Graphite carbon material for lithium-ion secondary battery anode, anode material for lithium-ion secondary battery, anode for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

In a graphite carbon material for a lithium-ion secondary battery anode, the crystallite diameter Lc (002) obtained by X-ray diffraction is 35 nm to 150 nm, and the compressive load is 2.0 kN / cm2 to 4.0 kN / cm2.

Description

Graphite carbon material for lithium ion secondary battery negative electrode, lithium ion secondary battery negative electrode material, lithium ion secondary battery negative electrode and lithium ion secondary battery

[0001] The present disclosure relates to a graphitic carbon material for a negative electrode of a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. The automotive industry, too, is also working to develop high-output, high-capacity batteries for electric and hybrid vehicles. Among various types of batteries, lithium-ion secondary batteries are currently attracting attention due to their high energy density.

[0003] Lithium-ion secondary batteries installed in electric vehicles and hybrid electric vehicles are required to have both rapid charging and long-term reliability. In other words, batteries that combine high input power and long life are desired. From the perspective of rapid charging, it has been proposed to reduce the particle size of the negative electrode active material to increase the diffusivity of lithium ions within the solid. Furthermore, from the perspective of long life, negative electrode active materials for lithium-ion secondary batteries with a small specific surface area have been proposed. Based on this concept, for example, Patent Document 1 proposes a graphitic carbon material for lithium-ion secondary battery negative electrodes that increases the diffusivity of lithium ions within the solid by reducing the particle size and reduces side reactions on the active material surface by reducing the specific surface area.

[0004] Japanese Patent Application Laid-Open No. 2018-6270

[0005] Although the above-mentioned Patent Document 1 has excellent initial charge / discharge efficiency, further improvement in long-term reliability is required. Therefore, one aspect of the present disclosure aims to provide a graphite carbon material for a negative electrode of a lithium ion secondary battery, a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery that can achieve excellent input characteristics, high-temperature storage characteristics, and cycle characteristics.

[0006] Specific means for solving the above problems include the following aspects.

[0007] <1> The crystallite diameter Lc(002) determined by X-ray diffraction is 35 nm to 150 nm, and the compressive load is 2.0 kN / cm ２ ~4.0 kN / cm ２ <2> The graphitic carbon material for a lithium ion secondary battery anode according to <1>, wherein, in a particle size distribution measured by a laser diffraction scattering method, when a volume cumulative distribution curve is drawn from the smallest diameter side, the particle size at 50% of the cumulative volume (D50) is 5 μm to 30 μm. <3> The graphitic carbon material for a lithium ion secondary battery anode according to <1>, wherein, in a particle size distribution measured by a laser diffraction scattering method, a particle size at 1580 cm －１ The intensity Ig of the maximum peak near 1330 cm －１ <4> The graphite carbon material for a lithium ion secondary battery negative electrode according to <1> or <2>, wherein the intensity ratio (Id / Ig) of the maximum peak intensity Id in the vicinity of the maximum peak intensity Id is 0.1 to 0.5. ２ / g~8m ２ / g. <5> The graphite carbon material for a lithium ion secondary battery anode according to any one of <1> to <4>, having a crystallite diameter La(110) of 50 nm to 450 nm as determined by X-ray diffraction. <6> The graphite carbon material for a lithium ion secondary battery anode according to any one of <1> to <5>, having an oil absorption of 30 mL to 75 mL per 100 g of the graphite material in a linseed oil absorption measurement. <7> A lithium ion secondary battery anode material comprising the graphite carbon material for a lithium ion secondary battery according to any one of <1> to <6>. <8> A lithium ion secondary battery anode comprising a graphite carbon material layer comprising the graphite carbon material for a lithium ion secondary battery according to any one of <1> to <6>, and a current collector. <9> A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to <8>, a positive electrode, and an electrolyte solution.

[0008] One aspect of the present disclosure can provide a graphite carbon material for a lithium ion secondary battery anode, a lithium ion secondary battery anode material, a lithium ion secondary battery anode, and a lithium ion secondary battery that can achieve excellent input characteristics, high-temperature storage characteristics, and cycle characteristics.

[0009] Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present invention. In this disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with the value shown in each test.

[0010] In the present disclosure, each component in the graphitic carbon material for a lithium-ion secondary battery anode and in the composition may contain multiple corresponding substances. Hereinafter, the "graphitic carbon material for a lithium-ion secondary battery anode" may be abbreviated as "graphitic carbon material." When multiple substances corresponding to each component are present in the graphitic carbon material and the composition, the content and amount of each component refer to the total content and amount of the multiple substances present in the graphitic carbon material and the composition, unless otherwise specified. In the present disclosure, the graphitic carbon material and the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the graphitic carbon material and the composition, the particle size of each component refers to the value for a mixture of the multiple types of particles present in the graphitic carbon material and the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire region when the region where the layer is present is observed, as well as cases where the layer is formed only in a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together, or two or more layers may be detachable.

[0011] In the present disclosure, the crystallite diameters Lc(002) and La(110) determined by X-ray diffraction are determined by the following method using an X-ray diffractometer (XRD). A measurement sample is prepared by mixing graphite powder:Si powder = 5:1 by mass in an agate mortar for 5 minutes, and the X-ray diffraction peak spectrum is measured under the following measurement conditions. The diffraction peak position is determined using standard silicon powder (e.g., NIST Si 640f, manufactured by NIST) as an internal standard. As the X-ray diffractometer (XRD), for example, a SmartLab 3kW manufactured by Rigaku Corporation can be used. The measurement conditions and calculation method are in accordance with JIS R 7651:2007 (Method for measuring lattice constant and crystallite size of carbon materials).

[0012] In the present disclosure, the compressive load of the graphitic carbon material is a density of 1.7 g / cm ３The larger the compression load, the less likely the graphite carbon material is to be deformed, broken, or the like by the pressure. Specifically, a predetermined mass (e.g., 3.0 g) of graphite carbon material is filled in a mold and compressed at a constant speed (e.g., 10 mm / min) until the density of the compressed graphite carbon material reaches 1.7 g / cm. ３ The pressure (kN / cm ２ ) is the compressive load of the graphite carbon material. In the above measurement, a mold having a diameter of, for example, 15 mm is used, and compression is performed using an autograph (for example, manufactured by Shimadzu Corporation). The density of the graphite carbon material is determined by the area of ​​the base of the mold (for example, 1.767 cm ２ ) and the volume of the graphite carbon material calculated from the distance from the bottom surface of the mold to the pressing surface of the graphite carbon material, and the mass of the graphite carbon material.

[0013] In the present disclosure, the particle diameters (D10), (D50), and (D90) are the particle diameters at which the cumulative volume distribution curve is plotted from the smallest diameter side in a particle diameter distribution measured using a laser diffraction particle size analyzer, such as the SALD-3000J manufactured by Shimadzu Corporation.

[0014] In the present disclosure, the 1580 cm －１ The intensity Ig of the maximum peak near 1330 cm －１ The intensity ratio (Id / Ig, hereinafter also referred to as "R value") of the maximum peak intensity Id in the vicinity of Ig is determined using a laser Raman spectrophotometer by the following method. The measurement sample is placed flat on a sample plate, which is irradiated with argon laser light, and measurement is performed using the laser Raman spectrophotometer. For example, an NRS-1000 manufactured by JASCO Corporation can be used as the laser Raman spectrophotometer. The measurement conditions are as follows: Wavelength of argon laser light: 532 nm Wavenumber resolution: 2.56 cm －１ Measurement range: 1180 cm －１ ~1730cm －１ Peak Research: Background Removal

[0015] The specific surface area (hereinafter sometimes abbreviated as "specific surface area") determined by nitrogen adsorption measurement at 77 K is determined using the BET method from the adsorption isotherm obtained from nitrogen adsorption measurement at 77 K in accordance with JIS Z 8830:2013. Nitrogen adsorption at liquid nitrogen temperature (77 K) is measured using a high-speed specific surface area / pore distribution analyzer (e.g., FlowSorb III, manufactured by Shimadzu Corporation) using the single-point method, and the specific surface area is calculated using the BET method. When measuring the BET specific surface area, moisture adsorbed on the sample surface and in the structure is thought to affect the gas adsorption capacity, so it is preferable to first perform a pretreatment by heating to remove moisture. In the pretreatment, a measurement cell containing 0.05 g of a measurement sample is depressurized to 10 Pa or less using a vacuum pump, heated to 110°C, and maintained for 3 hours or more, and then naturally cooled to room temperature (25°C) while maintaining the depressurized state. After this pretreatment, the evaluation temperature is set to 77K, and the evaluation pressure range is set to less than 1 in terms of relative pressure (equilibrium pressure relative to saturated vapor pressure).

[0016] In the present disclosure, the oil absorption per 100 g of a graphite material in the measurement of linseed oil absorption (hereinafter also referred to as "linseed oil absorption") is measured in accordance with the method described in JIS K6217-4:2008 "Carbon black for rubber use - Fundamental properties - Part 4: Determination of oil absorption", except that linseed oil (manufactured by Kanto Chemical Co., Inc.) is used as the reagent liquid in place of dibutyl phthalate (DBP).

[0017] The specific method for measuring linseed oil absorption is as follows: linseed oil is titrated into a measurement sample using a constant speed burette, and the change in viscosity characteristics is measured using a torque detector. The amount of reagent liquid added per 100 g of the measurement sample that corresponds to 70% of the maximum torque generated is defined as the linseed oil absorption (mL). An example of a measuring device is an absorption measuring device manufactured by Asahi Research Institute Co., Ltd.

[0018] In the present disclosure, tap density is measured in accordance with JIS R 1628:1997. Tap density can be measured using a packing density measuring device (for example, KRS-406, manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.). 100 mL of graphite carbon material is placed in a measuring cylinder, and the density is calculated by tapping (dropping the measuring cylinder from a predetermined height) until the density is saturated.

[0019] <Graphite Carbon Material for Lithium-Ion Secondary Battery Negative Electrode> The graphite carbon material for a lithium-ion secondary battery negative electrode according to the present disclosure has a crystallite diameter Lc(002) determined by X-ray diffraction of 35 nm to 150 nm and a compressive load of 2.0 kN / cm ２ ~4.0 kN / cm ２ is.

[0020] The graphitic carbon material for the negative electrode of a lithium ion secondary battery having the above-mentioned configuration exhibits excellent discharge specific capacity input characteristics and cycle characteristics. The reason for this is not clear, but is presumed to be as follows.

[0021] Compression load: 2.0 kN / cm ２ ~4.0 kN / cm ２ It has been experimentally found that by setting the crystallite diameter Lc(002) in the range of 35 nm to 150 nm, the input characteristics, high-temperature storage characteristics, and cycle characteristics are excellent. ２ ~4.0 kN / cm ２ By setting the range, the carbon material has an excellent degree of return to its original state when a predetermined pressure is applied to the compressed state and then the pressure is released (the so-called springback rate). This makes it difficult for irreversible deformation such as destruction of the particle structure to occur, and it is thought that the contact area between the carbon material and the solid electrolyte is sufficiently maintained even after repeated charge and discharge, further suppressing deterioration of cycle characteristics.

[0022] The crystallite diameter Lc(002) is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 60 nm or more. The crystallite diameter Lc(002) is preferably 150 nm or less, more preferably 130 nm or less, and even more preferably 120 nm or less.

[0023] The compression load was 2.0 kN / cm ２ or more, 2.1 kN / cm ２ More than 2.3 kN / cm is preferable. ２ More preferably, the compressive load is 4.0 kN / cm. ２ or less, 3.9 kN / cm ２ Preferably, 3.8 kN / cm or less ２ The following is more preferred:

[0024] In the particle size distribution measured by laser diffraction scattering, when a cumulative volume distribution curve is drawn from the small diameter side, the ratio (D90 / D10) of the particle size at 90% cumulative volume (D90) to the particle size at 10% cumulative volume (D10) is preferably 8.0 or less, more preferably 7.0 or less, and even more preferably 6.0 or less. The lower limit of the ratio (D90 / D10) is not particularly limited and may be, for example, 1.5 or more, or 2.0 or more.

[0025] The particle diameter (D50) is preferably 5 μm to 30 μm. When the particle diameter (D50) is 30 μm or less, the diffusion distance of lithium from the surface to the interior of the graphite carbon material is prevented from increasing, and the input characteristics of the lithium ion secondary battery tend to be further improved. The particle diameter (D50) is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 17 μm or less. When the particle diameter (D50) is 5 μm or more, the pressing pressure required to form the active material layer can be reduced, and as a result, the input characteristics tend to be better. The particle diameter (D50) is preferably 5.5 μm or more, more preferably 6.0 μm or more, and even more preferably 6.2 μm or more.

[0026] The tap density is 0.90 g / cm ３ It is preferable that the density is 0.91 g / cm or more. ３ More preferably, it is 0.92 g / cm or more. ３ It is more preferable that the tap density is 1.30 g / cm or more. ３ or less, 1.25 g / cm ３It may be the following:

[0027] The R value is preferably 0.10 to 0.50. When the R value is 0.10 or more, there are sufficient graphite lattice defects used for absorbing and releasing lithium ions, and the deterioration of input characteristics tends to be suppressed. The R value is more preferably 0.15 or more, and even more preferably 0.20 or more. When the R value is 0.50 or less, the capacity tends to be excellent. The R value is preferably 0.40 or less, more preferably 0.35 or less, and even more preferably 0.30 or less.

[0028] The specific surface area is 0.7 m ２ / g~8m ２ When the specific surface area is within the above range, a good balance between input characteristics and life characteristics tends to be obtained. ２ / g or more, and more preferably 0.9m ２ / g or more, and more preferably 1.0m ２ It is particularly preferable that the specific surface area is 4.0 m / g or more. ２ / g or less, and more preferably 3.5m ２ / g or less, and more preferably 2.5m ２ It is particularly preferable that the SiO2 content is 1 / g or less.

[0029] The crystallite diameter La (110) is preferably 50 nm to 450 nm. When the crystallite diameter La (110) is 50 nm or more, the capacity tends to be excellent. When the crystallite diameter La (110) is 450 nm or less, the input tends to be excellent. The crystallite diameter La (110) is more preferably 100 nm or more, and even more preferably 150 nm or more. La (110) is more preferably 440 nm or less, and even more preferably 400 nm or less.

[0030] The linseed oil absorption is preferably 30 mL / 100 g to 75 mL / 100 g. When the linseed oil absorption is within the above range, the slurry for forming the active material layer tends to be easy to prepare and workability tends to be excellent. The linseed oil absorption is more preferably 70 mL / 100 g or less, and even more preferably 65 mL / 100 g or less. The linseed oil absorption is more preferably 40 mL / 100 g or more.

[0031] Average interplanar spacing d determined by X-ray diffraction method ００２ The average interplanar spacing d is preferably 0.334 nm to 0.338 nm. ００２ When the average particle diameter is 0.338 nm or less, the initial charge / discharge efficiency and energy density of the lithium ion secondary battery tend to be excellent.

[0032] In the present disclosure, the average interplanar spacing d ００２ is calculated using Bragg's equation from the diffraction peak corresponding to the carbon 002 plane that appears at a diffraction angle 2θ of approximately 24° to 27° from the diffraction profile obtained by irradiating a sample with X-rays (CuKα rays) and measuring the diffraction rays with a goniometer. Specifically, the measurement sample is filled into the recess of a quartz sample holder and set on the measurement stage, and a wide-angle X-ray diffractometer (for example, manufactured by Rigaku Corporation) is used under the following measurement conditions: Radiation source: CuKα ray mean interplanar spacing (wavelength = 0.15418 nm) Output: 40 kV, 20 mA Sampling width: 0.010° ​​Scanning range: 10° to 35° Scanning speed: 0.5° / min

[0033] Examples of graphitic carbon materials include graphite such as artificial graphite, natural graphite, graphitized mesophase carbon, and graphitized carbon fiber. The shape of the graphite is not particularly limited, and examples include flake, spherical, block, and fibrous shapes. From the viewpoint of obtaining a high tap density, spherical shapes are preferred.

[0034] Artificial graphite can be obtained by firing a graphitizable aggregate. The graphitizable aggregate may be used alone or in combination of two or more types. Graphite may also be used together with the graphitizable aggregate. The graphite may be used alone or in combination of two or more types.

[0035] Examples of graphitizable aggregates that can be used include coke powder and resin carbides, but there are no particular limitations as long as they are graphitizable powder materials. Among these, coke powders that are easily graphitized are preferred, such as mosaic coke and needle coke. Mosaic coke is more preferred from the viewpoint of easily adjusting the crystallite diameter Lc(002) to the range of 35 nm to 150 nm.

[0036] A binder (organic binding agent) may be used together with the graphitizable aggregate. The binder may be used alone or in combination of two or more types. The binder (organic binding agent) is not particularly limited as long as it can be graphitized by firing. Examples of binders include organic materials such as tar, pitch, starch, thermosetting resins, and thermoplastic resins.

[0037] Other materials may be used together with the graphitizable aggregate. Examples of the other materials include a fluidity imparting agent and a graphitization catalyst. The other materials may be used alone or in combination of two or more.

[0038] The type of fluidity-imparting agent is not particularly limited. Specific examples of the fluidity-imparting agent include hydrocarbons such as liquid paraffin, paraffin wax, and polyethylene wax; fatty acids such as stearic acid, oleic acid, erucic acid, and 12-hydroxystearic acid; fatty acid metal salts such as zinc stearate, lead stearate, aluminum stearate, calcium stearate, and magnesium stearate; fatty acid amides such as stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide; fatty acid esters such as stearic acid monoglyceride, stearyl stearate, and hydrogenated oil; and higher alcohols such as stearyl alcohol. Among these, fatty acids are preferred, and stearic acid is more preferred.

[0039] The type of graphitization catalyst is not particularly limited. Specific examples of the graphitization catalyst include substances having a graphitization catalytic action, such as silicon, iron, nickel, titanium, and boron, as well as carbides, oxides, and nitrides of these substances.

[0040] The shape of the artificial graphite is not particularly limited, and may be either primary particles or agglomerated particles. In the case of agglomerated particles, it may or may not contain a carbon material derived from the binder. Alternatively, it may be graphite particles (hereinafter referred to as "aggregate graphite particles") in which a plurality of flat particles are aggregated or bonded together so that their orientation planes (main surfaces) are non-parallel. In aggregate graphite particles, the non-parallel main surfaces of a plurality of flat particles means that the surfaces (main surfaces) of the flat graphite particles with the largest cross-sectional areas are not aligned in a fixed direction. For aggregate graphite particles, reference may be made to Japanese Patent Publication No. 3285520, Japanese Patent Publication No. 3325021, etc. The shape of the artificial graphite can be confirmed by observation with a scanning electron microscope (SEM).

[0041] Before firing for graphitization, a mixture containing graphitizable aggregate, binder, and other components such as graphite may be molded into a predetermined shape, or may be fired in powder form without molding. ２ ~4.0 kN / cm ２ From the viewpoint of facilitating adjustment to a range of 0.90 g / cm, it is preferable to form the powder and then sinter it. ３ From the viewpoint of achieving the above and the viewpoint of making the particle size distribution ratio (D90 / D10) 8.0 or less, it is preferable to crush the molded product after molding and before graphitization, adjust the particle size using a sieve or the like, and then perform graphitization.

[0042] The method for molding into a predetermined shape is not particularly limited. Examples include a molding method in which the mixture is placed in a container such as a metal mold and pressurized in a uniaxial direction, a vibration molding method in which the mixture is placed in a container such as a metal mold, a weight is placed on top, and vibration and impact are applied to the metal frame to mold, and an extrusion molding method in which the mixture is extruded from a nozzle or the like using a horizontal press to mold. From the viewpoint of improving the production efficiency of molded products, extrusion molding is preferred.

[0043] The blending ratio of each material in the mixture is not particularly limited. For example, the binder content may be 0.5 parts by mass to 20 parts by mass, 1 part by mass to 18 parts by mass, or 1.2 parts by mass to 15 parts by mass, relative to 100 parts by mass of the graphitizable aggregate and graphite. A binder need not be used. For example, when graphitization is performed after molding, the binder content may be 1.0 parts by mass to 20 parts by mass, 1.5 parts by mass to 18 parts by mass, or 2.0 parts by mass to 15 parts by mass, relative to 100 parts by mass of the graphitizable aggregate and graphite. Furthermore, from the viewpoint of keeping the specific surface area of ​​the resulting graphitic carbon material low, the binder content may be 1.0 parts by mass to 14 parts by mass, 1.2 parts by mass to 12 parts by mass, or 1.5 parts by mass to 10 parts by mass, relative to 100 parts by mass of the graphitizable aggregate and graphite.

[0044] From the viewpoint of facilitating molding, the mixture preferably contains a fluidity imparting agent. In particular, when molding the mixture by extrusion molding, it is preferable to contain a fluidity imparting agent so that the mixture can be molded while being fluidized.

[0045] When the mixture contains a fluidity imparting agent, the amount thereof is not particularly limited. For example, the content of the fluidity imparting agent relative to the entire mixture may be 0.1% by mass to 20% by mass, 0.5% by mass to 10% by mass, or 0.5% by mass to 5% by mass. The mixture may not contain a fluidity imparting agent.

[0046] When the mixture contains a graphitization catalyst, the amount thereof is not particularly limited. For example, the content of the graphitization catalyst relative to the total mixture may be 0.1% by mass to 50% by mass, 0.5% by mass to 40% by mass, or 0.5% by mass to 30% by mass. The mixture may not contain a graphitization catalyst.

[0047] The calcination is preferably carried out under conditions that make the mixture less likely to oxidize, such as in a nitrogen atmosphere, an argon gas atmosphere, or a vacuum. The graphitization temperature is preferably 2000°C or higher, more preferably 2500°C or higher, and even more preferably 2800°C to 3200°C. A graphitization temperature of 2000°C or higher tends to facilitate the development of graphite crystals and improve discharge capacity. A graphitization temperature of 3200°C or lower tends to facilitate the adjustment of the crystallite size Lc(002) to a range of 35nm to 150nm.

[0048] The graphitized carbon material thus obtained is preferably pulverized to a desired volume average particle size. The method for pulverizing the graphitized material is not particularly limited, and known methods such as a jet mill, a vibration mill, a pin mill, and a hammer mill can be used.

[0049] At least a portion of the surface of the obtained graphite carbon material may be coated with amorphous carbon, which is preferably at least one selected from the group consisting of carbonaceous substances and carbonaceous particles obtained from organic compounds that can be converted into carbonaceous materials by heat treatment (hereinafter also referred to as precursors of amorphous carbon).

[0050] The precursor of amorphous carbon is not particularly limited, and examples thereof include pitch, organic polymer compounds, etc. Examples of pitch include ethylene heavy-end pitch, crude oil pitch, coal tar pitch, asphalt cracking pitch, pitch produced by thermal decomposition of polyvinyl chloride, etc., and pitch produced by polymerizing naphthalene, etc. in the presence of a super strong acid. Examples of organic polymer compounds include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral, and natural substances such as starch and cellulose.

[0051] The carbonaceous particles used as amorphous carbon are not particularly limited, and examples thereof include particles of acetylene black, oil furnace black, ketjen black, channel black, thermal black, soil graphite, and the like.

[0052] An example of a method for coating with amorphous carbon is a method of heat-treating a mixture containing a graphite carbon material and an amorphous carbon precursor. The temperature at which the mixture is heat-treated is preferably 800°C to 1500°C, more preferably 900°C to 1300°C, and even more preferably 1050°C to 1250°C, from the viewpoint of improving the input characteristics of a lithium-ion secondary battery. The temperature at which the mixture is heat-treated may be constant or may vary from the start to the end of the heat treatment.

[0053] <Negative Electrode Material for Lithium-Ion Secondary Battery> The negative electrode material for lithium-ion secondary batteries (hereinafter sometimes abbreviated as "negative electrode material") of the present disclosure includes the graphitic carbon material for lithium-ion secondary batteries of the present disclosure. The graphitic carbon material of the present disclosure can be suitably used as a negative electrode active material for lithium-ion secondary batteries. As the negative electrode active material, the graphitic carbon material of the present disclosure may be used alone or in combination with another negative electrode active material. The other negative electrode active material is not particularly limited, and examples thereof include artificial graphite, amorphous carbon, carbon black, fibrous carbon, and nanocarbon, which do not fall under the category of the graphitic carbon material of the present disclosure. The other carbon materials may be used alone or in combination. In addition, the negative electrode active material may contain particles containing an element other than the carbon material that can occlude and release lithium ions. The element that can occlude and release lithium ions is not particularly limited, and examples thereof include Si, Sn, Ge, and In.

[0054] The content of the graphite carbon material of the present disclosure in the negative electrode active material is not particularly limited, and is, for example, preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0055] <Negative electrode for lithium ion secondary battery> The negative electrode for lithium ion secondary battery of the present disclosure includes a graphite carbon material layer containing the graphite carbon material for lithium ion secondary batteries of the present disclosure, and a current collector. The negative electrode for lithium ion secondary battery may include other components as necessary in addition to the graphite carbon material layer containing the graphite carbon material for lithium ion secondary batteries of the present disclosure and the current collector.

[0056] The negative electrode for a lithium ion secondary battery can be produced, for example, by kneading a graphite carbon material and a binder with a solvent to prepare a slurry graphite carbon material composition, which is then applied to a current collector to form a graphite carbon material layer, or by forming the graphite carbon material composition into a shape such as a sheet or pellet and integrating it with a current collector. Kneading can be carried out using a dispersing device such as a stirrer, a ball mill, a super sand mill, or a pressure kneader.

[0057] The binder used in preparing the graphite carbon material composition is not particularly limited. Examples of binders include styrene-butadiene copolymers, polymers of ethylenically unsaturated carboxylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, methacrylonitrile, hydroxyethyl acrylate, and hydroxyethyl methacrylate, polymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, and polymeric compounds with high ionic conductivity such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, and polyacrylonitrile. When the graphite carbon material composition contains a binder, the amount thereof is not particularly limited. The content of the binder may be, for example, 0.5 parts by mass to 20 parts by mass per 100 parts by mass of the total of the graphite carbon material and the binder.

[0058] The solvent is not particularly limited as long as it can dissolve or disperse the binder. Specific examples include organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and γ-butyrolactone, as well as water. The amount of solvent used is not particularly limited as long as it can turn the graphite carbon material composition into a desired state such as a paste. The amount of solvent used is preferably, for example, 60 parts by mass or more but less than 150 parts by mass per 100 parts by mass of the graphite carbon material.

[0059] The graphite carbon material composition may contain a thickener. Examples of thickeners include carboxymethyl cellulose or a salt thereof, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, alginic acid or a salt thereof, oxidized starch, phosphated starch, and casein. When the graphite carbon material composition contains a thickener, the amount thereof is not particularly limited. The content of the thickener may be, for example, 0.1 to 5 parts by mass per 100 parts by mass of the graphite carbon material.

[0060] The graphite carbon material composition may contain a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as artificial graphite and carbon black (acetylene black, thermal black, furnace black, etc.), conductive oxides, and conductive nitrides. When the graphite carbon material composition contains a conductive auxiliary material, the amount thereof is not particularly limited. The content of the conductive auxiliary material may be, for example, 0.5 to 15 parts by mass per 100 parts by mass of the graphite carbon material.

[0061] The material of the current collector is not particularly limited and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc. The state of the current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. In addition, porous materials such as porous metal (foam metal) and carbon paper can also be used as the current collector.

[0062] When the graphite carbon material composition is applied to the current collector to form the graphite carbon material layer, the method is not particularly limited, and known methods such as metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, comma coating, gravure coating, and screen printing can be used. After the graphite carbon material composition is applied to the current collector, the solvent contained in the graphite carbon material composition is removed by drying. Drying can be performed using, for example, a hot air dryer, an infrared dryer, or a combination of these devices. If necessary, a rolling treatment can be performed. The rolling treatment can be performed using a plate press, a calendar roll, or the like.

[0063] When the graphite carbon material composition formed into a shape such as a sheet or pellet is integrated with a current collector to form a graphite carbon material layer, the integration method is not particularly limited. For example, the integration can be performed using a roll, a flat plate press, or a combination of these means. The pressure during integration is preferably, for example, 1 MPa to 200 MPa.

[0064] <Lithium-ion secondary battery> The lithium-ion secondary battery of the present disclosure includes the negative electrode for lithium-ion secondary batteries of the present disclosure (hereinafter also simply referred to as "negative electrode"), a positive electrode, and an electrolyte solution.

[0065] The positive electrode can be obtained by forming a positive electrode material layer on a current collector in the same manner as the negative electrode described above. The current collector can be made of a metal or alloy such as aluminum, titanium, or stainless steel, and can be in the form of a foil, perforated foil, mesh, or the like.

[0066] The positive electrode material used to form the positive electrode layer is not particularly limited. For example, metal compounds (metal oxides, metal sulfides, etc.) that can dope or intercalate lithium ions and conductive polymer materials can be used. More specifically, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese oxide (LiMnO ２ ), and their double oxides (LiCo ｘ Ni ｙ Mn ｚ O ２ , x+y+z=1), a composite oxide containing an additional element M' (LiCo ａ Ni ｂ Mn ｃ M' ｄ O ２ , a+b+c+d=1, M′: Al, Mg, Ti, Zr or Ge), spinel-type lithium manganese oxide (LiMn ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , V.O. ２ , MnO ２ , TiO ２ , MoV ２O ８ , TiS ２ , V ２ S ５ , V.S. ２ , MoS ２ , MoS ３ , Cr ３ O ８ , Cr ２ O ５ , olivine-type LiMPO ４ Examples of the positive electrode material include lithium-containing compounds such as (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, and porous carbon. The positive electrode material may be one type alone or two or more types.

[0067] The electrolyte solution is not particularly limited, and for example, a solution in which a lithium salt as an electrolyte is dissolved in a non-aqueous solvent (a so-called organic electrolyte solution) can be used. ４ , LiPF ６ , LiAsF ６ , LiBF ４ , LiSO ３ CF ３ and the like. The lithium salt may be used alone or in combination of two or more kinds. Examples of the non-aqueous solvent include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propane sultone, 3-methyl sulfolane, 2,4-dimethyl sulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, and triethyl phosphate. The non-aqueous solvent may be used alone or in combination of two or more kinds.

[0068] The state of the positive electrode and the negative electrode in the lithium ion secondary battery is not particularly limited. For example, the positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode as needed may be spirally wound or may be stacked in the form of flat plates.

[0069] The separator is not particularly limited, and may be, for example, a resin nonwoven fabric, cloth, microporous film, or a combination thereof. Resins include those primarily composed of polyolefins such as polyethylene and polypropylene. If the structure of the lithium-ion secondary battery does not allow the positive electrode and negative electrode to come into direct contact with each other, a separator may not be used.

[0070] The shape of the lithium ion secondary battery is not particularly limited, and examples thereof include laminated type batteries, paper type batteries, button type batteries, coin type batteries, stacked type batteries, cylindrical type batteries, and prismatic type batteries.

[0071] The lithium ion secondary battery of the present disclosure has excellent output characteristics and is therefore suitable as a large-capacity lithium ion secondary battery for use in electric vehicles, power tools, power storage devices, etc. In particular, it is suitable as a lithium ion secondary battery for use in electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc., which require large current charging and discharging to improve acceleration performance and brake regeneration performance.

[0072] The present disclosure will be specifically described below with reference to the following examples, but the present disclosure is not limited to these examples.

[0073] The particle size (D50) was measured by the following method. A solution prepared by dispersing a graphite carbon material sample in purified water together with 0.2% by mass of a surfactant (trade name: Liponol T / 15, manufactured by Lion Corporation) was placed in the sample water tank of a laser diffraction particle size distribution analyzer (SALD-3000J, manufactured by Shimadzu Corporation). Next, the solution was circulated with a pump while applying ultrasound (pump flow rate was 65% from the maximum), and the volumetric particle size distribution was measured by adjusting the amount of water so that the absorbance was 0.10 to 0.15. The particle size D50 (μm) (average particle size) was determined when the particle size was 50% from the smallest in the volume cumulative distribution (%). The crystallite size Lc (002), crystallite size La (110), compressive load, R value, specific surface area, linseed oil absorption, and tap density were measured using the methods described above.

[0074] [Preparation of Graphite Carbon Material] Petroleum-derived raw coke (needle coke, coke A) was used as the raw material for the graphite carbon material. The raw coke was crushed using a hammer mill. The crushed material was sieved using a 3 mm mesh sieve, and the remaining material was further sieved using a 1 mm mesh sieve to recover granules with particle sizes of 1 mm to 3 mm. The resulting coke particles were crushed and classified using a roller mill to obtain flat coke particles with a D50 of 10.1 μm. The standard deviation (σ) of the particle size distribution of the coke particles was 0.22. 65 parts by mass of the resulting coke particles (90% fixed carbon), 7 parts by mass of starch (20% fixed carbon), and 28 parts by mass of water were kneaded using a kneader to obtain a mixture. The binder amount in Table 1 is calculated as the ratio (%) of the fixed carbon content of the binder to the total fixed carbon content of the aggregate and binder. The resulting mixture was then subjected to a uniaxial press at room temperature (25°C) to a density of 1.3 g / cm ３ The resulting mixture was molded as follows to obtain a molded product. The molded product was then heat-treated in a nitrogen atmosphere at 850°C for 8 hours. It was then graphitized at 3000°C for 30 hours. The resulting particles were sieved through a 280-mesh screen to obtain graphitic carbon material A, which is a negative electrode material. The physical properties of the produced graphitic carbon material A were measured. The physical properties are shown in Table 1.

[0075] (Preparation of Negative Electrode) To 97 parts by mass of graphite carbon material A, an aqueous solution (CMC concentration: 1.5% by mass) of CMC (carboxymethyl cellulose, manufactured by Daicel FineChem Co., Ltd., product number 2200) as a thickener was added so that the solid content of CMC was 1.5 parts by mass, and the mixture was kneaded for 10 minutes. Next, purified water was added so that the total solid content of the negative electrode material and CMC was 40% to 50% by mass, and the mixture was kneaded for 10 minutes. Subsequently, an aqueous dispersion (SBR concentration: 40% by mass) of styrene butadiene copolymer rubber SBR (BM400-B, Zeon Corporation) was added as a binder so that the solid content of SBR was 1.5 parts by mass, and the mixture was mixed for 10 minutes to prepare a paste-like negative electrode material composition. Next, the negative electrode material composition was applied to an 11 μm thick electrolytic copper foil in a coating amount of 10.0 mg / cm per unit area. ２ The negative electrode material layer was formed by coating with a comma coater with an adjusted clearance so that the negative electrode material layer was 1.6 g / cm. ３ The electrode density was adjusted to

[0076] (Coin Cell Fabrication) The electrolytic copper foil on which the negative electrode material layer was formed was punched into a disk shape with a diameter of 14 mm to fabricate a sample electrode (negative electrode) for a coin cell. The fabricated sample electrode (negative electrode), separator, and counter electrode (metallic lithium) were placed in a coin battery container in this order, and an electrolyte solution was injected to fabricate a coin-type lithium ion secondary battery. The electrolyte solution was prepared by adding 0.5 mass % of vinylene carbonate (VC) to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio of EC to EMC was 3:7) with respect to the total amount of the mixed solution, and LiPF ６ The lithium ion secondary battery was fabricated in a glove box in an Ar atmosphere with an outdoor temperature of -70°C and an oxygen concentration of less than 10 ppm.

[0077] (Measurement of Discharge Specific Capacity) The prepared coin-type cell was left standing in a thermostatic chamber at 25°C for 3 hours, and then the cell was charged to 0 V (Li / Li ＋), and then constant voltage charging (CV charging) until a current value equivalent to 0.02 C was reached. After a 15-minute rest, the battery was CC discharged to 1.5 V at a current value equivalent to 0.2 C. The discharge specific capacity was calculated by dividing the amount of electricity at that time by the mass of the active material of the electrode (mass of the graphite material only). Discharge specific capacity (mAh / g) = discharged amount of electricity (mAh) ÷ mass of active material (g)

[0078] (Laminate Cell Fabrication) The negative electrode fabricated above was punched out so that the coated surface was 4 cm x 5 cm, the tab (uncoated portion) was 1 cm x 1.5 cm, and the positive electrode was 3.99 cm x 4.99 cm. For the tab portion, a nickel lead tab with a sealant was attached to the negative electrode, and an aluminum lead tab with a sealant was attached to the positive electrode by ultrasonic welding. The negative electrode was wrapped around the separator once, and the current collector side was heat-welded. A 12 cm wide x 10 cm long aluminum laminate sheet was folded in half horizontally, and the separator-wrapped negative electrode was placed in the area where the sealant portion and the edge of the aluminum laminate seal overlapped. The bottom of the sealant and the aluminum laminate seal were secured with polyimide tape. Next, the positive electrode was placed so that it just overlapped the coated surface of the negative electrode and similarly secured with polyimide tape. The overlapping portion (top) and side of the aluminum laminate sheet and sealant portion were each welded using a heat welding machine. After vacuum drying for 12 hours at 60°C in a vacuum dryer, an electrolyte solution was poured into the bottom, and the bottom was heat-sealed under vacuum using a vacuum heat welding machine. The electrolyte solution was a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio of EC to EMC was 3:7), to which 0.5 mass% of vinylene carbonate (VC) was added based on the total amount of the mixed solution. ６ The battery was prepared by dissolving the above-mentioned electrolyte to a concentration of 1 mol / L. A 20 μm-thick polyethylene microporous membrane was used as the separator. The laminated battery was fabricated in a dry room with an outdoor temperature of −50°C.

[0079] (Aging Treatment) The prepared laminated cell was left standing in a thermostatic chamber at 25 ° C. for 12 hours, then constant current charged (CC charged) to 4.2 V at a current value equivalent to 0.2 CA, and then constant voltage charged (CV charged) to a current value equivalent to 0.02 CA. Then, CC discharge was performed to 2.7 V at a current value equivalent to 0.2 CA. This constitutes one cycle, and after repeating three cycles, the cell was again CC-CV charged to 4.2 V (CC: equivalent to 0.2 CA, CV: equivalent to 0.02 CA) and left standing in a thermostatic chamber set at 60 ° C. for 12 hours. Then, the cell was discharged to 2.7 V at a current value equivalent to 0.2 CA for aging treatment. A 15-minute rest period was provided between charge and discharge.

[0080] (Input Characteristics) The input characteristics were measured by placing the aged battery in a thermostatic chamber set at 25°C for one hour, adjusting the state of charge (SOC) to 50%, and then charging it for 10 seconds at current values ​​equivalent to 0.2C, 1C, 3C, and 5C. The difference in voltage change at this time and the slope of each current value were calculated as the direct current internal resistance (DC-IR). A 15-minute rest period was provided between measurements at each current value. The smaller the DC internal resistance value, the better the input characteristics can be determined. The SOC can be adjusted by separately calculating the open circuit voltage for each SOC and performing CC-CV charging (CC: equivalent to 0.2A, CV: equivalent to 0.02C) up to that voltage.

[0081] (Cycle Characteristics) The aged battery was placed in a thermostatic chamber set at 25°C for 1 hour, and then subjected to constant current charging (CC charging) at a current value equivalent to 0.2 C up to 4.2 V, followed by constant voltage charging (CV charging) to a current value equivalent to 0.02 C. It was then CC discharged to 2.7 V at a current value equivalent to 0.2 C. The discharge capacity at this time was designated as the initial discharge capacity. The current value was then changed to 1 C, and the battery was charged at a constant current up to 4.2 V, followed by constant voltage charging to a current value equivalent to 0.02 C. It was then discharged to 2.7 V at a current value equivalent to 1 C. This cycle was repeated 100 times, after which the battery was subjected to constant current charging (CC charging) at a current value equivalent to 0.2 C up to 4.2 V, followed by constant voltage charging (CV charging) to a current value equivalent to 0.02 C. It was then CC discharged to 2.7 V at a current value equivalent to 0.2 C. The discharge capacity at this time was designated as the post-cycle discharge capacity. The cycle characteristics were calculated using the following formula: Cycle characteristics (%) = discharge capacity after cycling (mAh) / initial discharge capacity (mAh) × 100

[0082] (Expansion Coefficient) The thickness of the laminated cell after initial discharge and the thickness after 100 cycles of discharge were measured, and the expansion coefficient was calculated from the following formula: Expansion Coefficient (%) = Thickness after 100 cycles of discharge (mm) / Thickness after initial discharge (mm) × 100

[0083] (High-Temperature Storage Characteristics) The aged battery was placed in a thermostatic chamber set at 25°C for 1 hour, then subjected to constant current charging (CC charging) at a current value equivalent to 0.2 C to 4.2 V, followed by constant voltage charging (CV charging) to a current value equivalent to 0.02 C. It was then CC discharged to 2.7 V at a current value equivalent to 0.2 C. The discharge capacity at this time was recorded as the initial discharge capacity. The temperature of the thermostatic chamber was then changed to 60°C, and the battery was placed therein for 10 days. After 10 days, the thermostatic chamber was set to 25°C, and the battery was placed therein for 3 hours, followed by discharge to 2.7 V at a current value equivalent to 0.2 C. It was then CC charged to 4.2 V at a current value equivalent to 0.2 C, followed by constant voltage charging (CV charging) to a current value equivalent to 0.02 C. It was then CC discharged to 2.7 V at a current value equivalent to 0.2 C. The capacity at this time was recorded as the discharge capacity after storage. The high-temperature storage characteristics were calculated using the following formula: High temperature storage characteristics (%) = Discharge capacity after storage (mAh) / Initial discharge capacity (mAh) x 100

[0084] Examples 2 to 6 Graphite carbon materials B to F were obtained in the same manner as for graphite carbon material A, except that coke B (mosaic coke), coke C (mosaic coke), coke D (semi-needle coke), coke E (super needle coke), or coke F (mosaic coke) was used instead of coke A in Example 1. Batteries were fabricated using these graphite carbon materials B to F in the same manner as in Example 1, and the batteries were evaluated.

[0085] [Example 7] A graphite carbon material A2 was obtained in the same manner as in Example 1, except that the particle diameter (D50) of the graphite carbon material A was changed to 9 μm. A battery was produced using this graphite carbon material A2 in the same manner as in Example 1, and the battery was evaluated.

[0086] [Example 8] A graphite carbon material A3 was obtained in the same manner as in Example 1, except that the particle diameter (D50) of the graphite carbon material A was set to 30 µm. A battery was produced using this graphite carbon material A3 in the same manner as in Example 1, and the battery was evaluated.

[0087] Example 9 After obtaining graphite material A in Example 1, 5 parts by mass of coal tar pitch was mixed with 100 parts by mass of graphite material A, and the mixture was heated to 1000°C at a heating rate of 200°C / h and then held for 1 hour for firing. The firing was carried out in a nitrogen atmosphere. After cooling to room temperature (25°C), the fired sample was crushed to 15 μm using a cutter mill and sieved through a sieve with 0.109 mm openings to obtain graphite carbon material AC. A battery was produced using graphite carbon material AC in the same manner as in Example 1, and battery evaluation was performed.

[0088] Comparative Example 1: Needle coke (coke A) was crushed and then finely pulverized in a jet mill to a particle size (D50) of 16 μm. This was heat-treated in a nitrogen atmosphere at a maximum temperature of 1000°C for 1 hour, and then calcined at 3000°C for 1 hour to graphitize the graphitizable components. The resulting graphitic carbon material was crushed in a cutter mill and then sieved to obtain graphitic carbon material A4. The particle size (D50) of graphitic carbon material A4 was 15 μm. After obtaining graphitic material A4, 20 parts by mass of coal tar pitch was mixed with 100 parts by mass of graphitic material A4, and the mixture was heated to 1000°C at a heating rate of 200°C / h and then held for 1 hour for calcination. The calcination was carried out in a nitrogen atmosphere. The fired sample after cooling to room temperature (25°C) was crushed to 15 µm using a cutter mill and then sieved through a sieve with an opening of 0.109 mm to obtain graphite carbon material A4C. Using the graphite carbon material A4C, a battery was fabricated in the same manner as in Example 1, and the battery was evaluated.

[0089] Comparative Example 2 Super needle coke (coke G) was coarsely crushed and then finely pulverized in a jet mill to a particle size (D50) of 16 μm. This was heat-treated in a nitrogen atmosphere at a maximum temperature of 1000°C for 1 hour, and then fired at 3000°C for 1 hour to graphitize the graphitizable components. The resulting graphitic carbon material was crushed in a cutter mill and then classified to obtain graphitic carbon material G. The particle size (D50) of graphitic carbon material G was 15 μm.

[0090] Comparative Example 3 A graphite carbon material H was obtained in the same manner as in Comparative Example 2, except that the type of coke was changed to mosaic coke, Coke H. A battery was produced using this graphite carbon material H in the same manner as in Example 1, and the battery was evaluated.

[0091] [Comparative Example 4] A graphite carbon material B2 was obtained in the same manner as in Comparative Example 2, except that coke B (mosaic coke) was used, pulverized to a particle size (D50) of 5.5 μm, heat-treated at a maximum temperature of 1300° C., and then fired at 2800° C., and no sizing was performed after firing. A battery was produced using this graphite carbon material B2 in the same manner as in Example 1, and the battery was evaluated.

[0092]

[0093]

[0094] As shown in the results in Table 2, the lithium ion secondary batteries fabricated using the negative electrode materials of the Examples were superior in input characteristics, high-temperature storage characteristics, and cycle characteristics to the lithium ion secondary batteries fabricated using the negative electrode materials of the Comparative Examples. It can be seen that the other items showed characteristics equivalent to or better than those of the Comparative Examples.

Claims

1. The crystallite size Lc(002) determined by X-ray diffraction is 35 nm to 150 nm, and the compressive load is 2.0 kN / cm. ２ ~4.0 kN / cm ２ This is a graphite-based carbon material for the negative electrode of lithium-ion secondary batteries.

2. The graphite-based carbon material for the negative electrode of a lithium-ion secondary battery according to claim 1, wherein, in the particle size distribution measured by laser diffraction scattering, when the volume cumulative distribution curve is drawn from the smallest diameter side, the particle size (D50) at which the cumulative volume reaches 50% is 5 μm to 30 μm.

3. In laser Raman spectrophotometric measurements, 1580 cm⁻¹ －１ 1330 cm² relative to the intensity Ig of the largest peak in the vicinity －１ The graphite-based carbon material for the negative electrode of a lithium-ion secondary battery according to claim 1 or claim 2, wherein the intensity ratio (Id / Ig) of the intensity Id of the nearest maximum peak is 0.1 to 0.

5.

4. The specific surface area determined from nitrogen adsorption measurements at 77K is 0.7 m². ２ / g to 8m ２ A graphite-based carbon material for the negative electrode of a lithium-ion secondary battery according to claim 1 or claim 2, wherein the value is / g.

5. A graphite-based carbon material for a lithium-ion secondary battery anode according to claim 1 or claim 2, wherein the crystallite size La(110) determined by X-ray diffraction is 50 nm to 450 nm.

6. A graphite carbon material for the negative electrode of a lithium-ion secondary battery according to claim 1 or claim 2, wherein the amount of oil absorbed per 100 g of graphite material in the measurement of linseed oil absorption is 30 mL to 75 mL.

7. A negative electrode material for a lithium-ion secondary battery, comprising the graphite-based carbon material for lithium-ion secondary batteries described in claim 1 or claim 2.

8. A negative electrode for a lithium-ion secondary battery, comprising a graphite-carbon material layer containing the graphite-carbon material for lithium-ion secondary batteries described in claim 1 or claim 2, and a current collector.

9. A lithium-ion secondary battery comprising a negative electrode for a lithium-ion secondary battery according to claim 8, a positive electrode, and an electrolyte.