TWI530010B - Lithium ion battery and battery module using the same - Google Patents

Description

Lithium ion battery and battery module using same

The present invention relates to a lithium ion battery and a battery module using the same.

Lithium-ion batteries have high energy density and are attracting attention as batteries for electric vehicles or storage batteries. In particular, electric vehicles include a zero-emission electric vehicle that is not equipped with an engine, a hybrid vehicle equipped with both an engine and a secondary battery, and a plug-in hybrid that is directly charged by a system power source. car. In the present invention, the electric vehicle refers to the above various automobiles. Moreover, it is also expected to be used as a stationary storage system, that is, to store electric power and supply electric power at a very moment when the electric power system is disconnected.

For such a variety of uses, lithium ion batteries are required to have excellent durability. That is, even if the ambient temperature becomes high, the rate of decrease in the capacity of the chargeable discharge is small, and the capacity retention rate of the battery is high even after a long period of time. In particular, lithium-ion batteries for electric vehicles are exposed to high temperatures of 40 ° C to 70 ° C due to radiant heat from the road surface or heat transfer from the interior of the vehicle. It is important to improve the long-term storage characteristics and cycle life in these environments. Development issues.

As a prior art for suppressing capacity reduction or cycle deterioration at the time of high-temperature storage, various techniques such as a highly durable electrode material or an electrolytic solution have been studied. In particular, in the negative electrode, lithium absorbed in the negative electrode is consumed as the electrolytic solution is decomposed, resulting in a decrease in the capacity of the battery. In order to suppress this side reaction, reveal A variety of methods for modifying the surface of the negative electrode.

Japanese Laid-Open Patent Publication No. H6-1-68725 discloses an invention using a battery in which a carbon material is treated at a high temperature of 2000 ° C or higher and graphitized, and then pulverized and further applied 2000. A negative electrode active material containing a secondary particle which is a primary particle which coats a graphite surface with amorphous carbon, as disclosed in Japanese Laid-Open Patent Publication No. 2000-156230. It is formed by granulation.

Japanese Laid-Open Patent Publication No. 2002-134171 discloses an invention of a battery using a carbon which is a carbon coated surface by a negatively charged water-soluble polymer substance in a negative electrode active material; Japanese Patent Publication No. Hei 5-275077 discloses an invention of coating a film of a lithium ion conductive solid electrolyte on a carbon surface.

Japanese Laid-Open Patent Publication No. 2000-264614 discloses an invention of forming a coating layer containing carbon on the surface of graphite particles after treating the graphite particles with a surfactant; Japanese Patent Laid-Open Publication No. 2001-229914 discloses An invention in which an amorphous carbon coating layer is formed on the surface of graphite to inhibit decomposition of the electrolytic solution.

Japanese Patent Laid-Open Publication No. Hei. No. 2006-24374 discloses an invention of a carbon secondary particle which forms a carbon coating layer on the surface of crystalline carbon particles (primary particles) through which primary particles are coated. In the invention of the graphite for a negative electrode, the graphite for the negative electrode is characterized by an average particle diameter of 5 μm to 50 μm and a true specific gravity of 2.20 g/cm ³ or more. The specific surface area of nitrogen gas adsorption is 8 m ² /g or less, and the specific surface area of carbon dioxide gas adsorption is 1 m ² /g or less, and the oxygen atom concentration measured by X-ray photoelectron spectroscopy is 0.7 atom% or more.

Japanese Patent Publication No. 2007-42571 discloses an invention of a carbon material having a surface spacing d002 of a carbon 002 surface of 0.340 nm to 0.390 nm which is obtained by X-ray diffraction measurement, and particularly specifies He true density and CO. ₂ adsorption amount.

Japanese Patent Laid-Open Publication No. 2009-187924 discloses an invention in which the size Lc of the crystallites analyzed by the X-ray diffraction method is 20 nm to 90 nm, and the surface spacing d002 of the carbon 002 plane is 0.3354 nm to 0.3370 nm. Further, a negative electrode material having low crystalline carbon is formed on the surface.

Lithium-ion batteries for electric vehicles or for storage have a situation in which they are placed in a high-temperature environment under a state of charge, and the battery capacity is lowered due to self-discharge. An object of the present invention is to suppress self-discharge by a negative electrode and to achieve a long life of a lithium ion battery.

The present inventors have conducted intensive studies to solve the above problems, and as a result, it has been found that the capacity of the battery is hard to be lowered even after the lithium ion battery is charged, discharged, or placed in a high temperature environment.

According to a first aspect of the present invention, a lithium ion battery comprising a negative electrode, a positive electrode, a nonaqueous electrolyte, and a nonaqueous solvent, wherein the negative electrode active material is a negative electrode active material capable of occluding and releasing lithium a substance, and the negative electrode active material is a composite carbon particle having a low crystalline carbon coating layer on the surface of graphite particles (graphite core material), The layer has a functional group of C=O, C-OH and CO, and the oxygen atom content in the total amount of carbon atoms and oxygen atoms of the coating layer is 2 atom% to 5 atom%, and the thermogravimetric method in air In the temperature range of 350 ° C or more and less than 600 ° C and 600 ° C or more and 850 ° C or less, at least one oxidation peak, and in the range of 350 ° C or more and 850 ° C or less, the peak of the oxidation peak at the highest temperature and The peak temperature difference of the oxidation peak having a peak at the lowest temperature is 300 ° C or less. The above low crystalline carbon is amorphous or carbon having low crystallinity.

According to a second aspect of the invention, the lithium ion battery according to the first aspect, wherein, in the total oxygen amount of the coating layer, an oxygen content of C=O in the coating layer It is 7atom%~39atom%.

According to a third aspect of the present invention, there is provided a lithium ion battery according to the first aspect or the second aspect, wherein the low crystalline carbon of the coating layer is amorphous carbon.

According to a fourth aspect of the present invention, there is provided a lithium ion battery according to any one of the first aspect to the third aspect, wherein a ratio of C-OH to C=O in the coating layer is provided. It is 1:1 to 4:1 in terms of the composition ratio of oxygen atoms in the respective functional groups. The ratio of the C-OH to the C=O is preferably 1:1 to 2:1 in terms of the oxygen atom composition ratio in each functional group.

According to a fifth aspect, the lithium ion battery according to any one of the first aspect to the fourth aspect, wherein the negative electrode active material is obtained by an X-ray diffraction method ( 002) The surface spacing d002 is 0.3354 nm to 0.3370 nm, and the crystallite size Lc is 20 nm to 90 nm.

According to the sixth aspect, any of the first aspect to the fifth aspect is provided. In one aspect, the lithium ion battery has a thickness of the coating layer of 10 nm to 100 nm.

According to a seventh aspect, the lithium ion battery according to any one of the first aspect to the sixth aspect, wherein the intensity ratio of the Raman peak of the negative active material is (I ₁₃₆₀ /I ₁₅₈₀ ) It is 0.1~0.7.

According to the eighth aspect, the lithium ion battery according to any one of the first aspect to the seventh aspect, wherein the negative active material has an irreversible capacity per unit weight of 20 mAh/g to 31 mAh. /g, and the discharge capacity density of the negative electrode active material is from 350 mA/g to 365 mA/g.

According to a ninth aspect, the lithium ion battery according to any one of the first aspect to the eighth aspect, wherein the graphite core material is an isotropic pressure-treated graphite particle.

According to a tenth aspect, the lithium ion battery according to any one of the first aspect to the eighth aspect, wherein the coating layer is an organic compound or a non-oxidizing environment thereof The carbon film formed by the low crystalline carbon formed on the surface of the graphite core material by thermal decomposition of the mixture.

According to an eleventh aspect, the lithium ion battery according to the tenth aspect, wherein the coating layer is obtained by thermally decomposing the organic compound or a mixture thereof and the graphite core material under contact conditions. Carbon film.

According to a twelfth aspect, the lithium ion battery according to the tenth aspect or the eleventh aspect, wherein the organic compound is an organic polymer compound which is carbonized in a liquid phase.

According to a thirteenth aspect, the lithium ion battery according to the tenth aspect or the eleventh aspect, wherein the organic compound is carbonized in a solid phase Organic resin.

According to a fourteenth aspect, the lithium ion battery according to any one of the first aspect to the thirteenth aspect, wherein the content of the low crystalline carbon in the composite carbon particles is 0.1 wt% to 20 wt% of the total weight of the graphite core material and the low crystalline carbon.

According to a fifteenth aspect, the lithium ion battery according to any one of the first aspect to the fourteenth aspect, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector body.

According to a sixteenth aspect, the lithium ion battery according to any one of the first aspect to the fifteenth aspect, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector The positive electrode active material is selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn, or Ta; x = 0.01 to 0.2), Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu, or Zn), Li _1-x A _x Mn ₂ O ₄ (wherein A = Mg, B, Al, Fe, Co, Ni, Cr, Zn, or Ca; x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe, or Ga; x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, or Mn; x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where M = Mn, Fe, Co, Al, Ga, Ca, or Mg; x = 0.01 to 0.2), Fe(MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , and LiMnPO At least one of the groups consisting of _four .

According to a seventeenth aspect, the lithium ion battery according to any one of the first aspect to the sixteenth aspect, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector The positive electrode active material is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ .

According to an eighteenth aspect, there is provided a battery module in which two or more lithium ion batteries as described in any one of the first aspect to the seventeenth aspect are connected in series, in parallel or in series.

According to a nineteenth aspect, there is provided a mobile unit or a stationary power storage system, wherein the battery module of the eighteenth aspect is connected to a charge and discharge circuit connectable to an external device via an external terminal.

According to the present invention, it is possible to provide a lithium ion battery having improved cycle life and high temperature storage characteristics, a battery module using the lithium ion battery, a moving body or a stationary power storage system.

Other aspects of the invention will be apparent from the following detailed description. The terms used in the present invention use the ordinary meaning.

In this specification, the term "step" is not merely an independent step. If it is not clearly distinguishable from other steps, the intended effect of this step is also included in the term.

Further, the numerical range expressed by "~" in the present invention indicates a range including the values described before and after "~" and is a range of the minimum value and the maximum value, respectively.

Further, in the present invention, when referring to the amount of each component in the composition, when a plurality of substances corresponding to the respective components are present in the composition, if it is not particularly limited, it means that the composition exists. The total amount of multiple substances.

In the present invention, the composite carbon particles in which the surface of the graphite particles (graphite core material) is coated with a low crystalline carbon coating layer are included, and the oxygen concentration in the coating layer is in a specific range. Thereby, a lithium ion battery comprising a negative electrode, a positive electrode, a nonaqueous electrolyte and a nonaqueous solvent, wherein the negative electrode comprises composite carbon particles as a negative electrode active material, and the composite carbon particles are in a thermogravimetric method at 350 ° C or higher And at least one oxidation peak (peak value of temperature differential value of weight change) in a low temperature region of less than 600 ° C, and at least one oxidation peak in a high temperature region of 600 ° C or more and 850 ° C or less (temperature differential temperature change) The peak value is, and in the range of 350 ° C or more and 850 ° C or less, the peak temperature difference between the oxidation peak having the peak at the highest temperature and the oxidation peak having the peak at the lowest temperature is 300 ° C or lower. The lithium ion battery of the present invention is a battery excellent in high temperature storage characteristics and cycle characteristics.

The composite carbon particles of the present invention are obtained by coating a graphite core material with a low crystalline carbon coating layer to constitute a negative electrode active material. The low crystalline carbon includes amorphous or mesophase carbon (carbon having very low crystallinity, and the crystallization peak cannot be substantially confirmed by the X-ray diffraction method). The low-crystalline carbon coating can be obtained by various methods, and the organic substance which can be thermally decomposed in the liquid phase is heated in a non-oxidizing environment to be deposited on the graphite core material.

Preferably, the graphite core material is graphite particles subjected to an isotropic pressure treatment. Further, the coating layer of the low crystalline carbon may be a low crystalline carbon film formed on the surface of the graphite core material by thermal decomposition of an organic compound or a mixture thereof in a non-oxidizing atmosphere.

Moreover, the organic compound or a mixture thereof is thermally decomposed under the contact with the graphite core material, and may be organically high in the liquid phase. A molecular compound or an organic resin that is carbonized under a solid phase. The coating layer is preferably from 0.1% by weight to 20% by weight based on the total weight of the graphite core material and the low crystalline carbon.

The present invention is applicable to a battery module in which at least two lithium ion batteries are connected in parallel, in parallel or in series, and a mobile or stationary power storage system that passes the battery module through an external The terminals are connected to a charge and discharge circuit connectable to an external device, which will be specifically described later.

[Example]

(Example 1)

The internal structure of a cylindrical lithium ion battery 101 of an example of the present invention is schematically shown in Fig. 1. 110 is a positive electrode, 111 is a separator, 112 is a negative electrode, 113 is a battery can, 114 is a positive collector tab, 115 is a negative collector tab, 116 is an inner cap, and 117 is an internal pressure release valve, 118 is The gasket, 119 is a positive temperature coefficient (PTC) resistance element, and 120 is a battery cover. The battery cover 120 is an integral part including an inner cover 116, an internal pressure release valve 117, a spacer 118, and a PTC resistance element 119.

The positive electrode 110 includes a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector. When the positive electrode active material is exemplified, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O _{4 are} exemplified. Further, LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn, or Ta; x = 0.01~0.2), Li ₂ Mn ₃ MO ₈ (where M=Fe, Co, Ni, Cu, or Zn), Li _1-x A _x Mn ₂ O ₄ (where A=Mg, B, Al, Fe , Co, Ni, Cr, Zn, or Ca; x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe, or Ga; x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe, or Mn; x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where M = Mn, Fe , Co, Al, Ga, Ca, or Mg; x = 0.01 to 0.2), Fe(MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , and LiMnPO ₄ . In the present example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ may be selected as the positive electrode active material in terms of achieving high energy density and excellent cycle life. However, the present invention is not subject to any limitation of the positive electrode material, and thus is not limited to the materials.

The particle diameter of the positive electrode active material is set to be equal to or less than the thickness of the mixture layer containing the positive electrode active material, the conductive auxiliary agent, and the positive electrode binder. When the coarse particles having a size equal to or larger than the thickness of the mixture layer are present in the positive electrode active material powder, the coarse particles are removed in advance by sieve classification, gas flow classification, or the like to prepare particles having a thickness of the mixture layer or less.

Further, since the positive electrode active material is an oxide-based one and has high electrical resistance, a conductive auxiliary agent containing a carbon powder for replenishing the electrical conductivity is used. Thereby, there is an advantage that the positive resistance of the positive electrode or the battery characteristics are improved. A carbon material such as acetylene black, carbon black, graphite, or amorphous carbon, or a combination of two or more kinds of these carbon materials may be used for the conductive auxiliary agent. In order to form an electron mesh inside the positive electrode, it is desirable that the particle diameter of the conductive auxiliary agent is smaller than the average particle diameter of the positive electrode active material, and is 1/10 or less of the average particle diameter.

Since the positive electrode active material and the conductive auxiliary agent are both powders, the positive electrode binder is mixed in the powder to adhere the powder to the current collector while being bonded to each other.

An aluminum foil having a thickness of 10 μm to 100 μm or an aluminum perforated foil, an expanded metal, or a foamed metal plate having a thickness of 10 μm to 100 μm and having a diameter of 0.11 mm to 10 mm is used for the current collector. In addition to aluminum, the material is also available in stainless steel and titanium. In the present invention, the material, shape, manufacturing method, and the like of the current collector are not limited, and any current collector can be used.

In order to fabricate the positive electrode 110, it is necessary to prepare a positive electrode slurry. When the composition is exemplified, the positive electrode active material is 89 parts by weight, the acetylene black is 4 parts by weight, and the PVDF (polyvinylidene fluoride) positive electrode binder is 7 parts by weight, depending on the type of the material, the specific surface area, the particle size distribution, and the like. The change is not limited to the composition of the illustration. The solvent of the positive electrode slurry may be a solvent for dissolving the positive electrode binder, and in the case of the PVDF positive electrode binder, N-methyl-2-pyrrolidone is often used. However, the solvent can be appropriately selected depending on the kind of the positive electrode binder. A well-known kneader or disperser is used for the dispersion treatment of the positive electrode material.

After the positive electrode slurry in which the positive electrode active material, the conductive auxiliary agent, the positive electrode binder, and the solvent are mixed and dispersed is attached to the current collector by a doctor blade method, a dipping method, a spray method, or the like, the solvent is dried and pressed by a roll. The positive electrode is press-formed to form a mixture layer containing a positive electrode active material, a conductive auxiliary agent, and a positive electrode binder on the current collector, and the positive electrode can be produced by the above process. Further, a plurality of mixture layers may be laminated on the current collector by performing a plurality of operations from coating to drying.

The negative electrode 112 includes a negative electrode active material, a negative electrode binder, and a current collector. The negative electrode active material has a surface formed on a graphite core material (graphite particles) A core-shell structure with a coating. The negative electrode active material is a negative electrode active material which is an anode active material which can absorb and release lithium, and the negative electrode active material is a composite carbon having a low crystalline carbon coating layer on the surface of the graphite core material. The particles have a functional group of C=O, C-OH and CO on the surface of the coating layer, and the oxygen atom content in the total amount of carbon atoms and oxygen atoms of the coating layer is 2 atom% to 5 atom%. In the thermal gravimetric method in air, at least one oxidation peak is present in each temperature range of 350 ° C or more and less than 600 ° C and 600 ° C or more and 850 ° C or less, and is in a range of 350 ° C or more and 850 ° C or less. The peak temperature difference between the oxidation peak having the peak at the highest temperature and the oxidation peak having the peak at the lowest temperature is 300 ° C or lower. Specifically, a lithium ion battery of each of the negative electrode active materials was produced by using the negative electrode active materials produced in the respective examples described later.

In order to produce the negative electrode 112, it is necessary to prepare a negative electrode slurry. When the composition is exemplified, the negative electrode active material is 95 parts by weight, and the PVDF (polyvinylidene fluoride) negative electrode binder is 5 parts by weight, which may be changed depending on the type of the material, the specific surface area, the particle size distribution, and the like, and is not limited thereto. The composition of the illustration. The solvent of the negative electrode slurry may be a solvent for dissolving the negative electrode binder, and for the PVDF negative electrode binder, N-methyl-2-pyrrolidone is often used. However, the solvent can be appropriately selected depending on the kind of the negative electrode binder. A well-known kneader or disperser is used for the dispersion treatment of the negative electrode material.

After the negative electrode slurry in which the negative electrode active material, the negative electrode binder, and the solvent are mixed and dispersed is adhered to the current collector by a doctor blade method, a dipping method, a spray method, or the like, the solvent is dried, and the negative electrode is added by roll pressing. Press forming, Thereby, a mixture layer containing a negative electrode active material, a conductive auxiliary agent, and a negative electrode binder is formed on the current collector, and a negative electrode can be produced by the above process. Further, a plurality of mixture layers may be laminated on the current collector by performing a plurality of operations from coating to drying.

As shown in FIG. 1, a separator 111 is interposed between the positive electrode 110 and the negative electrode 112 to prevent short circuit between the positive electrode 110 and the negative electrode 112. As the separator 111, a polyolefin-based polymer film formed of polyethylene, polypropylene, or the like, or a multilayer structure in which a polyolefin-based polymer and a fluorine-based polymer film typified by polytetrafluoroethylene are fused can be used. Microporous membranes, etc. The separators 111 must pass lithium ions during charge and discharge of the battery, and therefore generally have pores having a pore diameter of 0.01 μm to 10 μm, and preferably have a porosity of 20% to 90%. Further, in order to prevent the separator 111 from shrinking when the battery temperature is increased, a mixture of ceramic and an organic resin-based adhesive may be formed into a thin layer on the surface of the separator 111. In the following description, a bulk structure including the positive electrode 110, the negative electrode 112, and the separator 111 is referred to as an electrode group.

Further, the separator 111 is also inserted between the electrode disposed at the end of the electrode group and the battery can 113 so that the positive electrode 110 and the negative electrode 112 are not short-circuited via the battery can 113. Further, an electrolyte containing an electrolyte and a nonaqueous solvent is held on the surface of the separator 111 and each of the electrodes (the positive electrode 110 and the negative electrode 112) and inside the pores.

The upper portion of the electrode group is electrically connected to the external terminal via a lead. The positive electrode 110 is connected to the battery cover 120 via the positive electrode current collecting tab 114. The negative electrode 112 is connected to the battery can 113 via the negative electrode current collecting tab 115. Further, the positive electrode current collecting tab 114 and the negative electrode current collecting tab 115 may have any shape such as a linear shape or a plate shape. The structure is such that the ohmic loss can be reduced when the current flows, and the shape and material of the positive electrode current collecting sheet 114 and the negative electrode current collecting sheet 115 can be arbitrary if it is a material that does not react with the electrolytic solution.

Although the structure of the electrode group is a wound shape structure as shown in FIG. 1, it can be made into an arbitrary shape according to the shape of the battery can 113. When the battery can 113 is of an angular shape, the shape of the positive electrode 110, the negative electrode 112, and the separator 111 may be further increased or wound into a flat shape.

The material of the battery can 113 can be selected from materials having corrosion resistance to nonaqueous electrolytes such as aluminum, stainless steel, and nickel plated steel. Further, in the case where the positive electrode current collecting tab 114 or the negative electrode current collecting tab 115 is electrically connected to the battery can 113, in the portion in contact with the nonaqueous electrolyte, corrosion of the battery can 113 or alloy with lithium ions is not generated. The material of the tab is selected in such a way as to deteriorate the material.

Thereafter, the battery cover 120 is brought into close contact with the battery can 113 to seal the entire battery. In the case of the shape of Fig. 1, a caulking method is employed. In addition to this method, there are known techniques such as welding and melting to seal the battery.

A typical example of the electrolytic solution which can be used in the present invention is a mixture of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or a combination of two or more thereof in ethylene carbonate. Among the solvents, lithium hexafluorophosphate (LiPF ₆ ) or lithium fluoroborate (LiBF ₄ ) is dissolved as a solution of the electrolyte. The present invention is not limited to the type of solvent or electrolyte, the mixing ratio of the solvent, and other electrolytes may be used. The electrolyte may be used in a state of being contained in an ion conductive polymer such as polyvinylidene fluoride or polyethylene oxide. In this case, the separator becomes unnecessary.

In addition, the solvents which can be used in the electrolyte are: propylene carbonate, ethylene carbonate, butylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, and carbonic acid. Ethyl ester, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl hydrazine, 1,3-dioxolane, formamide, dimethylformamide, propionic acid Methyl ester, ethyl propionate, triester phosphate, trimethoxymethane, dioxolane, diethyl ether, cyclobutyl hydrazine, 3-methyl-2-oxazolidinone, tetrahydrofuran, 1,2-di A nonaqueous solvent such as ethoxyethane, chloroethylene carbonate, or chloropropyl propylene carbonate. These solvents may be used singly or in combination of two or more. If it is not decomposed on the positive electrode or the negative electrode contained in the battery of the present invention, other solvents may be used.

Further, the electrolyte includes: LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , or lithium yttrium imide salt represented by lithium trifluoromethanesulfonimide. A variety of lithium salts. These electrolytes may be used singly or in combination of two or more. The nonaqueous electrolytic solution obtained by dissolving these salts in the above solvent can be used as the electrolyte solution for a battery. If it is not decomposed on the positive electrode or the negative electrode contained in the battery of this example, other electrolytes may be used.

When a solid polymer electrolyte (polymer electrolyte) is used, an ion conductive polymerization obtained by polymerizing monomers such as ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate, and hexafluoropropylene can be obtained. The substance is used in an electrolyte. These compounds may be used singly or in combination of two or more. In the case of using these solid polymer electrolytes, there is an advantage that the separator 111 can be omitted.

In addition, an ionic liquid can be used. For example, it can be selected from the group consisting of the following compounds for use in the lithium ion battery of the present invention: 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI) -BF ₄ ); a mixed salt of LiN(SO ₂ CF ₃ ) ₂ (LiTFSI) with triethylene glycol dimethyl ether and tetraethanol dimethyl ether; and a cyclic quaternary ammonium cation (example N -N-methyl-N-Propylpyrrolidinium) and quinone imine anion (exemplified by bis(trifluoromethylsulfonyl)imide) a combination of, and the combination is a combination that does not decompose on the positive or negative electrode. These compounds may be used singly or in combination of two or more.

The method of injecting the electrolytic solution is a method of directly adding the battery cover 120 to the electrode group in a state where the battery cover 120 is taken out from the battery can 113. In the case where the battery cover 120 has a liquid inlet, there is a method of adding from the liquid inlet.

Instead of the nonaqueous electrolyte, a solid polymer electrolyte (polymer electrolyte) or a gel electrolyte may be used. As the solid polymer electrolyte, a known polymer electrolyte such as polyethylene oxide or a mixture of polyvinylidene fluoride and a non-aqueous electrolyte (gel electrolyte) may be used. Moreover, an ionic liquid can also be used.

(Example 2)

This example is the same as Example 1 except for the matters specifically described below.

<Modulation of Graphite Nuclear Materials>

The graphite core material used in Example 2 used artificial graphite produced by an isotropic pressure treatment, but the present invention is not limited to this material. Here The isotropic pressurization treatment is not only a pressurization in a specific direction (an anisotropic pressurization treatment), but is generally known as a treatment of pressurization from all directions. When the carbon powder is subjected to an isotropic pressure treatment in this manner, the bulk density of the composite carbon particles for the lithium ion battery negative electrode and the fluidity of the negative electrode slurry are improved, and the density variation of the negative electrode of the produced lithium ion battery is small. The adhesion to the negative electrode current collector is improved. As a result, the cycle characteristics of the obtained lithium ion battery can be improved.

The method of isotropic pressure treatment of the carbon powder is not particularly limited as long as it is an isotropic pressure. For example, carbon powder is placed in a container such as a gum type, and water is used. The isostatic pressing of the hydrostatic pressure of the pressurized medium or the isostatic pressing using a gas such as air as the pressurized medium is performed by isostatic pressing of air pressure.

The pressure of the pressurized medium which is an isotropic pressure treatment of the carbon powder is preferably in the range of 4.9 × 10 ⁶ Pa to 1.96 × 10 ⁸ Pa (50 kgf / cm ² to 2000 kgf / cm ² ), and is 1.96. The range of ×10 ⁷ Pa~1.96×10 ⁸ Pa (200 kgf/cm ² to 2000 kgf/cm ² ) is more preferably 4.9×10 ⁷ Pa to 1.77×10 ⁸ Pa (500 kgf/cm ² to 1800 kgf/cm ^{2 ).} The scope of the) is even better. When the pressure is 4.9×10 ⁶ Pa (50 kgf/cm ² ) or more, the effect of improving the cycle characteristics of the obtained lithium ion battery tends to increase. Further, when the pressure is 1.96 × 10 ⁸ Pa (2000 kgf / cm ² ) or less, the specific surface area of the obtained composite carbon particles for a lithium ion battery negative electrode is suppressed, and as a result, the first lithium ion battery can be reduced. The tendency of the irreversible capacity of the secondary cycle.

If the carbon powder is subjected to isotropic pressure treatment as described above, the particles are Since it becomes easy to agglomerate with each other, it is preferable to perform processing such as crushing and screening after the isotropic pressure treatment. Further, when the particles do not aggregate with each other, they may not be broken.

By the above method, the cycle characteristics and the like can be greatly improved, and the composite carbon particles (negative electrode active material) for the lithium ion battery negative electrode produced by performing the isotropic pressure treatment can make the interlayer distance d (002) of the crystal at 0.3354 nm. In the range of 0.3370 nm, the crystallite size Lc (002) in the C-axis direction is in the range of 20 nm to 90 nm. The interlayer distance d (002) of the crystal and the crystallite size Lc in the C-axis direction can be obtained by an X-ray diffraction method. The X-ray diffraction method can be measured in accordance with the Gakushin-method method.

The carbon material to be subjected to the above-described isotropic pressure treatment is not particularly limited, and examples thereof include natural graphite, artificial graphite obtained by graphitizing coke, and graphitized organic polymer materials and pitch. Graphite, amorphous carbon, low temperature treated carbon, etc., of which artificial graphite is preferred.

In the main raw material that can be graphitized, such as coke powder or resin carbide, in addition to the asphalt or tar which is formed by bonding the main raw material to form a molded body, an organic material such as a thermosetting resin or a thermoplastic resin is added, and if necessary, part is required. The graphite powder and the catalyst (graphitization catalyst) for promoting the graphitization reaction are added, and the raw material mixture is graphitized and calcined at a temperature of 2500 ° C or higher. The obtained graphite calcined body is subjected to a pulverization step to produce artificial graphite. The crystallinity of the artificial graphite obtained by the above method is easily developed, and the discharge capacity of the obtained lithium ion battery can be improved.

Here, the graphitization catalyst is preferably a metal such as titanium (Ti), bismuth (Si), iron (Fe), nickel (Ni), or boron (B) or an oxide or carbide thereof. The graphitization catalyst is added when the main raw material and the organic material are mixed, and it is preferred to carry out mixing at the same time. The temperature at which mixing is carried out is preferably a temperature at which the organic material is softened and melted, and the temperature varies depending on the material to be used, and is preferably in the range of 50 ° C to 350 ° C. Further, when the organic material is brought into a solution by a solvent or the like, the graphitization catalyst may be mixed at a normal temperature.

Further, in the production of artificial graphite, the raw material mixture is pulverized and molded before being graphitized at a temperature of 2500 ° C or higher, and may be further calcined at a temperature of about 700 ° C to 1300 ° C. Further, the order of the process may be changed, and the preliminary calcination may be carried out at a temperature of about 700 ° C to 1300 ° C, followed by pulverization, and the powder having the adjusted particle size may be graphitized and calcined at a temperature of 2500 ° C or higher. The calcination temperature in the case of graphitization is preferably 2,500 ° C or more in terms of crystallinity and discharge capacity of the obtained graphite core material, more preferably 2800 ° C or more, and further preferably 3,000 ° C or more. . The environment at the time of calcination is not particularly limited as long as it is difficult to oxidize, and examples thereof include a self-volatile gas atmosphere, a nitrogen atmosphere, an argon atmosphere, and a vacuum.

In the preliminary calcination process described above, an organic material such as an aromatic organic molecule, coal tar or pitch is temporarily melted during the temperature rise, and the volatile component is detached to be condensed and carbonized.

The pulverization method of the graphitized calcined body is not particularly limited, and for example, a jet mill, a hammer mill, a needle mill can be used. Impact mill method such as pin mill. After the pulverization, the particle size was adjusted to prepare graphite particles. Further, in the case where the pulverization is performed before the graphitization to adjust the particle size, the pulverization may not be performed after the graphitization.

The graphite particles of the artificial graphite produced as described above were subjected to an isotropic pressure treatment to prepare a graphite core material. In addition, by coating the low-crystalline carbon described later, it is possible to obtain a composite carbon particle for a lithium ion battery negative electrode which is suitable for a lithium ion battery excellent in cycle characteristics and rapid charge and discharge characteristics.

<Formation of coating layer>

Here, as a treatment for coating the low-crystalline carbon, for example, a treatment of applying ultrasonic waves to a specific organic solvent in which a graphite core material is dispersed may be mentioned. In this treatment, first, an organic solvent is carbonized by application of a forward wave type ultrasonic wave to precipitate. The precipitation occurs on the surface of the dispersed graphite core material, so that a carbonaceous layer which does not adsorb unnecessary functional groups or the like can be formed on the surface of the graphite core material. As the specific organic solvent, for example, o-dichlorobenzene or the like can be mentioned, and o-dichlorobenzene is used in the present example.

Next, in order to fix the precipitated carbonaceous layer on the surface of the graphite core material by thermal decomposition, a coating layer of low crystalline carbon is formed and heat-treated. The heat treatment temperature varies depending on the starting material, and is preferably in the range of 400 ° C to 800 ° C, and particularly preferably in the range of 550 ° C to 750 ° C. The gas environment in the heat treatment is most preferably an inert gas atmosphere containing nitrogen or an inert gas. In the present example, the treatment was carried out in a state where nitrogen gas was circulated. Thereby, the combustion of the coating layer and the graphite core material can be prevented. Further, a small amount of oxygen is introduced into the coating layer, and when a carbonyl group or a hydroxyl group is actively introduced, a non-oxidizing ring having a trace amount of oxygen of 10% or less is mixed in an inert gas. Under the circumstances, adjust the oxygen concentration of the coating.

Further, as a method different from the above method of forming a coating layer on a graphite core material, a coating layer may be formed by using another organic polymer compound in a starting material of low crystalline carbon. Examples of the organic polymer compound include organic polymer compounds which are carbonized in a liquid phase such as various types of pitches (crude oil pitch, naphtha pitch, asphalt pitch, coal tar pitch, and decomposed pitch). A low crystalline carbon coating layer is formed on the surface of the graphite core material by thermal decomposition in a state in which the organic polymer compound is melted or the organic polymer compound is dissolved in a high boiling point solvent. Alternatively, a resin which is carbonized in a solid phase as described below may be used: a phenol resin, a furan methanol resin, a cellulose resin, a polyacrylonitrile, and a halogenated product such as polyvinyl chloride, polyvinylidene chloride, or chlorinated polyvinyl chloride. A vinyl resin, a polyamidoximine resin, a polyamide resin, or the like. The amount of the low crystalline carbon which coats the surface of the graphite core material is preferably 0.1% by weight or more based on the weight of the finally obtained composite carbon particles, and the balance between the effect of coating and the charge and discharge capacity is considered. More preferably, it is 0.1% by weight to 20% by weight, and still more preferably 1% by weight to 15% by weight, based on the weight of the composite carbon particles. Thereby, the thickness of the coating layer containing low crystalline carbon can be controlled to be 10 nm to 100 nm. Further, in the present invention, the content ratio of the low crystalline carbon in the composite carbon particles can be determined from the value of the weight change amount corresponding to the low crystalline carbon in the weight change measurement by the thermogravimetric analysis.

In the present example, the artificial graphite produced by the isotropic pressure treatment is a graphite core material, and the thickness of the coating layer is made 10 nm to 100 nm using o-dichlorobenzene. By making the heat treatment temperature when forming the cladding layer The composite carbon particles were obtained by treatment at 550 ° C under a nitrogen atmosphere.

The thickness of the coating layer can be measured by a transmission electron microscope (TEM) by cutting a cross section of the negative electrode active material by a focused ion beam processing apparatus (FIB). There is a variation in the thickness of the coating layer due to the measurement site. However, if at least the thickness of the coating layer is 10 nm or more, it is presumed that the electrolyte solution can be prevented from passing through the minute gap of the coating layer. Thereby, the electrolyte solution is prevented from directly contacting the edge surface of the highly active graphite core material, so that the decomposition reaction of the electrolytic solution accompanying the high temperature storage or the charge and discharge cycle is reduced, and the battery characteristics are improved. Further, when the thickness of the coating layer is 100 nm or less, the movement resistance of the coating portion of the lithium ion accompanying the charge and discharge reaction is preferably small.

(Example 3)

This example is the same as Example 1 except for the matters specifically described below.

<Modulation of Graphite Nuclear Materials>

In Example 3, artificial graphite was produced by adding coke powder as a main raw material for graphitization, petroleum pitch as a graphitizable organic material for bonding coke powder, and an iron-based graphitization catalyst. The addition of 1 wt% to 50 wt% of the graphitized catalyst is carried out, calcined and graphitized, and then pulverized to produce graphite.

Further, the present invention is not limited to the above materials. As the main raw material for graphitization, various cokes such as fluidized coke and needle coke can be used. As the main raw material for graphitization, it is preferable to contain coke powder in terms of charge and discharge capacity and rapid charge and discharge characteristics, and it is more preferable to contain needle coke powder. Further, a carbon material which has been graphitized such as natural graphite or artificial graphite may be added to one of the main raw materials. As in the above As the graphitizable organic material for bonding the main raw material to form a graphite molded body, various pitches and tars such as coal, petroleum, and artificial may be used. As the graphitization catalyst, iron, nickel, titanium, boron, rhodium, or the like, oxides, carbides, nitrides, or the like can be used.

By mixing the graphitizable organic material in the main material capable of graphitization in the above, the aspect ratio of the obtained graphite particles (graphite core material) can be reduced, and a plurality of flat particles can be assembled or combined. Made of graphite particles. As a result, the rapid charge and discharge characteristics and cycle characteristics of the produced lithium ion battery can be improved.

Further, as the graphitizable organic material, an organic material such as a thermosetting resin or a thermoplastic resin may be used in addition to the asphalt or the tar. The amount of addition of the organic material that can be graphitized varies depending on the residual carbon ratio and the adhesive strength of the organic material to be used. For example, in the case of using asphalt, it is relative to 100 parts by weight of the main raw material that can be graphitized. It is preferably 10 parts by weight to 100 parts by weight, more preferably 10 parts by weight to 70 parts by weight, still more preferably 10 parts by weight to 50 parts by weight.

The blending ratio of the graphitization catalyst can be selected according to the specific particle characteristics of the target graphite particles (graphite core material), and is preferably a raw material mixed with a main raw material such as coke, an organic material such as pitch, and a graphitization catalyst. For the total weight of the mixture, 1 wt% to 50 wt% of graphitization catalyst is added. The blending ratio of the graphitized catalyst can be selected according to the specific graphite characteristics of the target graphite particles (graphite core material). When the amount of the graphitization catalyst is 1% by weight or more, the development of crystals of the graphite particles is improved, and the charge and discharge capacity is increased, so that the discharge capacity of the obtained lithium ion battery can be increased. another On the other hand, when the amount of the graphitization catalyst is 50% by weight or less, it becomes easy to uniformly mix, and it is possible to avoid deterioration in workability and widening variation in characteristics of the obtained graphite particles. In particular, the addition amount of the graphitization catalyst is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 1% by weight to 5% by weight. When the addition amount of the graphitization catalyst is increased within the above range, the discharge capacity tends to increase. When the amount is decreased within the above range, the specific surface area tends to decrease and the bulk density tends to increase.

Further, the graphitization catalyst is preferably a metal such as Ti, Si, Fe, Ni, or B or an oxide or a carbide thereof, and is added when the main raw material and the organic material are mixed, and it is preferred to carry out mixing at the same time.

The temperature at which the graphitization catalyst is mixed in the above is preferably a temperature at which the organic material which can be graphitized is softened and melted. The temperature varies depending on the materials used, and is preferably in the range of 50 ° C to 350 ° C. Further, when the graphitizable organic material is brought into a solution by a solvent or the like, it may be mixed at normal temperature.

Next, the raw material mixture in which the graphitizable main raw material, the graphitizable organic material, and the graphitization catalyst are mixed is preliminarily calcined at 500 ° C to 2000 ° C, and the calcined product is further pulverized to have an average particle diameter. It is adjusted to 10 μm to 100 μm, and it is preferred to further graphitize the pulverized material by a temperature of 2500 ° C or higher.

The preliminary calcination temperature before the pulverization is preferably 500 ° C to 1500 ° C, and more preferably 700 ° C to 1500 ° C. When the preliminary calcination temperature before pulverization is 2000 ° C or lower, the obtained graphite particles (graphite core material) have a high bulk density, a small specific surface area, and a tendency to decrease the aspect ratio. and, When the preliminary calcination temperature before the pulverization is 500° C. or higher, there is a tendency that the carbonization of the added graphitizable organic material is sufficient, and as a result, the bonding between the particles can be suppressed after the pulverization or graphitization. Further, the raw material mixture may be shaped into an appropriate shape as needed before preliminary calcination. The preliminary calcination is preferably carried out in an environment where the raw material mixture is difficult to be oxidized, and for example, a method of calcining in a nitrogen atmosphere, argon gas or vacuum.

It is then graphitized. The method of graphitization is not particularly limited, and for example, the graphite particles obtained by graphitization at a temperature of 2500 ° C or higher in a self-volatile gas atmosphere, a nitrogen atmosphere, an argon atmosphere, a vacuum, etc., are in crystallinity and discharge capacity. It is better in terms of aspects. The graphitization temperature is more preferably 2700 ° C or more, more preferably 2900 ° C or more, and particularly preferably 3,000 ° C or more. The upper limit of the graphitization temperature is preferably 3200 ° C or lower. The higher the temperature of graphitization, the better the development of graphite crystals and the fact that the graphitization catalyst hardly remains in the produced graphite particles, and the charge and discharge capacity tends to increase in any case.

The pulverization treatment is carried out after the graphitization treatment. The method of pulverization is not particularly limited, and for example, a impact pulverization method such as a jet mill, a hammer mill, or a pin mill can be employed.

<Formation of coating layer>

On the graphite particles (graphite core material) obtained as described above, the low crystalline carbon was coated as follows. The type of the organic polymer compound which is a starting material of the low crystalline carbon which coats the graphite core material, and the coating amount of the low crystalline carbon obtained by carbonizing it are not particularly limited. As Examples of the organic polymer compound include organic polymer compounds which are carbonized in the liquid phase: various types of pitches (crude oil pitch, naphtha pitch, asphalt pitch, coal tar pitch, decomposed pitch, etc.). Alternatively, a phenol resin, a furan methanol resin, a cellulose resin, a polyacrylonitrile, and a halogenated vinyl resin such as polyvinyl chloride, polyvinylidene chloride or chlorinated polyvinyl chloride may be mentioned. The amount of the low crystalline carbon which coats the surface of the graphite core material is preferably 0.1% by weight or more based on the weight of the finally obtained composite carbon particles, and the balance between the effect of coating and the charge and discharge capacity is considered. More preferably, it is 0.1 wt% to 20 wt%, and still more preferably 1 wt% to 15 wt%. Thereby, the thickness of the coating layer containing low crystalline carbon can be controlled to be 10 nm to 100 nm.

In Example 3, the thickness of the coating layer was made 10 nm to 100 nm using a carboxymethylcellulose resin, and the heat treatment temperature at the time of forming the coating layer was 750 °C. The gaseous environment is nitrogen.

The thickness of the coating layer can be measured by a penetrating electron microscope (TEM) by cutting a cross section of the negative electrode active material by a focused ion beam (FIB). There is a variation in the thickness of the coating layer due to the measurement site. However, if at least the thickness of the coating layer is 10 nm or more, it is presumed that the electrolyte solution can be prevented from passing through the minute gap of the coating layer. Thereby, the electrolyte solution is prevented from directly contacting the edge surface of the highly active graphite core material, so that the decomposition reaction of the electrolytic solution accompanying the high temperature storage or the charge and discharge cycle is reduced, and the battery characteristics are improved. Further, when the thickness of the coating layer is 100 nm or less, the movement resistance of the coating portion of the lithium ion accompanying the charge and discharge reaction is preferably small.

(Example 4)

This example is the same as Example 1 except for the matters specifically described below.

<Modulation of Graphite Nuclear Materials>

The graphite core material used in Example 4 was a carbon material having a graphite structure. That is, natural graphite, artificial graphite, mesophase carbon, expanded graphite, carbon fiber, vapor-deposited carbon fiber, pitch-based carbonaceous material, needle coke, petroleum coke, which can electrochemically absorb and release lithium ions A carbonaceous material such as polyacrylonitrile-based carbon fiber or carbon black, or an amorphous carbon material synthesized by thermal decomposition of a 5-membered ring or a 6-membered ring hydrocarbon or a cyclic oxygen-containing organic compound.

The graphite core material can be produced by the following method. 50 parts by weight of coke powder having an average particle diameter of 5 μm, 20 parts by weight of tar pitch, 7 parts by weight of niobium carbide having an average particle diameter of 48 μm, and 10 parts by weight of coal tar were mixed, and mixed at 200° C. for 1 hour. The obtained mixture was pulverized, pelletized by pressure, and then calcined at 3000 ° C in a nitrogen atmosphere. The obtained calcined product was pulverized by a hammer mill to prepare graphite particles (graphite core material) having an average particle diameter of 20 μm.

The coke powder used herein is not limited to the above conditions, and a material of 1 μm to several tens of μm may be selected. Further, the composition of the coke powder or the tar pitch may be appropriately changed. Other conditions such as the heat treatment temperature are not limited to the above.

<Formation of coating layer>

A low crystalline carbon coating layer can be formed on the graphite core material produced in Example 4 by the following procedure. First, 100 parts by weight of the graphite particles (graphite core material) obtained above were immersed and dispersed in a novolac type phenol resin methanol solution (manufactured by Hitachi Chemical Co., Ltd.) 160 weight. A graphite particle-phenol resin mixture solution was prepared in portions. The solution is filtered, dried, and heat-treated in the range of 800 ° C to 1000 ° C to obtain composite carbon particles having a low crystalline carbon coating layer formed on the surface of the graphite core material. The gas atmosphere is a mixed gas atmosphere (non-oxidizing environment) in which 0.5% to 1% of oxygen is added to nitrogen. Further, in addition to the phenol resin, it may be replaced with a polycyclic aromatic compound such as naphthalene, anthracene or creosote.

The specific surface area of the above composite carbon particles obtained by the BET method was 3.6 m ² /g. Further, the interlayer distance d002 of the graphite crystal obtained by the X-ray wide-angle firing method is 0.3354 nm to 0.3370 nm, and the crystallite size Lc is in the range of 20 nm to 90 nm. The intensity ratio (I ₁₃₆₀ /I ₁₅₈₀ ) of the Raman peak at the position of 1580 cm ^-1 and 1360 cm ^-1 is in the range of 0.1 to 0.7.

Further, a coating method of low crystalline carbon by other methods can be applied. For example, there is also a method in which polyvinyl alcohol is coated on graphite particles (graphite core material) to thermally decompose it. In this case, it is desirable that the heat treatment temperature is in the range of 500 ° C to 800 ° C.

Further, as an alternative method, particles such as polyvinyl chloride or polyvinylpyrrolidone may be directly added, followed by heat treatment. These compounds are mixed with graphite particles (graphite core material), and then heated to a temperature at which thermal decomposition occurs to form a coating layer.

Further, in order to impart oxygen to the low-crystalline carbon coating layer to achieve the oxygen concentration necessary for the present invention, surface modification such as oxidation treatment, plasma treatment, or ultraviolet (UV) treatment using ozone or the like may be performed. When the coating material is thermally decomposed, a trace amount of oxygen of 10% or less can be added to the inert gas, so that The surface modification is carried out using the mixed gas.

A low-crystalline carbon coating layer was formed on the surface of the graphite core material as described above, and the powder was cut into a cross section by FIB, and the thickness of the carbon layer was measured by TEM. As a result, although there is a variation, the thickness of the low-crystalline carbon coating layer is in the range of 10 nm to 100 nm. When the thickness of the coating layer is 10 nm or more, it is presumed that the passage of the electrolytic solution from the minute gap of the coating layer can be suppressed. Thereby, the electrolyte solution is prevented from directly contacting the edge surface of the highly active graphite core material, so that the decomposition reaction of the electrolytic solution accompanying the high temperature storage or the charge and discharge cycle is reduced, and the battery characteristics are improved. Further, when the thickness of the coating layer is 100 nm or less, the movement resistance of the coating portion of the lithium ion accompanying the charge and discharge reaction is preferably small.

(Example 5)

The surface of the negative electrode active material (composite carbon particles) of the above Example 3 was treated with ozone to prepare a negative electrode active material having an increased oxygen content. Other than the example 3, the same.

(Example 6)

In the formation of the coating layer of the above Example 3, the starting material of the low crystalline carbon coated with the graphite core material was changed from the carboxymethyl cellulose resin to the crude oil pitch to prepare a negative electrode active material. Other than the example 3, the same.

(Comparative Example 1)

The graphite core material produced in Example 4 was used for the negative electrode active material.

<Evaluation of Negative Electrode Active Material of Example 2 to Example 6>

(1) Evaluation of Example 4

The anode active material (composite carbon) prepared in Example 4 in air Particles) Perform thermogravimetric/thermal differential synchronization analysis (TG-DTA). It is known that the combustion behavior of the carbon material reflects the crystallinity and the specific surface area, and the difference between the combustion behaviors can be used to separate the oxidation peak of the carbon derived from the coating layer and the carbon derived from the graphite core material. It is known that, in general, the peak of graphite derived from high crystallinity appears in the vicinity of 900 ° C (for example, FIG. 1 of Japanese Patent Laid-Open No. 2001-229914), and the lower the crystallinity and the high specific surface area, the more Oxidation at low temperatures. The thermogravimetric/thermal differential synchronization analyzer was used in the measurement, and the measurement temperature range was room temperature to 1100 ° C, the heating rate was 5 ° C / min, and the environment was air, 80 mL / min. The measurement container was made up of 70 μl of alumina tank, and the weight of the sample was 10 mg.

The results are shown in Figure 2. The TG-DTA data of Fig. 2 is the measurement result of the composite carbon particles corresponding to Example 4 of Table 1. The treatment weight change (left vertical axis) is substantially fixed to 350 ° C, but if it becomes a temperature of 350 ° C or higher, the weight starts to gradually decrease, and the weight becomes zero at about 700 ° C (that is, complete oxidation combustion). The temperature differential value (right vertical axis) of the weight change at this time shows two oxidation peaks in the low temperature region near 411 ° C and the high temperature region at 678 ° C. The former implies an oxidation reaction of the coating layer, and the weight reduction amount at this time is 10% by weight. It is presumed that since the coating layer of Example 4 has an oxygen functional group on the surface, it becomes easy to be oxidized at a lower temperature than ordinary graphite. Moreover, the latter is an oxidation reaction of a graphite core material. The peak value of the temperature differential value (right axis) attributed to the weight change of the oxidation reaction was 678 ° C, which became lower than the peak position of the general high crystalline graphite material. The reason is considered to be that the coating layer of Example 4 has high reactivity with oxygen, and also affects the oxidation reaction of the internal graphite core material covered by the low crystalline carbon coating layer.

That is, the oxidation peak temperature (678 ° C) of the graphite core material is within 300 ° C with respect to the oxidation peak temperature (411 ° C) of the coating layer, which is one of the characteristics of the present example. Further, the content of the coating layer in the composite carbon particles corresponds to the weight loss (10 wt%) with the oxidation reaction, and the content of the low crystalline carbon in the composite carbon particles in the present example is 0.1 wt%. 20wt% is also a feature.

(2) Evaluation of Example 3

Next, Fig. 3 shows the results of thermogravimetric/thermal differential synchronization analysis (TG-DTA) of the negative electrode active material (composite carbon particles) of Example 3 in which the conditions for forming the coating layer were changed. The weight change (left vertical axis) is substantially fixed to 450 ° C, but if it becomes a temperature of 450 ° C or higher, the weight starts to gradually decrease, and the weight becomes zero at about 900 ° C (that is, complete oxidation combustion). The temperature differential value (right vertical axis) of the weight change at this time shows two oxidation peaks of a low temperature range of 599 ° C and a high temperature range of 801 ° C. The former implies an oxidation reaction of the coating layer, and the weight reduction amount at this time is 15% by weight. It is presumed that since the coating layer of Example 3 has an oxygen functional group on the surface, it becomes easier to be oxidized than Example 4.

Further, similarly to Fig. 2, the temperature (801 ° C) of the temperature differential value peak (right axis) attributed to the weight change of the oxidation reaction of the latter becomes lower than the oxidation peak temperature of the general high crystalline graphite material. The reason is considered to be that the coating layer of Example 3 has high reactivity with oxygen and affects the oxidation reaction of the graphite core material inside the coating layer. That is, the oxidation peak temperature (801 ° C) of the graphite core material is within 300 ° C with respect to the oxidation peak temperature (599 ° C) of the coating layer, which is one of the characteristics of the present example.

At the same time, in the TG-DTA measurement data, there are at least one oxidation peak in each temperature range of at least 400 ° C to 600 ° C and 650 ° C to 850 ° C, and each oxidation peak is compared with that of a generally high crystalline graphite material. The phenomenon that the temperature at which the oxidation peak appears on the low temperature side is also another feature of this example. Further, the content of the coating layer in the composite carbon particles corresponds to the weight loss (15 wt%) according to the oxidation reaction, and the content of the low crystalline carbon in the composite carbon particles is also 0.1 wt% to 20 wt%. One of the features.

(3) Evaluation of Example 2

In the thermogravimetric/thermal differential-synchronization analysis (TG-DTA) result of the negative electrode active material (composite carbon particles) in Example 2, an oxidation peak derived from the coating layer was obtained at a low temperature side of 540 ° C to 560 ° C, at 810 The oxidation peak derived from the graphite core material is obtained on the high temperature side of °C to 830 °C. The weight reduction amount of the oxidation reaction of the coating layer was 1% by weight. From this, it is understood that the tendency of the two oxidation peaks of the negative electrode active material in Example 2 and the content ratio of the low crystalline carbon in the composite carbon material satisfy the above characteristics.

(4) Evaluation of Example 5

The negative electrode active material (composite carbon particles) in Example 5 was a material which treated the surface of the negative electrode active material in Example 3 by ozone to increase the oxygen content as described above. In the thermogravimetric/thermal differential synchronization analysis (TG-DTA) result of the negative electrode active material in Example 5, an oxidation peak derived from the coating layer appeared at 530 ° C to 550 ° C, and a source appeared at 750 ° C to 770 ° C. From the oxidation peak of the graphite core material, the weight reduction amount of the oxidation reaction of the coating layer was 0.1% by weight. The peak temperature was shifted toward the low temperature side as compared with the measurement results obtained with respect to the negative electrode active material in Example 3. Speculate The reason is that the oxygen content of the coating layer in Example 5 was increased as compared with Example 3, and thus it became easier to be oxidized. It is considered that the reactivity with oxygen is higher, and the oxidation reaction of carbon inside the coating layer becomes more likely to occur. Further, the coating layer is reduced by ozone treatment, but the content of the low crystalline carbon in the composite carbon particles is from 0.1% by weight to 20% by weight.

(5) Evaluation of Example 6

In the thermogravimetric/thermal differential-synchronization analysis (TG-DTA) result of the negative electrode active material (composite carbon particles) in Example 6, the oxidation peak derived from the coating layer was obtained at a low temperature side of 500 ° C to 520 ° C, at 760 The oxidation peak derived from the graphite core material is obtained on the high temperature side of °C to 780 °C. The weight reduction amount of the oxidation reaction of the coating layer is 20% by weight, which satisfies the features of the present invention.

(5) Surface analysis of the negative active material used in Examples 2 to 6

Next, surface analysis of the negative electrode active material (composite carbon particles) used in Example 2, Example 3, Example 4, Example 5, and Example 6 was carried out by X-ray photoelectron spectroscopy (XPS). The results are shown in Table 1. In this measurement, in order to remove a trace amount of pollutants from the atmosphere, argon etching was performed in advance before measurement. After the negative electrode active material was attached to an X-ray photoelectron spectroscopy (XPS) apparatus, vacuum evacuation was performed sufficiently, and argon ion etching was performed under high vacuum. The ion current and the etching time were set such that the etching amount (depth) in terms of cerium oxide was 2 nm. Thereafter, XPS spectrometry of C1s and O1s was performed.

The assignment of the chemical bond state from the XPS spectrum of C1s is carried out as follows. The C-O or C-OH bond is in the peak position in the range of 286.3 ± 0.3 eV, The C-H bond is in the peak position in the range of 285.1 ± 0.3 eV, and the C-C bond is in the peak position in the range of 284.3 ± 0.3 eV, curve fitting of each spectrum is performed, and the ratio of each key (atom%) is calculated. Similarly, the assignment of the chemical bond state of XPS from O1s is carried out as follows. That is, the CO bond is in the peak position in the range of 533.6±0.3 eV, the C-OH bond is in the peak position in the range of 532.3±0.3 eV, and the C=O bond is in the peak position in the range of 531.2±0.3 eV. The curve of each spectrum is fitted, and the ratio of each key (atom%) is calculated.

First, the carbon concentration (atomic percentage) of the surface (coating layer) of the negative electrode active material of Example 2 was 97.9 atom%, and the oxygen concentration was 2.1 atom%. According to the XPS analysis of C1s, the carbon containing 4 atom% of CO or C-OH relative to the total carbon amount, most of the carbon is in the bonding state of CC or CH, wherein the bonding state of CC is the total carbon amount. 70atom%~80atom%. In the case of Example 3, Example 4, and Example 5, no significant difference was found with respect to the state of carbon.

Secondly, according to the XPS analysis of O1s, the oxygenated chemical species are assigned to C=O, C-OH, and C-O. It can be seen that the surface of the negative electrode active material of Example 2, in which C-OH and C-O are main components, further contains a chemical species belonging to a high oxidation number state of C=O. The respective ratios of existence are C=O of 12 atom%, C-OH of 40 atom%, and C-O of 48 atom%. In addition, since this analysis has a measurement error of about ±3 atom%, it can be understood that the amount of C=O is in the range of 9 atom% to 15 atom% of the total oxygen amount.

The surface (coating layer) of the negative electrode active material of Example 3 had a carbon concentration (atomic percentage) of 97.8 atom% and an oxygen concentration of 2.2 atom%. and, According to the results of XPS analysis of O1s, it was found that the surface of the negative electrode active material of Example 3 had C-OH and C-O as main components, and C=O in a high oxidation number state.

The surface (coating layer) of the negative electrode active material of Example 4 had a carbon concentration (atomic percentage) of 97.1 atom% and an oxygen concentration of 2.9 atom%. Further, from the results of XPS analysis of O1s, it was found that the surface of the negative electrode active material of Example 4 had C-OH and C-O as main components, and C=O in a high oxidation number state.

The surface (coating layer) of the negative electrode active material of Example 5 had a carbon concentration (atomic percentage) of 95.7 atom% and an oxygen concentration of 4.3 atom%. According to the results of XPS analysis of O1s, it was found that C=O, C-OH, and C-O were present in substantially equal amounts on the surface of the negative electrode active material of Example 5. Specifically, the surface of the negative electrode active material of Example 5 contained C=O in a high oxidation number state of 36 atom% of the total oxygen amount. Considering that the analysis has a measurement error of ±3%, it can be understood that the surface of the negative electrode active material of Example 5 has a C=O amount ranging from 33 atom% to 39 atom% of the total oxygen amount.

Finally, the surface (coating layer) of the negative electrode active material of Example 6 had a carbon concentration (atomic percentage) of 97.5 atom% and an oxygen concentration of 2.5 atom%. Further, from the results of XPS analysis of O1s, it was found that the surface of the negative electrode active material of Example 6 had C-OH and C-O as main components, and C=O in a high oxidation number state.

XPS analysis of the graphite core material of Comparative Example 1 was carried out. The oxygen concentration on the surface of the graphite core material was substantially the same as that on the surface of the negative electrode active material of Examples 2 to 4, and the surface of the negative electrode active material of Examples 2 to 6 was apparent. The difference is that C=O is not found in the high oxidation number state.

It is understood that in the anode active materials of Example 2, Example 3, Example 4, Example 5, and Example 6, the oxygen-containing carbon layer shown in Table 1 was formed as a coating layer on the surface of the graphite core material. The coating is intimately bonded to the inner graphite core material, which is presumed to have some influence on the oxidation reaction characteristics of FIGS. 2 and 3. The effects and effects are as follows.

The oxidation peak on the high temperature side shown in Fig. 2 and Fig. 3 is produced by the oxidation reaction of the graphite core material of the anode active material (composite carbon particles) of the present invention. The temperature of the oxidation reaction is shifted to the low temperature side as compared with the oxidation peak of the graphite element (for example, about 900 in the vicinity of C in Fig. 1 described in Japanese Patent Laid-Open Publication No. 2001-229914). . It can be inferred that in the tests of Fig. 2 and Fig. 3, if the low crystalline carbon of the coating layer is oxidatively decomposed, the reaction becomes the starting point of the oxidation reaction of the graphite core material, and the oxidative decomposition of the graphite core material itself is promoted. Therefore, the high temperature side peak of the negative electrode active material of the present invention is shifted toward the low temperature side, suggesting that the coating layer containing low crystalline carbon is excellent in adhesion to the surface of the graphite core material and throwing power, that is, The coating layer coats the surface of the graphite core material uniformly and densely. However, the invention is not limited to this theory.

As shown in the above properties of the negative electrode active material of Examples 2 to 6, in the present invention, the surface of the coating layer can have C=O by changing the heat treatment conditions when the coating layer is formed on the graphite core material. a C-OH and a CO functional group, and the content of the oxygen atom of the functional group in the coating layer is equivalent to 2 atom% to 5 atom% of oxygen in the total amount of carbon atoms and oxygen atoms of the coating layer. The amount. It is particularly desirable that the surface of the coating be highly oxygenated In the case of the state of the number, that is, the amount of oxygen of C=O attributed to the spectrum of the XPS of O1s is 7 atom% to 39 atom% with respect to the total oxygen amount of the coating layer. Such a negative electrode active material is a material having a characteristic of at least 1 in a temperature range of at least 350 ° C and less than 600 ° C and 600 ° C or more and 850 ° C or less in a thermogravimetric/thermal differential synchronous analysis method in the atmosphere. The oxidation peak is in the range of 350 ° C or more and 850 ° C or less, and the peak temperature difference between the oxidation peak having the peak at the highest temperature and the oxidation peak having the peak at the lowest temperature is 300 ° C or lower. It has been found that when a negative electrode active material satisfying such a requirement is used in a lithium ion battery, the storage characteristics or cycle life of the battery are effectively improved. The detailed test results are as described later.

Here, it is presumed that since the adhesion between the coating layer and the surface of the graphite core material is increased, the coating layer is uniformly and densely coated on the surface of the graphite core material, thereby preventing the electrolyte from directly contacting the surface of the graphite core material. As a result, it becomes difficult for the electrolytic solution to reach the edge portion (the end portion of the graphite structure) of the high-activity graphite core material, so that the reduction decomposition of the electrolytic solution is suppressed and the battery characteristics are improved.

The atomic ratio of carbon and oxygen of the functional group on the surface of the low-crystalline carbon coating layer of the negative electrode active material (composite carbon particles) of Examples 2 to 6 above, the C1s analysis result, and the O1s analysis result are shown in Table 1. in. Further, the numerical values shown in the column of the C1s analysis result and the O1s analysis result of Table 1 indicate the respective key ratios (atom%). The coating layer containing the C=O bond in the coating layer of the negative electrode active material (composite carbon particles) of Examples 2 to 6 is a large feature, and the ratio of C-OH and C=O is a respective functional group. The atomic composition ratio of oxygen in the range is 1:1~4:1.

When the negative electrode active material (composite carbon particles) described above is used to produce a negative electrode, it becomes necessary to have a higher level of charge and discharge characteristics. In this case, a conductive additive may also be added to the negative electrode. The conductive auxiliary agent does not participate in the absorption and release of lithium ions, and functions as a medium for electrons, and thus does not affect the absorption and release reaction of lithium ions in the negative electrode active material.

Further, a conductive polymer material containing polyacene, polyparaphenylene, polyaniline or polyacetylene may be added to the negative electrode and used.

In the examples 2 to 6, the negative electrode active material is a powder, and thus the negative electrode binder is mixed therein to adhere the powder to the current collector while being bonded to each other. In the present invention, it is preferable that the particle diameter of the negative electrode active material in the negative electrode is equal to or less than the thickness of the mixture layer containing the negative electrode active material and the negative electrode binder. In the case where the negative electrode active material contains coarse particles having a size equal to or greater than the thickness of the mixture layer, it is preferred to remove coarse particles in advance by sieve classification, gas flow classification, or the like, and to use the thickness of the mixture layer or less. particle.

The current collector uses a copper foil with a thickness of 10 μm to 100 μm and a thickness of 10 A copper perforated foil, a porous metal, a foamed metal plate, etc. having a pore diameter of 0.1 mm to 10 mm and a material having a pore diameter of 0.1 mm to 10 mm may be made of stainless steel, titanium, nickel or the like in addition to copper. In the present invention, the material, shape, manufacturing method, and the like of the current collector are not limited, and any current collector can be used.

After the negative electrode slurry in which the negative electrode active material, the negative electrode binder, and a suitable solvent are mixed is attached to the current collector by a doctor blade method, a dipping method, a spray method, or the like, the solvent is dried and pressed by a roll. On the other hand, the negative electrode was formed by press molding the negative electrode.

<Electrochemical evaluation 1>

Using the negative electrode active material (composite carbon particles) shown in Table 1, Li metal was used as a counter electrode, and an electrochemical cell using Li metal as a reference electrode was assembled. The unit using the negative electrode active material of Example 2 was designated as C1, the unit using the negative electrode active material of Example 3 was designated as C2, and the unit using the negative electrode active material of Example 4 was designated as C3, and the negative electrode active material of Example 5 was used. The unit was C4, the unit using the negative electrode active material of Example 6 was C5, and the unit using the negative electrode active material of Comparative Example 1 was C6. 5 parts by weight of PVDF was mixed as a negative electrode binder in 95 parts by weight of each of the negative electrode active materials, and N-methyl-2-pyrrolidine was added in such a manner that the total solid content of the negative electrode active material and PVDF in the negative electrode slurry was 55 wt%. The ketone acts as a solvent. The mixture was thoroughly kneaded using a planetary mixer, and the obtained negative electrode slurry was applied onto the surface of a copper foil current collector having a thickness of 10 μm by a doctor blade method. N-methyl-2-pyrrolidone was dried using a drying oven at 120 ° C in an air atmosphere, and then subjected to press molding using a roll press to prepare respective negative electrodes. The negative electrode mixture density was 1.5 g/cm ³ . As the separator, a microporous sheet (having a thickness of 25 μm) in which polyethylene and polypropylene were laminated was used. As the electrolytic solution, an electrolyte containing ethylene carbonate dissolved in 1 M of LiPF ₆ and dimethyl carbonate and ethyl methyl carbonate was used. Further, the volume ratio of each solvent was 1:1:1.

The above six types of cells were charged at a current density of 0.1 mA/cm ² (corresponding to a current density of about 8 hours) at a lower limit voltage of 10 mV and a maximum charging time of 8 hours, after which 30 minutes passed. After the stop time, discharge was performed at a constant current density (0.1 mA/cm ² ) of an upper limit voltage of 1V. After the lapse of 30 minutes, the above-described charge-discharge cycle was repeated.

Table 2 shows the results of "initial discharge capacity" and the "irreversible capacity" obtained by the difference between the initial charge capacity and the discharge capacity. Further, each capacity is calculated per unit weight of the negative electrode active material used. It is understood that the unit (C1 to C5) using the negative electrode active material of the example of the present invention has a small irreversible capacity with respect to the unit C6 using the negative electrode active material of Comparative Example 1, and the initial discharge capacity is also large.

<Electrochemical evaluation 2>

Using the negative electrode active material (composite carbon particles) of Examples 2 to 6 shown in Table 1, the cylindrical battery of Fig. 1 was produced, and a battery characteristic evaluation test was performed. A battery using the negative electrode active material of Example 2 shown in Table 1 was set to B1, a battery using the negative electrode active material of Example 3 was set to B2, and a battery using the negative electrode active material of Example 4 was set to B3, which was used. The battery of the negative electrode active material of Example 5 was B4, the battery using the negative electrode active material of Example 6 was B5, and the battery using the negative electrode active material of Comparative Example 1 was B6. Mixing PVDF 5 in 95 parts by weight of each negative electrode active material In the negative electrode binder, N-methyl-2-pyrrolidone was added as a solvent so that the total solid content of the negative electrode active material and PVDF in the negative electrode slurry was 55 wt%. The mixture was thoroughly kneaded using a planetary mixer, and the obtained negative electrode slurry was applied onto the surface of a copper foil current collector having a thickness of 10 μm by a doctor blade method. N-methyl-2-pyrrolidone was dried using a drying oven at 120 ° C in an air atmosphere, and then subjected to press molding using a roll press to prepare respective negative electrodes.

The positive electrode active material used in each of the batteries (B1 to B6) was LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . The positive electrode active material was mixed with 89 parts by weight, acetylene black was 4 parts by weight, and PVDF as a positive electrode binder was added in an amount of 7 parts by weight to prepare a positive electrode slurry to which N-methyl-2-pyrrolidone was added. A well-known kneader or disperser is used for the dispersion treatment of the material. The weight per unit area of the positive electrode active material and the thickness and density of the positive electrode are the same conditions in each battery.

As the separator, a microporous sheet (having a thickness of 25 μm) in which polyethylene and polypropylene were laminated was used.

As the electrolytic solution, an electrolyte containing ethylene carbonate dissolved in 1 M of LiPF ₆ and dimethyl carbonate and ethyl methyl carbonate was used. Further, the volume ratio of each solvent was 1:1:1.

A charging current corresponding to a current value (15 A) at a rate of 1 hour was passed through each battery, and charging was performed for 1 hour by a constant voltage of 4.2 V. Next, a discharge current of 15 A was passed and discharged until the battery voltage reached 3.0V. Further, 100 cycles of charge and discharge were continued under the same conditions, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity was determined. Capacity retention rate over 100 cycles. The results are shown in the column "Capacity retention rate (%) after 100 cycles" in Table 2.

The above measurement results are summarized in Table 2. It is understood that the batteries (B1 to B5) of the examples of the present invention are superior to the battery (B6) of the comparative example in terms of capacity retention rate after 100 cycles.

<Electrochemical evaluation 3>

Eight cylindrical lithium ion batteries of Fig. 1 were connected in series, and the battery pack (battery module) 401 of Fig. 4 was assembled and assembled into the power supply system of Fig. 4. The lithium ion battery is the lithium ion battery fabricated in the above electrochemical evaluation 2. The power storage system can be used as a mobile body or a stationary power storage system.

In addition, in FIG. 4, 401 denotes a battery pack, 402 denotes a lithium ion battery (single cell), 403 denotes a positive electrode terminal, 404 denotes a bus bar, 405 denotes a battery can, 406 denotes a support part, 407 denotes a positive external terminal, and 408 denotes a positive electrode external terminal. The negative external terminal, 409 represents a calculation processing unit, 410 represents a charge and discharge circuit, 411 represents an external device, 412 represents a power line, 413 represents a signal line, and 414 represents an external power cable.

A cylindrical lithium ion battery (hereinafter referred to as "battery") 402 is supported by The part 406 is fixed. Each of the batteries alternately exchanges the direction of the positive electrode terminal 403 and the battery can 405, and is connected in series via the bus bar 404. In addition, in FIG. 4, the positive electrode terminal 403 corresponds to the battery cover 120 of FIG. 1, and the battery can 405 corresponds to the battery can 113 of FIG. The ends of the eight batteries 402 connected in series are connected to the positive external terminal 407 and the negative external terminal 408. Further, in the battery pack 401, eight batteries 402 are connected in series, and the number of connected batteries 402 is not limited to eight, and if it is two or more, it can be appropriately set according to the size of the battery pack 401. Further, the connection mode of the battery 402 in the battery pack 401 is not limited thereto, and may be in parallel or in series.

The positive external terminal 407 and the negative external terminal 408 are connected to a charge and discharge circuit 410 that performs charging and discharging of the battery pack 401 via a power line 412. The operation of the charge and discharge circuit 410 is controlled by the arithmetic processing unit 409 via the signal line 413. In addition to controlling the current and voltage of the charge and discharge circuit 410, the calculation processing unit 409 also controls the discharge current and discharge between the external terminals (positive external terminal 407 and negative external terminal 408) of the battery pack 401 to the external device 411. The voltage of time. At the time of discharge of the battery pack 401, electric power is supplied to the external device 411 via the external power cable 414.

The composition of the negative electrode active material in the evaluation was a composition in which 5 parts by weight of the negative electrode binder PVDF was added to 95 parts by weight of the negative electrode active material (composite carbon particles) of Example 4. The positive electrode active material is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . The other composition is the same as that described in the electrochemical evaluation 2 described above.

In addition, this evaluation is an experiment for confirming the effectiveness of the present invention, This is used as an external load device (for example, an electronic load device or a motor) for consuming power, and is used as a power supply load source for an external device 411 that supplies both power and consumption. When it is used, it does not bring about a difference in the effect of the present invention as compared with the actual use of an electric vehicle such as an electric vehicle or a work machine, or a distributed power storage system or a backup power supply system.

As a charging test after assembly of the system, a charge current corresponding to a current value (15 A) of a one-hour rate is supplied to the positive external terminal 407 and the negative external terminal 408 by the charge and discharge circuit 410, and a constant voltage of 33.6 V is used. Charge for 1 hour. The constant voltage value set here is a value eight times the constant voltage value of 4.2 V of the unit cell described above. The electric power necessary for charging and discharging the battery pack is supplied from the power supply load device (external device 411).

In the discharge test, a current which is reversed from the positive external terminal 407 and the negative external terminal 408 to the charge and discharge circuit 410 is consumed, and power is consumed by the power supply load device of the external device 411. The discharge current was set to a condition of 0.5 hour rate (discharge current was 7.5 A), and discharge was performed until the voltage between the terminals of the positive external terminal 407 and the negative external terminal 408 reached 24V.

Under the charge and discharge test conditions, an initial performance of a charge capacity of 15.0 Ah and a discharge capacity of 14.95 Ah was obtained. Further, a 1000 cycle charge and discharge cycle test was carried out to obtain a capacity retention rate of 92%. Further, the present system using the negative electrode active material of Example 4 was designated as S1.

According to the configuration of FIG. 4, the system S2 in which the negative electrode active material was changed to the negative electrode active material of Example 5 of Table 1 was changed, and the change was made to Comparative Example 1. System S3 of the negative active material. For each system, a 1000 cycle charge and discharge cycle test was carried out under the same conditions as described above. As a result, the capacity retention rate of S2 was 89%, and the capacity retention rate of S3 was 73%.

According to these phenomena, the negative electrode active materials of Examples 4 and 5 of the present invention can effectively improve the cycle characteristics of the lithium ion battery.

Next, regarding the above three systems, they were placed in a charged state under the same conditions, and were allowed to stand at an ambient temperature of 50 ° C for 30 days. Thereafter, the charge and discharge cycle test was started again from the discharge, and the discharge capacity at the 10th cycle was measured, and this was taken as the capacity retention rate after leaving at 50 °C. In addition, the capacity retention rate is a value obtained by setting the initial capacity before leaving at 50 ° C to 100% as a ratio with respect to the value. The results of this test were 93% in S1, 92% in S2, and 75% in S3. It is understood that the negative electrode active materials of Examples 4 and 5 of the present invention are also effective for the storage characteristics at 50 °C.

The specific application examples of the system will be described based on the above-described contents, and the effects of the present invention will be clarified. Further, specific constituent materials, parts, and the like may be changed without departing from the gist of the invention. Further, if the constituent elements of the present invention are included, a known technique or a known technique may be added.

The lithium ion battery and the battery module of the present invention can be used for portable electronic devices, mobile phones, power tools and the like, and can also be used for electric vehicles, storage batteries for renewable energy, unmanned vehicles, care machines, and the like. In the power supply. In addition, the lithium ion battery of the present invention can also be applied to a power source for exploring a space exploration ship such as the Moon or Mars. Moreover, it can be used in buildings or living spaces on space stations, on Earth or on other celestial bodies. (whether it is closed or open), spacecraft for interplanetary movement, land rover, confined space in the water or sea, submarine, fish observation equipment, air conditioning, temperature control, sewage or Among various power sources such as air purification and power.

According to the present invention, a lithium ion battery having improved cycle life and high temperature storage characteristics can be provided.

[Industrial availability]

The present invention can be applied to a lithium ion battery such as a lithium ion secondary battery, a moving body using the same, or a stationary power storage system.

The disclosure of Japanese Patent Application No. 2010-213866, the entire disclosure of which is incorporated herein in

All of the documents, patent applications, and technical specifications described in the specification are incorporated by reference in their entirety to the extent that they are specifically incorporated herein by reference.

101‧‧‧Lithium-ion battery

110‧‧‧ positive

111‧‧‧Parts

112‧‧‧negative

113‧‧‧Battery cans

114‧‧‧ positive current collector

115‧‧‧Negative current collector

116‧‧‧ inner cover

117‧‧‧Internal pressure relief valve

118‧‧‧shims

119‧‧‧PTC resistance element

120‧‧‧Battery cover

401‧‧‧Battery Pack

402‧‧‧Lithium Ion Battery/Single Battery

403‧‧‧ positive terminal

404‧‧‧ busbar

405‧‧‧Battery cans

406‧‧‧Support parts

407‧‧‧positive external terminal

408‧‧‧Negative external terminal

409‧‧‧ Calculation and Processing Department

410‧‧‧Charge and discharge circuit

411‧‧‧External machines

412‧‧‧Power line

413‧‧‧ signal line

414‧‧‧External power cable

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing an aspect of a cross-sectional structure of a lithium ion battery to which the present invention is applied.

Fig. 2 is a graph showing the results of thermogravimetric/thermal differential synchronization analysis (TG-DTA) of the negative electrode active material of Example 4 of the present invention.

Fig. 3 is a graph showing the results of thermogravimetric/thermal differential synchronization analysis (TG-DTA) of the negative electrode active material of Example 3 of the present invention.

Figure 4 is a plan view showing a module of a lithium ion battery to which the present invention is applied Schematic diagram.

101‧‧‧Lithium-ion battery

110‧‧‧ positive

111‧‧‧Parts

112‧‧‧negative

113‧‧‧Battery cans

114‧‧‧ positive current collector

115‧‧‧Negative current collector

116‧‧‧ inner cover

117‧‧‧Internal pressure relief valve

118‧‧‧shims

119‧‧‧PTC resistance element

120‧‧‧Battery cover

Claims (20)

A lithium ion battery comprising: a negative electrode comprising a negative active material, the negative active material occluding and releasing lithium, and the negative active material having a low crystalline carbon coating on the surface of the graphite core material The composite carbon particles have a functional group of C=O, C-OH and CO in the coating layer, and the oxygen atom content in the total amount of carbon atoms and oxygen atoms of the coating layer is 2 atom% to 5 atom. %, in the thermal gravimetric method in air, having at least one oxidation peak in a temperature range of 350 ° C or more and less than 600 ° C and 600 ° C or more and 850 ° C or less, and in a range of 350 ° C or more and 850 ° C or less The peak temperature difference between the oxidation peak having the peak at the highest temperature and the oxidation peak having the peak at the lowest temperature is 300 ° C or less; the positive electrode; and the nonaqueous electrolyte and the nonaqueous solvent. The lithium ion battery according to claim 1, wherein in the total oxygen amount of the coating layer, an oxygen content of C=O in the coating layer is from 7 atom% to 39 atom%. A lithium ion battery according to claim 1, wherein the low crystalline carbon of the coating layer is amorphous carbon. The lithium ion battery according to claim 1, wherein a ratio of C-OH to C=O in the coating layer is 1:1 to 4 in terms of an atomic composition ratio of oxygen in the respective functional groups: 1. The lithium ion battery according to the first aspect of the invention, wherein the (002) surface of the negative active material is obtained by an X-ray diffraction method. The interval d002 is 0.3354 nm to 0.3370 nm, and the crystallite size Lc is 20 nm to 90 nm. The lithium ion battery according to claim 1, wherein the coating layer has a thickness of 10 nm to 100 nm. The lithium ion battery according to claim 1, wherein the intensity ratio of the Raman peak of the negative active material (I ₁₃₆₀ /I ₁₅₈₀ ) is 0.1 to 0.7. The lithium ion battery according to claim 1, wherein the negative active material has an irreversible capacity per unit weight of 20 mAh/g to 31 mAh/g, and the negative electrode active material has a discharge capacity density of 350 mA/g. ~365mA/g. The lithium ion battery according to claim 1, wherein the graphite core material is graphite particles subjected to an isotropic pressure treatment. The lithium ion battery according to claim 1, wherein the coating layer is formed of the low crystalline carbon on the graphite by thermal decomposition of an organic compound or a mixture thereof in a non-oxidizing environment. The carbon film on the surface of the nuclear material. The lithium ion battery according to claim 10, wherein the coating layer is a carbon film obtained by thermally decomposing the organic compound or a mixture thereof and the graphite core material under contact conditions. The lithium ion battery according to claim 10, wherein the organic compound is an organic polymer compound which is carbonized in a liquid phase. A lithium ion battery according to claim 10, wherein the organic compound is an organic resin which is carbonized under a solid phase. A lithium ion battery as claimed in claim 1, wherein The content of the low crystalline carbon in the composite carbon particles is 0.1% by weight to 20% by weight based on the total weight of the graphite core material and the low crystalline carbon. The lithium ion battery according to claim 1, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector. The lithium ion battery according to claim 1, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector, wherein the positive electrode active material is selected from the group consisting of LiCoO ₂ and LiNiO ₂ . LiMn ₂ O ₄ , LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2-x M _x O ₂ (where M=Co, Ni, Fe, Cr, Zn or Ta; x= 0.01~0.2), Li ₂ Mn ₃ MO ₈ (where M=Fe, Co, Ni, Cu or Zn), Li _1-x A _x Mn ₂ O ₄ (where A=Mg, B, Al, Fe, Co, Ni, Cr, Zn or Ca; x = 0.01 to 0.1), LiNi _1-x M _x O ₂ (where M = Co, Fe or Ga; x = 0.01 to 0.2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , LiCo _1-x M _x O ₂ (where M = Ni, Fe or Mn; x = 0.01 to 0.2), LiNi _1-x M _x O ₂ (where M = Mn, Fe, Co, Al) At least one of a group consisting of Ga, Ca or Mg; x = 0.01 to 0.2), Fe(MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ and LiMnPO ₄ . The lithium ion battery according to claim 1, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a positive electrode binder, and a current collector, and the positive electrode active material is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ . A battery module in which two or more lithium ion batteries as described in claim 1 are connected in series, in parallel or in series. A mobile body is connected to a charge and discharge circuit connectable to an external device via an external terminal via a battery module according to claim 18. A stationary power storage system is a battery module according to claim 18, which is connected to a charge and discharge circuit connectable to an external device via an external terminal.