TW201742298A - Negative electrode material for lithium ion secondary battery, negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Abstract

The present invention provides a negative electrode material for Li ion secondary batteries, which is capable of sufficiently suppressing reductive decomposition of the electrolyte solution by an active material during the charging, while being capable of suppressing expansion of Si particles during the charging, and which enables the achievement of high discharge capacity that is higher than the theoretical capacity of graphite and excellent cycle characteristics. A negative electrode material for Li ion secondary batteries according to the present invention is configured such that aggregated particles have an average particle diameter of 0.5-10 [mu]m, each of said aggregated particles being obtained by forming, on the surfaces of Si particles, a coating film of an Li-containing oxide that is formed from a composition containing Li and at least one metal element M selected from among Si, Al, Ti and Zr, and by having a conductive binder material adhere to the surface of the coating film.

Description

Anode material for lithium ion secondary battery, anode for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to a negative electrode material for a lithium ion secondary battery which is coated with a Li ion conductive metal oxide on a surface of a Si particle which can be alloyed with Li, and further has a conductive surface on a surface of a Li ion conductive metal oxide film. Sexual bonding substance.

Lithium ion secondary batteries are widely used as power sources for electronic equipment because of their excellent characteristics of high voltage and high energy density. In recent years, the development of miniaturization and high performance of electronic devices has increased the demand for higher energy density of lithium ion secondary batteries.

The current lithium ion secondary battery uses LiCoO ₂ for the positive electrode and graphite for the negative electrode. The graphite of the negative electrode is excellent in reversibility of charge and discharge, but its discharge capacity has reached a value close to the theoretical value of 372 mAh/g of the intercalation compound LiC ₆ . Therefore, in order to achieve a higher energy density, it is necessary to develop a negative electrode material having a larger discharge capacity than graphite.

Therefore, as a negative electrode material for replacing graphite, Si and SiO have attracted attention as an active material which forms an alloy with Li having a discharge capacity far exceeding that of graphite. Since the Si-based negative electrode system has a large volume expansion due to alloying at the time of charging, it is likely to be deteriorated, and as a countermeasure against the expansion, the atomization of the particles is effective. However, by atomization, the surface of the active material becomes active, and the reductive decomposition of the electrolytic solution is promoted during charging, and therefore, practical cycle characteristics are not obtained.

Patent Document 1 proposes a carbon material which is a metal-encapsulated hollow carbon particle containing Si in a void in the interior, and is characterized in that Si is coated with a nano particle of Cu or Ni. However, only by the surface of Si being coated with a metal element imparting conductivity, the metal element not only reduces the conduction of Li ions, but also suppresses the accumulation of decomposition products due to insufficient reduction of the reductive decomposition of the electrolyte during charging. The electrode is expanded to cause cycle deterioration. Further, the bulk density of the hollow carbon particles becomes high, and the density of the negative electrode cannot be increased.

Patent Document 2 proposes a negative electrode material obtained by carbon-coating a mixture of a composite containing a nano-sized Si particle and a carbon material. However, in the present production method, since the amount of the oxide surrounding Si is excessively between about 35 and 88% by mass, the resistance of conduction of Li ions and electron conduction is increased, and the capacity and rapid charge and discharge characteristics are deteriorated.

Patent Document 3 proposes a negative electrode material, which The surface of the Si-based Si particles is bonded to a compound which inhibits swelling and has conductivity, and a resin such as a conductive polyimide or the like is used as a binder to granulate the Si particles. However, the compound bonded to the surface of Si not only lowers the conduction of Li ions, but also suppresses the reductive decomposition of the electrolytic solution during charging, thereby causing the electrode to swell and cause cycle deterioration due to the accumulation of the decomposition product residue.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 5,359,031

[Patent Document 2] Japanese Patent No. 5667609

[Patent Document 3] Japanese Patent No. 5525503

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a negative electrode material for a lithium ion secondary battery which is capable of suppressing reductive decomposition of an electrolyte during charging by coating a surface of a Si negative electrode active material with a Li-containing oxide. Further, by restraining the surface of the Li-containing oxide film with a conductive binder, the charge expansion of the Si negative electrode active material is alleviated, so that a high discharge capacity exceeding the theoretical capacity of graphite and excellent initial charge and discharge efficiency are exhibited. And cycle characteristics.

In the present invention, it has been found that a film containing Li oxide containing Li and other specific metal elements with high Li ion conductivity is coated on the surface of Si particles as an active material, and is further restrained by a conductive adhesive substance. The surface of the Li-containing oxide film is adjusted, and the size of the aggregated particles of the above-mentioned active material is adjusted to fine particles of a single micrometer, whereby high discharge capacity and good cycle characteristics are obtained.

It is presumed that the reason why the high discharge capacity and the cycle characteristics are obtained as described above is that the surface of the Si particles as the active material is coated with the above Li-containing oxide film having high Li ion conductivity and stability. The contact between the active material and the electrolytic solution is restricted, and the reductive decomposition of the electrolytic solution due to the active material during charging is suppressed, and the charge and discharge reaction accompanying the conduction of Li ions is not inhibited, and further, the surface of the film containing the Li oxide is prevented. By restraining the conductive adhesive material, the charge expansion of the active material can be alleviated, and the size of the aggregated particles of the active material can be adjusted to a single micron fine particle to locally expand and disperse the electrode. However, the invention is not limited to such mechanisms.

That is, the present invention provides the following.

(1) A negative electrode material for a lithium ion secondary battery, which is a coating material having a film containing Li oxide on the surface of the Si particle and further having conductivity on the surface of the film, and the film containing the Li oxide is composed of a composition comprising Li and at least one metal element M selected from the group consisting of Si, Al, Ti, and Zr, wherein the content of the Li-containing oxide is 10% by mass or less, and the content of the conductive binder is 10% by mass or more, the above-mentioned film containing Li oxide and conductive adhesive The aggregated particles of the aggregated Si particles have an average particle diameter of 0.5 to 10 μm.

(2) The negative electrode material for a lithium ion secondary battery according to (1) above, wherein the conductive adhesive material contains carbon.

(3) A negative electrode for a lithium ion secondary battery, which comprises the negative electrode material according to (1) or (2) above.

(4) A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to (3) above.

The negative electrode material for a lithium ion secondary battery of the present invention can sufficiently suppress excessive reduction and decomposition of the electrolytic solution due to the active material during charging, and further suppress the fine granulation of the conductive bonding material and the aggregated particles. The charge expands, thus exhibiting a high discharge capacity exceeding the theoretical capacity of graphite and excellent cycle characteristics.

1‧‧‧Outer cans

2‧‧‧Negative mixture

3‧‧‧Outer cans

4‧‧‧relative electrode

5‧‧‧Separators

6‧‧‧Insulation gasket

7a, 7b‧‧‧ collector

10A, 10B‧‧‧ aggregated particles

20‧‧‧Si particles

30‧‧‧Li-containing oxide

40‧‧‧ Conductive bonding materials

[Fig. 1] is a schematic view showing a structure of aggregated particles composed of Si particles having a coating film containing Li oxide and further having a conductive material on the surface of the film.

[Fig. 2] is a cross-sectional view of a button type secondary battery for unipolar evaluation.

Hereinafter, specific embodiments of the present invention will be described.

[Anode material for lithium ion secondary battery of the present invention]

The negative electrode material for a lithium ion secondary battery of the present invention can form a film containing a Li oxide having a stable and high Li ion conductivity by forming a surface of the Si particle as an active material, thereby restricting contact between the active material and the electrolytic solution to suppress At the time of charging, the electrolytic solution is decomposed and decomposed by the active material, and since the charge-discharge reaction accompanying the conduction of Li ions is not inhibited, there is no decrease in the discharge capacity, and the charge-discharge reaction at the high current also exhibits excellent characteristics. The film thickness of the film is preferably 10 nm or less. If it exceeds 10 nm, the resistance of Li ion conduction and electron conduction may increase, and the responsiveness of the electrode reaction may deteriorate. The film thickness of the film is preferably 0.5 to 10 nm. If it is thinner than 0.5 nm, there is a fear that the contact between the active material and the electrolytic solution cannot be sufficiently prevented. The film thickness of the film is more preferably 1 to 5 nm. The content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is affected by the specific surface area of the Si particles as the active material. In the case where the film thickness of the film is in the above range, the content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is preferably such that the coating amount by the Li-containing oxide is used. 10% by mass or less. When the content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is more than 10% by mass, the electric resistance of Li ion conduction may increase, and the responsiveness of the electrode reaction may deteriorate. The content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is more preferably 0.5~ 10% by mass. When the content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is less than 0.5% by mass, there is a fear that the contact between the active material and the electrolytic solution cannot be sufficiently prevented. The content of the Li-containing oxide in the negative electrode material for a lithium ion secondary battery of the present invention is more preferably from 1 to 5% by mass.

In the negative electrode material for a lithium ion secondary battery of the present invention, the film formed on the surface of the Si particles as the active material is composed of a Li-containing oxide which is stable and has high Li ion conductivity. The metal oxide containing a matrix of Li is one or more selected from the group consisting of SiO ₂ , Al ₂ O ₃ , TiO ₂ and ZrO ₂ .

The Li-containing oxide of the present invention preferably has a composition of M and Li = 0.1 to 20 in terms of a molar ratio of Li and a metal element M, more preferably 0.2 to 10. When the composition is M/Li<0.1 in terms of the molar ratio, Li ₂ O which is free from the film containing the Li oxide is precipitated, and defects are likely to occur, and there is a possibility that the contact of the active material with the electrolysis cannot be sufficiently restricted. When the composition of M/Li>20 is expressed by the molar ratio, there is a fear that the resistance of Li ion conduction increases, and the responsiveness of the electrode reaction deteriorates.

The Li phase-containing crystal phase of the present invention is affected by the heat treatment temperature. In general, when the heat treatment temperature is 200 to 600 ° C, crystallization does not proceed and is amorphous, and when it is 600 ° C or more, crystal formation starts. Specifically, when the Li-containing oxide contains Si as the metal element M, it is an amorphous or crystalline phase of SiO ₂ (scaly quartz type), Li ₄ SiO ₄ , Li ₂ SiO ₃ , and Li ₂ Si ₂ O. ₅ single phase or mixed phase. In the case where the Li-containing oxide contains Al as the metal element M, it is a single phase or a mixed phase of Al ₂ O ₃ (γ type), LiAl ₅ O ₈ , LiAlO ₅ , Li ₅ AlO _{4 which} is amorphous or crystalline. . In the case where Li-containing oxide contains Ti as the metal element M, it is a single phase of TiO ₂ (anatase type, rutile type), Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO _{3 which} is amorphous or crystalline. Or mixed phase. When the Li-containing oxide contains Zr as the metal element M, it is amorphous or crystalline phase of ZrO ₂ (monoclinic crystal, tetragonal crystal), Li ₂ ZrO ₃ , Li ₆ Zr ₂ O ₇ , Li ₈ ZrO ₆ Mixed phase or single phase.

Moreover, when it is necessary to impart conductivity to the film containing Li oxide of the present invention, the film may contain a conductive material.

In the negative electrode material for a lithium ion secondary battery of the present invention, a conductive material having conductivity is adhered to the surface of the Li-containing oxide film coated on the active material Si particles. In the conductive adhesive material, the charge expansion is relaxed by restraining the Si particles of the active material, and the size of the aggregated particles composed of the Si-coated active material is adjusted to a fine particle having an average particle diameter of 0.5 to 10 μm to form an electrode. The local expansion and dispersion, in turn, imparts electron conduction. When the average particle diameter of the aggregated particles exceeds 10 μm, the influence of the charge expansion is locally increased, and the deterioration of the electrode is promoted. When the average particle diameter is less than 0.5 μm, the handleability of the powder is deteriorated. The average particle diameter is more preferably in the range of 1 to 5 μm. The particle shape may be any of a spherical shape, a flat shape, and a broken shape, and is not particularly limited.

The matrix of the conductive binder is one or more selected from the group consisting of carbon, inorganic materials, and resins, and the conductive material exhibiting conductivity is obtained by dispersing carbon or graphite in the matrix. Therefore, the electrically conductive bonding material contains carbon.

The carbon which is a matrix of the binder of the present invention is preferably a glass which is a low-expansion and high-capacity hard carbon or inorganic substance (for example, sulfide glass Li ₁₀ GeP ₂ S ₁₂ ), a crystalline oxide, and a resin. Polyimine, anthrone or the like, but is not limited thereto. The hard carbon system of the carbon substrate can be obtained by heat-treating a precursor material such as a phenol resin or an infusible pitch in an inert atmosphere at 600 to 1200 °C. The inorganic matrix can be obtained by a mechanochemical method, a sol-gel method or the like from a sulfide or an oxide of a raw material. In the case of the sol-gel method, the hydroxide of the intermediate is heat-treated at 600 to 1200 ° C in an inert atmosphere to form an oxide. The resin matrix can be obtained by drying the varnish of the precursor and then thermally hardening it at 200 to 500 °C.

The conductivity imparting to the bonding material can be exhibited by dispersing a conductive material of carbon or graphite in the matrix material, and the shape of the conductive material can be any of fibrous, scaly, and tufted. There is no special limit. Specific conductive materials are carbon nanotubes, flake graphite, earthy graphite, hard carbon, carbon black, and the like.

The content of the conductive adhesive material of the present invention is preferably 10% by mass or more. When the content of the conductive binder is less than 10% by mass, there is a fear that the charge expansion of the coated Si particles cannot be sufficiently alleviated. When the content of the conductive binder is more than 50% by mass, the resistance of Li ion conduction may increase, and the responsiveness of the electrode reaction may deteriorate. The content of the conductive adhesive substance of the present invention is more preferably 10 to 50% by mass. When the content of the conductive binder is more than 50% by mass, the resistance of Li ion conduction may increase, and the responsiveness of the electrode reaction may deteriorate.

[The raw material of the negative electrode material for a lithium ion secondary battery of the present invention] <active substance>

In the negative electrode material for a lithium ion secondary battery of the present invention, Si particles are used as an active material. The Si crystal phase system may be either amorphous or crystalline, and is not particularly limited.

The average particle diameter of the Si particles is preferably 1 μm or less. When the average particle diameter exceeds 1 μm, the influence of the charge expansion becomes locally large, and the deterioration of the electrode is promoted. The average particle diameter is preferably 0.01 μm or more. When the average particle diameter is less than 0.01 μm, the activity of the surface of the Si particle as the active material is high, and it is difficult to suppress the reductive decomposition of the electrolytic solution during charging by the film. The average particle diameter is more preferably in the range of 0.01 μm to 0.2 μm. The shape of the particles is not particularly limited as long as it is a spherical shape, a flake shape or a fiber form synthesized by a vapor phase method, and a crushed shape obtained by pulverization in a block form.

<Li-containing oxide precursor solution>

In a solution (Li-containing oxide precursor solution) in which a Li compound as a precursor of a Li-containing oxide and a compound of a metal element M selected from at least one of Si, Al, Ti, and Zr are dispersed, When the solvent is an organic solvent, it is preferably a Li compound which is a Li source, and is preferably a compound of a metal element M which is a metal element M source, which is dissolved in an organic solvent, such as Li acetate, Li nitrate, Li chloride or the like. Alkoxides, nitrates, chlorides, etc. in organic solvents. Among the alkoxides, those in which the metal element M is Al, Ti, or Zr are unstable due to easy hydrolysis, and therefore are preferably stabilized by a chelating agent. Acetylacetate in the chelating agent Ethyl ester, acetamidine acetone, triethanolamine, etc., but it is not limited to this. As the organic solvent, ethanol, isopropyl alcohol, ethyl acetate, toluene or the like can be used. When the solvent is water, the compound which is a source of Li is preferably a compound of a metal element M which is a source of the metal element M, which is dissolved in water by a compound of Li, Li, Li, Li, etc. dissolved in water. Nitrate, chloride, oxyacid salt, peroxy acid, and the like. In the case where the metal element M is Si, an aqueous solution of citric acid Li can also be used.

<Electrically conductive bonding substance>

The raw material of carbon which is a matrix of the binder of the present invention is preferably a phenol resin obtained by heat treatment to form hard carbon, infusible pitch or the like. The phenol resin may be either a resol type or a novolak type. The asphalt is not melted. For example, the coal tar pitch may be heat-treated at 200 to 600 ° C in the air to crosslink the polycyclic aromatic compound in the pitch with oxygen. When the raw material of the inorganic substrate is produced by a mechanochemical method, it is preferably a powder containing a sulfide or an oxide of a constituent element, and when it is produced by a sol-gel method, it is preferably soluble in the material. A compound such as an alkoxide, a nitrate or a chloride in a solvent constituting the element. In the case of a polyimide varnish, a raw material of a resin matrix can be obtained by dissolving a polyamic acid obtained by polymerizing a tetracarboxylic dianhydride and a diamine as a raw material, and a molar polymerization. In the case of an anthrone varnish, a three-dimensional polymer having a high degree of branching which is composed of a decane bond such as a methyl group or a phenyl group can be dissolved in a solvent.

As the conductive material that imparts conductivity to the bonding material, a carbon nanotube, flake graphite, earthy graphite, hard carbon, carbon black, or the like can be used.

[Method for Producing Anode Material for Lithium Ion Secondary Battery of the Present Invention]

The method for producing a negative electrode material for a lithium ion secondary battery of the present invention is a Li compound in which a precursor material containing Li oxide is dispersed, and a metal element M selected from at least one selected from the group consisting of Si, Al, Ti, and Zr. In the solution of the compound (including the Li oxide precursor solution), Si particles which are alloyed with Li are added, dried, and then heat-treated at a temperature ranging from 200 to 1200 ° C, and further, a conductive bonding substance or a precursor substance is attached to The surface of the Li-containing oxide film is subjected to heat treatment at a temperature of 200 to 1200 ° C to adjust the aggregated particles composed of the coated Si particles to fine particles having a size of a single micron.

a solution (Li-containing oxide precursor solution) in which a Li compound as a precursor of a Li-containing oxide and a metal element M of at least one selected from Si, Al, Ti, and Zr are dispersed in a metal element In the case where M is Al, Ti or Zr, it is preferred to chelate the alkoxide of the element in an alcohol solvent with a chelating agent: ethyl acetate, ethyl acetonide, triethanolamine or the like. It stabilizes and suppresses the rapid hydrolysis reaction to improve film formability. The blending ratio of the chelating agent is preferably a chelating agent/alkoxide = 1 to 2 in terms of a molar ratio. When the molar ratio is less than 1, the unchelated alkoxide remains and the stability is poor. If the molar ratio is more than 2, the unnecessary chelating agent which does not undergo chelation will be excessive. Ground residue. The chelated alkoxide solution is more preferably added with water to appropriately promote hydrolysis in order to further improve film formability. The amount of water added is preferably water/alkoxide = 1 to 2 in terms of mol ratio. If the molar ratio is not When it is 1 , the progress of the hydrolysis may be insufficient, and the organic component may easily remain in the film formation. When the molar ratio is more than 2, the hydrolysis may be excessively performed to cause precipitation in the solution. Next, a solution in which a precursor material containing Li oxide is dispersed is prepared by dissolving a Li compound in a solvent and mixing it in the above solution. Further, in the case where the metal element M is Si, the chelating agent for alkoxide is not required to be stabilized, and after the hydrolysis is promoted by adding water and an acid catalyst, the Li compound is dissolved in a solvent and mixed in the above solution. A solution in which a precursor material containing Li oxide is dispersed can be prepared.

Next, Si particles which can be alloyed with Li are added to the above solution containing the precursor material containing Li oxide. The Si particle system may be in any form of a dry powder or a dispersed slurry. The dry powder can be obtained by removing the solvent from the raw material Si after dry pulverization or wet pulverization. The dispersion slurry system can be obtained by wet pulverization. The dispersion solvent containing the precursor of the Li oxide precursor and the slurry system of the Si particles remove the solvent to form a film containing the precursor of the Li oxide precursor on the surface of the Si particles. For the removal of the solvent, a method such as spray drying or reduced-pressure drying can be used. The film containing the precursor of the Li oxide precursor is preferably heat-treated at 200 to 1200 ° C in order to promote hardening. If it is less than 200 ° C, the hardness of the film and the adhesion to the Si particles are weak. When the temperature exceeds 1200 ° C, the reaction between the film and the Si particles proceeds, and the discharge capacity is lowered. The environment during the heat treatment is preferably a non-oxidizing atmosphere. More preferably, a non-reactive gas such as Ar or a low-reactivity gas such as N ₂ is used as a main component, and a concentration of an oxidizing gas such as O ₂ is 1000 ppm or less.

Next, the conductive binder is adhered to the Si particles coated with the Li-containing oxide to prepare aggregated particles having an average particle diameter of 0.5 to 10 μm. In the case where the coated Si particles are dried and granulated by spray drying, it is preferred to impregnate/coat the conductive binder to the granules, and after drying, heat-treat at 200 to 1200 °C. Fig. 1 (1) shows a schematic view of the aggregated particles 10A obtained by the above-described procedure, in which the film having the Li-containing oxide 30 on the surface and the Si particles 20 having the conductive binder 40 on the surface of the film are aggregated. . In the case where the coated Si particles are prepared by drying/crushing under reduced pressure, it is preferred to add a dry powder of the coated Si particles to a solution of the precursor before the conductive binder is dissolved to prepare a slurry. Drying is carried out by spray drying, followed by heat treatment at 200 to 1200 °C. Fig. 1 (2) shows a schematic view of the aggregated particles 10B obtained by the above-described procedure, in which the film having the Li-containing oxide 30 on the surface and the Si particles 20 having the conductive binder 40 on the surface of the film are aggregated. . The environment during the heat treatment is preferably a non-oxidizing atmosphere. More preferably, a non-reactive gas such as Ar or a low-reactivity gas such as N ₂ is used as a main component, and a concentration of an oxidizing gas such as O ₂ is 1000 ppm or less.

The negative electrode material for a lithium ion secondary battery of the present invention may be used in combination with a carbon material such as a different type of graphite material or hard carbon in order to adjust battery characteristics such as capacity, density, and efficiency of the electrode to be produced.

[negative electrode]

The negative electrode for a lithium ion secondary battery of the present invention contains the above lithium ion A negative electrode for a lithium ion secondary battery of a negative electrode material for secondary batteries.

The negative electrode for a lithium ion secondary battery of the present invention is produced by a usual method for forming a negative electrode. In the production of the negative electrode, a negative electrode mixture prepared by adding a binder and a solvent to the negative electrode material for a lithium ion secondary battery of the present invention is preferably applied to a current collector. The binder is preferably one which exhibits chemical and electrochemical stability to the electrolyte. For example, a fluorine resin powder such as polytetrafluoroethylene or polyvinylidene fluoride, a resin powder such as polyethylene or polyvinyl alcohol, or a carboxy group can be used. Methyl cellulose, etc. You can also use these together. The binder is usually a ratio of 1 to 20% by mass based on the total amount of the negative electrode mixture.

More specifically, first, the negative electrode material for a lithium ion secondary battery of the present invention is adjusted to a desired particle size by classification or the like, and a binder and a solvent are mixed to prepare a slurry-form negative electrode mixture. In other words, the negative electrode material for a lithium ion secondary battery of the present invention, a binder, and a solvent such as water, isopropyl alcohol, N-methylpyrrolidone, or dimethylformamide are used, and a known mixer and a mixture are used. The slurry is prepared by mixing and stirring with a machine, a kneading machine, a kneader or the like. The slurry system is applied to one side or both sides of the current collector and dried to obtain a negative electrode layer in which the negative electrode mixture layer is uniformly and strongly adhered. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 20 to 100 μm.

The shape of the current collector used in the production of the negative electrode is not particularly limited, but is a mesh shape such as a foil shape, a mesh, or a porous metal mesh. The material of the current collector is preferably copper, stainless steel, nickel or the like, and the thickness of the current collector is usually 5 to 20 μm.

In addition, the negative electrode for a lithium ion secondary battery of the present invention can also be used without damage Within the scope of the object of the present invention, a graphite material, a carbonaceous material such as hard carbon, or a conductive material such as CNT is mixed.

[Lithium ion secondary battery]

The lithium ion secondary battery of the present invention is laminated in the order of the negative electrode for a lithium ion secondary battery, a positive electrode, and a nonaqueous electrolyte, for example, a negative electrode, a nonaqueous electrolyte, and a positive electrode, and is housed in a battery. It is made up of exterior materials. In the case where the nonaqueous electrolyte is dissolved in the solvent, a separator is disposed between the negative electrode and the positive electrode. The structure, shape and form of the lithium ion secondary battery of the present invention are not particularly limited, and may be arbitrarily selected from the group consisting of a cylindrical type, an angular type, a coin type, a button type, and a laminate type depending on the application. In order to obtain a sealed non-aqueous electrolyte battery having higher safety, it is preferable to use a means for sensing an increase in the internal pressure of the battery to interrupt the current when an abnormality such as overcharge occurs.

<positive>

The positive electrode is formed by, for example, applying a positive electrode mixture composed of a positive electrode material, a binder, and a solvent to the surface of the current collector. The positive electrode active material is preferably one selected from a lithium-containing transition metal oxide capable of adsorbing/desorbing a sufficient amount of lithium. The lithium-containing transition metal oxide-based composite oxide of lithium and a transition metal may further contain four or more elements. The composite oxides may be used singly or in combination of two or more. Specifically, it has LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ , LiFePO _{4 ,} or the like.

The positive electrode active material may be used singly or in combination of two or more kinds. When the positive electrode is formed, various additives such as a conventionally known conductive agent or a binder can be suitably used.

The shape of the current collector is not particularly limited, but a mesh shape such as a foil or a mesh or a porous metal mesh can be used. The material of the current collector is aluminum, stainless steel, nickel, etc., and the thickness is usually 10 to 40 μm.

<nonaqueous electrolyte>

As the nonaqueous electrolyte used in the lithium ion secondary battery of the present invention, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) of an electrolyte salt used in a usual nonaqueous electrolytic solution can be used. , LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiN(CF ₃ CH ₂ OSO ₂ ) ₂ , LiN(CF ₃ CF ₂ OSO ₂ ) ₂ , LiN(HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ , LiN((CF ₃ ) ₂ CHOSO ₂ ) ₂ , LiB[{C ₆ H ₃ (CF ₃ ) ₂ }] ₄ , LiAlCl ₄ , LiSiF _6, etc. lithium salt. From the viewpoint of oxidation stability, LiPF ₆ and LiBF _{4 are particularly} preferred. The electrolyte salt concentration in the electrolyte is preferably from 0.1 to 5 mol/L, more preferably from 0.5 to 3.0 mol/L.

The nonaqueous electrolyte may be a liquid nonaqueous electrolyte, or may be a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the case of the former, the nonaqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the nonaqueous electrolyte battery is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte battery. It is composed of batteries.

As the electrolytic solution for preparing the nonaqueous electrolyte liquid, a carbonate such as ethylene carbonate, propylene carbonate, dimethyl carbonate or diethyl carbonate, or a 1,1- or 1,2-dimethoxy group can be used. Ethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-two 4-methyl-1,3-di An ether such as anisole or diethyl ether, a thioether such as cyclobutyl hydrazine or methylcyclobutyl fluorene, a nitrile such as acetonitrile, chloronitrile or propionitrile, trimethyl borate, tetramethyl phthalate or nitrate. Methane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzamidine chloride, benzamidine bromide, tetrahydrothiophene, dimethyl Chiazone, 3-methyl-2- An aprotic organic solvent such as oxazolone, ethylene glycol or dimethyl sulfite. Further, an additive may be added in order to prevent deterioration of the battery by reductive decomposition of the electrolytic solution during charging. The known additives include fluoroethylene carbonate (FEC), carbonic acid vinyl ester (VC), and vinyl sulfite (ES), and are not limited thereto. The amount of addition is usually about 0.5 to 10% by mass.

<spacer>

In the lithium ion secondary battery of the present invention, when the nonaqueous electrolyte is dissolved in the solvent, a separator is disposed between the negative electrode and the positive electrode. The material of the separator is not particularly limited, and for example, a woven fabric, a non-woven fabric, a microporous film made of a synthetic resin, or the like can be used. The material of the separator is preferably a microporous film made of a synthetic resin, and among them, the polyolefin-based microporous film has properties such as thickness, film strength, and film resistance. Specifically, it is preferably a microporous film made of polyethylene or polypropylene, or a microporous film which is composited by the like. Wait.

[Examples]

Next, the present invention will be specifically described by way of examples, but the invention is not limited to the examples. Further, in the following examples and comparative examples, as shown in Fig. 2, a unipolar evaluation consisting of a current collector (negative electrode) 7b and a counter electrode (positive electrode) 4 made of a lithium foil was prepared. In the button type secondary battery, the negative electrode mixture 2 having the negative electrode material of the present invention was adhered to at least a part of the surface of the current collector (negative electrode) 7b. The actual battery system can be fabricated in accordance with the teachings of the present invention in accordance with the teachings of the present invention.

The assay used in the examples is as follows.

[assay] (1) Determination of average particle size

The average particle diameter is a particle diameter at which the cumulative volume percentage measured by a laser diffraction type particle size meter is 50%.

(2) Content ratio of Li containing Li oxide to metal element M selected from at least one of Si, Al, Ti, and Zr

The content of the metal element M is defined by the amount of addition. In the case of performing quantitative measurement, ICP emission analysis, atomic absorption analysis, or the like can be performed.

(3) Battery characteristics

The evaluation battery prepared by the following configuration was subjected to the charge and discharge test shown below at a temperature of 25 ° C, and the initial charge and discharge characteristics, the rapid charge rate, the rapid discharge rate, and the cycle characteristics were calculated.

<Initial charge and discharge characteristics>

After constant current charging of 0.2 C (0.9 mA) is reached until the circuit voltage reaches 0 mV, the voltage is switched to constant voltage charging when the circuit voltage reaches 0 mV, and charging is further continued until the current value becomes 20 μA. The charging capacity per unit mass (unit: mAh/g) was determined from the amount of energization therebetween. Thereafter, it was maintained for 120 minutes. Next, constant current discharge was performed at a current value of 0.2 C until the circuit voltage reached 1.5 V, and the discharge capacity per unit mass (unit: mAh/g) was determined from the amount of energization therebetween. The initial charge and discharge efficiency is calculated by the following formula (1).

In this test, the process of adsorbing lithium ions on the negative electrode material was set as charging, and the process of detaching from the negative electrode material was set as discharge, and the results are shown in Table 1.

In addition, the 1C of the charge/discharge rate is an index of the relative ratio of the flow rate at the time of charge and discharge to the battery capacity, and the unit having the capacity of the nominal capacity value is subjected to constant current charge and discharge, and the charge and discharge are completed in exactly one hour. Current value.

Formula (1)... Initial charge and discharge efficiency (%) = (discharge capacity / charge capacity) × 100

<cycle characteristics>

The evaluation battery was prepared and evaluated for each unit mass of discharge capacity and initial charge and discharge efficiency, and evaluation was performed as follows.

After the constant current charging of 1 C is performed until the circuit voltage reaches 0 mV, the battery is switched to constant voltage charging, and charging is further continued until the current value becomes 20 μA, and then the rest is 120 minutes. Next, the operation of performing constant current discharge until the circuit voltage reached 1.5 V was repeated 30 times with a current value of 1 C. The cycle characteristics were calculated from the discharge capacity per unit mass obtained using the following formula (2) to evaluate the capacity retention rate. Each efficiency is calculated and evaluated by the following formula (3) from the charge capacity and discharge capacity in each cycle. Further, in each efficiency, the sum of the charge amount of the active material and the charge consumption amount used in the reductive decomposition of the electrolytic solution is a denominator. Therefore, the larger the display value, the more difficult the electrolyte solution is to be decomposed.

Formula (2)... Capacity retention ratio (%) = (discharge capacity in 30 cycles / discharge capacity in the first cycle) × 100

Equation (3)...Efficiency (%) = (discharge capacity in 30 cycles / charge capacity in 30 cycles) × 100

[Production of negative electrode material] (Example 1)

A first solution was prepared by dissolving 0.02 mol of Al-sec butoxide and 0.02 mol of ethyl acetate in an isopropanol solvent, and then adding a solution of 0.002 mol of ethanol dissolved in Li diacetate to the first solution. In the middle to make a second solution. Next, 29 g of Si particles having an average particle diameter of 0.15 μm was added to the second solution to remove the solvent, and thereafter, the nitrogen was not oxygenated. The firing was carried out at 1000 ° C in a chemical environment to obtain Si particles having a film containing Li and a film containing Li as a metal element M. Next, the above-mentioned coated Si particles were added to an aqueous solution in which a resol type phenol resin solution (nonvolatile component: 71% by mass) as a precursor of the conductive binder was dissolved to prepare a slurry. At this time, it was set as the phenol resin solution / coated Si particle = 1/2 mass ratio. The slurry system was spray-dried by a spray dryer, and then fired at 1000 ° C in a non-oxidizing atmosphere of nitrogen to obtain spherical dry granules.

(Example 2)

A spherical dry granule was obtained in the same manner as in Example 1 except that the Ti-isopropoxide was used instead of the Al-sec butane oxide of Example 1.

(Example 3)

A spherical dry granule was obtained in the same manner as in Example 1 except that the Zr-propoxide was used instead of the Al-sec butoxide of Example 1.

(Example 4)

0.02 mol of Si-methoxide was dissolved in an isopropanol solvent to prepare a first solution, and then an ethanol solution in which 0.002 mol of acetic acid Li dihydrate was dissolved was added to the first solution, and refluxed for 2 hours to prepare a second solution. In addition to the solution, in the same manner as in Example 1, a spherical stem was obtained. Dry granules.

(Example 5)

The polyacrylic acid solution in which carbon black was dispersed was used as the precursor of the conductive adhesive material of Example 1, and the heat treatment after the spray drying treatment by the spray drying apparatus was set to 300 ° C, and the same was carried out. In the same manner as in Example 1, a spherical dry granule was obtained.

(Example 6)

In the same manner as in Example 1, except that the coating amount of the Li-containing oxide was adjusted to 7.0%, spherical dry granules were obtained.

(Example 7)

In the same manner as in Example 1, except that the spray conditions of the spray drying apparatus were adjusted and the average particle diameter of the obtained spherical dry granules was 9.5 μm. Dry granules.

(Comparative Example 1)

A spherical dry granulated body was obtained in the same manner as in Example 1 except that Si particles having an uncoated average particle diameter of 0.15 μm were used.

(Comparative Example 2)

Granulation flattening by spray drying with a spray dryer In the same manner as in Example 1, except that the average particle diameter was adjusted to 15 μm, spherical dry granules were obtained.

(Comparative Example 3)

A spherical dry granulated body was obtained in the same manner as in Example 5 except that the carbon black-containing polyimine resin was used as the binder.

[Production of the working electrode (negative electrode)]

The Si particles having the Li-containing oxide film/conductive binding material, or 6 parts by mass of the Si composite particles of the comparative example, and 94 parts by mass of the spherical natural graphite particles, and the carboxymethyl group as a binder 1.5 parts by mass of cellulose and 1.5 parts by mass of styrene-butadiene rubber were placed in water and stirred to prepare a negative electrode mixture paste. The negative electrode mixture paste was applied to a copper foil having a thickness of 15 μm in a uniform thickness, and the water of the dispersion medium was evaporated and dried at 100 ° C in a vacuum. Next, the negative electrode mixture layer coated on the copper foil was pressurized by a hand press. Further, the copper foil and the negative electrode mixture layer were punched into a cylindrical shape having a diameter of 15.5 mm and pressurized to prepare a working electrode (negative electrode) having a negative electrode mixture layer adhered to the copper foil. The density of the negative electrode mixture layer was 1.65 g/cm ³ .

In the electrolytic solution, LiPF ₆ was dissolved in a mixed solvent of 33% by volume of ethylene carbonate (EC) and 67% by volume of ethylene carbonate (MEC) at a concentration of 1 mol/L to prepare a nonaqueous electrolytic solution. Further, the prepared nonaqueous electrolytic solution was impregnated with a separator of a polypropylene porous body having a thickness of 20 μm to prepare a separator impregnated with an electrolytic solution. Further, the actual battery system can be produced according to a known method in accordance with the concept of the present invention.

[Evaluation of battery production]

Fig. 2 shows a button type secondary battery as a configuration for evaluating the battery.

The outer cup 1 and the outer can 3 are provided with an insulating spacer 6 at the peripheral portion thereof, and the both end edges are riveted and sealed. A collector 7a made of a nickel mesh, a cylindrical counter electrode (positive electrode) 4 made of a lithium foil, and an electrolyte impregnated therein are laminated in this order from the inner surface of the outer can 3. The separator 5 is a battery in which the current collector 7b made of a copper foil is adhered to the negative electrode mixture 2.

In the evaluation battery, the separator 5 impregnated with the electrolyte is sandwiched between the working electrode (negative electrode) composed of the current collector 7b and the negative electrode mixture 2, and the counter electrode 4 adhered to the current collector 7a, and laminated. The current collector 7b is housed in the outer cup 1, the counter electrode 4 is housed in the outer can 3, and the outer cup 1 and the outer can 3 are combined, and the outer cup 1 and the outer can 3 are further combined. The peripheral portion is formed by interposing the insulating spacer 6 and caulking and sealing the both peripheral edges.

The above evaluation results are shown in Table 1. From the examples 1 to 7, it is known that the lithium ion secondary battery using the negative electrode material for a lithium ion secondary battery of the present invention has a high Li ion conductivity, so that the capacity without Si is reduced, and the electrolytic solution is reductively decomposed. It is suppressed, and further, the charge expansion of the Si particles themselves due to the conductive binder and the localized charge expansion due to the aggregated particles of a single micrometer are suppressed, and therefore, the capacity dimension after the cycle The holding rate is high. The uncoated Si particles of Comparative Example 1 were inferior in cycle characteristics because the decomposition of the electrolytic solution was large. In Comparative Example 2, since the average particle diameter of the aggregated particles was large, the expansion of the electrode film was increased and the cycle characteristics were poor. In Comparative Example 3, since the binder was not electrically conductive, the electric resistance of the electron conduction was large and the capacity was low.

[Industrial availability]

The present invention provides a negative electrode material which is coated with a Li oxide-containing film containing Li and other specific metal elements and having a Li ion conductivity, and is coated with a surface of Si particles as an active material, and further conductive. The binding substance binds the surface of the Li-containing oxide film, and the average particle diameter of the aggregated particles of the active material is adjusted to fine particles of 0.5 to 10 μm, thereby sufficiently suppressing the active substance due to charging. The excess reductive decomposition of the electrolytic solution suppresses the charge expansion of the Si particles, and therefore exhibits a high discharge capacity exceeding the theoretical charge capacity of graphite and excellent cycle characteristics. Therefore, the lithium ion secondary battery using the negative electrode material for lithium ions of the present invention satisfies the requirements for high energy density of batteries in recent years, and is useful for miniaturization and high performance of the mounted equipment. The negative electrode material for lithium ion of the present invention exhibits this property and can be used in a compact to large-sized high-performance lithium ion secondary battery.

10A, 10B‧‧‧ aggregated particles

20‧‧‧Si particles

30‧‧‧Li-containing oxide

40‧‧‧ Conductive bonding materials

Claims (4)

A negative electrode material for a lithium ion secondary battery, which is a coating material having a film containing Li oxide on the surface of the Si particle and further having conductivity on the surface of the film, the film containing Li oxide containing Li, And a composition of at least one metal element M selected from the group consisting of Si, Al, Ti, and Zr, wherein the content of the Li-containing oxide is 10% by mass or less, and the content of the conductive binder is 10% by mass. As described above, the average particle diameter of the aggregated particles in which the Si particles having the Li-containing oxide film and the conductive binder are aggregated is 0.5 to 10 μm. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the conductive adhesive material contains carbon. A negative electrode for a lithium ion secondary battery, characterized by containing the negative electrode material of claim 1 or 2. A lithium ion secondary battery characterized by having the negative electrode for a lithium ion secondary battery according to claim 3.