequently silane and hydrogen were introduced at flow rates of 50 ccm and 450 ccm, respectively, for a total of 30 minutes. The silane and nitrogen were then turned off, nitrogen was again introduced into the furnace, and the air inside was purged. At the same time, the furnace was turned off and allowed to cool to ambient temperature, and the finished Si—C material was then removed from the furnace.

Example 2. Analysis of Various Silicon-Composite Materials. Carbon scaffold materials using various carbon scaffold materials were characterized by nitrogen adsorption gas analysis to measure the specific surface area, total pore volume, and the percentage of pore volume including micropores, mesopores, and macropores. The characterization data for the carbon scaffold materials, i.e., the surface area, pore volume, and pore volume distribution (percentage of micropores, mesopores, and macropores) of the carbon scaffold (all measured by nitrogen adsorption analysis), are shown in Table 4.

Properties of various carbon scaffold materials

Using the carbon scaffold samples listed in Table 4, various silicon-carbon composites were fabricated by the CVI method in a static bed configuration as generally described in Example 1. These silicon-carbon samples were fabricated using the following range of process conditions: silane concentration from 1.25% to 100%; diluent gas from nitrogen or hydrogen; and starting carbon scaffold mass from 0.2 g to 700 g.

The surface area of the silicon-carbon composite was measured. The silicon content and Z of the silicon-carbon composite were also measured by TGA analysis. The silicon-carbon composite was also tested in a half-cell coin cell. The anode of the half-cell coin cell can contain 60-90% silicon-carbon composite, 5-20% Na-CMC (as a binder), and 5-20% Super C45 (as a conductivity enhancer), and the electrolyte can contain 2:1 ethylene carbonate:diethylene carbonate, 1 M LiPF ₆ , and 10% fluoroethylene carbonate. The half-cell coin cell can be cycled at 25°C at a C/5 rate for five cycles, followed by a C/10 rate. The voltage can be cycled from 0 V to 0.8 V, or alternatively, the voltage can be cycled from 0 V to 1.5 V. From the half-cell and coin cell data, the maximum capacity can be determined, as well as the average coulombic efficiency (CE) from cycle 7 to cycle 20. The physicochemical and electrochemical properties of various silicon-carbon composites are shown in Table 5.

Properties of various silicon-carbon composites

A plot of the average coulombic efficiency as a function of Z is shown in Figure 1. As can be seen, the average coulombic efficiency for silicon-carbon samples with low Z increased dramatically. In particular, all silicon-carbon samples with Z less than 10.0 exhibited average coulombic efficiencies of 0.9941 or greater, while all silicon-carbon samples with Z greater than 10 (silicon-carbon composite sample 12 to silicon-carbon composite sample 16) were observed to have average coulombic efficiencies of 0.9909 or less. Without being bound by theory, the higher coulombic efficiencies for silicon-carbon samples with Z less than 10 provide superior cycling stability in full-cell lithium-ion batteries. Further examination of the table revealed the surprising and unexpected result that the combination of silicon-carbon composite samples with Z less than 10 and silicon-carbon composite samples further comprising a carbon scaffold with greater than 70 microporosity exhibited average coulombic efficiencies of 0.9950 or greater.

Thus, in a more preferred embodiment, the silicon-carbon composite material has a Z of less than 10, such as a Z of less than 5, such as a Z of less than 3, such as a Z of less than 2, such as a Z of less than 1, such as a Z of less than 0.5, such as a Z of less than 0.1, or a Z of 0.

In certain preferred embodiments, the silicon-carbon composite material comprises a carbon scaffold having a Z of less than 10 and a microporosity of greater than 70%, for example, a Z of less than 10 and a microporosity of greater than 80%, for example, a Z of less than 10 and a microporosity of greater than 90%, for example, a Z of less than 10 and a microporosity of greater than 95%, for example, a Z of less than 5 and a microporosity of greater than 70%, for example, a Z of less than 5 and a microporosity of greater than 80%, for example, a Z of less than 5 and a microporosity of greater than 90%, for example, a Z of less than 5 and a microporosity of greater than 95%, for example, a Z of less than 3 and a microporosity of greater than 70%, for example, a Z of less than 3 and a microporosity of greater than 80%, for example, a Z of less than 3 and a microporosity of greater than 90%, for example, a Z of less than 3 and a microporosity of greater than 95%, for example, a Z of less than 2 and a microporosity of greater than 70%, for example, a Z of less than 2 and a microporosity of greater than 80%, for example, a Z of less than 2 and a microporosity of greater than 90%, for example, a Z of less than 2 and a microporosity of more than 95%, for example a Z of less than 1 and a microporosity of more than 70%, for example a Z of less than 1 and a microporosity of more than 80%, for example a Z of less than 1 and a microporosity of more than 90%, for example a Z of less than 1 and a microporosity of more than 95%, for example a Z of less than 0.5 and a microporosity of more than 70%, for example a Z of less than 0.5 and a microporosity of more than 80%, for example a Z of less than 0.5 and a microporosity of more than 90%, for example a Z of less than 0.5 and a microporosity of more than 95% microporosity, for example, a Z of less than 0.1 and a microporosity of more than 70%, for example, a Z of less than 0.1 and a microporosity of more than 80%, for example, a Z of less than 0.1 and a microporosity of more than 90%, for example, a Z of less than 0.1 and a microporosity of more than 95%, for example, a Z of 0 and a microporosity of more than 70%, for example, a Z of 0 and a microporosity of more than 80%, for example, a Z of 0 and a microporosity of more than 90%, for example, a Z of 0 and a microporosity of more than 95%, etc.

In certain preferred embodiments, the silicon-carbon composite comprises a Z of less than 10, greater than 70% microporosity, 15% to 85% silicon, and a surface area less than 100 m ² /g, for example, a Z of less than 10, greater than 70% microporosity, 15% to 85% silicon, and a surface area less than 50 m ² /g, for example, a Z of less than 10, greater than 70% microporosity, 15% to 85% silicon, and a surface area less than 30 m ² /g, for example, a Z of less than 10, greater than 70% microporosity, 15% to 85% silicon, and a surface area less than 10 m ² /g, for example, a Z of less than 10, greater than 70% microporosity, 15% to 85% silicon, and a surface area less than 5 m ² /g, for example, a Z of less than 10, greater than 80% microporosity, 15% to 85% silicon, and a surface area less than 50 m ² /g. /g surface area, for example Z less than 10, greater than 80% microporosity, 15% to 85% silicon, and less than 30 m ² /g surface area, for example Z less than 10, greater than 80% microporosity, 15% to 85% silicon, and less than 10 m ² /g surface area, for example Z less than 10, greater than 80% microporosity, 15% to 85% silicon, and less than 5 m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 15% to 85% silicon, and less than 50 m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 15% to 85% silicon, and less than 30 ...30 m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 15% to 85% silicon, and less than 30 m ^{2 /g} surface area. /g surface area, for example, Z less than 10, greater than 90% microporosity, 15% to 85% silicon, and less than 5 m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 15% to 85% silicon, and less than 50 m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 15% to 85% silicon, and less than 30 m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 15% to 85% silicon, and less than 10 m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 15% to 85% silicon, and less than 5 m ² /g surface area.

In certain preferred embodiments, the silicon-carbon composite comprises a Z of less than 10, greater than 70% microporosity, 30% to 60% silicon, and a surface area less than 100 m ² /g, for example a Z of less than 10, greater than 70% microporosity, 30% to 60% silicon, and a surface area less than 50 m ² /g, for example a Z of less than 10, greater than 70% microporosity, 30% to 60% silicon, and a surface area less than 30 m ² /g, for example a Z of less than 10, greater than 70% microporosity, 30% to 60% silicon, and a surface area less than 10 m ² /g, for example a Z of less than 10, greater than 70% microporosity, 30% to 60% silicon, and a surface area less than 5 m ² /g, for example a Z of less than 10, greater than 80% microporosity, 30% to 60% silicon, and a surface area less than 5 m ² /g. /g surface area, for example Z less than 10, greater than 80% microporosity, 30% to 60% silicon, and less than 30m ² /g surface area, for example Z less than 10, greater than 80% microporosity, 30% to 60% silicon, and less than 10m ² /g surface area, for example Z less than 10, greater than 80% microporosity, 30% to 60% silicon, and less than 5m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 30% to 60% silicon, and less than 50m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 30% to 60% silicon, and less than 30m ² /g surface area, for example Z less than 10, greater than 90% microporosity, 30% to 60% silicon, and less than 10m ² /g surface area, for example, Z less than 10, greater than 90% microporosity, 30% to 60% silicon, and less than 5m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 30% to 60% silicon, and less than 50m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 30% to 60% silicon, and less than 30m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 30% to 60% silicon, and less than 10m ² /g surface area, for example, Z less than 10, greater than 95% microporosity, 30% to 60% silicon, and less than 5m ² /g surface area.

In certain preferred embodiments, the silicon-carbon composite comprises a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9969 or greater. For example, the silicon-carbon composite comprises a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9970 or greater. For example, the silicon-carbon composite comprises a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9975 or greater. For example, the silicon-carbon composite comprises a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9980 or greater. For example, a silicon-carbon composite material may have a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9985 or greater. For example, a silicon-carbon composite material may have a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9990 or greater. For example, a silicon-carbon composite material may have a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9995 or greater. For example, a silicon-carbon composite material may have a Z of less than 10, a microporosity of greater than 80%, a silicon content of 30% to 60% silicon, a surface area of less than 30 m ² /g, and an average coulombic efficiency of 0.9999 or greater.

Example 3. dV/dQ in Silicon-Carbon Composites. Differential capacity curves (dQ/dV vs. voltage) are frequently used as a nondestructive tool to understand phase transformations as a function of voltage in lithium battery electrodes (M. N. Obrovac et al. Structural Changes in Silicon Anodes during Lithium Insertion/Extraction, Electrochemical and Solid-State Letters, 7 (5) A93-A96 (2004); Ogata, K. et al. Revealing lithium-silicide phase transformations in nano-structured silicon-based lithium ion batteries via in situ NMR spectroscopy. Nat. Commun. 5:3217). An alternative approach to plotting dQ/dV vs. voltage, but which performs a similar analysis, is plotting dQ vs. V. For example, differential capacity plots (dQ/dv vs. voltage) were calculated from data obtained by galvanostatic cycling from 5 mV to 0.8 V at a 0.1 C rate in half-cell coin cells at 25°C. Typical differential capacity curves for silicon-based materials versus lithium in half-cells can be found in numerous references (Loveridge, M. J. et al. Towards High Capacity Li-Ion Batteries Based on Silicon-Graphene Composite Anodes and Sub-micron V-doped LiFePO4 Cathodes. Sci. Rep. 6, 37787; doi: 10.1038/srep37787 (2016); M. N. Obrovac et al. Li15Si4 Formation in Silicon Thin Film Negative Electrodes, Journal of The Electrochemical Society, 163 (2) A255-A261 (2016); Q. Pan et al. Improved electrochemical performance of micro-sized SiO2-based composite anode by prelithiation of stabilized lithium metal powder, Journal of Power Sources 347 (2017) 170-177). The first-cycle lithiation behavior depends on the crystallinity of the silicon and the oxygen content, among other factors.

After the first cycle, prior amorphous silicon materials in the art exhibit two distinct phase transition peaks in a dQ/dV vs. V plot for lithiation, and similarly, two distinct phase transition peaks in a dQ/dV vs. V plot for delithiation. For lithiation, one peak corresponds to a lithium-poor Li—Si alloy phase occurring between 0.2 and 0.4 V, and the other peak corresponds to a lithium-rich Li—Si alloy phase occurring below 0.15 V. For delithiation, one delithiation peak corresponds to lithium extraction occurring below 0.4 V, and the other delithiation peak corresponds to lithium extraction occurring between 0.4 and 0.55 V. If the Li ₁₅ Si ₄ phase is formed during lithiation, it will be delithiated at about 0.45 V, resulting in a very narrow, sharp peak.

The dQ/dV vs. voltage curve for cycle 2 for a silicon-carbon composite corresponding to Silicon-Carbon Composite 3 of Example 1 is shown in Figure 2. Silicon-Carbon Composite 3 contains a Z of 0.6. For ease of identification, the plot is divided into regimes I, II, III, IV, V, and VI. Regimes I (0.8 V - 0.4 V), II (0.4 V - 0.15 V), and III (0.15 V - 0 V) contain the lithiation potential, while regimes IV (0 V - 0.4 V), V (0.4 V - 0.55 V), and VI (0.55 V - 0.8 V) contain the delithiation potential. As described above, previous amorphous silicon-based materials in the art have exhibited phase transition peaks at the lithiation potential in two regimes (Regime II and Regime III) and at the delithiation potential in two regimes (Regime IV and Regime V).

As can be seen from Figure 2, the dQ/dV vs. voltage curves reveal a surprising and unexpected result: silicon-carbon composite 3 with a Z of 0.6 contains two additional peaks in the dQ/dV vs. V curve: Regime 1 at the lithiation potential and Regime VI at the delithiation potential. As shown in Figure 3, all six peaks are reversible and are observed upon subsequent cycles as well.

Without being bound by theory, the trimodal behavior of the dQ/dV vs. V curves shown above is novel and also reflects a novel morphology of silicon.

Notably, the novel peaks observed in Regimes I and VI are more pronounced in certain scaffold matrices and are completely absent in other samples (silicon-carbon composite samples with Z greater than 10, see description and table below) that represent prior art.

Figure 4 shows the dQ/dV vs. V curve for silicon-carbon composite 3, in which the new peaks in regime I and regime VI are clearly evident. Also shown in Figure 4 are the dQ/dV vs. V curves for silicon-carbon composite 15, silicon-carbon composite 16, and silicon-carbon composite 14 (all three samples with Z greater than 10), in contrast, in which the peaks in regime I and regime VI are both absent.

Without being bound by theory, these new peaks observed in Regime I and Regime VI are related to the properties of silicon infiltrated into the porous carbon scaffold, i.e., the interactions and properties between the porous carbon scaffold, silicon infiltrated into the porous carbon scaffold by CVI, and lithium. To provide a quantitative analysis, the inventors calculated the peak I normalized with respect to Peak III using the following formula:

φ=(maximum peak height in regime I dQ/dV)/(maximum peak height in regime III dQ/dV)
[where dQ/dV is measured in half-cell co-in cells, with regime 1 being 0.8 V to 0.4 V and regime III being 0.15 V to 0 V; half-cell co-in cells were fabricated as known in the art.]

We defined a parameter φ, calculated as follows: If a Si—C sample exhibits a graphite-related peak in regime III of the derivative curve, the former peak is removed in favor of the Li—Si-related phase transition peak for the calculation of coefficient D. In this example, the half-cell co-in cell contains an anode containing 60-90% silicon-carbon composite, 5-20% SBR-Na-CMC, and 5-20% Super C45. An example of the calculation of φ for silicon-carbon composite 3 is shown in FIG. 5. In this example, the maximum peak height in regime I was −2.39 and was found at 0.53 V. Similarly, the maximum peak height in regime III was −9.71 at 0.04 V. In this example, φ can be calculated using the above formula, yielding φ = −2.39/−9.71 = 0.25. The value of φ was determined from half-cell data for various silicon-carbon composites, as shown in Example 2. These data are summarized in Table 6. Table 6 also includes first cycle efficiency data measured in half-cell coin cells cycled from 5 mV to 0.8 V.

Properties of various silicon-carbon materials
*The data in parentheses for the first cycle efficiency were measured in the potential window of 5 mV to 1.5 V.

The data in Table 6 reveal an unexpected relationship between decreasing Z and increasing φ. All silicon-carbon composites with Z less than 10 have a φ greater than or equal to 0.13, and all silicon-carbon composites with Z greater than 10 have a φ less than 0.13. In fact, all silicon-carbon composites with Z greater than 10 have a φ of 0. This relationship is also evident in Figure 6. Without being bound by theory, silicon materials with a φ greater than or equal to 0.10 (e.g., a φ greater than or equal to 0.13, e.g., a φ greater than or equal to 0.15, e.g., a φ greater than or equal to 0.20, e.g., a φ greater than or equal to 0.25, e.g., a φ greater than or equal to 0.30, etc.) correspond to novel forms of silicon. Alternatively, silicon materials with a φ greater than 0 correspond to novel forms of silicon. Silicon-carbon composite materials having a φ of 0.10 or greater (e.g., a φ of 0.13 or greater, e.g., a φ of 0.15 or greater, e.g., a φ of 0.20 or greater, e.g., a φ of 0.25 or greater, e.g., a φ of 0.30 or greater) correspond to novel silicon-carbon composite materials. Separately, silicon-carbon composite materials having a φ of greater than 0 correspond to novel silicon-carbon composite materials.

In certain embodiments, the silicon-carbon composite comprises a φ of 0.1 or greater, a φ of 0.11 or greater, a φ of 0.12 or greater, a φ of 0.13 or greater, a φ of 0.14 or greater, a φ of 0.15 or greater, a φ of 0.16 or greater, a φ of 0.17 or greater, a φ of 0.18 or greater, a φ of 0.19 or greater, a φ of 0.20 or greater, a φ of 0.24 or greater, a φ of 0.24 or greater, a φ of 0.25 or greater, a φ of 0.30 or greater, or a φ of 0.35 or greater. In some embodiments, φ is greater than 0. In some embodiments, φ is 0.001 or greater, φ is 0.01 or greater, φ is 0.02 or greater, φ is 0.05 or greater, φ is 0.1 or greater, φ is 0.11 or greater, or φ is 0.12 or greater.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 70% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 70% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 70% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 70% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 70% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 80% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 90% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 90% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 90% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 90% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 90% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 95% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 95% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 95% microporosity, 30-60% silicon, a surface area less than 100 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 50 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, and a φ greater than or equal to 0.1, such as a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 10 m ² /g, and a φ greater than or equal to 0.1, for example, a Z less than 10, greater than 95% microporosity, 30-60% silicon, a surface area less than 5 m ² /g, and a φ greater than or equal to 0.1.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 95% microporosity, 40-60% silicon, a surface area less than 100 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 50 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 30 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 10 m ² /g, and a φ greater than 0, such as a Z less than 10, greater than 95% microporosity, 40-60% silicon, a surface area less than 5 m ² /g, and a φ greater than 0.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9969, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9970, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9975 ^... A carbon scaffold having a microporosity of greater than 80%, a surface area less than 30m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9980, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m 2 /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9985, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9990, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.15, and an average coulombic efficiency equal to or greater than 0.9995, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, ² /g, a φ of 0.15 or greater, and an average coulombic efficiency of 0.9999 or greater.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.20, and an average Coulombic efficiency equal to or greater than 0.9969, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.20, and an average Coulombic efficiency equal to or greater than 0.9970, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.20, and an average Coulombic efficiency equal to or greater than 0.9975 ^.... a carbon scaffold with a surface area less than 30m ^{2 /g, a φ of 0.20 or greater, and an average coulombic efficiency of 0.9980 or greater, e.g., Z less than 10, a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m 2} /g, a φ of 0.20 or greater, and an average coulombic efficiency of 0.9985 or greater, e.g., Z less than 10, a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ of 0.20 or greater, and an average coulombic efficiency of 0.9990 or greater, e.g., Z less than 10, a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ of 0.20 or greater, and an average coulombic efficiency of 0.9995 or greater, e.g., Z less than 10, a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, ² /g, a φ of 0.20 or greater, and an average coulombic efficiency of 0.9999 or greater.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9969, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9970, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9975 ^... A carbon scaffold having a microporosity of greater than 80%, a surface area less than 30m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9980, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m 2 /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9985, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9990, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.25, and an average coulombic efficiency equal to or greater than 0.9995, e.g., Z less than 10, a carbon scaffold having a microporosity of greater than 80%, 30-60% silicon, ² /g, a φ of 0.25 or greater, and an average coulombic efficiency of 0.9999 or greater.

In certain embodiments, the silicon-carbon composite comprises a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ greater than or equal to 0.3, and an average Coulombic efficiency greater than or equal to 0.9969, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ greater than or equal to 0.3, and an average Coulombic efficiency greater than or equal to 0.9970, for example, a Z less than 10, a carbon scaffold with greater than 80% microporosity, 30-60% silicon, a surface area less than 30 m ² /g, a φ greater than or equal to 0.3, and an average Coulombic efficiency greater than or equal to 0.9975 ^.... a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ^{2 /g, a φ equal to or greater than 0.3, and an average coulombic efficiency equal to or greater than 0.9985, for example, a Z less than 10; a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m 2 /} g, a φ equal to or greater than 0.3, and an average coulombic efficiency equal to or greater than 0.9990, for example, a Z less than 10; a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.3, and an average coulombic efficiency equal to or greater than 0.9995, for example, a Z less than 10; a carbon scaffold with a microporosity of greater than 80%, 30-60% silicon, a surface area less than 30m ² /g, a φ equal to or greater than 0.3, and an average coulombic efficiency equal to or greater than 0.9995, for example, a Z less than 10; /g, a φ of 0.3 or greater, and an average coulombic efficiency of 0.9999 or greater.

Example 4. Particle size distribution of various carbon scaffold materials. The particle size distribution of various carbon scaffold materials was measured using a laser diffraction particle size analyzer known in the art. Table 7 provides data specifically for Dv1, Dv10, Dv50, Dv90, and Dv100.

Properties of various carbon scaffold materials

Example 5. Lithium-silicon battery with an anode comprising a composite containing silicon and carbon, both Group 14 elements. Novel composites containing silicon and carbon, both Group 14 elements, have utility for dramatically improving the performance of lithium-silicon batteries. As known in the art, lithium-silicon batteries include a variety of other properties, as illustrated in this example.

The lithium-silicon battery includes an anode containing a composite containing silicon, a Group 14 element, and carbon. The concentration of the composite containing silicon, a Group 14 element, and carbon in the anode by dry weight can vary, for example, from 1 to 90%, for example, from 5% to 95%, for example, from 10% to 70%, etc. In certain embodiments, the concentration of the composite containing silicon, a Group 14 element, and carbon in the anode by dry weight is 5% to 25%, 25% to 35%, 35% to 50%, 50% to 70%, or greater than 70%.

The anode may further include other components, such as graphite, conductive carbon additives, binders, and combinations thereof.

In some embodiments, the lithium-silicon battery includes an anode comprising graphite, or a combination thereof. In this regard, exemplary graphites include, but are not limited to, natural graphite, synthetic graphite, nanographite, or a combination thereof. The concentration of graphite in the anode by dry weight can vary, for example, from 5% to 95%, for example, from 10% to 70%, for example, from 20% to 60%, for example, from 30% to 50%, etc. In certain embodiments, the lithium-silicon battery includes an anode that does not include graphite.

In a preferred embodiment, the lithium-silicon battery includes an anode containing a conductive carbon additive, or a combination thereof. Typical conductive carbon additives include, but are not limited to, carbon black, conductive carbon black, superconductive carbon black, extraconductive carbon black, ultraconductive carbon black, Super C, Super P, Super [C45 or C65], Ketjen black, acetylene black, fullerene, graphene, carbon fiber, carbon nanofiber, carbon nanotube, or a combination thereof. The dry weight concentration of the conductive carbon additive in the anode can vary, for example, from 0.1% to 20%, such as from 1% to 10%, from 2% to 8%, or from 3% to 6%, for example. In certain embodiments, such as when the anode does not contain graphite, the concentration of the conductive carbon additive by dry weight may range from 5% to 20%, such as from 10% to 20%, for example, from 14% to 16%, etc.

In a preferred embodiment, the lithium-silicon battery includes an anode containing a binder, or a combination thereof. Typical binders include, but are not limited to, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (Na-CMC), polyacrylonitrile (PAN), polyacrylic acid latex, polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyamideimide (PAI), polyimide (PI), and combinations thereof. In certain embodiments, the binder may include lithium ions as counterions. The concentration of the binder in the anode by dry weight may vary, for example, from 0.1% to 20%, for example, from 1% to 10%, for example, from 2% to 8%, for example, from 3% to 6%, etc. In certain embodiments, such as when the anode does not contain graphite, the concentration of the binder by dry weight may range from 5% to 20%, such as from 10% to 20%, for example, from 14% to 16%, etc.

The anode of a lithium-silicon battery comprises a composite containing silicon, a Group 14 element, and carbon, and further comprises porosity in a dry state. The porosity of the dry anode is, for example, 10% to 90%, for example, 20% to 80%, for example, 30% to 70%, for example, 40% to 60%. In certain preferred embodiments, the porosity of the dry anode is 30% to 50%. In certain preferred embodiments, the porosity of the dry anode is 10% to 50%.

The lithium-silicon battery includes an anode containing a composite containing silicon, a Group 14 element, and carbon, and further includes a cathode. Typical cathodes include, but are not limited to, lithium cobalt oxide (LiCoO ₂ ) (LCO), lithium manganese oxide (LiMn ₂ O ₄ ) (LMO), lithium iron phosphate (LiFePo ₄ ) (LFP), lithium nickel cobalt aluminum oxide (LiNiCoAlO ₂ ) (NCA), lithium titanate (Li ₂ TiO ₃ ) (LTO), or lithium nickel manganese cobalt oxide (LiNi _x Mn _y Co _z O _{2 ).} ) (NMC, where x+y+z=1 and x:y:z=3:3:3 (NMC333), 4:3:3 (NMC433), 5:3:2 (NMC532), 6:1:1 (NMC611), 6:2:2 (NMC622), or 8:1:1 (NMC811)). In certain preferred embodiments, the cathode is NMC811.

Lithium-silicon batteries contain a ratio known as the N/P ratio, which represents the capacity ratio between the anode and cathode electrodes in the battery cell. N/P is important in determining the energy density of a lithium-silicon battery. Without being bound by theory, a lower N/P ratio provides less excess anode, and therefore a higher energy density of the lithium-silicon battery. The average discharge potential of a silicon-carbon anode is higher than that of a graphite anode. Without being bound by theory, the presence of φ in the anode reduces the excess anode required to prevent plating of the battery. Thus, without being bound by theory, the novel anode materials disclosed herein that include a φ greater than 0 (e.g., a φ of 0.15 or greater, e.g., a φ of 0.2 or greater, e.g., a φ of 0.25 or greater, e.g., a φ of 0.3 or greater, etc.) allow for a lower N/P ratio, thereby providing a higher energy density of the lithium-silicon battery. In certain embodiments, the N/P ratio is greater than 1.1, for example, an N/P ratio greater than 1.2, for example, an N/P ratio greater than 1.3, for example, an N/P ratio greater than 1.4, for example, an N/P ratio greater than 1.5, for example, an N/P ratio greater than 2.0, etc. In certain preferred embodiments, the N/P ratio is 2.0 or less, for example, an N/P ratio of 1.5 or less, for example, an N/P ratio of 1.4 or less, for example, an N/P ratio of 1.3 or less, for example, an N/P ratio of 1.2 or less, for example, an N/P ratio of 1.1 or less, for example, an N/P ratio of 1.0 or less, for example, an N/P ratio of 0.9 or less, for example, an N/P ratio of 0.8 or less, etc.

Lithium-silicon batteries contain an electrolyte, which in turn contains various components, including a solvent, a solvent additive, and electrolyte ions. Typical electrolyte components include, but are not limited to, ethylene carbonate (EC), diethylene carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl propyl ether (EPE), fluorinated cyclic carbonate (F-AEC), fluorinated linear carbonate (F-EMC), dimethylacrylamide (DMAA), succinic anhydride (SA), tris(trimethylsilyl)borate (TTMB), tris(trimethylsilyl)phosphate (TTSP), 1,3-propane sultone (PS), fluorinated ethers (F-EPE), enhanced organosilicon electrolyte materials fluoroethylene carbonate (FEC), and enhanced organosilicon electrolyte materials (e.g., OS3), vinylene carbonate (VC), LiPF ₆ , LiBF ₄ , LiBOB, LiTFSI, LiFSI, LiClO ₄ , and combinations thereof. In certain embodiments, the concentration of the electrolyte salt is greater than 1.0 M, such as greater than 1.2 M, such as greater than 1.3 M, such as greater than 1.4 M, such as greater than 1.5 M, for example greater than 2.0 M. In certain preferred embodiments, the concentration of the electrolyte salt is less than 2.0 M, such as less than 1.5 M, such as less than 1.4 M, such as less than 1.3 M, such as less than 1.2 M, such as less than 1.1 M, such as less than 1.0 M, for example less than 0.9 M.

Lithium-silicon batteries containing a Group 14 silicon and carbon-containing composite include a separator that maintains separation between the anode and cathode. The separator may be made of one or more layers of polymeric material, or may be coated with aramid, ceramic, or fluoride material. Typical separator materials include, but are not limited to, nonwoven fabrics (cotton, nylon, polyester, glass), polymer films (polyethylene, polypropylene, poly(tetrafluoroethylene), polyvinyl chloride), ceramics, and natural products (rubber, asbestos, wood). In certain preferred embodiments, the separator includes, but is not limited to, typical polymers, such as semi-crystalline polyolefin-based materials such as polyethylene and polypropylene, and graft polymers (including microporous grafted polymethyl methacrylate and polyethylene-grafted siloxane), polyvinylidene fluoride nanofiber webs, and polytriphenylamine (PTPA).

Lithium-silicon batteries containing a composite containing silicon, a Group 14 element, and carbon are cycled between the lower and upper limits of the lithium-silicon battery's operating voltage window during use. Without being bound by theory, lowering the lower limit of the operating voltage window provides a higher energy density for the lithium-silicon battery. Therefore, without being bound by theory, the novel anode materials disclosed herein, including a φ greater than 0 (e.g., a φ of 0.15 or greater, e.g., a φ of 0.2 or greater, e.g., a φ of 0.25 or greater, e.g., a φ of 0.3 or greater), lower the lower limit of the voltage window, thereby increasing the energy density of the lithium-silicon battery. In certain embodiments, the lower limit of the voltage window is 3.0 V or less (e.g., 2.9 V or less, e.g., 2.8 V or less, e.g., 2.7 V or less, e.g., 2.6 V or less, e.g., 2.5 V or less, e.g., 2.4 V or less, e.g., 2.3 V or less). The upper limit of the voltage window during cycling of a lithium-silicon battery may vary. For example, the upper limit of the voltage window can vary, such as 4.0V or higher (e.g., 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, 4.8V, 4.9V, or 5.0V).

Description of implementation

Embodiment 1. A material in which φ, calculated by Equation 4, is greater than 0.

Embodiment 2. A material in which φ, calculated using equation 4, is 0.1 or greater.

Embodiment 3. A silicon-carbon composite material in which φ, calculated by Equation 4, is greater than 0.

Embodiment 4. A silicon-carbon composite material in which φ, calculated using Equation 4, is 0.1 or greater.

Embodiment 5: A silicon-carbon composite material having Z less than 10 and φ calculated by equation 4 greater than 0.

Embodiment 6: A silicon-carbon composite material having Z less than 10 and φ calculated by equation 4 being 0.1 or greater.

Embodiment 7. A silicon-carbon composite material comprising a Z less than 10, a surface area less than 100 m ² /g, and a φ calculated by Equation 4 greater than 0.

Embodiment 8. A silicon-carbon composite material comprising a Z of less than 10, a surface area of less than 100 m ² /g, and a φ, calculated by Equation 4, of 0.1 or greater.

Embodiment 9. A silicon-carbon composite material comprising a Z less than 10, a surface area less than 50 m ² /g, and a φ calculated by Equation 4 greater than 0.

Embodiment 10. A silicon-carbon composite material having a Z of less than 10, a surface area of less than 50 m ² /g, and a φ, calculated by Equation 4, of 0.1 or greater.

Embodiment 11. A silicon-carbon composite material comprising a Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by Equation 4 greater than 0.

Embodiment 12. A silicon-carbon composite material having a Z of less than 10, a surface area of less than 30 m ² /g, and a φ, calculated by Equation 4, of 0.1 or greater.

Embodiment 13. A silicon-carbon composite material comprising a Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by Equation 4 greater than 0.

Embodiment 14. A silicon-carbon composite material having a Z of less than 10, a surface area of less than 10 m ² /g, and a φ, calculated by Equation 4, of 0.1 or greater.

Embodiment 15. A silicon-carbon composite material comprising a Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by Equation 4 greater than 0.

Embodiment 16. A silicon-carbon composite material having a Z of less than 10, a surface area of less than 5 m ² /g, and a φ, calculated by Equation 4, of 0.1 or greater.

Embodiment 17. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and φ, calculated by equation 4, greater than 0.

Embodiment 18. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and φ, as calculated by equation 4, greater than or equal to 0.1.

Embodiment 19. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, as calculated by equation 4, greater than 0.

Embodiment 20. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, as calculated by Equation 4, greater than or equal to 0.1.

Embodiment 21. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, as calculated by equation 4, greater than 0.

Embodiment 22. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than or equal to 0.1.

Embodiment 23. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0.

Embodiment 24. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, as calculated by equation 4, greater than or equal to 0.1.

Embodiment 25. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 26. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 27. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 28. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 29. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 30. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 31. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 32. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 33. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 34. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 35. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 36. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.12, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 37. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 38. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 39. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 40. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 41. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 42. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 43. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 44. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 45. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 46. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 47. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 48. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 49. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 50. A silicon-carbon composite comprising 30% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 51. A silicon-carbon composite according to any one of embodiments 1 to 50, wherein the silicon-carbon composite has a Dv50 of 5 nm to 20 microns.

Embodiment 52. The silicon-carbon composite of any one of embodiments 1 to 51, wherein the silicon-carbon composite has a capacity greater than 900 mA/g.

Embodiment 53. The silicon-carbon composite of any one of embodiments 1 to 51, wherein the silicon-carbon composite has a capacity greater than 1300 mA/g.

Embodiment 54. The silicon-carbon composite of any one of embodiments 1 to 51, wherein the silicon-carbon composite has a capacity greater than 1600 mA/g.

Embodiment 55. An energy storage device comprising the silicon-carbon composite described in any one of embodiments 1 to 53.

Embodiment 56. A lithium ion battery comprising the silicon-carbon composite of any one of embodiments 1 to 53.

Embodiment 57. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and φ, as calculated by Equation 4, greater than or equal to 0.1.

Embodiment 58. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, as calculated by equation 4, greater than 0.

Embodiment 59. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, as calculated by equation 4, greater than or equal to 0.1.

Embodiment 60. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, as calculated by equation 4, greater than 0.

Embodiment 61. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, as calculated by equation 4, greater than or equal to 0.1.

Embodiment 62. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, as calculated by equation 4, greater than 0.

Embodiment 63. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, as calculated by equation 4, greater than or equal to 0.1.

Embodiment 64. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 65. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 50 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 66. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 67. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 68. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 69. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 70. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 71. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 70% microporosity.

Embodiment 72. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 73. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 74. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 75. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 76. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 77. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 80% microporosity.

Embodiment 78. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 79. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 80. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 81. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 82. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 83. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 90% microporosity.

Embodiment 84. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 85. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 30 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 86. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 87. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 10 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 88. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and φ, calculated by equation 4, greater than 0, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 89. A silicon-carbon composite comprising 40% to 60% silicon by weight, Z less than 10, a surface area less than 5 m ² /g, and a φ calculated by equation 4 greater than or equal to 0.1, and a carbon scaffold comprising a pore volume, the pore volume comprising greater than 95% microporosity.

Embodiment 90. A silicon-carbon composite according to any one of embodiments 57 to 89, wherein the silicon-carbon composite has a Dv50 of 5 nm to 20 microns.

Embodiment 91. The silicon-carbon composite of any one of embodiments 57 to 89, wherein the silicon-carbon composite has a capacity greater than 900 mA/g.

Embodiment 92. The silicon-carbon composite of any one of embodiments 57 to 89, wherein the silicon-carbon composite has a capacity greater than 1300 mA/g.

Embodiment 93. The silicon-carbon composite of any one of embodiments 57 to 89, wherein the silicon-carbon composite has a capacity greater than 1600 mA/g.

Embodiment 94. An energy storage device comprising the silicon-carbon composite described in any one of embodiments 57 to 89.

Embodiment 95. A lithium ion battery comprising the silicon-carbon composite of any one of embodiments 57 to 89.

Embodiment 96. Any one of embodiments 1 to 95, in which φ is 0.11 or greater.

Embodiment 97. Any one of embodiments 1 to 95, in which φ is 0.12 or greater.

Embodiment 98. Any one of embodiments 1 to 95, in which φ is 0.13 or greater.

Embodiment 99. Any one of embodiments 1 to 95, in which φ is 0.14 or greater.

Embodiment 100. Any one of embodiments 1 to 95, in which φ is 0.15 or greater.

From the foregoing, it will be understood that, while specific embodiments of the invention have been described herein for purposes of disclosure, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

All U.S. patents, U.S. patent publications, and U.S. patent applications, patents and applications of other countries, and non-patent literature referenced herein and/or listed in the Application Data Sheets (including, but not limited to, U.S. Application Serial No. 16/996,694 filed August 18, 2020, U.S. Provisional Patent Application Serial No. 63/075,566 filed September 8, 2020, U.S. Patent Application Serial No. 17/336,104 filed June 1, 2021; and U.S. Patent Application Serial No. 17/336,085 filed June 1, 2021) are hereby incorporated by reference in their entirety.

Claims (24)

1. A silicon-carbon composite comprising:
a. a carbon scaffold comprising a pore volume, wherein the pore volume comprises greater than 70% microporosity;
b. a silicon content of 40% to 60% by weight;
c. Z less than 5 , where Z has the formula:
Z=1.875×[(M1100-M)/M1100]×100
[wherein, when a silicon-carbon composite is heated in air from about 25°C to about 1100°C, M is the mass of the silicon-carbon composite at 1100°C, and M is the minimum mass of the silicon-carbon composite from 800°C to 1100°C, and these masses are measured by thermogravimetric analysis.]
Represented by:
d. a surface area of less than 30 m ² /g; and e. φ greater than or equal to 0.1, where φ is defined by the following formula:
φ=(maximum peak height in regime I dQ/dV)/(maximum peak height in regime III dQ/dV)
[where dQ/dV is measured in a half-cell coin cell, regime I is 0.8 V to 0.4 V, and regime III is 0.15 V to 0 V]
It is expressed as:
A silicon-carbon composite comprising: 10. The silicon-carbon composite of claim 1, wherein the pore volume of the carbon scaffold is greater than 80% microporosity. 3. The silicon-carbon composite of claim 2, wherein the pore volume of the carbon scaffold is greater than 90% microporosity. 3. The silicon-carbon composite of claim 2, wherein the pore volume of the carbon scaffold is greater than 95% microporosity. 10. The silicon-carbon composite of claim 1, having a surface area of less than 10 m ² /g. 3. The silicon-carbon composite of claim 2, having a surface area of less than 10 m ² /g. 4. The silicon-carbon composite of claim 3, having a surface area of less than 10 m ² /g. The silicon-carbon composite of claim 1, wherein Z is less than 5. The silicon-carbon composite according to claim 2, wherein Z is less than 5. The silicon-carbon composite of claim 3, wherein Z is less than 5. The silicon-carbon composite of claim 1, wherein the silicon-carbon composite has a Dv50 in the range of 5 nm to 20 microns. The silicon-carbon composite of claim 2, wherein the silicon-carbon composite has a Dv50 in the range of 5 nm to 20 microns. The silicon-carbon composite of claim 3, wherein the silicon-carbon composite has a Dv50 in the range of 5 nm to 20 microns. 10. The silicon-carbon composite of claim 1, wherein the silicon-carbon composite comprises a capacity greater than 900 mA h /g. 3. The silicon-carbon composite of claim 2, wherein the silicon-carbon composite comprises a capacity greater than 900 mA h /g. 4. The silicon-carbon composite of claim 3, wherein the silicon-carbon composite comprises a capacity greater than 900 mA h /g. The silicon-carbon composite of claim 1, further comprising lithium ions. The silicon-carbon composite of claim 2, further comprising lithium ions. The silicon-carbon composite of claim 3, further comprising lithium ions. The silicon-carbon composite according to any one of claims 1 to 19, wherein φ is 0.11 or greater. The silicon-carbon composite according to any one of claims 1 to 19, wherein φ is 0.12 or greater. The silicon-carbon composite according to any one of claims 1 to 19, wherein φ is 0.13 or greater. The silicon-carbon composite according to any one of claims 1 to 19, wherein φ is 0.14 or greater. The silicon-carbon composite according to any one of claims 1 to 19, wherein φ is 0.15 or greater.