JP7537752B2 - Skeleton-forming agent, electrode using same, and method for manufacturing electrode - Google Patents

Description

The present invention relates to a skeleton-forming agent used to form the skeleton of an active material layer in an electrode of a non-aqueous electrolyte secondary battery, an electrode using the same, and a method for manufacturing the electrode.

The use of secondary batteries has expanded from electronic devices to automobiles and large-scale power storage systems, and the market size is expected to grow into an industry worth more than 10 trillion yen. In particular, information and communication devices such as smartphones and tablet terminals have become extremely popular, with the global penetration rate exceeding 30%.

In addition, the range of applications for secondary batteries is expanding to include power sources for next-generation automobiles, such as electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs). Furthermore, since the Great East Japan Earthquake in 2011, secondary batteries have been used for home backup power sources, natural energy storage, load leveling, and other purposes, and the uses of secondary batteries are expanding. In this way, secondary batteries are also indispensable in the introduction of energy-saving and new energy technologies.

Traditionally, alkaline secondary batteries such as nickel-cadmium batteries and nickel-hydrogen batteries have been the mainstream of secondary batteries, but the use of non-aqueous electrolyte secondary batteries, especially lithium secondary batteries (lithium ion batteries), is increasing due to their characteristics of small size, light weight, high voltage, and no memory effect. A non-aqueous electrolyte secondary battery is composed of a positive electrode, a negative electrode, a separator, an electrolytic solution or electrolyte, and a battery container (storage case).

Electrodes such as positive and negative electrodes are composed of an active material, a conductive additive, an organic polymer binder, and a current collector. In general, electrodes are manufactured by mixing the active material, conductive additive, and organic binder in a solvent to form a slurry, coating this on a current collector, drying it, and then rolling it with a roll press or the like.

The electrode is rolled after drying in order to shrink the volume of the electrode's active material layer, i.e., the coating layer consisting of the active material, conductive additive, and binder, thereby increasing the contact area with the conductive additive and current collector. This strengthens the electronic conductive network of the active material layer and improves electronic conductivity.

Binders are used to bind active materials together, active materials and conductive additives, active materials and current collectors, conductive additives and current collectors, etc. Binders can be broadly divided into "solution type" binders that are dissolved in a solvent and used in liquid form, "dispersion type (emulsion/latex type)" binders that are used by dispersing solids in a solvent, and "reactive type" binders that are used by reacting binder precursors with heat or light.

Binders can also be divided into water-based and organic solvent-based binders depending on the type of solvent. For example, polyvinylidene fluoride (PVdF) is a soluble binder, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) is used when preparing electrode slurry. Styrene butadiene rubber (SBR) is a dispersed binder, and SBR fine particles are dispersed in water for use. Polyimide (PI) is a reactive binder, and a PI precursor is dissolved or dispersed in a solvent such as NMP and heated to promote imidization and crosslinking reactions to obtain a tough PI.

Although it depends on the molecular weight and substituents of the binder, soluble binders include polyvinylidene fluoride (PVdF) and ethylene vinyl acetate (EVA). Dispersed binders include styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), urethane rubber, polypropylene (PP), polyethylene (PE), polyvinyl acetate (PVAc), and nitrocellulose. Reactive binders include polyimide (PI), polyamide (PA), polyamideimide (PAI), polybenzimidazole (PBI), and polybenzoxazole (PBO).

In addition, organic solvent binders such as N-methyl-2-pyrrolidone (NMP) are believed to have the potential to adversely affect the environment, and so they must be recovered when the electrodes are dried, which increases the cost of electrode production. In addition, organic solvent binders swell in high-temperature electrolytes and increase electrode resistance, making them difficult to use in high-temperature environments.

Water-based soluble binders have poor oxidation and reduction resistance, and many of them gradually decompose due to repeated charging and discharging, so they do not provide sufficient life characteristics. In addition, they lack output characteristics due to low ionic conductivity. Dispersed binders have the advantage that water can be used as a solvent, but the dispersion stability is easily compromised by the degree of acidity or alkalinity (pH), water concentration, or environmental temperature, and they are prone to segregation, aggregation, and precipitation during mixing of the electrode slurry. In addition, the binder particles dispersed in water have a particle size of 1 to 800 nm, and when the water is evaporated by drying, the particles fuse together to form a film. This film has no electrical conductivity or ionic conductivity, so even a slight difference in the amount used can have a significant effect on the output characteristics and life characteristics of the battery.

When the above-mentioned soluble or dispersed binders are combined with active materials that undergo drastic volume changes during charging and discharging, such as sulfur (S), silicon (Si), tin (Sn), and aluminum (Al), stable life characteristics cannot be obtained, and the charge/discharge capacity drops to less than half after a few cycles.

On the other hand, reactive binders are excellent in all aspects: heat resistance, binding properties, and chemical resistance. PI in particular exhibits high heat resistance and binding properties, and can provide stable life characteristics even with active materials that undergo large volume changes, and the binder is less likely to swell even in high-temperature electrolytes.

According to Non-Patent Document 1, by combining PI with a high-strength current collector, deterioration of the current collector can be prevented and the life characteristics can be further improved.

Patent Document 1 discloses that a LiFePO ₄ /SiO-based lithium ion secondary battery using PI for the positive and negative electrodes can be stably charged and discharged even at a high temperature of 120° C. On the other hand, when PI is used, it has excellent adhesion to the current collector, so when combined with an active material that undergoes large volume change, wrinkles, cracks, etc. may occur in the current collector during initial charge and discharge. Therefore, it is necessary to use iron foil or stainless steel foil, which has high mechanical strength, for the current collector.

Apart from the above organic binders, there have been few reports in the field of non-aqueous electrolyte secondary batteries, but Patent Documents 2 to 4 disclose techniques using inorganic binders in secondary battery electrodes. Patent Document 2 proposes an electrode mixture for non-aqueous electrolyte secondary batteries, an electrode, and a non-aqueous electrolyte secondary battery that contain an amorphous carbon material containing an inorganic binder, a conductive agent, a binder, and a solvent, and has a viscosity in the range of 2000 mPa·s to 10000 mPa·s. It also shows that the inclusion of an inorganic binder may suppress the decomposition reaction of the binder.

Patent Document 3 and Patent Document 4 provide a physically and chemically stable lithium ion battery using an inorganic binder. On the other hand, as mentioned above, an electrode generally comprises an active material layer (a layer made of an active material, a conductive additive, and a binder) and a current collector, but there are also cases where a layer different from the active material layer is provided on the active material layer.

For example, Patent Document 5 proposes a non-aqueous secondary battery using an electrode sheet having a layer mainly made of a metal or semi-metal oxide and at least one auxiliary layer containing water-insoluble particles. The auxiliary layer provided on the electrode sheet is composed of water-insoluble conductive particles and a binder, and may further contain particles that are substantially non-conductive. The particles that are substantially non-conductive are oxides, and oxides containing compounds that are soluble in both acidic and alkaline conditions are preferred. It is noted that the binder used in forming the electrode mixture can be used as the binder used in the auxiliary layer.

Such secondary batteries are widely available in various shapes, including cylindrical, rectangular, and laminated types. For batteries with relatively small capacity, cylindrical types are used because of their pressure resistance and ease of sealing, while for batteries with relatively large capacity, rectangular types are used because of their ease of handling.

In terms of the electrode structure of secondary batteries, they are broadly divided into two types: stacked and wound. That is, in stacked batteries, electrodes in which positive and negative electrodes are alternately stacked with a separator between them are housed in a battery case. Most stacked batteries have a rectangular battery case. On the other hand, in wound batteries, the positive and negative electrodes are housed in a battery case in a spirally wound state with a separator between them. Wound battery cases are available in cylindrical and rectangular shapes.

Patent 5728721 Patent 5293020 JP 11-144736 A JP 10-523411 A International Publication No. 1996/027910

Takashi Mukai et al., Development of Lithium-Ion Battery Active Materials and Electrode Material Technology, Science & Technology Co., Ltd., pp. 269-311 (2014), ISBN: 978-4-86428-089-1 Masahiro Yanagida et al., Abstracts of the 83rd Electrochemical Society, 1T28, (2016)

As mentioned above, in Non-Patent Document 1 and Patent Document 1, when a thin copper foil or the like is used for the current collector, wrinkles and cracks occur, and the electrode is not viable (see FIG. 19). On the other hand, if a high-strength iron foil or stainless steel foil is used for the current collector, wrinkles and cracks can be prevented from occurring even if the current collector is thin. However, because the current collector has very high strength and excellent toughness, the process of punching out the electrode is difficult, and the active material layer falls off when cutting, and burrs occur on the cut surface.

In addition, PI is so resistant to chemicals that it is insoluble in almost all organic solvents. Therefore, to prepare the electrode slurry, a PI precursor such as polyamic acid (polyamide acid) is dissolved in NMP and heated at 200°C or higher to promote an imidization reaction (dehydration cyclization reaction) to obtain PI. After the imidization reaction, a crosslinking reaction occurs by heat treatment at a higher temperature, resulting in a PI with high mechanical strength. From the viewpoint of the electrode life, it is preferable to heat treat the electrode at a high temperature so that the PI is not carbonized. However, heat treatment at 200°C or higher not only reduces the flexibility of the electrode, making it difficult to handle, but also oxidizes the active material and the surface of the current collector, which can cause irreversible capacity. Heat treatment at a high temperature also increases power consumption during electrode production.

Some PI binders exist that have been imidized to form PI and dispersed in a solvent, but if one that has already been imidized is used when added to the slurry, the electrode will have poor adhesion strength and poor life characteristics. In addition, many reactive binders, including PI, occlude alkali metal ions during initial charging, but cannot be released during discharge, which causes irreversible capacity. For example, depending on the molecular structure, PI has an irreversible capacity of 500 to 1000 mAh/g. Therefore, electrodes that use reactive binders have low initial charge/discharge efficiency and a large decrease in battery capacity.

Incidentally, nail penetration tests are conducted to confirm the safety of batteries. When a nail is penetrated into a fully charged battery, heat generation exceeding 600°C can be observed even in batteries with a nominal capacity of 1 Ah. Non-Patent Document 1 shows that batteries using Si-based active materials have a significantly improved nail penetration safety. It has also been shown that batteries using Si-based negative electrodes and heat-resistant nonwoven fabric separators have an even further improved safety.

Non-Patent Document 2 examines this phenomenon, and shows that if the electronic conductivity of the electrode active material layer is high, the temperature generated by the battery and the nail when the nail is penetrated will be high, and if the electronic conductivity of the electrode active material layer is low, the temperature generated by the battery and the nail when the nail is penetrated will also be low. In other words, the electronic conductivity of the electrode active material layer contributes greatly to the safety of the battery against nail penetration. If the electronic conductivity of the active material layer is high, the current value flowing through the nail will be large, and the amount of heat generated by the nail and the battery will also increase, and if the electronic conductivity is low, the current value flowing through the nail will be small, and the amount of heat generated per unit time will be small.

When alloy-based active materials are alloyed with alkali metals, their electronic conductivity improves. For example, Si in a discharged state is a semiconductor and has a low electronic conductivity, while Li _x Si alloy (0<x≦4.4) in a charged state is a conductor and has a high electronic conductivity. That is, in a Si-based negative electrode, an internal short circuit causes the Si-based active material in the shorted portion to be delithiated, the electronic conductivity of the electrode drops sharply, and the current is cut off, which is thought to suppress the temperature rise of the battery.

However, in electrodes with a large amount of conductive additive in the active material layer, or electrodes using materials in which highly conductive materials are coated or composited with the active material, the electronic conductivity of the active material layer becomes high, and even if a Si-based material is used, the current interruption mechanism described above does not function well, and the temperature rise of the battery cannot be sufficiently suppressed. Therefore, in order to design a battery that prioritizes safety, it was necessary to use an electrode with a low electrical conductivity active material layer. Conversely, an electrode composition that prioritizes safety is likely to result in a low-output battery due to its low electronic conductivity.

Even in batteries that use electrodes with low electronic conductivity in the active material layer, momentary heat generation during an internal short circuit cannot be eliminated. If this heat causes the binder to carbonize, the electrode's electronic conductivity will increase and safety will be compromised. Even with organic reactive binders that have excellent heat resistance, the heat resistance temperature is limited to around 400°C, and if the temperature rise caused by an internal short circuit exceeds the binder's heat resistance temperature, the binder will carbonize. Therefore, there is a demand for binders that do not carbonize.

In addition, it is generally known that active materials with small volume changes exhibit good life characteristics. For example, the charging reaction of Si (Si + 4.4Li++ 4.4e- → Li4.4Si) causes a volume change of about 4 times, while the charging reaction of SiO (SiO + 8.4Li++ 8.4e- → Li4.4Si + Li ₄ SiO ₄ ) causes a volume change of about 2.7 times, excluding the volume change for the initial generation of Li ₄ SiO ₄ , so SiO shows superior life characteristics compared to Si.

As another example, in a negative electrode that uses a mixture of Si and alumina, as the Si ratio decreases, the capacity decreases compared to a pure Si negative electrode, but the life characteristics tend to improve. Alumina is inactive with Li and does not contribute to the charge/discharge reaction, but it acts as a buffer against the volume change of Si, making it possible to reduce the volume change of the entire electrode.

For example, the charging reaction of a Si negative electrode is represented by the following reaction formula 1, and the volume changes by about four times compared to before charging, and the stress on the electrode binder also increases by about four times.
Si+4.4Li++4.4e-→Li4.4Si (Formula 1)

If the negative electrode is made by adding an equimolar amount of Al ₂ O ₃ to Si, the charging reaction will be as shown in formula (2) from a macroscopic point of view, since Al ₂ O ₃ is inactive with Li. In such an electrode, the volume change of the electrode will be half that of a pure Si electrode, and the stress on the electrode binder will also be half. Therefore, it is expected that the capacity of an electrode mixed with a material that changes in volume less than Si will decrease as the Si ratio decreases, but the life characteristics will tend to improve.
0.5Si+0.5Al ₂ O ₃ +2.2Li++2.2e-
→0.5Li4.4Si+0.5Al ₂ O ₃ (Formula 2)

However, in actual life characteristics, although there is a slight effect of improving life, the rate of Si degradation in each cycle does not change much. This is because, from a microscopic perspective, the volume change of the Si particles themselves is about four times, so the stress on the electrode binder is the same as in formula 1, and ultimately, stress is concentrated at the bonding parts. In particular, in electrodes in which electrode materials or electrode materials and current collectors are point-bonded with a binder, the bonding parts receive concentrated stress due to the volume change, losing bonding properties and making the conductive network of the electrode prone to destruction.

On the other hand, if the binder is surface-bonded, the bonded parts distribute stress evenly, making the conductive network less likely to be destroyed, but the binder inhibits the movement of ions, resulting in reduced output characteristics. Although it depends on the type of binder, point bonding is more likely to occur when the amount of binder is small, while surface bonding is more likely to occur when the amount of binder is large.

Of the many binders available, the current situation is that only reactive binders such as PI can stably charge and discharge alloy-based active materials. However, reactive binders require the use of organic solvents during slurry production and a heat treatment process at 200°C or higher, and the resulting electrodes have a large irreversible capacity derived from the binder, and there are also limitations in terms of safety.

In addition, reactive binders alone are not sufficient to provide sufficient life characteristics, and so they must be combined with SiO or high-strength collector foil. Organic substances have low melting points, are easily soluble in organic solvents, and are flammable, while inorganic substances are known to have high melting points, are poorly soluble in organic solvents, are non-flammable, and have high thermal conductivity. Therefore, if a binder composed of inorganic substances can be used, there is a high possibility that an electrode with high heat resistance, excellent electrolyte resistance, and excellent heat dissipation properties can be obtained.

However, many conventional inorganic binders have not been suitable for use in electrodes of non-aqueous electrolyte secondary batteries. Inorganic binders can be broadly divided into four types: silicate-based, phosphate-based, sol-based, and cement-based. Of these, the inventors focused on silicate-based and phosphate-based binders, and in particular alkali metal silicate-based binders, which have strong binding properties against metals, oxides, and carbon, and heat resistance of 1000°C or higher.

The silicate-based binder may be an alkali metal silicate, a silicate of a guanidine compound, or a silicate of an ammonium compound. A silicate-based inorganic binder is a compound whose main molecular skeleton is silicon (Si) and oxygen (O) with a siloxane bond (-Si-O-Si-), and is different from an organic binder whose main skeleton is carbon (see Figure 21a).

In addition, some of the Si sites in the siloxane bond may be replaced with transition metal elements such as Al, Zr, Ti, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y.

There _{are many kinds of silicates, such as polysilicates such as orthosilicate (A4SiO4 ) , metasilicate (A2SiO3 )} , pyrosilicate ( _A6Si2O7 ), disilicate ( _A2Si2O5 ), _{and tetrasilicate (A2Si4O9 ) , as well as A2Si2O5, A2Si3O7 , and A2Si4O9} , which may be hydrates. In terms of their structure, they can be roughly classified into _crystalline silicates _and non- _{crystalline silicates} ( _{A = alkali} metal element, _guanidine compound, or ammonium compound). As the proportion of A in the silicate increases, the melting point of such silicates tends to decrease, and at the same time, they show solubility in water.

Industrially, the proportion of A in silicate can be continuously changed, and any salt can be adjusted. The general molecular formula of silicate is expressed in _the form _A2O.nSiO2 .

Due to this difference in molecular structure, they exhibit higher heat resistance and oxidation resistance than organic binders, and are used in a variety of fields, including fire retardants, waterproofing agents, bleaches, detergents, soaps, coating agents, sealants, and civil engineering ground strengthening agents. However, there have been few reports of their use in non-aqueous electrolyte secondary batteries.

The phosphate salts may be aluminum phosphate salts, magnesium phosphate salts, or calcium phosphate salts.

When phosphate-based inorganic binders are heated, water is removed from the hydroxyl groups, forming covalent bonds between phosphorus and oxygen, and a dehydration condensation reaction occurs. This dehydration condensation reaction can occur at up to six sites per molecule centered on the transition metal (M), resulting in a three-dimensional polymerized transition metal phosphate. In other words, it is a compound whose main molecular skeleton is phosphorus (P), oxygen (O), and transition metal (M) with aluminophosphate bonds, and is different from organic binders which have a skeleton mainly made of carbon (see Figure 21b).

In addition, some of the transition metal sites may be replaced with transition metal elements such as Al, Mg, Ca, Cu, Fe, Ba, Ti, Mn, Mo, Mg, Si, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y.

Specifically, aluminum phosphates include monobasic aluminum phosphate (Al( _{H2PO4 ) 3} ), dibasic aluminum phosphate ( _Al2 ( _H2PO4 ) ₃ ), and dibasic aluminum metaphosphate (Al( _PO3 ) ₃ ). Magnesium phosphates include monobasic magnesium phosphate (Mg( _H2PO4 ) ₃ ), dibasic magnesium phosphate ( _MgHPO4 ), and dibasic magnesium metaphosphate (Mg( _PO3 ) ₂ ). Calcium phosphates include monobasic calcium phosphate (Ca( _{H2PO4 ) 3} ), dibasic calcium phosphate ( _CaHPO4 ), tribasic calcium phosphate ( _Ca3 ( _{H2PO4 ) 2} ), and dibasic calcium metaphosphate (Ca( _{PO3 ) 2} ), which may be hydrates. In terms of their _structure , they can be roughly divided into crystalline phosphates and noncrystalline phosphates.

Industrially, the ratio of M and P in phosphate can be continuously changed, and any salt can be prepared. The general molecular formula of _phosphate is expressed in the form _M.nHxPO4 (M=Al or Mg, Ca).

The sol system is a colloidal solution in which oxide particles are dispersed in water. The particle size of the oxide is 10 nm or more and 200 nm or less, and hydroxyl groups are present on the surface. For example, when the oxide is _SiO2 , a siloxane bond is formed by dehydration condensation, but since this siloxane bond is formed inside the oxide particle, the binding force is weaker than that of silicic acid salts. In addition, pH control is important, and there is a problem that it is difficult to maintain a stable sol state. In the present invention, the sol system is not preferably used as a skeleton forming agent because it is difficult to penetrate into the active material layer.

Patent Document 2 indicates that the inclusion of an inorganic binder in the binder may suppress the decomposition reaction of the binder. This is thought to be because carbon materials (graphite, soft carbon, hard carbon, etc.) have a charge/discharge plateau potential near 0.1 V (vs. Li+/Li) and the electrode has a strong reducing power, so the inorganic binder, which has excellent reduction resistance, suppresses the decomposition reaction.

However, because alloy-based materials have a higher charge/discharge plateau potential than carbon materials and a weaker reducing power than carbon-based electrodes, the binder decomposition reaction does not occur very often. Therefore, suppressing the binder decomposition reaction does not significantly improve the life characteristics of alloy-based electrodes.

Patent Document 2 also indicates that the inorganic binder contains inorganic particles, and that the particle size of the inorganic particles is preferably 1 nm or more and 100 nm or less, more preferably 1 nm or more and 50 nm or less, and even more preferably 1 nm or more and 10 nm or less. It also indicates that by setting the particle size in this range, a binder with superior dispersibility and adhesive strength of the electrode mixture can be obtained.

Inorganic particles have a larger specific gravity than carbon materials, so as the particle size of inorganic particles increases, the particle settling speed increases and dispersibility and adhesive strength decrease. For this reason, it is effective to use particles of 100 nm or less. However, when drying after electrode coating, there is a problem that particles of 100 nm or less prevent the escape of evaporated moisture, causing the coating film to foam, reducing the binding with the current collector, and making it difficult to obtain a uniform electrode. In addition, such electrodes are brittle because they do not contain an organic binder with excellent flexibility, and are damaged when the electrode is bent. For this reason, they are not suitable for wound-type batteries.

On the other hand, alloy-based active materials are known to have higher capacities than conventional carbon-based active materials. For example, Si has a high electrical capacity of 2800-4000 mAh/g, SiO 1300-2000 mAh/g, Sn 700-1000 mAh/g, and S 800-1500 mAh/g. Therefore, even a small error can cause a large variation in electrode capacity, which can deteriorate life and output characteristics. In addition, adjusting the viscosity of the electrode slurry is difficult to control, as it changes dramatically depending on the amount of solvent used.

Patent Documents 3 and 4 provide physically and chemically stable lithium ion batteries using inorganic binders. Examples of electrodes include a graphite negative electrode (graphite anode) and a _LiCoO2 positive electrode ( _LiCoO2 cathode). The graphite negative electrode is composed of 1.0 g of lithium hydroxide, 23.4 g of inorganic binder (lithium polysilicate), and 45.0 g of graphite powder.

Therefore, if the total solid content of the active material, conductive additive, and binder is 100% by mass, the active material is 64.8% by mass and the inorganic binder is 33.7% by mass.

The _LiCoO2 positive electrode was composed of 1.0 g lithium hydroxide, 1.9 g graphite powder, 2.9 g C-100 carbon black, 24 g inorganic binder (lithium polysilicate), and 85.6 g graphite powder.

Therefore, if the total solid content of the active material, conductive additive, and binder is 100% by mass, the active material is 74.2% by mass and the inorganic binder is 20.8% by mass. Note that in Patent Document 3 and Patent Document 4, there is no mention of inorganic particles in the inorganic binder, and no inorganic particles are included in the examples.

The above-mentioned Patent Documents 2 to 4 all aim to improve the decomposition reaction of the binder and swelling caused by the electrolyte, which were difficult to achieve with conventional organic binders. By using an alloy material such as a Si-based or Sn-based material as the active material and a binder that does not easily swell in the electrolyte, it is possible to expand the operating temperature of the electrode and achieve a high capacity.

However, silicate-based binders are strongly alkaline, and phosphate-based binders are strongly acidic, so when the electrode slurry is made, the alloy-based active material dissolves, generating hydrogen gas and causing the slurry to foam. In particular, the temperature rises when drying the electrodes, so the amount of hydrogen gas generated increases, making it difficult to even manufacture uniform electrodes. In addition, if a current collector that is not resistant to alkali or acid is used, the current collector will deteriorate.

For example, when a Si active material comes into contact with an alkali metal silicate, a reaction of Si+2OH-+H ₂ O→SiO ₃ -+2H ₂ ↑ occurs. Therefore, the current situation is that only alkali-resistant or acid-resistant active materials, that is, carbon-based materials, are available. In addition, the binder, which is one of the components of the electrode, is used to bind the active material to the active material, the active material to the conductive assistant, the active material to the current collector, and the conductive assistant to the current collector. However, since the current battery employs an organic binder such as PVdF or SBR, its thermal conductivity is small compared to inorganic materials such as the active material, the conductive assistant, and the current collector, and it is difficult to transfer heat. In addition, since silicate-based and phosphate-based inorganic binders have a large specific gravity compared to conventional organic binders, the amount of binder used when preparing the electrode must be 20% by mass or more, assuming that the total solid content of the active material, the conductive assistant, and the binder is 100% by mass, in order to exhibit sufficient binding strength. In particular, when a material with a large volume change is used, 30 to 70 mass % is required, which reduces the proportion of active material in the electrode and decreases the electrode energy density.

As described above, the inventors of the present application initially investigated the use of silicate-based or phosphate-based binders, but found that using silicate-based or phosphate-based binders as binders currently involves many issues and would not be viable as practical electrodes. The inventors therefore conducted extensive research into the application of silicate-based or phosphate-based binders to electrodes, rather than as binders, and came up with the present invention. The present invention can solve the above-mentioned conventional problems as well as problems newly discovered by the inventors.

The skeletal forming agent according to the present invention is used in the electrodes of non-aqueous electrolyte secondary batteries, and is characterized in that it contains a silicate having a siloxane bond as a component, or a phosphate having an aluminophosphate bond as a component. According to this configuration, by using a skeletal forming agent containing a silicate or a phosphate in an electrode, it is possible to obtain an electrode that has excellent heat resistance, high strength, and improved cycle life characteristics.

In addition, this skeleton-forming agent, the _silicate , has a crystalline or amorphous structure represented by the general formula _A2O.nSiO2 , where A is at least one of Li, Na, K, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a granidine group, and n is 0.5 or more and 5.0 or less.

Preferably, in the skeletal forming agent, A in the general formula is Li or Na, and n is 1.6 to 3.9, more preferably 2.0 to 3.5. A is preferably Na from the viewpoint of excellent mechanical strength, binding, and abrasion resistance of the skeletal formation. In addition, Li is excellent in input/output characteristics of the battery because it can obtain a skeletal forming body with high ion conductivity. However, even if it is Na, if the number n of SiO ₂ exceeds 5.0, the binding with the active material layer and the separator is poor, and peeling and cracking are significantly likely to occur due to external factors such as volume change of the electrode during charging and discharging and nail penetration tests. In addition, the viscosity becomes too low, and the dispersion stability with the ceramics described later decreases.

Conversely, if n is less than 0.5, the viscosity is high, making it difficult for the framework forming agent to penetrate or be applied to the electrode active material layer or separator. In addition, the amount of heat generated increases when kneading with ceramics.

It is preferable that the silicate is amorphous. Amorphous silicate does not crack in a specific direction like crystals, improving the life characteristics of the electrode. In addition, it has improved resistance to hydrofluoric acid, making it less likely for the electrode to collapse due to hydrofluoric acid.

Amorphous solids usually consist of disordered molecular arrangements and do not possess a distinct crystal lattice. Amorphous solids are also more soluble than crystalline forms and do not have a definite melting point. Thus, the absence of distinct peaks in powder X-ray diffraction (XRD) patterns and the absence of melting endothermic peaks in differential thermal analysis (DTA) and differential scanning calorimetry (DSC) curves indicate the amorphous form.

That is, amorphous silicates lack the sharp peaks characteristic of crystalline forms in XRD, and instead show broad peaks typical of diffraction angles (2θ) in the range of 15° to 40° using Cu-Kα radiation, a so-called halo pattern. More specifically, they show essentially the same XRD pattern as in Figure 17.

However, even if a halo pattern is obtained by XRD, it does not necessarily mean that all of the material is amorphous. However, this is only true under limited conditions where the crystal grains are less than 5 nm, according to the Scherrer equation shown in Equation 3. In other words, when the crystal grains are 5 nm or larger, the diffraction lines are broad and do not resemble the pattern of amorphous material.
D (Å) = 0.9λ/(β×cosθ) (Formula 3)
(In the formula, D is the size of the crystal grain, λ is the wavelength of the X-ray tube, β is the broadening of the diffraction line due to the size of the crystal grain, and θ is the diffraction angle.)

In addition, when changing from an amorphous to a crystalline state, a large amount of heat is generated, and by measuring this, it is possible to determine the crystalline state of the silicate. Amorphous silicate can be obtained by heat treating the electrode at a temperature of 80°C to 600°C at a heating rate of 10°C/h or more.

Preferably, the solids concentration of the silicate in this framework forming agent is 0.1% by mass or more and 30% by mass or less. More preferably, it is 0.1% by mass or more and 15% by mass or less.

The skeleton-forming agent further contains a surfactant, and the surfactant is 0.001% by mass or more and 5.0% by mass or less. With this configuration, the lyophilicity of the skeleton-forming agent to the active material layer is improved, and the skeleton-forming agent penetrates the active material layer uniformly. Therefore, a uniform skeleton is formed in the active material layer, and cycle life characteristics are further improved. If the amount is less than 0.001% by mass, the skeleton-forming agent does not penetrate easily into the active material layer, which contains a large amount of carbon-based materials such as graphite, hard carbon, and conductive additives. If the amount is more than 5% by mass, a defoaming agent is required, and without the defoaming agent, the surface of the active material layer will foam and it will be difficult to form a strong skeleton.

The skeletal forming agent further contains alkali-resistant inorganic particles. With this configuration, when the skeletal forming agent is applied to an electrode, the inorganic particles are layered on the surface of the active material layer of the electrode, the active material layer is covered with a layer of inorganic particles, and the inorganic particles also penetrate into the active material layer.

This allows a strong skeleton to be formed in the active material layer, and the occurrence of peeling and cracking during drying can be suppressed. In addition, pores are formed between the inorganic particles, providing good lyophilicity with the electrolyte. The layer of inorganic particles also results in an electrode with excellent heat resistance, high strength, and excellent abrasion resistance. The layer of inorganic particles also serves as a separator, making it possible to construct a battery without using a separate separator.

Preferably, when the total solid content including the silicate and the alkali-resistant inorganic particles is taken as 100 mass%, the skeleton-forming agent contains 5 mass% or more and 80 mass% or less of the silicate, 20 mass% or more and 95 mass% or less of the alkali-resistant inorganic particles, and the median diameter ( _D50 ) of the alkali-resistant inorganic particles is 0.2 μm or more and 20 μm or less.

Here, the median diameter ( _D50 ) means the volume-based particle diameter in a laser diffraction/scattering particle size distribution measurement method, which is a method for measuring particle size by utilizing the phenomenon that when a laser beam is applied to a particle, the light intensity distribution of the diffracted/scattered light differs depending on the particle size.

By including the alkali-resistant inorganic particles in the skeletal forming agent, the skeletal forming agent is less likely to foam when dried at high temperatures. If the skeletal forming agent foams, the adhesion to the active material layer and the separator decreases, making it difficult to obtain sufficient strength.

The reason why the median diameter ( _D50 ) of the alkali-resistant inorganic particles is set to 0.2 μm or more and 20 μm or less is that pores are formed between the inorganic particles, resulting in good lyophilicity with the electrolyte. From the viewpoint of the output characteristics of the battery, the median diameter (D50) is preferably 0.25 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 2 μm or less.

If the particle size of the inorganic particles is larger than this range, the thixotropy will be low and they will tend to show dilatancy, resulting in reduced dispersion stability when the inorganic particles are added to the skeleton-forming agent. Conversely, if the particle size is smaller than this range, when forming a skeleton with a thickness of more than 2 μm, there will be no escape route for the moisture evaporated during drying, causing the coating to foam, reducing the adhesion to the current collector and making it difficult to obtain a uniform electrode.

The reason why the inorganic particles need to be alkali resistant is because silicates exhibit strong alkalinity (pH 12 or higher). In addition to the alkali resistance, it is desirable for the framework forming agent to be inorganic particles that have excellent resistance to dissolution in the electrolyte.

Examples of inorganic particles that satisfy such conditions include oxides, hydroxides, nitrides, carbides, carbonates, and sulfates of at least one element selected from the group consisting of Al, Zr, Ti, Si, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y. Of these, from the viewpoint of being a material that is less susceptible to oxidative or reductive decomposition during charging and discharging of the battery _and has a small irreversible capacity, it _is preferable for the material to contain _Al2O3 , _ZrO2 , _TiO2 , _SiO2 , _CaO , MgO, CeO, _Y2O3 , AlN, WC, SiC, _B4C , BN, TaC, _TiC , _TiB2 , HfB2, _Si3N4 , TiN, _CaCO3 , _MgSO4 , _Al2 ( _SO4 ) ₃ , _CaSO4 , and _ZrSiO4 .

In addition, from the viewpoint of being a material with low irreversible capacity of the battery, _it is preferable to contain _Al2O3 , _ZrO2 , _TiO2 , _SiO2 , _MgO , CeO, _Y2O3 , WC, SiC, _B4C , TaC, _TiC , _Si3N4 , TiN, _CaCO3 , _MgSO4 , _CaSO4 , _ZrSiO4 . These materials have the effect of suppressing the large volumetric shrinkage of silicate that occurs during drying, and can maintain sufficient strength even when dried at low temperatures.

On the other hand, phosphate has a crystalline or amorphous structure represented by the general _{formula M.nHxPO4} , where M is at least one of Al, Ca, and Mg, x is 0 or more and 2 or less, and n is 0.5 or more and 5 or less.

M is preferably Al from the viewpoint of excellent mechanical strength, binding ability, and abrasion resistance of the skeleton formation. x is preferably 1 to 2, more preferably 2, from the viewpoint of excellent binding ability of the skeleton formation. n is preferably 0.5 to 5.0, more preferably 2.5 to 3.5, from the viewpoint of excellent mechanical strength, binding ability, and abrasion resistance of the skeleton formation. As in the case of silicates, it is preferable that the phosphate is amorphous.

Preferably, the solids concentration of the phosphate in this skeleton-forming agent is 0.1% by mass or more and 30% by mass or less. More preferably, it is 0.1% by mass or more and 15% by mass or less.

In addition, it is preferable that the framework forming agent contains a surfactant, and that the surfactant is present in an amount of 0.001% by mass or more and 5.0% by mass or less.

It is also preferable that the skeletal forming agent further contains acid-resistant inorganic particles. With this configuration, when the skeletal forming agent is applied to an electrode, the inorganic particles are layered on the surface of the active material layer of the electrode, the active material layer is covered with a layer of inorganic particles, and the inorganic particles also penetrate into the active material layer.

This allows a strong skeleton to be formed in the active material layer, and the occurrence of peeling and cracking during drying can be suppressed. In addition, pores are formed between the inorganic particles, providing good lyophilicity with the electrolyte. The layer of inorganic particles also results in an electrode with excellent heat resistance, high strength, and excellent abrasion resistance. The layer of inorganic particles also serves as a separator, making it possible to construct a battery without using a separate separator.

Preferably, when the total solid content including the phosphate and the acid-resistant inorganic particles is taken as 100 mass%, the skeleton-forming agent contains 5 mass% or more and 80 mass% or less of the phosphate, 20 mass% or more and 95 mass% or less of the acid-resistant inorganic particles, and the median diameter ( _D50 ) of the acid-resistant inorganic particles is 0.2 μm or more and 20 μm or less.

The skeleton-forming agent contains the acid-resistant inorganic particles, so that the skeleton-forming agent is less likely to foam when dried at high temperatures. If the skeleton-forming agent foams, the binding strength with the active material layer and the separator is reduced, making it difficult to obtain sufficient strength. The median diameter ( _D50 ) of the acid-resistant inorganic particles is preferably 0.2 μm or more and 20 μm or less.

The reason why the inorganic particles need to be acid resistant is because phosphates are highly acidic (pH 1 to 2). In addition to being acid resistant, it is also desirable for the skeletal forming agent to be inorganic particles that are highly resistant to dissolution in the electrolyte.

Examples of inorganic particles that satisfy such conditions include oxides, hydroxides, nitrides, carbides, carbonates, and sulfates of at least one element selected from the group consisting of Al, Zr, Ti, Si, Mo, Sr, Ba, B, W, Ta, Ce, Hf, and Y. Among these, from the viewpoint of being a material that is less susceptible to oxidative decomposition or reductive decomposition during charging and discharging of the battery and has a small irreversible capacity, it is preferable to contain _Al2O3 , _ZrO2 , _TiO2 , _SiO2 , CeO, _Y2O3 , WC, SiC, _B4C , BN, TaC _, TiC, _TiB2 , _{HfB2 , Si3N4} , TiN, and _ZrSiO4 .

In addition, from the viewpoint of being a material with low irreversible capacity of the battery _{, it is preferable to contain Al2O3, ZrO2, TiO2, SiO2, CeO, Y2O3 , WC , SiC , B4C ,} BN, TaC, _TiC , _Si3N4 , TiN, and _ZrSiO4 . These materials have the effect of suppressing the large volumetric shrinkage of phosphate that occurs during drying, and can maintain sufficient strength even when dried at low temperatures.

Between silicate-based and phosphate-based batteries, silicate-based batteries are preferred from the standpoints of battery life, input/output characteristics, irreversible capacity, resistance to moisture absorption, and heat resistance.

The electrode according to the present invention is an electrode for a non-aqueous electrolyte secondary battery, characterized in that the skeletal forming agent according to any one of claims 1 to 7 is present at least on the surface of the active material layer. According to this configuration, the skeletal forming agent containing silicate or phosphate constitutes the skeleton of the electrode, resulting in an electrode with excellent heat resistance, high strength, and improved cycle life characteristics. In addition, while a binder containing silicate or phosphate would not work as an electrode, applying the skeletal forming agent to the surface of the active material layer makes it possible to obtain an electrode with excellent cycle life characteristics.

Here, a non-aqueous electrolyte secondary battery is a secondary battery that uses an electrolyte that does not have water as a main component, and examples of such batteries include lithium secondary batteries (lithium ion batteries), sodium batteries (sodium ion batteries), and potassium batteries (potassium ion batteries). In addition, there are no particular limitations on the electrodes as long as they are electrodes that are used in non-aqueous electrolyte secondary batteries, and there are also no particular limitations on the material or shape of the electrodes.

Electrodes include negative and positive electrodes. First, regarding the negative electrode, the negative electrode active material used in the negative electrode is not particularly limited as long as it is a material capable of reversibly absorbing and releasing alkali metal ions (lithium ions, sodium ions, potassium ions, etc.). For example, it may be at least one element selected from the group consisting of Li, Na, K, C, Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Sb, W, Pb, and Bi, or an alloy, composite, oxide, chalcogenide, or halide using these elements.

From the viewpoint that the discharge plateau region can be observed within the range of 0 to 1 V (vs. Li+/Li), at least one element selected from the group consisting of Li, Na, K, C, Mg, Al, Si, Ti, Zn, Ge, Fe, Mn, Ag, Cu, In, Sn, and Pb, or an allotrope, alloy, or oxide using these elements is preferred.

Furthermore, from the viewpoint of energy density, preferred elements are Al, Si, Zn, Ge, Ag, Sn, etc., preferred alloys are combinations of Si-Al, Al-Zn, Si-Mg, Si-La, Al-Ge, Si-Ge, Si-Ag, Si-Sn, Si-Ti, Si-Y, Si-Cr, Si-Ni, Si-Zr, Si-V, Si-Nb, Si-Mo, Zn- _Sn , Ge-Ag, Ge-Sn, Ge-Sb, Ag-Sn, Ag-Ge, _Sn - _Sb , etc. _, and preferred oxides are _{Fe2O3 ,} CuO, _MnO2 , NiO _{, Li4Ti5O12} , _H2Ti12O25 , _{Na2Ti3O7 ,} etc. The alloy may be a complete solid solution type alloy, a eutectic alloy, a hypoeutectic alloy, a hypereutectic alloy, or a peritectic alloy. The surface of the active material particles may be coated with a material or ceramics having excellent electronic conductivity. Two or more of these materials capable of reversibly absorbing and releasing lithium may be used.

The shape of the active material particles is not particularly limited, and may be spherical, elliptical, faceted, strip-like, fibrous, flake-like, doughnut-like, or hollow. Materials capable of reversibly absorbing and releasing alkali metal ions (lithium ions, sodium ions, potassium ions) are preferably substances capable of absorbing and releasing alkali metal ions during the initial charging process and compounds that decompose into a solid electrolyte.

The solid electrolyte is not particularly limited as long as it is a material that has ion conductivity, but it is preferably a solid electrolyte represented by LiαXβYγ, where 0<α≦4, 0≦β≦2, and 0≦γ≦5. The solid electrolyte can also be used as a buffer material that can reversibly absorb and release alkali metal ions.

X is, for example, one or more of Si, Ti, Mg, Ca, Al, V, Ge, Zr, Mo, and Ni, and Y is one or more of O, S, F, Cl, _Br , _I , P, _B2O3 , _C2O4 , _CO3 , _PO4 , S, _{CF3SO3 ,} and _SO3 . More specifically, for example, LiF, LiCl, LiBr, LiI, Li ₃ N, LiPON, Li ₂ C2O ₄ , Li ₂ CO ₃ , LiAlCl ₄ , Li ₂ O, Li ₂ S, LiSO ₄ , Li ₂ SO ₄ , Li ₃ PO ₄ , Li ₃ VO ₄ , Li ₄ GeO ₄ , Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₄ ZrO ₄ , LiMoO ₄ , LiAlF ₄ , Li ₃ Ni ₂ , LiBF ₄ , LiCF ₃ SO ₃ , NaF, N aCl, NaBr, NaI, _Na3 N, NaPON, _Na2C2O4 , Na2CO3, NaAlCl4, Na2O _{, Na2S, NaSO4, Na2SO4, Na3PO4, Na3VO4, Na4GeO4, Na2Si2O 5, Na 2 SiO 3 , Na 4 SiO 4 , Na 4 ZrO 4 , NaMoO 4 , NaAlF 4 , Na 3 Ni 2 , NaBF 4 , NaCF 3 SO 3 , KF , KCl , KBr} , KI, _{K 3} N, _{KPON ,} K ₂ C ₂ O ₄ , K _{2 CO 3} , KAlCl ₄ , _{K 2 O} , _{K 2} S, _KSO4 , _{K2SO4 , K3PO4 , K3VO4 ,} K4GeO4 _{, K2Si2O5 , K2SiO3} , _{K4SiO4 , K4ZrO4 , KMoO4 , KAlF4 , K3Ni2} , _KBF4 , _{KCF3SO3 ,} and the _like can be mentioned, _and one or more of these can be used.

Examples of the substance capable of absorbing and releasing alkali metal ions and the compound decomposing into a solid electrolyte include SiO, GeO, GeS, GeS ₂ , SnO, SnO ₂ , SnC ₂ O ₄ , SnO-P ₂ O ₅ , SnO-B ₂ O ₃ , SnS, SnS ₂ , Sb ₂ S ₃ , SnF ₂ , SnCl ₂ , SnI ₂ , and SnI ₄ , and two or more of these may be used. However, it is preferable to pre-dope the substance capable of absorbing and releasing alkali metal ions and the compound decomposing into a solid electrolyte before assembling the battery, since the battery capacity is extremely reduced if the pre-doping is not performed in advance.

As described in a patent document (JP 2015-088437 A) and a non-patent document ("Collection of Measurement and Analysis Data for Lithium Secondary Battery Components," Chapter 3, Section 30, pp. 200-205, Technical Information Association), known methods such as electrochemical methods, alkali metal attachment methods, and mechanical methods can be used for the pre-doping method. Although the reason is unclear, in the present invention, when the electrode on which the skeleton is formed is made of Si, a Si alloy, a Si composite, a Si oxide, or a mixture containing one or more of these, a particularly significant cycle life improvement effect is exhibited.

Regarding the particle size of the active material, when an active material powder with a small particle size is used, the collapse of the particles is reduced, and the life characteristics of the electrode tend to be improved. In addition, the specific surface area tends to increase, and the output characteristics tend to be improved. For example, according to a non-patent document (Latest Technological Trends of Rare Metal-Free Secondary Batteries, Chapter 3, Section 1, Item 4, pp. 125-135, CMC Publishing, 2013), it is described that as the particle size of the active material becomes smaller, the initial discharge capacity increases and the cycle life is also improved, and it is clear that the particle size of the active material is correlated with the initial charge/discharge efficiency and the cycle life.

However, nano-order active materials are difficult to handle, so it is preferable to granulate them before use. For example, Patent No. 5525003 shows a negative electrode that uses nano-granules that use one or more of the following granulation binders: polyimide, polybenzimidazole, styrene butadiene rubber, polyvinylidene fluoride, carboxymethyl cellulose, and polyacrylic acid. Granulating the nano-order active material reduces the stress applied to the copper foil due to the expansion and contraction of the negative electrode active material, preventing deformation of the copper foil.

On the other hand, it is also possible to use the skeleton forming agent of the present invention as a binder for granulating the above-mentioned negative electrode active material. In that case, the primary particles of the active material preferably have a median diameter ( _D50 ) in the range of 0.01 μm to 10 μm, and the active material particles (secondary particles) after granulation preferably have a median diameter ( _D50 ) in the range of 1 μm to 100 μm.

As a method for granulating the active material, known granulation methods can be applied, such as fluidized bed granulation, stirring granulation, rolling granulation, spray drying, extrusion granulation, rolling granulation, and coating granulation. Of these, the spray drying and fluidized bed granulation methods are particularly preferred.

In the spray-drying method, for example, a suspension in which an active material is dispersed in a framework forming agent is sprayed from above into a greenhouse heated to 50-300°C at 1-30 mL/min and an air pressure of 0.01-5 MPa to produce agglomerated particles, which are then dried to obtain a granulated product.

In the fluidized bed granulation method, for example, the powder raw material is placed in a fluidized bed granulation device, and hot air heated to 50-300°C is blown in from below to fluidize and mix the powder raw material (granule precursor). Water in which a skeleton-forming agent has been dissolved is sprayed from a nozzle above into this mixed powder raw material, and the skeleton-forming agent is sprayed uniformly onto the powder surface at 1-30 mL/min with an air pressure of 0.01-5 MPa to create agglomerated particles, which are then dried to obtain the granules.

However, when using an active material with poor alkali resistance such as Si or Sn, there is a high possibility that it will react with the skeletal forming agent to generate hydrogen gas, and will not function as a negative electrode. Therefore, when using the skeletal forming agent of the present invention, it is believed that the generation of hydrogen gas can be minimized by spraying the skeletal forming agent onto secondary particles that have been granulated in advance with an organic granulation binder, and forming a skeleton in the granulated material.

As the organic binder for granulation, known binders can be used. For example, binders used for positive and negative electrodes may be used, but from the viewpoints of chemical stability, heat resistance, reduction resistance, etc. of the granules, polybenzimidazole, styrene butadiene rubber, polyvinylidene fluoride, carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid, cellulose nanofiber, polyimide, polyamide, and polyamideimide are preferred.

The amount of the granulation binder is not particularly limited as long as it is an amount capable of binding the active material particles, but it is preferably within the range of 0.1 to 30% by mass of the granules. In addition to the active material particles and the granulation binder, the granules may contain a conductive assistant to impart electronic conductivity as necessary. The skeleton forming agent is preferably contained within the range of 0.2 to 30% by mass of the granules. The granules obtained in this manner not only have improved cycle life characteristics, but also have improved coating properties of the slurry.

There are no particular limitations on the conductive assistant for the negative electrode, so long as it has electronic conductivity, and the above-mentioned metals, carbon materials, conductive polymers, conductive glass, etc. can be used. Specific examples include acetylene black (AB), ketjen black (KB), furnace black (FB), thermal black, lamp black, channel black, roller black, disc black, carbon black (CB), carbon fiber (for example, vapor-grown carbon fiber named VGCF, which is a registered trademark), carbon nanotubes (CNT), carbon nanohorns, graphite, graphene, glassy carbon, amorphous carbon, etc., and one or more of these may be used.

When the total of the active material, binder, and conductive assistant contained in the negative electrode is taken as 100% by mass, it is preferable that the conductive assistant is contained at 0 to 20% by mass. In other words, the conductive assistant is contained as needed. If it exceeds 20% by mass, the proportion of active material in the battery is small, and the electrode capacity density is likely to be low.

The negative electrode binder is generally used, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, aramid, polyacrylic, styrene butadiene rubber (SBR), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), xanthan gum, polyvinyl alcohol (PVA), ethylene vinyl alcohol, polyvinyl butyral (PVB), ethylene vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, methyl polyacrylate, ethyl polyacrylate, amine polyacrylate, polyacrylic acid, Organic materials such as acrylic acid esters, epoxy resins, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea resin, melamine resin, phenolic resin, latex, polyurethane, silylated urethane, nitrocellulose, dextrin, polyvinylpyrrolidone, vinyl acetate, polystyrene, chloropropylene, resorcinol resin, polyaromatic, modified silicone, methacrylic resin, polybutene, butyl rubber, 2-propenoic acid, cyanoacrylic acid, methyl methacrylate, glycidyl methacrylate, acrylic oligomer, 2-hydroxyethyl acrylate, alginic acid, starch, urushi lacquer, sucrose, glue, casein, and cellulose nanofibers may be used alone or in combination of two or more kinds.

Also, a mixture of these organic binders and inorganic binders may be used. The inorganic binder may be a silicate-based, phosphate-based, sol-based, cement-based, or other type of binder. For example, lithium silicate, sodium silicate, potassium silicate, cesium silicate, guanidine silicate, ammonium silicate, silicofluoride, borate, lithium aluminate, sodium aluminate, potassium aluminate, aluminosilicate, lithium aluminate, sodium aluminate, potassium aluminate, polyaluminum chloride, polyaluminum sulfate, polyaluminum silicate sulfate, aluminum sulfate, aluminum nitrate, ammonium alum, lithium alum, sodium alum, potassium alum, chrome alum, iron alum, manganese alum, nickel ammonium sulfate, diatomaceous earth, polyzirconoxane, polytantalum tallowane, mullite, white carbon, silica sol, colloidal silica, fumed silica, alumina sol, colloidal alumina, fumed alumina, zirconium phosphate, tetrahydrofuran ... Inorganic materials such as conia sol, colloidal zirconia, fumed zirconia, magnesia sol, colloidal magnesia, fumed magnesia, calcia sol, colloidal calcia, fumed calcia, titania sol, colloidal titania, fumed titania, zeolite, silicoaluminophosphate zeolite, sepiolite, montmorillonite, kaolin, saponite, aluminum phosphate, magnesium phosphate, calcium phosphate, iron phosphate, copper phosphate, zinc phosphate, titanium phosphate, manganese phosphate, barium phosphate, tin phosphate, low melting point glass, plaster, gypsum, magnesium cement, litharge cement, Portland cement, blast furnace cement, fly ash cement, silica cement, phosphate cement, concrete, and solid electrolytes may be used alone or in combination of two or more.

Among these, from the viewpoints of binding ability, resistance to electrolyte elution, resistance to oxidation and reduction, and energy density, inorganic materials such as lithium silicate, sodium silicate, potassium silicate, guanidine silicate, ammonium silicate, silicofluoride salt, aluminosilicate, aluminum phosphate salt, magnesium phosphate salt, and calcium phosphate salt are preferred.

However, when negative electrodes are made with inorganic binders, the specific gravity of the inorganic binders is high, so the electrode energy density per weight tends to be low. In addition, when inorganic binders that are highly acidic or alkaline are used and contain active materials with poor chemical resistance such as Si or Sn, hydrogen gas is generated during mixing of the slurry, making it not only difficult to coat the electrode, but also foaming during the heating and drying process, making it impossible to produce a uniform electrode. In addition, using current collectors with poor chemical resistance causes the current collectors to deteriorate.

Conventionally, when using an alloy-based negative electrode active material, PI, for example, has been considered to be preferable as a negative electrode binder from the viewpoint of suppressing the volume change of the active material accompanying charge and discharge and improving the cycle life characteristics of the battery. However, in the present invention, since it is possible to suppress the volume change with a framework forming agent, all of the above-mentioned commonly used binders can be used.

If the total of the active material, binder, and conductive additive contained in the negative electrode is 100% by mass, the binder is preferably contained in an amount of 0.1 to 60% by mass, and more preferably 0.5 to 30% by mass.

If the binder is less than 0.1% by mass, the mechanical strength of the electrode is low, and the active material is likely to fall off during skeleton formation, which may result in poor cycle life characteristics of the battery. On the other hand, if the binder is more than 60% by mass, the ionic conductivity is low, the electrical resistance is high, and the proportion of active material in the battery is low, which tends to result in low electrode capacity density.

The current collector used in the negative electrode is not particularly limited as long as it is a material that has electronic conductivity and can pass electricity through the negative electrode active material held therein. For example, conductive materials such as C, Ti, Cr, Ni, Cu, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Al, and Au, and alloys containing two or more of these conductive materials (e.g., stainless steel) can be used. When a conductive material other than the above is used, it may be a multilayer structure of heterogeneous metals, such as iron coated with Cu or Ni.

From the viewpoint of high electrical conductivity and good stability in the electrolyte, the current collector is preferably made of C, Ti, Cr, Au, Fe, Cu, Ni, stainless steel, etc., and from the viewpoint of reduction resistance and material cost, C, Cu, Ni, stainless steel, etc. are more preferable. When iron is used as the current collector substrate, it is preferable that it is coated with Ni or Cu to prevent oxidation of the surface of the current collector substrate. In addition, in conventional alloy-based negative electrodes, the volume change of the negative electrode material due to charging and discharging is large, so stainless steel or iron was considered to be preferable as the current collector substrate, but in the present invention, the framework forming agent can relieve the stress on the current collector, so all of the commonly used materials mentioned above can be used.

The shape of the current collector may be linear, rod-like, plate-like, foil-like, or porous. Of these, the porous shape may be used since it is possible to increase the packing density and the skeleton-forming agent can easily penetrate into the active material layer. Examples of the porous shape include mesh, woven fabric, nonwoven fabric, embossed body, punched body, expanded body, and foam. Of these, the shape of the current collector substrate is preferably embossed or foamed because it has good output characteristics.

Next, regarding the positive electrode, the active material used for the positive electrode is not particularly limited as long as it is a positive electrode active material used in non-aqueous electrolyte secondary batteries. Known electrodes including alkali metal transition metal oxide-based, vanadium-based, sulfur-based, solid solution-based (lithium excess-based, sodium excess-based, potassium excess-based), carbon-based, organic-based, etc. can be used.

Examples of the alkali metal transition metal oxides include _LiCoO2 , _{Li0.9Na0.1CoO2 , LiNiO2 , LiNi0.5Co0.5O2 , LiNi0.33Mn0.33Co0.33O2 , LiNi0.5Mn0.2Co0.3O2 , LiNi0.6Mn0.2Co0.2O2 , LiNi0.8Mn0.1Co0.1O2 , Li ( Ni} , _{Co ,} Al _{) O2 , LiMnO2 , LiMn2O4 , LiFePO4 , LiFe0.5Mn0.5 PO4} , _LiMnPO4 , _{Li2MnSiO4 ,} Li2FeSiO4, _Li2 (Mn,Fe) _SiO4 , Li2CoSiO4, _{Li2MgSiO4 , Li2CaSiO4 , Li2ZnSiO4 ,} Li _{Nb2O5 , LiNbO2 , LiFeO2} , _LiMgO2 , _LiCaO2 , _LiTiO2 , _{LiTiS2 , LiCrO2 , LiRuO2 ,} LiCuO2, _LiZnO2 , _LiMoO2 , _LiMoS2 , LiTa _{O 2 ,} LiWO ₂ , NaCoO ₂ , NaNiO ₂ , NaNi _0.33 Mn _0.33 Co _0.33 O ₂ , NaMnO ₂ , NaMn ₂ O ₄ , _{NaFePO 4} , NaFe _0.5 Mn _0.5 PO ₄ , NaMnPO ₄ , Na _{2 Mn SiO4} , _{Na2FeSiO4 , Na2} (Mn, _Fe ) _SiO4 , _{Na2CoSiO4 , Na2MgSiO4} , Na2CaSiO4, _{Na2ZnSiO4 , NaNb2O5 , NaNbO2} , NaFeO ₂ , _NaMgO2 , _NaCaO2 , _NaTiO2 , NaTiS ₂ , NaCrO ₂ , NaRuO ₂ , NaCuO ₂ , NaZnO ₂ , NaMoO ₂ , NaMoS ₂ , NaTaO ₂ , NaWO ₂ , KCoO ₂ , KNiO ₂ , KNi _0.33 Mn _0.33 Co _{0.3 3} O ₂ , KMnO ₂ , KMn ₂ O ₄ , KFePO ₄ , KFe _0.5 Mn _0.5 PO ₄ , KMnPO ₄ , K ₂ MnSiO ₄ , K ₂ FeSiO ₄ , K ₂ (Mn,Fe)SiO ₄ , K ₂ CoSiO ₄ , K ₂ MgSiO ₄ , K ₂ Examples of such oxides include _CaSiO4 , _K2ZnSiO4 , _KNb2O5 , KNbO2, _{KFeO2 , KMgO2} , _KCaO2 , _KTiO2 , KTiS2 _{, KCrO2 , KRuO2} , _KCuO2 , _KZnO2 , _KMoO2 , _KMoS2 , _{KTaO2 ,} and _KWO2 .

Examples of vanadium-based materials include _LiV2O5 , _LiVO2 , _Li3VO4 , _{Li3V2 ( PO4 ) 3} , _{NaV2O5 , NaVO2 ,} Na3VO4 _, Na3V2( _PO4 ) ₃ , _{KV2O5 ,} KVO2, _K3VO4 , _K3V2 ( _PO4 ) ₃ , etc. Examples of sulfur-based materials include sulfur, _{carbon sulfide} , _polysulfide , _{polycarbon sulfide} , sulfur _- modified polyacrylonitrile, disulfide compounds, sulfur-modified rubber, sulfur _- modified pitch, sulfur-modified anthracene, and metal sulfide. Examples of solid solution systems include Li ₂ MnO ₃ -LiNiO ₂ , Li ₂ MnO ₃ -LiMnO ₂ , Li ₂ MnO ₃ -LiCoO ₂ , Li ₂ MnO ₃ -Li(Ni,Mn)O ₂ , Li ₂ MnO ₃ -Li(Ni,Co ₎ O ₂ , Li2MnO3-Li(Mn,Co) _{O2 , Li2MnO3} - _Li (Ni,Mn,Co) _O2 , _{Na2MnO3 - NaNiO2 , Na2MnO3 - NaMnO2 ,} Na2MnO3-NaCoO2 _{, Na2M nO3} -Na(Ni,Mn ₎ O2 _{, Na2MnO3} -Na(Ni,Co)O2 _, Na2MnO3 _-Na (Mn,Co _{)O2, Na2MnO3 -Na(Ni,Mn,Co)O2, K2MnO3 -KNiO2, K2MnO 3 -KMnO 2 , K 2 MnO 3 -KCoO 2 , K 2 MnO 3 -K ( Ni ,} Mn) _{O 2} , K ₂ MnO _{3 -K} ( _{Mn, Co)O 2 , K 2 MnO 3 -K ( Ni} , _Mn , Co ) _O2 , etc.

Carbon-based materials include, for example, graphite, soft carbon, hard carbon, and glassy carbon. Organic materials include rubeanic acid, tetracyanoquinodimethane, triquinoxalinylene, phenazine dioxide, trioxotriangulene, indigo carmine, nitronyl nitroxide radical compounds, radialene compounds, aliphatic cyclic nitroxyl radicals, and benzoquinones.

The above-mentioned positive electrode active materials may _be used alone or in combination of two or more kinds. From the viewpoint of energy density, for example _{, LiCoO2 , LiMn2O4 , LiFePO4 , LiFe0.5Mn0.5PO4 , LiMnPO4 , LiNi0.33Mn0.33Co0.33O2 , LiNi0.5Mn0.2Co0.3O2 , LiNi0.6Mn0.2Co0.2O2 , LiNi0.8Mn0.1Co0.1O2} , _Li (Ni,Co,Al) _O2 , solid _solution systems _, vanadium systems _{, and} sulfur systems are preferred. The shape of the active material particles is not particularly limited, and may be spherical, elliptical, faceted, strip-like, fibrous, flake-like, doughnut-like, or hollow.

On the other hand, as in the case of the negative electrode, it is also possible to use the skeleton forming agent of the present invention as a binder for granulation of the above-mentioned positive electrode active material. In that case, the primary particles of the active material preferably have a median diameter (D ₅₀ ) in the range of 0.01 μm to 10 μm, and the active material particles (secondary particles) after granulation preferably have a median diameter (D ₅₀ ) in the range of 1 μm to 100 μm. The granulation method of the active material is substantially the same as the granulation method of the negative electrode active material, and known granulation methods can be applied.

The conductive assistant is not particularly limited as long as it has electronic conductivity, and examples thereof include metals, carbon materials, conductive polymers, conductive glass, etc., but carbon materials are preferred from the viewpoint of high electronic conductivity and oxidation resistance. Specific examples include acetylene black (AB), ketjen black (KB), furnace black (FB), thermal black, lamp black, channel black, roller black, disc black, carbon black (CB), carbon fiber (for example, vapor-grown carbon fiber named VGCF, which is a registered trademark), carbon nanotubes (CNT), carbon nanohorns, graphite, graphene, glassy carbon, amorphous carbon, etc., and one or more of these may be used.

When the total of the active material, binder, and conductive assistant contained in the positive electrode is taken as 100% by mass, it is preferable that the conductive assistant is contained in an amount of 0 to 20% by mass. In other words, the conductive assistant is contained as needed. If it exceeds 20% by mass, the proportion of active material in the battery is small, and the electrode capacity density tends to be low.

Positive electrode binders include those that are commonly used, such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), ethylene-vinyl acetate copolymer (EVA), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), xanthan gum, polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene vinyl alcohol, polyethylene (PE), polypropylene (PP), polyacrylic acid, lithium polyacrylate, sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, methyl polyacrylate, ethyl polyacrylate, amine polyacrylate, polyacrylic ester, epoxy resin, etc. Organic materials such as grease, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, vinyl chloride, silicone rubber, nitrile rubber, cyanoacrylate, urea resin, melamine resin, phenolic resin, latex, polyurethane, silylated urethane, nitrocellulose, dextrin, polyvinylpyrrolidone, vinyl acetate, polystyrene, chloropropylene, resorcinol resin, polyaromatic, modified silicone, methacrylic resin, polybutene, butyl rubber, 2-propenoic acid, cyanoacrylic acid, methyl methacrylate, glycidyl methacrylate, acrylic oligomer, 2-hydroxyethyl acrylate, polyacetal, alginic acid, starch, sucrose, lacquer, glue, casein, and cellulose nanofibers may be used alone or in combination of two or more. Also, a mixture of these organic binders and inorganic binders may be used.

The inorganic binder may be, for example, a silicate-based, phosphate-based, sol-based, or cement-based binder. However, if a positive electrode is manufactured using only an inorganic binder, the electrode energy density per weight tends to be low because the inorganic binder has a large specific gravity.

Conventionally, when using sulfur-based, vanadium-based, or solid solution-based positive electrode active materials, a binder with high binding properties has been considered preferable from the viewpoint of suppressing the volume change of the active material due to charging and discharging and improving the cycle life characteristics of the battery. However, in the present invention, since it is possible to suppress the volume change with the framework forming agent, all of the commonly used binders mentioned above can be used.

When the total of the active material, binder, and conductive additive contained in the positive electrode is taken as 100% by mass, it is preferable that the binder is contained at 0.1 to 60% by mass. If the binder is less than 0.1% by mass, the mechanical strength of the electrode is low, so that the active material is likely to fall off during skeleton formation, and the cycle life characteristics of the battery may deteriorate. On the other hand, if the binder exceeds 60% by mass, the ion conductivity is low, the electrical resistance is high, and the proportion of active material in the battery is small, so the electrode capacity density is likely to be low.

The current collector used for the positive electrode is not particularly limited as long as it has electronic conductivity and can pass electricity through the positive electrode active material held therein. For example, conductive materials such as C, Ti, Cr, Ni, Cu, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al, and alloys containing two or more of these conductive materials (e.g., stainless steel) can be used. When using conductive materials other than those mentioned above, for example, a multilayer structure of different metals such as iron coated with Al may be used. From the viewpoint of high electrical conductivity and good stability in the electrolyte, C, Ti, Cr, Au, Al, stainless steel, etc. are preferred as the current collector, and further from the viewpoint of oxidation resistance and material cost, C, Al, stainless steel, etc. are preferred. Carbon-coated Al and carbon-coated stainless steel are more preferred.

The shape of the current collector may be linear, rod-like, plate-like, foil-like, or porous. Of these, the porous shape may be used because it allows for a high packing density and allows the skeleton-forming agent to easily penetrate into the active material layer. Examples of porous shapes include mesh, woven fabric, nonwoven fabric, embossed body, punched body, expanded body, and foam. Of these, the shape of the current collector substrate is preferably embossed or foamed because of its good output characteristics.

This electrode is an electrode for a non-aqueous electrolyte secondary battery, and the skeletal forming agent according to any one of claims 1 to 7 is present at least in the active material layer. According to this configuration, by applying the skeletal forming agent to the electrode, the skeletal forming agent penetrates into the active material layer and forms a strong skeleton in the active material layer. This reduces the volume change of the electrode and improves the insulation of the electrode surface.

In addition, in this electrode, the skeletal former according to any one of claims 1 to 7 is present in the active material layer, and gaps exist between the active materials in the active material layer. According to this configuration, by applying the skeletal former to the electrode, the skeletal former penetrates into the active material layer, so that the gaps between the active materials in the active material layer are not completely filled with the skeletal former, and gaps between the active materials remain. This allows the active materials to expand and contract during charging and discharging, and suppresses the occurrence of wrinkles, cracks, etc. in the electrode current collector.

This electrode also has a layer containing the alkali-resistant inorganic particles on the surface of the layer of silicate-based skeletal forming agent. With this configuration, the layer of inorganic particles can form a strong skeleton and can suppress peeling and cracking during drying. The layer of inorganic particles also serves as a separator, making it possible to construct a battery without using a separate separator. When the skeletal forming agent is a phosphate-based agent, the layer contains acid-resistant inorganic particles.

Preferably, the amount of the skeletal former per unit area of the electrode coated on one side is from 0.01 mg/ ^cm2 to 3 mg/ ^cm2 , or the amount of the skeletal former per unit area of the electrode coated on both sides is from 0.02 mg/ ^cm2 to 6 mg/ ^cm2 . More preferably, the amount of the skeletal former per unit area of the electrode coated on one side is from 0.05 mg/ ^cm2 to 3 mg/ ^cm2 , or the amount of the skeletal former per unit area of the electrode coated on both sides is from 0.1 mg/ ^cm2 to 6 mg/ ^cm2 .

The electrode also includes an active material capable of being alloyed with an alkali metal or capable of absorbing alkali metal ions, an organic binder, and the skeletal forming agent.

When the total solid content of the active material, conductive assistant, binder, and skeletal former is taken as 100% by mass, the skeletal former is preferably 0.1% by mass to 30% by mass, more preferably 0.2% by mass to 20% by mass, and even more preferably 0.5% by mass to 10% by mass.

The separator according to the present invention is a separator for a non-aqueous electrolyte secondary battery, characterized in that the framework forming agent according to any one of claims 1 to 7 is present at least on the surface.

This configuration results in a separator with high strength, excellent heat resistance, and improved cycle life characteristics. Here, the separator may be one that is generally used in non-aqueous electrolyte secondary batteries. The material of the separator is not particularly limited. The separator may be coated or filled with a ceramic layer to prevent meltdown due to localized heat generation during a short circuit. The shape of the separator is not particularly limited, and examples of the shape include a microporous membrane, a woven fabric, a nonwoven fabric, and a powder compact.

By applying a framework-forming agent to the separator, localized heat generation during a short circuit can cause the separator base material to melt down, preventing the battery from shorting out. In addition, oxidation of the separator on the positive electrode side can be suppressed when the battery is charged, thereby preventing the battery from self-discharge. In addition, the heat resistance of the separator is improved, improving safety against nail penetration and overcharging.

The silicate-based skeleton-forming agent may also contain inorganic particles such as alkali-resistant ceramics. In this case, the particle size of the ceramics is preferably within the range of 0.2 to 20 μm, and more preferably within the range of 0.25 to 10 μm. However, the phosphate-based agent may also contain inorganic particles such as acid-resistant ceramics. In this case, the same applies as for the silicate-based agent.

Alternatively, a separator with improved heat resistance may be used by applying and filling a skeleton-forming agent onto the ceramic layer of an existing ceramic-coated separator.

The porosity of the separator is preferably 30% or more, and from the viewpoint of alkali metal ion conductivity and dendrite resistance, it is more preferably 40% to 90%. In addition, it is preferable that the air permeability obtained by the Gurley test method is 3000 seconds/100cc or less. Here, the porosity is a value calculated from the apparent density of the separator and the true density of the solid content of the constituent materials by the formula: porosity (%) = 100 - (apparent density of separator / true density of material solid content) x 100. In addition, the Gurley air permeability is the air permeability resistance measured by the Gurley tester method specified in JIS P 8117.

Preferably, the amount of the skeletal forming agent per unit area of the separator coated on one side is 0.01 mg/ ^cm2 or more and 3 mg/ ^cm2 or less, or the amount of the skeletal forming agent per unit area of the separator coated on both sides is 0.02 mg/ ^cm2 or more and 6 mg/ ^cm2 or less.

The method for manufacturing an electrode according to the present invention is a method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, and includes a step A of applying a skeletal former containing a silicate having a siloxane bond or a skeletal former containing a phosphate to the surface of the active material layer of the electrode, and a step B of drying the electrode. According to this configuration, by using a skeletal former in the manufacture of the electrode, it is possible to manufacture an electrode that has excellent heat resistance, high strength, and improved cycle life characteristics.

In addition, in the manufacturing method of this electrode, in step A, the framework forming agent penetrates from the surface to the inside of the active material layer.

In addition, in the manufacturing method of this electrode, step A is a step of impregnating the electrode in a tank containing the skeleton-forming agent.

Preferably, in the method for producing this electrode, the solids concentration of the silicate or phosphate in the framework forming agent is 0.1 to 30 parts by mass, and step B is a step of heat treating at a temperature of 60°C or higher. If the material is dried at a temperature below 60°C, the bonding strength with the electrodes and separator is low, and the moisture cannot be sufficiently removed, making it difficult to obtain stable life characteristics when assembled into a battery.

Here, the electrode is manufactured, for example, by mixing an active material, a binder, and an optional conductive assistant to form a slurry, applying the mixture to a current collector, pre-drying, and then filling the active material layer with water in which a skeletal forming agent has been dissolved, and performing heat treatment at 60°C or higher to obtain an electrode. That is, the electrode obtained by the slurry coating method is filled with a skeletal forming agent in the active material layer, and then performing heat treatment to obtain an electrode. Pre-drying is not particularly limited as long as it is a method that can volatilize and remove the solvent in the slurry, but an example of the method is a method in which heat treatment is performed in air at a temperature of 50 to 200°C.

In addition, the heat treatment is preferably performed at 80°C or higher, more preferably 100°C or higher, and desirably 110°C or higher, because a higher temperature can shorten the heat treatment time and improve the strength of the skeleton-forming agent. The upper limit of the heat treatment temperature is not particularly limited as long as the current collector does not melt, and may be increased to, for example, about 1000°C, which is the melting point of copper. In conventional electrodes, the upper limit of the temperature was estimated to be much lower than 1000°C because the electrode binder could carbonize or the current collector could soften, but in the present invention, the skeleton-forming agent exhibits excellent heat resistance and is stronger than the current collector, so the upper limit of the temperature is 1000°C.

The heat treatment can be performed for 0.5 to 100 hours. The heat treatment can be performed in air, but it is preferable to perform the treatment in a non-oxidizing atmosphere to prevent oxidation of the current collector. A non-oxidizing atmosphere means an environment in which the amount of oxygen gas present is less than that in air. For example, it may be a reduced pressure environment, a vacuum environment, a hydrogen gas atmosphere, a nitrogen gas atmosphere, a rare gas atmosphere, etc.

In addition, in the case of an electrode using a material with irreversible capacity, it is preferable to cancel the irreversible capacity by lithium doping. The lithium doping method is not particularly limited, but examples include (i) a method in which metallic lithium is attached to a part of the electrode collector where there is no active material layer, and a local cell is formed by injecting the lithium, and lithium is doped into the electrode active material, (ii) a method in which metallic lithium is attached to the active material layer on the electrode collector, and a forced short circuit is caused by injecting the lithium, and lithium is doped into the electrode active material, (iii) a method in which metallic lithium is formed on the active material layer by deposition or sputtering, and lithium is doped into the electrode active material by a solid-phase reaction, (iv) a method in which lithium is electrochemically doped in an electrolyte before the battery is constructed, and (v) a method in which metallic lithium is added to an active material powder and mixed to dope lithium into the active material.

Other methods for manufacturing electrodes include forming an active material layer on a current collector using, for example, chemical plating, sputtering, vapor deposition, or gas deposition of an active material or an active material precursor, and integrating the active material layer onto the current collector. From the viewpoint of the lyophilicity of the framework-forming agent and the cost of manufacturing the electrode, however, a slurry coating method is preferred.

The battery according to the present invention is characterized by comprising the electrode according to any one of claims 8 to 13 or the separator according to claim 14. This configuration makes it possible to obtain a battery with excellent cycle life characteristics and good safety.

For example, in the case of a battery using the above-mentioned electrodes (positive or negative electrodes), the positive and negative electrodes are joined via a separator, and the battery structure is sealed while immersed in an electrolyte. Note that the battery structure is not limited to this, and the battery can be applied to existing battery forms and structures such as stacked batteries and wound batteries.

The electrolyte used in this battery may be a liquid or solid that can transfer alkali metal ions from the positive electrode to the negative electrode or from the negative electrode to the positive electrode, and the same electrolytes used in known nonaqueous electrolyte secondary batteries can be used. Examples include electrolytic solutions, gel electrolytes, solid electrolytes, ionic liquids, and molten salts. Here, electrolytic solutions refer to electrolytes dissolved in a solvent.

Since the electrolyte must contain an alkali metal ion, the electrolyte salt is not particularly limited as long as it is used in nonaqueous electrolyte secondary batteries, but alkali metal salts such as lithium salts, sodium salts, and potassium salts are preferred. As the alkali metal salt, at least one selected from the group consisting of lithium hexafluorophosphate (LiPF ₆ ), lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₄ ), lithium bistrifluoromethanesulfonylimide (LiN(SO ₂ CF ₃ ) ₂ ), lithium bispentafluoroethanesulfonylimide (LiN(SO ₂ C ₂ F ₅ ) ₂ ), lithium bisoxalateborate (LiBC ₄ O ₈ ), sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethanesulfonate, sodium trifluoromethanesulfonimide, potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, and potassium trifluoromethanesulfonimide can be used.

Examples of electrolyte solvents include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), gamma-butyrolactone (GBL), methyl-gamma-butyrolactone, methyl lactone, 2-methyltetrahydrofuran, 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, furan, dimethylfuran, tetrahydrofuran (THF), methyltetrahydrofuran (MeTHF), tetrahydrofuran (THP), dioxane (DIOX), and clathrate. ether, dimethoxymethane (DMM), dimethoxyethane (DME), diglyme, triglyme, tetraglyme, methyl acetate (MA), ethyl acetate (EA), propyl acetate, isopropyl acetate, butyl acetate, methyl fluoroacetate, ethyl trifluoroacetate, methyl propionate, ethyl propionate, propyl propionate, methyl formate, ethyl formate, propyl formate, ethyl butyrate, propyl butyrate, methyl propyl butyrate, vinyl acetate, methyl cyanoacetate, γ-valerolactone, σ-valerolactone, ε-caprolactone, γ-hexalactone, γ-undecalactone, trimethyl phosphate (TMP), triethyl phosphate (TEP), tri- n-Propyl phosphate, trioctyl phosphate, triphenyl phosphate, N,N-dimethylformamide (DMF), ethylenediamine, pyridine, N-methylimidazole, dimethyl sulfate, dimethyl sulfite, dipropyl sulfite, ethylene sulfite, dimethyl sulfone, ethyl methyl sulfone, diphenyl sulfone, sulfolane, methyl sulfolane, methyl methanesulfonate, methyl benzenesulfonate, methyl trifluoromethanesulfonate, propanesulfone, butanesulfone, dimethylsulfoxide, diphenyl disulfide, dimethyl sulfide, diethyl sulfide, acetonitrile, propanenitrile, azido At least one selected from the group consisting of polynitrile, valeronitrile, glutanitrile, malononitrile, succinonitrile, pimelonitrile, suberonitrile, isobutyronitrile, biphenyl, succinic anhydride, t-butylbenzene, naphthalene, cyclohexylbenzene, benzotriazole, thiophene, toluene, methyl ethyl ketone, benzene, fluorobenzene, hexafluorobenzene, nitromethane, N,N-dimethylformamide, dimethyl sulfoxide, vinylene carbonate (VC), vinylethylene carbonate (EVC), fluoroethylene carbonate (FEC), and ethylene sulfite (ES) can be used.

Ionic liquids and molten salts are classified according to the type of cation (positive ion), such as pyridine, alicyclic amine, and aliphatic amine. By selecting the type of anion (negative ion) to be combined with this, a variety of ionic liquids and molten salts can be synthesized. Cations include ammonium ions such as imidazolium salts and pyridinium salts, phosphonium ions, and inorganic ions, while examples of anions include halogen ions such as bromide ions and triflates, boron ions such as tetraphenylborate, and phosphorus ions such as hexafluorophosphate.

Ionic liquids and molten salts can _be obtained by known _synthesis methods, for example, by combining a cation such as imidazolinium with an anion such as Br-, Cl-, _BF4- , _PF6- , ( _CF3SO2 ) _2N- , _CF3SO3- , _FeCl4- , etc. Ionic liquids and molten salts can function as an electrolytic solution without the addition of an electrolyte.

The electrical device according to the present invention is characterized by comprising the battery described in claim 19.

Examples of electrical equipment include irons, whisks, all-in-one computers, clothes dryers, medical equipment, intercoms, wearable devices, video equipment, air conditioners, air circulators, gardening machinery, motorcycles, ovens, music players, music recorders, hot air heaters, toys, car components, flashlights, loudspeakers, car navigation systems, cassette stoves, home batteries, nursing care machinery, humidifiers, dryers, fuel dispensers, water dispensers, suction machines, safes, glue guns, mobile phones, portable information devices, air purifiers, air-conditioned clothing, game consoles, fluorescent lights, lint removers, cordless phones, coffee makers, coffee water dispensers, ice shaver, kotatsu, copy machine, haircutting equipment, shaver, lawnmower, automobile, lighting equipment, dehumidifier, sealer, shredder, automated external defibrillator, rice cooker, stereo, stove, speaker, trouser press, smartphone, rice polisher, washing machine, toilet seat with cleaning function, sensor, electric fan, submarine, blower, vacuum cleaner, tablet, body fat scale, fishing tackle, digital camera, television, television receiver, video game, display, disc changer, desktop computer, railway, television, electric carpet, electric lamp, electric stove, electric kettle, electric blanket, electric Tables, electric carts, electric wheelchairs, power tools, electric cars, electric floats, electric toothbrushes, telephones, electric bicycles, electric insect killers, induction cookers, electronic organizers, electronic musical instruments, electronic locks, electronic cards, microwave ovens, electronic mosquito repellents, electronic cigarettes, telephones, toasters, hair dryers, walkie-talkies, watches, drones, food waste processors, laptops, incandescent light bulbs, soldering irons, panel heaters, halogen heaters, fermenters, bread bakers, hybrid cars, personal computers, computer peripherals, hair clippers, panel heaters, video cameras, video decks, airplanes, emergency lights, emergency batteries, ships, beauty machines These include appliances, printers, copiers, grinders, sprayers, fax machines, forklifts, plug-in hybrid cars, projectors, hair dryers, hair irons, headphones, disaster prevention equipment, security equipment, home theaters, hot sandwich makers, hot plates, pumps, aroma diffusers, massage machines, mixers, mills, movie players, monitors, rice cake makers, water heaters, underfloor heating panels, radios, radio cassette players, lanterns, radio-controlled cars, laminators, remote controls, microwave ovens, water coolers, refrigerators, air coolers, cooling fans, air conditioning equipment, robots, word processors, GPS, etc.

By using the skeleton-forming agent according to the present invention in an electrode, unlike when it is used as a binder, the occurrence of wrinkles, cracks, etc. can be suppressed. In addition, better life characteristics can be obtained than in the past. Furthermore, even when the electronic conductivity of the active material layer is high, heat generation due to internal short circuits can be reduced.

FIG. 2 is a diagram showing a cross section of an electrode coated with a framework forming agent according to one embodiment of the present invention. FIG. 2 is a diagram showing an example of coating of a framework forming agent according to one embodiment of the present invention. 1A to 1C are diagrams illustrating an example of a manufacturing process for an electrode according to an embodiment of the present invention. FIG. 4 is a graph showing cycle life characteristics of an electrode according to one embodiment of the present invention. FIG. 2 is a graph showing the relationship between the skeletal density and the discharge capacity of an electrode according to one embodiment of the present invention. FIG. 4 is a graph showing cycle life characteristics of an electrode according to one embodiment of the present invention. FIG. 2 is a graph showing the relationship between the skeletal density and the discharge capacity of an electrode according to one embodiment of the present invention. FIG. 4 is a graph showing cycle life characteristics of an electrode according to one embodiment of the present invention. FIG. 1 is a diagram showing the cycle life characteristics of an electrode to which a framework forming agent containing a surfactant according to one embodiment of the present invention is applied. FIG. 1 is a diagram comparing the cycle life characteristics of an electrode coated with a framework-forming agent according to one embodiment of the present invention and an electrode that is not coated with the framework-forming agent. FIG. 1 is a diagram comparing the cycle life characteristics of an electrode coated with a framework-forming agent according to one embodiment of the present invention and an electrode that is not coated with the framework-forming agent. FIG. 1 is a diagram showing a cross section of an electrode coated with a framework forming agent containing inorganic particles according to one embodiment of the present invention. FIG. 2 is a diagram showing the initial charge/discharge curves of a battery not using a separator according to one embodiment of the present invention. FIG. 2 is a diagram showing an SEM image of a Si granule to which a framework forming agent according to one embodiment of the present invention is applied. FIG. 4 is a diagram showing charge/discharge curves at various rates according to one embodiment of the present invention. FIG. 1 is a diagram showing the results of a peel test comparing an electrode coated with a framework-forming agent according to one embodiment of the present invention and an electrode that is not coated. FIG. 2 shows an X-ray diffraction (XRD) pattern of silicate (Na ₂ O.nSiO ₂ ) powder. FIG. 13 is a diagram showing the cycle life characteristics of a reference electrode containing an alkali metal silicate (Li _0.05 Na _1.95 O.2.8SiO ₂ ) as a binder and the electrode after 200 cycles. 1 is a copy of a photograph showing a current collector in a conventional Si negative electrode. FIG. 13 is a graph showing the results of glow discharge optical emission spectroscopy comparing an electrode coated and impregnated with a framework-forming agent with an electrode not coated and impregnated. FIG. 1 is a diagram showing a silicate-based molecular formula and a phosphate-based molecular formula.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to this embodiment. In particular, in this embodiment, an electrode of a lithium secondary battery (lithium ion battery) will be described as an example, but the present invention is not limited to this. In addition, as a framework forming agent, an alkali metal silicate aqueous solution containing _Na2O.3SiO2 will be mainly described as an example, but the present _invention is not limited to this.

-First embodiment-
[1. Electrode manufacturing method]
First, as an example of this embodiment, a method for manufacturing an electrode of a lithium secondary battery will be described. Although there are negative and positive electrodes in the electrodes, the negative and positive electrodes are manufactured in the same manner, with only the difference being the current collector and the active material. Therefore, the method for manufacturing the negative electrode will be described, and the method for manufacturing the positive electrode will be omitted as appropriate.

The negative electrode is manufactured by applying an electrode material to copper foil. First, rolled copper foil with a thickness of, for example, 10 μm is manufactured, and the copper foil is prepared by winding it into a roll. The electrode material for the negative electrode is made by baking a carbon precursor to graphite artificial graphite, which is mixed with a binder and a conductive additive to form a paste. In this embodiment, as an example, PVdF is used as the binder and acetylene black (AB) is used as the conductive additive. Then, the electrode material is applied to the surface of the copper foil, dried, and pressure-adjusted to complete the negative electrode body.

The positive electrode is manufactured by applying the electrode material to aluminum foil. The electrode material for the positive electrode is made into a paste by mixing lithium-transition metal oxide with a binder and a conductive assistant. In this embodiment, as an example, PVdF is used as the binder and AB is used as the conductive assistant. Hereinafter, the positive electrode body and the negative electrode body are collectively referred to as the electrode body, the copper foil and the aluminum foil are collectively referred to as the current collector, and the electrode material applied to the current collector may be referred to as the active material layer.

On the other hand, in this embodiment, the skeletal forming agent to be used for the electrode body is prepared in advance. The skeletal forming agent is produced by purifying _Na2O.3SiO2 , an alkali metal _silicate having a siloxane bond, by a dry or wet method, and adjusting the amount of water added thereto. For example, the dry method is according to the following formula ₄ , and the wet method is according to the following formula 5. At this time, a surfactant is mixed. As an example of the skeletal forming agent of this embodiment, the solid concentration of _Na2O.3SiO2 in the skeletal forming agent is 5 mass %, and the surfactant is 0.04 mass %.
Na ₂ CO ₃ +3SiO ₂ →Na ₂ O.3SiO ₂ +CO ₂ ↑ ... (Formula 4)
2NaOH+3SiO ₂ →Na ₂ O.3SiO ₂ +H ₂ O (Formula 5)

Then, the surface of each electrode body is coated with a skeleton-forming agent to coat the active material layer. The skeleton-forming agent can be applied by immersing the electrode body in a tank that contains the skeleton-forming agent, by dripping or applying the skeleton-forming agent to the surface of the electrode body, spray coating, screen printing, curtain printing, spin coating, gravure coating, die coating, or other methods. The skeleton-forming agent applied to the surface of the electrode body penetrates into the active material layer and enters the gaps between the active material and the conductive assistant. The electrode body is then dried with hot air at 110°C to 160°C, heat, or the like to harden the skeleton-forming agent. As a result, the skeleton-forming agent forms the skeleton of the active material layer.

Finally, each electrode body, i.e., the negative electrode body and the positive electrode body, is cut to the desired size, and the electrodes with skeletal formation are completed.

The above-mentioned electrode manufacturing method can be realized by a manufacturing device. A current collector wound into a roll is sent out, and an electrode material is applied to the current collector in an active material layer coating device, the electrode material is dried with hot air in a first drying device, a skeletal forming agent is applied to the surface of the electrode body in a skeletal forming agent coating device, the skeletal forming agent is dried and hardened with hot air in a second drying device, and the electrode is wound into a roll again. Finally, the electrode wound into a roll is cut to the desired size.

The above-mentioned electrode manufacturing method allows for the continuous manufacture of electrodes with high strength, excellent heat resistance, and improved cycle life characteristics. In addition, by using silicate having siloxane bonds as a skeleton-forming agent rather than as a binder, the copper foil can be used as an electrode without wrinkles or cracks, cracks or warping in the active material layer, or expansion due to generated gas.

The positive and negative electrodes obtained as described above can be joined together via a separator and sealed while immersed in an electrolyte to form a lithium secondary battery. A lithium secondary battery with this structure can function as a lithium secondary battery with good safety. There are no particular limitations on the structure of the lithium secondary battery, and it can be applied to existing battery forms and structures such as stacked batteries and wound batteries.

2. Electrode configuration
The negative electrode for a non-aqueous electrolyte secondary battery manufactured by the above manufacturing process includes a copper foil current collector and an active material layer containing an active material, a conductive assistant, and a binder on the surface of the current collector. The surface of the active material layer is coated with a hardened skeletal former, and the hardened skeletal former is also present inside the active material layer. The skeletal former inside the active material layer is present in the gaps between the active material, the conductive assistant, and the binder so as to cover them. The density of the skeletal former in the active material layer is, for example, 0.7 mg/ ^cm2 , and is preferably within the range of 0.1 mg to 3 mg/ ^cm2 .

The positive electrode includes an aluminum foil current collector and an active material layer on the surface of the current collector, the active material layer containing an active material, a conductive assistant, and a binder. The surface of the active material layer is coated with a hardened skeletal former, and the hardened skeletal former is also present inside the active material layer. The skeletal former in the active material layer is present in the gaps between the active material, the conductive assistant, and the binder so as to cover them. The density of the skeletal former in the active material layer is, for example, 0.5 mg/ ^cm2 , and is preferably 0.1 mg to 3 mg/ ^cm2 .

The electrode of this embodiment has high strength and excellent heat resistance, and the cycle life characteristics are improved. In addition, as shown in the nail penetration test results described later, the nail penetration safety is also improved. In addition, since the skeletal former is applied from the surface of the electrode by coating or impregnation, the skeletal former is present in the gaps inside the active material layer so as to cover the active material, the conductive assistant, and the binder. In other words, when the skeletal former is mixed with the binder and used, the skeletal former is present inside the active material layer with almost no gaps, but in the electrode of this embodiment, a certain amount of gaps are present inside the active material layer. This allows the electrode to expand and contract, and suppresses the occurrence of wrinkles, cracks, etc. in the current collector.

[3. Structure of the skeleton forming agent]
As described above, the skeleton-forming agent of this embodiment has a solid concentration of 7.5 mass % _Na2O.3SiO2 , _which is an alkali metal silicate having a siloxane bond, 0.09 mass % surfactant, and the remainder water. Note that the surfactant is not essential, but it improves the lyophilicity of the skeleton-forming agent to the active material layer and allows the skeleton-forming agent to uniformly penetrate the active material layer.

In addition, the skeleton forming agent of this embodiment uses alkali metal sodium silicate _Na2O.3SiO2 as the _silicate , but is not limited to this, and Li, K, triethanolammonium group, tetramethanolammonium group, tetraethanolammonium group, or granidine group may be used instead of Na.

Na is used because it has high strength and excellent cycle life characteristics. Na and Li can also be used in combination, and the use of Li improves ionic conductivity. In this case, it is preferable that Li<Na, which maintains a certain strength and provides a framework-forming agent with good ionic conductivity. More specifically, if the total of Na and Li is 100 mol %, it is preferable that Na is in the range of 51-99% and Li is in the range of 1-49%, and it is even more preferable that Na is in the range of 70-98% and Li is in the range of 2-30%.

In addition, in the skeleton forming agent of this embodiment, the coefficient of SiO ₂ is set to 3, but this is not limited thereto, and may be 0.5 or more and 5.0 or less, preferably 2.0 or more and 4.5 or less, and more preferably 2.2 or more and 3.8 or less.

The skeletal forming agent of this embodiment can also be used to coat existing electrodes. In this way, the resulting electrodes have high strength, excellent heat resistance, and improved cycle life characteristics.

The framework forming agent of this embodiment can also be used by coating the surface of the separator. In this way, the separator has high strength, excellent heat resistance, and improved cycle life characteristics.

4. Examples
Hereinafter, in this embodiment, examples in which the solid content concentration of the skeleton-forming agent and the skeleton density were variously changed, and their tests, results, and effects will be described.

<Study on n number and _skeletal density in _Na2O.nSiO2 >
(Examples 1 to 18 and Comparative Example 1)
This test was conducted to determine cycle life characteristics when Si-C granules were used as the electrode active material, the solid concentration of the skeleton forming agent _Na2O.nSiO2 was changed from 0% by mass to 20% by mass, and the value of n was changed to 2.0, 2.5, and 3.0 under conditions of 0.2C-rate, cutoff potential of _0.01V to 1.2V (vs. Li+/Li), and 30°C. The Si-C granules ( _D50 = 9.8 μm) were prepared by spray-drying a suspension consisting of Si ( _D50 = 1.1 μm), artificial graphite ( _D50 = 1 μm) (Si: artificial graphite = 29: 71% by mass), and a granulation aid at a liquid delivery rate of 6 g/min, a spray pressure of 0.1 MPa, and a drying temperature of 80 to 180°C.

The granulation aid used was polyvinyl alcohol (PVA, Poval 1400). The PVA was contained at 1% by mass relative to 100% by mass of the solid content consisting of Si, artificial graphite, and PVA. The _D50 value indicates the median diameter measured by a laser diffraction/scattering particle size distribution measurement method.

The test electrode (1.4 mAh/cm ² ) was prepared by applying a slurry (solid content ratio: 85:3:1:1:10% by mass) consisting of Si-C granules, AB, vapor grown carbon fiber (VGCF), copper flakes, and PVdF to a copper foil, immersing it in an aqueous solution in which a specific framework forming agent was dissolved, and then heat treating it at 160° C. The counter electrode was a metallic lithium foil. The separator was a glass nonwoven fabric (GA-100, manufactured by Toyo Roshi Co., Ltd.) and a polyethylene (PE) microporous membrane (20 μm). The electrolyte was 1.0 M LiPF ₆ /(EC:DEC=50:50 vol%, +vinylene carbonate 1% by mass).

Table 1 shows the solid concentration of the skeleton-forming agent and the value of n in _{Na2O.nSiO2 for} each of Examples 1 to 18 and Comparative Example _1. The inorganic skeleton-forming agent was prepared by blending a mixture of _Na2CO3 and _SiO2 to the composition shown in Table 1 below, heating and melting it to 1000°C or higher, cooling, and then dissolving it in water.

4 is a graph showing the cycle life characteristics of Examples 1 to 18 and Comparative Example 1. As is clear from FIG. 4, the negative electrodes coated with the framework forming agent (Examples 1 to 18) have significantly improved life characteristics compared to the negative electrode not coated with the framework forming agent (Comparative Example 1). Among these, the solid concentration of Na ₂ O.nSiO ₂ in the range of 2 to 10 mass % showed particularly excellent cycle life characteristics. The value of n in Na ₂ O.nSiO ₂ of 3.0 showed particularly excellent cycle life characteristics.

Fig. 5 is a graph showing the relationship between the density (skeleton density) of the skeletal body and the discharge capacity at each cycle for Examples 1 to 18 and Comparative Example 1. As is clear from Fig. 5, in an electrode using Si-C granules (Si:artificial graphite = 29:71 mass%) as the active material, a sufficient discharge capacity can be obtained when the skeletal density is 0.04 to 3.15 mg/ ^cm2 . More preferably, the skeletal density is 0.1 to 2.5 mg/ ^cm2 .

(Examples 19 to 36 and Comparative Example 2)
Examples 19 to 36 and Comparative Example 2 were similar to the previous tests (Examples 1 to 18 and Comparative Example 1) except that the composition of the Si-C granules as the active material was changed from 29:71% by mass of Si:artificial graphite to 46:54% by mass, and the capacity density of the test electrode was 1.2 mAh/ ^cm2 . Table 2 shows the solid content concentration of the skeleton forming agent and the value of n in _Na2O.nSiO2 for Examples 19 to 36 and Comparative Example ₂ , respectively.

6 is a graph showing the cycle life characteristics of Examples 19 to 36 and Comparative Example 2. As is clear from FIG. 6, the negative electrodes coated with the framework forming agent (Examples 19 to 36) have significantly improved life characteristics compared to the negative electrode not coated with the framework forming agent (Comparative Example 2). Among these, the solid concentration of Na ₂ O.nSiO ₂ in the range of 2 to 10 mass % showed particularly excellent cycle life characteristics. The value of n in Na ₂ O.nSiO ₂ of 3.0 showed particularly excellent cycle life characteristics.

Fig. 7 is a graph showing the relationship between the density (skeleton density) of the skeletal body and the discharge capacity at each cycle for Examples 19 to 36 and Comparative Example 2. As is clear from Fig. 7, in an electrode using Si-C granules (Si:artificial graphite = 46:54 mass%) as the active material, a sufficient discharge capacity can be obtained when the skeletal density is 0.03 to 3.45 mg/ ^cm2 . More preferably, the skeletal density is 0.1 to 2.5 mg/ ^cm2 .

(Examples 37 to 40 and Comparative Example 3)
In Examples 37 to 40, the active material was Si (D ₅₀ =1.1 μm), the skeletal former was Li _0.05 Na _1.95 O.3SiO ₂ , the capacity density of the test electrode was 3.0 mAh/cm ² , and the charge/discharge test was performed under the conditions of 0.1 C-rate and cutoff potential of 0.01 V to 1.4 V (vs. Li + /Li), and was otherwise similar to the previous test (Examples 1 to 18 and Comparative Example 1). Table 3 shows the solid content concentration of the skeletal former and the skeletal density of the electrode in Examples 37 to 40 and Comparative Example 3. The inorganic skeletal former was prepared by mixing a mixture of Li ₂ CO ₃ , Na ₂ CO ₃ , and SiO ₂ to the composition shown in Table 3, heating and melting the mixture to 1000° C. or higher, cooling, and then dissolving the mixture in water.

FIG. 8 is a graph showing the cycle life characteristics of Examples 37 to 40 and Comparative Example 3. As is clear from FIG. 8, the negative electrodes coated with the skeletal forming agent (Examples 37 to 40) had an initial discharge capacity of more than 1800 mAh/g, while the negative electrode without the skeletal forming agent (Comparative Example 3) had a discharge capacity of 56.7 mAh/g. As can be seen by comparing the negative electrodes coated with the skeletal forming agent (Examples 37 to 40) with the negative electrode without the skeletal forming agent (Comparative Example 3), a dramatic improvement in cycle life characteristics was shown. Among these, the solid concentration of Li _0.05 Na _1.95 O.3SiO ₂ in the range of 0.5 to 2.5 mass% showed particularly excellent cycle life characteristics. It was found that in an electrode using Si as the active material, a discharge capacity exceeding 2000 mAh/g can be obtained when the skeletal density is 0.12 to 0.90 mg/cm ² .

Next, the batteries of Examples 37 to 40 and Comparative Example 3 were disassembled after charging and discharging (after 20 cycles), and the test electrodes were observed. It was found that the active material layer had peeled off from the current collector in Comparative Example 3, whereas it had not peeled off from the current collector in Examples 37 to 40, and no wrinkles or cracks were observed in the current collector. From these results, it became clear that the electrodes coated and filled with the framework-forming agent had improved adhesion between the active material layer and the current collector, improving electrode performance.

<Surfactant study>
(Example 41 and Example 42)
In Example 41, Si-C granules (Si: artificial graphite = 29: 71 mass%) were used as the electrode active material, and the solid content concentration of Na ₂ O.nSiO ₂ as the skeleton forming agent was adjusted to 6 mass%, the value of n was 2.5, and the skeleton density was 0.84 mg/cm ^2. The other conditions were the same as those of Example 10.

In Example 42, 0.05% by mass of a nonionic surfactant (registered trademark: Triton X-100) was added as a skeleton-forming agent, but the other conditions were the same as in Example 41.

Figure 9 is a graph showing a comparison of the cycle life characteristics of an electrode in which no surfactant is added to the skeletal forming agent (Example 41) and an electrode in which a surfactant is added to the skeletal forming agent (Example 42). As is clear from Figure 9, the cycle life characteristics are improved by adding a surfactant. This is because the surfactant improves the lyophilicity of the skeletal forming agent to the active material layer, forming a uniform skeleton in the active material layer. In addition, the surfactant used in this embodiment is a nonionic surfactant, but is not limited to this, and may be an anionic surfactant, a cationic surfactant, an amphoteric surfactant, or a nonionic surfactant.

<Nail penetration safety>
(Example 43 and Comparative Example 4)
The safety of the battery using the negative electrode using the framework forming agent was tested. The test method was a nail penetration test in which a nail was inserted into a battery model to examine the state of smoke and fire of the battery model. For the test, a 1.1 Ah battery model was used in which a negative electrode, a separator, and a positive electrode were laminated in an aluminum laminate casing and an electrolyte was sealed. The positive electrode (4.2 mAh/cm ² ) was produced by applying a slurry consisting of LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , AB, and PVdF to an aluminum foil (20 μm) and adjusting the pressure, and then heat-treating it at 160° C. The negative electrode (4.6 mAh/cm ² ) was produced by applying a slurry consisting of artificial graphite (D ₅₀ =20 μm), AB, and an acrylic binder to a copper foil (10 μm) and adjusting the pressure, and then heat-treating it at 160° C.

In Example 43, as shown in FIG. 2, the negative electrode was immersed in an aqueous solution in which a skeletal forming agent was dissolved, and then heat-treated at 150° C. The skeletal forming agent was an aqueous solution of Na ₂ O.3SiO ₂ and a nonionic surfactant (registered trademark: Triton X-100), with a solid content concentration of Na ₂ O.3SiO ₂ of 6 mass % and a solid content concentration of the surfactant of 0.05 mass %. The skeletal density of the electrode was 0.9 mg/cm ² per side. In this test, the positive electrode and the negative electrode were prepared by coating on both sides, so that the skeletal density of both sides was 1.8 mg/cm ^2. In addition, a battery using a negative electrode to which a skeletal forming agent was not applied was used as Comparative Example 4.

The electrolyte used was 1M _LiPF6 /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1 mass%. The separator used was a polypropylene (PP) microporous membrane (23 μm). The nail penetration test was performed by charging this battery model to 4.2 V at 0.1 C-rate, and then piercing the center of the battery with an iron nail (φ3 mm, round) at a speed of 1 mm/sec in a 25°C environment until it penetrated, and measuring the battery voltage, nail temperature, and casing temperature.

When a nail was pierced in a conventional battery model (Comparative Example 4) that used a negative electrode without a framework-forming agent, the battery voltage dropped to 0 V and a large amount of smoke was emitted. This was because a short circuit occurred inside the battery model, generating heat and causing the separator to melt down.

On the other hand, the battery model using an artificial graphite negative electrode with a skeleton-forming agent (Example 43) maintained a voltage of 3 V or more even when a nail was pierced, no smoke was generated, and the temperature of the casing and nail was below 50°C, with almost no heat generation due to short circuit. This is thought to be because the skeleton present inside the active material layer of the negative electrode coats the active material, blocking the movement of electrons and suppressing short circuit.

<Electrode peeling test>
(Example 43 and Comparative Example 4)
A peel test was performed on the negative electrodes used in the batteries of Example 43 and Comparative Example 4. The peel test was performed in accordance with JIS K685, in which an adhesive tape (Scotch, No. 845, Book Tape) was pressed onto the active material layer of the negative electrode with a 1 kg roller, and evaluated under conditions of a pulling speed of 300 mm/min and an angle of 180° in a 25°C environment. FIG. 16 shows a photograph of the negative electrodes and adhesive tapes of Example 43 and Comparative Example 4 after the peel test. As is clear from FIG. 16, the negative electrode of Comparative Example 4, which did not use a skeletal forming agent, has a peeled active material layer attached to the adhesive tape, while the negative electrode of Example 43, which used a skeletal forming agent, has almost no active material layer attached to the adhesive tape. It was shown that the peel strength was improved.

<Consideration of negative electrode active material>
(Examples 44 to 59 and Comparative Examples 5 to 20)
The effects of the presence or absence of a skeletal former were compared using various negative electrode active materials shown in Table 4. Examples 44 to 59 were produced by applying a slurry consisting of the negative electrode active material, AB, and PVdF shown in Table 4 to a copper foil (10 μm) under an adjusted pressure, then using a spray gun to coat and impregnate the active material layer with the skeletal former, and heat treating at 160° C. The solid content ratio of the electrode slurry was 88 mass % for the electrode active material, 4 mass % for AB, and 8 mass % for PVdF.

The framework forming agent _was an aqueous solution of _{Li0.05Na1.95O.3SiO2} and a non-ionic _surfactant (registered trademark _: Triton X- ₁₀₀ ), with a solid concentration of _{Li0.05Na1.95O.3SiO2} of 7.5 mass% and a solid concentration of the surfactant of 0.03 mass%. In this test, the test electrode was prepared by coating on one side.

The test battery used lithium metal as the counter electrode and 1M _LiPF6 /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1 mass% as the electrolyte. A polypropylene (PP/PE/PP) three-layer microporous membrane (25 μm) was used as the separator. The charge/discharge test was performed at a current density of 0.1 mA/ ^cm2 and a test environment temperature of 30°C. The cutoff potential, active material density of the electrode (one side), electrode thickness, and skeletal density (one side) are as shown in Table 4.

Table 5 shows the cycle life characteristic test results of each electrode having a skeleton (Examples 44 to 59). Table 6 shows the cycle life characteristic test results of each electrode not having a skeleton (Comparative Examples 5 to 20) for comparison. As is clear from a comparison of Tables 5 and 6, the electrodes using Si, SiO, Ge, In, and Fe ₂ O ₃ as active materials showed excellent cycle life characteristics by using a skeleton forming agent. Among these, the electrodes using Si as the active material (Example 56 and Comparative Example 17) showed a particularly significant difference. This is thought to be due to the fact that a strong skeleton forming agent was constructed in the active material layer, suppressing the destruction of the electronic conductive network due to volume change.

On the other hand, no significant difference was observed in cycle life characteristics with or without _a framework former for Ag, _Ag2O , Sb, _Sb2S3 , _SnO2 , CuO, NiO, artificial graphite, and hard carbon. These active materials have smaller volume changes than Si, SiO, Ge, In, _{and Fe2O3} , which is probably why no clear difference was observed under the test conditions.

However, when Sn was used as a skeletal forming agent, the cycle life characteristics deteriorated. This is thought to be due to the fact that Sn dissolved too quickly in the skeletal forming agent and was unable to maintain the shape of the active material, resulting in a deterioration in capacity.

<Study on the Si and graphite mixing ratio>
(Examples 60 to 63 and Comparative Examples 21 to 24)
The effect of skeletal formation was compared in an electrode using a mixture of Si (1 μm) and artificial graphite (19 μm) as the negative electrode active material. Examples 60 to 63 were produced by applying a slurry consisting of the negative electrode active material, AB, and PVdF shown in Table 7 to a copper foil (10 μm) under an adjusted pressure, then using a spray gun to coat and impregnate the active material layer with a skeletal former, and then heat-treating at 160°C.

For comparison, electrodes that were not coated and impregnated with the skeletal former were prepared (Comparative Examples 21 to 24). The solid content ratio of the electrode slurry was 88% by mass for the electrode active material, 4% by mass for AB, and 8% by mass for PVdF. The skeletal former was an aqueous solution of _{Li0.05Na1.95O.3SiO2} and a _{nonionic surfactant} (registered trademark: Triton X- ₁₀₀ ), with a solid content concentration of _{Li0.05Na1.95O.3SiO2} of 7.5% by mass and a solid content concentration of the surfactant of 0.03% _by mass. In this test, the test electrodes were prepared by coating on one side.

The test battery used lithium metal as the counter electrode and 1M LiPF ₆ /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1 mass% as the electrolyte. A polypropylene (PP/PE/PP) three-layer microporous membrane (25 μm) was used as the separator. The charge/discharge test was performed with a current density of 0.1 C-rate, a test environment temperature of 30°C, and a cutoff potential of 0.0 to 1.4 V (vs. Li+/Li). The skeletal density (one side) is as shown in Table 8. The capacity density of the test electrode was 3.0 mAh/cm ² .

Figure 10 is a graph showing a comparison of cycle life characteristics of Examples 60 to 63 in which a skeletal forming agent was applied and Comparative Examples 21 to 24 in which a skeletal forming agent was not applied. As is clear from Figure 10, when the total amount of active material contained in the negative electrode is taken as 100 mass%, electrodes with Si of 10 mass% or less (Examples 60, 61, Comparative Examples 21 and 22) did not show much change, but electrodes with Si of 20 mass% or more (Examples 62, 63, Comparative Examples 23 and 24) clearly showed improved life characteristics. In particular, electrodes with Si of 50 mass% (Example 63 and Comparative Example 24) showed an overwhelming improvement in life characteristics by forming a skeletal structure.

<Study of various positive electrode materials>
The effect of the coating amount of the skeletal former was compared using each positive electrode active material. The test electrode was produced by applying a slurry consisting of the positive electrode active material, AB, and PVdF shown in Table 9 to an aluminum foil (20 μm) under an adjusted pressure, impregnating the active material layer with the skeletal former using a spray gun, and heat-treating at 170° C. The solid content ratio of the electrode slurry was 90% by mass for the electrode active material, 5% by mass for AB, and 5% by mass for PVdF.

The skeletal forming agent used in Examples 64 to 72 was an aqueous solution of Na ₂ O.2.8SiO ₂ and a nonionic surfactant (registered trademark: Triton X-100), with a solid concentration of Na ₂ O.3SiO ₂ of 5.5% by mass and a solid concentration of the surfactant of 0.03% by mass. The skeletal forming agent used in Examples 73 to 81 was an aqueous solution of Na ₂ O.2.8SiO ₂ and a nonionic surfactant (registered trademark: Triton X-100), with a solid concentration of Na ₂ O.3SiO ₂ of 1.1% by mass and a solid concentration of the surfactant of 0.03% by mass.

Table 9 shows the skeletal density and cutoff potential per electrode side for Examples 64 to 81. However, for Examples 72 and 81, charging was performed to 4.6 V only for the first charge.

In this test, the test electrode was prepared by coating one side so that the electrode capacity was 2.0 mAh/ ^cm2 . The test battery used lithium metal as the counter electrode and 1M _LiPF6 /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol% as the electrolyte. A polypropylene (PP/PE/PP) three-layer microporous membrane (25 μm) was used as the separator. The charge/discharge test was performed at a test environment temperature of 30°C and a charge/discharge rate of 0.1 C-rate for 1 to 10 cycles.

Table 10 shows the cycle life characteristic test results of Examples 64 to 81. As is clear from Table 10, the positive electrodes having a skeletal density of more than 0.5 mg/ ^cm2 (Examples 64 to 72) have a smaller discharge capacity than the positive electrodes having a skeletal density of 0.5 mg/cm2 or ^less (Examples 73 to 81). It was found that the skeletal density (one side) of the positive electrode is preferably 0.5 mg/ ^cm2 or less.

<High temperature durability of positive electrode>
(Examples 82 to 84 and Comparative Examples 21 to 23)
Example 82 is the same as Example 74, except that the electrode capacity is changed to 1.0 mAh/cm ² and the skeleton density is changed to 0.06 mg/cm ^2. Example 83 is the same as Example 76, except that the electrode capacity is changed to 1.0 mAh/cm ² and the skeleton density is changed to 0.07 mg/cm ^2. Example 84 is the same as Example 81, except that the electrode capacity is changed to 1.0 mAh/cm ² and the skeleton density is changed to 0.11 mg/cm ^2. Comparative Example 21 is the same as Example 74, except that the electrode capacity is 1.0 mAh/cm ² and the skeleton former is not provided. Comparative Example 22 is the same as Example 76, except that the electrode capacity is 1.0 mAh/cm ² and the skeleton former is not provided. Comparative Example 23 is the same as Example 81, except that the electrode capacity is 1.0 mAh/cm ² and the skeleton former is not provided.

All batteries were prepared using the positive electrodes of Examples 82 to 84 and Comparative Examples 21 to 23. The negative electrode (2 mAh/cm ² ) was prepared by applying a slurry consisting of SiO, AB, and polyimide (PI) to a copper foil (40 μm) and adjusting the pressure, followed by heat treatment at 300° C. The solid content ratio of the negative electrode slurry was 79 mass % electrode active material, 3 mass % AB, and 18 mass % PI. The negative electrode was electrochemically filled with Li to compensate for the irreversible capacity before being assembled into a battery.

The test battery used 1M LiPF ₆ /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1 mass% as electrolyte. The separator used glass nonwoven fabric (GA-100, manufactured by Toyo Roshi Co., Ltd.). The charge-discharge test was performed at a test environment temperature of 80°C, with 10 cycles of charge-discharge repeated at a current density of 0.1 C-rate, followed by 30 cycles of charge-discharge at 1 C-rate. The cut-off potential was 4.15V to 2.0V for Example 82 and Comparative Example 21, 4.15V to 2.0V for Example 83 and Comparative Example 22, and 4.25V to 2.0V for Example 84 and Comparative Example 23.

Figure 11 is a graph showing a comparison of the cycle life characteristics of Examples 82 to 84 in which a skeletal forming agent was applied and Comparative Examples 21 to 23 in which a skeletal forming agent was not applied. As is clear from Figure 11, it can be seen that Examples 82 to 84 in which a skeletal forming agent was applied have improved cycle life characteristics compared to Comparative Examples 21 to 23. When exposed to a high-temperature electrolyte, the PVdF binder absorbs the electrolyte and swells, increasing the electrode resistance, but by using electrodes (Examples 82 to 84) coated with a skeletal forming agent that has excellent swelling resistance, it is believed that the swelling of the binder is suppressed even in electrolytes as hot as 80°C. In addition, the application of the skeletal forming agent to the positive electrode active material layer also suppresses the decomposition of the electrolyte, which is believed to have contributed to the improvement of the cycle life characteristics.

5. Effects of this embodiment
According to the above embodiment, the following effects are achieved. By using a _{skeleton-forming agent containing A2O.3SiO2 (} A = Na, Li) for the electrode, the electrode has excellent heat resistance, high strength, and improved cycle life characteristics. In addition, a tough current collector is not essential, and the occurrence of wrinkles, cracks, etc. in the current collector can be suppressed. In addition, it is not necessary to use a binder with a large irreversible capacity. In addition, even if the electronic conductivity of the active material layer is high, heat generation due to internal short circuit can be reduced. In addition, the skeleton-forming agent has heat resistance exceeding 1000 ° C. and is not carbonized. Even if an electrode uses an alloy-based material with a large volume change and a binder with low adhesive strength, good life characteristics can be obtained. In addition, the active material layer does not swell much even when it comes into contact with a high-temperature electrolyte.

-Second embodiment-
[1. Structure of the skeleton forming agent and the electrode]
Next, a second embodiment of the present invention will be described. The main difference between the first and second embodiments is that the skeleton forming agent contains ceramics. Fig. 12 shows an image of a cross section of an electrode in the second embodiment, and the skeleton forming agent in the second embodiment contains a ceramic powder or a solid electrolyte powder having excellent alkali resistance.

Figure 3 shows an example of the manufacturing process. By applying the skeletal forming agent of the second embodiment to the surface of the electrode body, the alumina in the skeletal forming agent is laminated on the surface of the active material layer to form an electrically insulating ceramic layer or solid electrolyte layer, and the skeletal forming agent penetrates into the active material layer.

This allows a strong skeleton to be formed, and peeling and cracking during drying to be suppressed. Also, pores are formed between the inorganic particles, providing good lyophilicity with the electrolyte. The ceramic layer also serves as a separator, making it possible to construct a battery without using a separate separator.

2. Examples
Next, in the second embodiment, examples in which the composition of the skeleton-forming agent and the like are variously changed will be described.

<Study on the ratio _{of Na2O.3SiO2} and α _{- Al2O3} >
(Examples 85 to 87 and Comparative Example 23)
Table 11 shows the solid content composition of the skeleton-forming agent used in Examples 85 to 87. An electrode was also produced using polyimide (PI) as the skeleton-forming agent (Comparative Example 23). α-Al ₂ O ₃ was used as a powder with a median diameter (D ₅₀ ) of 0.95 μm as measured by a laser diffraction/scattering particle size distribution measurement method. The solid content concentration of the skeleton-forming agent was 10 mass% when the solid content of Na ₂ O.3SiO ₂ and α-Al ₂ O ₃ was 100 mass%.

The negative electrode (4.0 mAh/cm ² ) was produced by applying a slurry consisting of SiO, carbon black (CB), and an acrylic binder to a copper foil (10 μm) under an adjusted pressure, then using a spray gun to coat and impregnate the active material layer with the skeletal forming agent shown in Table 11, and heat treating at 160° C. The skeletal density of the electrode was 3.0 mg/cm ² per side. The solid content ratio of the negative electrode slurry was 90% by mass of SiO, 5% by mass of CB, and 5% by mass of the acrylic binder. The negative electrode was electrochemically filled with Li for the irreversible capacity before being assembled into a battery.

The positive electrode (2.0 mAh/ ^cm2 ) was prepared by applying a slurry consisting of _LiFePO4 , CB, and an acrylic binder to an aluminum foil (20 μm) and then heat-treating it at 160° C. The solid content ratio of the positive electrode slurry was 91% by mass of _LiFePO4 , 5% by mass of CB, and 4% by mass of the acrylic binder. The test battery used 1M _LiPF6 /ethylene carbonate (EC):diethyl carbonate (DEC) = 50:50 vol%, + vinylene carbonate 1% by mass as the electrolyte.

In this test, no separator was used. The charge/discharge test was performed at a test environment temperature of 60°C and a current density of 0.1 C-rate. The cutoff potential was 4.0 V to 2.5 V.

Figure 13 shows the initial charge/discharge curves of the test batteries of Examples 85 to 87. It can be seen that they function as batteries without using a separator. Note that no battery tests were conducted for Comparative Example 23. This is because coating the active material layer with PI increased the electrode resistance, making it impossible to electrochemically dope Li ions.

<Study on particle size of alkali-resistant ceramic>
As shown in Table 12, the particle diameter of α-Al ₂ O ₃ was changed, the skeleton forming agent was applied to the surface of the electrode body, and dried, and the coating property, liquid property, binding property, foaming state, aggregation state, and sedimentation state were observed. The skeleton forming agent was an aqueous solution consisting of Li _0.05 Na _1.95 O.3SiO ₂ and α-Al ₂ O _3. The solid content concentration of the skeleton forming agent was 25 mass% when the solid content of Li _0.05 Na _1.95 O.3SiO ₂ and α-Al ₂ O ₃ was 100 mass%. The particle diameter of the inorganic particles shown in Table 12 means the median diameter (D ₅₀ ) by the laser diffraction/scattering type particle size distribution measurement method. As shown in Table 12, it can be seen that in the second embodiment, the particle diameter of the ceramic is preferably within the range of 0.2 to 20 μm.

3. Effects of this embodiment
The above-described embodiment of the present invention has the following advantages. By applying the skeletal forming agent used in the first embodiment and a powder with excellent alkali resistance ( _D50 = 0.2 to 20 μm) to the electrode surface, a strong skeleton can be formed in the active material layer, peeling and cracking during drying can be suppressed, and pores are formed between the inorganic particles, resulting in good lyophilicity with the electrolyte. Furthermore, the ceramic layer serves as a separator, making it possible to construct a battery without using a separate separator.

-Other embodiments-
<Formation of skeleton of active material granules>
(Examples 88 to 93)
This is a test on the manufacturing method of Si granules using a skeleton forming agent.
The Si granules were prepared by spray-drying a suspension of Si ( _D50 = 1 μm), AB, VGCF and PI at a liquid feed rate of 5 g/min, a spray pressure of 0.1 MPa and a drying temperature of 80 to 180° C., so that the _D50 was 5 to 8 μm. The solid content ratio of the suspension is as shown in Table 13.

Next, the Si granules to which the skeleton-forming agent was applied were prepared by transferring the granules obtained by spray drying into a fluidized bed and particle-coating with a skeleton-forming agent ( _{Li0.2Na1.8O.nSiO2 )} adjusted to a solid content concentration of 0.5% by mass. The skeleton-forming agent was adjusted to 1% _by mass when the granules obtained by spray drying and the skeleton-forming agent were taken as 100% by mass.

Figure 14 shows SEM images of the Si granules (Examples 88 to 93) to which the obtained skeleton-forming agent was applied. In Example 88, the amount of PI contained in the suspension was small, making it difficult to obtain spherically shaped granules, but it was found that as the amount of PI increased, it became easier to obtain spherical granules. It was also found that adding fibrous particles such as VGCF made it easier to form sea urchin-shaped granules.

<Aluminum phosphate-based skeleton-forming agent (Example 94)>
The test electrode (4.0 mAh/cm ² ) was produced by applying a slurry consisting of Si (1 μm), CB, and PVdF binder to a copper foil (40 μm) at an adjusted pressure, then using a spray gun to coat and impregnate the active material layer with a skeleton-forming agent, and heat-treating at 300° C. As the skeleton-forming agent, aluminum phosphate (Al ₂ O ₃ ·3P ₂ O ₅ ) was dissolved in water and adjusted to a solid content of 5 mass%. The skeleton density of the electrode was 2.0 mg/cm ² per side. The solid content ratio of the negative electrode slurry was 90 mass% Si, 4 mass% CB, and 8 mass% PVdF binder.

The test battery had a counter electrode of metallic Li, and an electrolyte of 1M LiPF ₆ /ethylene carbonate (EC):diethyl carbonate (DEC)=50:50 vol%, +vinylene carbonate 1 mass%. A glass nonwoven fabric (GA-100, manufactured by Toyo Roshi Co., Ltd.) was used as the separator. The charge/discharge test was performed at a test environment temperature of 30° C. and at current densities of 0.1 C-rate, 0.5 C-rate, and 1.0 C-rate. The cutoff potential was 1.0 V to 0.01 V. FIG. 15 shows the charge/discharge curves at each rate of Example 94. It was found that a stable reversible capacity was exhibited even when aluminum phosphate (Al ₂ O ₃ ·3P ₂ O ₅ ) was used as the framework forming agent.

<Evaluation as a binder>
(Comparative Example 24)
This is a test using a skeleton-forming agent as a binder. As the binder, water was added to adjust the solid concentration of alkali metal silicate ( _{Li0.05Na1.95O.2.8SiO2} ) to ⁴⁰ mass%. For the test negative electrode ( _2mAh / _cm2 ), a slurry consisting of Si ( _D50 = 1 μm), carbon black, and an inorganic binder was applied to a copper foil (10 μm) and heat-treated at 150°C. The solid content ratio of the electrode slurry was 19 mass% Si, 4 mass% CB, and 76 mass% binder.

(Comparative Example 25)
Comparative Example 25 is the same as Comparative Example 24, except that the binder was changed from alkali metal silicate to primary aluminum phosphate (Al ₂ O ₃ .3P ₂ O ₅ ). Note that a commercially available reagent (manufactured by Aesar) was used as the aluminum phosphate.

(Reference Example 1)
As the binder, an _alkali metal silicate ( _{Li0.05Na1.95O.2.8SiO2} ) and α _{- Al2O3} ( _D50 = ₃ μm) were mixed in a ratio of 50:50 by mass, and water was added to adjust the solid content of the mixture to 40 by mass. The other conditions were the same as those of Comparative Example 24.

(Reference Example 2)
As the binder, aluminum _phosphate ( _Al2O3.3P2O5 ) and α _{-Al2O3 ( D50} = 3 _μm ) were mixed at a ratio of _50:50 by mass, and water was added to adjust the solid content of the mixture to 40 by mass. The other conditions were the same as those of Comparative Example 25.

In Comparative Example 25, when the slurry was mixed, Si reacted with the alkali metal silicate, generating hydrogen gas and causing the slurry to foam. In Comparative Examples 25 and 26, when the electrodes were pre-dried at 80°C, the active material layer expanded, and a uniform electrode was not obtained. Furthermore, when the electrodes of Comparative Examples 25 and 26 were heat-treated at 150°C, the active material layer significantly shrunk in volume, cracked, and fell off from the current collector.

On the other hand, in Reference Example 1, when the slurry was mixed, the Si reacted with the alkali metal silicate, generating hydrogen gas and causing the slurry to foam, but the active material layer did not expand when pre-dried at 80°C. Furthermore, when this electrode was heat-treated at 150°C, volumetric shrinkage was suppressed compared to Comparative Example 25, and the active material layer did not crack or fall off from the current collector.

In Reference Example 2, hydrogen gas was not generated during mixing of the slurry, so the slurry did not foam, and the active material layer did not expand even when pre-dried at 80°C. Furthermore, when this electrode was heat-treated at 150°C, the active material layer did not crack or fall off from the current collector, as compared to Comparative Example 25.

The reason why the active material layer expanded at 80°C in Comparative Examples 25 and 26 is thought to be because vaporized gas (water vapor) was trapped in the active material layer when the slurry was dried, causing the active material layer to expand. Furthermore, at 150°C, the large volumetric shrinkage caused by the alkali metal silicate and aluminum phosphate likely caused cracks in the active material layer, causing the active material layer to fall off from the current collector.

On the other hand, in Reference Examples 1 and ₂ , non-binding _Al2O3 was included as a binder _, and it is believed that gas was discharged from between _{the Al2O3 and Al2O3} particles when the electrode was dried, and the active material layer did not expand. Furthermore, it is believed that at 150°C, _Al2O3 suppressed _the volumetric shrinkage of the alkali metal silicate and aluminum phosphate, preventing the active material layer from cracking and falling off from the current collector.

These phenomena are the same as when, for example, mochi is heated, the water vapor inside becomes trapped within the mochi and expands, but in cookies, which are primarily made from wheat flour, the water vapor can escape through the gaps in the flour, making them less likely to expand like mochi.

A charge-discharge test was carried out using the electrodes of Reference Example 1 and Reference Example 2. A half cell was produced using 1M LiPF ₆ /EC:DEC=50:50 vol.%, +VC1 mass%) as the electrolyte, a separator made by stacking a polyolefin microporous film (20 μm) and a glass nonwoven fabric (GA-100), and metallic Li as the counter electrode. The charge-discharge test was carried out at an environmental temperature of 30° C., a current density of 0.25 C-rate, and a cut-off potential of 1.5 V to 0.01 V.

Comparing the initial charge-discharge efficiency, the alkali metal silicate system (Reference Example 1) had a 71% efficiency, while the aluminum phosphate system (Reference Example 2) had a 67% efficiency, meaning that the alkali metal silicate system had a better initial charge-discharge efficiency. This means that the alkali metal silicate has a smaller irreversible capacity than aluminum phosphate.

Figure 18 shows the cycle life characteristics of Reference Example 1 and a photograph of the electrode (collector side) after 200 cycles. The initial discharge capacity was 2609 mAh/g, and the capacity retention rate after 100 cycles was 78%. It is believed that the formation of a strong inorganic binder (alkali metal silicate) skeleton in the active material layer made the conductive network less susceptible to destruction by the expansion and contraction of Si, resulting in the excellent capacity retention rate. The reason that even thin copper foil could be used without distortion is believed to be that the strength of the inorganic binder (alkali metal silicate) is greater than that of copper.

<Confirmation analysis of inorganic framework forming agent>
(Reference Example 3)
This test was conducted to confirm whether the skeletal former penetrated the electrode. The simulated electrode was prepared by applying a slurry consisting of Al ₂ O ₃ (D ₅₀ =9 μm), AB, and PVdF binder to a copper foil (10 μm) under an adjusted pressure, then using a spray gun to coat and impregnate the active material layer with the skeletal former, and heat treating at 150° C. The skeletal former was prepared by dissolving an alkali metal silicate (Na ₂ O.3SiO) in water and adjusting the solid content to 8% by mass. No surfactant was added. The solid content ratio of the simulated electrode slurry was 85% by mass for α-Al ₂ O ₃ , 5% by mass for CB, and 10% by mass for PVdF binder.

(Reference Example 4)
Reference Example 4 is the same as Reference Example 3 except that the electrode was not coated and impregnated with the framework forming agent for comparison. FIG. 20 shows the results of glow discharge optical emission spectroscopy (GDS) of Reference Example 3 and Reference Example 4. The GDS measurement conditions were a measurement diameter of 4 mmφ and a Ne gas pressure of 2000 Pa. The measurement wavelengths were 121 nm for H, 685 nm for F, 130 nm for O, 156 nm for C, 396 nm for Al, and 251 nm for Si. The time on the horizontal axis is the time of sputtering treatment, which is an index corresponding to the depth direction of the active material layer (direction from the electrode surface to the current collector). The intensity on the vertical axis is the emission intensity, which is an index corresponding to the content of the element. As is clear from FIG. 20, the presence of Si could not be confirmed in Reference Example 4, whereas in Reference Example 3, although the presence of Si was not constant from the surface to the inside, it was confirmed that Si was present in the deep layer. This result proves that by applying the skeletal forming agent to the electrode surface, the skeletal forming agent can penetrate into the active material layer.

As described above, the preferred embodiment of the present invention has been described with reference to the drawings, but various additions, modifications, or deletions are possible within the scope of the present invention. For example, various concentrations and ratios such as the solid content concentration of the alkali metal silicate of the skeleton forming agent are not limited to the numerical values of the above-mentioned embodiment. In addition, in the above-mentioned embodiment, the alkali metal silicate is not limited to A ₂ O.3SiO ₂ (A=Li, Na) Li or Na, and the coefficient of SiO ₂ is not limited to 2 to 3. In addition, the skeleton forming agent is not limited to aluminum monophosphate (Al ₂ O _{3.3P 2} O ₅ ) as a phosphate, and the coefficient of P ₂ O ₅ is not limited to 3. Therefore, such things are also included in the scope of the present invention.

Claims (8)

A skeletal forming agent used for forming a skeleton of an active material layer in an electrode of a non-aqueous electrolyte secondary battery, the skeletal forming agent comprising an active material capable of alloying with an alkali metal or an active material capable of occluding alkali metal ions, and a binder, the skeletal forming agent comprising:
The composition contains an amorphous silicate having a siloxane bond or an amorphous phosphate having an aluminophosphate bond ,
A framework-forming agent in which a portion of the Si sites in the siloxane bonds is substituted with at least one transition metal element selected from the group consisting of Al, Zr, Ti, Mg, Mo, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y. A skeletal forming agent used for forming a skeleton of an active material layer in an electrode of a non-aqueous electrolyte secondary battery, the skeletal forming agent comprising an active material capable of alloying with an alkali metal or an active material capable of occluding alkali metal ions, and a binder, the skeletal forming agent comprising:
The composition contains an amorphous silicate having a siloxane bond or an amorphous phosphate having an aluminophosphate bond ,
A framework-forming agent in which a portion of the transition metal sites is substituted with at least one transition metal element selected from the group consisting of Al, Mg, Ca, Cu, Fe, Ba, Ti, Mn, Mo, Mg, Si, Sr, Ca, Zn, Ba, B, W, Ta, Ce, Hf, and Y. The silicate is represented by the general _{formula A2O.nSiO2} ,
A is at least one of Li, Na, K, other alkali metal elements, a guanidine compound, an ammonium compound, a triethanolammonium group, a tetramethanolammonium group, a tetraethanolammonium group, and a guanidine group;
The phosphate is represented by the general formula M.nH _x PO ₄ ,
M is at least one of Al, Ca, Mg, Zr, Ti, Mo, Sr, Zn, Ba, B, W, Ta, Ce, Hf, Y, and a transition metal;
In the general formula of the silicate, n is 1.6 or more and 3.9 or less,
In the general formula of the phosphate, x is 2 or less, and n is 0.5 or more and 5 or less.
The skeletal formation agent according to claim 1 or 2 . In the general formula of the silicate, A is Na and n is 2.0 or more and 3.5 or less;
In the general formula of the phosphate, x is 2 or less, and n is 0.5 or more and 5 or less.
The skeletal formation agent according to claim 3 . Further, the surfactant is
The skeletal formation agent according to any one of claims 1 to 4. Further, the inorganic particles include alkali-resistant or acid-resistant inorganic particles.
The skeletal formation agent according to any one of claims 1 to 5. An electrode comprising the skeleton forming material according to any one of claims 1 to 6, an active material capable of alloying with an alkali metal or capable of occluding alkali metal ions, and a binder. The framework forming material is
At least on the surface of the active material layer,
8. The electrode of claim 7.