JP2013206535A - Method for producing nonaqueous electrolyte secondary battery negative electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery negative electrode material improved in charge/discharge cycle characteristics and including silicon or a silicon compound.SOLUTION: A method for producing a nonaqueous electrolyte secondary battery negative electrode active material comprising silicon or a silicon compound includes a process of pulverizing silicon or a silicon compound in an atmosphere where a dew point temperature at atmospheric pressure is -80°C or above and 30°C or below. According to the present invention, the charge/discharge characteristics of a nonaqueous electrolyte secondary battery can be improved, the nonaqueous electrolyte secondary battery including a nonaqueous electrolyte secondary battery negative electrode active material that is obtained by a production method including a process of pulverizing silicon or a silicon compound in an atmosphere where a dew point temperature at atmospheric pressure is -80°C or above and 30°C or below and comprises silicon or a silicon compound.

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery negative electrode active material, a non-aqueous electrolyte secondary battery negative electrode active material, a lithium ion secondary battery, and an electrochemical capacitor.

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for non-aqueous electrolyte secondary batteries with high energy density from the viewpoints of economy and downsizing and weight reduction of devices. Conventionally, as a measure for increasing the capacity of this type of non-aqueous electrolyte secondary battery, for example, negative electrode materials such as oxides such as B, Ti, V, Mn, Co, Fe, Ni, Cr, Nb, and Mo and composites thereof Method using oxide (Patent No. 3008228, Patent No. 3242751: Patent Literatures 1 and 2), M _100-x Si _x (x ≧ 50 at%, M = Ni, Fe, Co, Mn) rapidly quenched ) As a negative electrode material (Japanese Patent No. 3846661: Patent Document 3), a method using silicon oxide as the negative electrode material (Japanese Patent No. 2999741: Patent Document 4), and Si ₂ N ₂ O, Ge as the negative electrode material. _A method using ₂ N ₂ O and Sn ₂ N ₂ O (Japanese Patent No. 391831: Patent Document 5) is known.

Since silicon exhibits a theoretical capacity of 4,200 mAh / g, which is much higher than the theoretical capacity of 372 mAh / g of carbon materials currently in practical use, it is the most promising material for reducing the size and increasing the capacity of batteries. Various forms of silicon having different crystal structures are known depending on the production method. For example, Japanese Patent No. 2964732 (Patent Document 6) discloses a lithium ion secondary battery using single crystal silicon as a support for a negative electrode active material, and Japanese Patent No. 3079343 (Patent Document 7). A lithium ion secondary battery using a lithium alloy of Li _x Si (where x is 0 to 5) of silicon, polycrystalline silicon, and amorphous silicon is disclosed, and in particular, Li _x using amorphous silicon. Si is preferable, and a pulverized product of crystalline silicon coated with amorphous silicon obtained by plasma decomposition of monosilane is exemplified. However, in this case, as in the example, 30 parts of silicon and 55 parts of graphite as a conductive agent were used, and the battery capacity of silicon could not be fully exhibited.

  Further, as a purpose of imparting conductivity to the negative electrode material, a method of mechanically alloying a metal oxide, such as silicon oxide, and graphite, followed by carbonization (Japanese Patent Laid-Open No. 2000-243396: Patent Document 8), Si Method of coating particle surface with carbon layer by chemical vapor deposition method (Japanese Patent Laid-Open No. 2000-215887: Patent Document 9), Method of coating silicon oxide particle surface with carbon layer by chemical vapor deposition method (Japanese Patent Laid-Open No. 2002-42806) : Patent Document 10). Although it is possible to improve the conductivity by providing a carbon layer on the particle surface, alleviation of a large volume change accompanying charging / discharging, which is a problem to be overcome with the silicon negative electrode, deterioration of current collection and deterioration of cycle characteristics accompanying this Could not be prevented.

For this reason, in recent years, methods for suppressing volume expansion by limiting the battery capacity utilization rate of silicon (Japanese Patent Laid-Open Nos. 2000-215887, 2000-173596, 3291260, and 2005-317309). Gazette: Patent Documents 9, 11 to 13), or rapid cooling of a silicon melt to which alumina is added as a method of using a grain boundary of polycrystalline particles as a buffer zone for volume change (Japanese Patent Laid-Open No. 2003-109590: Patent Document 14) , Α, β-FeSi ₂ polycrystalline particles (Japanese Patent Laid-Open No. 2004-185991: Patent Document 15), high-temperature plastic processing of single crystal silicon ingot (Japanese Patent Laid-Open No. 2004-303593: Patent Document) 16) is disclosed.

  A method of reducing volume expansion by devising a laminated structure of a silicon active material has also been disclosed. For example, a method of disposing a silicon negative electrode in two layers (Japanese Patent Laid-Open No. 2005-190902: Patent Document 17), carbon and others A method of suppressing particle collapse by coating or encapsulating with a metal and an oxide (JP 2005-235589 A, JP 2006-216374 A, JP 2006-236684 A, JP 2006-339092 A, Japanese Patent No. 362629, Japanese Patent Laid-Open No. 2002-75351, Japanese Patent No. 3622631: Patent Documents 18 to 24) are disclosed. In addition, in a method in which silicon is directly vapor-grown on a current collector, a method is also disclosed in which a growth direction is controlled to suppress a decrease in cycle characteristics due to volume expansion (Japanese Patent Laid-Open No. 2006-338996: Patent Document). 25).

  As described above, the method of improving the cycle characteristics of the negative electrode material by, for example, coating the silicon surface with carbon to make it conductive or coating it with an amorphous metal layer can exhibit about half of the original battery capacity of silicon. However, a further increase in capacity has been demanded. In addition, with polycrystalline silicon having a grain boundary, it is difficult to control the cooling rate by the disclosed method, and it is difficult to reproduce stable physical properties. Sufficient suppression of volume change due to insertion and extraction of Li, reduction of fineness due to cracking of particles and reduction of conductivity due to peeling from current collector can be mitigated, mass production is possible, and cost advantage In addition, there has been a demand for a negative electrode active material that can be applied to applications in which repeated cycle characteristics are particularly important, such as for mobile phones.

Japanese Patent No. 3008228 Japanese Patent No. 3242751 Japanese Patent No. 3846661 Japanese Patent No. 2999741 Japanese Patent No. 3918311 Japanese Patent No. 2964732 Japanese Patent No. 3079343 JP 2000-243396 A JP 2000-215887 A JP 2002-42806 A JP 2000-173596 A Japanese Patent No. 3291260 JP 2005-317309 A JP 2003-109590 A JP 2004-185991 A JP 2004-303593 A JP 2005-190902 A JP 2005-235589 A JP 2006-216374 A JP 2006-236684 A JP 2006-339092 A Japanese Patent No. 3622629 JP 2002-75351 A Japanese Patent No. 3622631 JP 2006-338996 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery negative electrode material containing silicon or a silicon compound with improved charge / discharge cycle characteristics.

  As a result of intensive investigations to achieve the above object, the present inventor is a method for producing a non-aqueous electrolyte secondary battery negative electrode active material comprising silicon or a silicon compound, wherein the silicon or silicon compound has an atmospheric dew point temperature of − Knowledge that charge / discharge cycle characteristics are improved by producing a non-aqueous electrolyte secondary battery using the obtained negative electrode material by including a step of grinding in an atmosphere of 80 ° C. or higher and 30 ° C. or lower. However, the present invention has been achieved.

Accordingly, the present invention provides the following.
[1]. A method for producing a non-aqueous electrolyte secondary battery negative electrode active material comprising silicon or a silicon compound, comprising a step of pulverizing silicon or a silicon compound in an atmosphere having an atmospheric pressure dew point temperature of −80 ° C. or higher and −30 ° C. or lower. The manufacturing method characterized by this.
[2]. [1] A non-aqueous electrolyte secondary battery negative electrode active material obtained by the production method according to [1].
[3]. [2] A lithium ion secondary battery comprising the nonaqueous electrolyte secondary battery negative electrode active material according to [2].
[4]. [2] An electrochemical capacitor comprising the nonaqueous electrolyte secondary battery negative electrode active material according to [2].

  According to the present invention, a non-aqueous electrolyte secondary composed of silicon or a silicon compound obtained by including a step of pulverizing silicon or a silicon compound in an atmosphere having an atmospheric dew point temperature of −80 ° C. or higher and 30 ° C. or lower. The charge / discharge cycle characteristics of a non-aqueous electrolyte secondary battery using a battery negative electrode active material can be improved.

It is a flowchart which shows an example of embodiment of this invention.

Hereinafter, the present invention will be described in detail.
The production method of the present invention is a production method of a non-aqueous electrolyte secondary battery negative electrode active material comprising silicon or a silicon compound, wherein silicon or a silicon compound (hereinafter sometimes abbreviated as a silicon compound or the like) is atmospheric pressure. It includes a step of pulverizing in an atmosphere having a dew point temperature of −80 ° C. to 30 ° C.

It does not specifically limit as silicon before a grinding | pulverization, or a silicon compound, It can use individually by 1 type or in combination of 2 or more types. As the silicon compound, for _{example, CaSi 2, CoSi 2, CrSi} 2, Cu 5 Si, FeSi 2, Mg 2 Si, MnSi 2, MoSi 2, NbSi 2, NiSi 2, TaSi 2, TiSi 2, VSi 2, WSi 2 , SiC, SiB ₄ , SiB ₆ , Si ₃ N _4, and ZnSi ₂ . These silicon compounds may be of stoichiometric composition or non-stoichiometric composition.

  The silicon compound or the like is pulverized in an atmosphere having an atmospheric pressure dew point temperature of −80 ° C. or higher and 30 ° C. or lower to form a fine powder. The reason why the pulverization is performed in a predetermined atmospheric pressure dew point temperature atmosphere is to thin the oxide film formed on the surface of the silicon compound or the like. This is because the thick oxide film formed on the surface is considered to be a cause of shortening the cycle life of the secondary battery using the negative electrode containing a silicon compound or the like. Furthermore, agglomeration of fine powder can be suppressed by performing pulverization at an appropriate dew point.

  When the atmospheric pressure dew point temperature during pulverization is less than −80 ° C., if the humidity is too low, fine powder aggregates during pulverization, making it difficult to obtain particles of the desired particle size, while when higher than 30 ° C., This is because the formed oxide film becomes too thick and the resistance during charging and discharging increases. The atmospheric dew point temperature during pulverization is preferably −60 ° C. or higher and 10 ° C. or lower, and more preferably −60 ° C. or higher and 0 ° C. or lower. The atmospheric dew point temperature can be controlled by using a humidifier (such as bubbling) for the pulverized gas.

  The conditions of the atmosphere for pulverization are not particularly limited, but it is preferable to mix air and nitrogen so that the oxygen concentration is in the range of 3 to 15% by volume, particularly 8 ± 2% by volume.

  In addition, when using multiple types of silicon compounds etc., this grinding | pulverization process may be performed about them individually, and may be mixed and performed simultaneously.

  As for the pulverizer, a dry pulverizer, for example, a ball mill, a medium agitating mill, or a roller that moves a pulverizing medium such as a ball or a bead and pulverizes a material to be crushed using an impact force, a frictional force, or a compressive force due to its kinetic energy. A roller mill that performs pulverization using the compressive force of a jet, a jet mill that pulverizes the object to be collided with the lining material or particles with each other at high speed, and pulverizes with the impact force of the impact, hammers, blades, pins, etc. A hammer mill, a pin mill, a disc mill, a colloid mill using a shearing force, or the like is appropriately used to pulverize the material to be crushed using the impact force generated by the rotation of a fixed rotor.

  In order to adjust the particle size distribution after pulverization, dry classification or sieving classification may be used. In a dry type in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained. The size of the silicon compound and the like before pulverization is not particularly limited, and a large amount does not affect the final pulverized product, but it is desirable that no fine powder of 1 μm or less is contained.

The average particle size after pulverization is preferably from 0.1 to 50 μm, more preferably from 5 to 20 μm. If the average particle size is too small, the specific surface area may be large and the negative electrode film density may be too small. If it is too large, the separator may be penetrated and short-circuited. The average particle diameter is a value measured as a cumulative mass average value D ₅₀ (that is, a particle diameter or a median diameter when the cumulative mass is 50%) by a laser diffraction / scattering particle size distribution measurement method.

  An oxide film is formed on the surface of a silicon compound or the like by exposure to air, but a thick oxide film is formed on the newly generated surface depending on the oxygen concentration and humidity of the atmosphere during pulverization. For this reason, the electron conductivity between the particles of the silicon compound is lowered, and in the secondary battery using this, the resistance at the time of charge / discharge is increased, and the charge / discharge reaction does not proceed smoothly. Furthermore, since silicon compounds and the like expand and contract with charge / discharge, the contact state between the particles gradually weakens and the contact resistance increases with repeated charge / discharge. Thus, it is considered that the electron conduction between the particles does not proceed smoothly with charge / discharge, the number of particles that do not contribute to charge / discharge gradually increases, the charge / discharge capacity is reduced, and the cycle life is shortened. Therefore, in the method of the present invention, a thin oxide film is formed on the surface of a silicon compound or the like in advance to prevent the formation of a thick oxide film, thereby improving electron conductivity between particles and improving cycle characteristics. I try to let them.

FIG. 1 shows an example of pulverization using a jet mill.
The pressure air generated by the compressor 1 and the pressure nitrogen supplied from the nitrogen generator 2 are mixed in the tank 3 and monitored with an oximeter to be about 8% by volume. Each dehumidifier is once dehumidified by the dryer 4 before entering the tank, but after leaving the tank 3, a bypass line is provided and a humidifier (such as bubbling) 5 is installed there, so that the dew point can be controlled by the dew point meter 6. It has become. The gas is supplied to the jet mill 7 at about 0.7 MPa to obtain a pulverized gas. The raw material 8 is pulverized in a jet mill 7, and the pulverized raw material particles are separated into fine powders by a cyclone 9 and recovered as a final product 10. The fine powder separated by the cyclone 9 is collected by the bug 11.

  The obtained pulverized silicon or silicon compound particles are further subjected to a hydrocarbon compound gas in a short time as possible at a temperature of 600 to 1,200 ° C., preferably 800 to 1,000 ° C. under normal pressure or reduced pressure. And / or by performing thermal chemical vapor deposition treatment by introducing steam to form a carbon film on the surface of silicon or silicon compound particles, and at the same time, a silicon composite in which a silicon carbide layer is formed at the silicon-carbon layer interface It is good also as a particle.

  The silicon or silicon compound particles obtained in the present invention can be used as a negative electrode active material for a negative electrode of a non-aqueous electrolyte secondary battery, and have a higher capacity than current graphite and the like. Silicon oxide and silicon oxide The initial efficiency is high compared to materials made from a material (for example, a (silicon / silicon dioxide) dispersion composite obtained by disproportionating silicon oxide), and the volume change associated with charge / discharge compared to silicon itself Is controlled to be small, and the adhesion between the particles and the binder is excellent, and therefore, a non-aqueous electrolyte secondary battery with excellent cycle characteristics, particularly a lithium ion secondary battery can be manufactured.

  When a negative electrode is produced using a negative electrode material containing silicon or silicon compound particles as the active material, a polyimide resin or an aromatic polyimide resin can be particularly preferably used as the binder. The aromatic polyimide resin is excellent in solvent resistance, and can follow the volume expansion due to charging / discharging to suppress separation from the current collector and separation of the active material.

  Aromatic polyimide resins are generally poorly soluble in organic solvents, and in particular need not swell or dissolve in the electrolyte. Therefore, since it is generally only dissolved in a high boiling point organic solvent such as cresol, it is a polyimide precursor for the preparation of the electrode paste, and various organic solvents such as dimethylformamide, dimethyl Acetamide, N-methylpyrrolidone, ethyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, added in the state of polyamic acid that is relatively soluble in dioxolane, and dehydrated by heat treatment at a temperature of 300 ° C. or higher for a long time. It is imidized to form a binder.

  In this case, the aromatic polyimide resin has a basic skeleton composed of tetracarboxylic dianhydride and diamine. Specific examples thereof include pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride and biphenyltetra. Arocyclic tetracarboxylic dianhydrides such as aromatic tetracarboxylic dianhydrides such as carboxylic dianhydrides, cyclobutane tetracarboxylic dianhydrides, cyclopentane tetracarboxylic dianhydrides and cyclohexane tetracarboxylic dianhydrides And aliphatic tetracarboxylic dianhydrides such as butanetetracarboxylic dianhydride.

  Examples of the diamine include p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 2,2′-diaminodiphenylpropane, 4,4′-diaminodiphenylsulfone, 4,4′-diaminobenzophenone, 2,3-diaminonaphthalene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-di (4- Aminophenoxy) diphenyl sulfone, aromatic diamines such as 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, alicyclic diamines, aliphatic diamines and the like.

  As a method for synthesizing the polyamic acid intermediate, a solution polymerization method is usually used. Solvents used in the solution polymerization method include N, N′-dimethylformamide, N, N′-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, dimethyl sulfoxide, tetramethylurea, pyridine, dimethyl Examples include sulfone, hexamethylphosphoramide and butyrolactone. These may be used alone or in combination. The reaction temperature is usually in the range of −20 to 150 ° C., but the range of −5 to 100 ° C. is particularly desirable.

  Furthermore, in order to convert the polyamic acid intermediate into a polyimide resin, a method of dehydrating and ring-closing by heating is usually employed. The heating and dehydration ring-closing temperature can be selected from 140 to 400 ° C, preferably 150 to 250 ° C. The time required for this dehydration and ring closure is 30 seconds to 10 hours, preferably 5 minutes to 5 hours, although it depends on the reaction temperature.

  Examples of such polyimide resin include polyimide resin powder and N-methylpyrrolidone solution of a polyimide precursor. For example, U-varnish A, U-varnish S, UIP-R, UIP-S (Ube Industries) KAYAFLEX KPI-121 (manufactured by Nippon Kayaku Co., Ltd.), Rika Coat SN-20, PN-20, EN-20 (manufactured by Shin Nippon Rika Co., Ltd.).

  The compounding amount of the non-aqueous electrolyte secondary battery negative electrode active material comprising silicon or silicon compound in the negative electrode material of the present invention is preferably 60 to 97% by mass, particularly 70 to 95% by mass, and particularly preferably 75 to 95% by mass. In addition, when the electrically conductive agent mentioned later is mix | blended, the upper limit is preferably 96 mass% or less, more preferably 94 mass% or less, and further preferably 93 mass% or less. Moreover, the ratio of 3-20 mass% is preferable in the whole active material, and, as for the compounding quantity of the said binder, 5-15 mass% is more preferable. If the amount of the binder is too small, the negative electrode active material may be separated. If the amount is too large, the porosity is decreased and the insulating film becomes thick, which may inhibit the movement of Li ions.

  When a negative electrode material is produced using the silicon or silicon compound particles as an active material and a polyimide resin as a binder, a conductive agent such as graphite can be added. In this case, the type of the conductive agent is not particularly limited, and may be any electronic conductive material that does not cause decomposition or alteration in the configured battery. Specifically, Al, Ti, Fe, Ni, Cu, Zn , Ag, Sn, Si and other metal powders and fibers, natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, various resin fired bodies Such as graphite can be used. These conductive agents can be prepared by previously preparing a dispersion of water or a solvent such as N-methyl-2-pyrrolidone and adding it to prepare an electrode paste that is uniformly attached and dispersed on silicon or silicon compound particles. Since it can do, it is preferable to add as said solvent dispersion. The conductive agent can be dispersed in the solvent using a known surfactant. The solvent used for the conductive agent is preferably the same as the solvent used for the binder.

  The addition amount of the conductive agent is 0 to 37% by mass in the whole negative electrode material, and when blended, it is preferably 1 to 37% by mass, more preferably 1 to 20% by mass, and 2 to 10% by mass. Further preferred. When the amount of the conductive agent is small, the conductivity of the negative electrode material may be poor and the initial resistance tends to be high. On the other hand, an increase in the amount of conductive agent may lead to a decrease in battery capacity.

  In addition to the polyimide resin binder, carboxymethyl cellulose, polyacrylic acid soda, other acrylic polymers or fatty acid esters may be added as a viscosity modifier.

  The non-aqueous electrolyte secondary battery negative electrode material of the present invention can be formed into a negative electrode molded body as follows, for example. That is, the negative electrode active material, the conductive agent, the binder, and other additives are kneaded with a solvent suitable for dissolving and dispersing the binder, such as N-methylpyrrolidone or water, to form a paste. The mixture is applied as a sheet to the current collector. In this case, as the current collector, any material that is usually used as a negative electrode current collector, such as a copper foil or a nickel foil, can be used without any particular limitation on thickness and surface treatment. In addition, the shaping | molding method which shape | molds a mixture into a sheet form is not specifically limited, A well-known method can be used.

  A non-aqueous electrolyte secondary battery can be manufactured by using the molded negative electrode thus obtained. In this case, the nonaqueous electrolyte secondary battery is characterized in that the negative electrode active material is used, and other materials such as a positive electrode, a separator, an electrolytic solution, an electrolyte, and a battery shape are not limited.

Examples of the positive electrode active material include oxides or sulfides capable of inserting and extracting lithium ions, and any one or more of these are used. Specifically, TiS ₂ , MoS ₂ , NbS ₂ , ZrS ₂ , VS ₂ , V ₂ O ₅ , MoO _3, Mg (V ₃ O ₈ ) ₂ or other metal sulfide or oxide not containing lithium, or Examples thereof include lithium and lithium composite oxides containing lithium, and also include composite metals such as NbSe ₂ . Among these, in order to increase the energy density, a lithium composite oxide mainly composed of Li _p MetO ₂ is preferable. Met is preferably at least one of cobalt, nickel, iron and manganese, and p is usually a value in the range of 0.05 ≦ p ≦ 1.10. Specific examples of the lithium composite _{oxide, LiCoO 2, LiNiO 2, LiFeO} 2, Li q Ni r Co 1-r O 2 ( where, the values of q and r is a charge-discharge state of the battery having the layer structure Usually, 0 <q <1, 0.7 <r ≦ 1), spinel-structured LiMn ₂ O ₄ and orthorhombic LiMnO ₂ may be mentioned. Furthermore, LiMet _s Mn _1-s O ₄ (0 <s <1) is also used as a substituted spinel manganese compound for high voltage applications, where Met is titanium, chromium, iron, cobalt, nickel, copper and zinc. Etc.

  The lithium composite oxide is obtained by, for example, grinding lithium carbonate, nitrate, oxide or hydroxide, and transition metal carbonate, nitrate, oxide or hydroxide according to a desired composition. It can prepare by mixing and baking at the temperature within the range of 600-1,000 degreeC in oxygen atmosphere.

  Furthermore, an organic substance can also be used as the positive electrode active material. Illustrative examples include polyacetylene, polypyrrole, polyparaphenylene, polyaniline, polythiophene, polyacene, polysulfide compounds and the like.

  The above positive electrode active material is kneaded together with the conductive agent and binder used for the negative electrode mixture and applied to the current collector, and can be formed into a positive electrode molded body by a known method.

  The separator used between the positive electrode and the negative electrode is not particularly limited as long as it is stable with respect to the electrolytic solution and has excellent liquid retention, but generally polyolefins such as polyethylene and polypropylene, and copolymers thereof. Or a porous sheet such as aramid resin or a non-woven fabric. These may be used as a single layer or multiple layers, and ceramics such as metal oxide may be laminated on the surface. Moreover, porous glass, ceramics, etc. are also used.

The solvent for the non-aqueous electrolyte secondary battery used in the present invention is not particularly limited as long as it can be used as a non-aqueous electrolyte. Generally, aprotic high dielectric constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, diethyl ether, tetrahydrofuran, 1,2, -Aprotic low viscosity such as acetate ester or propionate ester such as dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, methyl acetate A solvent is mentioned. These aprotic high dielectric constant solvents and aprotic low viscosity solvents are preferably used in an appropriate mixing ratio. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. The ionic liquid can be used by mixing with the non-aqueous electrolyte solvent described above.

  When a solid electrolyte or a gel electrolyte is used, it is possible to contain a silicone gel, a silicone polyether gel, an acrylic gel, a silicone acrylic gel, an acrylonitrile gel, poly (vinylidene fluoride), or the like as a polymer material. These may be polymerized in advance or may be polymerized after injection. These can be used alone or as a mixture.

Examples of the electrolyte salt include light metal salts. Light metal salts include alkali metal salts such as lithium salts, sodium salts, or potassium salts, alkaline earth metal salts such as magnesium salts or calcium salts, or aluminum salts. Selected. For example, in the case of a lithium salt, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, C ₄ F ₉ SO ₃ Li, CF ₃ CO ₂ Li, ( CF ₃ CO ₂ ) ₂ NLi, C ₆ F ₅ SO ₃ Li, C ₈ F ₁₇ SO ₃ Li, (C ₂ F ₅ SO ₂ ) ₂ NLi, (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) NLi , (FSO ₂ C ₆ F ₄ ) (CF ₃ SO ₂ ) NLi, ((CF ₃ ) ₂ CHOSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, (3,5- (CF ₃ ) ₂ C ₆ F ₃ ) ₄ BLi, LiCF ₃ , LiAlCl _4, or C ₄ BO ₈ Li may be used, and any one or two of these may be used in combination.

  The concentration of the electrolyte salt in the nonaqueous electrolytic solution is preferably 0.5 to 2.0 mol / L from the viewpoint of electrical conductivity. The conductivity of the electrolyte at 25 ° C. is preferably 0.01 S / cm or more, and is adjusted according to the type of electrolyte salt or its concentration.

  Furthermore, various additives may be added to the nonaqueous electrolytic solution as necessary. For example, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4-vinylethylene carbonate and the like for the purpose of improving cycle life, biphenyl, alkylbiphenyl, cyclohexylbenzene, t-butylbenzene, diphenyl ether for the purpose of preventing overcharge, Examples include benzofuran, various carbonate compounds for the purpose of deoxidation and dehydration, various carboxylic acid anhydrides, various nitrogen-containing compounds, and sulfur-containing compounds.

  The shape of the nonaqueous electrolyte secondary battery is arbitrary and is not particularly limited. In general, a coin type battery in which an electrode punched into a coin shape and a separator are stacked, and a square type or cylindrical type battery in which an electrode sheet and a separator are wound in a spiral shape are included.

  In the case of obtaining an electrochemical capacitor, the electrochemical capacitor is characterized in that the negative electrode active material is used, and other materials such as an electrolyte and a separator, and a capacitor shape are not limited. For example, non-aqueous solutions containing lithium salts such as lithium hexafluorophosphate, lithium perchlorate, lithium borofluoride, lithium hexafluoroarsenate, etc. are used as the electrolyte, and propylene carbonate, ethylene carbonate, dimethyl carbonate are used as the non-aqueous solvent. , Diethyl carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran and the like. Various other non-aqueous electrolytes and solid electrolytes can also be used.

EXAMPLES Hereinafter, although a manufacture example, an Example, and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples,% indicates mass%, and the average particle diameter indicates a value measured by a cumulative mass average value D ₅₀ (or median diameter) in particle size distribution measurement by a laser light diffraction method.

[Examples 1-7]
The silicon was pulverized according to the flow chart using the jet mill shown in FIG.
The silicon crushed with a jaw crusher was pulverized at 6,800 rpm with a classifier using a jet mill (AFG-100 manufactured by Hosokawa Micron Corporation) and recovered with a cyclone. The pulverized gas was mixed with compressed air and compressed nitrogen to adjust the oxygen concentration to 8% by volume, and the dew point temperature at atmospheric pressure was changed as shown in Examples 1 to 7 in Table 1. The particle size distribution was measured with SALD-3100 manufactured by Shimadzu Corporation, and the oxygen content of the powder was measured with EMGA-920 manufactured by Horiba.

[Comparative Example 1]
Secondary batteries were fabricated in the same manner as in Examples 1 to 7, except that the gas dew point temperature during pulverization was −100 ° C. under atmospheric pressure. Due to the aggregation of the fine powder, the particle size distribution of the cyclone recovered product became smaller than that of the example.

[Comparative Example 2]
Secondary batteries were fabricated in the same manner as in Examples 1 to 7, except that the gas dew point temperature during pulverization was 40 ° C under atmospheric pressure.

  Using the obtained silicon particles as a negative electrode active material, a coin-type lithium ion secondary battery was prepared by the following method, and cycle characteristics were evaluated.

<Cycle characteristics>
1. 81% by mass of the negative electrode active material, 9% by mass of artificial graphite (average particle diameter D ₅₀ = 3 μm) as a conductive agent, N-methylpyrrolidone dispersion of acetylene black (solid content: 17.5% by mass) The mixture with 5% by weight was diluted with N-methylpyrrolidone. As a binder, polyimide resin (trade name: U-varnish A, solid content 18% by mass) manufactured by Ube Industries, Ltd. was added in an amount of 7.5% by mass in terms of solids to obtain a slurry.

This slurry was applied to a copper foil with a thickness of 12 μm using a 50 μm doctor blade, dried at 200 ° C. for 2 hours, then pressure-formed with a roller press at 60 ° C., and finally punched to 2 cm ² . A negative electrode molded body was obtained.

  The obtained molded negative electrode was prepared using a lithium foil as a counter electrode, and lithium bis (trifluoromethanesulfonyl) imide as a nonaqueous electrolyte in a 1/1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / L. Four lithium ion secondary batteries for evaluation each using a 30 μm thick polyethylene microporous film as a separator were prepared using the non-aqueous electrolyte solution dissolved in (1).

  The produced coin-type lithium ion secondary battery was allowed to stand at room temperature for two nights, and then used a secondary battery charge / discharge test apparatus (manufactured by Nagano Co., Ltd.), and 1.2 mA until the test cell voltage reached 4.2V. The battery was charged with a constant current of 0.25c (positive electrode reference), and after reaching 4.2V, the battery was charged by decreasing the current so as to keep the cell voltage at 4.2V. The charging was terminated when the current value was less than 0.3 mA. The discharge was performed at a constant current of 0.6 mA, and when the cell voltage reached 2.5 V, the discharge was terminated and the discharge capacity was determined. This was continued for 200 cycles. These results are shown in Table 1.

  Compared with the negative electrode materials of Examples 1 to 7, those of Comparative Example 1 had much fine powder and were inferior in cycle characteristics. Moreover, although the thing of the comparative example 2 is not so inferior in cycling characteristics, the initial charge / discharge efficiency used as a base is low, and it is guessed that this is due to a thick oxide film due to a high pulverization gas dew point. As described above, a high-capacity, high-cycle silicon negative electrode material can be obtained by controlling the atmospheric gas dew point during pulverization. Although not specifically described here, the same result can be obtained when another silicon compound is used as the negative electrode material. Similar results can be obtained even when silicon and a silicon compound are mixed and used as the negative electrode material.

1 Compressor 2 Nitrogen generator 3 Tank 4 Dryer 5 Humidifier 6 Dew point meter 7 Jet mill 8 Raw material 9 Cyclone 10 Ground product (final product)
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Claims (4)

  A method for producing a non-aqueous electrolyte secondary battery negative electrode active material comprising silicon or a silicon compound, comprising a step of pulverizing silicon or a silicon compound in an atmosphere having an atmospheric pressure dew point temperature of −80 ° C. or higher and −30 ° C. or lower. The manufacturing method characterized by this.   A non-aqueous electrolyte secondary battery negative electrode active material obtained by the production method according to claim 1.   The lithium ion secondary battery containing the nonaqueous electrolyte secondary battery negative electrode active material of Claim 2.   The electrochemical capacitor containing the nonaqueous electrolyte secondary battery negative electrode active material of Claim 2.

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