JP2005149957A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery reducing the swelling of the battery even when the battery is stored at a high temperature in a charged state. <P>SOLUTION: A lithium composite oxide represented by a general formula, Li<SB>x</SB>Co<SB>1-y</SB>M<SB>y</SB>O<SB>2</SB>(wherein, 0.9≤x≤1.1; 0.005≤y≤0.1; M is at least one selected from a group comprising Cr, Fe, Cu, Zn, Al, and Mg) is used as a positive active material, and a negative active material is prepared by covering silicon-containing particles obtained by disproportionating SiO<SB>2</SB>particles in Si and SiO<SB>z</SB>(O<z≤2) with carbon materials. Thereby, the nonaqueous electrolyte secondary battery reducing the swelling of the battery even when the battery is stored at a high temperature in the charged state can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

A lithium ion secondary battery that functions as a battery by the positive electrode active material and the negative electrode active material inserting and extracting lithium ions from each other has a high voltage and high energy density, so that it can be used for mobile phones, portable personal computers, video cameras, It can use suitably for uses, such as a car. As such a lithium ion secondary battery, a lithium cobaltate which is a layered composite oxide as a positive electrode active material and a graphite-based carbon material as a negative electrode active material can obtain a high voltage of 4V. Since it is possible and has a high energy density, it has already been widely put into practical use (see Patent Document 1).
Japanese Patent Laid-Open No. 11-12102

  However, according to the above configuration, there is a problem that the battery may swell when the lithium ion secondary battery is stored in a charged state at a high temperature.

  The present invention has been completed based on the above circumstances, and an object thereof is to provide a nonaqueous electrolyte secondary battery in which the swelling of the battery is reduced even when stored under high temperature in a charged state. To do.

As a means for achieving the above object, the invention of claim 1 includes a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, and non-water In a non-aqueous electrolyte secondary battery comprising an electrolyte, the positive electrode active material has a general formula Li _x Co _{1- y My} O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0). .1, M is a lithium composite oxide represented by at least one selected from the group consisting of Cr, Fe, Cu, Zn, Al, and Mg, and the negative electrode active material contains silicon-containing particles. Features.

  According to a second aspect of the present invention, in the nonaqueous electrolyte secondary battery according to the first aspect, the negative electrode active material contains particles obtained by coating the silicon-containing particles with a carbon material.

  According to a third aspect of the present invention, in the nonaqueous electrolyte secondary battery according to the first aspect, the negative electrode active material is obtained by coating the composite particles composed of the silicon-containing particles and the first carbon material with a second carbon material. It is characterized by containing the particle | grains which become.

According to a fourth aspect of the present invention, in the nonaqueous electrolyte secondary battery according to any one of the first to third aspects, the silicon-containing particles include SiO particles, Si, and SiO _z (0 <z ≦ 2). It is obtained by disproportionation.

Here, “disproportionation” is called “disproportionation, disproportionation, etc.” according to the chemical dictionary (Tokyo Dojin, published in October 1994). Defined as "changing". In the present invention, “disproportionation” means that the SiO particles are changed into Si and SiO _z (0 <z ≦ 2) by heat treatment or the like.

  5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode includes a conductive carbon material.

When the lithium ion secondary battery is stored in a charged state at a high temperature, the battery swells because the electrolytic solution decomposes at the positive electrode and CO ₂ is generated.

In the invention of claim 1, the positive electrode active material is represented by the general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.1, M is Cr, When a lithium composite oxide represented by a group consisting of Fe, Cu, Zn, Al, and Mg is used, a metal element M (Cr, Fe, Cu, Zn, Al, or the like) contained in the positive electrode active material is used. Since at least one selected from the group consisting of Mg suppresses the generation of CO _{2 in} the positive electrode, the swelling of the nonaqueous electrolyte secondary battery can be suppressed. As the metal element M, Al is particularly preferable because it has a high effect of suppressing generation of CO ₂ .

  In the invention of claim 1, the silicon-containing particles contained in the negative electrode active material contain Si. Since this Si forms a solid solution or intermetallic compound with lithium ions, a large amount of lithium ions can be occluded, so that a non-aqueous electrolyte secondary battery with high energy density can be obtained.

Also, CO ₂ generated in the battery is absorbed by the reaction of lithium ions and CO ₂ to produce Li ₂ CO ₃ . When a carbon material is used for the negative electrode active material, CO ₂ reacts only with the lithium ions occluded between the layers of the carbon material on the edge surface of the layered structure. On the other hand, when silicon-containing particles are used for the negative electrode active material, lithium ions can be desorbed from an arbitrary site of the three-dimensional crystal structure of Si, so that lithium ions and CO ₂ react actively. As a result, it is possible to absorb a large amount of CO ₂ as compared with the conventional case where only the carbon material is used for the negative electrode active material. Thereby, the swelling of the nonaqueous electrolyte secondary battery can be suppressed.

  In the invention of claim 2, a non-aqueous electrolyte secondary battery with improved cycle characteristics can be obtained by coating the surface of the silicon-containing particles with a carbon material. This is considered as follows. Si can store a large amount of lithium ions, but it has a large volume expansion due to occlusion of lithium ions, and is easily pulverized by repeated charge and discharge. As a result of the pulverization, Si is removed from the silicon-containing particles, and as a result, the conductive path is interrupted and the cycle characteristics may be deteriorated. If the surface of the silicon-containing particles is coated with a carbon material, it is possible to prevent Si from falling off from the silicon-containing particles and to maintain a conductive path, which is considered to improve cycle characteristics.

  In addition, in Si contained in silicon-containing particles, there is a portion that is more reactive with lithium ions than others, and lithium ion storage / release reactions proceed intensively in these highly reactive portions. So-called reaction unevenness may occur. Then, in the highly reactive part, the volume of the negative electrode active material expands due to occlusion of lithium ions, whereas in the low reactive part, the volume expansion of the negative electrode active material becomes small. When such unevenness in volume variation occurs, the shape of Si collapses and a portion isolated from the surroundings is generated, and the conductive path may be interrupted.

  By covering the surface of the silicon-containing particles with a conductive carbon material, the reaction unevenness as described above is alleviated, and lithium ions and Si are reacted uniformly. Thereby, since Si expands in volume uniformly, isolation is prevented and the conductive path is maintained, so that a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained.

  In the invention of claim 3, when the negative electrode active material includes composite particles made of silicon-containing particles and the first carbon material, a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be obtained. This is considered to be due to the following reason. As described above, Si can occlude a large amount of lithium ions, but greatly expands when lithium ions are occluded. For this reason, when charge and discharge are repeated, the silicon-containing particles may be pulverized due to volume expansion and contraction. By including the silicon-containing particles and the first carbon material in the negative electrode active material, even if the silicon-containing particles are pulverized by volume expansion and contraction due to charge / discharge, the conductive path is maintained by the first carbon material. Therefore, it is considered that the decrease in power collection is suppressed.

  The first carbon material is not particularly limited as long as it has electronic conductivity and can maintain the conductive path of the silicon-containing particles. For example, selected from the group consisting of natural graphite (such as flake graphite), artificial graphite, graphitized MCMB, graphitized mesophase pitch carbon fiber, graphite whisker, carbon black, acetylene black, ketjen black, vapor grown carbon fiber, etc. At least one of the above can be used. Among these, it is preferable to use scaly graphite having a number average particle diameter of 1 to 15 μm because conductivity can be sufficiently secured. In addition, you may use what has the capability to occlude and discharge | release lithium ion.

  Further, by covering the composite particles with the second carbon material having conductivity, lithium ions and Si contained in the composite particles react uniformly. Thereby, since Si expands uniformly, isolation is prevented and the conductive path is maintained. As a result, a non-aqueous electrolyte secondary battery having further excellent cycle characteristics can be obtained.

In the invention according to claim 4, by using silicon-containing particles obtained by disproportionating SiO particles to Si and SiO _z (0 <z ≦ 2), the non-aqueous electrolyte 2 having excellent charge / discharge cycle characteristics. A secondary battery can be obtained. The reason for this is not necessarily clear, but is considered as follows. SiO _z (0 <z ≦ 2) formed by disproportionation of SiO particles is amorphous, while Si is microcrystalline. Therefore, the silicon-containing particles after being disproportionated are considered to be in a form in which Si crystallites are dispersed as domains in an amorphous SiO _z (0 <z ≦ 2) matrix. As described above, when lithium ions are occluded in microcrystalline Si dispersed in a matrix of silicon oxide SiO _z (0 <z ≦ 2), amorphous SiO _z (0 As a result of the volume change absorbed by <z ≦ 2), it is considered that the volume expansion of the silicon-containing particles is suppressed to a small level. For this reason, as a result of suppressing the volume change of the negative electrode active material accompanying charging / discharging, it is thought that charging / discharging cycling characteristics improve.

  5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the use of the negative electrode containing a conductive carbon material can improve the conductivity of the negative electrode. The conductive carbon material is not particularly limited as long as it has electronic conductivity. For example, natural graphite, artificial graphite, graphitized MCMB, graphitized mesophase pitch-based carbon fiber, graphite whisker, carbon black, acetylene black, At least one selected from the group consisting of ketjen black, vapor grown carbon fiber, and the like can be used. Regarding the shape of the conductive carbon material, various shapes such as a spherical shape, a fiber shape, and a scale shape can be used as appropriate. Among them, it is preferable to use scaly graphite having a number average particle diameter of 1 to 15 μm because conductivity can be sufficiently secured. In addition, since the cycle characteristics are improved, it is preferable to use mesocarbon microbeads, mesocarbon fibers, or materials obtained by adding boron to these carbon materials. In addition, you may use what has the capability to occlude and discharge | release lithium ion.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present invention. This rectangular nonaqueous electrolyte secondary battery 1 includes a positive electrode 3 formed by applying a positive electrode mixture to a positive electrode current collector made of aluminum foil, and a negative electrode formed by applying a negative electrode mixture to a negative electrode current collector made of copper foil. A flat wound electrode group 2 wound with a separator 5 through a separator 5 and a nonaqueous electrolyte solution are housed in a battery case 6.

  A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, a negative electrode terminal 9 is connected to the negative electrode 4 via a negative electrode lead 11, and a positive electrode 3 is connected to the battery lid 7 via a positive electrode lead 10. It is connected.

As the positive electrode active material in the present invention, a general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.1, M is Cr, Fe, A lithium composite oxide represented by (at least one selected from the group consisting of Cu, Zn, Al, and Mg) can be used. When the value of x is less than 0.9, lithium ions are excessively released from the lithium composite oxide, and as a result, the crystal structure of the lithium composite oxide is distorted. On the other hand, if the value of x is larger than 1.1, the lithium composite oxide is excessively filled with lithium ions, and as a result, the crystal structure of the lithium composite oxide is distorted. When the value of y is smaller than 0.005, it is not preferable because the effect of suppressing the generation of CO ₂ from the positive electrode is reduced when stored at a high temperature during charging. On the other hand, a value of y larger than 0.1 is not preferable because the discharge capacity becomes small. Therefore, the range of y is 0.005 ≦ y ≦ 0.1, more preferably 0.01 ≦ y ≦ 0.05.

  The lithium composite oxide in the present invention is a known method, for example, lithium source such as lithium carbonate, lithium nitrate, lithium oxide, lithium hydroxide, cobalt carbonate, cobalt oxide, etc. A metal source such as a metal M carbonate, a metal M nitrate, a metal M oxide, a metal M hydroxide and the like is pulverized and mixed at a predetermined ratio, for example, in an oxygen-containing atmosphere. It can be obtained by baking at a temperature of from 1000C to 1000C.

The metal M used in the lithium composite oxide in the present invention is preferably Cr, Fe, Cu, Zn, Al, Mg, more preferably Cr, Zn, since it can suppress the generation of CO ₂ from the positive electrode. Al and Mg, and Al is particularly preferable.

  For example, the positive electrode plate is prepared by mixing the positive electrode active material, a conductive agent, and a binder to prepare a positive electrode mixture, and applying the positive electrode mixture to a positive electrode current collector made of a metal foil. Can be manufactured.

  There is no restriction | limiting in particular as a electrically conductive agent, A various material can be used suitably. For example, Ni, Ti, Al, Fe, or an alloy of two or more of these, or a carbon material can be used. Among these, it is preferable to use a carbon material. Examples of the carbon material include amorphous carbon such as natural graphite, artificial graphite, vapor-grown carbon fiber, acetylene black, ketjen black, and needle coke.

  There is no restriction | limiting in particular as a binder used for a positive electrode, A various material can be used suitably. For example, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine At least one selected from the group consisting of rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, or derivatives thereof can be used.

  Examples of the positive electrode current collector include Al, Ta, Nb, Ti, Hf, Zr, Zn, W, Bi, and alloys containing these metals. Since these metals form a passive film on the surface by anodic oxidation in the electrolytic solution, it is possible to effectively prevent the nonaqueous electrolyte from being oxidatively decomposed at the contact portion between the positive electrode current collector and the electrolytic solution. it can. As a result, the cycle characteristics of the non-aqueous secondary battery can be effectively improved.

Examples of the silicon-containing particles used in the negative electrode active material according to the present invention include Si, Si and alloys of typical nonmetallic elements such as B, N, O, P, F, Cl, Br, and I, Si, Li, and Na. Alloys with typical metal elements such as Mg, Al, K, Ca, Zn, Ga, Ge, Si and Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf An alloy with a transition metal element such as Nb, W, or an oxide of a Si alloy can be used alone or in admixture of two or more. Among these, Si, SiO _z (0 <z ≦ 2), or a mixture thereof is preferable, and in particular, a material in which SiO particles are disproportionated into Si and SiO _z (0 <z ≦ 2) is preferable.

Whether or not the silicon-containing particles obtained by heat-treating the SiO particles according to the present invention are disproportionated to Si and SiO _z (0 <z ≦ 2) can be confirmed by X-ray diffraction. For example, measurement can be performed using CuKα rays using an X-Ray Diffractometer, RINT2000, manufactured by Rigaku Corporation. Si can be identified by a peak at a diffraction angle 2θ of around 28.5 °, a peak around 47.4 °, and a peak around 55.9 °. SiO ₂ can be identified by a peak having a diffraction angle 2θ of around 21.5 ° (see FIG. 2).

  When the half-value width of a diffraction peak appearing in a diffraction angle 2θ in the range of 46 ° to 49 ° is B, it is preferable that B <3 ° (2θ). This is because when a substance satisfying B ≧ 3 ° (2θ) is used, cycle characteristics deteriorate.

Moreover, it can be confirmed that the silicon-containing particles are disproportionated into Si and SiO _z (0 <z ≦ 2) also by TEM observation of the silicon-containing particles. The TEM observation can be performed using an HF-2200 manufactured by HITACHI with an acceleration voltage of 200 kV and a measurement time of 80 sec (see FIG. 3). A black point is Si, and a white part is SiO, SiO ₂ or the like.

  The composite particles according to the present invention can be obtained by milling silicon-containing particles and the first core carbon material using a mill. At this time, although it may be in the air, milling is preferably performed in an inert atmosphere such as argon or nitrogen. Examples of the mill include ball mill, vibration mill, sanitary ball mill, tube mill, jet mill, rod mill, hammer mill, roller mill, disk mill, attritor mill, planetary ball mill, impact mill and the like. Further, a mechanical alloy method may be used. The milling temperature can be performed in the range of 10 ° C to 300 ° C. The milling time can be in the range of 30 seconds to 48 hours.

  In order to coat the surface of the silicon-containing particles or composite particles with the second carbon material, the surface of the silicon-containing particles or composite particles is coated with pitch, tar, or a thermoplastic resin (for example, furfuryl alcohol resin) and then fired. A method using a mechanochemical reaction to form a composite by applying mechanical energy between a silicon-containing particle or composite particle and a carbon material, a chemical vapor deposition (CVD) method, or the like can be used. . Among these, the CVD method is preferable because the carbon material can be uniformly coated.

  In the CVD method, organic compounds such as methane, acetylene, benzene, toluene, and xylene can be used as the reaction gas. The reaction temperature can be in the range of 700 ° C to 1300 ° C, and the reaction time can be in the range of 30 seconds to 72 hours. According to the CVD method, the carbon material can be coated at a lower reaction temperature than the above-described method in which pitch, tar, or thermoplastic resin is coated on silicon-containing particles or composite particles and then fired. For this reason, it is preferable because the coating process can be performed below the melting point of Si.

Whether or not the carbon material is coated on the surface of the silicon-containing particles or the composite particles can be confirmed by performing Raman spectroscopic analysis. Since the Raman spectroscopic analysis analyzes the surface portion of the sample, when the carbon material is entirely coated on the surface of the silicon-containing particles or the composite particles, the R value indicating the crystallinity of the carbon material coated on the surface. (peak intensity of 1360 cm ^-1 to the peak intensity of the intensity ratio 1580 cm ^-1) is, be measured anywhere in the anode active material particles will exhibit a constant value. For this Raman spectroscopic analysis, for example, T64000 manufactured by JOBIN, YVON can be used.

  The disproportionation reaction of the SiO particles by the heat treatment may be performed, for example, by firing the SiO particles in advance, or when the second carbon material is coated on the SiO particles using the CVD method, And the disproportionation reaction may be performed simultaneously. Further, when mixing the SiO particles and the first carbon material, a disproportionation reaction may be performed simultaneously, or when the composite particles are coated with the second carbon material using the CVD method, The carbon coating and the disproportionation reaction may be performed simultaneously. As the SiO particles, those washed with an acid such as hydrofluoric acid or sulfuric acid, or those reduced with hydrogen can be used.

  The negative electrode plate is prepared, for example, by mixing the negative electrode active material obtained as described above, a conductive carbon material, and a binder to prepare a negative electrode mixture, and using this negative electrode mixture as a negative electrode current collector. It can be manufactured by coating.

The ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material and the conductive carbon material is preferably 0.01 to 50% by mass (wt%), more preferably 0.5 to 20% by mass (wt%). ). If it is smaller than this range, the absorption amount of CO ₂ generated at the positive electrode tends to decrease, and the swelling of the battery tends to increase. On the other hand, if it is larger than this range, the influence of the expansion of Si or SiO _z during charging increases, and the expansion of the battery tends to increase due to the expansion of the negative electrode plate itself.

  As the negative electrode current collector, iron, copper, stainless steel, or nickel can be used. Examples of the shape include a sheet, a sheet, a net, a foam, a sintered porous body, and an expanded lattice. Furthermore, it is possible to use those current collectors having holes formed in an arbitrary shape.

  There is no restriction | limiting in particular as an organic solvent of electrolyte solution, A various solvent can be used suitably. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane hydrocarbons, etc. Among these, ethers, ketones, esters, lactones, halogenated hydrocarbons, carbonates, and sulfolane hydrocarbons are preferable.

  Furthermore, examples of the organic solvent include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate. 1,2-dichloroethane, γ-butyrolactone, γ-valerolactone, dimethoxyethane, diethoxyethane, methyl formate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate , Vinylene carbonate, butylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfur Examples include holane, trimethyl phosphate, triethyl phosphate, and phosphazene derivatives and mixed solvents thereof. Especially, it is preferable to use ethylene carbonate, propylene carbonate, (gamma) -butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate individually or in mixture of 2 or more types.

There is no restriction | limiting in particular as a solute of electrolyte, Various solutes can be used suitably. For example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF (CF ₃ ) ₅ , LiCF ₂ (CF ₃ ) ₄ , LiCF ₃ (CF ₃ ) ₃ , LiCF ₄ (CF ₃ ) ₂ , LiCF ₅ (CF ₃ ), LiCF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ or the like can be used alone or in admixture of two or more. Of these, LiPF ₆ is preferably used. Furthermore, the lithium salt concentration is preferably 0.50 to 2.0 mol / l.

In the electrolyte, carbonates such as vinylene carbonate and butylene carbonate, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, tetraethyl It can also be used by containing at least one selected from the group consisting of ammonium fluoride hydrogen fluoride complexes or derivatives thereof, phosphazenes and derivatives thereof, amide group-containing compounds, imino group-containing compounds, or nitrogen-containing compounds. _{Moreover, CO 2, NO 2, CO} , also contain at least one selected from such SO ₂ may be used.

  A solid or gel ion conductive electrolyte can be used alone or in combination as the electrolyte. When combining a plurality of ion conductive electrolytes, the non-aqueous electrolyte battery can be composed of, for example, a positive electrode, a negative electrode, a separator, an organic or inorganic solid electrolyte, and a non-aqueous electrolyte. It can also comprise a negative electrode, an organic or inorganic solid electrolyte membrane as a separator, and a non-aqueous electrolyte. A porous polymer solid electrolyte membrane can also be used for the ion conductive electrolyte.

Examples of the ion conductive electrolyte include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyethylene glycol and derivatives thereof, LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _0.5-3x R _{0.5 + x} TiO ₃ (R = La, Pr, Nd, Sm), or using thiolysicon typified by Li _4-x Ge _1-x P _x S ₄ it can. Furthermore, oxide glass such as LiI-Li ₂ O—B ₂ O ₅ system, Li ₂ O—SiO ₂ system, or LiI—Li ₂ S—B ₂ S ₃ system, LiI—Li ₂ S—SiS ₂ system, Sulfide glass such as Li ₂ S—SiS ₂ —Li ₃ PO ₄ can be used.

  There is no restriction | limiting in particular as a separator, A various material can be used suitably. For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. are mentioned, and among them, a synthetic resin microporous film is preferable. As the material of the synthetic resin microporous membrane, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, and polyolefins such as polyethylene, polypropylene, and polybutene are used. Among them, polyethylene and polypropylene microporous membranes, Alternatively, a polyolefin microporous film in which these are combined is preferable in terms of thickness, film strength, film resistance, and the like.

  In addition, a laminate of a plurality of microporous membranes of different materials, a laminate of a plurality of microporous membranes of the same material having different weight average molecular weight and porosity, and these microporous membranes A film containing appropriate amounts of additives such as various plasticizers, antioxidants, and flame retardants can be used.

Examples of the present invention are shown below, but the present invention is not limited thereto.
<Example 1>
Lithium carbonate, cobalt oxide, and aluminum hydroxide were mixed at a molar ratio of Li / Co / Al = 1 / 0.995 / 0.005, and then fired at 900 ° C. for 10 hours. LiCo _0.995 Al _0.005 O ₂ was prepared as a positive electrode active material.

A positive electrode paste was prepared by dispersing 90 parts by weight of the above LiCo _0.995 Al _0.005 O ₂ , 5 parts by weight of acetylene black, and 5 parts by weight of polyvinylidene fluoride in NMP. After applying this positive electrode paste to a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, it was dried at 150 ° C. to evaporate NMP. After this operation was performed on both sides of the positive electrode current collector, compression molding was performed with a roll press to produce a positive electrode plate having a positive electrode mixture layer formed on both sides.

By firing the SiO particles in an argon atmosphere at 1000 ° C. for 5 hours, a disproportionation reaction from SiO to Si and SiO _z (0 <z ≦ 2) was caused to prepare silicon-containing particles. The silicon-containing particles were subjected to X-ray diffraction by the method described above. The presence of Si was confirmed by the presence of a peak at a diffraction angle 2θ of around 28.5 °, a peak at around 47.4 °, and a peak at around 55.9 °. Further, SiO ₂ was confirmed by a peak having a diffraction angle 2θ of around 21.5 °. Thus, it was confirmed that SiO was disproportionated into Si and SiO ₂ by heat-treating SiO. Further, assuming that the half-value width of the diffraction peak where the diffraction angle 2θ is in the range of 46 ° to 49 ° is B, B <3 ° (2θ).

Further, TEM observation was performed on the silicon-containing particles. Also by TEM observation, it was confirmed that SiO was disproportionated into Si and SiO ₂ by heat treatment of SiO.

  The silicon-containing particles thus prepared are coated with a carbon material on the surface by a method (CVD) in which benzene gas is thermally decomposed at 1000 ° C. in an argon atmosphere to obtain silicon-containing particles coated with the carbon material. It was. The amount of the carbon material supported was 20% by mass with respect to the mass of the silicon-containing particles coated with the carbon material. The number average particle diameter of the silicon-containing particles coated with the carbon material was 1 μm.

  The silicon-containing particles coated with the carbon material obtained as described above were subjected to Raman spectroscopic analysis by the method described above, and the R value was measured. This R value was about 0.8 as measured on any part of the silicon-containing particles coated with the carbon material. Thus, it was found that the surface of the silicon-containing particles coated with the carbon material was uniformly coated with the carbon material.

  0.005 parts by weight of the silicon-containing particles coated with the carbon material obtained as described above and 99.995 parts by weight of the conductive carbon material were mixed. As the conductive carbon material, a mixture of 40 parts by weight of mesocarbon microbeads, 39.995 parts by weight of natural graphite and 20 parts by weight of artificial graphite was used. The ratio of the mass of the silicon-containing particles coated with the carbon material to the total mass of the silicon-containing particles coated with the carbon material and the conductive carbon material was 0.005% by mass.

  97 parts by weight of a mixture of carbon-containing silicon-containing particles coated with a carbon material and a conductive carbon material (negative electrode active material), 2 parts by weight of styrene-butadiene rubber (SBR), and 1 part by weight of carboxymethyl cellulose (CMC) A negative electrode paste was prepared by dispersing in water. The negative electrode paste was applied to a negative electrode current collector made of a copper foil having a thickness of 15 μm, and then dried at 150 ° C. to evaporate water. After this operation was performed on both surfaces of the negative electrode current collector, compression molding was performed with a roll press to prepare a negative electrode plate having a negative electrode mixture layer formed on both surfaces.

  As the separator, a polyethylene separator which is a continuous porous body having a thickness of 20 μm and a porosity of 40% was used.

  The positive electrode plate, the separator, and the negative electrode plate obtained as described above were sequentially overlapped, and then wound in an elliptical spiral shape to produce a wound power generation element. The power generation element was inserted into a container having a height of 48 mm, a width of 30 mm, and a thickness of 4.2 mm, and a nonaqueous electrolyte solution was injected into the battery to obtain a rectangular nonaqueous electrolyte secondary battery.

As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / l LiPF ₆ in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1 was used.

(Measurement of discharge capacity before leaving at high temperature)
The square non-aqueous electrolyte secondary battery produced as described above was charged at a constant current of 1 CmA (750 mA) at 25 ° C. until the voltage reached 4.2 V, and then 2 at a constant voltage of 4.2 V. Charged at a constant voltage for an hour. Then, it discharged to 2.0V with the electric current 1CmA (750mA), and measured the discharge capacity.

(Battery thickness measurement)
After measuring the discharge capacity, the non-aqueous electrolyte secondary battery was again charged with a constant current at 25 ° C. with a current of 1 CmA (750 mA) until the voltage reached 4.2 V, followed by a constant voltage of 4.2 V. The battery was charged at a constant voltage for 2 hours. Thereafter, the thickness of the central portion of the prismatic nonaqueous electrolyte secondary battery immediately after being left at 100 ° C. for 5 days was measured with a caliper.

(Measurement of discharge capacity after standing at high temperature)
After leaving it at 100 ° C. for 5 days, it was discharged to 2.0 V at a current of 1 CmA (750 mA), and the discharge capacity was measured. The ratio of the discharge capacity after standing at high temperature to the discharge capacity before standing at high temperature (hereinafter, capacity retention) was calculated.

<Examples 2 to 9>
Similar to Example 1 except that the ratio of the mass of the silicon-containing particles coated with the carbon material to the total mass of the silicon-containing particles coated with the carbon material and the carbon material for electrical conduction was changed to the ratio shown in Table 1. Thus, a square nonaqueous electrolyte secondary battery was produced.

<Examples 10 to 18>
Lithium carbonate, cobalt oxide, and aluminum hydroxide were mixed at a molar ratio of Li / Co / Al = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours. Preparation of LiCo _0.97 Al _0.03 O ₂ as a positive electrode active material, and carbon-coated silicon-containing particles with respect to the total mass of the carbon-coated silicon-containing particles and the conductive carbon material A square non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1 except that the mass ratio was changed to the ratio shown in Table 1.

<Examples 19 to 27>
Lithium carbonate, cobalt oxide, and aluminum hydroxide were mixed at a molar ratio of Li / Co / Al = 1 / 0.9 / 0.1, and then fired at 900 ° C. for 10 hours. Preparation of LiCo _0.9 Al _0.1 O ₂ as a positive electrode active material, and silicon material-coated particles of carbon material with respect to the total mass of silicon-containing particles coated with carbon material and carbon material for conduction A square non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1 except that the mass ratio was changed to the ratio shown in Table 1.

<Example 28>
Lithium carbonate, cobalt oxide, and magnesium oxide were mixed at a molar ratio of Li / Co / Mg = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours to obtain a positive electrode. Preparation of LiCo _0.97 Mg _0.03 O ₂ as an active material and the total of the mass of the silicon-containing particles coated with the carbon material and the mass of the conductive carbon material A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the mass ratio was 5 mass%.

<Example 29>
Lithium carbonate, cobalt oxide, and zinc oxide are mixed so that the molar ratio is Li / Co / Zn = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours to obtain a positive electrode. Preparation of LiCo _0.97 Zn _0.03 O ₂ as an active material and the total of the mass of the silicon-containing particles coated with the carbon material and the mass of the conductive carbon material of the silicon-containing particles coated with the carbon material A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the mass ratio was 5 mass%.

<Example 30>
Lithium carbonate, cobalt oxide, and chromium oxide were mixed so that the molar ratio was Li / Co / Cr = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours to obtain a positive electrode. The preparation of LiCo _0.97 Cr _0.03 O ₂ as an active material and the total of the mass of the carbon-containing silicon-containing particles and conductive carbon material of the carbon material, A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the mass ratio was 5 mass%.

<Comparative Example 1>
Lithium carbonate and cobalt oxide were mixed so that the molar ratio was Li / Co = 1/1, and then calcined at 900 ° C. for 10 hours to prepare LiCoO ₂ as a positive electrode active material, and Except that the ratio of the mass of the silicon-containing particles coated with the carbon material to the total mass of the silicon-containing particles coated with the carbon material and the conductive carbon material was 5% by mass, the same as in Example 1. A square nonaqueous electrolyte secondary battery was produced.

<Comparative example 2>
Lithium carbonate, cobalt oxide, and aluminum hydroxide were mixed at a molar ratio of Li / Co / Al = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours. A prismatic non-aqueous electrolyte secondary battery in the same manner as in Example 1 except that LiCo _0.97 Al _0.03 O ₂ was prepared as the positive electrode active material and only the conductive carbon material was used as the negative electrode active material. Was made.

<Comparative Example 3>
LiCoO ₂ was prepared as a positive electrode active material by mixing lithium carbonate and cobalt oxide in a molar ratio of Li / Co = 1/1, followed by firing at 900 ° C. for 10 hours, and A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that only the conductive carbon material was used as the negative electrode active material.

  For the prismatic nonaqueous electrolyte secondary batteries of Examples 2 to 30 and Comparative Examples 1 to 3, the discharge capacity before and after being left at high temperature was measured in the same manner as in Example 1, and the thickness of the battery after being left at high temperature was measured. It was measured. These measurement results are summarized in Table 1.

<Result>
In Comparative Examples 1 and 3 using LiCoO ₂ as the positive electrode active material, the battery thickness after standing at high temperature was 12.30 mm (Comparative Example 1) or more, whereas Al as a metal element other than Co in the positive electrode active material. In Examples 1 to 30 using the lithium metal composite oxide containing Mg, Zn, and Cr, the battery thickness after being left at high temperature was 10.37 mm (Example 9) or less.

  In Comparative Examples 1 and 3, the capacity retention was 21% (Comparative Example 1) or less, whereas in Examples 1 to 30, the capacity retention was 31% (Example 1) or more. .

The nonaqueous electrolyte secondary battery of Comparative Example 2 does not include the silicon-containing particles according to the present invention. In the battery of Comparative Example 2, the mixture of 40 parts by weight of mesocarbon microbeads, 39.995 parts by weight of natural graphite and 20 parts by weight of artificial graphite added as a conductive carbon material has the ability to occlude and release lithium. Therefore, charging / discharging is possible. In Comparative Example 2, the thickness of the battery after being left at high temperature was 13.10 mm, whereas the negative electrode active material was prepared by disproportionating SiO particles, and Si and SiO _z (0 <z ≦ 2). In Examples 1 to 30 including the silicon-containing particles formed by coating a carbon material, the thickness of the battery after being left at high temperature was 10.37 mm (Example 9) or less.

  In Comparative Example 2, the capacity retention rate was 24%, while in Examples 1 to 30, the capacity retention rate was 31% (Example 1) or more.

From the above results, the positive electrode active material has the general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.1, where M is Cr, Fe And at least one selected from the group consisting of Cu, Zn, Al, and Mg), and the negative electrode active material contains particles in which silicon-containing particles are coated with a carbon material. It was found that a non-aqueous electrolyte secondary battery with reduced battery swelling can be obtained even when stored under high temperature in a charged state.

<Example 31>
Lithium carbonate, cobalt oxide, and aluminum hydroxide were mixed at a molar ratio of Li / Co / Al = 1 / 0.97 / 0.03, and then fired at 900 ° C. for 10 hours. LiCo _0.97 Al _0.03 O ₂ was prepared as a positive electrode active material.

Compound particles were prepared by mixing 30 parts by weight of silicon-containing particles and 50 parts by weight of artificial graphite in a nitrogen atmosphere at 25 ° C. for 30 minutes with a ball mill, and preparing the composite particles thus prepared in an argon atmosphere A carbon material was coated on the surface by a method (CVD) in which benzene gas was thermally decomposed at 1000 ° C., and composite particles coated with the carbon material were obtained. The ratio of the carbon material to the total mass of the composite particles coated with the carbon material obtained as described above was 20 mass% (wt%). Thus obtained 5 parts by weight of the composite particles coated with the carbon material and 95 parts by weight of the conductive carbon material were mixed. As the conductive carbon material, a mixture of 40 parts by weight of mesocarbon microbeads, 40 parts by weight of natural graphite and 20 parts by weight of artificial graphite was used. Thus obtained 97 parts by weight of a composite particle of carbon material-coated composite particles and a conductive carbon material (negative electrode active material), 2 parts by weight of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) ) A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that 1 part by weight was dispersed in water to prepare a negative electrode paste.

<Examples 32 to 34>
The ratio of the mass of the composite particles coated with the carbon material to the total mass of the composite particles coated with the carbon material and the conductive carbon material was as shown in Table 2 except that the ratio was the same as in Example 31. A water electrolyte secondary battery was produced.

  For the rectangular nonaqueous electrolyte secondary batteries of Examples 31 to 34, the discharge capacity before and after being left at high temperature was measured in the same manner as in Example 1, and the thickness of the battery after being left at high temperature was measured. These measurement results are summarized in Table 2.

<Result>
In Comparative Examples 1 and 3 using LiCoO ₂ as the positive electrode active material, the battery thickness after standing at high temperature was 12.30 mm (Comparative Example 1) or more, whereas Al as a metal element other than Co in the positive electrode active material. In Examples 31 to 34 using the lithium metal composite oxide containing, the battery thickness after standing at high temperature was 8.89 mm (Example 34) or less.

  In Comparative Examples 1 and 3, the capacity retention was 21% (Comparative Example 1) or less, while in Examples 31 to 34, the capacity retention was 65% (Example 34) or more. .

In Comparative Example 2, the thickness of the battery after being left at high temperature was 13.10 mm, whereas the negative electrode active material was composed of Si and SiO _z (0 <z ≦ 2) prepared by disproportionating SiO particles. In Examples 31 to 34 including the composite particles obtained by mixing the silicon-containing particles and the first carbon material with the second carbon material coated, the thickness of the battery after being left at high temperature is 8.89 mm ( Example 34) was the following.

  Further, in Comparative Example 2, the capacity retention was 24%, while in Examples 31 to 34, the capacity retention was 65% (Example 34) or more.

From the above results, the positive electrode active material has the general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.1, where M is Cr, Fe , Cu, Zn, Al, Mg, at least one selected from the group consisting of lithium composite oxides, and the negative electrode active material is a composite particle composed of silicon-containing particles and a first carbon material. It was found that a non-aqueous electrolyte secondary battery with reduced battery swelling can be obtained even when stored under high temperature in a charged state by containing particles formed by coating the carbon material.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  In the above-described embodiment, the prismatic nonaqueous electrolyte secondary battery 1 has been described. However, the battery structure is not particularly limited, and may be a cylindrical shape, a bag shape, a lithium polymer battery, or the like.

The longitudinal cross-sectional view of the square nonaqueous electrolyte secondary battery of one Embodiment of this invention X-ray diffraction chart of negative electrode active material according to the present invention TEM photograph of negative electrode active material according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Square nonaqueous electrolyte secondary battery 2 ... Electrode group 3 ... Positive electrode 4 ... Negative electrode 5 ... Separator 6 ... Battery case 7 ... Battery cover 8 ... Safety valve 9 ... Negative electrode terminal 10 ... Positive electrode lead 11 ... Negative electrode lead

Claims (4)

In a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode including a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte,
The positive electrode active material has a general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.1, M is Cr, Fe, Cu, Zn , At least one selected from the group consisting of Al and Mg)
The non-aqueous electrolyte secondary battery, wherein the negative electrode active material contains silicon-containing particles. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material contains particles obtained by coating the silicon-containing particles with a carbon material. 2. The non-aqueous electrolyte 2 according to claim 1, wherein the negative electrode active material contains particles formed by coating the second carbon material on the composite particles made of the silicon-containing particles and the first carbon material. Next battery. 4. The silicon-containing particle according to claim 1, wherein the silicon-containing particle is obtained by disproportionating SiO particles into Si and SiO _z (0 <z ≦ 2). 5. Non-aqueous electrolyte secondary battery.

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