JP5156195B2 - Negative electrode material for lithium ion secondary battery and method for producing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery containing a metal and a graphite material and a method for producing the same, a negative electrode for a lithium ion secondary battery using the negative electrode material, a discharge capacity using the negative electrode, and an initial charge / discharge The present invention relates to a lithium ion secondary battery excellent in efficiency and cycle characteristics.

Lithium ion secondary batteries have a higher voltage and higher energy density than other secondary batteries, and are therefore widely used as power sources for electronic devices. In recent years, electronic devices have been rapidly reduced in size and performance, and there is an increasing demand for further improving the energy of lithium ion secondary batteries.
Currently, lithium ion secondary batteries generally use LiCoO _{2 for} the positive electrode and graphite for the negative electrode. However, although the graphite negative electrode is excellent in reversibility of charge and discharge, the discharge capacity has already reached a value close to the theoretical value (372 mAh / g) of the intercalation compound (LiC ₆ ). Therefore, in order to further increase the energy density of the battery, it is necessary to develop a negative electrode material having a discharge capacity larger than that of graphite.

Metallic lithium has the maximum discharge capacity as a negative electrode material. However, since lithium is deposited in a dendritic state during charging and the negative electrode is deteriorated, there is a problem that the charge / discharge cycle of the battery is shortened. In addition, lithium deposited in a dendrite shape may penetrate the separator and reach the positive electrode, and the battery may be short-circuited.
Therefore, a metal or a metal compound (hereinafter also referred to as a metal) that forms an alloy with lithium has been studied as a negative electrode material that can replace metal lithium. These alloy negative electrodes have discharge capacities far surpassing that of graphite, though not as much as metallic lithium. However, the active material is pulverized and peeled off due to volume expansion accompanying alloying, and the cycle characteristics of a lithium ion secondary battery using an alloy negative electrode have not yet reached a practical level.

Patent Document 1 discloses an electrode material formed by bonding or covering with a carbonaceous material having a specific crystal structure in order to bond a metal or the like and a graphite material to prevent powdering or peeling. However, such a carbonaceous material is not graphitized, so that the crystal structure is not completely developed, and has a structure in which many small pores (micropores) exist between randomly oriented crystallites. Not all lithium ions doped in the micropores contribute to charging / discharging, and some of the lithium ions remain doped and do not desorb, which results in charging / discharging loss. Therefore, when a carbonaceous material is used as a bond between a metallic material and a graphite material or as a coating material, there is a problem that charging / discharging loss increases and initial charge / discharge efficiency decreases.
Japanese Patent No. 3369589

  The present invention has been made in view of the situation as described above, and is used as a negative electrode material for a lithium ion secondary battery. The negative electrode material has high discharge capacity, and excellent cycle characteristics and initial charge / discharge efficiency can be obtained. An object is to provide a negative electrode. Another object of the present invention is to provide a lithium ion secondary battery having a high discharge capacity, excellent cycle characteristics and initial charge / discharge efficiency, using the obtained negative electrode.

The above object can be achieved by the present invention having the following features. That is, the present invention is a negative electrode material for a lithium ion secondary battery containing a metal powder that can be alloyed with lithium, a graphite material powder , and a metal that does not form an alloy with lithium. The metal melting point is lower than the melting point of the metal that can be alloyed with lithium, and the metal powder that can be alloyed with lithium adheres to the surface of the graphite material powder. A negative electrode material for a lithium ion secondary battery, wherein the metal powder that can be alloyed with lithium and the graphite material powder are bonded and / or coated by fusion.

  In the negative electrode material for a lithium ion secondary battery, the metal that is the binding material is preferably copper and / or gold.

  In the negative electrode material for a lithium ion secondary battery, the metal that can be alloyed with lithium is preferably silicon.

  The negative electrode material for a lithium ion secondary battery includes 3 to 50% by mass of the metal that can be alloyed with lithium, 30 to 90% by mass of the graphite material, and 5 to 30% by mass of the metal that is the binding material. It is preferable to include.

The present invention also provides a method for producing a negative electrode material for a lithium ion secondary battery, wherein the negative electrode material for a lithium ion secondary battery is obtained, wherein the metal powder is alloyable with lithium, a graphite material powder , and a binding material After the mechanochemical treatment of a mixture containing a metal that does not form an alloy with lithium and has a melting point lower than that of the metal that can be alloyed with lithium, the binding material melts the mechanochemical treatment product. Lithium ion secondary, wherein the metal as the binding material is heated in a temperature range to bond and / or coat the metal powder that can be alloyed with lithium and the graphite material powder by fusion. It is a manufacturing method of the negative electrode material for batteries.

The present invention also provides a method for producing a negative electrode material for a lithium ion secondary battery, wherein the negative electrode material for a lithium ion secondary battery is obtained, wherein a metal powder and a graphite material powder that can be alloyed with lithium are combined with a binding material. After a metal having a melting point lower than the melting point of the metal that can be alloyed with lithium is deposited by a vapor phase method without forming an alloy with lithium, the deposited product is melted with the metal as the binding material. The metal as the binding material is bonded to and / or coats the metal powder that can be alloyed with the lithium and the graphite material powder by fusion in a temperature range of It is a manufacturing method of the negative electrode material for secondary batteries.

  Moreover, this invention is a negative electrode for lithium ion secondary batteries characterized by using any one of the negative electrode materials for lithium ion secondary batteries.

  Moreover, this invention is a lithium ion secondary battery characterized by using the said negative electrode for lithium ion secondary batteries.

When the negative electrode material for lithium ion secondary batteries of the present invention is used, a high discharge capacity exceeding the theoretical capacity of graphite can be obtained, and at the same time, a lithium ion secondary battery exhibiting excellent initial charge / discharge efficiency and cycle characteristics can be obtained. .
Therefore, the lithium ion secondary battery using the negative electrode material of the present invention satisfies the recent demand for higher energy density of the battery, and is effective in reducing the size and performance of the mounted device.

Hereinafter, the present invention will be described more specifically.
(Negative electrode material)
The negative electrode material for a lithium ion secondary battery of the present invention is a metal that does not form an alloy with lithium and has a melting point lower than that of a metal that can be alloyed with lithium (hereinafter, a metal that is a binder). Is also a composite formed by bonding a metal that can be alloyed with lithium and a graphitic material by fusion, and in some cases, the metal that is the binding material further forms part of the surface of the composite. Further, a part of the surface of the composite in which the metal that can be alloyed with lithium and the graphite material is bonded without intermediation of the metal that is the binding material is coated with the binding material. It is a composite coated with a certain metal.

The negative electrode material of the present invention contains 3 to 50% by mass, preferably 5 to 40% by mass, more preferably 5 to 30% by mass of a metal that can be alloyed with lithium, when the total amount of the negative electrode material is 100% by mass. The graphite material is contained in an amount of 30 to 90% by mass, preferably 40 to 85% by mass, more preferably 50 to 82% by mass, and the metal as a binding material is 5 to 30% by mass, preferably 5 to 25% by mass. More preferably, it contains 5 to 20% by mass. In addition, the ratio as a binder of the metal which is a binding material, and the ratio as a coating | covering material are not specifically limited. The coating may be distributed in a mottled pattern or may be continuous.
Moreover, the thickness of the said coating | covering material is although it does not specifically limit, Preferably it is 0.05-2 micrometers, More preferably, it is 0.1-1 micrometer. The shape of the negative electrode material of the present invention is generally massive, and the average particle size is about 1 to 30 μm, preferably 5 to 20 μm. The average particle diameter means a particle diameter at which the cumulative frequency measured by a laser diffraction particle size meter is 50% by volume.

(Metal that can be alloyed with lithium)
Examples of the metal that can be alloyed with lithium constituting the negative electrode material of the present invention include silicon (Si, melting point 1414 ° C.), boron (B, melting point 2300 ° C.), platinum (Pt, melting point 1772 ° C.), palladium (Pd, melting point). 1554 ° C.). Preferred is silicon. Further, the metal may be an alloy made of two or more metals. The alloy may contain elements other than those described above. It may be a compound such as a carbide, nitride or oxide of the metal. In addition, the metal may be crystalline or amorphous, but if the metal is amorphous, expansion during charging of the lithium ion secondary battery is reduced. preferable. In particular, a metal containing amorphous silicon (Si) is most preferable.

The shape of the metal that can be alloyed with lithium is not particularly limited, and any shape such as powder, plate, granule, fiber, lump, and sphere can be used. The average particle diameter is preferably 5 μm or less, more preferably 0.01 to 5 μm, and still more preferably 0.01 to 1 μm.
Further, as described above, the metal that can be alloyed with lithium is contained in the negative electrode material of the present invention in an amount of 3 to 50% by mass, preferably 5 to 40% by mass, more preferably 5 to 30% by mass. . If it deviates from the above range, the discharge capacity and the cycle characteristics tend to decrease, which is not preferable.

(Graphite material)
The graphite material constituting the negative electrode material of the present invention is not particularly limited as long as it can absorb and release lithium ions as the negative electrode active material.
The graphite material is preferably highly crystalline from the viewpoint of obtaining a high discharge capacity. As an index of crystallinity, it is preferable that an average lattice spacing d ₀₀₂ of (002) plane in X-ray wide angle diffraction is 0.34 nm or less, particularly 0.337 nm or less.
Here, the average lattice spacing d ₀₀₂ of the (002) plane in the X-ray wide angle diffraction is the diffraction peak of the (002) plane of the graphite material using CuKα ray as the X-ray and using high-purity silicon as a standard substance. Is calculated from the position of the peak. The calculation method follows the Japan Science and Technology Act (measurement method defined by the 117th Committee of the Japan Society for the Promotion of Science). Specifically, “carbon fiber” [Sugirou Otani, pp. 733-742 (March 1986) ), Modern Editorial Company].

Examples of the graphite material include artificial graphite and natural graphite obtained by heat-treating tar or pitch at a temperature of 1500 ° C. or higher, for example, part or all of which is formed of graphite. It is done. Specifically, a mesophase calcined product, mesophase spherule, mesophase carbon fiber or coke obtained by polycondensation using petroleum-based or coal-based tars and pitches, which are called graphitizable carbon materials, as a raw material, preferably 1500 What was obtained by graphitizing at 2800-3300 ° C or more can be used.
The graphite material may be subjected to various chemical treatments in a liquid phase, a gas phase, or a solid phase, heat treatment, oxidation treatment, physical treatment, and the like.

The shape of the graphite material is not particularly limited, but is preferably a scaly shape or a shape close to a scaly shape. This is because it is easy to secure a contact between the composite particles or in the particles, and the conductivity is further improved. Moreover, the above-mentioned various artificial graphite and a mixture of natural graphite, a granulated material, a coating, and a laminate may be used. The average particle diameter of the graphite material is preferably 1 to 50 μm, more preferably 5 to 30 μm. If it deviates from the above range, the charge / discharge efficiency tends to decrease or the cycle characteristics tend to deteriorate, which is not preferable.
As described above, the graphite material is contained in the negative electrode material of the present invention in an amount of 30 to 90% by mass, preferably 40 to 85% by mass, more preferably 50 to 82% by mass. If it deviates from the above range, the discharge capacity and the cycle characteristics tend to decrease, which is not preferable.

(Metal that is a binding material)
The metal that is the binding material of the present invention is a metal that does not form an alloy with lithium and has a melting point lower than that of the metal that can be alloyed with lithium. Specifically, copper (melting point: 1085 ° C.), gold (melting point: 1064 ° C.), titanium (melting point: 1675 ° C.), nickel (melting point: 1455 ° C.), and the like. Preference is given to copper and / or gold. Two or more of these metals can be used in combination. Of course, it is also possible to use an alloy containing the metal.
Moreover, the metal which is the said binding material is 5-30 mass% in the negative electrode material of this invention as mentioned above, Preferably it is 5-25 mass%, More preferably, 5-15 mass% is contained. Deviating from the above range is not preferable because the cycle characteristics tend to deteriorate.
In the negative electrode material of the present invention, since a carbonaceous material is not used as the binding material, the conventional problem of an increase in charge / discharge loss derived from the carbonaceous material, that is, a decrease in charge / discharge efficiency can be solved.

(Method for producing negative electrode material)
The negative electrode material of the present invention can be produced by various methods for compounding a metal that can be alloyed with lithium, a graphite material, and a metal that is a bonding material, and, if necessary, subsequent heat treatment of the compound. The compounding may be performed by any method out of a mechanical method and a physical method, but is preferably performed by a mechanical method.
The above-mentioned compounding by a mechanical method is performed by adding a metal, which is a bonding material, to a primary compound obtained by first compounding a metal that can be alloyed with lithium and a graphite material, and heating and melting the resulting material. A method of obtaining a secondary composite containing the three components by bonding and / or coating the primary particles by welding a certain metal, or mixing the three components and heating and melting the metal that is a binding material, This is a method in which a metal that can be alloyed with lithium and a graphite material are bonded to each other by welding of a metal that is a bonding material, and then coating is performed.

Specific examples of the mechanical method include mechanochemical treatment that imparts mechanical energy such as compression, shearing, collision, and friction. Granulators such as “GRANUREX” [manufactured by Freund Sangyo Co., Ltd.], “Newgra Machine” [manufactured by Seishin Enterprises], “Agromaster” [manufactured by Hosokawa Micron Co., Ltd.] , Roll mill, “hybridization system” [manufactured by Nara Machinery Co., Ltd.], “mechano micro system” [manufactured by Nara Machinery Co., Ltd.], “mechano fusion system” [manufactured by Hosokawa Micron Corporation], etc. Examples include processing equipment.
These devices also have the effect of rolling the particles so that the primary composite becomes a pseudo-sphere. In particular, when scaly graphite is used as one of the graphite materials, the scaly graphite is arranged concentrically, and voids that absorb expansion during charging of a metal that can be alloyed with lithium are formed inside the composite particles. Can be formed.

  The physical method is not particularly limited as long as it is a method capable of complexing a metal that is a binding material in a gas phase, a liquid phase, or a solid phase, but a gas phase method is preferable. Gas phase methods include vacuum vapor deposition, sputtering, ion plating, molecular beam epitaxy and other PVD (Physical Vapor Deposition) methods, atmospheric pressure CVD (Chemical Vapor Deposition) methods, low pressure CVD methods, and plasma CVD methods. There are CVD methods such as MO (Magneto-Optic) CVD method and photo CVD method, but sputtering method is particularly preferable. As the sputtering method, a direct current sputtering method, a magnetron sputtering method, a high frequency sputtering method, a reactive sputtering method, a bias sputtering method, an ion beam sputtering method, or the like can be used.

In the sputtering method, a metal target as a binding material is installed on the cathode side, and generally a glow discharge is generated between the electrodes in an inert gas atmosphere of about 1 to 10 ⁻² Pa to ionize the inert gas, In this method, the target metal is knocked out and the target metal is deposited on the primary composite provided on the anode side. A plurality of the target metals may be used simultaneously. That is, an alloy may be synthesized by simultaneously sputtering a plurality of the metals as targets, or a plurality of the metals may be laminated in order. In addition to the vapor phase method, for example, a thermal spraying method, a plating method, or the like can be used as a method for depositing the metal.

Further, a mechanical method and a physical method can be used in combination. That is, first, a metal compound that can be alloyed with lithium and a graphite material is composited by the mechanical method described above to obtain a primary composite containing two components, and the metal that is the binding material is mixed with the gas phase described above. The metal that is deposited by the method, heated at a temperature higher than the temperature at which the deposited metal melts, melts the metal as the binding material, and bonds and / or coats the metal that can be alloyed with lithium and the graphite material by welding. The next composite, that is, the negative electrode material of the present invention can be manufactured.
The melting temperature is not particularly limited, but when silicon is used as the metal that can be alloyed with lithium, it is preferably less than 1200 ° C. This is because silicon carbide (SiC) that does not contribute to an increase in discharge capacity is generated when the temperature is 1200 ° C. or higher.

(Negative electrode)
The present invention is a negative electrode for a lithium ion secondary battery containing the negative electrode material, and a lithium ion secondary battery using the negative electrode.
The negative electrode for a lithium ion secondary battery according to the present invention is manufactured in accordance with a normal method for preparing a negative electrode for graphite. However, any method can be used as long as it can obtain a chemically and electrochemically stable negative electrode. Not. When preparing the negative electrode, it is preferable to use a negative electrode mixture prepared in advance by adding a binder for negative electrode mixture to the negative electrode material of the present invention.
As the binder, those that are chemically and electrochemically stable with respect to the electrolyte are preferable. For example, fluorine resin powders such as polytetrafluoroethylene and polyvinylidene fluoride, resins such as polyethylene and polyvinyl alcohol, and the like. Powder, carboxymethylcellulose, etc. are used. These can also be used together. A binder is normally used in the ratio of about 1-20 mass% in the whole quantity of a negative electrode mixture.
In addition to the negative electrode material and the binder, the negative electrode of the present invention includes a conductive material such as a graphite material such as natural graphite and a carbonaceous material such as amorphous hard carbon, an organic substance such as a phenol resin, a metal such as silicon, You may mix | blend metal compounds, such as a tin oxide, in the quantity of the range which does not affect the original effect which is anticipated as a negative electrode of this invention.

  More specifically, first, the negative electrode material of the present invention is adjusted to a desired particle size by classification or the like, and a mixture obtained by mixing with a binder is dispersed in a solvent to prepare a negative electrode mixture in the form of a paste. That is, a slurry obtained by mixing the negative electrode material of the present invention and a binder with a solvent such as water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, etc., using a known stirrer, mixer, kneader, kneader or the like. Mix with stirring to prepare a paste. If the paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly and firmly bonded can be obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 20 to 100 μm.

The negative electrode of the present invention can also be produced by dry-mixing the negative electrode material of the present invention and resin powders such as polyethylene and polyvinyl alcohol and hot pressing in a mold. However, dry mixing requires a large amount of binder to obtain sufficient strength of the negative electrode, and if the binder is excessive, the discharge capacity and rapid charge / discharge efficiency of the lithium ion secondary battery may be reduced. . In addition, the negative electrode of this invention can be made high so that a negative electrode density may exceed 1.7 g / cm < ³ >.
When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.
The shape of the current collector used for production of the negative electrode is not particularly limited, but may be a foil shape, a mesh shape, a net shape such as expanded metal, or the like. The material for the current collector is preferably copper, stainless steel, nickel or the like. The thickness of the current collector is preferably about 5 to 20 μm in the case of a foil shape.

(Lithium ion secondary battery)
A lithium ion secondary battery usually has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main battery components. Each of the positive electrode and the negative electrode is composed of a lithium ion carrier, and during charging, lithium ions are occluded in the negative electrode and discharged. It depends on the battery mechanism that is detached from the negative electrode.
The lithium ion secondary battery of the present invention is not particularly limited except that the negative electrode material of the present invention is used as a negative electrode material, and other lithium battery components such as a positive electrode, an electrolyte, and a separator are general lithium ions. Conforms to secondary battery elements.

(Positive electrode)
The positive electrode is formed, for example, by applying a positive electrode mixture composed of a positive electrode material (positive electrode active material), a binder, and a conductive agent to the surface of the current collector. It is preferable to select a positive electrode material that can occlude / release a sufficient amount of lithium. Lithium-containing compounds such as lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides and lithium compounds thereof, and general formula M _x Mo ₆ S _8-Y (wherein M is at least one transition metal element, X is a number in the range of 0 ≦ X ≦ 4, Y is 0 ≦ Y ≦ 1) Compounds, activated carbon, activated carbon fibers and the like.

  The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. Lithium-containing transition metal oxides are, for example, lithium, transition metal oxides, hydroxides, salts, etc. as starting materials, mixed with these starting materials, and fired at a temperature of 600 to 1000 ° C. in an oxygen atmosphere. Can be obtained.

Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-X M ² _X O ₂ (wherein M ¹ and M ² are at least one transition metal element, and X is 0 ≦ X ≦ 1) LiM ¹ _1-Y M ² _Y O ₄ (wherein M ¹ and M ² are at least one transition metal element, and Y is a number in the range of 0 ≦ Y ≦ 1). ). Transition metal elements represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, etc., preferably Co, Mn, Cr, Ti, V, Fe, Al and the like. Preferable specific examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ and the like.
The lithium-containing transition metal oxide is prepared by mixing starting materials such as lithium, transition metal oxide, hydroxide, and salt according to the composition of the desired metal oxide, and in an oxygen atmosphere, 600 to 1000 ° C. It can obtain by baking at the temperature of.
Lithium-containing transition metal oxides may be used alone or in combination of two or more.

  The positive electrode material may be used alone or in combination of two or more. For example, a carbon salt such as lithium carbonate can be added to the positive electrode. Moreover, when forming a positive electrode, conventionally well-known various additives, such as a electrically conductive agent, can be used suitably.

As the binder used for producing the positive electrode, the same binder as used for producing the negative electrode can be used. As the conductive agent, known materials such as graphitized materials and carbon black are used.
The shape of the current collector is not particularly limited, but a foil shape or a mesh shape such as a mesh or expanded metal is used. The material of the current collector is aluminum, stainless steel, nickel or the like. The thickness is preferably 10 to 40 μm.

  Similarly to the negative electrode, the positive electrode mixture may be formed in a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After forming the agent layer, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, an electrolyte salt used for preparing a normal non-aqueous electrolyte can be used. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , 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 and other lithium salts can be used. In particular, LiPF ₆ and LiBF ₄ are preferable from the viewpoint of oxidation stability.
The electrolyte salt concentration in the electrolytic solution is preferably from 0.1 to 5 mol / l, more preferably from 0.5 to 3.0 mol / l.
The non-aqueous electrolyte may be liquid, or may be a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte or a polymer gel electrolyte battery. .

  Nonaqueous solvents for preparing a nonaqueous electrolyte include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2- Diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, acetonitrile, chloro Nitriles such as nitrile and propionitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitric acid Robenzen, benzoyl chloride, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, may be used an aprotic organic solvent such as dimethyl sulfite.

When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it is preferable to use a polymer compound gelled with a plasticizer (non-aqueous electrolyte) as a matrix. Examples of the polymer compound constituting the matrix include ether polymer compounds such as polyethylene oxide and cross-linked products thereof, polymethacrylate polymer compounds, polyacrylate polymer compounds, polyvinylidene fluoride and vinylidene fluoride-hexafluoro. Fluorine polymer compounds such as propylene copolymers are preferably used alone or in combination. In particular, it is preferable to use a fluorine-based polymer compound from the viewpoint of oxidation-reduction stability.
As the plasticizer necessary for the gelation, the electrolyte salt and the non-aqueous solvent can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the non-aqueous electrolyte as a plasticizer is preferably 0.1 to 5 mol / l, and more preferably 0.5 to 2.0 mol / l.

The method for producing the polymer solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer), and heating to melt the polymer compound, for mixing Method of evaporating organic solvent for mixing after dissolving polymer compound, lithium salt and non-aqueous solvent in organic solvent, mixing polymerizable monomer, lithium salt and non-aqueous solvent, ultraviolet ray, electron beam or molecule in mixture Examples include a method of polymerizing a polymerizable monomer by irradiating a line and the like to obtain a polymer.
Here, the ratio of the nonaqueous solvent in the polymer solid electrolyte is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. When the content is less than 10% by mass, the electrical conductivity is low, and when it exceeds 90% by mass, the mechanical strength decreases and film formation becomes difficult.

In the lithium ion secondary battery of the present invention, a separator can also be used.
Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. can be used. A synthetic resin microporous membrane is preferred, and among them, a polyolefin microporous membrane is preferred in terms of thickness, membrane strength, and membrane resistance. Specifically, it is a microporous membrane made of polyethylene and polypropylene, or a microporous membrane that combines these.

  The lithium ion secondary battery of the present invention is a negative electrode material including at least a metal that can be alloyed with lithium and a graphite material having the above-described configuration, wherein the metal and the graphite material are conductive materials other than the carbonaceous material. For example, the negative electrode, the positive electrode, and the non-aqueous electrolyte that are bonded and / or coated with are stacked in the order of the negative electrode, the non-aqueous electrolyte, and the positive electrode, and are housed in the battery exterior material. Further, a non-aqueous electrolyte may be disposed outside the negative electrode and the positive electrode.

In addition, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and the shape and form thereof are not particularly limited, and are cylindrical, depending on the application, mounted equipment, required charge / discharge capacity, and the like. , Square shape, coin shape, button shape, and the like. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to use a battery equipped with means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharging occurs.
In the case where the lithium ion secondary battery is a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure in which the lithium ion secondary battery is enclosed in a laminate film may be used.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the following examples and comparative examples, as shown in FIG. 1, at least part of the surface of the current collector (negative electrode) 7b is a metal that can be alloyed with lithium, a graphite material, and a metal that is a binding material. A button-type secondary battery for single electrode evaluation composed of a current collector (negative electrode) 7b to which a composite material containing lithium was adhered and a counter electrode (positive electrode) 4 made of a lithium foil was prepared to evaluate charge / discharge characteristics. An actual battery can be produced according to a known method based on the concept of the present invention.

Example 1
(Preparation of negative electrode material)
Graphite powder (manufactured by Chuetsu Graphite Industry Co., Ltd., average particle diameter of 15 μm), silicon powder corresponding to 10% by mass (manufactured by High Purity Chemical Laboratory, average particle diameter of 2 μm), and copper powder corresponding to 10% by mass [Wako Pure Chemical Industries, Ltd., average particle size 75 μm or less] pulverized product was added, and the resulting mixture was used with a dry powder compounding device [“Mechanofusion System”, manufactured by Hosokawa Micron Co., Ltd.] Then, under the conditions of a peripheral speed of the rotating drum of 20 m / s, a time of 60 min, and a distance of 5 mm between the rotating drum and the internal member, a compressive force and a shearing force are repeatedly applied, mechanochemical treatment is performed, and silicon powder is applied to the surface of the graphite powder. And a composite with copper powder dispersed and adhered. The obtained composite was heat treated at 1100 ° C. to melt the copper powder, and a negative electrode material in which a part of the graphite powder and a part of the silicon powder were coated by copper welding was prepared.

(Preparation of negative electrode mixture)
90% by mass of the negative electrode material and 10% by mass of polyvinylidene fluoride were placed in N-methylpyrrolidone, and stirred and mixed at 2000 rpm for 30 minutes using a homomixer to prepare an organic solvent-based pasty negative electrode mixture.

[Production of working electrode (negative electrode)]
The negative electrode mixture paste is applied to a copper foil (thickness: 16 μm) with a uniform thickness, and the solvent is evaporated and dried at 90 ° C. in a vacuum to form a negative electrode mixture layer. Pressurized. A copper foil and a negative electrode mixture layer were punched into a cylindrical shape with a diameter of 15.5 mm, and a negative electrode mixture layer (thickness 60 μm, density 1.72 g / cm ³ ) adhered to the current collector (copper foil) and the current collector. A working electrode (negative electrode) 2 was prepared.

[Production of counter electrode (positive electrode)]
A lithium metal foil (thickness 0.5 mm) is pressed against a nickel net and punched into a circular shape with a diameter of 15.5 mm, and a current collector made of nickel net and a counter electrode made of a lithium metal foil in close contact with the current collector (Positive electrode) was produced.

(Electrolyte / Separator)
LiPF ₆ was dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate 33 vol% -methyl ethyl carbonate 67 vol% to prepare a non-aqueous electrolyte. The obtained non-aqueous electrolyte was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolyte.

(Production of evaluation battery)
A button-type secondary battery shown in FIG. 1 was prepared as an evaluation battery.
In the evaluation battery, the separator 5 impregnated with the electrolytic solution was sandwiched between the working electrode 2 in close contact with the current collector 7b and the counter electrode 4 in close contact with the current collector 7a. Thereafter, the collector 7 b side of the working electrode 2 was accommodated in the exterior cup 1 and the collector 7 a side of the counter electrode 4 was accommodated in the exterior can 3, and the exterior cup 1 and the exterior can 3 were combined. At that time, the outer peripheral cup 1 and the outer can 3 were prepared by interposing an insulating gasket 6 between the outer peripheral cup 1 and the outer can 3 and caulking both peripheral portions.

  The evaluation battery produced as described above was subjected to the following charge / discharge test at a temperature of 25 ° C., and the initial charge / discharge efficiency and cycle characteristics were calculated. Table 1 shows the evaluation results of charge / discharge characteristics (discharge capacity, initial charge / discharge efficiency, cycle characteristics).

(Discharge capacity, initial charge / discharge efficiency)
After constant current charging of 0.9 mA until the circuit voltage reached 0 mV, switching to constant voltage charging was performed when the circuit voltage reached 0 mV, and charging was continued until the current value reached 20 μA. The charging capacity was determined from the amount of electricity applied during that time. Thereafter, the operation was stopped for 120 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity was obtained from the energization amount during this period. This was the first cycle. The initial charge / discharge efficiency was calculated from the following equation (1).
Initial charge / discharge efficiency (%) = (Discharge capacity of the first cycle / Charge capacity of the first cycle)
× 100 (1)
In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of detaching lithium ions from the negative electrode material was discharge.

(Cycle characteristics)
Then, after performing constant current charging of 4.0 mA until the circuit voltage reaches 0 mV, switching to constant voltage charging when the circuit voltage reaches 0 mV, and further continuing charging until the current value reaches 20 μA, Paused for 120 minutes. Next, constant current discharge was performed at a current value of 4.0 mA until the circuit voltage reached 1.5V. This charge / discharge was repeated 100 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following equation (2).
Cycle characteristics (%) = (discharge capacity in the 100th cycle / in the first cycle)
Discharge capacity) x 100 (2)

(Examples 2-3)
In Example 1, except that the composition of the components of the composite is changed as shown in Table 1, the production of the negative electrode material, the production of the negative electrode mixture, the production of the negative electrode, the production of the evaluation battery, and the battery are the same as in Example 1. The charge / discharge characteristics were evaluated. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

Example 4
In Example 1, except that the copper powder is replaced with gold powder [Aldrich Co., Ltd., average particle diameter of 1.5 μm], production of a negative electrode material, production of a negative electrode mixture, production of a negative electrode, as in Example 1, The evaluation battery was produced and the charge / discharge characteristics of the battery were evaluated. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

(Comparative Example 1)
In Example 1, except that the copper powder is replaced with the pulverized product of petroleum coke (average particle size 5 μm), the production of the negative electrode material, the production of the negative electrode mixture, the production of the negative electrode, and the production of the evaluation battery are performed in the same manner as in Example 1. In addition, the charge / discharge characteristics of the battery were evaluated. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

(Comparative Example 2)
A composite (non-heated composite) in which the silicon powder and the copper powder are dispersed and adhered to the surface of the graphite powder after the mechanochemical treatment of Example 1, and thus the copper powder has a role in bonding the graphite powder and the silicon powder. In addition, the composite material not coated with the composite material was used to prepare a negative electrode material, a negative electrode material mixture, a negative electrode material, an evaluation battery, and a battery charge / discharge characteristic as in Example 1. Went. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

(Example 5)
In Example 1, first, graphite powder and silicon powder were mechanochemically treated in the same manner as in Example 1 without mixing copper powder to obtain a primary composite. Next, the primary composite is disposed on the anode side stage of the DC bipolar sputtering apparatus, and a 99.999% purity copper target is disposed on the cathode side. The pressure is 0.5 Pa, the voltage is 600 V, and the current is 0.5 A. Sputtering was performed for 2 hours under the conditions. Thereafter, the primary composite was stirred. Again, sputtering was performed for 2 hr under the same conditions as described above, followed by stirring. Thereafter, similar sputtering was performed for 2 hours. The amount of copper deposited on the primary composite after sputtering by emission spectroscopic analysis was 10% by mass.
The primary composite with the copper adhered was heated at 1100 ° C. to melt the copper, and a negative electrode material in which copper covered a part of the graphite powder and a part of the silicon powder was produced.
Except using the said negative electrode material, preparation of the negative mix, preparation of a negative electrode, preparation of an evaluation battery, and evaluation of the charging / discharging characteristic of a battery were performed like Example 1. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

(Example 6)
In Example 5, except that the copper target is replaced with a gold target, the production of the negative electrode material, the production of the negative electrode mixture, the production of the negative electrode, the production of the evaluation battery, and the evaluation of the charge / discharge characteristics of the battery are performed in the same manner as in Example 5. It was. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

(Comparative Example 3)
Using the primary composite after sputtering of Example 5 (unheated composite), and therefore, the composite in which the copper powder does not participate in the bonding of the graphite powder and the silicon powder and does not cover the composite In the same manner as in Example 1, production of a negative electrode material, production of a negative electrode mixture, production of a negative electrode, production of an evaluation battery, and evaluation of charge / discharge characteristics of the battery were performed. The characteristics of the negative electrode material and the evaluation results of the battery are shown in Table 1.

  From the comparison between Examples 1 to 6 and Comparative Examples 1 to 3, the present invention using the composite (negative electrode material) in which the metal as the binder binds and / or covers the composite is carbonaceous as the binding material. It can be seen that the initial charge and discharge efficiency and the cycle characteristics are superior compared to the case where the material is used or the metal which is the binder is melted and the composite is not bonded and / or coated.

  The negative electrode material for lithium ion secondary batteries of the present invention can be used for high performance lithium ion secondary batteries ranging from small to large, taking advantage of the characteristics.

It is a schematic cross section of the button type evaluation battery for evaluating the charge / discharge characteristics of the negative electrode material of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Working electrode 3 Exterior can 4 Counter electrode 5 Electrolyte solution impregnation separator 6 Insulation gasket 7a, 7b Current collector

Claims (8)

A negative electrode material for a lithium ion secondary battery including a metal powder that can be alloyed with lithium, a graphite material powder , and a metal that does not form an alloy with lithium, and the melting point of the metal that is the binder material The metal powder that can be alloyed with lithium adheres to the surface of the graphite material powder that is lower than the melting point of the metal that can be alloyed with lithium, and the metal that is the binding material is fused, A negative electrode material for a lithium ion secondary battery, wherein the metal powder that can be alloyed with lithium and the graphite material powder are bonded and / or coated.   The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the metal as the binding material is copper and / or gold.   3. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the metal that can be alloyed with lithium is silicon.   The negative electrode material for a lithium ion secondary battery includes 3 to 50% by mass of a metal that can be alloyed with lithium, 30 to 90% by mass of the graphite material, and 5 to 30% by mass of the metal that is the binding material. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the negative electrode material is contained. It is a manufacturing method of the negative electrode material for lithium ion secondary batteries which obtains the negative electrode material for lithium ion secondary batteries in any one of Claims 1-4,
A metal powder that can be alloyed with lithium, a graphite material powder , and a binder material that does not form an alloy with lithium and has a lower melting point than that of the metal that can be alloyed with lithium is mechanized. After the chemical treatment, the mechanochemical treatment product is heated in a temperature range in which the binding material melts, and the metal as the binding material is fused with the metal powder that can be alloyed with the lithium and the graphitic material. A method for producing a negative electrode material for a lithium ion secondary battery, wherein the powder is bound and / or coated. It is a manufacturing method of the negative electrode material for lithium ion secondary batteries which obtains the negative electrode material for lithium ion secondary batteries in any one of Claims 1-4,
Lithium can be alloyed metal powder and graphitic material powder, a binding material, does not form an alloy with lithium, a metal having the lithium can be alloyed metal melting point lower than the melting point in a gas phase method After adhering, the adhering product is heated in a temperature range in which the metal as the bonding material melts, and the metal as the bonding material is fused to the metal powder that can be alloyed with the lithium and the graphite. A method for producing a negative electrode material for a lithium ion secondary battery, comprising bonding and / or coating a material powder .   The negative electrode for lithium ion secondary batteries using the negative electrode material for lithium ion secondary batteries in any one of Claims 1-4.   A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery according to claim 7.

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