KR102010093B1 - Lithium ion battery, and battery module utilizing same - Google Patents

Abstract

The present invention is a negative electrode active material capable of occluding and releasing lithium, wherein the negative electrode active material is a composite carbon particle having a coating layer of low crystalline carbon on the surface of the graphite nucleus material, and C = 0, C-OH and C on the surface of the coating layer. It has a functional group of -0, and the content rate of the oxygen atom in the total amount of the carbon atom and the oxygen atom of the said coating layer is 2 atom%-5 atom%, In a thermogravimetric method, 350 degreeC or more and less than 600 degreeC and 600 degreeC or more and 850 degrees C or less The peak temperature difference between an oxidation peak having a peak at the highest temperature and an oxidation peak having a peak at the lowest temperature is 300, having at least one oxidation peak in each temperature range of 300 ° C. Lithium ion battery containing the negative electrode containing the said negative electrode active material which is below degrees C, and a positive electrode, a nonaqueous electrolyte, and a nonaqueous solvent, the battery module using this, a mobile body, or a stationary electrical storage sheath. Provide the system.

Description

Lithium ion battery, and battery module using the same {LITHIUM ION BATTERY, AND BATTERY MODULE UTILIZING SAME}

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

Lithium ion batteries have a high energy density and are attracting attention as batteries for electric vehicles and power storage. In particular, electric vehicles include a zero emission electric vehicle without an engine, a hybrid electric vehicle equipped with both an engine and a secondary battery, and a plug-in hybrid electric vehicle that is directly charged from a system power source. In the present invention, the electric vehicle means the aforementioned various vehicles. It is also expected to be used as a stationary power storage system that stores power and supplies power in an emergency when the power system is shut off.

For such various uses, excellent durability is required for lithium ion batteries. That is, even if the environmental temperature is high, the rate of decrease of the chargeable discharge capacity is small, and the capacity retention rate of the battery is high over a long period of time. In particular, lithium ion batteries for electric vehicles are exposed to high temperature environments of 40 ° C. to 70 ° C. by radiant heat from road surfaces or heat transfer from inside of vehicles, and long-term storage characteristics and improvement of cycle life in these environments are improved. It is an important development task.

As a conventional technique for suppressing capacity reduction or cycle deterioration at high temperature storage, various techniques such as high durability electrode materials or electrolyte solutions have been studied. In particular, in the negative electrode, lithium occluded in the negative electrode is consumed in accordance with the decomposition reaction of the electrolyte solution, resulting in a decrease in capacity of the battery. In order to suppress this side reaction, various various methods of modifying the surface of the negative electrode are disclosed.

Japanese Patent Application Laid-open No. Hei 6-168725 discloses an invention related to a battery using a negative electrode which is treated by a carbon material at a high temperature of 2000 ° C. or higher, graphitized, pulverized, and subjected to a heat treatment of 2000 ° C. or higher. Japanese Patent Laid-Open No. 2000-156230 discloses a negative electrode active material comprising secondary particles formed by assembling primary particles coated with amorphous carbon on a graphite surface.

Japanese Laid-Open Patent Publication No. 2002-134171 discloses an invention relating to a battery using carbon coated with a surface as a negative electrode active material with a water-soluble high molecular material charged negatively in water. 275077 discloses an invention for coating a carbon surface with a thin film of a lithium ion conductive solid electrolyte.

Japanese Patent Laid-Open No. 2000-264614 discloses an invention for forming a coating layer made of carbon on the surface of graphite particles after treating the graphite particles with a surfactant, and Japanese Patent Laid-Open No. 2001-229914 discloses graphite. Disclosed is an invention in which an amorphous carbon film layer is formed on a surface to suppress decomposition of an electrolyte solution.

Japanese Laid-Open Patent Publication No. 2006-24374 discloses an invention relating to carbon secondary particles in which a carbon coating layer is formed on the surface of crystalline carbon particles (primary particles) and primary particles are bonded through the carbon coating layer. Japanese Patent Laid-Open No. 2006-228505 has an average particle diameter of 5 µm to 50 µm, a specific gravity of 2.20 g / cm 3 or more, a specific surface area of 8 m 2 / g or less by nitrogen gas adsorption, and a specific surface area of carbon dioxide gas adsorption. Disclosed is an invention relating to graphite for a negative electrode, characterized in that the oxygen atom concentration measured in the range of 1 m 2 / g or less and X-ray photoelectron spectroscopy is 0.7 atom% or more.

Japanese Patent Application Laid-Open No. 2007-42571 relates to a carbon material in which the surface spacing d002 of the carbon 002 plane obtained by X-ray diffraction measurement is 0.340 nm to 0.390 nm, and He density and CO ₂ adsorption amount are specified. Doing.

Japanese Patent Laid-Open Publication No. 2009-187924 discloses that the crystallite size Lc analyzed by 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, and the surface is low crystallized. Disclosed is a negative electrode material in which carbon is formed.

Summary of the Invention

Problems to be Solved by the Invention

A lithium ion battery for an electric vehicle or an electric power storage may be left in a high temperature environment in a charged state, and a decrease in the capacity of the battery due to self discharge occurs. An object of the present invention is to suppress self discharge caused by a negative electrode and to prolong the life of a lithium ion battery.

Means to solve the problem

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the above-mentioned subject, the present inventors came to discover the means by which the capacity of a battery is hard to fall even after charging or discharging a lithium ion battery in high temperature environment.

According to the first aspect of the present invention, a negative electrode active material capable of occluding and releasing lithium, wherein the negative electrode active material is a composite carbon particle having a coating layer of low crystalline carbon on the surface of graphite particles (graphite nucleus material), and C It has functional groups of 0, C-OH, and C-0, and the content rate of the oxygen atom in the total amount of the carbon atom and oxygen atom of the said coating layer is 2 atom%-5 atom%, At least 350 degreeC in the thermal mass measurement method in air. At least one oxidation peak in each temperature range of 600 degrees C or less and 600 degrees C or more and 850 degrees C or less, The oxidation peak which has a peak at the highest temperature in the range of 350 degreeC or more and 850 degrees C or less, and the lowest temperature Provided is a lithium ion battery comprising a negative electrode including the negative electrode active material having a peak temperature difference of 300 ° C. or lower from an oxidized peak having a peak, a positive electrode, a nonaqueous electrolyte and a nonaqueous solvent. . The low crystalline carbon is amorphous and low crystalline carbon.

According to the 2nd aspect of this invention, in the said 1st aspect, the lithium ion battery whose content rate of C = O oxygen in the said coating layer is 7 atom%-39 atom% in the total amount of oxygen of the said coating layer is provided. do.

According to the 3rd aspect of this invention, in the said 1st or 2nd aspect, the lithium ion battery in which the low crystalline carbon of the said coating layer is amorphous carbon is provided.

According to the 4th aspect of this invention, in any one of said 1st-3rd aspect, the ratio of C-OH and C = 0 in the said coating layer is the atomic composition ratio of oxygen in each functional group. There is provided a lithium ion battery in 1: 1 to 4: 1. The ratio of C-OH and C = O is preferably 1: 1 to 2: 1 as the oxygen atom composition ratio in each functional group.

According to the fifth aspect, in any one of the first to fourth aspects, the (002) plane interval d002 obtained by the X-ray diffraction method of the anode active material is 0.3354 nm to 0.3370 nm, and the crystallite size Lc is 20 nm. A lithium ion battery of ˜90 nm is provided.

According to the sixth aspect, in any one of the first to fifth aspects, a lithium ion battery having a thickness of the coating layer is 10 nm to 100 nm.

According to the seventh aspect, in any one of the first to sixth aspects, a lithium ion battery having an intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of the Raman peak of the negative electrode active material is 0.1 to 0.7.

According to the eighth aspect, in any one of the first to seventh aspects, the irreversible capacity per unit mass of the negative electrode active material is 20 mAh / g to 31 mAh / g, and the discharge capacity density of the negative electrode active material is Lithium ion batteries ranging from 350 mA / g to 365 mA / g are provided.

According to the ninth aspect, in any one of the first to eighth aspects, the lithium ion battery is a graphite particle in which the graphite nucleus material is graphite particles subjected to an isotropic pressurization treatment.

According to the tenth aspect, in any one of the first to eighth aspects, the coating layer is formed of the graphite nucleus material by the low crystalline carbon by thermal decomposition of an organic compound or a mixture thereof in a non-oxidizing atmosphere. A lithium ion battery which is a carbon film formed on the surface is provided.

According to the eleventh aspect, in the tenth aspect, a lithium ion battery is provided, wherein the coating layer is a carbon film obtained by thermal decomposition of the organic compound or its mixture and the graphite nucleus material under contact conditions.

According to a twelfth aspect, in the tenth or eleventh aspect, a lithium ion battery is provided, wherein the organic compound is an organic polymer compound that carbonizes in a liquid phase.

According to a thirteenth aspect, in the tenth or eleventh aspect, a lithium ion battery is provided, wherein the organic compound is an organic resin that carbonizes in a solid phase.

According to a fourteenth aspect, in any one of the first to thirteenth aspects, the content ratio of the low crystalline carbon in the composite carbon particles is determined by the total mass of the graphite nucleus material and the low crystalline carbon. The lithium ion battery which is 0.1 mass%-20 mass% is provided.

According to a fifteenth aspect, in any one of the first to fourteenth aspects, a lithium ion battery is provided in which the positive electrode includes a positive electrode active material, a conductive aid, a positive electrode binder, and a current collector.

According to a sixteenth aspect, in any one of the first to fifteenth aspects, the positive electrode includes a positive electrode active material, a conductive aid, a positive electrode binder, and a current collector, and the positive electrode active material is

There is provided at least one lithium ion battery selected from the group consisting of:

According to the aspect of claim 17, in any of the embodiments of the first to 16, wherein the positive electrode, the positive electrode active material, conductive auxiliary agent, comprising: a positive electrode binder, and a house, that the positive electrode active material LiNi _1/3 Mn _{1 / 3} Co _- is provided with a _{/ 3} O ₂ lithium ion cell.

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

According to a nineteenth aspect, the moving body or the stationary power storage system, wherein the battery module according to the eighteenth aspect is connected to a charge / discharge circuit that can be connected to an external device via an external terminal.

To practice the invention  Form for

Other aspects of the present invention will become apparent from the following detailed description. The term used in the present invention is used in a general sense.

In this specification, the term "process" is included in this term as long as the desired action of this process is achieved, even if it is not only an independent process but also a case where it cannot be clearly distinguished from other processes.

In addition, the numerical range shown using "-" in this invention represents the range which included the numerical value described before and after "-" as minimum value and the maximum value, respectively.

In addition, in this invention, when referring to the quantity of each component in a composition, when there exist two or more substances corresponding to each component in a composition, unless there is particular notice, the total amount of the said some substance in a composition. Means.

In this invention, the composite carbon particle which coat | covered the graphite particle (graphite nucleus) surface with the coating layer of low crystalline carbon is included, and the oxygen concentration in the coating layer is made into the specific range. Thereby, in a thermogravimetric method, at least 1 oxidation peak (peak of the temperature differential value of mass change) in the low temperature range of 350 degreeC or more and less than 600 degreeC, and at least 1 oxidation in the high temperature range of 600 degreeC or more and 850 degrees C or less. The peak temperature difference between the oxidation peak having a peak at the highest temperature and the oxidation peak having a peak at the lowest temperature is 300 ° C with a peak (peak of temperature differential of mass change) and within a range of 350 ° C or more and 850 ° C or less. The lithium ion battery containing the negative electrode containing a composite carbon particle below as a negative electrode active material, a positive electrode, a nonaqueous electrolyte, and a nonaqueous solvent can be provided. The lithium ion battery of the present invention is a battery excellent in high temperature storage characteristics and cycle characteristics.

The composite carbon particle in this invention coat | covered the graphite nucleus material with the coating layer of low crystalline carbon, and comprises a negative electrode active material. Low crystalline carbon includes amorphous or mesomorphic carbon (which is substantially crystalline with very low carbon and whose crystal peaks have not been identified by X-ray diffraction). Although this low crystalline carbon coating is obtained by various methods, the organic material which can be thermally decomposed in the liquid phase is heated in a non-oxidizing atmosphere to precipitate on the graphite nucleus material.

It is preferable that the said graphite nucleus material is graphite particle in which the isotropic pressurization process was performed. The low crystalline carbon coating layer may be a low crystalline carbon film formed on the surface of the graphite nucleus material by thermal decomposition of an organic compound or a mixture thereof in a non-oxidizing atmosphere.

The organic compound or a mixture thereof may be pyrolyzed under contact conditions with the graphite nucleus material, an organic polymer compound carbonized in a liquid phase, or an organic resin carbonized in a solid phase. It is preferable that the said coating layer is 0.1 mass%-20 mass% of the total mass of the said graphite nucleus material and the said low crystalline carbon.

The present invention relates to a battery module in which the lithium ion battery is connected at least two in series, in parallel or in parallel, and the battery module connected to a charge / discharge circuit connectable to an external device via an external terminal. Applicable to a moving body or stationary power storage system, these will also be described in detail later.

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

1 shows one embodiment of a cross-sectional structure of a lithium ion battery to which the present invention is applied.
2 is a graph showing the results of differential thermal thermogravimetry (TG-DTA) measurement of a negative electrode active material according to Example 4 of the present invention.
FIG. 3 is a graph showing the differential thermal thermogravimetric simultaneous measurement (TG-DTA) results of the negative electrode active material according to Example 3 of the present invention. FIG.
4 is a schematic plan view showing a module of a lithium ion battery to which the present invention is applied
to be.

Example

( Example  One)

In FIG. 1, the internal structure of the cylindrical lithium ion battery 101 which concerns on one Embodiment of this invention is shown typically. 110 is a positive electrode, 111 is a separator, 112 is a negative electrode, 113 is a battery can, 114 is a positive current collecting tab, 115 is a negative current collecting tab, 116 is an inner plug, 117 is a pressure relief valve, 118 is a gasket, and 119 is a constant temperature coefficient ( PTC (Positive temperature coefficient) resistance element, 120 is a battery stopper. The battery stopper 120 is an integrated component including an inner stopper 116, a pressure resistant release valve 117, a gasket 118, and a PTC resistance element 119.

The positive electrode 110 is composed of a positive electrode active material, a conductive aid, a positive electrode binder, and a current collector. Illustrative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . etc,

And the like. In this embodiment, in that it can realize a high energy density and excellent cycle life, and chose the _{LiNi 1/3 Mn 1/3} Co 1/3 O 2 as a positive electrode active material. However, the present invention is not limited to these materials because the present invention is not subject to any limitations.

The particle diameter of the positive electrode active material is defined to be equal to or less than the thickness of the mixture layer containing the positive electrode active material, the conductive aid, and the positive electrode binder. When granules having a size greater than or equal to the thickness of the mixture layer are contained in the positive electrode active material powder, granulation is removed by sieve classification, air flow classification, or the like to produce particles having a thickness less than or equal to the mixture layer.

In addition, since the positive electrode active material is an oxide type and has high electrical resistance, a conductive aid made of carbon powder for supplementing those electrical conductivity is used. This has advantages such as low resistance of the positive electrode, improvement of battery characteristics, and the like. As the conductive aid, carbon materials such as acetylene black, carbon black, graphite, amorphous carbon, or a combination of two or more thereof can be used. Since the electronic network is formed inside the positive electrode, the particle size of the conductive assistant is smaller than the average particle diameter of the positive electrode active material, and is preferably set to 1/10 or less of the average particle diameter.

Since both the positive electrode active material and the conductive aid are powders, a positive electrode binder is mixed with the powder to bond the powders together and adhere to the current collector.

An aluminum foil having a thickness of 10 μm to 100 μm or a perforated foil made of aluminum having a hole having a thickness of 10 μm to 100 μm and a diameter of 0.11 mm to 10 mm, an expanded metal, or a foamed metal plate is used for the current collector. In addition to aluminum, stainless steel, titanium, and the like are also applicable. In the present invention, any current collector can be used without being limited to materials, shapes, manufacturing methods, and the like.

In order to manufacture the positive electrode 110, it is necessary to prepare a positive electrode slurry. The composition is exemplified by 89 parts by mass of the positive electrode active material, 4 parts by mass of acetylene black, and 7 parts by mass of the positive electrode binder of PVDF (polyvinylidene fluoride). However, the composition is changed depending on the type of material, specific surface area, and particle size distribution. It is not limited to one composition. The solvent of a positive electrode slurry should just melt | dissolve a positive electrode binder, and N-methyl- 2-pyrrolidone is used abundantly about the positive electrode binder of PVDF. However, the solvent is appropriately selected depending on the type of the positive electrode binder. A well-known kneader and a disperser were used for the dispersion process of a positive electrode material.

After attaching the positive electrode slurry in which the positive electrode active material, the conductive aid, the positive electrode binder, and the solvent are mixed and dispersed to the current collector by the doctor blade method, the dipping method, the spray method, etc., the solvent is dried, and the positive electrode is press-molded by a roll press. Thereby, the mixture layer containing a positive electrode active material, a conductive support agent, and a positive electrode binder is formed on an electrical power collector, and a positive electrode can be manufactured by the above process. Moreover, it is also possible to laminate | stack a some mixture layer on an electrical power collector by performing several times from application | coating to drying.

The negative electrode 112 is composed of a negative electrode active material, a negative electrode binder, and a current collector. The negative electrode active material has a core-shell structure in which a coating layer is formed on the surface of the graphite nucleus material (graphite particles). As the negative electrode active material, a negative electrode active material capable of occluding or releasing lithium, the negative electrode active material is a composite carbon particle having a coating layer of low crystalline carbon on the surface of the graphite nucleus material, and C = O, C-OH and C on the surface of the coating layer. It has a functional group of -0, and the content rate of the oxygen atom in the total amount of the carbon atom and the oxygen atom of the said coating layer is 2 atom%-5 atom%, In the thermogravimetric method in air, 350 degreeC or more and less than 600 degreeC and 600 degreeC or more and 850 Difference in peak temperature between an oxidation peak having at least one oxidation peak in each temperature range of degrees C or less and having a peak at the highest temperature within a range of 350 ° C. or more and 850 ° C. or less and an oxidation peak having a peak at the lowest temperature. The said negative electrode active material whose 300 degrees C or less is used. Specifically, the lithium ion battery was produced for each negative electrode active material using the negative electrode active material manufactured in each Example mentioned later.

In order to manufacture the negative electrode 112, it is necessary to prepare a negative electrode slurry. The composition is exemplified by 95 parts by mass of the negative electrode active material and 5 parts by mass of the negative electrode binder of polyvinylidene fluoride (PVDF), which is changed depending on the type of material, the specific surface area and the particle size distribution, and is not limited to the illustrated composition. Do not. The solvent of a negative electrode slurry should just melt | dissolve a negative electrode binder, and N-methyl- 2-pyrrolidone is used abundantly in the negative electrode binder of PVDF. However, according to the kind of negative electrode binder, a solvent is selected suitably. A well-known kneader and a disperser were used for the dispersion process of the negative electrode material.

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 the doctor blade method, the dipping method, the spray method, and the like, and then the solvent is dried and the negative electrode is press-molded by a roll press, The mixture layer containing a negative electrode active material, a conductive support agent, and a negative electrode binder is formed on the whole, and a negative electrode can be manufactured by the above process. Moreover, it is also possible to laminate | stack a some mixture layer on an electrical power collector by performing several times from application | coating to drying.

As shown in FIG. 1, the separator 111 is inserted between the positive electrode 110 and the negative electrode 112 to prevent a short circuit between the positive electrode 110 and the negative electrode 112. As the separator 111, it is possible to use a polyolefin-based polymer film made of polyethylene, polypropylene, or the like, or a microporous film having a multilayer structure in which a polyolefin-based polymer and a fluorine-based polymer film represented by polytetrafluoroethylene are welded. It is possible. Since these separators 111 need to permeate lithium ions at the time of charge / discharge of the battery, the pore size generally has a pore of 0.01 μm to 10 μm, and the porosity is 20% to 90%. desirable. In addition, you may form the mixture of ceramic and an organic resin binder in thin layer on the surface of the separator 111 so that separator 111 may not shrink when battery temperature becomes high. In the following description, the integral structure which consists of the anode 110, the cathode 112, and the separator 111 is called an electrode group.

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 do not short-circuit through the battery can 113. Doing. Moreover, the electrolyte solution which consists of electrolyte and a non-aqueous solvent is hold | maintained in the surface and the pore of the separator 111 and each electrode (anode 110, cathode 112).

The upper part of the electrode group is electrically connected to an external terminal via a lead wire. The positive electrode 110 is connected to the battery plug 120 via the positive electrode current collector tab 114. The negative electrode 112 is connected to the battery can 113 through the negative electrode current collector tab 115. In addition, the positive electrode current collector tab 114 and the negative electrode current collector tab 115 may take arbitrary shapes such as a wire shape and a plate shape. As long as the ohmic loss is reduced when a current flows, and the material does not react with the electrolyte, the shape and material of the positive electrode current collector tab 114 and the negative electrode current collector tab 115 are arbitrary.

Although the structure of an electrode group is a thing of the winding shape shown in FIG. 1, it can be set to arbitrary shapes according to the shape of the battery can 113. FIG. If the battery can 113 is a rectangular shape, it can be changed into the shape which laminated | stacked the positive electrode 110, the negative electrode 112, and the separator 111, or the shape wound to the flat shape.

The material of the battery can 113 is selected from a material having corrosion resistance to a nonaqueous electrolyte such as aluminum, stainless steel, nickel plated steel, and the like. In addition, in the case where the positive electrode current collector tab 114 or the negative electrode current collector tab 115 is electrically connected to the battery can 113, corrosion or lithium ions of the battery can 113 are formed in a portion in contact with the nonaqueous electrolyte. The material of the tab is selected so that material deterioration does not occur by alloying with.

Thereafter, the battery cap 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, the method by caulking is employ | adopted. In addition to this method, the method of sealing a battery has well-known techniques, such as welding and welding.

As a representative example of the electrolyte solution usable in the present invention, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte in a solvent in which ethylene carbonate is mixed with dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, or a combination of two or more thereof. Or a solution in which lithium boron fluoride (LiBF ₄ ) is dissolved. The present invention is not limited to the kind of the solvent, the electrolyte, and the mixing ratio of the solvent, and other electrolyte solutions can also be used. The electrolyte can also be used in a state in which it is contained in an ion conductive polymer such as polyvinylidene fluoride or polyethylene oxide. In this case, the separator becomes unnecessary.

Moreover, the solvent which can be used for electrolyte solution is propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, (gamma) -butyrolactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 2- Methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, methyl propionate, ethyl propionate, triester triester, trimethoxymethane, dioxolane, diethyl ether, sulfolane, 3- And non-aqueous solvents such as methyl-2-oxazolidinone, tetrahydrofuran, 1,2-diethoxyethane, crawlethylene carbonate, and chloropropylene carbonine. These can be used individually or in combination of 2 or more types. As long as it does not decompose on the positive electrode or negative electrode built in the battery of this invention, you may use solvent other than this.

In the electrolyte, lithium imide salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , or lithium trifluoromethanesulfonimide There is a kind of lithium salt. These can be used individually or in combination of 2 or more types. These non-aqueous electrolytes which melt | dissolve these salts in the solvent mentioned above can be used as battery electrolyte solution. As long as it does not decompose on the positive electrode or negative electrode incorporated in the battery of this embodiment, you may use electrolyte other than this.

When using a solid polymer electrolyte (polymer electrolyte), an ion conductive polymer obtained by polymerizing monomers such as ethylene oxide, acrylonitrile, vinylidene fluoride, methyl methacrylate and hexafluoropropylene can be used as the electrolyte. . These can be used individually or in combination of 2 or more types. When using these solid polymer electrolytes, there is an advantage that the separator 111 can be omitted.

Ionic liquids can also be used. For example, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF ₄ ); a mixed complex of lithium salt LiN (SO ₂ CF ₃ ) ₂ (LiTFSl) with trilime and tetragram; And a combination of a cyclic quaternary ammonium cation (N-methyl-N-propylpyrrolidinium is exemplified) and an imide anion (bis (trifluoromethylsulfonyl) imide is exemplified), which does not decompose on the positive or negative electrode; It can select from the group which consists of, and can use for the lithium ion battery of this invention. These can be used individually or in combination of 2 or more types.

The injection method of electrolyte solution has the method of adding it directly to an electrode group in the state which removed the battery stopper 120 from the battery can 113. When there is a pouring hole in the battery plug 120, there is a method of adding from the pouring hole.

Instead of the nonaqueous electrolyte, a solid polymer electrolyte (polymer electrolyte) or a gel electrolyte may be used. As the solid polymer electrolyte, it is also possible to use a known polymer electrolyte such as polyethylene oxide or a mixture (gel electrolyte) of polyvinylidene fluoride and nonaqueous electrolyte. Moreover, you may use an ionic liquid.

(Example 2)

This embodiment is the same as that of Example 1 except the matter mentioned below.

<Preparation of graphite nucleus material>

Although the artificial graphite manufactured by the isotropic pressurization process was used for the graphite nucleus material used in Example 2, this invention is not limited to this material. An isotropic pressurization process is not pressurization only in a specific direction (anisotropic pressurization process) here, but is a process generally pressurized in all directions. Thus, when isotropic pressurization is performed on carbon powder, the bulk density of the composite carbon particle for lithium ion battery negative electrodes obtained, and the fluidity | liquidity of a negative electrode slurry improve, the density imbalance of the lithium ion battery negative electrode produced is small, and a negative electrode collector Adhesion with the whole improves. As a result, the cycle characteristics of the obtained lithium ion battery can be improved.

There is no restriction | limiting in particular as a method of isotropic pressurization of carbon powder, if it is a method which can isotropically pressurized, For example, the hydrostatic isotropic which puts carbon powder in a container, such as rubber type, and makes water a pressurized medium, Pressurization processes, such as an isotropic press by air pressure which uses presses and gas, such as air, as a pressurizing medium, are mentioned.

As pressure of the pressurizing medium of the isotropic pressurization of carbon powder, the range of 4.9 * 10 <^6> Pa-1.96 * 10 <^8> Pa (50kgf / cm <2> -2000kgf / cm <2>) is preferable, and 1.96 * 10 <^7> Pa-1.96 * 10 <^8> Pa It is more preferable in it being the range of (200kgf / cm <2> -2000kgf / cm <2>), and it is still more preferable in it being the range of 4.9 * 10 <^7> Pa-1.77 * 10 <^8> Pa (500kgf / cm <2> -1800kgf / cm <2>). If the pressure is 4.9 × 10 ⁶ Pa (50 k0 gf / cm 2) or more, the effect of improving the cycle characteristics of the obtained lithium ion battery tends to increase. When the pressure is 1.96 × 10 ⁸ Pa (2000 kgf / cm 2) or less, the expansion of the specific surface area of the composite carbon particles for lithium ion battery negative electrode obtained is suppressed, and as a result, the irreversible capacity of the first cycle of the lithium ion battery obtained is reduced. It tends to be small.

When the isotropic pressurization treatment is applied to the carbon powder as described above, the particles tend to agglomerate. Therefore, after the isotropic pressurization treatment, treatment such as disintegration and sieving is preferable. In addition, when particle | grains do not aggregate, it is not necessary to disintegrate.

Although the cycle characteristics etc. can be improved significantly by the above method, the composite carbon particle (cathode active material) for lithium ion battery negative electrodes produced by performing isotropic pressurization treatment has the interlayer distance d (002) of a crystal | crystallization 0.3354 nm. It is in the range of ˜0.3370 nm, and the crystallite size Lc (002) in the C-axis direction can be 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 were determined by X-ray diffraction. The X-ray diffraction method is measured based on the academic method.

The carbon material to be subjected to the isotropic pressurization is not particularly limited, and natural graphite, artificial graphite obtained by graphitizing coke, organic polymer material, artificial graphite obtained by graphitizing pitch, etc., amorphous carbon, low temperature treated carbon, etc. Although it is mentioned, artificial graphite is preferable among them.

Artificial graphite is a graphite, which is a part of the organic material such as pitch, tar, thermosetting resin, thermoplastic resin, etc., which binds the main raw material to a graphitizable main raw material such as coke powder, resin carbide, and the like to form a molded body, and optionally, graphite. A catalyst (graphitization catalyst) for promoting the oxidization reaction is added and these raw material mixtures are graphitized and calcined at a temperature of 2500 ° C or higher. Artificial graphite can be produced through the obtained graphite firing body through a grinding step. The crystallinity of the artificial graphite obtained by the above method tends to develop, and the discharge capacity of the lithium ion battery obtained can be improved.

Here, as the graphitization catalyst, metals such as Ti, Si, Fe, Ni, and B or oxides or carbides thereof are preferable. It is preferable to add a graphitization catalyst when mixing the said main raw material and the said organic type material, and to mix simultaneously. It is preferable that the temperature to mix is the temperature which the said organic type material softens and fuses, and although the temperature changes with the material to be used, the range of 50 degreeC-350 degreeC is preferable. In addition, when making the said organic type material into a solution etc. with a solvent, you may mix a graphitization catalyst at normal temperature.

In addition, in manufacture of artificial graphite, before graphitizing the raw material mixture at the temperature of 2500 degreeC or more, you may grind | pulverize and shape | mold and may also pre-calculate at the temperature of about 700 to 1300 degreeC. In addition, after changing the order of the process, prebaking at a temperature of about 700 ° C to 1300 ° C, the powder may be pulverized and graphitized firing may be performed at a temperature of 2500 ° C or higher. 2500 degreeC or more is preferable at the point of the crystallinity and discharge capacity of the graphite nucleus material obtained at the time of graphitization, It is more preferable if it is 2800 degreeC or more, It is further more preferable if it is 3000 degreeC or more. There is no restriction | limiting in particular if the atmosphere at the time of baking is a condition which is hard to oxidize, For example, a self-volatile gas atmosphere, nitrogen atmosphere, argon atmosphere, vacuum etc. are mentioned.

In the preliminary firing process, organic materials such as aromatic organic molecules, coal tar, or pitch are melted once in the course of the temperature increase, and volatiles are released to condense and carbonize them.

There is no restriction | limiting in particular as a grinding | pulverization method of a graphitized fired body, For example, impact grinding methods, such as a jet mill, a hammer mill, and a pin mill, can be chosen. After grinding, the particle size is adjusted to obtain graphite particles. In addition, when grind | pulverizing before graphitization and adjusting particle size, it is not necessary to grind after graphitization.

Using graphite particles of artificial graphite produced as described above, isotropic pressure treatment was performed to obtain a graphite nucleus material. Furthermore, by coating the low crystalline carbon described later, the composite carbon particles for a lithium ion battery negative electrode suitable for a lithium ion battery excellent in cycle characteristics and rapid charge and discharge characteristics can be obtained.

<Formation of coating layer>

Here, as a process which coat | covers low crystalline carbon, the process of applying an ultrasonic wave to the specific organic solvent which disperse | distributed the graphite nucleus material is mentioned, for example. In this treatment, first, the organic solvent is carbonized and precipitated by application of traveling wave ultrasonic waves. Since precipitation occurs on the surface of the dispersed graphite nucleus material, a carbonaceous layer without adsorption of unnecessary functional groups or the like can be formed on the surface of the graphite nucleus material. As said specific organic solvent, o-dichlorobenzene etc. are mentioned, for example, In this Example, o-dichlorobenzene was used.

Next, in order to fix the deposited carbonaceous layer on the surface of the graphite nucleus material by thermal decomposition, to form a coating layer of low crystalline carbon, heat treatment is performed. Although heat processing temperature changes with starting materials, it is preferable to set it as the range of 400 to 800 degreeC, and it is especially preferable to set to the range of 550 to 750 degreeC. The gas atmosphere at the time of heat processing is most preferably made into the inert gas atmosphere which consists of nitrogen and a rare gas. In the present Example, the process was performed in the state which made nitrogen gas flow. By doing in this way, combustion of a coating layer and a graphite nucleus material can be prevented. In addition, when a small amount of oxygen is introduced into the coating layer and the carbonyl group or the hydroxyl group are actively introduced, the oxygen concentration of the coating layer can be adjusted in a non-oxidizing atmosphere in which 10% or less of the oxygen is mixed with an inert gas.

In addition, as a method different from the above-mentioned method of forming a coating layer in a graphite nucleus material, you may form a coating layer using another organic high molecular compound in the starting material of low crystalline carbon. As an organic polymer compound, the organic polymer compound carbonized in a liquid phase, such as various pitches (crude oil pitch, naphtha pitch, asphalt pitch, coal tar pitch, decomposition pitch, etc.), is mentioned. In the state in which the organic polymer compound is molten or the organic polymer compound is dissolved in a high boiling point solvent, a low crystalline carbon coating layer is formed on the graphite nucleus material surface by thermal decomposition. Or halogenated vinyl resins such as phenol resins, furfuryl alcohol resins, cellulose resins, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, and polyamideimide resins and polyamide resins. In addition, the resin which carbonizes in solid state can also be used. As the amount of low crystalline carbon to coat the surface of the graphite nucleus material, the mass of the composite carbon particles finally obtained is preferably 0.1% by mass or more, and from the balance between the effect of the coating and the charge / discharge capacity, It is more preferable that they are 0.1 mass%-20 mass% with respect to mass, and it is still more preferable that they are 1 mass%-15 mass%. Thereby, it becomes possible to control the thickness of the coating layer which consists of low crystalline carbon to 10 nm-100 nm. In addition, in this invention, the content rate of the low crystalline carbon in a composite carbon particle can be calculated | required from the value of the mass change amount corresponding to low crystalline carbon in the mass change measurement by thermomass spectrometry.

In the present Example, the artificial graphite manufactured by the isotropic pressurization process was made into the graphite nucleus material, and the thickness of the coating layer was 10 nm-100 nm using o-dichlorobenzene. The heat treatment temperature at the time of forming a coating layer was set to 550 degreeC, and composite carbon particle | grains were obtained by performing a process in nitrogen gas atmosphere.

The thickness of the coating layer cut out the cross section for the negative electrode active material with the focused ion beam processing apparatus (FlB), and measured it with the transmission electron microscope (TEM). Although there exists a gap in the thickness of a coating layer according to a measurement place, it is inferred that an electrolyte solution passes through the minute space | interval (gap) of a coating layer if the thickness of a coating layer is 10 nm or more at least. This prevents direct contact of the electrolyte solution with the edge surface of the highly active graphite nucleus material. Therefore, decomposition reaction of the electrolyte solution with high temperature storage and charge / discharge cycles is reduced, and battery characteristics are considered to be improved. Moreover, when the thickness of a coating layer is 100 nm or less, the transfer resistance of the coating layer part of lithium ion accompanying charge / discharge reaction is small, and preferable.

(Example 3)

This embodiment is the same as that of Example 1 except the matter mentioned below.

<Preparation of graphite nucleus material>

In Example 3, artificial graphite was manufactured by adding coke powder, petroleum pitch as a graphitizable organic material for binding coke powder, and iron-based graphitization catalyst as graphitizable main raw materials. Graphitization catalyst mixes what added 1 mass%-50 mass%, calcinates, and graphitizes, and it grind | pulverizes and graphite is manufactured.

In addition, this invention is not limited to the said material. As the main raw material that can be graphitized, various cokes such as fluid cokes and needle cokes can be used. As a main raw material which can be graphitized, it is preferable that coke powder is included from the point of charge / discharge capacity and rapid charge / discharge characteristic, and it is more preferable especially if needle coke powder is included. Moreover, you may add and use already graphitized carbon material, such as natural graphite and artificial graphite, to a part of main raw material. As the graphitizable organic material for binding the main raw material to form a graphite molded body, various pitches and tars such as coal-based, petroleum-based and artificial can be used. As the graphitization catalyst, oxides, carbides, nitrides, and the like, such as iron, nickel, titanium, boron, and silicon, can be used.

By mixing the graphitizable organic material with the graphitizable main raw material as described above, the aspect ratio of the obtained graphite particles (graphite nucleus material) can be reduced, and it is possible to produce graphite particles in which a plurality of flat particles are combined or bonded. Done. As a result, the rapid charge and discharge characteristics and cycle characteristics of the produced lithium ion battery can be improved.

Moreover, as said graphitizable organic type material, organic materials, such as a thermosetting resin and a thermoplastic resin, can also be used besides pitch and tar. As the addition amount of the graphitizable organic material, depending on the residual carbon ratio and the binding force of the organic material to be used, for example, when a pitch is used, 10 parts by mass to 100 parts by mass is preferable with respect to 100 parts by mass of the main raw material that can be graphitized. It is more preferable in it being 10 mass parts-70 mass parts, and still more preferable in it being 10 mass parts-50 mass parts.

The blending ratio of the graphitization catalyst can be selected according to the particle characteristics, in particular, of the target graphite particles (graphite nucleus material), and the total mass of the raw material mixture of the main raw materials such as coke, organic materials such as pitch, and the graphitization catalyst are combined. It is preferable to add 1 mass%-50 mass% of graphitization catalyst. The blending ratio of the graphitization catalyst is selected in accordance with the particle characteristics in particular of the target graphite particles (graphite nucleus material). Regarding the graphitization catalyst, when the addition amount is 1% by mass or more, the development of crystals of the graphite particles is improved, the charge and discharge capacity is improved, and the discharge capacity of the obtained lithium ion battery can be increased. On the other hand, when the amount of the graphitization catalyst is 50% by mass or less, it is easy to mix uniformly, and it is possible to avoid deterioration of workability and expansion of the gap of the characteristics of the obtained graphite particles. In particular, the addition amount of the graphitization catalyst is more preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass to 5% by mass. When the addition amount of the graphitization catalyst is increased within the above range, the discharge capacity tends to increase, while when it decreases within the above range, the specific surface area tends to decrease and the bulk density tends to increase.

Moreover, as a graphitization catalyst, metals, such as Ti, Si, Fe, Ni, and B, its oxide, or carbide are preferable, are added when mixing a main raw material and an organic type material, and it is preferable to mix simultaneously.

In the above, it is preferable that the temperature at the time of mixing a graphitization catalyst is the temperature which the said organic type material which can be graphitized soft-melts. Although the temperature changes with the material to be used, the range of 50 degreeC-350 degreeC is preferable. Moreover, when making a graphitizable organic type material into a solution with a solvent etc., you may mix at normal temperature.

Next, the raw material mixture which mixed the graphitizable main raw material, the graphitizable organic material, and the graphitization catalyst was pre-baked at 500 ° C to 2000 ° C, and further, the fired product was pulverized, and the average particle diameter was 10 µm to 100 µm. It is preferable to adjust and to graphitize the pulverized product at the temperature of 2500 degreeC or more.

500 to 1500 degreeC is preferable and, as for the preliminary baking temperature before grinding | pulverization, it is more preferable if it is 700 to 1500 degreeC. If the preliminary baking temperature before grinding | pulverization is 2000 degrees C or less, the bulk density of the graphite particle (graphite nucleus material) obtained will be high, the specific surface area will be small, and there will be a tendency for an aspect ratio to become small. Moreover, when the preliminary baking temperature before grinding | pulverization is 500 degreeC or more, the carbonization of the graphitizable organic type material added becomes sufficient, As a result, there exists a tendency which can suppress the bonding of particle | grains after grinding | pulverization and graphitization. In addition, you may shape | mold the said raw material mixture to a suitable form before preliminary baking. It is preferable to perform preliminary baking in the atmosphere which is hard to oxidize the said raw material mixture, For example, the method of baking in a nitrogen atmosphere, argon gas, and a vacuum is mentioned.

Next, graphitization treatment is performed. The method of graphitization is not particularly limited. For example, the graphitization is preferably performed at a temperature of 2500 ° C. or higher in a self-volatile gas atmosphere, a nitrogen atmosphere, an argon atmosphere, or a vacuum, in view of crystallinity and discharge capacity of the obtained graphite particles. Do. Graphitization temperature is more preferable if it is 2700 degreeC or more, It is further more preferable if it is 2900 degreeC or more, It is especially preferable if it is 3000 degreeC or more. As an upper limit of graphitization temperature, it is preferable that it is 3200 degrees C or less. The higher the graphitization temperature, the better the development of the crystals of the graphite, the more difficult it is to remain in the graphite particles produced by the graphitization catalyst, and in all cases, the charge and discharge capacity tends to improve.

After the graphitization treatment, a pulverization treatment is performed. There is no restriction | limiting in particular as a grinding | pulverization method, For example, the impact grinding system, such as a jet mill, a hammer mill, a pin mill, can be chosen.

<Formation of coating layer>

The low crystalline carbon is coated on the graphite particles (graphite nucleus material) obtained as described above as follows. There is no restriction | limiting in particular about the kind of organic high molecular compound used as the starting material of the low crystalline carbon which coat | covers a graphite nucleus material, and the coating amount of the low crystalline carbon obtained by carbonizing this. Examples of the organic polymer compound include organic polymer compounds that carbonize in liquid form, such as various pitches (crude oil pitch, naphtha pitch, asphalt pitch, coal tar pitch, decomposition pitch, and the like). Or halogenated vinyl resins, such as a phenol resin, furfuryl alcohol resin, a cellulose resin, polyacrylonitrile, and polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, are mentioned. As an amount of low crystalline carbon which coat | covers the graphite nucleus material surface, it is preferable that it is 0.1 mass% or more with respect to the mass of the composite carbon particle finally obtained, and it is 0.1 mass%-20 from the balance of the effect by the coating | cover and charge / discharge capacity. It is more preferable that it is mass%, and it is still more preferable that it is 1 mass%-15 mass%. Thereby, it becomes possible to control the thickness of the coating layer which consists of low crystalline carbon to 10 nm-100 nm.

In Example 3, the thickness of the coating layer was 10 nm-100 nm using the carboxymethylcellulose resin, and the heat processing temperature at the time of forming a coating layer was 750 degreeC. The gas atmosphere was made into nitrogen gas.

The thickness of the coating layer cut out the cross section for the negative electrode active material by FIB, and measured it by TEM. Although there exists a gap in the thickness of a coating layer according to a measurement place, it is inferred that an electrolyte solution passes through the minute space | interval (gap) of a coating layer if the thickness of a coating layer is 10 nm or more at least. This prevents direct contact of the electrolyte solution with the edge surface of the highly active graphite nucleus material. Therefore, decomposition reaction of the electrolyte solution with high temperature storage and charge / discharge cycles is reduced, and battery characteristics are considered to be improved.

Moreover, when the thickness of a coating layer is 100 nm or less, the transfer resistance of the coating layer part of lithium ion accompanying charge / discharge reaction is small, and preferable.

(Example 4)

This embodiment is the same as that of Example 1 except the matter mentioned below.

<Preparation of graphite nucleus material>

The graphite nucleus material used in Example 4 is a carbon material which has a graphene structure. That is, natural graphite, artificial graphite, mesopez carbon, expanded graphite, carbon fiber, vapor-grown carbon fiber, pitch carbonaceous material, needle coke, petroleum coke, polyacrylonitrile, which can electrochemically occlude and release lithium ions. Carbonaceous materials, such as a system carbon fiber and carbon black, or the amorphous carbon material which synthesize | combined 5- or 6-membered cyclic hydrocarbon or cyclic oxygen-containing organic compound by thermal decomposition, etc. can be used.

The graphite nucleus material was produced as follows. 50 mass parts of coke powder with an average particle diameter of 5 micrometers, 20 mass parts of tar pitches, 7 mass parts of silicon carbide of 48 micrometers, and 10 mass parts of coal tar were mixed, and it mixed at 200 degreeC for 1 hour. The obtained mixture was pulverized, pressure molded into pellets, and then calcined at 3000 ° C. in a nitrogen atmosphere. The obtained fired material was ground by a hammer mill to produce graphite particles (graphite nucleus material) having an average particle diameter of 20 µm.

The coke powder used here is not limited to said conditions, A material of 1 micrometer-several tens of micrometers can be selected. Moreover, it is possible to change the composition of coke powder and a tar pitch suitably. Other conditions, such as heat processing temperature, are not limited to the above-mentioned content, either.

<Formation of coating layer>

The coating layer of low crystalline carbon can be formed in the graphite nucleus material produced in Example 4 in the following order. First, 100 mass parts of graphite particles (graphite nucleus material) obtained above were immersed and dispersed in 160 mass parts of novolak-type phenol resin methanol solutions (made by Hitachi Chemical Co., Ltd.), and the graphite particle phenol resin mixture solution was produced. By filtering, drying and heat-processing in 800 degreeC-1000 degreeC this solution, the composite carbon particle which formed the coating layer of low crystalline carbon on the surface of the graphite nucleus material was obtained. The gas atmosphere was made into the mixed gas atmosphere (non-oxidizing atmosphere) which added 0.5%-1% of oxygen to nitrogen gas. Moreover, in addition to a phenol resin, it is also possible to substitute by polycyclic aromatics, such as naphthalene, anthracene, and creosote oil.

The specific surface area by the BET method of the composite carbon particle mentioned above was 3.6 m <2> / g. Moreover, the interlayer distance d002 of the graphite crystal by X-ray wide-angle diffraction method was 0.335 nm-0.3370 nm, and crystallite size Lc existed in the range of 20 nm-90 nm. The intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of the Raman peak at the position of ₁₅₈₀ cm ^-1 and 1360 cm ^-1 was in the range of 0.1 to 0.7.

It is also possible to apply another method of coating low crystalline carbon. For example, there is also a method of coating polyvinyl alcohol on graphite particles (graphite nucleus material) and thermally decomposing it. In this case, it is preferable to make heat processing temperature into the range of 500 to 800 degreeC.

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

In addition, in order to impart oxygen to the coating layer of low crystalline carbon up to the oxygen concentration required by the present invention, it is also possible to perform surface modification such as oxidation treatment using ozone or the like, plasma treatment or ultraviolet (UV) treatment. When thermally decomposing the coating material, 10% or less of a small amount of oxygen can be added to the inert gas, and surface modification can be performed using the mixed gas.

The coating layer of low crystalline carbon was formed in the graphite nucleus material surface as mentioned above, the powder was cut out in the cross section by FlB, and the thickness of the carbon layer was measured by TEM. As a result, although there were gaps, the thickness of the coating layer of low crystalline carbon was in the range of 10 nm-100 nm. If the thickness of the coating layer is 10 nm or more, it is estimated that the passage of the electrolyte solution from the minute gaps of the coating layer is suppressed. This prevents direct contact of the electrolyte solution with the edge surface of the highly active graphite nucleus material. Therefore, decomposition reaction of the electrolyte solution with high temperature storage and charge / discharge cycles is reduced, and battery characteristics are considered to be improved. Moreover, when the thickness of a coating layer is 100 nm or less, the transfer resistance of the coating layer part of lithium ion accompanying charge / discharge reaction is small, and preferable.

(Example 5)

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

(Example 6)

In formation of the coating layer of Example 3 mentioned above, the starting material of the low crystalline carbon which coat | covers a graphite nucleus material was changed from carboxymethylcellulose resin to crude oil pitch, and the negative electrode active material was produced. Other than that is the same as that of Example 3.

(Comparative Example 1)

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

<Evaluation of the negative electrode active material of Examples 2-6>

(1) Evaluation of Example 4

Differential thermal mass simultaneous measurement (TG-DTA) was performed in air for the negative electrode active material (composite carbon particle) produced in Example 4. It is known that the combustion behavior of a carbon material reflects crystallinity and specific surface area, and the oxidation peak of carbon derived from a coating layer and carbon derived from a graphite nucleus material can be separated using this difference in combustion behavior. Generally, peaks derived from high crystalline graphite appear around 900 ° C (for example, in FIG. 1 of Japanese Patent Laid-Open No. 2001-229914), and it is known that the lower the crystallite and the higher specific surface area, the lower the oxidation temperature is. . For measurement, a differential thermal mass simultaneous measurement device was used, and the measurement temperature range was from room temperature to 1100 ° C, the temperature increase rate was 5 ° C / min, and the atmosphere was 80 mL / min in air. A 70 microliter alumina cell was used for the measurement container, and sample mass was 10 mg.

The results are shown in FIG. The TG-DTA data of FIG. 2 is a measurement result of the composite carbon particles corresponding to Example 4 of Table 1. FIG. The treatment mass change (left vertical axis) was almost constant up to 350 ° C., but when the temperature reached 350 ° C. or more, the mass began to decrease gradually, and the mass became zero at about 700 ° C. (ie, it was completely oxidized and burned). The temperature differential value (right vertical axis) of the mass change at this time showed two oxidation peaks of the low temperature range of 411 degreeC vicinity, and the high temperature range of 678 degreeC. The former suggested oxidation reaction of the coating layer, and the amount of mass reduction at that time was 10 mass%. Since the coating layer of Example 4 has an oxygen functional group on the surface, it is estimated that it is easy to oxidize at low temperature compared with general graphite. The latter is an oxidation reaction of the graphite nucleus material. The temperature differential peak (right axis) of the mass change attributable to this oxidation reaction is 678 ° C, which is lower than the peak position of the general high crystalline graphite material. This may be considered that the coating layer of Example 4 has high reactivity with oxygen and also affects the oxidation reaction of the internal graphite nucleus material covered with the coating layer of low crystalline carbon.

That is, one of the features of this embodiment is that the oxidation peak temperature (678 ° C.) of the graphite nucleus material is within 300 ° C. with respect to the oxidation peak temperature (411 ° C.) of the coating layer. In addition, the content rate of the coating layer in a composite carbon particle is corresponded in mass reduction amount (10 mass%) according to the oxidation reaction, and in this Example, the content rate of the low crystalline carbon in a composite carbon particle is 0.1 mass%-20 Mass% is another feature.

(2) Evaluation of Example 3

Next, the result of differential thermal mass measurement (TG-DTA) of the negative electrode active material (composite carbon particle) of Example 3 which changed the production | generation conditions of a coating layer was shown. The mass change (left vertical axis) was almost constant up to 450 ° C., but when the temperature reached 450 ° C. or more, the mass began to decrease gradually, and the mass became zero at about 900 ° C. (ie, it was completely oxidized and burned). The temperature differential value (right vertical axis) of the mass change at this time showed two oxidation peaks, a low temperature region of 599 ° C and a high temperature region of 801 ° C. The former suggested oxidation reaction of the coating layer, and the amount of mass reduction at that time was 15 mass%. Since the coating layer of Example 3 has an oxygen functional group on the surface, it is estimated that it becomes easier to oxidize than Example 4.

In addition, the temperature (801 degreeC) of the temperature differential peak (right axis) of the mass change which belongs to the latter oxidation reaction becomes lower than the oxidation peak temperature of general high crystalline graphite material is the same as FIG. This is considered that the coating layer of Example 3 has high reactivity with oxygen and influences the oxidation reaction of the graphite nucleus material in a coating layer. That is, one of the features of this embodiment is that the oxidation peak temperature (801 ° C) of the graphite nucleus material is within 300 ° C with respect to the oxidation peak temperature (599 ° C) of the coating layer.

At the same time, in the TG-DTA measurement data, it has 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 seen as a general high crystalline graphite material. It is another feature of this embodiment that all appear on the low temperature side with respect to the appearance temperature of the losing oxidation peak. Moreover, the content rate of the coating layer in a composite carbon particle is corresponded to the mass reduction amount (15 mass%) according to the oxidation reaction, and it is also characterized by the content rate of the low crystalline carbon in a composite carbon particle being 0.1 mass%-20 mass%. Is one of.

(3) Evaluation of Example 2

In the differential thermal thermomass simultaneous measurement (TG-DTA) result of the negative electrode active material (composite carbon particle) in Example 2, the oxidation peak derived from a coating layer and the high temperature of 810 degreeC-830 degreeC on the low temperature side of 540 degreeC-560 degreeC The oxidation peak derived from graphite nucleus material was obtained by the side. The mass reduction amount according to the oxidation reaction of the coating layer was 1 mass%. From this, it turns out that both the tendency of the two oxidation peaks of the negative electrode active material in Example 2, and the content rate of the low crystalline carbon in a composite carbon material satisfy | fill the said characteristic.

(4) Evaluation of Example 5

As described above, the negative electrode active material (composite carbon particles) in Example 5 is a material obtained by treating the surface of the negative electrode active material in Example 3 with ozone to increase the oxygen content. In the differential thermal thermogravimetry (TG-DTA) result of the negative electrode active material in Example 5, the oxidation peak derived from a coating layer from 530 degreeC-550 degreeC, and the oxidation peak derived from a graphite nucleus material from 750 degreeC-770 degreeC, Each appeared, and the mass reduction amount by the oxidation reaction of the coating layer was 0.1 mass%. Compared with the measurement result obtained with respect to the negative electrode active material in Example 3, it turns out that the peak temperature shifted all to the low temperature side. This is presumably because oxygen content of the coating layer in Example 5 increased more easily than Example 3, and became easier to oxidize. It is thought that it is more reactive with oxygen and the oxidation reaction of carbon inside a coating layer is more likely to occur. Moreover, although the coating layer decreased by ozone treatment, it was shown that the content rate of the low crystalline carbon in a composite carbon particle is 0.1 mass%-20 mass%.

(5) Evaluation of Example 6

In the differential thermal thermomass simultaneous measurement (TG-DTA) result of the negative electrode active material (composite carbon particle) in Example 6, the oxidation peak derived from a coating layer and the high temperature of 760 degreeC-780 degreeC on the low temperature side of 500 degreeC-520 degreeC The oxidation peak derived from graphite nucleus material was obtained by the side. The mass reduction amount according to the oxidation reaction of the coating layer is 20 mass%, satisfying the characteristics of the present invention.

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

Next, the surface analysis of the negative electrode active material (composite carbon particle) used in Example 2, 3, 4, 5, 6 was performed by X-ray photoelectron spectroscopy (XPS). The results are shown in Table 1. In this measurement, in order to remove traces of contaminants from the atmosphere, argon etching was performed before measurement. After setting a negative electrode active material in an X-ray photoelectron spectroscopy (XPS) apparatus, it vacuum-exhausted fully and etched argon ion under high vacuum. The etching amount (depth) set ion current and etching time so that it might become 2 nm in conversion of silicon dioxide. Then, XPS spectrum measurement of C1s and 01s was performed.

The attribution of the chemical bond state from the XPS spectrum of C1s was performed as follows. CO or C-OH bonds are at peak positions in the range of 286.3 ± 0.3 eV, CH bonds are at peak positions in the range of 285.1 ± 0.3 eV, and CC bonds are at peak positions in the range of 284.3 ± 0.3 eV. Spectral curve fitting was performed and the respective bonding ratios (atom%) were calculated. Similarly, attribution to the chemical bonding state from the XPS of 01s was performed as follows. That is, C-0 bonds are at peak positions in the range of 533.6 ± 0.3 eV, C-OH bonds are at peak positions in the range of 532.3 ± 0.3 eV, and C═O bonds are at peak positions in the range of 531.2 ± 0.3 eV. Curve fitting of each spectrum was performed, and each coupling ratio (atom%) was computed.

First, the carbon concentration (atomic percentage) on the surface of the negative electrode active material (coating layer) of Example 2 was 97.9 atom%, and the oxygen concentration was 2.1 atom%. By XPS analysis of C1s, carbon in the C-0, or C-OH state is included in 4 atom% of the total carbon amount, and most of the carbon is in a bonded state of CC or CH, wherein the bonded state of CC is It is 70 atom%-80 atom% of total carbon amount. Also in the case of Example 3, 4, 5, it is the same about carbon state, and the significant difference was not confirmed.

Next, in the XPS analysis of 01s, the species containing oxygen were attributed to C═O, C—OH, and C—O. On the surface of the negative electrode active material of Example 2, it turned out that C-OH and C-0 are the main components, and the chemical species of the high oxidation water state which belongs to C = 0 is contained. Each abundance ratio was 12 atom% for C = 0, 40 atom% for C-OH, and 48 atom% for C-0. In addition, since the measurement error by this analysis has about +/- 3 atom%, it is interpreted that the amount of C = O exists in the range of 9 atom%-15 atom% of the total amount of oxygen.

The carbon concentration (atomic percentage) of the negative electrode active material surface (coating layer) of Example 3 is 97.8 atom%, and the oxygen concentration is 2.2 atom%. In addition, it was found from the XPS analysis results of 01s that C-OH and C-0 were the main components and C = 0 in a high oxidation water state on the surface of the negative electrode active material of Example 3.

The carbon concentration (atomic percentage) of the negative electrode active material surface (coating layer) of Example 4 is 97.1 atom%, and the oxygen concentration is 2.9 atom%. In the XPS analysis results of 01 s, it was found that C-OH and C-0 were the main components and C = O in the high oxidation water state was present on the surface of the negative electrode active material of Example 4.

The carbon concentration (atomic percentage) of the negative electrode active material surface (coating layer) of Example 5 is 95.7 atom%, and the oxygen concentration is 4.3 atom%. On the surface of the negative electrode active material of Example 5, in the XPS analysis result of 01s, it was found that almost equal amounts of C = 0, C-OH, and C-O existed. In particular, on the surface of the negative electrode active material of Example 5, 36 atom% of the total amount of oxygen contained C = O in a high oxidation water state. Considering that the measurement error by this analysis has ± 3%, the amount of C═O is interpreted to be in the range of 33 atom% to 39 atom% of the total amount of oxygen on the surface of the negative electrode active material of Example 5.

Finally, the carbon concentration (atomic percentage) of the surface of the negative electrode active material (coating layer) of Example 6 was 97.5 atom%, and the oxygen concentration was 2.5 atom%. In the XPS analysis results of 01 s, it was found that C-OH and C-O were the main components and C = 0 in a high oxidation water state on the surface of the negative electrode active material of Example 6.

XPS analysis of the graphite nucleus material of Comparative Example 1 was conducted. The oxygen concentration of the surface of the graphite nucleus material was almost the same as that of the negative electrode active material of Examples 2 to 4, but the remarkable difference with the surface of the negative electrode active material of Examples 2 to 6 was that C = O in the state of high oxidation water was not confirmed. I did not.

In the negative electrode active materials of Examples 2, 3, 4, 5 and 6, it turned out that the oxygen-containing carbon layer shown in Table 1 is formed in the surface of the graphite nucleus material as a coating layer. It is estimated that this coating layer is in close contact with the internal graphite nucleus material and has some influence on the characteristics of the oxidation reaction of FIGS. 2 and 3. The effects and effects are as follows.

The oxidation peak on the high temperature side shown in FIGS. 2 and 3 is due to the oxidation reaction of the graphite nucleus material of the negative electrode active material (composite carbon particles) of the present invention. The temperature of this oxidation reaction is shifted to the lower temperature side than the oxidation peak of the conventional graphite single-piece (for example, the oxidation peak of about 900 degreeC of FIG. 1 described in Unexamined-Japanese-Patent No. 2001-229914). In the test of FIG. 2 and FIG. 3, when the low crystalline carbon of a coating layer oxidizes and decomposes, it is estimated that the reaction becomes a starting point of the oxidation reaction of a graphite nucleus material, and promotes the oxidative decomposition of graphite nucleus material itself. Therefore, the shift of the high temperature side peak of the negative electrode active material according to the present invention to the low temperature side is excellent in the adhesion and adhesion rotation of the coating layer made of low crystalline carbon on the surface of the graphite nucleus material, that is, the coating layer makes the surface of the graphite nucleus material uniform. It is suggested to cover closely and closely. However, this invention is not restrained by the theory.

As shown in the above properties of the negative electrode active materials of Examples 2 to 6, in the present invention, C = O, C-OH, and CO are applied to the surface of the coating layer by changing the heat treatment conditions when forming the coating layer on the graphite nucleus material. It has a functional group of, and the content rate of the oxygen atom of the said functional group in a coating layer can be made into the quantity equivalent to 2 atom%-5 atom% of oxygen in the total amount of the carbon atom and oxygen atom of a coating layer. In particular, when the surface of the coating layer is in a high oxidation water state, that is, the oxygen amount of C = O attributed to the XPS spectrum of 01 s is preferably in the range of 7 atom% to 39 atom% with respect to the total oxygen amount of the coating layer. Such a negative electrode active material has at least 1 oxidation peak in each temperature range of at least 350 degreeC or more and less than 600 degreeC and 600 degreeC or more and 850 degrees C or less in the differential thermal thermogravimetry simultaneous measurement in air | atmosphere, and 350 degreeC or more and 850 degrees C or less The peak temperature difference between an oxidation peak having a peak at the highest temperature and an oxidation peak having a peak at the lowest temperature is 300 ° C. or less within the range of. When the negative electrode active material which satisfy | filled these requirements was used for a lithium ion battery, it turned out that it is effective for the improvement of the storage characteristic of a battery, and a cycle life. Detailed test results will be described later.

Here, it is assumed that the adhesion between the coating layer and the surface of the graphite nucleus material increases, and that the coating layer uniformly and densely covers the surface of the graphite nucleus material, thereby preventing the electrolyte solution from directly contacting the surface of the graphite nucleus material. As a result, since the electrolyte solution hardly reaches the edge portion (the end of the graphene structure) of the highly active graphite nucleus material, it is estimated that the reduction decomposition of the electrolyte solution is suppressed and contributes to the improvement of battery characteristics.

As mentioned above, about the negative electrode active material (composite carbon particle) of Examples 2-6, the atomic ratio of carbon and oxygen of the functional group of the surface of the coating layer of low crystalline carbon, C1s analysis result, and 01s analysis result are shown in Table 1. In addition, the numerical value shown in the column of the C1s analysis result and 01s analysis result of Table 1 represents each bonding ratio (atom%). The coating layer of the negative electrode active material (composite carbon particles) of Examples 2 to 6 is characterized in that a functional group including a C = 0 bond is contained, and the ratio of C-OH and C = 0 is oxygen in each functional group. It is 1: 1 to 4: 1 as an atomic composition ratio of.

When producing a negative electrode using the negative electrode active material (composite carbon particle) mentioned above, high rate charge / discharge characteristic may be needed. In such a case, the conductive aid may be added to the negative electrode. Since the conductive aid does not participate in the occlusion and release of lithium ions and acts as a medium for electrons, it does not affect the occlusion and release reaction of lithium ions in the negative electrode active material.

Moreover, the conductive polymer material which consists of polyacene, polyparaphenylene, polyaniline, and polyacetylene can also be added and used for the said negative electrode.

In Examples 2-6, since the said negative electrode active material is powder, the negative electrode binder is mixed with it, the powders are bonded together, and they are adhere | attached on an electrical power collector. In this invention, in the said negative electrode, it is preferable to make the particle diameter of a negative electrode active material below the thickness of the mixture layer containing a negative electrode active material and a negative electrode binder. In the negative electrode active material, when there is granulation having a size greater than or equal to the thickness of the mixture layer, it is preferable to remove the granulation by sifting, airflow classification, or the like, and to use particles having a thickness of the mixture layer or less.

A copper foil having a thickness of 10 µm to 100 µm, a copper perforated foil having a thickness of 10 µm to 100 µm, a hole diameter of 0.1 mm to 10 mm, an expanded metal, a foamed metal sheet, or the like is used for the current collector. Titanium, nickel, etc. are also applicable. In the present invention, any current collector can be used without being limited to materials, shapes, manufacturing methods, and the like.

After attaching the negative electrode slurry containing the negative electrode active material, the negative electrode binder, and a suitable solvent to a 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 press-molded by a roll press. And the negative electrode was produced.

<Electrochemical Evaluation 1>

Using the negative electrode active material (composite carbon particles) shown in Table 1, an electrochemical cell was fabricated using Li metal as a counter electrode and Li metal as a reference electrode. C1 the cell using the negative electrode active material of Example 2, C2 the cell using the negative electrode active material of Example 3, C3 the cell using the negative electrode active material of Example 4, C4 the cell using the negative electrode active material of Example 5, Example The cell using the negative electrode active material of 6 is C5, and the cell using the negative electrode active material of Comparative Example 1 is C6. 5 mass parts of PVDF was mixed with 95 mass parts of each negative electrode active material as a negative electrode binder, and N-methyl- 2-pyrrolidone was added as a solvent so that the density | concentration of the solid content which combined the negative electrode active material and PVDF in a negative electrode slurry might be 55 mass%. . The negative electrode slurry obtained by kneading sufficiently using a planetary mixer was applied to the surface of a copper foil current collector having a thickness of 10 µm according to the doctor blade method. N-methyl-2-pyrrolidone was dried using the drying oven of 120 degreeC, and air atmosphere, and it press-molded using the roll press machine, and each negative electrode was produced. The negative electrode mixture density was 1.5 g / cm 3. The microporous sheet (25 micrometers in thickness) which laminated | stacked polyethylene and polypropylene was used for the separator. In the electrolytic solution it was used an electrolytic solution which comprises ethylene carbonate and dimethyl carbonate and ethylmethyl carbonate was dissolved LiPF ₆ 1M. In addition, the volume ratio of each solvent was 1: 1.

The six kinds of cells described above were charged at a current density of 0.1 mA / cm 2 (current density corresponding to about 8 hours rate) under the condition of a lower limit voltage of 10 mV and a maximum charging time of 8 hours, and then a 30 minute rest time. After elapsed, discharge of a constant current density (0.1 mA / cm 2) up to an upper limit voltage of 1 V was performed. In addition, after 30 minutes of rest time, the above-described charge-discharge cycle was repeated.

In Table 2, the "reversible capacity" result calculated | required from the "first discharge capacity" and the difference of initial charge capacity and discharge capacity was shown. In addition, each capacity was computed per unit mass of the used negative electrode active material. It was found that the cells C1 to C5 using the negative electrode active material according to the examples of the present invention had a small irreversible capacity and a large initial discharge capacity to the cell C6 using the negative electrode active material according to Comparative Example 1.

Electrochemical Evaluation 2

The cylindrical battery of FIG. 1 was produced using the negative electrode active material (composite carbon particle) of Examples 2-6 shown in Table 1, and the battery characteristic evaluation test was done. The battery using the negative electrode active material of Example 2 shown in Table 1 B1, the battery using the negative electrode active material of Example 3 B2, the battery using the negative electrode active material of Example 4 The battery using the negative electrode active material of Example 3 B3 The battery using B4 and the negative electrode active material of Example 6 is B5 and the battery using the negative electrode active material of Comparative Example 1 is B6. 5 parts by mass of PVDF was mixed with 95 parts by mass of each negative electrode active material as a negative electrode binder, and N-methyl-2-pyrrolidone was added as a solvent so that the concentration of the solid content obtained by combining the negative electrode active material and PVDF in the negative electrode slurry was 55% by mass. . The mixture was sufficiently 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 according to the doctor blade method. N-methyl-2-pyrrolidone was dried using the drying oven of 120 degreeC, and air atmosphere, and it press-molded using the roll press machine, and each negative electrode was produced.

Using the positive electrode active material in each cell (B1 ~ B6) is made by _{LiNi 1/3 Mn 1/3} Co 1/3 O 2. 89 mass parts of this positive electrode active material, 4 mass parts of acetylene black, and 7 mass parts of PVDF as a positive electrode binder were mixed, and the positive electrode slurry which added N-methyl- 2-pyrrolidone was prepared. A well-known kneader and a disperser were used for the dispersion process of a material. The mass per unit area of the positive electrode active material, the thickness and the density of the positive electrode were to be the same conditions for each battery.

As a separator, the microporous sheet (25 micrometers in thickness) which laminated | stacked polyethylene and polypropylene was used.

As electrolyte solution, the electrolyte solution which consists of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate which melt | dissolved 1M LiPF ₆ was used. In addition, the volume ratio of each solvent was 1: 1.

Each battery was supplied with a charging current having a current value of 15 A corresponding to a rate of 1 hour, and charged at a constant voltage of 4.2 V for 1 hour. Next, a discharge current of 15 A was flowed and discharged until the battery voltage reached 3.OV. In addition, the charge / discharge cycle was continued 100 times under the same conditions, and the capacity retention rate at the time of 100 cycles was determined from the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity. The result was shown in the column of "Capacity retention rate (%) at the time of 100 cycle elapse" of Table 2.

The above measurement results are summarized in Table 2. It was found that the batteries B1 to B5 according to the examples of the present invention were also superior in terms of capacity retention rate after 100 cycles, compared to the batteries B6 of the comparative example.

Electrochemical Evaluation 3

The cylindrical lithium ion battery of FIG. 1 was connected in 8 series, the assembled battery (battery module) 401 of FIG. 4 was assembled, and it was assembled to the power supply system of FIG. The lithium ion battery is produced by the electrochemical evaluation 2 described above. This power storage system is useful as a mobile body or a stationary power storage system.

In Fig. 4, reference numeral 401 denotes an assembled battery, 4O2 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 component, and 407 denotes an external positive electrode. The terminal, 408 denotes a negative external terminal, 409 denotes an arithmetic processing unit, 410 denotes a charge and discharge circuit, 411 denotes an external device, 412 denotes a power line, 413 denotes a signal line, and 414 denotes an external power cable.

The cylindrical lithium ion battery (hereinafter only referred to as "battery") 40 is fixed by the support component 406. Each battery is alternately changed in the directions of the positive electrode terminal 403 and the battery can 405, and is connected in series via the bus bar 404. In FIG. 4, the positive electrode terminal 403 corresponds to the battery plug 120 of FIG. 1, and the battery can 405 corresponds to the battery can 113 of FIG. 1, respectively. The terminals of the eight batteries 40 connected in series are connected to the positive external terminal 407 and the negative external terminal 408. In addition, in the assembled battery 401, eight batteries 40 are connected in series, but the number of connected batteries 40 is not limited to eight, and if it is two or more, it depends on the size of the assembled battery 401. It is set appropriately. In addition, the connection mode of the battery 40 in the assembled battery 401 is not limited to this, and may be in parallel or in parallel.

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

The composition of the negative electrode active material in this evaluation is a composition which added PVDF which is 5 mass parts of negative electrode binders to 95 mass parts of negative electrode active materials (composite carbon particle) of Example 4. The positive electrode active material is a _{LiNi 1/3 Mn 1/3} Co 1/3 O 2. About other composition, it is the same as that described in the electrochemical evaluation 2 mentioned above.

In addition, since this evaluation was a test for confirming the validity of this invention, the function of both supply and consumption of an electric power is provided in the place which installed the external apparatus (for example, an electronic load device or a motor) for consuming electric power. A power supply load power source as an external device 411 having a configuration was used. Use of this does not cause a difference in the effects of the present invention as compared with the actual use of an electric vehicle such as an electric vehicle, a machine tool, or a distributed power storage system or a backup power supply system.

In the charging test immediately after the assembly of the system, a charging current having a current value of 15 A corresponding to a one hour rate flows from the charge / discharge circuit 410 to the positive electrode external terminal 407 and the negative electrode external terminal 408 at a constant voltage of 33.6 V. Charge for 1 hour was performed. The constant voltage value set here is 8 times the constant voltage value of 4.2V of the unit cell mentioned above. Power required for charging and discharging of the assembled battery was supplied by a power supply load device (external device 411).

In the discharge test, a reverse current flows from the positive electrode external terminal 407 and the negative electrode external terminal 408 to the charge / discharge circuit 410, and consumes electric power in the power supply device as the external device 411. The discharge current was a condition of 0.5 hour rate (7.5 A as the discharge current), and was discharged until the voltage between the terminals of the positive electrode external terminal 407 and the negative electrode external terminal 408 reached 24V.

Under these charge and discharge test conditions, initial performance of charge capacity 15.OAh and discharge capacity 14.95Ah was obtained. Furthermore, when 1000 cycles of charge / discharge cycle tests were conducted, 92% of capacity retention was obtained. In addition, this system using the negative electrode active material of Example 4 is set to S1.

In the structure of FIG. 4, the system S2 which changed the negative electrode active material into the negative electrode active material of Example 5 of Table 1, and the system S3 which changed the negative electrode active material of Comparative Example 1 were produced, respectively. For each system, 1000 cycles of charge and discharge cycle tests were conducted 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%.

From this, it turned out that the negative electrode active materials of Example 4 and Example 5 of this invention are effective for the improvement of the cycling characteristics of a lithium ion battery.

Next, the three types of systems described above were charged under the same conditions and allowed to stand for 30 days under an environment temperature of 50 ° C. Then, the charge / discharge cycle test was restarted from discharge, the discharge capacity of the 10th cycle was measured, and it was set as the capacity retention ratio after 50 degreeC standing. In addition, a capacity | capacitance retention rate is the value calculated | required as the ratio with respect to the initial capacity before 50 degreeC standing to 100%. As a result of this test, it was found that the anode active materials of Examples 4 and 5 of the present invention were 93% in S1, 92% in S2, and 75% in S3, and were also effective in terms of storage properties at 50 ° C.

Based on the content described above, the specific application example of this system is shown and the effect of this invention is made clear. In addition, you may change a concrete structural material, a component, etc. in the range which does not change the summary of this invention. In addition, if it contains the component of this invention, it is also possible to add a well-known technique, or to substitute by a well-known technique.

The lithium ion battery and the battery module of the present invention can be used for power supplies such as electric vehicles, storage batteries for storage of renewable energy, unmanned mobile vehicles, and nursing equipment, as well as consumer electronic products such as portable electronic devices, mobile phones, and power tools. It is possible to use. Moreover, the lithium ion battery of this invention is applicable to the power supply of the space search ship for the search of the moon, Mars, etc. In addition, observation of buildings or living spaces (enclosed, not open) on space stations, on Earth or other celestial bodies, spacecraft for interplanetary transport, planetary rovers, confined spaces underwater or in the sea, submarines, fish It can be used for various power sources such as air conditioning of various spaces such as industrial facilities, warm water, purification of sewage and air, 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

Industrial Applicability The present invention can be applied to lithium ion batteries such as lithium ion secondary batteries, mobile bodies or stationary power storage systems using the same.

As for the indication of the Japan patent application 2010-213866 for which it applied on September 24, 2010, the whole is integrated in this specification by reference.

All documents, patent applications, and technical specifications described in this specification are specifically incorporated by reference in the individual documents, patent applications, and technical specifications, and are incorporated into and incorporated into this specification to the same extent as if individually described. do.

Claims (19)

A negative electrode active material capable of occluding and releasing lithium, wherein the negative electrode active material is a composite carbon particle having a coating layer of low crystalline carbon on the surface of the graphite nucleus material, and has a functional group of C = 0, C-OH, and C-0 in the coating layer. The content rate of the oxygen atom in the total amount of carbon atoms and oxygen atoms of the coating layer is 2.5 atom% to 5 atom%, and in the thermogravimetric method in the air, each of 350 ° C or more and less than 600 ° C and 600 ° C or more and 850 ° C or less The peak temperature difference between an oxidation peak having a peak at the highest temperature and an oxidation peak having a peak at the lowest temperature in the range of 350 ° C. or more and 850 ° C. or less in the temperature range is 300 ° C. or less. A negative electrode including a negative electrode active material,
With the anode,
Nonaqueous electrolyte and nonaqueous solvent,
Lithium ion battery comprising a. The method of claim 1,
The lithium ion battery whose C content of C = O oxygen in the said coating layer is 7 atom%-39 atom% in the total amount of oxygen of the said coating layer. The method according to claim 1 or 2,
The low crystalline carbon of the coating layer is an amorphous carbon lithium ion battery. The method of claim 1,
The lithium ion battery whose ratio of C-OH and C = 0 in the said coating layer is 1: 1 to 4: 1 as an atomic composition ratio of oxygen in each functional group. The method of claim 1,
A lithium ion battery having a (002) plane spacing d002 of 0.3354 nm to 0.3370 nm and a crystalline size Lc of 20 nm to 90 nm determined by the X-ray diffraction method of the negative electrode active material. The method of claim 1,
A lithium ion battery, wherein the coating layer has a thickness of 10 nm to 100 nm. The method of claim 1,
A lithium ion battery having an intensity ratio (I ₁₃₆₀ / I ₁₅₈₀ ) of a Raman peak of the negative electrode active material of 0.1 to 0.7. The method of claim 1,
The irreversible capacity | capacitance per unit mass of the said negative electrode active material is 20 mAh / g-31 mAh / g, and the discharge capacity density of the said negative electrode active material is 350 mA / g-365 mA / g. The method of claim 1,
The graphite nucleus material is a lithium ion battery is a graphite particle isotropic pressure treatment. The method of claim 1,
The coating layer is a lithium ion battery that is a carbon film formed on the surface of the graphite nucleus material by the low crystalline carbon by thermal decomposition of an organic compound or a mixture thereof in a non-oxidizing atmosphere. The method of claim 10,
The lithium ion battery, wherein the coating layer is a carbon film obtained by pyrolyzing the organic compound or a mixture thereof and the graphite nucleus material under contact conditions. The method of claim 10,
The organic compound is a lithium ion battery which is an organic polymer compound carbonized in the liquid phase. The method of claim 10,
The said organic compound is a lithium ion battery which is an organic resin which carbonizes in a solid phase. The method of claim 1,
The content rate of the said composite carbon particle | grains of the said low crystalline carbon is a lithium ion battery whose 0.1 mass%-20 mass% of the total mass of the said graphite nucleus material and the said low crystalline carbon. The method of claim 1,
The positive electrode comprises a positive electrode active material, a conductive aid, a positive electrode binder and a current collector. The method of claim 1,
The positive electrode comprises a positive electrode active material, a conductive aid, a positive electrode binder and a current collector, the positive electrode active material,

At least one lithium ion battery selected from the group consisting of. The method of claim 1,
The positive electrode includes a positive electrode active material, a conductive aid, 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 according to claim 1 are connected in series, in parallel, or in parallel. A moving body or stationary power storage system, wherein the battery module according to claim 18 is connected to a charge / discharge circuit connectable to an external device via an external terminal.

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