Negative electrode material for lithium ion secondary battery, negative electrode material composition for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Abstract

A negative electrode material for lithium ion secondary batteries, the negative electrode material being composed of graphite particles wherein: if x (kN / cm2) is the compression load necessary for consolidation to 1.7 g / cm3 in an autographic measurement, x ≥ 2.0 is satisfied; if y (μm) is the particle diameter at which the integrated value from the smallest particle diameter reaches 50% in the volume-based particle size distribution as determined by a laser diffraction method, 5.0 ≤ y ≤ 20.0 is satisfied; x and y satisfy formula (1) described below; and the degree of graphitization is 90.0% or more.　Formula (1): 11.3x – 0.66y + 1.4 ≥ 14.5

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode material for a lithium ion secondary battery, a negative electrode material composition for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery. [Background technology]

[0002] Taking advantage of their small size, light weight, and high energy density, lithium-ion secondary batteries have been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smartphones, and tablet PCs. In recent years, environmental issues such as global warming caused by CO2 emissions have led to the widespread use of clean electric vehicles (EVs) that run solely on batteries, hybrid electric vehicles (HEVs) that combine gasoline engines with batteries, and plug-in hybrid electric vehicles (PHEVs). Development of lithium-ion secondary batteries (automotive lithium-ion secondary batteries) for use in these vehicles is underway.

[0003] The input characteristics of lithium-ion secondary batteries are significantly affected by the performance of their negative electrode materials. Carbon materials are widely used as negative electrode materials for lithium-ion secondary batteries. For example, highly crystalline carbon materials such as artificial graphite and spherical natural graphite, which is made by spheroidizing scaly natural graphite, have been proposed as materials for obtaining high-density negative electrodes.

[0004] As an example of artificial graphite, Patent Document 1 discloses a negative electrode material for lithium ion secondary batteries that includes composite particles containing spherical graphite particles and a plurality of flat graphite particles that are aggregated or bonded so that their oriented planes are non-parallel. Patent Document 2 also discloses a negative electrode active material for lithium secondary batteries that includes carbon powder particles that have a morphology in which plate-like particles are oriented and stacked along their planes to assemble into a primarily stable structure, and that have micropores formed on the surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 147012 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-302725 Summary of the Invention [Problem to be solved by the invention]

[0006] The rapid growth of the EV market is driving demand for anode materials for lithium-ion secondary batteries. In particular, there is a strong need for increased discharge capacity and rapid charging to improve convenience, and high-rate charging is required for anode active materials.

[0007] The problem with such high-rate charging is that, due to the IR drop caused by the application of a large current, some of the lithium ions are unable to insert between the graphite layers, and lithium metal is likely to precipitate on the surface of the graphite particles, etc. If lithium metal precipitates in the form of needles, it may break through the separator, causing an internal short circuit and potentially leading to thermal runaway.

[0008] From the above viewpoints, it is desirable to have a negative electrode material for lithium ion secondary batteries that can suppress the deposition of lithium metal and that can produce lithium ion secondary batteries that are excellent in resistance to lithium (Li) deposition. In view of the above circumstances, an object of one embodiment of the present disclosure is to provide a negative electrode material for lithium ion secondary batteries that can produce lithium ion secondary batteries having excellent discharge capacity, capable of suppressing lithium metal precipitation, and excellent Li precipitation resistance, as well as a negative electrode material composition for lithium ion secondary batteries that includes the same, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery. Another aspect of the present disclosure has an object to provide a negative electrode material for lithium ion secondary batteries that can suppress lithium metal precipitation and enable the production of lithium ion secondary batteries that are excellent in Li precipitation resistance, as well as a negative electrode material composition for lithium ion secondary batteries that includes the same, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery. [Means for solving the problem]

[0009] Means for solving the above problems include the following aspects. <1> 1.7g / cm in autograph measurement 3 The compressive load required to compact the material to x (kN / cm 2 ), x≧2.0, and when y (μm) is the particle size at which the cumulative total from the smallest diameter side in a volume-based particle size distribution measured by a laser diffraction method is 50%, 5.0≦y≦20.0, the above-mentioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more. 11.3x-0.66y+1.4≧14.5···(1) <2> A negative electrode material for lithium ion secondary batteries, which is graphite particles such that when a negative electrode material layer is formed using the negative electrode material for lithium ion secondary batteries, the ratio L / T, which is the ratio of the tortuous path length L (μm), which is the distance from one surface to the other surface in the thickness direction through voids inside the negative electrode material layer, to the thickness T (μm) of the negative electrode material layer, is 1.7 or less. <3> A negative electrode was formed using the negative electrode material for lithium ion secondary batteries, and the negative electrode was pressed at 0.8 t / cm. The peak intensity (I 002 ) and the peak intensity of the 110 diffraction line (I 110 ) is the ratio of I 002 / I 110 is less than or equal to 350 <1> or <2> The negative electrode material for a lithium ion secondary battery according to claim 1. <4> The surface of the graphite particles is not subjected to a treatment to coat with low crystalline carbon. <1> ~ <3> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <5> 1300cm measured by Raman spectroscopy -1 ~1400cm -1 The peak intensity (I D ) and 1580cm -1 ~1620cm -1 The peak intensity (I G ) is the ratio of I D / I Gis the R value, the R value of the graphite particles is 0.10 to 0.40. <1> ~ <4> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <6> the graphite particles are subjected to a treatment of coating surfaces with low-crystalline carbon, 1300cm measured by Raman spectroscopy -1 ~1400cm -1 The peak intensity (I D ) and 1580cm -1 ~1620cm -1 The peak intensity (I G ) is the ratio of I D / I G is the R value, the R value of the graphite particles is 0.20 to 0.60. <1> ~ <5> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <7> The particle size of the graphite particles is 0.1 μm to 7.0 μm when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction method is 10%. <1> ~ <6> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <8> The zero tap density of the graphite particles is 0.3 g / cm 3 ~0.6g / cm 3 is <1> ~ <7> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <9> The 30 tap density of the graphite particles is 0.4 g / cm 3 ~0.7g / cm 3 is <1> ~ <8> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <10> The 250 tap density of the graphite particles is 0.7 g / cm 3 ~1.1g / cm 3 is <1> ~ <9> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <11> The specific surface area of ​​the graphite particles determined by nitrogen adsorption measurement at 77 K is 0.2 m 2 / g~6.0m 2 / g <1> ~ <10> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <12> The particle size distribution D90 / D10 of the graphite particles is 3.0 to 7.0. <1> ~ <11> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <13> The graphite particles include composite particles in which a plurality of graphite particles are aggregated or bonded together. <1> ~ <12> 10. The negative electrode material for a lithium ion secondary battery according to claim 9, wherein the negative electrode material is a material for a lithium ion secondary battery. <14> <1> ~ <13> 1. A negative electrode material composition for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to any one of 1 to 3, a binder, and a solvent. <15> <1> ~ <13> 10. A negative electrode for a lithium ion secondary battery, comprising: a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery according to any one of 1 to 8; and a current collector. <16> <15> A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 1, a positive electrode, and an electrolyte solution. [Effects of the Invention]

[0010] One embodiment of the present disclosure can provide a negative electrode material for lithium ion secondary batteries that is excellent in discharge capacity, can suppress lithium metal precipitation, and can produce a lithium ion secondary battery that is excellent in Li precipitation resistance, as well as a negative electrode material composition for lithium ion secondary batteries that includes the same, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery. Another aspect of the present disclosure can provide a negative electrode material for lithium ion secondary batteries that can suppress lithium metal precipitation and enable the production of lithium ion secondary batteries with excellent Li precipitation resistance, as well as a negative electrode material composition for lithium ion secondary batteries that includes the same, a negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an example of a graph used to evaluate Li precipitation resistance. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the 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 the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be contained. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area. 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.

[0014] In the present disclosure, the particle size distribution of the negative electrode material and the primary particles contained in the composite particles can be measured using a laser diffraction particle size distribution analyzer. The average particle size of the particles is the particle size (D50) at which the cumulative total from the small diameter side in the volume-based particle size distribution is 50%. D99.9 is the particle size at which the cumulative total from the small diameter side in the volume-based particle size distribution is 99.9%, D90 is the particle size at which the cumulative total from the small diameter side in the volume-based particle size distribution is 90%, and D10 is the particle size at which the cumulative total from the small diameter side in the volume-based particle size distribution is 10%.

[0015] <Anode material for lithium-ion secondary batteries> Hereinafter, the negative electrode material for lithium ion secondary batteries of the present disclosure will be described in order, including a first embodiment and a second embodiment. Note that the present invention is not limited to these embodiments.

[0016] [First embodiment] The negative electrode material for a lithium ion secondary battery according to the first embodiment of the present disclosure (hereinafter also simply referred to as the negative electrode material) has a densitometric value of 1.7 g / cm in autograph measurement. 3 The compressive load required to compact the material to x (kN / cm 2 ), x≧2.0, and when the particle size at which the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction is 50% is y (μm), the particle size satisfies 5.0≦y≦20.0, and the above-mentioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more. 11.3x-0.66y+1.4≧14.5···(1)

[0017] By using the negative electrode material of the first embodiment, it is possible to manufacture a lithium ion secondary battery that has excellent discharge capacity, can suppress lithium metal precipitation, and is excellent in resistance to lithium (Li) precipitation. The reason for this is presumed to be as follows, for example: When the graphitization degree of the graphite particles is 90.0% or more, the lithium ion secondary battery tends to have excellent discharge capacity.

[0018] In lithium-ion secondary batteries, lithium ions begin to intercalate from the graphite particles on the surface of the negative electrode during charging, and gradually transition to intercalation into graphite particles located deeper inside. The inventors believed that lithium metal deposition during charging could be suppressed by reducing the time difference between the charging reaction on the surface of the negative electrode and that deep inside the negative electrode. The reason for this is as follows: By allowing lithium ions to diffuse to the deep part of the current collector in a short time, the amount of active material available to react with lithium ions increases, and the internal resistance decreases as the effective reaction area increases relative to the applied current. This reduces the IR drop and allows the negative electrode potential to be maintained high, which is thought to increase the time and amount of electricity required to reach the lithium deposition onset potential.

[0019] Here, it is presumed that by reducing the particle size of the graphite particles, the distance that lithium ions travel from the surface side of the negative electrode to the graphite particles deep inside the negative electrode can be shortened. By increasing the compressive load required to compact the graphite particles to a specific density, the graphite particles are less likely to be crushed when used in an anode material. As a result, the lithium ion pathways are less likely to be blocked. This is thought to shorten the distance that lithium ions must travel to reach the graphite particles deep inside the anode. As described above, by reducing the particle size of the graphite particles and increasing the compressive load on the graphite particles, the distance that lithium ions travel from the surface of the negative electrode to the graphite particles deep inside the negative electrode can be shortened. As a result, it is believed that the time difference in the charging reaction between the surface of the negative electrode and the deep inside of the negative electrode can be reduced. Furthermore, the inventors have found that when the particle size and compressive load on the graphite particles satisfy the above formula (1), lithium metal deposition during charging is effectively suppressed and Li deposition resistance can be improved.

[0020] (Compression load) The compressive load of the graphite particles, x in equation (1), is 2.0 kN / cm 2There are no particular limitations on the compressive load of the graphite particles as long as it satisfies the above formula (1). For example, the compressive load of the graphite particles is set to 2.3 kN / cm from the viewpoint of suitably suppressing deformation of the graphite particles due to pressing during the preparation of the negative electrode. 2 It is preferable that the resistance is 2.5kN / cm or more. 2 More preferably, it is 2.8 kN / cm or more. 2 More preferably, it is 3.0 kN / cm or more. 2 More preferably, it is equal to or greater than this.

[0021] To prevent deformation of the current collector caused by pressing during negative electrode production and separation of the current collector from the active material, the compressive load on the graphite particles was set to 5.0 kN / cm. 2 may be less than 4.5kN / cm 2 may be less than 4.0 kN / cm 2 may be less than 3.5kN / cm 2 It may be the following:

[0022] In the present disclosure, the compression load of graphite particles can be determined as follows: A predetermined mass (e.g., 3.0 g) of graphite particles is filled into a mold and compressed at a constant speed (e.g., 10 mm / min). When the density of the compressed graphite particles is 1.7 g / cm 3 pressure (kN / cm 2 ) is the compressive load of the graphite particle. 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 particles is calculated based on the area of ​​the base of the mold (for example, 1.767 cm 2 ) and the volume of the graphite particles calculated from the distance from the bottom surface of the mold to the pressing surface of the graphite particles, and the mass of the graphite particles. The greater the compressive load on the graphite particles, the less likely the graphite particles are to be deformed, broken, or the like due to pressure.

[0023] (Average particle size) The particle size (hereinafter also referred to as "average particle size") at which the cumulative total from the smallest diameter side in the volume-based particle size distribution of graphite particles measured by laser diffraction is 50% is 5.0 μm to 20.0 μm. The average particle size of the graphite particles is y in formula (1).

[0024] From the viewpoint of further improving resistance to Li precipitation, the average particle size of the graphite particles is preferably 17.0 μm or less, more preferably 14.5 μm or less, and even more preferably 11.0 μm or less. The average particle size of the graphite particles may be 6.0 μm or more, or 7.0 μm or more.

[0025] The average particle size of the graphite particles can be measured using a laser diffraction particle size distribution analyzer (for example, SALD3100, Shimadzu Corporation).

[0026] Methods for measuring the average particle size of graphite particles contained in a negative electrode include preparing a sample electrode, embedding the electrode in epoxy resin, mirror-polishing the electrode, and observing the electrode cross section with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"), and preparing an electrode cross section using an ion milling device (e.g., Hitachi High-Technologies Corporation, "E-3500") and measuring the electrode cross section with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"). In this case, the average particle size is the median value of the particle sizes of 100 arbitrarily selected particles.

[0027] From the viewpoint of being able to suitably suppress lithium metal precipitation and to manufacture a lithium ion secondary battery having better Li precipitation resistance, the negative electrode material of the first embodiment preferably satisfies the following formula (2), more preferably satisfies the following formula (3), and further preferably satisfies the following formula (4). 11.3x-0.66y+1.4≧20 (2) 11.3x-0.66y+1.4≧25 (3) 11.3x-0.66y+1.4≧30 (4)

[0028] (D10) The D10 of the graphite particles is preferably 0.1 μm to 7.0 μm, more preferably 0.1 μm to 6.0 μm, even more preferably 1.0 μm to 6.0 μm, and particularly preferably 2.5 μm to 5.5 μm.

[0029] The D10 of the graphite particles can be measured using a laser diffraction particle size distribution analyzer (for example, SALD3100, Shimadzu Corporation).

[0030] (Particle size distribution D90 / D10) The particle size distribution D90 / D10 of the graphite particles is not particularly limited, and the lower limit thereof may be 3.0 or more, 3.5 or more, or 4.0 or more. The upper limit of the particle size distribution D90 / D10 of the graphite particles may be 7.0 or less, 6.5 or less, or 6.2 or less. By making the particle size distribution of the graphite particles D90 / D10 7.0 or less, the distance that lithium ions must travel to reach the graphite particles deep inside the anode can be shortened. As a result, the time difference between the charging reaction on the surface side and deep inside the anode can be reduced, which tends to suppress lithium metal deposition during charging. The particle size distribution D90 / D10 can be measured using a laser diffraction particle size distribution analyzer (for example, SALD3100, Shimadzu Corporation).

[0031] Methods for measuring the particle size distribution D90 / D10 of graphite particles contained in a negative electrode include preparing a sample electrode, embedding the electrode in epoxy resin, mirror-polishing the electrode, and observing the electrode cross section with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"), or preparing an electrode cross section using an ion milling device (e.g., Hitachi High-Technologies Corporation, "E-3500") and measuring the cross section with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"). The particle size distribution D90 / D10 in this case can be determined by the following method. (1) Using a binarization method or the like, the area Sn (n is the particle unique number assigned to the selected particle) of the projected particle is calculated. (2) Assuming that the particle is an ideal spherical shape, calculate the circle-equivalent diameter Ln = √Sn / π from the area Sn. (3) From the equivalent circle diameter Ln, the sphere volume Vn = (4 / 3)π(Ln) 3 Ask for. (4) Repeat steps (1) to (3) for the selected 100 particles. (5) D90 / D10 can be calculated by taking the particle size at the point where the distribution curve, with the vertical axis representing the cumulative percentage of the volume of 100 particles and the horizontal axis representing particle size, intersects with the 10% horizontal axis as the 10% diameter (D10) and the particle size at the point where it intersects with the 90% horizontal axis as the 90% diameter (D90).

[0032] (Standard deviation of particle size distribution) The standard deviation of the particle size distribution of the graphite particles may be 0.18 to 0.40, or may be 0.25 to 0.35. The standard deviation of the particle size distribution can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD3100, Shimadzu Corporation) based on a frequency distribution graph in which the horizontal axis represents the logarithmic scale of particle size and the vertical axis represents the particle amount (%).

[0033] (Graphitization degree) The graphite particles have a degree of graphitization of 90.0% or more, and from the viewpoint of discharge capacity when a lithium ion secondary battery is produced, it is preferably 90.5% or more, more preferably 91.0% or more, and even more preferably 92.0% or more. The upper limit of the degree of graphitization of the graphite particles is not particularly limited, and may be 100% or less. When the average particle size of the graphite particles is large (for example, greater than 12.0 μm), the graphite particles may have a sufficiently high hardness and are less likely to deform, break, or the like, so the upper limit may be 97.0% or less.

[0034] The degree of graphitization of graphite particles can be determined, for example, as follows. A graphite sample is mixed with 10 or 20 parts by mass of silicon powder (e.g., NIST SRM640f) in an agate mortar for 5 minutes, and the resulting mixture is placed in a sample holder for X-ray diffraction measurement. Using an X-ray diffractometer (e.g., Rigaku X-ray Diffraction Meter MultiFlex) and a CuKα beam, the diffraction angles corresponding to the graphite (002) plane and the silicon (111) plane are measured by X-ray diffraction measurement (2θ = 25° to 29°). The theoretical diffraction angle of Si (2θ=28.441°) is used to correct the observed diffraction angles of silicon and graphite to determine the correct diffraction angle of graphite. The interplanar spacing (Å) of the d(002) plane of the negative electrode material is calculated using Bragg's equation (2d sinθ=nλ), and the degree of graphitization is calculated using the following formula. Degree of graphitization = [(3.44 - interplanar spacing) / (0.086)] x 100

[0035] (I 002 / I 110 ) A negative electrode is formed using the negative electrode material of the present disclosure, and from the viewpoint of input characteristics in a lithium ion secondary battery, the negative electrode is pressed at 0.8 t / cm. When the negative electrode is subjected to X-ray diffraction measurement using CuKα rays, the peak intensity (I 002 ) and the peak intensity of the 110 diffraction line (I 110 ) is the ratio of I 002 / I 110 is preferably 350 or less, more preferably 330 or less, and even more preferably 300 or less. I 002 / I 110 The lower limit is not particularly limited, and may be 200 or more. I 002 / I 110 can be determined by the method described in the Examples. 002 / I 110 When measuring the electrode orientation, the components other than the graphite particles, the ratio thereof, and the manufacturing conditions of the negative electrode are the same as those described in the measuring method of electrode orientation in the Examples.

[0036] (0 tap density) The zero tap density of the graphite particles is set to 0.3 g / cm from the viewpoint of easily improving the input / output characteristics and energy density of the lithium ion secondary battery, and easily improving the compressive load. 3 ~0.6g / cm 3 and preferably 0.35 g / cm 3 ~0.55g / cm 3 It is more preferable that:

[0037] The zero tap density of graphite particles is 150 cm 3 100 cm of graphite powder sample is placed in a graduated flat-bottom test tube (e.g., KRS-406 manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.). 3 The density is the value determined from the mass and volume of the sample powder before the stoppered, graduated, flat-bottomed test tube is dropped.

[0038] (30 tap density) The 30 tap density of the graphite particles is set to 0.4 g / cm from the viewpoint of easily improving the input / output characteristics and energy density of the lithium ion secondary battery, and from the viewpoint of easily improving the compressive load. 3 ~0.7g / cm 3 and preferably 0.45 g / cm 3 ~0.65g / cm 3 It is more preferable that:

[0039] The 30 tap density of graphite particles can be determined, for example, as follows. Capacity 150cm 3 100 cm of graphite powder sample is placed in a graduated flat-bottom test tube (e.g., KRS-406 manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.). 3 The graduated flat-bottom test tube is then stopped up, and the graduated flat-bottom test tube is then dropped 30 times from a height of 5 cm. The density value calculated from the mass and volume of the sample powder is the 30-tap density.

[0040] (250 tap density) The 250 tap density of the graphite particles is set to 0.7 g / cm from the viewpoint of easily improving the input / output characteristics and energy density of the lithium ion secondary battery, and from the viewpoint of easily improving the compressive load. 3 ~1.1g / cm 3 and preferably 0.75 g / cm 3 ~1.0g / cm 3 It is more preferable that:

[0041] The 250 tap density of graphite particles can be determined, for example, as follows. Capacity 150cm 3 100 cm of graphite powder sample is placed in a graduated flat-bottom test tube (e.g., KRS-406 manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.). 3 The graduated flat-bottom test tube is then stopped up, and the graduated flat-bottom test tube is then dropped 250 times from a height of 5 cm. The density value calculated from the mass and volume of the sample powder is the 250 tap density.

[0042] (specific surface area) The specific surface area of ​​graphite particles determined by nitrogen adsorption measurement at 77 K is not particularly limited. For example, from the viewpoint of improving rapid charge / discharge performance and suppressing decomposition of the electrolyte, the specific surface area of ​​the graphite particles is 0.2 m 2 / g~6.0m 2 / g, and 1.5m 2 / g~5.0m 2 / g, more preferably 2.0m 2 / g~4.0m 2 / g is more preferred.

[0043] The specific surface area determined by nitrogen adsorption measurement at 77 K can be determined by the BET method from the adsorption isotherm obtained by nitrogen adsorption measurement at 77 K. Specifically, the specific surface area can be determined by the method described in the Examples.

[0044] The specific surface area of ​​the graphite particles can be adjusted by the particle size distribution, particle structure, and the like. The specific surface area of ​​the graphite particles may be adjusted by coating the graphite particles with low-crystalline carbon, etc. When it is desired to reduce the particle size, the specific surface area increases significantly due to the irregularities caused by pulverization, but by coating, the irregularities are filled in with the coating material, making them smooth and allowing the specific surface area to be adjusted.

[0045] The graphite particles may be subjected to a treatment for coating the surface with low-crystalline carbon, or may not be subjected to a treatment for coating the surface with low-crystalline carbon. When the surface of graphite particles is coated with low-crystalline carbon, the charging characteristics at low temperatures tend to be further improved when a lithium ion secondary battery is constructed. On the other hand, if the surface of the graphite particles is not coated with low-crystalline carbon, cracks, peeling, etc., tend to occur in the graphite particles during pressing during electrode fabrication, which increases the decomposition activity of the electrolyte and reduces storage characteristics. This also has the advantage of allowing greater freedom in manufacturing conditions. Furthermore, with the negative electrode material disclosed herein, lithium metal deposition during charging can be suppressed even when low-crystalline carbon is not disposed on the surface.

[0046] 1300cm measured by Raman spectroscopy -1 ~1400cm -1 The peak intensity (I D ) and 1580cm -1 ~1620cm -1 The peak intensity (I G ) is the ratio of I D / I G is the R-value, the R-value of the graphite particles may be 0.10 to 0.40, or may be 0.10 to 0.35. In particular, it is preferable that the surface is not subjected to a treatment for coating with low crystalline carbon, and that the R-value is 0.10 to 0.40.

[0047] In the present disclosure, the R value can be measured by the method described in the Examples. 1300cm -1 ~1400cm -1 The peak intensity (I D) is a peak identified as corresponding to the amorphous structure of carbon, for example, 1360 cm -1 This is a peak that appears nearby. 1580cm -1 ~1620cm -1 The peak intensity (I G ) is a peak identified as corresponding to the graphite crystal structure, for example, 1580 cm -1 This is a peak that appears nearby.

[0048] When the surface of the graphite particles is treated to be coated with low crystalline carbon, the R value may be 0.20 to 0.60, or 0.20 to 0.40.

[0049] (Springback rate) The springback ratio of the graphite particles is not particularly limited. For example, from the viewpoint of further suppressing breakage of the graphite particles due to pressing during the production of the negative electrode, the springback ratio of the graphite particles may be 15% or more, or may be 20% or more.

[0050] From the viewpoint of ease of densification by pressing during negative electrode production, the springback rate of the graphite particles may be 40% or less, or may be 35% or less.

[0051] In the present disclosure, the springback rate of graphite particles refers to the degree to which density decreases when graphite particles are compressed to a reference density and then pressure is released. The greater the springback rate, the more easily graphite particles that have been deformed by compression return to their original state. Specifically, a predetermined mass (e.g., 3.0 g) of graphite particles is filled into a mold, and the density of the graphite particles is measured to see if it is equal to the reference density (e.g., 1.7 g / cm 3 The material is compressed at a constant speed (for example, 10 mm / min) until it reaches a compressive stress of 0.01 mm / s. The pressure is then released, and the density after pressure release is measured when the press surface stops moving due to elasticity. The springback rate is calculated from the obtained value using the following formula: Springback rate (%) = {(standard density - density after pressure release) / standard density} x 100 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 particles is calculated based on the area of ​​the base of the mold (for example, 1.767 cm 2 ) and the volume of the graphite particles calculated from the distance from the bottom surface of the mold to the pressing surface of the graphite particles, and the mass of the graphite particles.

[0052] The compression load and springback rate of the graphite particles can be adjusted by changing the physical properties, composition, etc. of the raw material of the graphite particles (for example, needle coke), or by changing the graphitization conditions, etc.

[0053] In the present disclosure, the average interplanar spacing (d 002 ) is less than 0.340 nm is considered graphite. In the present disclosure, as will be described later, graphite particles in which low-crystalline carbon is arranged on at least a portion of the surface thereof are also referred to as "graphite particles." The average interplanar spacing of graphite crystals (d 002 The theoretical value of ) is 0.3354 nm, and the closer this value is, the more graphitized it is. From the viewpoint of the initial charge / discharge efficiency and energy density of lithium-ion secondary batteries, the average interplanar spacing (d 002 ) is preferably 0.33600 nm or less, more preferably 0.33596 nm or less, and even more preferably 0.33592 nm or less. From the above viewpoint, the average interplanar spacing of graphite particles (d 002 ) is preferably 0.3354 nm to 0.33600 nm, more preferably 0.3354 nm to 0.33596 nm, and even more preferably 0.3354 nm to 0.33592 nm.

[0054] The average interplanar spacing of graphite particles (d 002The average interplanar spacing (d) can be calculated using the Bragg equation based on the diffraction peak corresponding to the carbon 002 plane, which appears at a diffraction angle 2θ of approximately 24° to 27° in the diffraction profile obtained by irradiating a sample with X-rays (CuKα rays) and measuring the diffraction rays with a goniometer. 002 ) can be measured under the following conditions: Radiation source: CuKα radiation (wavelength = 0.15418nm) Output: 40kV, 20mA Sampling width: 0.010° Scanning range: 10°~35° Scan speed: 0.5° / min

[0055] Bragg's equation: 2d sinθ=nλ Here, d is the length of one period, θ is the diffraction angle, n is the order of reflection, and λ is the X-ray wavelength.

[0056] <Graphite particle structure> The graphite particles may include composite particles in which a plurality of graphite particles (preferably a plurality of flaky graphite particles) are aggregated or bonded together, or may include composite particles having a structure in which a plurality of flaky graphite particles are stacked (hereinafter also referred to as specific composite particles). It is believed that the specific composite particles can reduce the contact area with the electrolyte inside the particles, and thus effectively suppress decomposition of the electrolyte, compared to composite particles having a structure in which the main surfaces of multiple flaky graphite particles are oriented in random directions. Furthermore, it is believed that the particles are less likely to deform or break even when pressure is applied during the preparation of the negative electrode, and that electrolyte paths between the particles are more easily secured. Furthermore, the electrolyte located inside composite particles having a structure in which the main surfaces of multiple flaky graphite particles are oriented in random directions has a complex and slow-moving diffusion path. Therefore, even active materials with a larger number of particle interfaces are thought to be unable to exhibit high input / output performance due to diffusion obstructions. This tendency is particularly pronounced under input / output conditions with a high C rate.

[0057] The flat graphite particles contained in the specific composite particles refer to non-spherical graphite particles having anisotropic shapes. Examples of flat graphite particles include graphite particles having a scaly, flake, or partially lumpy shape. Composite particles refer to particles in a state in which primary particles are aggregated or bonded together. That is, the specific composite particles have a structure in which a plurality of flaky graphite particles are stacked and aggregated or bonded together with their main surfaces facing each other. Therefore, a plurality of flaky graphite particles are stacked in a substantially parallel state to form a composite particle. Whether or not the flaky graphite particles are stacked can be confirmed by microscopic observation.

[0058] The state in which multiple flaky graphite particles are aggregated or bonded refers to a state in which two or more flaky graphite particles are aggregated or bonded. Bonding refers to a state in which the particles are chemically bonded to each other directly or via a carbon substance. Aggregation refers to a state in which the particles are not chemically bonded to each other but maintain the shape of an aggregate due to their shape, etc. The flaky graphite particles may be aggregated or bonded via a carbon substance. Examples of the carbon substance include graphite obtained by graphitizing a binder such as tar, pitch, starch, PVA (polyvinyl alcohol), or CMC (carboxymethyl cellulose), and carbides. From the viewpoint of mechanical strength, it is preferable that two or more flaky graphite particles are bonded via a carbon substance. Whether the flaky graphite particles are aggregated or bonded can be confirmed, for example, by observation using a scanning electron microscope.

[0059] To reduce the proportion of composite particles with a structure in which the main faces of multiple flaky graphite particles are oriented in random directions, it is best to use as little binder as possible. Composite particles are not produced without a binder. On the other hand, excessive binder causes more primary particles to form around the binder clumps, i.e., aggregate intermediates in which multiple primary particles are coordinated, and the primary particles coordinated in these intermediates are likely to be in a non-equilibrium facing state.

[0060] A dispersant may be used to reduce clumps due to uneven distribution of binders such as tar and pitch. The use of a dispersant makes it easier to disperse the binder uniformly, and tends to reduce binder clumps. This is thought to have the effect of reducing the proportion of composite particles having a structure in which the main surfaces of multiple flat graphite particles are oriented in random directions. This also enhances the functionality of the binder, improves block moldability, and allows the binder blending ratio to be reduced. Examples of dispersants include those that can be used in step (b) described below.

[0061] From the viewpoint of reducing the amount of binder such as pitch used, an aromatic compound may be used together with the binder. Examples of the aromatic compound include aromatic compounds that can be used in step (a) described below.

[0062] The flake graphite particles and their raw materials are not particularly limited, and examples thereof include artificial graphite, scaly natural graphite, scaly natural graphite, coke, resin, etc. Among these, artificial graphite obtained by graphitizing coke is preferred from the viewpoints of resistance to deformation and a low specific surface area. When natural graphite is used as part of the raw materials, it is preferable to adjust the blending amount while monitoring the compression load, since it is prone to softening.

[0063] When the graphite particles contain specific composite particles, all of the graphite particles may be specific composite particles, or a portion of the graphite particles may be graphite particles other than the specific composite particles.

[0064] [Second embodiment] The negative electrode material for lithium ion secondary batteries according to the second embodiment of the present disclosure is graphite particles such that, when a negative electrode material layer is formed using the negative electrode material for lithium ion secondary batteries, the ratio L / T, which is the ratio of a tortuous path length L (μm), which is the distance from one surface to the other surface in the thickness direction through voids inside the negative electrode material layer, to a thickness T (μm) of the negative electrode material layer, is 1.7 or less.

[0065] In the negative electrode material for lithium ion secondary batteries of the second embodiment, the L / T ratio is 1.7 or less, which shortens the distance that lithium ions travel to reach the graphite particles deep inside the negative electrode from the surface side of the negative electrode. As a result, it is possible to reduce the time difference between the charging reaction on the surface side and the deep part of the negative electrode, and it is presumed that it is possible to manufacture a lithium ion secondary battery that has excellent resistance to lithium (Li) precipitation, similar to the negative electrode material of the first embodiment.

[0066] L / T can be measured as follows. X-ray CT measurements were performed using a microfocus X-ray CT system SMX-160CTS (Shimadzu Corporation) under the following conditions: tube voltage 48 kV, SID axis 350 mm, SOD axis 3 mm, two multi-scans, and a slice pitch of 0.001065 mm. The electrodes were cut into 2 mm x 15 mm strips for measurement. Using the obtained CT images, 3D analysis was performed using EXFactVR and ExFact Analysis for Porous Particles (both manufactured by Nippon Visual Science Co., Ltd.). The minimum length of the meandering path that passes through the voids inside the negative electrode material layer and reaches the electrodeposited copper foil surface in the thickness direction from the voids on the surface of the negative electrode material layer in the thickness direction was determined, and the arithmetic mean value was taken as the meandering path length L (μm). The meandering path length L was then divided by the thickness T (μm) of the negative electrode material layer to determine the meandering path ratio. When multiple meandering paths existed that reached the surface of the negative electrode material layer in the thickness direction from a single void on the surface of the electrodeposited copper foil, the value with the smallest meandering path was selected. When measuring L / T, the components other than graphite particles, and their ratios, which are the conditions for producing the negative electrode material layer, as well as the production conditions for the negative electrode material layer, are the same as the production conditions described in the method for measuring electrode orientation in the Examples, except that no pressing process is performed.

[0067] In the negative electrode material for lithium ion secondary batteries of the second embodiment, L / T is preferably 1.65 or less, and more preferably 1.6 or less. The lower limit of L / T is not particularly limited as long as it is 1.0 or more, and from the viewpoint of ease of production, it may be 1.5 or more.

[0068] The configuration described in the section on the negative electrode material of the first embodiment and the configuration described in the section on the negative electrode material for lithium ion secondary batteries of the second embodiment may be combined as appropriate.

[0069] <Method for manufacturing negative electrode material for lithium-ion secondary batteries> The method for producing a negative electrode material for lithium ion secondary batteries according to the present disclosure includes a step of graphitizing coke. More specifically, from the viewpoints of improving the handling properties during graphitization and the like and improving the cycle characteristics of lithium ion secondary batteries, the method for producing a negative electrode material for lithium ion secondary batteries according to the present disclosure preferably includes the following steps (a) to (d): (a) obtaining a mixture comprising a graphitizable aggregate (coke) and a graphitizable binder; (b) Molding the mixture to a density of 1.3 g / cm 3 obtaining a molded product, (c) graphitizing the molded product to obtain a graphitized product; (d) pulverizing the graphitized material to obtain a pulverized material. The steps of the above method may be performed consecutively or discontinuously, and may be performed at the same location or at different locations.

[0070] The type of coke used in the above production method is not particularly limited, and examples include petroleum-based or coal-based cokes such as fluid coke, needle coke, mosaic coke, and semi-needle coke, which has properties intermediate between needle coke and mosaic coke.

[0071] The method for obtaining coke particles (coke particles) is not particularly limited and can be carried out by a known method. The particle size of the coke particles is not particularly limited and can be selected taking into consideration the desired particle size, particle structure, etc. of the graphite particles. In order to obtain particles with a lower specific surface area, it is preferable to pulverize the coke in the raw coke state. Such particles have fewer voids, cracks, etc. due to cleavage, and the compressive load of the graphite particles tends to be higher.

[0072] In the manufacturing method of the present disclosure, a mixture containing a graphitizable aggregate and a graphitizable binder is obtained, and then the mixture is molded to form a graphitizable aggregate having a density of 1.3 g / cm 3 The following molded product is obtained. In the manufacturing method of the present disclosure, a mixture containing an aromatic compound may be used as the mixture for forming the molded product. This improves the appearance of the molded product and also improves the strength of the molded product, thereby improving the handling properties in subsequent graphitization treatments, etc.

[0073] The reason why the appearance of the molded product is improved and the strength of the molded product is further increased by using a mixture containing an aromatic compound to form the molded product is presumed to be as follows. (1) By adding a liquid aromatic compound to a mixture containing graphitizable aggregate, the surface of the graphitizable aggregate becomes slippery when the mixture is molded, promoting the alignment of the mixture and reducing voids. (2) By dissolving a graphitizable binder in the mixture, the binder is dispersed with high uniformity. The above (1) and (2) are thought to improve the appearance and strength of the molded product.

[0074] Furthermore, the manufacturing method of the present disclosure tends to produce a lithium-ion secondary battery with excellent cycle characteristics by obtaining a molded product with a relatively low density, graphitizing the molded product, and then pulverizing the graphitized product. The reason for this is presumed to be as follows. The manufacturing method of the present disclosure allows the graphitized product to be pulverized more easily than when pulverizing a graphitized product obtained using a molded product with a relatively high density, resulting in a pulverized product with a small specific surface area. By using a negative electrode material containing a pulverized product with a small specific surface area to manufacture a lithium-ion secondary battery, the contact area of ​​the negative electrode material with the electrolyte can be reduced. This suppresses the decomposition reaction of the electrolyte, extending the battery life and resulting in excellent cycle characteristics of the lithium-ion secondary battery.

[0075] In step (a), a mixture containing graphitizable aggregate, a graphitizable binder, and optionally an aromatic compound is obtained. The mixing is preferably carried out at a temperature at which the graphitizable binder softens. Specifically, if the graphitizable binder is pitch, tar, or the like, the temperature may be 50°C to 300°C, and if the graphitizable binder is a thermosetting resin, the temperature may be 20°C to 100°C.

[0076] The mixing method is not particularly limited. For example, a method using a planetary mixer, a kiln mixer, a huddle mixer, etc. is preferred. A kneader, which involves kneading, may also be used.

[0077] When the graphitizable aggregate is particulate, the average particle size (D50) of the graphitizable aggregate is, for example, preferably 5 μm to 40 μm, more preferably 10 μm to 30 μm, and even more preferably 10 μm to 25 μm.

[0078] The standard deviation of the particle size distribution of the graphitizable aggregate is, for example, preferably 0.35 or less, more preferably 0.20 or less, even more preferably 0.18 or less, and particularly preferably 0.16 or less. By having the standard deviation of the particle size distribution of the aggregate be 0.35 or less, the particle size variation of the aggregate can be reduced, and the particle size variation of the resulting pulverized material can also be suppressed. By using a negative electrode material containing pulverized material with small particle size variation in the production of a lithium ion secondary battery, the resistance distribution within the negative electrode can be made uniform. As a result, the rapid charging performance of the lithium ion secondary battery tends to be improved. Furthermore, by reducing the particle size variation of the aggregate, the binder function can be suitably ensured even when the content or amount of the graphitizable binder is reduced. The standard deviation of the particle size distribution is, for example, a value (volume basis) measured by laser diffraction. The lower limit of the standard deviation of the particle size distribution of the graphitizable aggregate is not particularly limited, and may be, for example, 0.05 or more, or 0.10 or more.

[0079] Methods for adjusting the average particle size of the graphitizable aggregate and the standard deviation of the particle size distribution of the graphitizable aggregate to fall within the above-mentioned ranges include sieve classification, air classification, wet classification, and the like.

[0080] The graphitizable binder is not particularly limited as long as it can be graphitized by a graphitization treatment. Specific examples include coal-based, petroleum-based, and artificial pitch and tar, starch, PVA, CMC, thermoplastic resins, and thermosetting resins.

[0081] The mixture may contain only one type of graphitizable aggregate and one or more types of graphitizable binder.

[0082] When starch is used as a binder, the resulting carbide is harder than when coal tar pitch is used, and the compressive load of the graphite particles tends to be improved. Therefore, based on equation (1), the input characteristics of lithium-ion secondary batteries, such as Li precipitation resistance, tend to be improved. When starch is used, the moldability of the mixture tends to be improved, making it possible to use a smaller amount of binder. As a result, the coke ratio in the mixture increases, and the discharge capacity of the lithium-ion secondary battery tends to be improved.

[0083] The content of each material in the mixture is not particularly limited. For example, the content of the graphitizable binder may be 10 to 30 parts by mass, 12 to 25 parts by mass, or 14 to 20 parts by mass relative to 100 parts by mass of the graphitizable aggregate. When the binder is added to a solvent or dispersion medium to be used as a solution or dispersion, the parts by mass of the solvent or dispersion medium are excluded. When the content of the binder is 10 parts by mass or more, the binder tends to function favorably as a binder for the graphitizable aggregate. When the content of the binder is 30 parts by mass or less, the amount of fixed carbon in the mixture is sufficiently ensured, and the yield tends to be excellent.

[0084] The mixture may contain only one type of graphitizable aggregate and one or more types of graphitizable binder.

[0085] The aromatic compound is not particularly limited as long as it has an aromatic ring. The aromatic compound may be a compound having an aromatic ring and a molecular weight of 500 or less, or may be a compound having a molecular weight of 300 or less. Examples of aromatic compounds include naphthalene, methylnaphthalenes such as 1-methylnaphthalene and 2-methylnaphthalene, acenaphthene, biphenyl, fluorene, benzopyrene, benzanthracene, dibenzanthracene, diphenylene oxide, quinoline, and isoquinoline. The mixture may contain only one type of aromatic compound or two or more types of aromatic compounds.

[0086] Among these, methylnaphthalene and naphthalene are preferred as the aromatic compound from the viewpoint of moldability when forming a molded product.

[0087] When the mixture contains an aromatic compound, the content of the aromatic compound in the mixture is preferably 1% by mass to 20% by mass, more preferably 2% by mass to 18% by mass, and even more preferably 3% by mass to 15% by mass, relative to 100% by mass of the total of the aggregate and binder.

[0088] The mixture may contain other components in addition to the graphitizable aggregate, graphitizable binder, and aromatic compound, such as graphite, dispersants, and graphitization catalysts.

[0089] The mixture may contain graphite. Examples of graphite include natural graphite and artificial graphite. The graphite is preferably in particulate form. The mixture may contain only one type of graphite or two or more types of graphite.

[0090] From the viewpoint of facilitating dispersion of the components in the mixture in the step (b) described below, it is preferable that the mixture contains a dispersant. By containing a dispersant in the mixture, it is possible to suppress variation in particle size of the pulverized material obtained by pulverizing the graphitized material, and it is easy to obtain pulverized material with a uniform particle size. As a result, the rapid charging performance of the lithium ion secondary battery tends to be improved. Furthermore, the inclusion of a dispersant in the mixture leads to a reduction in the amount of graphitizable binder, which is expected to improve battery characteristics such as the initial charge / discharge efficiency of the negative electrode material.

[0091] The type of dispersant is not particularly limited. Specific examples 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, because they do not affect the performance of the negative electrode material, are easy to handle because they are solid at room temperature, melt at the temperature of step (a) and therefore disperse uniformly, disappear in the process up to the graphitization treatment, and are inexpensive.

[0092] When the mixture contains a dispersant, the amount thereof is not particularly limited. For example, the content of the dispersant relative to the total 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.

[0093] From the viewpoint of promoting graphitization of the graphitizable aggregate or binder, the mixture preferably contains a graphitization catalyst. The type of graphitization catalyst is not particularly limited. Specific examples include substances having graphitization catalytic activity such as silicon, iron, nickel, titanium, and boron, as well as carbides of these substances, oxides of these substances, and nitrides of these substances.

[0094] 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 mass of the mixture may be 0.1 to 50 mass%, 0.5 to 40 mass%, or 0.5 to 30 mass%.

[0095] In step (b), the mixture obtained in step (a) is molded to obtain a molded product. Preferably, the mixture is molded into a predetermined shape using a uniaxial press or the like. By molding the mixture in this manner, it is possible to increase the amount of material packed into a graphitization furnace when graphitizing the mixture, thereby improving productivity and improving the effectiveness of the graphitization catalyst.

[0096] The method for molding the mixture in step (b) is not particularly limited, and examples thereof 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 the top, and vibration and impact are applied to the metal frame to mold the mixture, and an extrusion molding method in which the mixture is extruded from a nozzle or the like using a horizontal press to mold the mixture.

[0097] In step (b), the density of the resulting molded product is 1.3 g / cm 3 From the viewpoint of productivity of the negative electrode material and cycle characteristics of the lithium ion secondary battery, it is preferable that the density is 0.8 g / cm. 3 ~1.3g / cm 3 is preferred, and 1.0 g / cm 3 ~1.25g / cm 3 more preferably 1.05 g / cm 3 ~1.2g / cm 3is more preferable. This allows a molded product with a relatively low density to be obtained, graphitized, and then pulverized. Therefore, the graphitized product can be pulverized more easily than when a graphitized product obtained using a molded product with a relatively high density is pulverized. As a result, a pulverized product with a small specific surface area tends to be obtained. By using a negative electrode material containing a pulverized product with a small specific surface area in the production of a lithium ion secondary battery, the contact area of ​​the negative electrode material with the electrolyte can be reduced. As a result, the decomposition reaction of the electrolyte can be suppressed, the battery life can be extended, and a lithium ion secondary battery with excellent cycle characteristics tends to be produced.

[0098] As described above, it is believed that reducing the density of the graphitized molded product is advantageous in improving the performance of lithium-ion secondary batteries. For example, the density of the graphitized molded product tends to be adjusted to be low by reducing the fixed carbon derived from the binder. From the viewpoint of reducing the density of the graphitized molded product, for example, binders with a low fixed carbon ratio and exhibiting adhesiveness, such as corn starch, tapioca starch, PVA, and CMC, are preferably used.

[0099] The amount of fixed carbon in the graphitizable binder in the mixture is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less, relative to 100% by mass of the total of the aggregate and binder (before graphitization). As the amount of fixed carbon in the graphitizable binder in the mixture decreases, the proportion of coke in the mixture increases, and the discharge capacity of the lithium-ion secondary battery tends to improve. The lower limit of the fixed carbon content of the graphitizable binder in the mixture is not particularly limited, and may be 0.5% by mass or more, or 1.0% by mass or more, relative to 100% by mass of the total of the aggregate and binder (before graphitization).

[0100] The molded product obtained in step (b) is preferably subjected to a heat treatment before being graphitized in step (c). By performing the heat treatment, organic components contained in the mixture that do not contribute to graphitization are removed, and gas generation during the graphitization process tends to be suppressed.

[0101] The temperature of the heat treatment is not particularly limited, and is preferably lower than the temperature of the heat treatment in step (c), and may be, for example, within the range of 500°C to 1000°C.

[0102] In step (c), the molded product obtained in step (b) is graphitized. The method for graphitizing the molded product is not particularly limited as long as the conditions are such that the graphitizable components contained in the mixture can be graphitized. For example, a method of heat treating the mixture in an atmosphere in which the mixture is unlikely to be oxidized can be used. The atmosphere in which the mixture is unlikely to be oxidized is not particularly limited, and examples include an inert atmosphere such as nitrogen or argon, and a vacuum.

[0103] The temperature of the heat treatment for graphitization may be, for example, 1500°C or higher, 2000°C or higher, 2500°C or higher, or 2800°C or higher. The upper limit of the heat treatment temperature is not particularly limited, but may be, for example, 3200°C or lower. When the heat treatment temperature is 1500°C or higher, crystal changes tend to occur, making graphitization more likely to progress. When the heat treatment temperature is 2000°C or higher, the development of graphite crystals tends to be better. On the other hand, when the heat treatment temperature for graphitization is 3200°C or lower, sublimation of part of the graphite tends to be suppressed.

[0104] In step (d), the graphitized material obtained in step (c) is pulverized to obtain a pulverized product. The pulverization method is not particularly limited, and can be performed by a known method using a jet mill, a vibration mill, a pin mill, a hammer mill, or the like. The particle size of the pulverized product may be adjusted to a desired size. The method for adjusting the particle size is not particularly limited, and examples thereof include a method using the above-mentioned pulverizing device and a method using a sieve.

[0105] If necessary, the pulverized material obtained in step (d) may be subjected to steps such as (e) disposing low-crystalline carbon on at least a portion of the surface of the pulverized material, and (f) mixing the pulverized material with other negative electrode active materials.

[0106] In step (e), low-crystalline carbon can be disposed on at least a portion of the surface of the pulverized material by, for example, mixing the pulverized material with a substance (such as a resin) that can be converted to low-crystalline carbon by heat treatment, followed by heat treatment. Disposing low-crystalline carbon on at least a portion of the surface of the pulverized material can improve the input / output characteristics, such as rapid charge / discharge characteristics, of a lithium-ion secondary battery using the pulverized material as a negative electrode material.

[0107] [Other steps] The method for producing the negative electrode material of the present disclosure may include steps other than the steps described above. For example, the method for producing a negative electrode material may include a step of attaching an organic compound to the surface of the secondary particles after graphitization and then performing a heat treatment. By attaching the organic compound to the surface of the secondary particles and performing the heat treatment, the organic compound attached to the surface is converted into low-crystalline carbon. This allows the surface of the graphite particles to be coated with low-crystalline carbon.

[0108] The method for attaching an organic compound to the surface of secondary particles is not particularly limited, and examples thereof include a wet method in which secondary particles are dispersed and mixed in a mixed solution in which an organic compound is dissolved or dispersed in a solvent, and then the solvent is removed to attach the secondary particles; and a dry method in which mechanical energy is applied to a mixture obtained by mixing secondary particles and a solid organic compound to attach the secondary particles.

[0109] The organic compound is not particularly limited as long as it is a compound (carbon precursor) that can be converted into low-crystalline carbon by heat treatment. Examples include petroleum pitch, naphthalene, anthracene, phenanthroline, coal tar, phenolic resin, polyvinyl alcohol, etc. One type of organic compound may be used alone, or two or more types may be used in combination.

[0110] The heat treatment temperature when the secondary particles having an organic compound attached to their surfaces are heat treated is not particularly limited as long as the organic compound attached to the surfaces of the secondary particles is converted into low-crystalline carbon, and is preferably, for example, 400° C. to 1500° C. From the viewpoint of particularly enhancing high-temperature resistance, a temperature of 1000° C. to 1500° C. is more preferable. The heat treatment is preferably carried out in an inert gas atmosphere such as a nitrogen atmosphere.

[0111] The method for mixing the pulverized material with other negative electrode active materials in step (f) is not particularly limited. By mixing the pulverized material with other negative electrode active materials, the desired characteristics of the lithium ion secondary battery may be improved compared to when the pulverized material is used alone as the negative electrode active material. Examples of other negative electrode active materials include, but are not limited to, graphite particles such as natural graphite and artificial graphite, and particles containing elements capable of absorbing and desorbing lithium ions. Examples of elements capable of absorbing and desorbing lithium ions include, but are not limited to, Si, Sn, Ge, and In.

[0112] The pulverized material obtained in step (f) may contain particles in which a plurality of flat graphite particles are aggregated or bonded together, or may contain particles in which a plurality of flat graphite particles are aggregated or bonded together so that the main surfaces of the graphite particles are non-parallel to each other (hereinafter also referred to as secondary graphite particles).

[0113] When the pulverized material is in the form of graphite secondary particles, the phenomenon in which the particles of the negative electrode material are oriented along the direction of the current collector when pressed to densify the negative electrode is suppressed, and there tends to be sufficient pathways for lithium ions to enter and exit the negative electrode material.

[0114] Furthermore, by including particles in which a plurality of flat graphite particles are aggregated or bonded together, the influence of the pressure applied during pressing on the individual graphite particles is reduced due to the voids present between the plurality of flat graphite particles, and fracture, cracking, etc. of the graphite particles tend to be suppressed. As a result, the compressive load of the graphite particles is improved, and the Li precipitation resistance tends to be excellent.

[0115] In the present disclosure, the term "flat graphite particles" refers to non-spherical graphite particles having an anisotropic shape. Examples of flat graphite particles include graphite particles having a scaly, flake, or partially lumpy shape.

[0116] The flat graphite particles preferably have an aspect ratio, expressed as A / B, where A is the length in the major axis direction and B is the length in the minor axis direction, of 1.2 to 20, more preferably 1.3 to 10. When the aspect ratio is 1.2 or more, the contact area between particles increases, tending to further improve conductivity. When the aspect ratio is 20 or less, input / output characteristics such as rapid charge / discharge characteristics of the lithium ion secondary battery tend to further improve.

[0117] The aspect ratio is determined by observing graphite particles under a microscope, randomly selecting 100 graphite particles, measuring the A / B ratio for each, and then calculating the arithmetic mean of these measurements. In observing the aspect ratio, the major axis length A and the minor axis length B are measured as follows. That is, in a projected image of a graphite particle observed under a microscope, two parallel tangents circumscribing the periphery of the graphite particle are selected, with tangents a1 and a2 having the greatest distance between them, and the major axis length A is defined as the distance between these tangents a1 and a2. Two parallel tangents circumscribing the periphery of the graphite particle are selected, with tangents b1 and b2 having the smallest distance between them, and the minor axis length B is defined as the distance between these tangents b1 and b2.

[0118] In the present disclosure, the phrase "main surfaces are non-parallel" of graphite secondary particles means that the surfaces (main surfaces) of the plurality of flat graphite particles with the largest cross-sectional areas are not aligned in a fixed direction. Whether the main surfaces of the plurality of flat graphite particles are non-parallel to each other can be confirmed by observation with a microscope. When the plurality of flat graphite particles are aggregated or bonded together with their main surfaces non-parallel to each other, the orientation of the main surfaces of the flat graphite particles in the negative electrode is suppressed, and expansion of the negative electrode during charging is suppressed, which tends to further improve the cycle characteristics of the lithium-ion secondary battery. The secondary graphite particles may partially include a structure in which a plurality of flat graphite particles are aggregated or bonded together with their respective main faces parallel to one another.

[0119] From the viewpoint of ease of aggregation or bonding, the average particle size of the flat graphite particles is, for example, preferably 1 μm to 50 μm, more preferably 1 μm to 25 μm, and even more preferably 1 μm to 15 μm. The average particle size of the flat graphite particles can be measured by a scanning electron microscope, and the average particle size of the flat graphite particles is, for example, the arithmetic mean value of the particle sizes of 100 flat graphite particles.

[0120] The flat graphite particles and the raw material thereof are not particularly limited, and examples thereof include artificial graphite, scaly natural graphite, scaly natural graphite, coke, resin, tar, pitch, etc. Among these, graphite obtained from artificial graphite, natural graphite, or coke tends to be soft particles with high crystallinity, which makes it easier to increase the density of the negative electrode.

[0121] The negative electrode material may contain spherical graphite particles. When the negative electrode material contains spherical graphite particles, the spherical graphite particles themselves have a high density, so that the pressing pressure required to obtain a desired electrode density tends to be reduced.

[0122] Examples of spherical graphite particles include spherical artificial graphite and spherical natural graphite. From the viewpoint of increasing the density of the negative electrode, the spherical graphite particles are preferably high-density graphite particles. Specifically, spherical natural graphite that has been subjected to a particle spheroidization treatment to enable a high tap density is preferred. Furthermore, a negative electrode material layer containing spherical natural graphite has excellent peel strength and tends to be less likely to peel off from the current collector even when pressed with a strong force.

[0123] When the negative electrode material contains spherical graphite particles, it may contain both the above-mentioned flat graphite particles and spherical graphite particles. When the negative electrode material contains the above-mentioned flat graphite particles and spherical graphite particles, the ratio between the two is not particularly limited and can be set depending on the desired electrode density, pressure conditions during pressing, desired battery characteristics, etc.

[0124] When the negative electrode material contains flat graphite particles and spherical graphite particles, it may be a mixture of flat graphite particles and spherical graphite particles, or a combination of flat graphite particles and spherical graphite particles (hereinafter also referred to as flat-spherical composite particles). Examples of flat-spherical composite particles include particles in which flat graphite particles and spherical graphite particles are combined via an organic carbide.

[0125] The flat-spherical composite particles can be produced, for example, by using a mixture containing flat graphite particles or raw materials thereof and spherical graphite particles in the step (a).

[0126] <Negative electrode material composition for lithium ion secondary battery> The negative electrode material composition for lithium ion secondary batteries of the present disclosure includes the negative electrode material for lithium ion secondary batteries of the present disclosure, a binder, and a solvent. The negative electrode material composition for lithium ion secondary batteries of the present disclosure may be in the form of a slurry obtained by kneading the negative electrode material for lithium ion secondary batteries and the binder together with the solvent. The kneading can be carried out using a dispersing device such as a dispersing mixer or a planetary kneader.

[0127] The binder used in preparing the negative electrode material composition for lithium ion secondary batteries is not particularly limited. Examples of binders include styrene-butadiene copolymer (SBR), homopolymers or copolymers of ethylenically unsaturated carboxylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate, and 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, polyacrylonitrile, and polymethacrylonitrile. When the negative electrode material composition for lithium ion secondary batteries contains a binder, the content of the binder is not particularly limited. For example, the binder content may be 0.5 to 20 parts by mass per 100 parts by mass of the total of the negative electrode material for lithium ion secondary batteries and the binder.

[0128] The negative electrode material composition for lithium ion secondary batteries may contain a thickener. Examples of the thickener that can be used include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, oxidized starch, phosphated starch, and casein. When the negative electrode material composition for lithium ion secondary batteries contains a thickener, the content of the thickener is not particularly limited. For example, the content may be 0.1 to 5 parts by mass per 100 parts by mass of the negative electrode material for lithium ion secondary batteries.

[0129] The negative electrode material composition for lithium ion secondary batteries may contain a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as carbon black, graphite, and acetylene black, and inorganic compounds such as conductive oxides and conductive nitrides. When the negative electrode material composition for lithium ion secondary batteries contains a conductive auxiliary material, the content of the conductive auxiliary material is not particularly limited. For example, it may be 0.5 to 15 parts by mass per 100 parts by mass of the negative electrode material for lithium ion secondary batteries.

[0130] <Negative electrode for lithium-ion secondary batteries> The negative electrode for a lithium ion secondary battery of the present disclosure includes a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery of the present disclosure and a current collector. The negative electrode for a lithium ion secondary battery may include other components as necessary in addition to the negative electrode material layer containing the negative electrode material for a lithium ion secondary battery of the present disclosure and the current collector.

[0131] The negative electrode for a lithium ion secondary battery can be produced, for example, by preparing the above-described negative electrode material composition for a lithium ion secondary battery according to the present disclosure and applying it onto a current collector to form a negative electrode material layer, or by forming the negative electrode material composition for a lithium ion secondary battery into a shape such as a sheet or pellet and integrating it with a current collector.

[0132] 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. Porous materials such as porous metal (foam metal), carbon paper, etc. can also be used as the current collector.

[0133] When the negative electrode material composition for lithium ion secondary batteries is applied to a current collector to form a negative electrode 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 negative electrode material composition for lithium ion secondary batteries is applied to the current collector, the solvent contained in the negative electrode material composition for lithium ion secondary batteries 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, the negative electrode material layer may be subjected to a rolling treatment. The rolling treatment can be performed using a plate press, a calendar roll, or the like.

[0134] When the negative electrode material composition for lithium ion secondary batteries formed into a shape such as a sheet or pellet is integrated with a current collector to form a negative electrode material layer, the integration method is not particularly limited. For example, it can be performed by rolling, flat pressing, or a combination of these means. The pressure when integrating the negative electrode material composition for lithium ion secondary batteries with the current collector is preferably, for example, about 1 MPa to 200 MPa.

[0135] The negative electrode density of the negative electrode material layer is not particularly limited, and is, for example, 1.1 g / cm 3 ~1.8g / cm 3 and preferably 1.1 g / cm 3 ~1.7g / cm 3 More preferably, it is 1.1 g / cm 3 ~1.6g / cm 3 It is more preferable that the negative electrode density is 1.1 g / cm 3 By setting the density to 1.8 g / cm or more, the increase in electrical resistance is suppressed and the capacity tends to increase. 3 By setting the above, deterioration of input characteristics and cycle characteristics tends to be suppressed.

[0136] <Lithium-ion secondary battery> The lithium ion secondary battery of the present disclosure includes the negative electrode for a lithium ion secondary battery of the present disclosure, a positive electrode, and an electrolyte solution.

[0137] 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 in the form of a foil, perforated foil, mesh, or the like.

[0138] The positive electrode material used to form the positive electrode layer is not particularly limited. Examples of the positive electrode material include metal compounds (metal oxides, metal sulfides, etc.) that can dope or intercalate lithium ions, conductive polymer materials, etc. More specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and their double oxides (LiCox Ni y Mn z O2, x+y+z=1), and a double oxide containing an additional element M' (LiCo a Ni b Mn c M' d O2, a+b+c+d=1, M': Al, Mg, Ti, Zr or Ge), spinel-type lithium manganese oxide (LiMn2O4), lithium vanadium compounds, V2O5, V6O 13 , VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, olivine-type LiMPO4 (M: Co, Ni, Mn, Fe) and other metal compounds, conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. The positive electrode material may be one type alone or two or more types.

[0139] The electrolytic 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 electrolytic solution) can be used. Examples of lithium salts include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. The lithium salts may be one type alone or two or more types. Examples of non-aqueous solvents 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, triethyl phosphate, etc. The non-aqueous solvents may be used alone or in combination of two or more.

[0140] 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.

[0141] The separator is not particularly limited, and for example, a resin nonwoven fabric, cloth, microporous film, or a combination thereof can be used. Examples of resins include those containing polyolefins such as polyethylene and polypropylene as the main component. If the positive electrode and negative electrode do not come into contact with each other due to the structure of the lithium ion secondary battery, a separator may not be used.

[0142] 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.

[0143] The lithium ion secondary battery of the present disclosure is suitable as a large-capacity lithium ion secondary battery for use in electric vehicles, power tools, power storage devices, and the like. [Example]

[0144] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0145] [Example 1] Petroleum-derived raw coke (needle coke) was used as the raw material for graphite particles. The raw coke was crushed using a hammer mill. The crushed material was sieved using a sieve with 3 mm openings, and the under-sieve material was sieved using a sieve with 1 mm openings to collect granules with particle sizes of 1 mm to 3 mm.

[0146] The obtained coke particles were pulverized and classified using a roller mill to obtain flat coke particles with a D50 of 9 μm. The standard deviation (σ) of the particle size distribution of the coke particles was 0.14.

[0147] 85 parts by mass of the obtained coke particles, 15 parts by mass of coal tar pitch (softening point 80°C to 130°C, quinoline insoluble content 15% by mass or less, fixed carbon 50% by mass, denoted as "Pitch 1" in Table 1), and 15 parts by mass of the aromatic compound methylnaphthalene per 100 parts by mass of the total of the coke particles and the coal tar pitch were kneaded using a kneader to obtain a mixture.

[0148] The resulting mixture was then uniaxially pressed at room temperature to a density of 1.3 g / cm 3 The following molding was performed to obtain a molded product. The molded product was then heat-treated in a nitrogen atmosphere at 850°C for 8 hours, and then graphitized at 3000°C for 30 hours. The resulting graphitized product was pulverized to obtain particles. The resulting particles were then sieved through a 280-mesh mesh to obtain graphite particles, which are the negative electrode material. The volume-based particle size distribution of the graphite particles was determined using a laser diffraction particle size distribution analyzer (SALD3100, Shimadzu Corporation). The results were D10 5.5 μm, D50 10.0 μm, D90 25.5 μm, and D99.9 69.9 μm. The standard deviation (σ) of the particle size distribution of the graphite particles was 0.26.

[0149] [Example 2] Graphite particles as a negative electrode material were obtained in the same manner as in Example 1, except that the coke particles and coal tar pitch were mixed by stirring using a stirrer instead of kneading using a kneader. The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0150] [Example 3] Graphite particles serving as a negative electrode material were obtained in the same manner as in Example 1, except that the coal tar pitch used in Example 1 (softening point 80°C to 130°C, quinoline insoluble content 15% by mass or less, fixed carbon 50% by mass, denoted as "Pitch 1" in Table 1) was changed to coal tar pitch (softening point 220°C to 280°C, quinoline insoluble content 20% by mass or less, fixed carbon 70% by mass, denoted as "Pitch 2" in Table 1). The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0151] [Examples 4 to 6] Graphite particles as negative electrode materials were obtained in the same manner as in Examples 1 to 3, except that coke particles with a D50 of 5 μm and a standard deviation (σ) of particle size distribution of 0.16 were used to prepare the graphite particles in Examples 1 to 3. The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0152] [Example 7] The graphite particles produced in Example 1 were treated with coal tar pitch ("Pitch 2" in Table 1) under the following conditions to produce graphite particles whose surfaces were coated with low-crystalline carbon (hereinafter also referred to as "coated graphite particles"). 100 parts by mass of the graphite particles prepared in Example 1 and 4 parts by mass of coal tar pitch were mixed. Next, the resulting mixture was heated to 1200°C at a heating rate of 200°C / hour under a nitrogen flow and held at 1200°C (the calcination temperature) for 2 hours. Thereafter, the calcined graphite particles were crushed using a cutter mill and sieved through a 280-mesh sieve, and the coated graphite particles that remained under the sieve were obtained as a negative electrode material. The volume-based particle size distribution of the coated graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0153] [Example 8] The graphite particles produced in Example 6 were treated with coal tar pitch ("Pitch 2" in Table 1) under the same conditions as in Example 7 to produce coated graphite particles. The volume-based particle size distribution of the coated graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0154] [Example 9] 85 parts by mass of the coke particles having a D50 of 9 μm used in Example 1, 5 parts by mass of coal tar pitch 2, and 10 parts by mass of starch (10% by mass of fixed carbon) were mixed and stirred using a stirrer to obtain a mixture.

[0155] The resulting mixture was then uniaxially pressed at room temperature to a density of 1.3 g / cm 3 The following molding was performed to obtain a molded product. The molded product was then heat-treated in a nitrogen atmosphere at 850°C for 8 hours, and then graphitized at 3000°C for 30 hours. The resulting graphitized product was pulverized to obtain particles. The resulting particles were then sieved through a 280-mesh mesh to obtain graphite particles, which are the negative electrode material. The volume-based particle size distribution of the graphite particles was determined using a laser diffraction particle size distribution analyzer (SALD3100, Shimadzu Corporation). The results were D10 6.7 μm, D50 12.7 μm, D90 27.9 μm, and D99.9 68.8 μm. The standard deviation (σ) of the particle size distribution of the graphite particles was 0.24.

[0156] [Example 10] 90 parts by mass of the coke particles having a D50 of 9 μm used in Example 1 and 10 parts by mass of starch (fixed carbon 10% by mass) were mixed by stirring using a stirrer to obtain a mixture.

[0157] The resulting mixture was then uniaxially pressed at room temperature to a density of 1.3 g / cm 3 The following molding was performed to obtain a molded product. The molded product was then heat-treated in a nitrogen atmosphere at 850°C for 8 hours, and then graphitized at 3000°C for 30 hours. The resulting graphitized product was pulverized to obtain particles. The resulting particles were then sieved through a 280-mesh mesh to obtain graphite particles, which are the negative electrode material. The volume-based particle size distribution of the graphite particles was determined using a laser diffraction particle size distribution analyzer (SALD3100, Shimadzu Corporation). The results were D10 6.8 μm, D50 11.5 μm, D90 20.3 μm, and D99.9 47.7 μm. The standard deviation (σ) of the particle size distribution of the graphite particles was 0.19.

[0158] [Comparative Example 1] As the raw material for the graphite particles, flat coke particles with a D50 of 16 μm, made from petroleum-derived calcined coke (semi-needle coke), were used.

[0159] Graphite particles were produced in the same manner as in Example 1, except that 85 parts by mass of the obtained coke particles, 15 parts by mass of coal tar pitch, and 15 parts by mass of graphitization catalyst SiC per 100 parts by mass of the total of the coke particles and the coal tar pitch were kneaded using a kneader.

[0160] The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0161] Comparative Example 2 The raw coke used in Example 1 was pulverized and classified using a roller mill to obtain flat coke particles with a D50 of 14 μm. These coke particles were packed into a graphitization case without being mixed with coal tar pitch and fired at 850°C to evaporate impurities in the mixture, followed by graphitization at 3000°C. The resulting particles were then sieved through a 280-mesh screen to obtain graphite particles as the negative electrode material. 50% by mass of these graphite particles and 50% by mass of scaly natural graphite with a D50 of 3 μm were combined in a spheronizing machine to obtain graphite composite particles. The volume-based particle size distribution of the graphite composite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0162] Comparative Example 3 Petroleum-derived raw coke (needle coke) was used as the raw material for graphite particles. The coke was crushed using a hammer mill. The crushed material was sieved using a sieve with 3 mm openings, and the remaining material was sieved using a sieve with 1 mm openings to collect granules with particle sizes of 1 mm to 3 mm. The resulting granules were then ground using a roller mill to obtain particles with an average particle size of 200 μm. The resulting particles were then pulverized and classified using a roller mill to obtain flat coke particles with a D50 of 16 μm. The coke particles were packed into a graphitization case without being mixed with coal tar pitch and fired at 850°C to evaporate impurities in the mixture, followed by graphitization at 3000°C. The resulting particles were then sieved using a 280-mesh screen to obtain graphite particles as a negative electrode material. The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0163] [Comparative Examples 4 and 5] Petroleum-derived calcined coke (needle coke) was pulverized and classified using a roller mill to obtain flat coke particles with a D50 of 12 μm. These coke particles were packed into a graphitization case without being mixed with coal tar pitch, and baked at 850°C to evaporate impurities in the mixture. They were then graphitized at 3000°C or 2800°C. The resulting particles were then sieved through a 280-mesh screen to obtain graphite particles as a negative electrode material. The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0164] Comparative Example 6 Graphite particles as negative electrode material were obtained in the same manner as in Comparative Examples 4 and 5, except that the coke particles having a D50 of 12 μm used to prepare the graphite particles in Comparative Examples 4 and 5 were used and the graphitization temperature was changed to 2600°C. The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0165] Table 1 below shows the manufacturing conditions for graphite particles and coated graphite particles, which are negative electrode materials, and the particle size distribution results for the graphite particles and coated graphite particles. Note that the units for the amounts of coke and binder in Table 1 are "parts by mass." The amount of fixed carbon in the binder (% by mass) in Table 1 refers to the ratio to 100% by mass of the total of the coke and binder (before graphitization).

[0166] [Table 1]

[0167] The negative electrode materials obtained in each of the examples and comparative examples were used to measure and evaluate the physical properties shown below. The results are shown in Tables 2 and 3.

[0168] (specific surface area) The negative electrode material was filled into a measurement cell and pre-treated by heating at 200°C while being degassed under vacuum. Nitrogen gas was adsorbed into the sample using a gas adsorption apparatus (ASAP2010, manufactured by Shimadzu Corporation). The obtained sample was subjected to BET analysis using the five-point method to determine the specific surface area.

[0169] (tap density) Capacity 150cm 3 100 cm of graphite powder sample was placed in a graduated flat-bottom test tube (Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-406). 3 The graduated flat-bottom test tube was then stoppered. Before dropping the graduated flat-bottom test tube, the zero tap density was determined from the mass and volume of the sample powder. Next, the graduated flat-bottom test tube was dropped from a height of 5 cm 30 times and after dropping 250 times, the 30 tap density and the 250 tap density were determined from the mass and volume of the sample powder, respectively.

[0170] (Graphitization degree) A graphite sample is mixed with 10 or 20 parts by mass of silicon powder (e.g., NIST SRM640f) in an agate mortar for 5 minutes, and the resulting mixture is placed in a sample holder for X-ray diffraction measurement. Using an X-ray diffractometer (e.g., Rigaku X-ray Diffraction Meter MultiFlex) and a CuKα beam, the diffraction angles corresponding to the graphite (002) plane and the silicon (111) plane are measured by X-ray diffraction measurement (2θ = 25° to 29°). The theoretical diffraction angle of Si (2θ=28.441°) is used to correct the observed diffraction angles of silicon and graphite to determine the correct diffraction angle of graphite. The interplanar spacing (Å) of the d(002) plane of the negative electrode material is calculated using Bragg's equation (2d sinθ=nλ), and the degree of graphitization is calculated using the following formula. Degree of graphitization = [(3.44 - interplanar spacing) / (0.086)] x 100

[0171] (R value) The R value of the negative electrode material was determined by measuring the Raman spectrum using a Raman spectrum measuring device (XploRA PLUS, manufactured by HORIBA, Ltd.) under the following conditions, with the following range as the baseline for the spectrum obtained. - Raman spectrum measurement conditions - Laser wavelength: 532nm Laser power: 100mW or more Neutral density filter: 1% ·Irradiation intensity: 1mW Measurement range: 1000cm -1 ~1800cm -1 Irradiation time: 30 seconds ·Irradiation area: 1μm 2 Baseline (D band): 1100cm -1 ~1470cm -1 Baseline (G band): 1450cm -1 ~1710cm -1 Number of times per particle is accumulated: 2 times Number of particles measured: 30 particles

[0172] (Compression load) 3.0 g of negative electrode material was filled into a 15 mm diameter mold and compressed at a constant rate of 10 mm / min using an Autograph (Shimadzu Corporation). During this compression, the distance from the bottom of the negative electrode material to the press surface was measured, and this was multiplied by the bottom area of ​​the mold to obtain the volume of the negative electrode material, from which the density during compression was calculated. A load cell was attached to the Autograph press hammer, and the specified density of 1.7 g / cm was calculated. 3 The applied pressure (kN / cm 2 ) was used as the compressive load.

[0173] (Springback rate) 3.0 g of negative electrode material was filled into a 15 mm diameter mold and compressed at a constant speed of 10 mm / min using an autograph (Shimadzu Corporation). The pressure was then released, and the density after pressure release was measured when the elastic movement of the press surface stopped. The reference density was 1.7 g / cm. 3 The absolute value of the difference between the density of the negative electrode material after springback and the density of the negative electrode material after springback is 1.7 g / cm 3 The value divided by this was multiplied by 100 to obtain the springback rate (%).

[0174] (electrode orientation) A negative electrode for a lithium ion secondary battery was prepared as follows, and the electrode orientation was evaluated under the conditions shown below. - Fabrication of negative electrodes for lithium-ion secondary batteries - Graphite particles (97.6 parts by mass), carboxymethyl cellulose (CMC) (1.2 parts by mass), and styrene-butadiene rubber (SBR) (1.2 parts by mass) were mixed together to prepare a slurry. This slurry was applied to the shiny surface of the electrolytic copper foil at a rate of 10 g / cm. 2 After pre-drying at 90°C for 2 hours, the electrode density was adjusted to 1.65 g / cm using a roll press. 3 Thereafter, a curing treatment was carried out by drying at 120°C for 4 hours in a vacuum atmosphere, and a negative electrode material layer was formed on the electrolytic copper foil, thereby obtaining a negative electrode for a lithium ion secondary battery. - Evaluation of electrode orientation - The resulting negative electrode for lithium ion secondary batteries was placed on a plate with a width of 5 cm and an area of ​​600 cm. 2 The negative electrode was formed into a rectangular sheet, and the resulting molded product was pressed with a 4 t hydraulic pressure using a roll-type press. The linear pressure was 4 t / 5 cm = 0.8 t / cm. The pressed negative electrode was placed in an X-ray diffraction measurement cell, and an X-ray diffraction pattern was measured using CuKα radiation (2θ = 25.5° to 27.5°, 76.5° to 78.5°) under the conditions of a scan rate of 0.25° / min, a tube voltage of 40 kV, a tube current of 30 mA, a divergence slit of 1°, a scattering slit of 1°, and a receiving slit of 0.3 mm, using an X-ray diffraction measurement device (X-RAY DIFFRACTIOMETER MultiFlex manufactured by Rigaku Corporation). 002 ) and the peak intensity of the 110 diffraction line (I 110 ) is the ratio of I 002 / I 110 was calculated and this value was taken as the electrode orientation.

[0175] (discharge capacity) The lithium-ion secondary battery fabricated as described above was placed in a thermostatic chamber set at 25°C, and the current was set at 0.2 C and the voltage was set at 0 V (V vs. Li / Li + ), then constant voltage charging was performed at 0 V until the current value reached 0.02 C. After a 30-minute rest, the battery was charged at a current value of 0.2 C and a voltage of 1.5 V (V vs. Li / Li). +The battery was discharged at a constant current until the discharge capacity reached 100 kJ / s.

[0176] (SOC-Li (Li precipitation resistance)) A lithium ion secondary battery was fabricated using the negative electrode obtained above, and the Li deposition resistance was evaluated as follows. - Fabrication of lithium-ion secondary batteries - A coin cell, which is a lithium-ion secondary battery, was fabricated using the negative electrode obtained above, metallic lithium as a counter electrode, a mixed solution of ethylene carbonate / ethyl methyl carbonate (3:7 volume ratio) containing 1 M LiPF6 and vinylene carbonate (VC) (1.0 mass%) as an electrolyte, a 25 μm thick polyethylene microporous membrane as a separator, and a 250 μm thick copper plate as a spacer. -Evaluation of Li precipitation resistance- The fabricated lithium-ion secondary battery was placed in a thermostatic chamber set at 25°C, and the voltage was maintained at 0.005V (V vs. Li / Li) at a current of 0.1C from the first to third cycle. + ), then constant voltage charging was performed at 0.005 V until the current value reached 0.05 C. After a 30-minute rest, the battery was charged at a current value of 0.2 C and a voltage of 1.5 V (V vs. Li / Li). + ) was discharged at a constant current until the discharge capacity at the third cycle was 1C in the Li deposition test. The fourth cycle was charged at a current density of 3C and a controlled voltage of 1.5V, which allowed charging to the discharge capacity at the third cycle in 20 minutes. The first inflection point in the differential profile (dV / dQ, where V is voltage and Q is capacitance; see Figure 1) of the obtained fourth cycle charge curve was taken as the Li deposition onset point, and the capacity at this point was expressed as a percentage of the discharge capacity at the third cycle (or the charge capacity at the fourth cycle set to the same capacity) to evaluate the Li deposition resistance. The results are shown in Table 3.

[0177] (input characteristics) When various graphite particles other than those in the Examples and Comparative Examples were examined for the physical properties shown in Tables 2 and 3, it was found that when the compressive load was large and the D50 was small, the results of the Li deposition resistance regarding the input characteristics of the battery tended to be good. 2 ) and D50 (μm) were used as explanatory variables, and Li precipitation resistance was used as the objective variable. A multiple regression analysis was performed, and the regression equation (2) was obtained. The coefficient of determination R 2 was 0.84. Li precipitation resistance=11.3x-0.66y+1.4···(2)

[0178] The compressive load (kN / cm) measured in each example and comparative example 2 ) and D50 (μm) were substituted into the above formula (2), and the resulting value was used as the evaluation value of the input characteristics. It is believed that the higher the evaluation value of this input characteristics, the higher the measured value of Li precipitation resistance tends to be.

[0179] (curvature rate) In Example 6 and Comparative Example 1, a negative electrode material layer was formed on an electrolytic copper foil in the same procedure as in the evaluation of electrode orientation, to obtain a negative electrode for a lithium ion secondary battery. The resulting negative electrode for a lithium ion secondary battery was used to determine the tortuosity, which is the ratio L / T of the tortuosity length L (μm), which is the distance from one surface to the other surface in the thickness direction through the voids inside the negative electrode material layer, to the thickness T (μm) of the negative electrode material layer. Specifically, X-ray CT measurements were performed using a microfocus X-ray CT system (Shimadzu Corporation) SMX-160CTS under the following conditions: tube voltage 48 kV, SID axis 350 mm, SOD axis 3 mm, two multi-scans, and a slice pitch of 0.001065 mm. The electrodes were cut into 2 mm x 15 mm strips for measurement. Using the obtained CT images, 3D analysis was performed using EXFactVR and ExFact Analysis for Porous Particles (both manufactured by Nippon Visual Science Co., Ltd.). The minimum length of the tortuous path that passes through the voids inside the negative electrode material layer and reaches the voids on the surface of the negative electrode material layer in the thickness direction was determined, and the arithmetic mean value was taken as the tortuous path length L (μm). The tortuous path ratio was calculated by dividing the tortuous path length L by the thickness T (μm) of the negative electrode material layer. When there are multiple tortuous paths extending from one gap on the surface of the electrolytic copper foil to the surface side of the negative electrode material layer in the thickness direction, the value that provides the smallest tortuous path was selected. The tortuosity ratio of Example 6 was 1.585, and the tortuosity ratio of Comparative Example 1 was 1.712. It is presumed that Example 6 had a smaller tortuosity ratio value than Comparative Example 1, and therefore had excellent Li precipitation resistance, as shown in the results in Table 3.

[0180] [Table 2]

[0181] [Table 3]

[0182] The evaluation criteria for each physical property in Table 3 are as follows: (D50) A: The D50 of the negative electrode material is 11.0 μm or less. B: The D50 of the negative electrode material is more than 11.0 μm and 14.5 μm or less. C: The D50 of the negative electrode material is more than 14.5 μm and 17.0 μm or less. D: The D50 of the negative electrode material exceeds 17.0 μm. (specific surface area) A: The specific surface area of ​​the negative electrode material is 2.0 m 2 / g~6.0m 2 / g. B: The specific surface area of ​​the negative electrode material is 2.0 m 2 / g. C: The specific surface area of ​​the negative electrode material is 6.0 m 2 / g. (Graphitization degree) A: The graphitization degree of the negative electrode material is 92.0% or more. B: The graphitization degree of the negative electrode material is 90.0% or more and less than 92.0%. C: The graphitization degree of the negative electrode material is less than 90.0%. (Compression load) A: The compressive load of the negative electrode material is 2.80 kN / cm 2 That's all. B: The compressive load of the negative electrode material is 2.30 kN / cm 2 More than 2.80kN / cm 2 is less than. C: Compressive load of negative electrode material is 1.90 kN / cm 2 More than 2.30kN / cm 2 is less than. D: Compressive load of negative electrode material is 1.90 kN / cm 2 is less than. (electrode orientation) A: The electrode orientation value is 300 or less. B: The electrode orientation value is greater than 300 and less than or equal to 400. C: The electrode orientation value is greater than 400 and less than or equal to 999. D: The electrode orientation value is greater than 999.

[0183] The evaluation criteria for each value representing the performance of the lithium-ion secondary battery in Table 3 are as follows: (discharge capacity) A: The discharge capacity of the lithium-ion secondary battery is 350Ah / kg or more. B: The discharge capacity of the lithium-ion secondary battery is greater than 340 Ah / kg and less than 350 Ah / kg. C: The discharge capacity of the lithium-ion secondary battery is greater than 330 Ah / kg and less than or equal to 340 Ah / kg. D: The discharge capacity of the lithium-ion secondary battery is 330 Ah / kg or less. (Li precipitation resistance) A: The lithium ion secondary battery has a Li deposition tolerance of 30% or more. B: The Li deposition tolerance of the lithium ion secondary battery is 25% or more and less than 30%. C: The Li deposition tolerance of the lithium ion secondary battery is 20% or more and less than 25%. D: The Li deposition tolerance of the lithium ion secondary battery is less than 20%.

[0184] (Evaluation value of input characteristics) A: The evaluation value of the input characteristics is 30 or more. B: The evaluation value of the input characteristics is 25 or more and less than 30. C: The evaluation value of the input characteristics is 20 or more and less than 25. D: The evaluation value of the input characteristics is less than 20.

[0185] In Table 3, it was confirmed that a high evaluation value of the input characteristics and a high degree of graphitization tend to result in excellent discharge capacity and Li deposition resistance of the lithium ion secondary battery.

[0186] The disclosure of PCT / JP2021 / 003761, filed February 2, 2021, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. 1.7 g / cm in autograph measurement ３ The compressive load required to compact the ２ ), x≧2.0, and when y (μm) is the particle size at which the cumulative total from the small diameter side in a volume-based particle size distribution measured by a laser diffraction method is 50%, 5.0≦y≦20.0, the above x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more: The negative electrode material for lithium ion secondary batteries is used to form a negative electrode, which is pressed at 0.8 t / cm. X-ray diffraction measurement of the negative electrode reveals that the ratio I 002 / I 110 of the peak intensity (I 002 ) of the 002 diffraction line to the peak intensity (I 110 ) of the 110 diffraction line is 350 or less. 11.3x-0.66y+1.4≧14.5...(1)

2. When the compressive load required to compact to 1.7 g / cm 3 in autograph measurement is x (kN / cm 2 ), x≧2.0; when the particle size when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction is 50% is y (μm), 5.0≦y≦20.0; the aforementioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more; The negative electrode material for lithium ion secondary batteries is such that the surface of the graphite particles is not subjected to a treatment of coating with low-crystalline carbon.

3. Graphite particles in which the compressive load required to compact to 1.7 g / cm 3 in autograph measurement is x (kN / cm 2 ), where x≧2.0, and the particle size when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction is 50% is y (μm), where 5.0≦y≦20.0, and the aforementioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more: The negative electrode material for a lithium ion secondary battery, wherein the particle size of the graphite particles is 0.1 μm to 7.0 μm when the cumulative total from the small diameter side in a volume-based particle size distribution measured by a laser diffraction method is 10%.

4. When the compressive load required to compact to 1.7 g / cm 3 in autograph measurement is x (kN / cm 2 ), x≧2.0; when the particle size when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction method is 50% is y (μm), 5.0≦y≦20.0; the aforementioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more; The graphite particles have a zero tap density of 0.3 g / cm 3 to 0.6 g / cm 3 .

5. Graphite particles in which the compressive load required to compact to 1.7 g / cm 3 in autograph measurement is x (kN / cm 2 ), where x≧2.0, and the particle size when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction is 50% is y (μm), where 5.0≦y≦20.0, and the aforementioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more: The graphite particles have a 30 tap density of 0.4 g / cm 3 to 0.7 g / cm 3 .

6. Graphite particles in which the compressive load required to compact to 1.7 g / cm 3 in autograph measurement is x (kN / cm 2 ), where x≧2.0, and the particle size when the cumulative total from the small diameter side in the volume-based particle size distribution measured by laser diffraction is 50% is y (μm), where 5.0≦y≦20.0, and the aforementioned x and y satisfy the following formula (1), and the graphitization degree is 90.0% or more: The graphite particles have a 250 tap density of 0.7 g / cm 3 to 1.1 g / cm 3 .

7. 7. The negative electrode material for lithium ion secondary batteries according to claim 1, wherein the graphite particles are graphite particles such that, when a negative electrode material layer is formed using the negative electrode material for lithium ion secondary batteries, the ratio L / T of a tortuous path length L (μm), which is a distance from one surface to the other surface in a thickness direction through voids inside the negative electrode material layer, to a thickness T (μm) of the negative electrode material layer, is 1.7 or less.

8. 1300 cm measured by Raman spectroscopy －１ ~1400cm －１ Peak intensity (I Ｄ ) and 1580 cm －１ ~1620cm －１ Peak intensity (I Ｇ ) and I Ｄ / I Ｇ The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 7, wherein the R value of the graphite particles is 0.10 to 0.

40.

9. the graphite particles are subjected to a treatment of coating surfaces with low-crystalline carbon, 1300 cm measured by Raman spectroscopy －１ ~1400cm －１ Peak intensity (I Ｄ ) and 1580 cm －１ ~1620cm －１ Peak intensity (I Ｇ ) and I Ｄ / I Ｇ The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 8, wherein the R value of the graphite particles is 0.20 to 0.

60.

10. The specific surface area of ​​the graphite particles determined by nitrogen adsorption measurement at 77 K is 0.2 m ２ / g to 6.0m ２ The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 9, wherein:

11. The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 10, wherein the particle size distribution D90 / D10 of the graphite particles is 3.0 to 7.

0.

12. The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 11, wherein the graphite particles include composite particles in which a plurality of graphite particles are aggregated or bonded together.

13. A negative electrode material composition for a lithium ion secondary battery, comprising the negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 12, a binder, and a solvent.

14. A negative electrode for a lithium ion secondary battery, comprising: a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 12; and a current collector.

15. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 14, a positive electrode, and an electrolyte solution.

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