JP2016100226A - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide negative electrode material for a lithium ion secondary battery capable of manufacturing a negative electrode which has high capacity and is excellent in cycle characteristics, to provide a negative electrode using the negative electrode material and the lithium ion secondary battery.SOLUTION: Negative electrode material for a lithium ion secondary battery includes a composite particle A made of a silicon particle and a conductive fine particulate, where ratio r(=t/l) between a longest diameter l and a shortest diameter t of the silicon particle is 0.5 or less.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

Carbon materials that occlude and release lithium ions are widely used as negative electrode materials for lithium ion secondary batteries. An example of the carbon material is graphite. When graphite is used as a carbon material, a lithium ion secondary battery having good cycle characteristics can be obtained because the lithium ion occlusion and release reaction during charge and discharge is excellent in reversibility. However, the lithium ion storage / release capacity of graphite is 372 mAh / g forming LiC _6, which is a theoretical value, and there is a limit to further increasing the capacity.

Since silicon (Si) forms an alloy (intermetallic compound) with lithium, it is possible to occlude and release lithium ions electrochemically. The lithium ion storage / release capacity has a theoretical value of 4197 mAh / g forming Li ₂₂ Si ₅ , and can have a higher capacity than a lithium ion secondary battery using a graphite negative electrode.
On the other hand, silicon causes a large volume change of 3 to 4 times with occlusion and release of lithium ions. For this reason, when a charge / discharge cycle is performed, the expansion and contraction is repeated, so that silicon collapses and becomes finer, so that there is a problem that good cycle characteristics cannot be obtained.

  Therefore, a carbonaceous material which is at least one kind of material selected from graphite or carbon black is disposed on the surface of the composite particles containing graphite particles, silicon fine particles, and amorphous carbon, and the carbonaceous material is A lithium ion secondary battery material having a structure covered with amorphous carbon is disclosed (for example, see Patent Document 1).

JP 2008-277232 A

  Amid the increasing demand for higher capacity and improved cycle characteristics of lithium ion secondary batteries, there is a need for a negative electrode material capable of producing a lithium ion secondary battery with higher capacity and excellent cycle characteristics. Accordingly, the present invention provides a negative electrode material for a lithium ion secondary battery capable of producing a negative electrode having a high capacity and excellent cycle characteristics, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the negative electrode material. Is an issue.

Means for solving the above problems are as follows.
<1> A lithium ion secondary containing composite particles A of silicon particles and conductive fine particles, wherein the ratio r (= t / l) of the longest diameter l to the shortest diameter t of the silicon particles is 0.5 or less. Negative electrode material for batteries.

<2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein a ratio r (= t / l) between the longest diameter l and the shortest diameter t of the silicon particles is 0.001 or more.

<3> The negative electrode material for a lithium ion secondary battery according to <1> or <2>, wherein the longest diameter l of the silicon particles is 10 nm to 5000 nm.

<4> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <3>, wherein the content of the silicon particles in the composite particle A is 40% by mass to 85% by mass.

<5> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <4>, including the composite particles B of the composite particles A and graphite particles.

<6> The negative electrode material for a lithium ion secondary battery according to <5>, wherein a part or all of the surface of the composite particle B is coated with a carbonaceous material.

<7> The negative electrode material for a lithium ion secondary battery according to <5> or <6>, wherein the content of the silicon particles in the composite particle B is 40% by mass to 85% by mass.

<8> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <7>, further including carbonaceous particles having pores therein.

<9> In the carbonaceous particle, the cumulative pore volume of pores having a size in the range of 0.1 μm to 1 μm is 0.05 × 10 ⁻³ m ^{3 /} kg to 0.4 × 10 ⁻³ m ^3. The negative electrode material for lithium ion secondary batteries according to the above <8>, which is / kg.

<10> the carbonaceous particles is graphite particles, saturated tapping density of the graphite particles is ^{0.4g / cm 3 ~0.9g / cm 3} , the lithium ions described above <8> or <9> Secondary battery negative electrode material.

<11> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <10>, wherein the content of the silicon particles is 3% by mass to 50% by mass.

<12> A negative electrode for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to any one of <1> to <11>.

<13> A lithium ion secondary battery comprising the negative electrode for lithium ion secondary batteries according to <12> above, a positive electrode, and an electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries which can produce the negative electrode which is excellent in a capacity | capacitance and cycling characteristics, the negative electrode for lithium ion secondary batteries using this negative electrode material, and a lithium ion secondary battery are provided. The

2 is a schematic cross-sectional view showing an example of composite particles A. FIG. 2 is a schematic cross-sectional view showing an example of composite particles B. FIG. It is a schematic sectional drawing which shows an example of the composite particle B coat | covered with the carbonaceous layer. It is a figure which shows an example of a carbonaceous particle. It is a figure which shows an example of the negative electrode for lithium ion secondary batteries. It is a figure which shows an example of a lithium ion secondary battery.

  Hereinafter, modes for carrying out the present invention will be described. The following are specific examples of the present invention, and the present invention is not limited to these, and various changes and modifications can be made within the scope of the technical idea disclosed in the present specification. .

  In addition, the numerical value range shown using "to" in this specification shows the range which includes the numerical value described before and behind "to" as a minimum value and a maximum value, respectively. In addition, in the present specification, the content of each component in the composition is the sum of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. Means quantity. In the present specification, the particle diameter of each component in the composition is such that when there are a plurality of particles corresponding to each component in the composition, the plurality of particles present in the composition unless otherwise specified. The value for a mixture of In addition, in the present specification, the term “layer” includes a configuration of a shape formed in part in addition to a configuration of a shape formed on the entire surface when observed as a plan view.

<Anode material for lithium ion secondary battery>
The negative electrode material for lithium ion secondary batteries of the present invention (hereinafter also simply referred to as “negative electrode material”) includes composite particles A of silicon particles and conductive fine particles, and the longest diameter l and shortest diameter t of the silicon particles. The ratio r (= t / l) is 0.5 or less.

  The lithium ion secondary battery produced using the negative electrode material of the present invention has a high capacity and excellent cycle characteristics. The reason for this is estimated by the inventors as follows. The silicon particles constituting the composite particle A have a ratio r (= t / l) of the longest diameter l to the shortest diameter t of 0.5 or less. For this reason, even if the silicon particles are cracked due to expansion and contraction accompanying the insertion and extraction of lithium ions, it is possible to suppress the loss of the contact with the conductive fine particles mainly due to the crack in the thickness direction. In addition, the electrical conduction of the negative electrode material is ensured by the conductive fine particles constituting the composite particle A. Furthermore, moderate voids that can relieve stress due to expansion and contraction of silicon particles accompanying the insertion and release of lithium ions are formed inside the composite particles A. For these reasons, it is considered that a higher capacity and improved cycle characteristics of the lithium ion secondary battery can be realized.

(Composite particle A)
FIG. 1 is a schematic cross-sectional view showing an example of the composite particle A. As shown in FIG. 1, the composite particle A shown by the code | symbol 12 is comprised by making the silicon particle 11 and the electroconductive fine particles 13 adhere.

  The silicon particles constituting the composite particle A have a ratio r (= t / l) of the longest diameter l to the shortest diameter t of 0.5 or less. The longest diameter of a silicon particle is a value when the inter-surface distance is maximum when the silicon particle is sandwiched between two parallel surfaces. The shortest diameter of a silicon particle is the silicon particle between two parallel surfaces. This is the value when the inter-surface distance is minimum when sandwiched.

  The ratio r (= t / l) between the longest diameter l and the shortest diameter t of the silicon particles is preferably 0.001 or more.

  From the viewpoint of suppressing the loss of the contact in the negative electrode, the number average value of the ratio r of the silicon particles in the composite particles A is preferably 0.5 or less. Further, the number average value of the ratio r of the silicon particles in the composite particles A is preferably 0.001 or more.

  The longest diameter l of the silicon particles is preferably 10 nm or more. The longest diameter l of the silicon particles is preferably 5000 nm or less. In addition, the number average value of the longest diameter l of the silicon particles in the composite particles A is preferably 10 nm to 5000 nm.

  The shape of the silicon particles is not particularly limited as long as the condition that the ratio r is 0.5 or less is satisfied, and may be any of a flake shape, a plate shape, a rod shape, a needle shape, and the like. In the negative electrode material of the present invention, silicon particles having different shapes may be mixed.

  The conductive fine particles constituting the composite particle A adhere to the silicon particles by the composite treatment. Thereby, electrical conduction of the composite particles A is ensured. In addition, moderate voids that can relieve stress due to expansion and contraction of the silicon particles accompanying the insertion and extraction of lithium ions are formed inside the composite particles A.

Examples of the conductive fine particles include graphite fine powder; amorphous carbon fine powder; carbonaceous conductive fine particles such as carbon black (acetylene black, thermal black, furnace black, etc.); copper (Cu), nickel (Ni And metal metal conductive fine particles that do not form an alloy with lithium; and metal oxide conductive fine particles having conductivity such as CuO and Fe ₂ O ₃ . The conductive fine particles may be used alone or in combination of two or more. Among these conductive fine particles, copper fine particles and carbon black having a primary particle size of 200 nm or less are preferable, and carbon black having a primary particle size of 200 nm or less is more preferable.

  The particle diameter of the conductive fine particles is not particularly limited as long as the effect of the present invention is achieved.

In addition, the average particle diameter in this specification is calculated | required with the following method.
(1) A sample is dispersed in purified water containing a surfactant, and in the particle size distribution measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, SALD-3000J), the volume accumulation from the small diameter side becomes 50%. The corresponding value (50% D) is determined.
(2) Observation with a scanning electron microscope (SEM) or the like, and obtain the number average value of randomly selected samples.

  The means for combining silicon particles and conductive fine particles is not particularly limited. For example, there may be mentioned a method of attaching silicon particles and conductive fine particles by applying a mechanical shearing force using a particle composite processing apparatus such as a ball mill or a bead mill.

  The particle diameter of the composite particle A is not particularly limited as long as the effect of the present invention is achieved. From the viewpoint of ensuring a sufficient specific surface area and suppressing a decrease in the initial charge / discharge efficiency of the lithium ion secondary battery, and also suppressing a decrease in input / output characteristics due to deterioration of contact between particles, the composite particle A It is preferable that the average particle diameter (50% D) of this is 5 micrometers or more. In addition, unevenness is generated on the electrode surface, causing a short circuit of the lithium ion secondary battery, and the diffusion distance of lithium from the particle surface to the inside becomes long, and the input / output characteristics of the lithium ion secondary battery are deteriorated. From the viewpoint of suppressing this, the average particle size (50% D) of the composite particles A is preferably 30 μm or less, and more preferably 25 μm or less.

The content of the silicon particles in the composite particles A is preferably 35% by mass to 90% by mass, and 40% by mass to 85% by mass from the viewpoint of increasing the capacity of the lithium ion secondary battery and improving the cycle characteristics. More preferably.
Moreover, it is preferable that the content rate of the silicon particle in the negative electrode material of this invention is 3 mass%-50 mass% from a viewpoint of the high capacity | capacitance of a lithium ion secondary battery, and the improvement of cycling characteristics.

(Composite particle B)
The composite particles A may be composited with graphite particles to form composite particles B. Thus, by combining with graphite particles, the particle strength is increased, and it is possible to reduce the collapse of the form of the composite particles A when a negative electrode is produced. FIG. 2 is a schematic sectional view showing an example of the composite particle B. As shown in FIG. As shown in FIG. 2, the composite particle A shown by the code | symbol 14 is comprised by the composite particle A and the graphite particle 15 shown by the code | symbol 12 adhering.

  The particle diameter of the graphite particles is not particularly limited as long as the effect of the present invention is achieved.

  The means for combining the composite particles A and the graphite particles is not particularly limited. For example, a method of attaching the composite particles A and the graphite particles by applying a mechanical shearing force using a particle composite processing apparatus such as a ball mill or a bead mill can be used.

  From the viewpoint of maintaining good electrical continuity between the silicon particles and the conductive fine particles and between the composite particles A and the graphite particles, part or all of the surface of the composite particles B is coated with a carbonaceous material. Preferably it is. That is, as shown in FIG. 3, a part or all of the surface of the composite particle B in which the composite particle A indicated by reference numeral 12 and the graphite particle 15 are combined is covered with the carbonaceous material (carbonaceous layer) 17. Thus, it is preferable that the composite particle B covered with the carbonaceous layer indicated by reference numeral 16 is constituted.

  A method of coating a part or all of the surface of the composite particle B with the carbonaceous material is not particularly limited. For example, methods such as the following wet mixing method, dry mixing method, and gas phase method are exemplified.

  As a wet mixing method, a method of removing the solvent after dispersing and mixing the composite particles B in a mixed solution in which a substance (organic compound or the like) that is a precursor of a carbonaceous material is dissolved or dispersed in a solvent. Is mentioned.

  As a dry mixing method, the composite particles B and the organic compound are mixed in a solid state, and an organic compound is adhered to the surface of the composite particles B by applying mechanical energy to the resulting mixture. The composite particle B can be coated with a carbonaceous material by heat-treating the composite particle B in a state of adhering to carbonize the organic compound.

  Examples of the vapor phase method include a method of coating the surface of the composite particle B with a carbonaceous material by a gas decomposition reaction such as acetylene or propylene, such as a CVD method.

  Specific examples of organic compounds are prepared by polymerizing ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracking pitch, pitch generated by pyrolyzing polyvinyl chloride, naphthalene, etc. in the presence of a super strong acid. Synthesis pitch and the like. In addition, thermoplastic synthetic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral can also be used as the organic compound. Natural products such as starch and cellulose can also be used as the organic compound.

  The temperature of the heat treatment is preferably 750 ° C to 2000 ° C, more preferably 800 ° C to 1800 ° C, and further preferably 850 ° C to 1400 ° C. The atmosphere during the heat treatment is not particularly limited as long as the negative electrode material is not easily oxidized, and a nitrogen gas atmosphere, an argon gas atmosphere, a self-decomposing gas atmosphere, or the like can be applied. The type of furnace to be used is not particularly limited, but a batch furnace, a continuous furnace or the like using electricity or gas as a heat source is preferable.

  The particle diameter of the composite particle B (including the case where it is coated with a carbonaceous material) is not particularly limited as long as the effect of the present invention is achieved. From the viewpoint of ensuring a sufficient specific surface area and suppressing a decrease in the initial charge / discharge efficiency of the lithium ion secondary battery, and also suppressing a decrease in input / output characteristics due to deterioration in contact between particles, the composite particle B It is preferable that the average particle diameter (50% D) of this is 5 micrometers or more. In addition, unevenness is generated on the electrode surface, causing a short circuit of the lithium ion secondary battery, and the diffusion distance of lithium from the particle surface to the inside becomes long, and the input / output characteristics of the lithium ion secondary battery are deteriorated. From the viewpoint of suppressing this, the average particle size (50% D) of the composite particles B is preferably 30 μm or less, and more preferably 25 μm or less.

  The content rate of the silicon particles in the composite particle B (including the case where it is coated with a carbonaceous material) is 35% by mass to 90% by mass from the viewpoint of increasing the capacity of the lithium ion secondary battery and improving the cycle characteristics. It is preferable that there is 40% by mass to 85% by mass.

(Carbonaceous particles)
The negative electrode material preferably further includes carbonaceous particles having pores therein. The pores present in the carbonaceous particles serve as an appropriate cushion when the silicon particles expand and contract as the lithium ions are stored and released, and therefore tend to relieve stress due to expansion and contraction.

  The carbonaceous particles are preferably secondary particles formed by aggregating a plurality of primary particles composed of a carbonaceous material. That is, as shown in FIG. 4, the carbonaceous particles 18 are secondary particles formed by aggregating the primary particles 19 and preferably have pores 20 inside the particles.

From the standpoint that the lithium ion storage / release capacity of the carbonaceous particles is large, the carbonaceous material is preferably graphite, and the graphite interlayer distance (d ₀₀₂ ) is more preferably 0.335 nm to 0.337 nm.

Pores having carbonaceous particles, size cumulative pore volume of pores in the range of 0.1 to 1 m (. Hereinafter, simply referred to as "cumulative pore volume") is, 0.04 × 10 ^- is preferably ^{3 m 3 /kg~0.5×10 -3 m 3 /} kg, to be ^{0.05 × 10 -3 m 3 /kg~0.4×10 -3} m 3 / kg More preferred. The integrated pore volume is a value measured by a mercury intrusion method.

In order to set the cumulative pore volume of the carbonaceous particles in the above range, the saturated tap density of the carbonaceous particles is preferably 0.4 g / cm ^{3 to} 0.9 g / cm ³ or less.

  The particle diameter of the carbonaceous particles is not particularly limited as long as the effects of the present invention are achieved.

  The content of carbonaceous particles in the negative electrode material of the present invention is not particularly limited. From the viewpoint of increasing the capacity of a lithium ion secondary battery and improving cycle characteristics, the content of carbonaceous particles is such that the content of silicon particles in the negative electrode material of the present invention is 3% by mass to 50% by mass. It is preferable that it is a rate.

<Anode for lithium ion secondary battery>
The negative electrode for lithium ion secondary batteries of the present invention (hereinafter also simply referred to as “negative electrode”) includes the negative electrode material of the present invention and, if necessary, other components. Examples of other components include a binder and an additive. Examples of the additive include a thickener and a conductive auxiliary agent.

As binder, ethylenically unsaturated carboxylic acid such as styrene-butadiene copolymer, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxyethyl (meth) acrylate, etc. Esters; Ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid; ionic conductivity such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, etc. Large polymer compounds; and the like. The (meth) acrylate means acrylate or methacrylate, and the (meth) acrylonitrile means acrylonitrile or methacrylonitrile. A binder may be used individually by 1 type, or may be used in combination of 2 or more type.
The content of the binder is not particularly limited, but is preferably 1 part by mass to 20 parts by mass with respect to 100 parts by mass in total of the negative electrode material and the binder of the present invention.

  As the thickener, carboxymethylcellulose or a salt thereof (for example, sodium salt), methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof (for example, a sodium salt), alginic acid or a salt thereof (for example, a sodium salt) ), Oxidized starch, phosphorylated starch, casein and the like. A thickener may be used individually by 1 type, or may be used in combination of 2 or more type.

  Examples of the conductive auxiliary agent include carbon black (acetylene black, thermal black, furnace black, etc.), graphite, conductive oxide, conductive nitride, and the like. A conductive support agent may be used individually by 1 type, or may be used in combination of 2 or more type.

  The content of additives such as thickeners and conductive additives is not particularly limited as long as it does not deteriorate the characteristics of the lithium ion secondary battery, but is 0.1 mass relative to the total amount of the negative electrode material and the additives. % Or more and less than 10.0% by mass.

  The method for producing the negative electrode of the present invention is not particularly limited. For example, a paste-like negative electrode material slurry containing the negative electrode material of the present invention, a binder, various additives added as necessary, and a solvent is prepared, and the obtained negative electrode material slurry is used as a current collector. It can be produced by applying the composition onto a substrate, drying it, and compression-molding it by a molding method such as a flat plate press or roll press, if necessary. In addition, the paste-like negative electrode material slurry can be formed into a sheet shape, a pellet shape, or the like, and can be produced by integrating it with a current collector by a forming method such as a roll press.

  The negative electrode material slurry can be prepared by, for example, stirring and kneading the components constituting the negative electrode material slurry using a stirrer, a ball mill, a super sand mill, a pressure kneader, etc., and adjusting the viscosity as necessary. it can.

  The solvent used for the preparation of the negative electrode material slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the binder. Examples thereof include organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, and γ-butyrolactone. The usage-amount of a solvent will not be restrict | limited especially if a negative electrode material slurry can be made into desired states, such as a paste. For example, the amount can be 60 parts by mass or more and less than 150 parts by mass with respect to 100 parts by mass of the negative electrode material.

  The type and shape of the current collector are not particularly limited, and can be selected according to the purpose. For example, it is possible to use a belt-like one made of aluminum, copper, nickel, titanium, stainless steel, or the like into a foil shape, a perforated foil shape, a mesh shape, or the like. In addition, a porous material such as porous metal (foamed metal), carbon paper, or the like can be used.

  The method in particular of apply | coating a negative electrode material slurry to a collector is not restrict | limited, A well-known method can be selected suitably. Specific examples include a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a gravure coating method, and a screen printing method. The coating amount of the negative electrode material paste is not particularly limited and can be selected according to the purpose.

  FIG. 5 is a diagram showing an example of the negative electrode of the present invention. As shown in FIG. 5, the composite particle B (symbol 14), the composite particle B (symbol 16) in which part or all of the surface is covered with a carbonaceous layer, and the carbonaceous particle having a pore inside (symbol 18) Is formed on the surface of the negative electrode current collector 32. The negative electrode structure shown in FIG. 5 is preferable from the viewpoint of increasing the capacity of the lithium ion secondary battery and improving the cycle characteristics.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention contains the negative electrode of this invention, a positive electrode, and electrolyte (preferably electrolyte solution). The lithium ion secondary battery of the present invention can be obtained, for example, by disposing the negative electrode and the positive electrode of the present invention so as to face each other with a separator interposed therebetween and injecting an electrolytic solution.

  In the same manner as the negative electrode, the positive electrode is produced by forming a positive electrode material layer containing an additive such as a positive electrode material and, if necessary, a thickener and a conductive auxiliary agent on the surface of the current collector.

The positive electrode material is not particularly limited and can be appropriately selected as necessary. For example, metal compounds, metal oxides, metal sulfides, and conductive polymer materials that can be doped or intercalated with lithium ions are preferable. Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and composite oxides thereof (LiCo _x Ni _y Mn _z O ₂ , X + Y + X = 1), Lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound, V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Cr ₃ O ₈ , Cr ₂ O ₅ , olivine type LiMPO ₄ (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. Is mentioned. A positive electrode material may be used individually by 1 type, or may be used in combination of 2 or more type.

  The positive electrode is coated on at least one surface of the current collector with a positive electrode material slurry containing a positive electrode material, a binder, a solvent capable of dissolving or dispersing the binder, and an additive added as necessary. Then, the solvent can be removed by drying, and rolled if necessary.

  As the binder, the solvent, the additive, and the current collector, those exemplified in the section of the negative electrode of the present invention can be similarly used.

  The electrolyte used in the lithium ion secondary battery of the present invention is not particularly limited, and a known one can be used. For example, a non-aqueous lithium ion secondary battery can be manufactured by using an electrolytic solution in which an electrolyte is dissolved in an organic solvent.

As the electrolyte, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiSO 3 CF 3, LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiN (CF 3 SO 2) 2, LiN (C 2 F 5 _{SO 2) 2, LiC (CF} 3 SO 2) 3, LiCl, LiI , and the like.

  Examples of the organic solvent include carbonate solvents such as propylene carbonate, ethylene carbonate, and diethyl carbonate; lactone solvents such as γ-butyrolactone; chain ether solvents such as 1,2-dimethoxyethane, dimethyl ether, and diethyl ether; tetrahydrofuran, 2 -Cyclic ether solvents such as methyltetrahydrofuran, dioxolane, 4-methyldioxolane; sulfolane solvents such as sulfolane; sulfoxide solvents such as dimethyl sulfoxide; nitrile solvents such as acetonitrile, propionitrile, benzonitrile; N, N- Examples include amide solvents such as dimethylformamide and N, N-dimethylacetamide; and polyoxyalkylene glycol solvents such as diethylene glycol. An organic solvent may be used individually by 1 type, or may be used in combination of 2 or more type.

  Various known separators can be used as the separator. Examples of the separator include paper, polypropylene, polyethylene, glass fiber, and ceramic. In the case where the positive electrode and the negative electrode of the lithium ion secondary battery are not in direct contact, it is not necessary to use a separator.

The structure of the lithium ion secondary battery of the present invention is not particularly limited. For example, as shown in FIG. 6, a cylindrical lithium ion secondary battery in which a positive electrode, a negative electrode, and a separator are wound into a cylindrical shape and sealed in a battery can is given. In FIG. 6, reference numeral 21 is a positive electrode, reference numeral 22 is a negative electrode, reference numeral 23 is a separator, reference numeral 24 is a positive electrode terminal tab, reference numeral 25 is a negative electrode terminal tab, reference numeral 26 is a battery can, reference numeral 27 is a gasket, reference numeral 28 is an internal pressure valve, Reference numeral 29 denotes a PTC (positive temperature coefficient resistor) element, reference numeral 30 denotes a positive electrode cover, and reference numeral 31 denotes a positive electrode inner cover.
Moreover, it is wound in a flat spiral shape to form a wound-type electrode plate group, and these are laminated in a flat plate shape to form a laminated electrode plate group. A secondary battery is mentioned.

The type of the lithium ion secondary battery of the present invention is not particularly limited, and can be used as a paper-type battery, a button-type battery, a coin-type battery, a stacked battery, a cylindrical battery, or the like.
The lithium ion secondary battery of the present invention described above has a higher capacity and excellent cycle characteristics than a lithium ion secondary battery using a conventional carbon material as a negative electrode material.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

<Example 1>
(Preparation of negative electrode material)
Silicon particles (in the form of flakes) and acetylene black were mixed uniformly and subjected to mechanical alloying using a ball mill to produce composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a ball mill in the same manner as described above. Next, polyvinyl acetate was added to the composite particles B and mixed with a blender mixer. This mixed powder was heat-treated at 800 ° C. in a nitrogen atmosphere to form a carbonaceous layer on the surface of the composite particle B. Thereafter, the composite particle B having the carbonaceous layer and the carbonaceous particles (average particle size = 22 μm) of which the primary particles are graphite (d ₀₀₂ = 0.3358 nm) were mixed uniformly to prepare a negative electrode material. .
The average value of r and l of silicon particles used in Example 1, the type and average particle size of conductive fine particles, the cumulative pore volume and saturated tap density of carbonaceous particles, and silicon contained in the composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Example 2>
(Preparation of negative electrode material)
Silicon particles (flaky) and copper (Cu) fine particles were mixed so as to be uniform, and a mechanical alloying process was performed using a ball mill to produce composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a ball mill in the same manner as described above. Next, polyvinyl acetate was added to the composite particles B and mixed with a blender mixer. This mixed powder was heat-treated at 800 ° C. in a nitrogen atmosphere to form a carbonaceous layer on the surface of the composite particle B. Thereafter, the composite particles B on which the carbonaceous layer is formed and the carbonaceous particles (average particle diameter = 22 μm) whose primary particles are graphite (d ₀₀₂ = 0.3358 nm) are mixed so as to be uniform, thereby producing a negative electrode material. did.
The average value of r and l of silicon particles used in Example 2, the type and average particle size of conductive fine particles, the cumulative pore volume and saturated tap density of carbonaceous particles, and silicon contained in the composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Example 3>
(Preparation of negative electrode material)
Silicon particles (in the form of flakes) and acetylene black were mixed so as to be uniform, and a mechanical alloying process was performed using a bead mill to prepare composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a bead mill in the same manner as described above. Thereafter, composite particles B and carbonaceous particles (average particle size = 18 μm) whose primary particles are graphite (d ₀₀₂ = 0.3358 nm) were mixed uniformly to produce a negative electrode material.
Average values of r and l of silicon particles used in Example 3, types and average particle sizes of conductive fine particles, integrated pore volume and saturated tap density of carbonaceous particles, and silicon contained in composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Example 4>
(Preparation of negative electrode material)
Silicon particles (in the form of flakes) and acetylene black were mixed so as to be uniform, and a mechanical alloying process was performed using a bead mill to prepare composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a bead mill in the same manner as described above. Subsequently, the coal tar pitch was added to the composite particles B and mixed with a blender mixer. This mixed powder was heat-treated at 800 ° C. in a nitrogen atmosphere to form a carbonaceous layer on the surface of the composite particle B. Thereafter, the composite particles B on which the carbonaceous layer is formed and the carbonaceous particles (average particle size = 18 μm) whose primary particles are graphite (d ₀₀₂ = 0.3358 nm) are mixed so as to be uniform to produce a negative electrode material. did.
The average values of r and l of the silicon particles used in Example 4, the type and average particle size of the conductive fine particles, the cumulative pore volume and saturated tap density of the carbonaceous particles, and the silicon contained in the composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Example 5>
(Preparation of negative electrode material)
Silicon particles (in the form of flakes) and acetylene black were mixed so as to be uniform, and a mechanical alloying process was performed using a bead mill to prepare composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a bead mill in the same manner as described above. Next, polyvinyl chloride was added to the composite particles B and mixed with a blender mixer. This mixed powder was heat-treated at 800 ° C. in a nitrogen atmosphere to form a carbonaceous layer on the surface of the composite particle B. Thereafter, the composite particles B having the carbonaceous layer and the carbonaceous particles (average particle size = 20 μm) of which the primary particles are graphite (d ₀₀₂ = 0.3358 nm) are mixed uniformly to produce a negative electrode material. did.
The average value of r and l of silicon particles used in Example 5, the type and average particle size of conductive fine particles, the cumulative pore volume and saturated tap density of carbonaceous particles, and silicon contained in the composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Example 6>
(Preparation of negative electrode material)
Silicon particles (in the form of flakes) and acetylene black were mixed so as to be uniform, and a mechanical alloying process was performed using a bead mill to prepare composite particles A. Next, graphite particles (average particle size = 5 μm) were added to the composite particles A and mixed so as to be uniform, and composite particles B were prepared by performing mechanical alloying using a bead mill in the same manner as described above. Next, polyvinyl chloride was added to the composite particles B and mixed with a blender mixer. This mixed powder was heat-treated at 800 ° C. in a nitrogen atmosphere to form a carbonaceous layer on the surface of the composite particle B. Thereafter, the composite particles B having the carbonaceous layer and the carbonaceous particles (average particle size = 20 μm) of which the primary particles are graphite (d ₀₀₂ = 0.3358 nm) are mixed uniformly to produce a negative electrode material. did.
The average value of r and l of the silicon particles used in Example 6, the type and average particle size of the conductive fine particles, the cumulative pore volume and saturated tap density of the carbonaceous particles, and the silicon contained in the composite particles B and the whole negative electrode material The proportion of particles is shown in Table 1.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

<Comparative Example 1>
(Preparation of negative electrode material)
A commercially available graphite powder (d ₀₀₂ = 0.3358 nm, average particle size = 20 μm) and silicon particles (average particle size = 1 μm) were mixed uniformly to produce a negative electrode material.
Table 1 shows the average values of r and l of the silicon particles used in Comparative Example 1, the cumulative pore volume and saturation tap density of the carbonaceous particles, and the ratio of the silicon particles contained in the whole negative electrode material. Note that “-” in Table 1 means that the corresponding item does not exist.

(Production of lithium ion secondary battery)
Using the negative electrode material prepared above, a cylindrical lithium battery shown in FIG. 6 was prepared according to the procedure described above. About this lithium ion secondary battery, after confirming initial stage battery capacity, the cycle test was done. The results are shown in Table 1.

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 6 have a large battery capacity compared to the lithium ion secondary battery of Comparative Example 1 and a high capacity retention rate after 100 cycles, which is favorable. Cycle characteristics were obtained.

11 Silicon particles 12 Composite particles A
13 Conductive Fine Particle 14 Composite Particle B
15 Graphite particle 16 Composite particle B covered with carbonaceous layer
17 carbonaceous layer 18 carbonaceous particle 19 primary particle 20 pore 21 positive electrode 22 negative electrode 23 separator 24 positive electrode terminal tab 25 negative electrode terminal tab 26 battery can 27 gasket 28 internal pressure valve 29 PTC (positive temperature coefficient resistance) element 30 positive electrode lid 31 positive electrode Inner lid 32 Negative electrode current collector

Claims (13)

  A negative electrode for a lithium ion secondary battery comprising composite particles A of silicon particles and conductive fine particles, wherein the ratio r (= t / l) of the longest diameter l to the shortest diameter t of the silicon particles is 0.5 or less. Wood.   2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein a ratio r (= t / l) of the longest diameter l and the shortest diameter t of the silicon particles is 0.001 or more.   The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein a longest diameter l of the silicon particles is 10 nm to 5000 nm.   The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein a content of the silicon particles in the composite particles A is 40% by mass to 85% by mass.   5. The negative electrode material for a lithium ion secondary battery according to claim 1, comprising composite particles B of the composite particles A and graphite particles.   The negative electrode material for a lithium ion secondary battery according to claim 5, wherein a part or all of the surface of the composite particle B is coated with a carbonaceous material.   The negative electrode material for a lithium ion secondary battery according to claim 5 or 6, wherein the content of the silicon particles in the composite particle B is 40% by mass to 85% by mass.   The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 7, further comprising carbonaceous particles having pores therein. In the carbonaceous particle size cumulative pore volume of pores in the range of 0.1μm~1μm is at ^{0.05 × 10 -3 m 3 /kg~0.4×10 -3} m 3 / kg The negative electrode material for lithium ion secondary batteries according to claim 8. The carbonaceous particles is graphite particles, saturation tap density of the graphite particles is ^{0.4g / cm 3 ~0.9g / cm 3} , for a lithium ion secondary battery according to claim 8 or claim 9 Negative electrode material.   The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 10, wherein a content of the silicon particles is 3% by mass to 50% by mass.   The negative electrode for lithium ion secondary batteries containing the negative electrode material for lithium ion secondary batteries of any one of Claims 1-11.   The lithium ion secondary battery containing the negative electrode for lithium ion secondary batteries of Claim 12, a positive electrode, and electrolyte.