JP6037052B2 - Porous silicon-based particles, production method thereof, and negative electrode active material including the same - Google Patents

Description

  The present invention relates to porous silicon-based particles, a production method thereof, and a negative electrode active material including the same.

  Recently, with the development of the information and communication industry, electronic devices have become smaller, lighter, thinner, and more portable, so that there is an increasing demand for higher energy density of batteries used as power sources for such electronic devices. . The lithium secondary battery is a battery that can best satisfy such a requirement, and research on this is now actively underway.

  As a negative electrode active material of a lithium secondary battery, various types of carbon-based materials including artificial graphite capable of inserting / extracting lithium, natural graphite, or hard carbon have been applied. Of the carbon series, graphite provides advantages in terms of the energy density of lithium batteries and is most widely used because of excellent plasticity and ensuring a long life of lithium secondary batteries.

  However, graphite has a problem that the capacity is low in terms of energy density per unit volume of the electrode, and a side reaction with the organic electrolyte used tends to occur at a high discharge voltage, and it is ignited or malfunctioned due to battery malfunction or overcharge. There is a risk of explosion.

  Therefore, metal-based negative electrode active materials such as silicon (Si) have been studied. Si metal-based negative electrode active materials are known to exhibit a high lithium capacity of about 4200 mAh / g. However, it causes a volume change of up to 300% before and after reaction with lithium, that is, during charge and discharge. As a result, the conductive network in the electrode is damaged, the interparticle contact resistance is increased, and the battery performance is deteriorated.

  Therefore, there has been an attempt to reduce the size of silicon particles to nano-size to reduce the substantial diameter change due to volume change. However, a uniform nano-silicon negative electrode active material can be synthesized and uniformly mixed in the slurry. There is a problem in that it is difficult to distribute to the electrolyte, and the surface area is maximized to increase the side reaction with the electrolyte.

  Therefore, development of a negative electrode active material that can replace the conventional negative electrode active material and can solve problems with side reactions with the electrolyte, volume expansion during charge and discharge, and performance degradation of the secondary battery is required. ing.

Korean Published Patent No. 2012-0109080

  The first technical problem to be solved by the present invention is that the dispersion in the negative electrode active material slurry can be further facilitated, the side reaction with the electrolytic solution can be minimized, and the volume expansion during charge / discharge It is an object of the present invention to provide porous silicon-based particles that can reduce the number of particles.

  A second technical problem to be solved by the present invention is to provide a method for producing the porous silicon-based particles.

  The third technical problem to be achieved by the present invention is to provide a negative electrode active material containing the porous silicon-based particles.

  The fourth technical problem to be achieved by the present invention is to provide a negative electrode and a lithium secondary battery including the negative electrode active material.

In order to solve the above-mentioned problem, the present invention includes Si or SiO _x (0 <x <2) particles, the particles include a plurality of nonlinear pores, and the nonlinear pores are formed by open pores on the particle surface. Provided porous silicon-based particles.

In addition, the present invention includes a core portion including Si or SiO _x (0 <x <2), and includes a Si or SiO _x shell portion including a plurality of nonlinear pores on the core portion, and the surface of the shell portion is opened. Porous silicon-based particles having open pores are provided.

The present invention also includes (i) a step of removing an oxide film layer existing on the surface of Si or SiO _x (0 <x <2) particles using an etching solution; and (ii) the oxide film layer is removed. By mixing and stirring the metal catalyst in an etching solution containing Si or SiO _x (0 <x <2) particles and stirring, nonlinear pores are formed on the Si or SiO _x (0 <x <2) particles. Provided is a method for producing the porous silicon-based particles including the step of forming.

  In addition, the present invention provides a negative electrode active material containing the porous silicon-based particles.

  In addition, the present invention provides a negative electrode including the negative electrode active material.

  The present invention also provides a lithium secondary battery including the negative electrode.

In the porous silicon-based particles according to an embodiment of the present invention, Si or SiO _x (0 <x <2) particles may include a plurality of nonlinear pores, thereby further facilitating dispersion in the negative electrode active material slurry. In addition, side reactions with the electrolyte can be minimized, and volume expansion during charging and discharging can be reduced.

  Also, according to one embodiment of the present invention, the porous silicon-based particles are controlled by controlling the pattern, form and size of the pores formed by adjusting the type, concentration and etching time of the metal catalyst. Can do.

The following drawings and the like in the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the invention described above. It should not be construed as being limited to the matters described in the figures.
FIG. 3 is a schematic view showing porous silicon-based particles including nonlinear pores according to an embodiment of the present invention. It is the schematic diagram which showed the porous silicon type particle | grains containing a linear pore. It is the scanning electron microscope (SEM) photograph which observed the pore form of the porous silicon type particle | grains by the etching time manufactured by Example 1-6 of this invention. It is a scanning electron microscope (SEM) photograph which shows the surface shape of the porous silicon-type particle manufactured in Example 7 of this invention. It is a scanning electron microscope (SEM) photograph with respect to the internal cross section of the porous silicon-type particle manufactured in Example 7 of this invention. 3 is a scanning electron microscope (SEM) photograph of an internal cross section of silicon-based particles including linear pores manufactured in Comparative Example 1. FIG. 6 is a graph showing pore distributions of porous silicon-based particles of Examples 1 to 6 through a mercury permeation method (Hg porosity) analysis according to Experimental Example 3 of the present invention.

  Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention.

  Terms and words used in this specification and claims should not be construed to be limited to ordinary and lexicographic meanings, and the inventor should describe his invention in the best way possible. In accordance with the principle that the terminology can be defined as appropriate, it must be interpreted as a meaning and concept consistent with the technical idea of the present invention.

The porous silicon-based particles according to an embodiment of the present invention include Si or SiO _x (0 <x <2) particles, the particles include a plurality of nonlinear pores, and the nonlinear pores are open pores (open pores) on the particle surface. pores).

According to an embodiment of the present invention, the porous silicon-based particles may be more easily dispersed in the negative electrode active material slurry because the Si or SiO _x (0 <x <2) particles include a plurality of nonlinear pores. The side reaction with the electrolyte can be minimized, and the volume expansion at the time of charging / discharging of the lithium secondary battery can be reduced.

  In addition, as shown in FIG. 1, the porous silicon-based particles according to an embodiment of the present invention include nonlinear pores, and the nonlinear pores include open pores on the particle surface. The presence of open pores on the particle surface during application can suppress the volume expansion of the negative electrode active material during charging and / or discharging, and the specific surface area of the negative electrode active material can be increased to increase the contact area with the electrolyte. Therefore, the lithium secondary battery including such a negative electrode active material can improve life characteristics and rate characteristics.

  At this time, the average diameter of the open pores may be about 30 nm to 500 nm, preferably 30 nm to 300 nm, when observed on the surface.

  According to an embodiment of the present invention, the diameter of the non-linear pores may be gradually decreased along the center direction of the porous silicon-based particle, for example, having a non-linear Corn type structure. Can do.

  According to an embodiment of the present invention, at least two of the nonlinear pores may be connected to each other.

  The depth of the nonlinear pores is preferably 0.1 μm to 5 μm. At this time, the depth of the non-linear pores means from the open pores formed on the surface of the porous silicon-based particle to the pore end portion gradually decreasing along the center direction of the particle. It can be measured with a (SEM) photograph or a mercury porosimeter.

  According to an embodiment of the present invention, the porous silicon-based particles may have a mercury intrusion change rate of 30 nm to 2500 nm, preferably 50 nm to 600 nm, as measured by a mercury porosimeter. A peak can be shown by the average diameter of the pores. The total mercury intrusion volume at the peak may be from 0.5 mL / g to 1.2 mL / g.

  The total mercury intrusion amount means the intrusion amount of mercury into a plurality of pores measured using a mercury porosimeter, and the average surface pore size is assumed to be 485 mN / m and 130 ° respectively. 180 / pressure = a value measured when the relationship between the diameter and the pressure is approximated to the average diameter of the pores.

  In addition, from the measurement result of the mercury porosimeter, the meaning that the rate of change of mercury intrusion can show a peak at the average diameter of pores of about 30 nm to 2500 nm is the result of the measurement of the mercury porosimeter, the average of the pores in the above range It means that the change rate of mercury intrusion amount by diameter is distributed so as to draw an upward convex peak curve.

The average particle diameter (D ₅₀ ) of the porous silicon-based particles according to an embodiment of the present invention may be 1 μm to 20 μm, preferably 3 μm to 12 μm, more preferably 5 μm to 10 μm.

  When the average particle diameter of the porous silicon-based particles is less than 1 μm, dispersion in the negative electrode active material slurry may be difficult, and when the average particle diameter exceeds 20 μm, the expansion of the particles due to lithium ion charging is significant. Thus, by repeating charging and discharging, the settlement between particles and the settlement between the particles and the current collector are lowered, and the cycle characteristics can be greatly reduced.

In the present invention, the average particle size of the particles can be defined as the particle size based on 50% of the particle size distribution of the particles. The average particle diameter (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. In general, the laser diffraction method can measure a particle size of about several millimeters from a submicron region, and can obtain results of high reproducibility and high resolution.

The porous silicon-based particles according to an embodiment of the present invention preferably have a specific surface area (BET-SSA) of 5 m ² / g to 50 m ² / g, and the porous silicon-based particles satisfying the specific surface area in the above range. When used as a negative electrode active material to produce a lithium secondary battery, the rate characteristics of the lithium secondary battery can be improved.

When the specific surface area exceeds 50 m ² / g, it may be difficult to control a side reaction with the electrolyte due to a wide specific surface area. When the specific surface area is less than 5 m ² / g, sufficient pores are not formed, This is not preferable because it may be difficult to effectively accommodate the volume expansion during charging and discharging.

  According to an embodiment of the present invention, the specific surface area of the porous silicon-based particles can be measured by a BET (Brunauer-Emmett-Teller; BET) method. For example, it can be measured by a BET 6-point method by a nitrogen gas adsorption flow method using a pore distribution analyzer (Bell Japan Inc, Belsorb-II mini).

Meanwhile, according to still another embodiment of the present invention, a Si or SiO _x shell portion including a core portion including Si or SiO _x (0 <x <2) and including a plurality of nonlinear pores on the core portion. And the surface of the shell part provides porous silicon-based particles having open pores.

  In the porous silicon-based particle, the length ratio of the core part to the shell part is preferably 1: 9 to 9: 1.

  The form of nonlinear pores and open pores according to an embodiment of the present invention, and the average diameter of the pores are as described above. These are the types of metal catalyst, the concentration, and the etching during the production of the porous silicon-based particles. The time can be adjusted and controlled.

The method for producing porous silicon-based particles according to an embodiment of the present invention includes (i) removing an oxide film layer present on the surface of Si or SiO _x (0 <x <2) particles using an etching solution; and (ii) the oxide layer is removed Si or _{SiO x (0 <x <2} ) a metal catalyst in an etching solution that contains particles mixed and stirred to by etching, Si or _SiO x (0 <X <2) The method may include forming nonlinear pores on the particles.

First, the step (i) may be a step of removing an oxide film layer existing on the surface of Si or SiO _x (0 <x <2) particles using an etching solution.

That is, the step (i) is a step of removing an oxide layer existing on the surface of Si or SiO _x (0 <x <2) particles, and the step of removing the oxide layer is Si or SiO _x (0 <x <2) It may be a process of surface treatment so that electroless plating of metal catalyst can be coated more smoothly and uniformly.

Specifically, when Si or SiO _x (0 <x <2) particles are supported on an etching solution heated to a temperature of about 20 ° C. to 90 ° C., the particles are supported for about 30 minutes to 3 hours. The natural oxide film layer (SiO ₂ ) present on the surface of Si or SiO _x (0 <x <2) particles can be removed by stirring for a period of time.

The etching solution that can be used according to an embodiment of the present invention is one or more selected from the group consisting of hydrogen fluoride (HF), silicon fluoride (H ₂ SiF ₆ ), and ammonium fluoride (NH ₄ F). Solution, preferably hydrogen fluoride (HF).

  The concentration of the etching solution may be 5M to 20M.

In the step (ii), etching is performed by adding a metal catalyst to an etching solution containing Si or SiO _x (0 <x <2) particles from which the oxide film layer has been removed, and mixing and stirring. This may be a step of forming non-linear pores on Si or SiO _x (0 <x <2) particles.

According to an embodiment of the present invention, the average diameter and form of pores that can be formed on Si or SiO _x (0 <x <2) particles are controlled by the type and concentration of the metal catalyst and the etching (stirring) time. be able to.

That is, by adding a metal catalyst to an etching solution containing Si or SiO _x (0 <x <2) particles from which the oxide film layer has been removed, and mixing and stirring, Si or SiO _x (0 < x <2) Metals can be uniformly electrodeposited on the particle surface via electroless plating and etching can be performed to form nonlinear pores.

  The metal catalyst that can be used according to an embodiment of the present invention is any one selected from the group consisting of copper (Cu), platinum (Pt), and nickel (Ni), or two or more of these elements, Preferably it can contain copper.

The metal catalyst used in a general chemical etching method can contain silver, but the metal catalyst containing copper, platinum, nickel, etc. can etch only the portion in contact with the catalyst when compared with the metal catalyst containing silver. In the case where a metal catalyst containing silver is used, etching occurs in the vertical direction on the Si or SiO _x (0 <x <2) particle surface as shown in the schematic diagram of FIG. It can be formed linearly.

On the other hand, when the metal catalyst containing copper, platinum, or nickel is used according to an embodiment of the present invention, the crystal form of the metal catalyst is a square shape, and thus electrodeposition is performed in a square shape. Since etching is not affected by the crystallinity of Si or SiO _x (0 <x <2), etching may occur in the form of non-linear pores with no fixed orientation (see FIG. 1) . Further, cone-type etching occurs as the etched shape enters the Si or SiO _x (0 <x <2) particle, and the average diameter of the nonlinear pores gradually increases along the center direction of the particle. Can be reduced.

The metal catalyst is not particularly limited as long as it contains the metal element, but may be a salt form containing the metal. At this time, the negative ions of the salt are selected from the group consisting of nitric acid (NO ₃ ⁻ ), sulfuric acid (SO ₄ ²⁻ ), iodo (I ⁻ ), perchloric acid (ClO ₄ ⁻ ), and acetic acid (CH ₃ COO ⁻ ). It may be any one selected or a mixture of two or more thereof.

  The concentration of the metal catalyst may be 5 mM to 100 mM.

  According to an embodiment of the present invention, the etching (stirring) time may be performed between about 3 hours and 24 hours, and the degree of formation of nonlinear pores may vary depending on the etching time.

If the etching time is less than 3 hours, the pores targeted by the present invention cannot be formed, so that the intended effect of the present invention cannot be achieved, and the etching time exceeds 24 hours. Since no further etching occurs due to the consumption of the etching solution, only the process time is lengthened and there is no effect due to the etching time. If the etching time exceeds 24 hours, cracks are observed on the surface of the porous silicon-based particles. In addition, Si or SiO _x (0 <x <2) particles may be excessively etched to deteriorate the mechanical properties of the negative electrode active material.

According to an embodiment of the present invention, the electrodeposition time of the metal catalyst may be performed for about 1 to 12 hours. Further, in terms of process efficiency such as time and cost, a metal catalyst is mixed in an etching solution containing Si or SiO _x (0 <x <2) particles from which the oxide film layer has been removed, and stirred to form a metal. It is preferred to perform the catalytic electrodeposition and the etching step simultaneously.

  In addition, according to an embodiment of the present invention, a weak oxidizing agent may be further added to the etching solution in the step ii). At this time, the weak oxidant can increase the chemical etching rate, can further form additional pores through the oxidation of silicon, and promote the etching so that the pores are connected to each other. The average diameter of the pores formed by the metal catalyst can be increased.

  If a strong oxidant is used in the etching process, the chemical etching rate becomes too high compared to a weak oxidant, and the metal can be formed by being etched vertically on silicon. Since it is difficult to form nonlinear pores, it is not preferable.

  The kind of weak oxidizing agent that can be used according to an embodiment of the present invention is any one selected from the group consisting of phosphorous acid, sulfurous acid, and phosphoric acid, or a mixture of two or more thereof. Preferably, phosphorous acid can be used, and the concentration of the weak oxidizing agent can be 0.25M to 1.0M.

According to an embodiment of the present invention, after forming non-linear pores in the Si or SiO _x (0 <x <2) particles in the step (ii), the metal catalyst remaining in the particles is removed. The method may further include the step of:

In order to remove the metal catalyst, the metal catalyst can be removed by bringing Si or SiO _x (0 <x <2) particles having non-linear pores into contact with a metal removal solution.

The metal removal solution may be any one selected from the group consisting of nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), and hydrochloric acid (HCl), or a mixture of two or more thereof. .

  The porous silicon-based particles may further include a carbon coating layer on the porous silicon-based particles.

  The carbon coating layer may be formed by a conventional coating method using a carbon precursor. For example, after the etching step, the porous silicon-based particles are mixed with the carbon precursor and then heat-treated. In addition, the method may further include coating the outer wall of the porous silicon-based particle with carbon.

  Any carbon precursor can be used without limitation as long as it generates carbon by heat treatment. For example, a pitch or a hydrocarbon-based material can be used. Examples of the hydrocarbon material include furfuryl alcohol and phenol resin.

  According to an embodiment of the present invention, the carbon precursor may be used in an amount of 10 wt% to 40 wt% based on the total weight of the porous silicon-based particles.

  When the carbon precursor is used in an amount of less than 10% by weight, a uniform coating layer may not be formed, and thus there may be a problem that electrical conductivity is reduced. The pores and internal pores are all coated with the carbon material, so that the effect of improving the performance due to the porous structure cannot be obtained, and there is a problem that additional irreversible reaction occurs to reduce the capacity and initial efficiency.

  Moreover, tetrahydrofuran (THF), alcohol, etc. can be used for the solvent which forms a carbon coating layer, for example, and it can coat by performing heat processing temperature in the temperature range of 300 to 1400 degreeC, for example.

  On the other hand, the porosity of the porous silicon-based particles according to an embodiment of the present invention is 5% to 90%, preferably 10% to 70%, more preferably 10% to the total volume of the porous silicon-based particles. It can be 40%.

Here, the porosity (%) can be defined as follows.
Porosity (%) = {1− (bulk density of porous silicon particles / bulk density of pure silicon particles)} × 100

  The measurement of the porosity is not particularly limited, and can be measured by, for example, a BET (Brunauer-Emmett-Teller) measurement method or a mercury permeation method (Hg porosimeter) according to an embodiment of the present invention.

  When the porosity of the porous silicon-based negative electrode active material is less than 5%, the volume expansion of the negative electrode active material during charge / discharge cannot be suppressed, and when it exceeds 90%, the negative electrode active material Due to the large number of pores present inside, the mechanical strength is lowered, and the negative electrode active material can be destroyed during the battery manufacturing process (slurry mixing, pressing after coating, etc.).

  In addition, the present invention provides a negative electrode active material containing the porous silicon-based particles.

  The negative active material according to an embodiment of the present invention may further include a carbon-based material. That is, the porous silicon-based particles can be mixed with a conventionally used carbon-based material and used in a secondary battery.

  The normally used negative electrode active material may be one or more selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fiber, and carbon black.

  The carbon-based material may be 0 to 90 parts by weight, preferably 70 to 95 parts by weight with respect to 100 parts by weight of porous silicon-based particles.

  The present invention also provides a negative electrode including the negative active material.

  Furthermore, the present invention relates to a lithium secondary battery including a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte in which a lithium salt is dissolved. The negative electrode includes porous silicon-based particles. A lithium secondary battery including an active material is provided.

  The negative electrode active material manufactured as described above can be used to manufacture a negative electrode by a manufacturing method generally used in this field. For example, a negative electrode active material according to an embodiment of the present invention is mixed with a binder and a solvent, and if necessary, a conductive agent and a dispersing agent and stirred to produce a slurry, which is then applied to a current collector and compressed to form a negative electrode Can be manufactured.

  Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl MC, and polyvinyl alcohol. ), Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butylene rubber (SBR), fluororubber, Polyacrylic acid (poly crylic acid) and may these hydrogen Li, polymer substituted like Na or Ca or various diverse types of binder polymer such as a copolymer, is used. As the solvent, N-methylpyrrolidone, acetone, water or the like can be used.

  The conductive agent is not particularly limited as long as it does not induce a chemical change in the battery but has conductivity. For example, graphite such as natural graphite or artificial graphite; carbon black, acetylene black, kettle, etc. Carbon black such as chain black, channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; conductive tube such as carbon nanotube; metal powder such as fluorocarbon, aluminum and nickel powder; oxidation Conductive whiskers such as zinc and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

  As the dispersant, an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone can be used.

  Similar to the negative electrode production described above, a positive electrode active material, a conductive agent, a binder and a solvent are mixed to produce a slurry, which is then coated directly on a metal current collector or cast on a separate support. The positive electrode active material film peeled off from the support can be laminated on a metal current collector to produce a positive electrode.

The positive active material, lithium cobalt oxide (LiCoO _2), lithium nickel oxide _{(LiNiO 2),} in _{Li [Ni x Co y Mn z} Mv] O 2 ( Formula, M is Al, comprises Ga and In Any one selected from the group or two or more of these elements; 0.3 ≦ x <1.0, 0 ≦ y, z ≦ 0.5, 0 ≦ v ≦ 0.1, x + y + z + v = 1), Li (Li _a M _{b-a-b ′} M ′ _{b ′} ) O _2-c A _c (in the above formula, 0 ≦ a ≦ 0.2, 0.6 ≦ b ≦ 1, 0 ≦ b ′ ≦ 0.2, 0 ≦ c ≦ 0.2; M includes Mn and one or more selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn and Ti M ′ is one or more selected from the group consisting of Al, Mg and B, and A is selected from the group consisting of P, F, S and N; . That is one or more) and layered compounds such as compounds substituted with one or more transition metals; formula _{Li 1 + y Mn 2-y} O 4 ( where, y is 0-0.33) , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and other lithium manganese oxides; lithium copper oxide (Li ₂ CuO ₂ ); LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ Vanadium oxides such as: Chemical formula LiNi _1-y M _y O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01-0.3) Ni-site type lithium nickel oxide represented by chemical formula LiMn _2−y M _y O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, and y = 0.01-0. 1) or L (Where, M = Fe, Co, Ni , a is Cu or Zn) ₂ Mn ₃ MO ₈ lithium-manganese composite oxide represented by; LiMn a part of the chemical formula of Li is substituted with alkaline earth metal ions ₂ O ₄ ; disulfide compound; Fe ₂ (MoO ₄ ) _{3 and the} like can be mentioned, but are not limited thereto.

  The separation membrane is a conventional porous polymer film conventionally used as a separation membrane, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer. A porous polymer film made of a polyolefin-based polymer such as a coalescence can be used alone or by laminating these, and a normal porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. Further, at least one surface of the polymer separation membrane substrate can be coated with ceramic, but is not limited thereto.

In the electrolytic solution used as an embodiment of the present invention, the lithium salt that can be contained in the electrolyte can be used without limitation as long as it is usually used in an electrolytic solution for a secondary battery. The ions include F ⁻ , Cl ⁻ , I ⁻ , NO ₃ ⁻ , N (CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , and (CF ₃ ) ₃ PF. _{^{3 -, (CF 3) 4}} PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N _{^{-, (FSO 2) 2 N}} -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF ₃ (CF ₂ ) ₇ SO ₃ ⁻ , CF One selected from the group consisting of ₃ CO ₂ ⁻ , CH ₃ CO ₂ ⁻ , SCN ⁻ and (CF ₃ CF ₂ SO ₂ ) ₂ N ⁻ can be used.

  In the electrolytic solution used in an embodiment of the present invention, any organic solvent that is usually used can be used without limitation as long as it is a typical organic solvent, and representative examples thereof include propylene carbonate, ethylene carbonate, diethyl carbonate, and dimethyl. Carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, fluoro-ethylene carbonate, dimethyl sulfoxide, asset nitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfide, tetrahydrofuran , Methyl formate, methyl acetate, acetic acid Ethyl acetate, Isopropyl acetate, Isoamyl acetate, Methyl propionate, Ethyl propionate, Propyl propionate, Propyl propionate Any one selected from the group consisting of butyl propionate, methyl butyrate and ethyl butyrate, or a mixture of two or more thereof may be used.

  In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are high-viscosity organic solvents, which have a high dielectric constant and can be preferably used because they dissociate lithium salts in the electrolyte well. It is more preferable to use a low viscosity, low dielectric constant linear carbonate such as dimethyl carbonate and diethyl carbonate mixed with an appropriate ratio in an appropriate ratio because an electrolytic solution having high electrical conductivity can be prepared. Can be used.

  Optionally, the electrolyte stored according to the present invention may further include an additive such as an overcharge inhibitor contained in a normal electrolyte.

  A separation membrane is disposed between the positive electrode and the negative electrode to form an electrode assembly. After the electrode assembly is placed in a cylindrical battery case, a rectangular battery case, or an aluminum pouch, an electrolyte is injected to form a secondary battery. Completed. Alternatively, after laminating the electrode assembly, it is impregnated with an electrolytic solution, and the resultant product is put in a battery case and sealed to complete a lithium secondary battery.

  The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source of a small device, but also as a unit battery in a medium-sized battery module including a plurality of battery cells. Preferable examples of the medium-large-sized device include, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified in several forms, and the scope of the present invention should not be construed to be limited to the embodiments detailed below. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

<Manufacture of porous silicon particles>
Example 1
<Step (i): Step of removing an oxide film layer existing on the surface of Si or SiO _x (0 <x <2) particles using an etching solution>
After impregnating the powdered silicon with 8.5 M hydrogen fluoride heated to 50 ° C., it was stirred for about 30 minutes. Through this process, a natural oxide film layer (SiO ₂ ) present on the silicon surface in a powder state is removed, and a metal catalyst electroless plating can be coated more smoothly and uniformly on the silicon surface. Processing was performed to obtain silicon particles from which the oxide film layer had been removed.

<Step (ii): by etching the oxide layer has been removed Si or _{SiO x (0 <x <2} ) a metal catalyst in an etching solution that contains particles mixed and stirred to, Si or SiO _x (0 <x <2) Step of forming nonlinear pores on particle>
15 mM copper sulfate produced in the same volume as hydrogen fluoride in an aqueous solution in which 8.5 M hydrogen fluoride containing silicon from which the oxide film layer (SiO ₂ ) obtained in step (i) was removed was mixed. An aqueous solution of (CuSO ₄ ) was added and stirred for about 3 hours for etching. Through this process, copper was electrodeposited on the silicon surface from which the oxide film layer (SiO ₂ ) was removed, and etching was performed.

  In the aqueous solution state, the porous silicon particles were washed several times using a filter press equipped with a filter press capable of simultaneously filtering, washing and dewatering to remove residual hydrogen fluoride. Thereafter, this was filtered and dehydrated, and dried at about 150 ° C. for about 1 hour to obtain porous silicon particles in which non-linear pores were connected to each other.

  In order to remove copper remaining in the porous silicon particles produced by the above method, nitric acid was heated to 50 ° C., and then the porous silicon particles were immersed for about 2 hours to remove copper.

Examples 2 to 6
15 mM produced in the same volume as hydrogen fluoride in an aqueous solution in which 8.5 M hydrogen fluoride containing silicon from which the oxide film layer (SiO ₂ ) obtained in step (i) of Example 1 was removed was mixed. Porous silicon by performing the same method as in Example 1 except that an aqueous solution of copper sulfate (CuSO ₄ ) was added and stirred for about 6 hours, 9 hours, 12 hours, 18 hours, and 24 hours, respectively. Particles were produced.

Example 7
<Step (i): Step of removing an oxide film layer existing on the surface of Si or SiO _x (0 <x <2) particles using an etching solution>
Powdered silicon was immersed in 17.5 M hydrogen fluoride heated to 50 ° C., and then stirred for about 30 minutes. Through this process, a natural oxide film layer (SiO ₂ ) present on the silicon surface in a powder state is removed, and a metal catalyst electroless plating can be coated more smoothly and uniformly on the silicon surface. Processing was performed to obtain silicon particles from which the oxide film layer was removed.

<Step (ii): by etching the oxide layer has been removed Si or _{SiO x (0 <x <2} ) a metal catalyst in an etching solution that contains particles mixed and stirred to, Si or SiO _x (0 <x <2) Step of forming nonlinear pores on particle>
The aqueous solution obtained by mixing the silicon film obtained in the step (i) from which the oxide film layer (SiO ₂ ) has been removed and 17.5 M hydrogen fluoride is mixed with 30 mM copper sulfate (vol. A CuSO ₄ ) aqueous solution was added and stirred for about 1 hour. Through this process, copper was uniformly electrodeposited on the silicon surface from which the oxide film layer (SiO ₂ ) was removed.

On the other hand, 0.5 M phosphorous acid (H ₃ PO ₃ ) aqueous solution is mixed with an aqueous solution containing 17.5 M hydrogen fluoride containing silicon from which the oxide film layer (SiO ₂ ) has been removed. After being manufactured in a volume of about / 3, this was put on an aqueous silicon solution electrodeposited with copper obtained in the metal electrodeposition step. When this mixture was mixed for about 21 hours at 50 ° C., the non-porous pores and the like were connected to each other by selectively etching only the portion where copper was electrodeposited by chemical etching and the surface oxidized by phosphorous acid. Porous silicon was produced.

  At this time, copper electrodeposited on silicon was used as a catalyst for reducing silicon, and phosphorous acid was used as a weak oxidizing agent for oxidizing silicon to increase the chemical etching rate.

  That is, phosphorous acid used as the weak oxidant plays a role of increasing the size of pores formed by copper or forming additional pores through oxidation of silicon. be able to.

Comparative Example 1
Porous silicon particles were produced in the same manner as in Example 1 except that an aqueous silver nitrate solution was used in place of the aqueous copper sulfate (CuSO ₄ ) solution in step (ii) of Example 1.

Comparative Example 2
Instead of using 0.5 M phosphorous acid (H ₃ PO ₃ ) aqueous solution in step (ii) of Example 7, iron nitrate (Fe (NO ₃ ) ₃ ) (or other strong oxidizing agent) was used. Except for the above, porous silicon particles were produced in the same manner as in Example 7.

Comparative Example 3
Porous silicon particles were produced in the same manner as in Example 1 except that the etching was performed for 28 hours in step (ii) of Example 1.

Comparative Example 4
Porous silicon particles were produced in the same manner as in Example 1 except that etching was performed for 1 hour in step (ii) of Example 1.

<Manufacture of lithium secondary batteries>
Example 8
The porous silicon-based particles produced in Example 1 were used as negative electrode active materials. The negative electrode active material, acetylene black was mixed in a weight ratio of 70:10:20 using a conductive agent and polyvinylidene fluoride as a binder, and these were mixed with N-methyl-2-pyrrolidone as a solvent to form a slurry. Manufactured. The prepared slurry was coated on one surface of a copper current collector with a thickness of 30 μm, dried and rolled, and then punched to a certain size to produce a negative electrode.

10% by weight of fluorethylene carbonate is added to a mixed solvent containing ethylene carbonate and diethyl carbonate mixed at a weight ratio of 30:70 and 1.0M LiPF _{6 based} on the total amount of electrolyte. Thus, a non-aqueous electrolyte was produced.

  A lithium metal foil was used as a counter electrode. A polyolefin separation membrane was interposed between the two electrodes, and then the electrolyte was injected to manufacture a coin-type half-cell.

Examples 9 to 14
Same as Example 8 except that the porous silicon-based particles manufactured in Examples 2 to 7 were used instead of the porous silicon-based particles manufactured in Example 1 as the negative electrode active material. A coin-shaped half-cell was manufactured by this method.

Example 15
As the negative electrode active material, a negative electrode active material obtained by coating the porous silicon particles manufactured in Example 5 with 10% by weight of carbon and mixing the carbon-coated porous silicon particles and graphite in a ratio of 50:50. A coin-shaped half battery was manufactured in the same manner as in Example 8 except that it was used.

Comparative Example 5
A coin-type half battery was manufactured in the same manner as in Example 8 except that pure Si particles were used instead of the porous silicon-based particles manufactured in Example 1 as the negative electrode active material.

Comparative Examples 6 to 9
Same as Example 8 except that the porous silicon-based particles manufactured in Comparative Examples 1 to 4 were used instead of the porous silicon-based particles manufactured in Example 1 as the negative electrode active material. A coin-shaped half-cell was manufactured by this method.

Comparative Example 10
As the negative electrode active material, 10% by weight of carbon was coated on the porous silicon particles produced in Comparative Example 4, and the negative electrode active material in which the carbon-coated porous silicon particles and graphite were mixed at a ratio of 50:50 was used. Except for this, a coin-type half battery was manufactured in the same manner as in Example 8.

Experimental example 1
<SEM micrograph>
The surface shape of the nonlinear pores contained in the porous silicon-based particles according to the etching time obtained in Examples 1 to 6 was confirmed with a scanning electron microscope (SEM) photograph. The results are shown in FIG.

  Examining FIG. 3, it can be confirmed that pores are formed on the surface of the porous silicon particles of Example 1 which was etched for 3 hours, and the etching time was 6 as in Examples 2 to 6. As the etching time was increased over time, 9 hours, 12 hours, 18 hours, and 24 hours, the degree of pore formation formed in the particles and the diameter of the pores increased.

  Further, it can be confirmed that at least two or more pores and the like are connected to each other in the non-linear pores included in the porous silicon-based particles of Examples 2 to 6 where the etching time is 6 hours or more.

  On the other hand, in the case of Example 6 where etching was performed for about 24 hours, it was confirmed that the non-linear pores contained in the porous silicon particles were almost connected to each other, and the pore depth was also measured for about 24 hours. It was confirmed that Example 6 was deepest.

  This is considered to be due to the fact that the size of copper, which is a metal catalyst that is electrodeposited on the silicon surface by hydrogen fluoride, increases as the etching time elapses, and therefore the depth of the nonlinear pores of the particles also increases.

On the other hand, the surface shape of the porous silicon particles of Example 7 etched using phosphorous acid (H ₃ PO ₃ ), which is a weak oxidant, was confirmed with a scanning electron microscope (SEM). The results are shown in FIG.

  As can be confirmed in FIG. 4, a large number of non-linear pores were formed in the entire porous silicon particle, and it was observed that the non-linear pores were formed as open pores on the particle surface. The average diameter of the formed non-linear pores was confirmed to be about several tens of nanometers to several hundreds of nanometers.

  Compared to silver used as a catalyst for general chemical etching methods, there is a common point that etching occurs only at the part where the catalyst contacts, but when silver is used as a catalyst, etching occurs vertically on the silicon surface, A linear wire configuration can be formed (see FIGS. 2 and 6).

  On the other hand, when copper is used as a catalyst as in the embodiment of the present invention, the copper crystal form is square, so that copper electrodeposition occurs in the square form, and the etching is silicon crystalline. Therefore, it can be confirmed that etching occurs in the form of non-linear pores having no fixed direction.

  FIG. 5 is an electron micrograph of the internal cross section of the porous silicon particles obtained in Example 7 after cutting the cross section.

  In order to confirm the internal cross-sectional shape of the porous silicon particles produced in Example 7, the cross-section of the porous silicon particles was cut using an argon ion milling equipment (Ar-ion milling), and then the internal cross-section was observed with an electron microscope. analyzed.

  If FIG. 5 is examined, it is confirmed that the porous silicon particles manufactured in Example 7 have pores formed therein, and there is no fixed directionality inside the porous silicon particles. Etc. were confirmed to be connected to each other.

  When comparing the average diameter of the pores formed inside / outside of the porous silicon particles, it was confirmed that the average diameter of the pores formed inside showed a tendency to be smaller than the average diameter of the pores formed outside. .

  This is because the copper catalyst is hardly affected by the crystal orientation of silicon, etching occurs without a certain directionality, and the more the etched shape enters the center of the porous silicon particle, the more nonlinear the cone. It is determined that a type of etching has occurred.

  In addition, due to the additional pore formation by phosphorous acid and active connection between pores, the average diameter of internal pores tends to gradually decrease along the center direction of the particles compared to the porous silicon particle surface. It can be predicted to represent.

  On the other hand, when FIG. 6 showing the internal cross-sectional view of the silicon-based particles produced in Comparative Example 1 is examined, it is confirmed that etching occurs in the vertical direction on the silicon surface and the pores are linearly formed. it can.

Experimental Example 2: Measurement of physical properties of porous silicon-based particles Tab density (g / cc), total mercury penetration (mL / g), bulk density (g) of the porous silicon-based particles produced in Examples 1 to 6 / Cc) and porosity (%) were measured and shown in Table 1 below.

<Measurement of tab density>
The tab density is obtained by measuring the apparent density of particles obtained by filling the porous silicon-based particles obtained in Examples 1 to 6 into a container and then vibrating them under certain conditions.

<Measurement of total mercury penetration (Mercury porosity)>
On the other hand, the total mercury penetration (mL / g) was measured using a mercury porosimeter (device name: AutoPore VI 9500, Micromerities, USA).

  Capillary phenomenon in which liquid penetrates into fine pores. Non-wetting liquid such as mercury penetrates only when pressure is applied from the outside, and the pore size is small. High pressure is required. The measurement results can be shown as a function of the cumulative volume of mercury that is permeated by pressure (or pore size).

Principle of operation Porous silicon particles were placed in a capillary and sealed, and then a vacuum was applied to fill the mercury. When pressure is applied to the capillary, mercury penetrates into the pores of the porous silicon particles and the height of the mercury in the capillary decreases, but if this reduction is measured as a function of pressure, the volume of mercury that has penetrated into the pores is reduced. I understand. Mercury penetration results can be expressed in terms of pore radius or osmotic pressure and cumulative volume permeated per specimen mass.

  Since mercury becomes penetrating into the pores between the particles when the pressure is low, the pore size can become smaller as the pressure increases. In the specimen molded with porous powder, the permeation cumulative curve can be a bimodal curve due to such pores.

<Measurement of bulk density>
The bulk density of the porous silicon-based particles can be determined by using the total permeation volume when the pressure is maximum at the time of measuring the total mercury penetration (Mercury porosity), that is, when mercury does not permeate any more.

<Measurement of porosity>
On the other hand, the porosity of the porous silicon-based particles obtained in Examples 1 to 6 was calculated using the following mathematical formula (1).
Porosity (%) = {1− (bulk density of porous silicon particles of Examples 1 to 6 / bulk density of pure silicon particles)} × 100 (1)

  As can be seen from Table 1, the porosity of the porous silicon-based particles of Examples 1 to 6 in which nonlinear pores were formed by etching for 3 to 24 hours was about 11% to 39%. In particular, in the case of the porous silicon-based particles of Example 6 in which nonlinear pores are formed by etching for 24 hours, the porosity is close to about 40% compared to pure Si particles not subjected to the porous treatment. It was.

  On the other hand, the Si particles have a tab density of 1.02 (g / cc) and a bulk density of 0.85 (g / cc), whereas the porous silicon-based particles of Examples 1 to 6 are Reduced from tab density and bulk density.

  Further, the total mercury penetration amount was 0.53 g / cc for Si particles, and Examples 1 to 6 were 0.64 to 1.19 g / cc, which was remarkably increased as compared with the Si particles.

  In particular, in the case of Examples 5 and 6 where the etching was performed for 18 hours and 24 hours, they were 1.05 g / cc and 1.19 g / cc, respectively, which is more than double that of Si particles. expressed.

  On the other hand, the etching time was the same as in Example 1, but in the case of Comparative Example 1 using an aqueous silver nitrate solution, the porosity was 9.5%, which was significantly reduced compared to Example 1. I understand.

  On the other hand, in the case of Comparative Example 3 in which the etching time was performed for 28 hours, only the etching solution was consumed, and there was no effect due to the excessive etching time. In the case of Comparative Example 1 in which the etching was performed for only 1 hour, the porosity was It was 7.1%, and sufficient pores could not be formed.

  In addition, in Examples 1 to 6 of the present invention, the tab density and the bulk density decrease as compared with pure Si particles, and the total mercury penetration increases, indicating that the depth of the non-linear pores formed as the etching time increases. It is determined that a large number of nonlinear pores were formed.

On the other hand, in order to confirm the physical properties of the porous silicon particles obtained in Example 7 etched using the weak oxidizing agent, the tab density (Tap density, g / cc), the BET specific surface area (BET surface area, m ² / g) and particle size distribution (Particle size distribution) were performed, and the results are shown in Table 2 below.

<Measurement of tab density>
At this time, the tab density measurement was performed by the same method as the measurement of the tab density of the porous silicon-based particles of Examples 1 to 6.

<Measurement of specific surface area>
The specific surface area of the porous silicon-based particles of Example 7 can be measured by the BET (Brunauer-Emmett-Teller; BET) method. For example, the BET 6-point method was measured by a nitrogen gas adsorption flow method using a pore distribution analyzer (Bello Japan Inc., Belsorb-II mini).

<Measurement of particle size distribution>
On the other hand, the particle size distribution of the porous silicon-based particles of Example 7 is the average particle size distribution of the porous silicon-based particles, and D _min , D ₁₀ , D ₅₀ , D ₉₀ , and D _max are measured. , D _min , D ₁₀ , D ₅₀ , D ₉₀ , and D _max mean the particle diameters on the basis of less than 10%, 10%, 50%, 90%, and 90% exceeding the particle size distribution, respectively.

The particle size distribution of the porous silicon-based particles in Example 7 was measured using a laser diffraction particle size method (Laser Diffraction Method: Microtrac MT 3000).

  As can be seen from Table 2, the tab density of the porous silicon particles obtained in Example 7 was 0.61 g / cc, and the Si particles were 1.02 g / cc. It can be confirmed that the tab density is reduced by about 0.41 g / cc compared to the Si particles.

  As can be seen from the scanning electron microscope (SEM) photograph of Experimental Example 1, it can be assumed that pores are formed in the porous silicon particles obtained in Example 7.

On the other hand, as can be seen in Table 2, the BET specific surface area was 20.87 m ² / g for the porous silicon particles produced in Example 7, and 1.56 m ² / g for the Si particles. The produced porous silicon particles increased about 13 times compared to the Si particles.

  This is considered to be an increase in the specific surface area due to the formation of pores, because Example 7 and Si particles exhibit the same particle size distribution.

Experimental Example 3: Mercury penetration method analysis FIG. 7 is a diagram showing the pore distribution of the porous silicon produced in Examples 1 to 6 through a mercury penetration method analysis.

  Considering FIG. 7, the porous silicon-based particles have a peak at an average diameter of pores between about 30 nm and 2500 nm where the rate of change of mercury intrusion into the pores is measured by a mercury porosimeter. Indicated.

  When the two enlarged graphs of the graph of FIG. 7 were examined, peaks at average diameters of pores of 800 nm to 2000 nm and 50 nm to 600 nm appeared. Here, the peak in the average diameter of the pores from 800 nm to 2000 nm is a peak with respect to the void between the porous silicon particles, and the peak in the average diameter of the pores from 50 nm to 600 nm is with respect to the nonlinear pores contained in the porous silicon particles. It is a peak.

  It was confirmed that the total intrusion volume of mercury at the average diameter of the 50 nm to 500 nm pores was 0.5 mL / g to 1.2 mL / g.

  Further, if FIG. 7 is examined, the etching time is 3 hours, 6 hours, 9 hours, 12 hours, 18 hours, and 24 hours as in Examples 1 to 6, and as the etching time increases. It was confirmed that the pore volume increased. In particular, it was confirmed that the porous silicon particles of Example 6 etched for 24 hours exhibited the highest pore volume.

  Further, in the porous silicon particles of Examples 1 to 6, the average pore diameter distribution was such that mesopores and macropores of 20 nm to 100 nm coexisted from 3 hours to 18 hours of etching time. It is confirmed that the distribution of macropores of 50 nm or more increases as the etching time increases. This is considered to be because the pores formed are connected to each other as the etching time increases.

  Further, it was confirmed that the porous silicon particles of Example 5 etched for 18 hours almost formed macropores having a pore distribution of 50 nm or more.

  On the other hand, it is judged that the porous silicon particles of Example 6 etched for 24 hours show a pore form in which the pores are almost bonded to each other and connected to each other.

Experimental Example 4: Analysis of life characteristics and thickness change rate The following experiments were conducted to examine the life characteristics and thickness change rates of the secondary batteries manufactured in Examples 8 to 15 and Comparative Examples 5 to 10. Went.

  As for the life characteristics of the lithium secondary battery, charging / discharging was performed at 0.1 C in the first cycle, and charging / discharging was performed at 0.5 C in the subsequent cycles. The ratio of the discharge capacity at the 49th cycle to the discharge capacity at the 1st cycle was measured. The thickness change rate was compared with the electrode thickness before the first cycle after each lithium secondary battery was disassembled in the charged state at the 50th cycle and the electrode thickness was measured.

−寿命特性：（４９サイクル目の放電容量／１サイクル目の放電容量）×１００
−厚さ変化率：（５０サイクル目の充電状態における電極厚さ−１サイクル目前の電極厚さ）／１サイクル目前の電極厚さ×１００ Table 3 below shows the life characteristics and thickness change rates of the secondary batteries manufactured in Examples 8 to 15 and Comparative Examples 5 to 10.

Life characteristics: (discharge capacity at 49th cycle / discharge capacity at 1st cycle) × 100
-Thickness change rate: (electrode thickness in charge state at 50th cycle-electrode thickness before 1 cycle) / electrode thickness before 1 cycle x 100

  As can be seen in Table 3, the secondary batteries of Examples 8 to 15 of the present invention are generally significantly superior in the life characteristics and thickness change rate of the secondary batteries as compared with Comparative Examples 5 to 10. Can be confirmed.

  Specifically, when comparing Example 8 in which etching was performed for 3 hours with Comparative Example 6, Example 8 using an aqueous copper sulfate solution as a metal catalyst was a comparative example using silver nitrate. It can be confirmed that the rate of change in thickness is reduced compared to 6.

  Further, comparing Example 14 and Comparative Example 7 in which etching was performed for 21 hours, Example 14 using phosphorous acid as a weak oxidizing agent was compared with Comparative Example 7 using iron nitrate as a strong oxidizing agent. In comparison, the life characteristics and thickness change rate were all excellent.

  On the other hand, when porous silicon particles coated with 10% by weight of carbon and graphite were mixed as in Example 15, the life characteristics were 90%, the thickness change rate was 120%, and the secondary battery It can be seen that the performance has improved significantly.

  On the other hand, in the case of Comparative Example 9 where etching was performed for only one hour, the rate of change in thickness was 300%, and it was confirmed that volume expansion during charge / discharge could not be reduced due to insufficient pore formation. did it.

In the porous silicon-based particles according to an embodiment of the present invention, Si or SiO _x (0 <x <2) particles may include a plurality of nonlinear pores, thereby further facilitating dispersion in the negative electrode active material slurry. In addition, side reactions with the electrolyte can be minimized, and volume expansion during charge / discharge can be reduced. Therefore, it can be usefully used in the field of secondary batteries.

Claims (38)

Si or SiO _x (0 <x <2) particles are included,
The particles include a plurality of nonlinear pores;
The plurality of non-linear pores are formed as open pores on the particle surface ,
Porous silicon-based particles in which the average diameter of the plurality of non-linear pores gradually decreases along the center direction of the particles.   2. The porous silicon-based particle according to claim 1, wherein at least two of the plurality of nonlinear pores are connected to each other. 3. The porous silicon-based particle according to claim 1, wherein an average diameter of the open pores is 30 nm to 500 nm on the surface. The porous silicon-based particles, any one of claims 1 to 3, showing a peak with an average diameter of the pores of 2500nm from intrusion rate of change of mercury 30nm to pores as measured by mercury porosimetry (Mercury Porosimeter) Porous silicon-based particles as described in 1. The porous silicon-based particle according to claim 4 , wherein the mercury penetration amount change rate has a peak at an average diameter of pores of 50 nm to 600 nm. The porous silicon-based particle according to claim 4 or 5 , wherein a total intrusion volume of mercury at the peak is 0.5 mL / g to 1.2 mL / g. The specific surface area of the porous silicon particles (BET-SSA), the porous silicon-based particles according to any one of claims 1 to 6 ^{5 m} 2 / g is ^{50 m} 2 / g. The porous silicon-based particle according to any one of claims 1 to 7 , wherein a depth of the plurality of nonlinear pores is 0.1 μm to 5 μm. The average particle size of the porous silicon particles (D _50), the porous silicon-based particles according to any one of claims 1 to 8 is 20μm from 1 [mu] m. Including a core portion including Si or SiO _x (0 <x <2),
Porous silicon-based particles including a Si or SiO _x shell portion including a plurality of nonlinear pores on the core portion, and a surface of the shell portion having open pores. 11. The porous silicon-based particle according to claim 10 , wherein a ratio of the length of the core portion to the shell portion is 1: 9 to 9: 1. The porous silicon-based particle according to claim 10 or 11 , wherein at least two of the plurality of nonlinear pores are connected to each other. The porous silicon-based particle according to any one of claims 10 to 12 , wherein the diameter of the pores gradually decreases along the center direction of the particle. The porous silicon-based particle according to any one of claims 10 to 13 , wherein an average diameter of the open pores is 30 nm to 500 nm. The porous silicon-based particle according to any one of claims 1 to 14 , further comprising a carbon coating layer on the porous silicon-based particle. The porous silicon-based particle according to any one of claims 1 to 15 , wherein a porosity of the porous silicon-based particle is 5% to 90% with respect to a total volume of the porous silicon-based particle. The porous silicon-based particle according to any one of claims 1 to 16 , wherein a porosity of the porous silicon-based particle is 10% to 70% with respect to a total volume of the porous silicon-based particle. A negative electrode active material comprising the porous silicon-based particles according to any one of claims 1 to 17 . The negative electrode active material according to claim 18 , wherein the negative electrode active material further includes a carbon-based material. The negative electrode active material according to claim 19 , wherein the carbon-based material includes at least one selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fiber, and carbon black. The negative electrode active material according to claim 19 or 20 , wherein the carbon-based material is included in an amount of 0 to 90 parts by weight with respect to 100 parts by weight of porous silicon-based particles. Removing an oxide layer present on the surface of Si or SiO _x (0 <x <2) particles using an etching solution;
A metal catalyst is mixed and stirred in the etching solution containing Si or SiO _x (0 <x <2) particles from which the oxide film layer has been removed, thereby etching Si or SiO _x (0 <x <. 2) A method for producing porous silicon-based particles, comprising the step of forming nonlinear pores on the particles. The porosity according to claim 22 , wherein the metal catalyst includes any one selected from the group consisting of copper (Cu), platinum (Pt), and nickel (Ni), or two or more of these elements. A method for producing silicon-based particles. The method for producing porous silicon-based particles according to claim 22 or 23 , wherein the removal of the oxide film layer is performed at 20 ° C to 90 ° C for 30 minutes to 3 hours. The etching solution is a fluorinated hydrogen (HF), fluorinated silicon from _(H 2 SiF ₆₎ and fluoro ammonium _(NH 4 F) according to claim 22 is at least one solution selected from the group consisting of 24 The manufacturing method of the porous silicon-type particle as described in any one. The method for producing porous silicon-based particles according to any one of claims 22 to 25 , wherein the concentration of the etching solution is 5M to 20M. The method for producing porous silicon-based particles according to any one of claims 22 to 26 , wherein the concentration of the metal catalyst is 5 mM to 100 mM. 28. The method for producing porous silicon particles according to claim 27 , wherein the electrodeposition of the metal catalyst is performed for 1 hour to 12 hours. 29. The method for producing porous silicon-based particles according to any one of claims 22 to 28 , wherein a weak oxidizing agent is further added in the step of forming the nonlinear pores. 30. The production of porous silicon-based particles according to claim 29 , wherein the weak oxidizing agent is any one selected from the group consisting of phosphorous acid, sulfurous acid and phosphoric acid, or a mixture of two or more thereof. Method. The method for producing porous silicon-based particles according to claim 29 or 30 , wherein the concentration of the weak oxidizing agent is 0.25M to 1.0M. 32. The method for producing porous silicon-based particles according to any one of claims 22 to 31 , wherein the etching is performed for 3 hours to 24 hours. The method according to any one of claims 22 to 32 , further comprising the step of coating the outer wall of the porous silicon-based particles with carbon after the step of forming the non-linear pores, mixing the porous silicon-based particles with the carbon precursor, and then performing a heat treatment. The method for producing porous silicon-based particles according to claim 1. The method for producing porous silicon-based particles according to claim 33 , wherein the carbon precursor is a pitch or a hydrocarbon-based material. 35. The method for producing porous silicon-based particles according to claim 33 or 34 , wherein the carbon precursor is used in an amount of 10 to 40% by weight based on the total weight of the porous silicon-based particles. 36. The method for producing porous silicon-based particles according to any one of claims 33 to 35 , wherein the heat treatment is performed in a temperature range of 300 ° C to 1400 ° C. A negative electrode comprising the negative electrode active material according to any one of claims 18 to 21 . A lithium secondary battery comprising the negative electrode according to claim 37 .

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