Anode material for lithium-ion secondary batteries, anode for lithium-ion secondary batteries, and lithium-ion secondary batteries

Abstract

A negative electrode material for a lithium ion secondary battery, said negative electrode material including graphite particles, wherein the graphite particles satisfy conditions in which, with regard to an R value which is the intensity ratio Id / Ig of the intensity Ig of the maximum peak in the range 1580 cm–1 to 1620 cm–1 and the intensity Id of the maximum peak in the range 1300 cm–1 to 1400 cm–1 in a Raman spectrum obtained through Raman spectroscopy, the percentage of particles for which R≥0.2 is greater than or equal to 10% by number, and the average value of the half-value width of Id in the R-value top 10 spectrum is less than or equal to 60 cm–1.

Description

[Technical Field]

[0001] This disclosure relates to a negative electrode material for lithium-ion secondary batteries, a negative electrode for lithium-ion secondary batteries, and lithium-ion secondary batteries. [Background technology]

[0002] Lithium-ion rechargeable batteries have long been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smartphones, and tablet PCs, taking advantage of their characteristics of being small, lightweight, and having high energy density. In recent years, against the backdrop of environmental problems such as global warming caused by CO2 emissions, electric vehicles such as clean electric vehicles (EVs) that run solely on batteries, hybrid electric vehicles (HEVs) that combine gasoline engines and batteries, and plug-in hybrid electric vehicles (PHEVs) have become popular, and development of lithium-ion rechargeable batteries (automotive lithium-ion rechargeable batteries) for use in these vehicles is progressing.

[0003] The performance of the negative electrode material significantly influences the input characteristics of lithium-ion secondary batteries. 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 spheroidal natural graphite (spheroidal natural graphite, which is spheroidized scaly natural graphite) have been proposed as materials to obtain 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 comprising a plurality of flattened graphite particles aggregated or bonded together so that their orientation planes are non-parallel, and spherical graphite particles. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2015 / 147012 [Overview of the project] [Problems that the invention aims to solve]

[0006] The rapid growth of the EV market is driving increased demand for negative electrode materials for lithium-ion secondary batteries. In particular, from the perspective of improving battery performance, it is desirable to reduce the irreversible capacity during the initial charge and discharge phases to increase initial efficiency. There is a strong need for rapid charging and other features to enhance convenience, and high-rate charging is required for negative electrode active materials.

[0007] A challenge during high-rate charging is that, due to IR drop when high current is applied, some lithium ions cannot be inserted between the graphite layers, and lithium metal tends to precipitate on the surface of the graphite particles. If lithium metal precipitates in a needle-like shape, it can pierce the separator, causing an internal short circuit and potentially leading to thermal runaway.

[0008] For the reasons stated above, a negative electrode material for lithium-ion secondary batteries is desirable that can suppress the deposition of lithium metal and enable the manufacture of lithium-ion secondary batteries with excellent lithium (Li) deposition resistance.

[0009] The object of this disclosure is to provide a negative electrode material for lithium-ion secondary batteries that can manufacture lithium-ion secondary batteries that have excellent initial efficiency, can suppress lithium metal deposition, and have excellent resistance to Li deposition, as well as a negative electrode for lithium-ion secondary batteries containing the same, and a lithium-ion secondary battery. [Means for solving the problem]

[0010] The means for solving the above problems include the following embodiments. <1> Contains graphite particles, The aforementioned graphite particles, in the Raman spectral spectrum obtained by Raman spectroscopy, showed a value of 1580 cm⁻¹. -1 ~1620cm -1 The maximum peak intensity Ig within the range, and 1300cm -1 ~1400cm -1Regarding the R value which is the intensity ratio Id / Ig of the intensity of the maximum peak within the range of 1580 cm -1 A negative electrode material for a lithium ion secondary battery that satisfies the following. <2> Containing graphite particles, In the Raman spectrum obtained by Raman spectroscopy measurement, the graphite particles are within the range of 1580 cm -1 ~1620 cm -1 Regarding the R value which is the intensity ratio Id / Ig of the intensity of the maximum peak Ig within the range and the intensity of the maximum peak Id within the range of 1300 cm -1 ~1400 cm -1 A negative electrode material for a lithium ion secondary battery in which the proportion of particles with R≥0.2 is 10% or more by number, and the starting temperature T of the mass reduction reaction due to oxidation of the graphite particles obtained by TG-DTA measurement in a dry air atmosphere satisfies 700°C or higher. <3> The graphite particles contain artificial graphite particles, and the negative electrode material for a lithium ion secondary battery according to <1> or <2>. <4> The artificial graphite particles are particles obtained by graphitizing a mixture containing a graphitizable aggregate and a graphitizable binder, and the binder contains a water-soluble or water-absorbent polymer compound. The negative electrode material for a lithium ion secondary battery according to <3>. <5> The circularity of the graphite particles is 93% or less, and the negative electrode material for a lithium ion secondary battery according to any one of <1> to <4>. <6> The oil absorption amount of the graphite particles is 40 mL / 100 g to 70 mL / 100 g, and the negative electrode material for a lithium ion secondary battery according to any one of <1> to <5>. <7> The proportion of particles with R≥0.2 in the graphite particles is 80% or less by number, and the negative electrode material for a lithium ion secondary battery according to any one of <1> to <6>. <8> The surface of the graphite particles has not been treated with low-crystalline carbon coating, and the negative electrode material for a lithium ion secondary battery according to any one of <1> to <7>. <9> <1> ~ <8> 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 described in any one of the above, and a current collector. <10> <9> A lithium-ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, as described in [reference]. [Effects of the Invention]

[0011] This disclosure provides a negative electrode material for lithium-ion secondary batteries that can be used to manufacture lithium-ion secondary batteries that have excellent initial efficiency, can suppress lithium metal deposition, and have excellent resistance to Li deposition, as well as a negative electrode for lithium-ion secondary batteries containing the same, and a lithium-ion secondary battery. [Modes for carrying out the invention]

[0012] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the present invention.

[0013] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of such process is achieved. In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance 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 types of substances present in the composition, unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when the region in which the layer or film exists is observed, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable.

[0014] In this disclosure, the particle size distribution of the negative electrode material can be measured by a laser diffraction particle size distribution analyzer. The average particle size is the particle size (D50) at which the integration from the smallest diameter side in the volume-based particle size distribution is 50%. D90 is the particle size at which the integration from the smallest diameter side in the volume-based particle size distribution is 90%, and D10 is the particle size at which the integration from the smallest diameter side in the volume-based particle size distribution is 10%.

[0015] ≪Anode material for lithium-ion secondary batteries≫ The anode material for lithium-ion secondary batteries of this disclosure will be described below, starting with the anode material for lithium-ion secondary batteries of the first embodiment and the anode material for lithium-ion secondary batteries of the second embodiment. However, 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 this disclosure (hereinafter also simply referred to as the negative electrode material) contains graphite particles, and the graphite particles have a Raman spectral spectrum of 1580 cm² obtained by Raman spectroscopy measurement. -1 ~1620cm -1The maximum peak intensity Ig within the range, and 1300cm -1 ~1400cm -1 For the R value, which is the intensity ratio Id / Ig of the maximum peak intensity Id within the range, the proportion of particles with R ≥ 0.2 (hereinafter also referred to as "proportion of R ≥ 0.2") is 10 percent or more, and the average half-width of Id in the top 10 R-value spectra is 60 cm². -1 The following conditions must be met.

[0017] By using the negative electrode material of the first embodiment, it is possible to manufacture a lithium-ion secondary battery that has excellent initial efficiency, suppresses the deposition of lithium metal, and has excellent resistance to lithium (Li) deposition. The reason for this is presumed to be, for example, as follows.

[0018] In Raman spectroscopy measurements, 1580 cm⁻¹ -1 ~1620cm -1 Peak intensity Ig within this range is identified as a peak corresponding to the graphite crystal structure, for example, 1580 cm². -1 This is a peak that appears in the vicinity. 1300cm -1 ~1400cm -1 Peak intensity Id in the range is identified as a peak corresponding to the amorphous structure of carbon, for example, 1360 cm⁻¹. -1 This is a peak that appears in the vicinity.

[0019] The graphite particles contained in the negative electrode material satisfy the requirement that a certain proportion of them have an R value (intensity ratio Id / Ig) of 0.2 or higher, meaning that the surface crystallinity of the graphite particles is relatively low. This low surface crystallinity makes it possible to improve Li deposition resistance without compromising discharge capacity in lithium-ion secondary batteries using the negative electrode material of this embodiment.

[0020] Graphite particles have an average half-width of Id in the top 10 R-value spectra of 60 cm². -1The following conditions are met: In other words, for graphite particles with low surface crystallinity contained in the negative electrode material, the full width at half maximum (FWHM) of the peak identified as corresponding to the amorphous structure of carbon is relatively narrow. It is presumed that this relatively narrow FWHM suppresses the occurrence of carbon defects, and thus suppresses the irreversible increase in capacity during the first charge due to the presence of various functional groups in the carbon defects. As a result, lithium-ion secondary batteries using the negative electrode material of this embodiment tend to have excellent initial efficiency.

[0021] The graphite particles contained in the negative electrode material have an R value (strength ratio Id / Ig) where R ≥ 0.2 is preferably 10% or more, and more preferably 15% or more, and more preferably 20% or more, from the viewpoint of Li deposition resistance in lithium-ion secondary batteries. Using graphite particles with an R ≥ 0.2 ratio of 10% or more tends to result in good input characteristics for lithium-ion secondary batteries.

[0022] Regarding the R value, which is the intensity ratio Id / Ig of graphite particles, from the viewpoint of the initial efficiency of lithium-ion secondary batteries, the percentage of R ≥ 0.2 may be 80 percent or less, or 70 percent or less.

[0023] The graphite particles contained in the negative electrode material have an average half-width of Id in the top 10 R-value spectra of 60 cm². -1 The following conditions must be met, and from the perspective of the initial efficiency of lithium-ion secondary batteries, 55cm -1 Preferably, the following conditions are met, and 50cm -1 It is more preferable that the following conditions be met: The average half-width of Id in the top 10 R-value spectra is 60 cm². -1 Using graphite particles that satisfy the following conditions tends to improve the storage characteristics of lithium-ion secondary batteries.

[0024] Graphite particles have an average half-width of Id in the top 10 R-value spectra of 20 cm². -1 The above conditions may also be met, and 30cm -1 It is acceptable if the above conditions are met.

[0025] In this disclosure, the R value (Id / Ig), the percentage of R ≥ 0.2, and the mean value of the full width at half maximum of Id can be measured by the following method.

[0026] The R-value of graphite particles may also be determined by measuring the Raman spectrum using a Raman spectroscopy device (e.g., XploRA PLUS, Horiba, Ltd.) under the following conditions. In this case, the arithmetic mean of the 400 particles measured is taken as the R-value. - Raman spectroscopy measurement conditions - • Laser wavelength: 532nm • Laser intensity: 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 a single particle is counted: 2 • Number of particles measured: 400 particles

[0027] By classifying the R values ​​of the 400 particles measured as described above, the percentage of particles with R ≥ 0.2 and the percentage of particles with R < 0.2 can be determined.

[0028] As described above, the R-values ​​of the 400 particles were measured, and the full width at half maximum (FWHM) of Id was determined for the top 10 spectra with the highest R-values. The arithmetic mean of these values ​​was taken as the average of the FWHMs of Id for the top 10 spectra with the highest R-values.

[0029] The graphite particles contained in the negative electrode material of this disclosure preferably include artificial graphite particles from the viewpoint of resistance to Li deposition in lithium-ion secondary batteries. The artificial graphite particles are preferably particles obtained by graphitizing a mixture containing a graphitizable aggregate and a graphitizable binder. The proportion of R≧0.2 is easily satisfied at 10 percent or more, and from the viewpoint of resistance to Li deposition in lithium-ion secondary batteries, the graphitizable binder preferably contains a water-soluble or water-absorbing polymer compound, and more preferably contains an aqueous binder containing a water-soluble or water-absorbing polymer compound.

[0030] The water-soluble or water-absorbing polymeric compound is not particularly limited and may include, for example, at least one selected from the group consisting of starch, amylose, amylopectin, polyacrylic acid, carboxymethylcellulose, polyvinyl alcohol, and water-soluble protein.

[0031] By using artificial graphite particles as graphite particles, using a binder containing a water-soluble or water-absorbing polymer compound when producing artificial graphite particles by graphitizing a mixture containing graphitizable aggregate and a graphitizable binder, and not applying a treatment to the surface of the graphite particles to coat them with low-crystalline carbon, it becomes easier to obtain a negative electrode material that satisfies the aforementioned numerical conditions for the R value and the average value of the half-width of Id.

[0032] (Average particle size) The particle size when the cumulative sum from the smaller diameter side in the volume-based particle size distribution measured by laser diffraction of graphite particles reaches 50% (hereinafter also referred to as "average particle size" or "D50") may be between 5.0 μm and 20.0 μm.

[0033] The average particle size of the graphite particles may be 18.0 μm or less, or 17.0 μm or less, from the viewpoint of further improving resistance to Li precipitation. The average particle size of the graphite particles may be 8.0 μm or larger, or 10.0 μm or larger.

[0034] The average particle size of graphite particles can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD3100, Shimadzu Corporation).

[0035] Methods for measuring the average particle size of graphite particles contained in the negative electrode include preparing a sample electrode, embedding it in epoxy resin, mirror-polishing it, and observing the electrode cross-section with a scanning electron microscope (e.g., VE-7800, manufactured by Keyence Corporation), or preparing an electrode cross-section using an ion milling device (e.g., E-3500, manufactured by Hitachi High-Technologies Corporation) and measuring it with a scanning electron microscope (e.g., VE-7800, manufactured by Keyence Corporation). In this case, the average particle size is the median value of 100 arbitrarily selected particle sizes.

[0036] (D10) The D10 of the graphite particles may be 0.1 μm to 10.0 μm, 0.5 μm to 8.0 μm, more preferably 1.0 μm to 7.0 μm, and particularly preferably 3.0 μm to 7.0 μm.

[0037] The D10 of graphite particles can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD3100, Shimadzu Corporation).

[0038] (Particle size distribution D90 / D10) The particle size distribution D90 / D10 of the graphite particles is not particularly limited and may be 2.0 to 7.0 or 2.5 to 6.0. The particle size distribution D90 / D10 can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD3100, Shimadzu Corporation).

[0039] Methods for measuring the particle size distribution D90 / D10 of graphite particles contained in the negative electrode include preparing a sample electrode, embedding it in epoxy resin, mirror-polishing it, and observing the electrode cross-section with a scanning electron microscope (e.g., VE-7800, manufactured by Keyence Corporation), or preparing an electrode cross-section using an ion milling device (e.g., E-3500, manufactured by Hitachi High-Technologies Corporation) and measuring it with a scanning electron microscope (e.g., VE-7800, manufactured by Keyence Corporation). In this case, the particle size distribution D90 / D10 can be determined by the following method. (1) Use a binarization method or similar to determine the area Sn of the projected particle (where n is the particle-specific number assigned to the selected particle). (2) Assuming the particle is an ideal sphere, we find the equivalent diameter Ln = √Sn / π from the area Sn. (3) From the equivalent diameter Ln, the volume of the sphere Vn = (4 / 3)π(Ln) 3 We seek. (4) Repeat steps (1) to (3) for the 100 selected particles. (5) The distribution curve, with the vertical axis representing the cumulative percentage of the volume of 100 units and the horizontal axis representing the particle size, can be used to determine the 10% diameter (D10) at the point where it intersects with the 10% horizontal axis, and the 90% diameter (D90) at the point where it intersects with the 90% horizontal axis, thereby allowing us to calculate D90 / D10.

[0040] (Standard deviation of particle size distribution) The standard deviation of the particle size distribution of graphite particles may be between 0.18 and 0.40, or between 0.25 and 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 with the horizontal axis representing particle size on a logarithmic scale and the vertical axis representing particle quantity (%).

[0041] (I 002 / I 110 ) A negative electrode is formed using the negative electrode material disclosed herein, and from the viewpoint of input characteristics in a lithium-ion secondary battery, the peak intensity of the 002 diffraction line obtained when the negative electrode pressed at 0.8 t / cm is measured by X-ray diffraction using CuKα rays is (I 002 ) and the peak intensity of the 110 diffraction line (I 110 I is the ratio of ) 002 / I 110 It may be 700 or less, 600 or less, or 500 or less. I 002 / I 110 The lower limit is not particularly limited and may be 200 or higher. I 002 / I 110 This can be determined by the method described in the examples. 002 / I 110 When measuring, the components other than graphite particles, their ratios, and the manufacturing conditions for the negative electrode are the same as those described in the measurement method for electrode orientation in the examples.

[0042] (250 taps density) The 250-tap density of graphite particles is 0.80 g / cm³, which is considered to be an ideal value for improving input / output characteristics and energy density in lithium-ion secondary batteries. 3 ~1.20g / cm 3 Preferably, it is 0.90 g / cm³. 3 ~1.10g / cm 3 It is preferable that it be so.

[0043] The density of graphite particles after 250 taps can be calculated, for example, as follows: Capacity 150cm 3 A flat-bottomed test tube with graduated markings (for example, KRS-406, manufactured by Kuramochi Scientific Instruments Co., Ltd.) contains 100 cm³ of graphite particle powder. 3 The sample is then added, the graduated flat-bottomed test tube is stoppered, and the density value obtained from the mass and volume of the sample powder after dropping the graduated flat-bottomed test tube from a height of 5 cm 250 times is defined as the 250-tap density.

[0044] (specific surface area) The specific surface area determined by nitrogen adsorption measurement of graphite particles at 77K is not particularly limited. For example, from the viewpoint of improving rapid charge / discharge performance and suppressing electrolyte decomposition, the specific surface area of ​​graphite particles is 0.2 m². 2 / g~6.0m 2 It is preferable that it be / g, and 1.5m 2 / g~5.0m 2 It is more preferable that it be / g, 2.0m 2 / g~4.0m 2 It is even more preferable that it be / g.

[0045] The specific surface area obtained from nitrogen adsorption measurements at 77K can be determined using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurements at 77K. Specifically, the specific surface area can be determined by the method described in the examples.

[0046] The specific surface area of ​​graphite particles can be adjusted by controlling the particle size distribution, particle structure, and other factors. The specific surface area of ​​graphite particles may be adjusted by coating the graphite particles with low-crystallinity carbon or the like, or by adjusting the amount of water-based binder used when a water-based binder is used as the binder that can be graphitized. When it is desired to make the particle size finer, the specific surface area will increase significantly due to the irregularities created by grinding, but the specific surface area can be adjusted by coating the particles to fill in the irregularities with the coating material and make the surface smooth.

[0047] (Circularity) From the viewpoint of resistance to Li deposition in lithium-ion secondary batteries, the circularity of the graphite particles is preferably 95% or less, more preferably 93% or less, and even more preferably 92% or less. The circularity of the graphite particles may be 85% or higher, or 88% or higher.

[0048] The circularity of graphite particles can be measured using a wet flow-type particle size and shape analyzer, and the circularity based on the number of particles at a cumulative 50% (so-called average circularity) should be used as the circularity.

[0049] (Oil absorption amount) The oil absorption capacity of graphite particles is preferably 40 mL / 100g to 70 mL / 100g, and more preferably 45 mL / 100g to 60 mL / 100g. The amount of oil absorbed by graphite particles is an indicator of the amount of pores present inside and on the surface of the particles, as well as the amount of voids between particles. When graphite particles absorb 60 mL / 100 g or less of oil, it is considered that the number of pores within and on the particle surface is small, resulting in a sufficiently small contact area with the electrolyte. In addition, because the interface is small, it is possible to reduce the amount of binder used when manufacturing the negative electrode, which tends to reduce electrical resistance and improve battery performance. Furthermore, because there are fewer pores, it is possible to reduce the amount of solvent used when drying the electrodes, which has advantages in terms of cost and environmental impact on the manufacturing line, such as reducing the amount of equipment and electricity used for drying. When graphite particles absorb 40 mL / 100 g or more of oil, it tends to suppress the increase in slurry viscosity that occurs when mixing with binders, etc., which can occur when the voids between particles are too small. In addition, the binder tends to spread more easily, making mixing easier. Furthermore, it becomes easier to secure voids between particles for lithium ions to move.

[0050] In this disclosure, the amount of oil absorbed by graphite particles is measured using the method described in JIS K6217-4:2017 "Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption," but using linseed oil (for example, manufactured by Kanto Chemical Co., Ltd.) instead of dibutyl phthalate (DBP) as the reagent liquid. Specifically, linseed oil is titrated onto the target powder using a constant-speed burette, and the change in viscosity characteristics is measured using a torque detector. The amount of linseed oil added per unit mass of the target powder corresponding to 70% of the maximum torque generated is defined as the oil absorption amount (mL / 100g). As a measuring instrument, for example, an absorption amount measuring device (product name: S-500) from Asahi Research Institute Co., Ltd. can be used.

[0051] The graphite particles may or may not be treated with a coating of low-crystalline carbon on their surface. When graphite particles are coated with low-crystallinity carbon, the charging characteristics at low temperatures tend to improve when used to construct a lithium-ion secondary battery. On the other hand, if the surface of the graphite particles is not coated with low-crystallinity carbon, cracks and peeling may occur in the graphite particles during pressing when the electrodes are manufactured, which tends to suppress the decomposition activity of the electrolyte and the resulting decrease in storage characteristics. This also has the advantage of increasing the degree of freedom in manufacturing conditions. Furthermore, in the negative electrode material of this disclosure, even if low-crystallinity carbon is not arranged on the surface, it is possible to suppress lithium metal deposition during charging. When graphite particles are artificial graphite particles graphitized using a graphitizable binder that includes the aforementioned aqueous binder (for example, an aqueous binder containing compounds that do not contain aromatic rings, such as starch), compounds that do not contain aromatic rings, such as starch, are less likely to change into graphite. As a result, the surface crystallinity of the graphite particles tends to be low, and good charging characteristics at low temperatures tend to be obtained even without the treatment of coating the surface of the graphite particles with low-crystallinity carbon. Thus, by manufacturing artificial graphite particles using the aforementioned aqueous binder, it is possible to achieve both process simplification and improved charging characteristics.

[0052] The R value of the graphite particles may be 0.10 to 0.40 or 0.15 to 0.30. In particular, it is preferable that the surface is not coated with low-crystallinity carbon and that the R value is 0.10 to 0.40, and more preferably 0.15 to 0.30.

[0053] In this disclosure, the average interplanar spacing (d) determined by X-ray diffraction is used. 002 ) A carbon material with a wavelength of less than 0.340 nm is defined as graphite. In this disclosure, as described later, particles in which low-crystallinity carbon is arranged on at least a portion of the surface of the graphite particles 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 the value is to this, the more advanced the graphitization is. From the viewpoint of the initial charge-discharge efficiency and energy density of lithium-ion secondary batteries, the average interplanar spacing (d 002 The wavelength 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 perspective, the average interplanar spacing of graphite particles (d 002 The wavelength is preferably 0.3354nm to 0.33600nm, more preferably 0.3354nm to 0.33596nm, and even more preferably 0.3354nm to 0.33592nm.

[0054] Average interplanar spacing of graphite particles (d 002 The mean interplanar spacing (d) can be calculated using Bragg's formula, based on the diffraction peaks corresponding to the carbon O02 plane that appear around the diffraction angle 2θ of 24° to 27° in the diffraction profile obtained by irradiating the sample with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer. 002 ) can be measured under the following conditions. Radiation source: CuKα ray (wavelength=0.15418nm) Output: 40kV, 20mA Sampling width: 0.010° Scanning range: 10°~35° Scan speed: 0.5° / min

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

[0056] ≪Particle structure of graphite particles≫ The graphite particles may include a state in which multiple graphite particles are aggregated or bound together (composite particles), and may also include composite particles having a structure in which multiple flattened graphite particles are stacked (hereinafter also referred to as specific composite particles). Specific composite particles, compared to composite particles with a structure in which the main surfaces of multiple flattened graphite particles are oriented in random directions, can reduce the contact area with the electrolyte inside the particles, and are thought to effectively suppress the decomposition of the electrolyte. Furthermore, even when pressurized during the fabrication of the negative electrode, deformation or breakage of the particles is less likely to occur, and the path of the electrolyte between particles is more easily ensured. In addition, the electrolyte located inside composite particles with a structure in which the main surfaces of multiple flattened graphite particles are oriented in random directions has a complex and slow migration and diffusion path. For this reason, even with active materials that have many particle interfaces, diffusion problems occur, and it is thought that high input / output performance cannot be achieved. This tendency is particularly pronounced under input / output conditions with a high C rate.

[0057] Flattened graphite particles contained in specific composite particles refer to non-spherical graphite particles that exhibit anisotropy in shape. Examples of flattened graphite particles include those with scaly, flakey, or partially lumpy shapes. A composite particle refers to a particle formed by the aggregation or bonding of primary particles. Specifically, a particular composite particle has a structure in which multiple flattened graphite particles overlap and aggregate or bond together with their main surfaces facing each other. Therefore, multiple flattened graphite particles overlap in a nearly parallel manner, forming a composite particle. Whether or not flattened graphite particles are stacked can be confirmed by microscopic observation.

[0058] The state of multiple flattened graphite particles being aggregated or bonded refers to a state in which two or more flattened graphite particles are aggregated or bonded together. Bonding refers to a state in which the particles are chemically bonded to each other, either directly or through a carbon substance. Aggregation refers to a state in which the particles are not chemically bonded to each other, but maintain a collective shape due to their shape or other factors. Flattened graphite particles may be aggregated or bonded via a carbon material. Examples of carbon materials include graphite and carbides obtained by graphitizing a graphitizable binder. From the viewpoint of mechanical strength, it is preferable that two or more flattened graphite particles are bonded via a carbon material. Whether or not flattened graphite particles are aggregated or bonded can be confirmed, for example, by observation with a scanning electron microscope.

[0059] To reduce the proportion of composite particles, which have a structure in which the main faces of multiple flattened graphite particles are oriented in random directions, the amount of binder used should be as small as possible. No composite particles are formed when there is no binder. On the other hand, if there is an excess of binder, more primary particles are formed around the binder clumps, that is, aggregate intermediates with multiple primary particles coordinated to them are formed, and the primary particles coordinated to these intermediates tend to face each other in a non-equilibrium state.

[0060] To reduce clumping caused by uneven distribution of binders such as tar and pitch, a dispersant may be used. Using a dispersant makes it easier to uniformly disperse the binder, and tends to reduce binder clumping. This is thought to reduce the proportion of composite particles in which the main surfaces of multiple flattened graphite particles are oriented in random directions. In addition, the function of the binder is improved, block moldability is enhanced, and the binder blending ratio can be reduced. Examples of dispersants include those that can be used in step (b) described later.

[0061] The flattened graphite particles and their raw materials are not particularly limited and include artificial graphite, scaly natural graphite, flakey natural graphite, coke, resin, etc. Among these, artificial graphite obtained by graphitizing coke is preferred from the viewpoint of being difficult to deform and having a low specific surface area.

[0062] When graphite particles contain specific composite particles, it is acceptable if all of the graphite particles are specific composite particles, or if some of them are graphite particles other than specific composite particles.

[0063] [Second Embodiment] The negative electrode material for a lithium-ion secondary battery according to the second embodiment of this disclosure (hereinafter also simply referred to as the negative electrode material) contains graphite particles, and the graphite particles have a Raman spectral spectrum of 1580 cm² obtained by Raman spectroscopy measurement. -1 ~1620cm -1 The maximum peak intensity Ig within the range, and 1300cm -1 ~1400cm -1 The R value, which is the intensity ratio Id / Ig of the maximum peak intensity Id within the range, satisfies the condition that the proportion of particles with R ≥ 0.2 is 10 or more, and the starting temperature T of the mass reduction reaction due to oxidation of the graphite particles, obtained by TG-DTA measurement in a dry air atmosphere, is 700°C or higher.

[0064] By using the negative electrode material of the second embodiment, it is possible to manufacture a lithium-ion secondary battery that has excellent initial efficiency, suppresses the deposition of lithium metal, and has excellent resistance to lithium (Li) deposition. The reason for this is presumed to be, for example, as follows.

[0065] In the negative electrode material of this embodiment, as in the negative electrode material of the first embodiment, the proportion of R values, which are the strength ratio Id / Ig, that are 0.2 or higher is relatively high, meaning that the surface crystallinity of the graphite particles is relatively low. By having low surface crystallinity, lithium-ion secondary batteries using the negative electrode material of this embodiment can improve Li deposition resistance without impairing discharge capacity.

[0066] The graphite particles satisfy the requirement that the onset temperature T of the mass loss reaction due to oxidation of the graphite particles, obtained by TG-DTA measurement (differential thermal-thermogravimetric simultaneous measurement) in a dry air atmosphere, is 700°C or higher. Specifically, using a TG-DTA measuring device, the onset temperature of the mass loss reaction due to oxidation of graphite particles (for example, the temperature at which DTA > 0) is 700°C or higher, as determined from the TG curve and DTA curve. As a result, lithium-ion secondary batteries using this negative electrode material tend to have excellent initial efficiency and suppress lithium metal deposition.

[0067] The starting temperature for the aforementioned mass reduction reaction may be 700°C to 800°C, or 700°C to 750°C.

[0068] The onset temperature of the aforementioned mass reduction reaction tends to be higher when the graphite particles include artificial graphite particles. On the other hand, the onset temperature of the aforementioned mass reduction reaction tends to be lower when the graphite particles are natural graphite particles, or when the surface of the graphite particles is coated with low-crystallinity carbon, etc.

[0069] 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.

[0070] ≪Manufacturing method for negative electrode material for lithium-ion secondary batteries≫ The method for manufacturing a lithium-ion secondary battery anode material according to the present disclosure includes a step of graphitizing coke. More specifically, from the viewpoint of improving handling properties in the graphitization process and improving the cycle characteristics of the lithium-ion secondary battery, the method for manufacturing a lithium-ion secondary battery anode material according to the present disclosure preferably includes the following steps (a) to (d). (a) A step of obtaining a mixture containing graphitizable aggregate (coke) and graphitizable binder, (b) A step of molding the mixture to obtain a molded product, (c) A step of graphitizing the molded product to obtain a graphitized product, (d) A step of crushing the graphitized material to obtain a pulverized product. Furthermore, each step of the above method may be performed consecutively or not. Each step of the above method may be performed in the same location or in different locations.

[0071] The type of coke used in the above manufacturing method is not particularly limited and includes 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.

[0072] The method for obtaining coke particles is not particularly limited and can be carried out by known methods. The particle size of the coke particles is not particularly limited and can be selected considering the desired particle size and particle structure of the graphite particles. To obtain particles with a lower specific surface area, it is preferable to crush the coke in its green state. Such particles tend to have fewer voids and cracks due to cleavage, and the compressive load of the graphite particles tends to be higher.

[0073] 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 obtain a molded product. In the manufacturing method of the present disclosure, from the viewpoint of resistance to Li deposition in lithium-ion secondary batteries, the graphitizable binder preferably contains a water-soluble or water-absorbing polymer compound, and more preferably contains an aqueous binder containing a water-soluble or water-absorbing polymer compound. The use of the aforementioned aqueous binder improves the strength of the molded product, thereby improving handling during subsequent graphitization treatments. Generally, when the strength of a molded product is increased, the graphitized material after graphitization treatment tends to become more difficult to crush. However, in the above manufacturing method, the use of the aforementioned aqueous binder improves the strength of the molded product while allowing for easy crushing of the graphitized material.

[0074] The reason why the above manufacturing method allows for easy pulverization of graphite while improving the strength of the molded product is presumed to be as follows. However, this disclosure is not limited to the following presumption.

[0075] In the above manufacturing method, by using an aqueous binder containing a water-soluble or water-absorbing polymer compound, the aggregate is incorporated into the binder, which swells with water. As a result, the surface of the graphitizable aggregate becomes slippery during the molding of the mixture, promoting the arrangement of the aggregate and reducing voids. Consequently, the density and strength of the molded product tend to improve. Furthermore, water not incorporated into the binder fills the gaps between the aggregates, causing liquid crosslinking to occur, thus improving the strength of the molded product.

[0076] In the above manufacturing method, the molded product is heat-treated by heating as needed, and then graphitized to obtain graphitized material. By using a water-based binder, water evaporates during heat treatment, graphitization, etc. Therefore, the molded product is dense before heat treatment, graphitization, etc., but the graphitized material has a lower density after graphitization. Consequently, the graphitized material can be easily crushed.

[0077] Furthermore, the above manufacturing method allows for easy pulverization of graphite, resulting in the easier acquisition of pulverized material with a small specific surface area. By using a negative electrode material containing pulverized material with a small specific surface area in the manufacture of a lithium-ion secondary battery, the contact area between the negative electrode material and the electrolyte can be reduced. This suppresses the decomposition reaction of the electrolyte, extending the battery life and resulting in a tendency for lithium-ion secondary batteries to exhibit superior cycle characteristics.

[0078] Conventionally, when using green coke, molding was difficult and the strength of the molded product was low, requiring heat treatment of the green coke to improve moldability and the strength of the molded product. On the other hand, with the above manufacturing method, even when using green coke without heat treatment, molded products with excellent moldability and high strength can be obtained. Therefore, as a graphitizable aggregate, heat-treated green coke may be used to form the molded product, or unheat-treated green coke may be used to form the molded product.

[0079] The above manufacturing method results in superior strength of the molded product, eliminating the need to pack the mixture into a graphitizing crucible or similar vessel during graphitization. In other words, there is no need to use a graphitizing crucible or similar vessel; graphitization can be performed by simply placing the molded product in the graphitizing furnace. Therefore, compared to methods using a graphitizing crucible or similar vessel, this method tends to have superior manufacturing efficiency for negative electrode materials for lithium-ion secondary batteries.

[0080] Normally, increasing the amount of graphitizable binder can increase the strength of a molded product. However, if the amount of graphitizable binder is excessive, the density of the graphitized material tends to be high, making it difficult to pulverize, and battery characteristics such as the initial charge-discharge efficiency of the negative electrode material tend to decrease. In this embodiment, it is possible to increase the strength of the molded product without increasing the amount of graphitizable binder, and the decrease in battery characteristics due to excessive binder use can also be prevented. Furthermore, by reducing the amount of binder, it becomes easier to coat the surface of the pulverized material with a hard carbon-derived coating, and the input characteristics of the lithium-ion secondary battery also tend to improve.

[0081] In step (a), a mixture containing graphitizable aggregate and graphitizable binder is obtained. The mixing may be carried out at a temperature at which the graphitizable binder softens. Specifically, if the graphitizable binder is pitch, tar, etc., the temperature may be 50°C to 300°C, and if it is a thermosetting resin, the temperature may be 20°C to 100°C. If the graphitizable binder is an aqueous binder containing a water-soluble or water-absorbing polymer compound, the mixing may be carried out at room temperature or by heating.

[0082] The mixing method is not particularly limited. For example, mixing methods using a planetary mixer, kiln mixer, huddle agitator, etc., are preferred. A kneader, which incorporates kneading, may also be used.

[0083] When the graphitizable aggregate is in particulate form, the average particle size (D50) of the graphitizable aggregate is preferably, for example, 5 μm to 40 μm, more preferably 10 μm to 30 μm, and even more preferably 10 μm to 25 μm.

[0084] The standard deviation of the particle size distribution of the graphitizable aggregate is 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 a standard deviation of 0.35 or less for the aggregate particle size distribution, the variation in aggregate particle size can be reduced, and the variation in particle size 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 manufacture 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 improve. Furthermore, by reducing the variation in aggregate particle size, the function of the binder can be suitably ensured even if the content or amount of graphitizable binder is reduced. The standard deviation of the particle size distribution is, for example, a value (volume-based) measured by laser diffraction. The lower limit of the standard deviation of the particle size distribution of graphitizable aggregate is not particularly limited; for example, it may be 0.05 or higher, or 0.10 or higher.

[0085] Methods for adjusting the average particle size of graphitizable aggregates and the standard deviation of the particle size distribution of graphitizable aggregates to the aforementioned ranges include sieving classification, wind classification, and wet classification.

[0086] The binders that can be graphitized are not particularly limited as long as they can be graphitized by the graphitization treatment. Specifically, examples include the aforementioned water-based binders, coal-based, petroleum-based, and artificial pitch and tar, thermoplastic resins, and thermosetting resins.

[0087] The graphitizable aggregate and graphitizable binder contained in the mixture may be one type or two or more types.

[0088] 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 per 100 parts by mass of graphitizable aggregate. When the binder is added to a solvent or dispersion medium and used as a solution or dispersion, the parts by mass of the solvent or dispersion medium are excluded. When the binder content is 10 parts by mass or more, it tends to function suitably as a binder for graphitizable aggregate. When the binder content is 30 parts by mass or less, a sufficient amount of fixed carbon in the mixture is secured, and the yield tends to be excellent.

[0089] The graphitizable aggregate and graphitizable binder contained in the mixture may be one type or two or more types.

[0090] The mixture may contain other components besides graphitizable aggregate and graphitizable binder. Other components include aromatic compounds, graphite, dispersants, graphitization catalysts, etc.

[0091] The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring. The aromatic compound may be a compound having an aromatic ring and a molecular weight of 500 or less, or a compound with a molecular weight of 300 or less. Aromatic compounds include naphthalene, methylnaphthalenes such as 1-methylnaphthalene and 2-methylnaphthalene, acenaphthene, biphenyl, fluorene, benzopyrene, benzoanthracene, dibenzoanthracene, diphenylene oxide, quinoline, and isoquinoline. The mixture may contain one or more aromatic compounds.

[0092] Among these, methylnaphthalene and naphthalene are preferred as aromatic compounds from the viewpoint of moldability when forming molded articles.

[0093] If the mixture contains aromatic compounds, the amount is not particularly limited. The content of aromatic compounds in the mixture is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0% by mass, based on the total amount of the mixture.

[0094] 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.

[0095] From the viewpoint of facilitating the dispersion of components in the mixture in step (b) described later, it is preferable that the mixture contains a dispersant. By including a dispersant in the mixture, variations in particle size of the pulverized material obtained by crushing the graphite can be suppressed, making it easier to obtain pulverized material with uniform particle size. As a result, the rapid charging performance of lithium-ion secondary batteries tends to improve. Furthermore, the inclusion of a dispersant in the mixture helps to reduce the amount of graphitizable binder, which can be expected to improve battery characteristics such as the initial charge-discharge efficiency of the negative electrode material.

[0096] The type of dispersant is not particularly limited. Specifically, 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 stearamide, oleamide, erucamide, methylenebisstearate, and ethylenebisstearate; 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 significantly affect the performance of the negative electrode material, are solid at room temperature and therefore easy to handle, disperse uniformly by melting at the temperature of process (a), disappear during the process up to the graphitization treatment, and are inexpensive.

[0097] If the mixture contains a dispersant, the amount is not particularly limited. For example, the dispersant content relative to the whole mixture may be 0.1% to 20% by mass, 0.5% to 10% by mass, or 0.5% to 5% by mass.

[0098] From the viewpoint of promoting the graphitization of graphitizable aggregates or binders, it is preferable that the mixture contains a graphitization catalyst. The type of graphitization catalyst is not particularly limited. Specifically, examples include substances having graphitization catalytic activity such as silicon, iron, nickel, titanium, and boron, carbides of these substances, oxides of these substances, and nitrides of these substances.

[0099] If the mixture contains a graphitization catalyst, the amount is not particularly limited. For example, the content of the graphitization catalyst relative to the whole mixture may be 0.1% to 50% by mass, 0.5% to 40% by mass, or 0.5% to 30% by mass.

[0100] In step (b), the mixture obtained in step (a) is molded to obtain a molded product. Preferably, it is molded into a predetermined shape using a single-axis press or the like. By molding in this way, it is possible to increase the amount of material packed into the graphitization furnace when graphitizing the mixture, thereby improving productivity, and to improve the effect of the graphitization catalyst.

[0101] In step (b), the method of molding the mixture is not particularly limited. Examples include a mold molding method in which the mixture is placed in a container such as a mold and pressed in a uniaxial direction; a vibration molding method in which the mixture is placed in a container such as a mold, a weight is placed on the top surface, and the metal frame is vibrated and impacted to form the mixture; and an extrusion molding method in which the mixture is pushed out from a nozzle or the like using a lateral press to form the mixture.

[0102] In step (b), the density of the resulting molded product is not particularly limited, but from the viewpoint of the productivity of the negative electrode material and the cycle characteristics of the lithium-ion secondary battery, 0.8 g / cm³ is preferred. 3 ~1.7g / cm 3 Preferably, 1.0 g / cm³ 3 ~1.5g / cm 3More preferably, 1.2 g / cm³ 3 ~1.5g / cm 3 That is even more preferable.

[0103] 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, based on 100% by mass of the total aggregate and binder (before graphitization). The lower the amount of fixed carbon in the graphitizable binder in the mixture, the higher the coke ratio in the mixture tends to be, and the better the discharge capacity of the lithium-ion secondary battery. 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, based on 100% by mass of the total aggregate and binder (before graphitization).

[0104] The molded product obtained in step (b) is preferably heat-treated before being graphitized in step (c). Heat treatment removes organic components in the mixture that do not contribute to graphitization, and tends to suppress gas generation and other issues during the graphitization process.

[0105] The temperature of the above heat treatment is not particularly limited, but it is preferably lower than the temperature of the heat treatment in step (c). For example, it may be carried out in the range of 500°C to 1000°C.

[0106] 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 allow the graphitizable components in the mixture to be graphitized. For example, a method of heat treatment in an atmosphere in which the mixture is not easily oxidized can be used. The atmosphere in which the mixture is not easily oxidized is not particularly limited and can be an inert atmosphere such as nitrogen or argon, or a vacuum.

[0107] The temperature for 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. There is no particular upper limit to the heat treatment temperature, but for example, it may be 3200°C or lower. When the heat treatment temperature is 1500°C or higher, crystal changes tend to occur and graphitization tends to proceed easily. 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, the sublimation of some of the graphite tends to be suppressed.

[0108] In step (d), the graphite obtained in step (c) is pulverized to obtain a pulverized product. The pulverization method is not particularly limited and can be carried out by known methods using a jet mill, vibratory mill, pin mill, hammer mill, etc. The particle size of the pulverized product may be adjusted to a desired size. The method of adjusting the particle size is not particularly limited and can be done using the pulverization apparatus described above, or by using a sieve, etc.

[0109] If necessary, the pulverized material obtained in step (d) may be subjected to the following steps: (e) placing low-crystallinity carbon on at least a portion of the surface of the pulverized material, (f) mixing the pulverized material with other negative electrode active materials, etc.

[0110] One method for arranging low-crystallinity carbon on at least a portion of the surface of the pulverized material in step (e) is to mix the pulverized material with a substance that can be converted into low-crystallinity carbon by heat treatment (such as resin) and then heat treat the mixture. When low-crystallinity carbon is arranged on at least a portion of the surface of the pulverized material, the input / output characteristics, such as the rapid charge / discharge characteristics, of a lithium-ion secondary battery using this material as a negative electrode may be improved.

[0111] [Other processes] The method for manufacturing the negative electrode material described herein may include steps other than those described above. For example, a method for manufacturing a negative electrode material may include a step of attaching an organic compound to the surface of secondary particles after graphitization and then heat-treating them. By attaching an organic compound to the surface of secondary particles and heat-treating them, the organic compound attached to the surface is transformed into low-crystalline carbon. This makes it possible to coat the surface of the graphite particles with low-crystalline carbon.

[0112] The method for attaching the organic compound to the surface of secondary particles is not particularly limited. Examples include a wet method in which secondary particles are dispersed and mixed in a mixed solution obtained by dissolving or dispersing the organic compound in a solvent, and then the solvent is removed to attach the compound; 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 compound.

[0113] The organic compound is not particularly limited as long as it is a carbon precursor that can be converted into low-crystalline carbon by heat treatment. Examples include petroleum pitch, naphthalene, anthracene, phenanthroline, coal tar, phenolic resin, and polyvinyl alcohol. The organic compound may be used alone or in combination of two or more.

[0114] The heat treatment temperature when heat-treating secondary particles with organic compounds attached to their surface is not particularly limited as long as it is the temperature at which the organic compounds attached to the surface of the secondary particles change into low-crystalline carbon, and is preferably, for example, 400°C to 1500°C. From the viewpoint of particularly increasing high-temperature resistance, it is more preferable to be 1000°C to 1500°C. The heat treatment is preferably carried out in an inert gas atmosphere such as a nitrogen atmosphere.

[0115] The method of 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, it may be possible to improve the desired characteristics of the lithium-ion secondary battery compared to using only the pulverized material 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 intercalating and releasing lithium ions. Examples of elements capable of intercalating and releasing lithium ions are not particularly limited, and include Si, Sn, Ge, In, etc.

[0116] The pulverized material obtained in step (f) may include particles in which multiple flattened graphite particles are aggregated or bound together, or it may include particles in which multiple flattened graphite particles are aggregated or bound together such that the main surfaces of the graphite particles are non-parallel to each other (hereinafter also referred to as secondary graphite particles).

[0117] When the pulverized material is in the form of secondary graphite particles, the phenomenon of the negative electrode material particles oriented along the direction of the current collector when pressed to increase the density of the negative electrode is suppressed, and a sufficient path for lithium ions to enter and exit the negative electrode material tends to be secured.

[0118] Furthermore, the inclusion of particles in which multiple flattened graphite particles are aggregated or bonded reduces the effect of pressure applied during pressing on individual graphite particles due to the voids between the flattened graphite particles, thereby suppressing the fracture and cracking of graphite particles. As a result, lithium-ion secondary batteries tend to have superior resistance to Li deposition.

[0119] In this disclosure, "flattened graphite particles" refers to non-spherical graphite particles having anisotropic shape. Examples of flattened graphite particles include graphite particles having shapes such as scaly, flakey, or partially lumpy.

[0120] The flattened graphite particles have an aspect ratio, expressed as A / B, where A is the length along the long axis and B is the length along the short axis. This aspect ratio is preferably 1.2 to 20, and more preferably 1.3 to 10. When the aspect ratio is 1.2 or higher, the contact area between particles increases, which tends to improve conductivity. When the aspect ratio is 20 or lower, the input / output characteristics, such as the rapid charge / discharge characteristics of lithium-ion secondary batteries, tend to improve.

[0121] The aspect ratio is determined by observing graphite particles under a microscope, selecting 100 arbitrary graphite particles, measuring the A / B ratio for each, and taking the arithmetic mean of these measurements. In observing the aspect ratio, the length A in the long axis direction and the length B in the short axis direction are measured as follows: In the projection image of the graphite particle observed using a microscope, two parallel tangents that circumscribe the outer circumference of the graphite particle are selected, and the tangents a1 and a2 with the maximum distance between them are taken as the length A in the long axis direction. Two parallel tangents that circumscribe the outer circumference of the graphite particle are selected, and the tangents b1 and b2 with the minimum distance between them are taken as the length B in the short axis direction.

[0122] In this disclosure, "the principal surfaces of secondary graphite particles are non-parallel" means that the plane with the largest cross-sectional area (principal surface) of multiple flattened graphite particles is not aligned in a certain direction. Whether or not the principal surfaces of multiple flattened graphite particles are non-parallel to each other can be confirmed by microscopic observation. When multiple flattened graphite particles are aggregated or bonded with their principal surfaces non-parallel to each other, the increase in the orientation of the principal surfaces of the flattened graphite particles within the negative electrode is suppressed, the expansion of the negative electrode during charging is suppressed, and the cycle characteristics of the lithium-ion secondary battery tend to be improved. Furthermore, the secondary graphite particles may partially include a structure in which multiple flattened graphite particles are aggregated or bonded together such that their respective principal surfaces are parallel.

[0123] The average particle size of the flattened graphite particles is preferably, for example, 1 μm to 50 μm, more preferably 1 μm to 25 μm, and even more preferably 1 μm to 15 μm, from the viewpoint of ease of aggregation or bonding. A method for measuring the average particle size of the flattened graphite particles is to measure it using a scanning electron microscope, and the average particle size of the flattened graphite particles is, for example, the arithmetic mean of the particle sizes of 100 flattened graphite particles.

[0124] The flattened graphite particles and their raw materials are not particularly limited and include artificial graphite, scaly natural graphite, flakey natural graphite, coke, resin, tar, pitch, etc. Among these, graphite obtained from artificial graphite, natural graphite, or coke tends to have a high degree of crystallinity and soft particles, making it easier to increase the density of the negative electrode.

[0125] The negative electrode material may contain spherical graphite particles. When the negative electrode material contains spherical graphite particles, the spherical graphite particles themselves are dense, which tends to reduce the press pressure required to obtain the desired electrode density.

[0126] Examples of spherical graphite particles include spherical artificial graphite and spherical natural graphite. From the viewpoint of increasing the density of the negative electrode, it is preferable that the spherical graphite particles are high-density graphite particles. Specifically, it is preferable that the spherical natural graphite is treated to form spherical particles so that it can be made highly tapped. Furthermore, the negative electrode material layer containing spherical natural graphite has excellent peel strength and tends not to peel off from the current collector even when pressed with strong force.

[0127] When the negative electrode material contains spherical graphite particles, it may also contain both the flattened graphite particles and spherical graphite particles described above. When the negative electrode material contains both the flattened graphite particles and spherical graphite particles described above, the ratio of the two is not particularly limited and can be set according to the desired electrode density, pressing pressure conditions, desired battery characteristics, etc.

[0128] When the negative electrode material contains both flattened and spherical graphite particles, examples include a state in which the flattened and spherical graphite particles are mixed, and a state in which the flattened and spherical graphite particles are bonded together (hereinafter also referred to as composite particles). Examples of composite particles include particles in which flattened and spherical graphite particles are bonded together via organic carbides.

[0129] The above-mentioned composite particles can be manufactured, for example, by using a mixture in step (a) that includes flattened graphite particles or their raw materials and spherical graphite particles.

[0130] ≪Composition for negative electrode material used in lithium-ion secondary batteries≫ The negative electrode material composition for lithium-ion secondary batteries comprises the negative electrode material for lithium-ion secondary batteries of this disclosure, a binder, and a solvent. The negative electrode material composition for lithium-ion secondary batteries of this 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. Mixing can be carried out using dispersion equipment such as a disperser agitator or a planetary mixer.

[0131] The binder used in the preparation of the negative electrode material composition for lithium-ion secondary batteries is not particularly limited. Examples of binders include styrene-butadiene copolymer (SBR), 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 homopolymers or copolymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, as well as highly ionically conductive polymer compounds 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 binder content 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 and binder for lithium-ion secondary batteries.

[0132] The negative electrode material composition for lithium-ion secondary batteries may contain a thickening agent. Suitable thickening agents include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid or its salts, starch oxide, phosphated starch, casein, etc. When the negative electrode material composition for lithium-ion secondary batteries contains a thickening agent, the amount of the thickening agent is not particularly limited. For example, it may be 0.1 to 5 parts by mass per 100 parts by mass of the negative electrode material for lithium-ion secondary batteries.

[0133] The negative electrode material composition for lithium-ion secondary batteries may contain a conductive additive. Examples of conductive additives 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 additive, the amount of the conductive additive 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.

[0134] ≪Negative electrode for lithium-ion secondary batteries≫ The negative electrode for a lithium-ion secondary battery according to this disclosure includes a negative electrode material layer containing the negative electrode material for a lithium-ion secondary battery according to this disclosure, and a current collector. In addition to the negative electrode material layer containing the negative electrode material for a lithium-ion secondary battery according to this disclosure and the current collector, the negative electrode for a lithium-ion secondary battery may include other components as necessary.

[0135] A negative electrode for a lithium-ion secondary battery can be manufactured, for example, by preparing the lithium-ion secondary battery negative electrode material composition described above and applying it to a current collector to form a negative electrode material layer, or by molding the lithium-ion secondary battery negative electrode material composition into a sheet, pellet, or other shape and integrating it with a current collector.

[0136] The material of the current collector is not particularly limited and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc. The state of the current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. In addition, porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors.

[0137] When forming a negative electrode material layer by applying a lithium-ion secondary battery negative electrode material composition to a current collector, the method is not particularly limited, and known methods such as metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade method, comma coating, gravure coating, and screen printing can be employed. After applying the lithium-ion secondary battery negative electrode material composition to the current collector, the solvent contained in the lithium-ion secondary battery negative electrode material composition is removed by drying. Drying can be performed, for example, using a hot air dryer, an infrared dryer, or a combination of these devices. If necessary, the negative electrode material layer may be subjected to rolling. Rolling can be performed by methods such as a flat plate press or a calender roll.

[0138] When a negative electrode material composition for lithium-ion secondary batteries, molded into the shape of a sheet, pellet, or the like, is integrated with a current collector to form a negative electrode material layer, the method of integration is not particularly limited. For example, it can be done by rolling, flat plate pressing, or a combination of these means. The pressure applied 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.

[0139] The negative electrode density of the negative electrode material layer is not particularly limited, for example, 1.1 g / cm³. 3 ~1.8g / cm 3 Preferably, it is 1.1 g / cm³. 3 ~1.7g / cm 3 It is more preferable that it be 1.1 g / cm³ 3 ~1.6g / cm 3 It is even more preferable that the negative electrode density be 1.1 g / cm³. 3 By doing so, the increase in electrical resistance is suppressed, and the capacitance tends to increase, reaching 1.8 g / cm³. 3 The following measures tend to suppress the degradation of input characteristics and cycle characteristics.

[0140] Lithium-ion rechargeable batteries The lithium-ion secondary battery of this disclosure includes a negative electrode, a positive electrode, and an electrolyte for the lithium-ion secondary battery of this disclosure.

[0141] 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 manufacturing method described above. As the current collector, metals or alloys such as aluminum, titanium, and stainless steel can be used in the form of foil, perforated foil, mesh, etc.

[0142] The cathode material used to form the cathode layer is not particularly limited. Examples of cathode materials include metal compounds (metal oxides, metal sulfides, etc.) that can be doped or intercalated with lithium ions, and conductive polymer materials. More specifically, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and their complex oxides (LiNix Mn y Co z A complex oxide containing O2, x + y + z = 1), and adding element M' (LiNi a Mn b Co c M' d O2, a + b + c + d = 1, M': Al, Mg, Ti, Zr or Ge), spinel-type lithium manganese oxide (LiMn2O4), lithium vanadium compound, V2O5, V6O 13 , VO2, MnO2, TiO2, MoV2O8, TiS2, V2S5, VS2, MoS2, MoS3, Cr3O8, Cr2O5, metal compounds such as olivine-type LiMPO4 (M: Co, Ni, Mn, Fe), polyacetylene, polyaniline, polypyrrole, polythiophene, conductive polymers such as polyacene, porous carbon, etc. The positive electrode material may be one kind alone or two or more kinds.

[0143] The electrolyte is not particularly limited. For example, a solution obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent (so-called organic electrolyte) can be used. Examples of the lithium salt include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. The lithium salt may be one kind alone or two or more kinds. Examples of non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propanesultone, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl 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 ester, triethyl phosphate ester, etc. The non-aqueous solvent may be used alone or in combination of two or more types.

[0144] The state of the positive and negative electrodes in a lithium-ion secondary battery is not particularly limited. For example, the positive and negative electrodes, along with a separator placed between them as needed, may be wound in a spiral shape, or they may be stacked in a flat plate shape.

[0145] The separator is not particularly limited, and for example, a nonwoven fabric made of resin, cloth, microporous film, or a combination thereof can be used. Examples of resins include those mainly composed of polyolefins such as polyethylene and polypropylene. If the positive and negative electrodes do not come into contact due to the structure of the lithium-ion secondary battery, a separator may not be used.

[0146] The shape of lithium-ion secondary batteries is not particularly limited. Examples include laminated batteries, paper batteries, button batteries, coin batteries, stacked batteries, cylindrical batteries, and prismatic batteries.

[0147] The lithium-ion secondary battery of this disclosure is suitable as a high-capacity lithium-ion secondary battery for use in electric vehicles, power tools, power storage devices, and the like. [Examples]

[0148] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0149] [Example 1] Raw coke (needle coke) derived from petroleum was used as the raw material for the graphite particles. The above-mentioned raw coke was coarsely crushed using a hammer mill. The coarse material was sieved using a 3 mm mesh sieve, and the material that remained after sieving was sieved using a 1 mm mesh sieve to recover granules with a particle size of 1 mm to 3 mm.

[0150] The obtained coke particles were crushed and classified using a roller mill to obtain flattened coke particles with a D50 of 10.1 μm. The standard deviation (σ) of the particle size distribution of the coke particles was 0.22.

[0151] The obtained coke particles (65 parts by mass, 90% fixed carbon), starch (7 parts by mass, 20% fixed carbon), and water (28 parts by mass) were kneaded using a kneader to obtain a mixture. The amount of binder in Table 1 is calculated as the ratio (%) of the amount of fixed carbon of the binder to the total amount of fixed carbon of the aggregate and binder.

[0152] Next, the resulting mixture was subjected to a uniaxial press at room temperature to obtain a density of 1.3 g / cm³. 3 The following molding process was performed to obtain molded products. Next, the obtained molded products were heat-treated in a nitrogen atmosphere at 850°C for 8 hours. After that, graphitization was performed at 3000°C for 30 hours. Subsequently, the obtained particles were sieved through a 280-mesh net to obtain graphite particles, which are the negative electrode material. Using a laser diffraction particle size distribution analyzer (SALD3100, Shimadzu Corporation), the volume-based particle size distribution of the graphite particles was determined to be 6.2 μm for D10, 12.2 μm for D50, and 18.9 μm for D90.

[0153] [Example 2] A mixture was obtained in the same manner as in Example 1, except that flattened coke particles with a D50 of 10.5 μm and a particle size distribution standard deviation (σ) of 0.33 were used. Then, graphite particles, which are the negative electrode material, were obtained using the obtained mixture in the same manner as in Example 1. The volume-based particle size distribution of graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0154] [Example 3] A mixture was obtained in the same manner as in Example 1, except that 57 parts by mass of coke particles (90% by mass of fixed carbon) obtained in Example 1, 15 parts by mass of starch (20% by mass of fixed carbon), and 28 parts by mass of water were kneaded using a kneader to obtain a mixture. Then, graphite particles, which are the negative electrode material, were obtained using the obtained mixture in the same manner as in Example 1. The volume-based particle size distribution of graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0155] [Example 4] Flattened coke particles were obtained in the same manner as in Example 1, except that raw coke (mosaic coke) derived from petroleum was used as the raw material for the graphite particles. For the coke particles, the D50 was 9.1 μm and the standard deviation (σ) of the particle size distribution was 0.24. A mixture was obtained in the same manner as in Example 1, except that the flattened coke particles obtained in Example 4 were used. Then, graphite particles, which are the negative electrode material, were obtained using the obtained mixture in the same manner as in Example 1. The volume-based particle size distribution of graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0156] [Comparative Example 1] The coke particles obtained in Example 1 were packed into a graphitization case without being mixed with a binder, and calcined at 850°C to evaporate impurities in the mixture. After that, they were graphitized at 3000°C. The resulting particles were then sieved through a 280-mesh net to obtain graphite particles, which are the negative electrode material. The volume-based particle size distribution of graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0157] [Comparative Examples 2-4] Artificial graphite particles having the volume-based particle size distribution shown in Table 1 were prepared. The artificial graphite particles prepared in Comparative Examples 2 to 4 were formed by graphitizing a mixture of coke particles and coal tar pitch. In the artificial graphite particles of Comparative Examples 3 and 4, the surface of the graphite particles was coated with low-crystallinity carbon.

[0158] [Table 1]

[0159] The negative electrode materials obtained in each example and comparative example were used to measure and evaluate the following physical properties. The results are shown in Table 2.

[0160] (specific surface area) The negative electrode material was packed into a measurement cell and pre-treated by heating at 200°C while vacuum degassing. Nitrogen gas was then adsorbed onto the sample using a gas adsorption device (ASAP2010, manufactured by Shimadzu Corporation). The specific surface area of ​​the obtained sample was determined by performing a five-point BET analysis.

[0161] (Tap density) Capacity 150cm 3 A flat-bottomed test tube with graduations (manufactured by Kuramochi Scientific Instruments Co., Ltd., KRS-406) contains 100 cm³ of graphite particle powder. 3 The sample was added, and the graduated flat-bottomed test tube was stoppered. The tap density was determined from the mass and volume of the sample powder after dropping the graduated flat-bottomed test tube from a height of 5 cm 250 times.

[0162] (R-value) The R-value of the negative electrode material was determined by measuring the Raman spectrum using a Raman spectroscopy analyzer (XploRA PLUS, Horiba, Ltd.) under the following conditions. The arithmetic mean of the 400 particles measured was defined as the R-value. - Raman spectroscopy measurement conditions - • Laser wavelength: 532nm • Laser intensity: 100mW or more • Neutral density filter: 1% · Irradiation intensity: 1 mW · Measurement range: 1000 cm -1 ~1800 cm -1 · Irradiation time: 30 seconds · Irradiation area: 1 μm 2 · Baseline (D band): 1100 cm -1 ~1470 cm -1 · Baseline (G band): 1450 cm -1 ~1710 cm -1 · Integration times for one particle: 2 times · Number of measured particles: 400 particles

[0163] (Ratio of particles with R ≥ 0.2 and ratio of particles with R < 0.2) The R values of the 400 particles measured as described above were classified, and the ratio (number %) of particles with R ≥ 0.2 and the ratio (number %) of particles with R < 0.2 were determined.

[0164] (Average value of the full width at half maximum of Id) Among the 400 particles whose R values were measured as described above, the full width at half maximum of Id in the top 10 spectra of the R values was determined respectively, and then their arithmetic mean value was determined.

[0165] (Measurement of the starting temperature T of the mass reduction reaction due to oxidation of graphite particles) By TG-DTA measurement in a dry air atmosphere, the starting temperature (oxidation reaction starting temperature) T of the mass reduction reaction due to oxidation of graphite particles contained in the negative electrode material was measured. Specifically, with about 20 mg of the sample, a Pt pan as the container, and a dry air flow rate of {300} ml / min, the weight reduction and differential heat from room temperature to 900 °C (heating rate 20 °C / min) were measured. The temperature at which DTA > 0 was taken as the oxidation reaction starting temperature T.

[0166] (Oil absorption) The oil absorption capacity of the negative electrode material was measured using the method described in JIS K6217-4:2017 "Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption," but using linseed oil (e.g., manufactured by Kanto Chemical Co., Ltd.) instead of dibutyl phthalate (DBP) as the reagent liquid. Specifically, linseed oil was titrated onto the target powder using a constant-speed burette, and the change in viscosity characteristics was measured using a torque detector. The amount of linseed oil added per unit mass of the target powder corresponding to 70% of the maximum torque generated was defined as the oil absorption amount (mL / 100g). The measurement instrument used was an absorption amount analyzer (product name: S-500) manufactured by Asahi Research Institute Co., Ltd.

[0167] (Circularity) The circularity of the negative electrode material was measured using a wet flow particle size and shape analyzer (Malvern FPIA-3000). The circularity was defined as the number-based circularity at a cumulative 50% (so-called average circularity).

[0168] (Electrode orientation) The negative electrode for the lithium-ion secondary battery was fabricated as described below, and the electrode orientation was evaluated under the conditions shown below. - Fabrication of negative electrodes for lithium-ion secondary batteries - A slurry was prepared by kneading graphite particles (97.6 parts by mass), carboxymethylcellulose (CMC) (1.2 parts by mass), and styrene-butadiene rubber (SBR) (1.2 parts by mass). This slurry was applied to the glossy surface of electrolytic copper foil at a rate of 10 g / cm². 2 The mixture is applied in this manner, pre-dried at 90°C for 2 hours, and then roll-pressed to achieve an electrode density of 1.65 g / cm³. 3 The material was adjusted to achieve the desired result. Subsequently, a curing treatment was performed by drying it at 120°C for 4 hours under a vacuum atmosphere to form a negative electrode material layer 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 measured in a size of 5 cm in width and 600 cm² in area. 2The material was formed into strip-shaped sheets, and the resulting molded material was pressed using a roll-type press with a hydraulic pressure of 4 tons. The linear pressure at this time was 4 tons / 5 cm = 0.8 tons / cm. The pressed negative electrode was placed in an X-ray diffraction measurement cell, and the X-ray diffraction pattern using CuKα rays was measured using an X-ray diffraction measuring device (Rigaku X-RAY DIFFRACTIOMETER MultiFlex) under the following conditions: scanning speed 0.25° / min, tube voltage 40kV, tube current 30mA, divergence slit 1°, scattering slit 1°, and receiving slit 0.3 mm (2θ = 25.5°~27.5°, 76.5°~78.5°). The peak intensity of the obtained 002 diffraction line (I 002 ) and the peak intensity of the 110 diffraction line (I 110 I is the ratio of ) 002 / I 110 (The 002 / 110 ratio in Table 2) was determined, and this value was used as the electrode orientation.

[0169] (discharge capacity) The lithium-ion secondary battery prepared as described above was placed in a constant temperature bath set to 25°C, and the voltage was set to 0.005V (V vs. Li / Li) at a current of 0.2C. + Constant current charging was performed until the current value reached 0.02C, and then constant voltage charging was performed at 0.005V until the current value reached 0.02C. After a 30-minute pause, the voltage was 1.5V (V vs. Li / Li) at a current value of 0.2C. + A constant current discharge was performed up to ). The discharge capacity at this time was determined.

[0170] (Initial efficiency) Using the lithium-ion secondary battery prepared as described above, the initial efficiency was determined by following the steps (1) to (3) below. (1) The battery was charged with a constant current of 0.2C to 0.005V (vs. Li / Li+), and then constant voltage charging was performed at 0.005V until the current value reached 0.02C. The capacity at this time was defined as the initial charge capacity. (2) After a 30-minute rest period, the battery was discharged to 1.5V (vs. Li / Li+) with a constant current of 0.2C. The capacity at this time was defined as the initial discharge capacity. (3) The initial efficiency was calculated using the following equation (Equation 1) from the charge and discharge capacities obtained in (1) and (2) above. Initial efficiency (%) = (Initial discharge capacity (mAh) / Initial charge capacity (mAh)) × 100 …(Equation 1)

[0171] (SOC-Li (Li precipitation resistance)) A lithium-ion secondary battery was fabricated using the negative electrode obtained above, and its resistance to Li deposition was evaluated as follows. - Manufacturing of lithium-ion secondary batteries - A coin cell, a lithium-ion secondary battery, was fabricated using the following materials: metallic lithium as the negative electrode and counter electrode, a mixture of ethylene carbonate / ethyl methyl carbonate (3:7 volume ratio) containing 1M LiPF6 and vinylene carbonate (VC) (1.0 mass%) as the electrolyte, a 25 μm thick polyethylene microporous membrane as the separator, and a 250 μm thick copper plate as the spacer. - Evaluation of Li precipitation resistance - The fabricated lithium-ion secondary battery was placed in a constant temperature bath set to 25°C, and for the first three cycles, the voltage was set to 0.005V (V vs. Li / Li) at a current of 0.1C. + Constant current charging was performed until the current value reached 0.05C, and then constant voltage charging was performed at 0.005V until the current value reached 0.05C. After a 30-minute pause, the voltage was 1.5V (V vs. Li / Li) at a current value of 0.2C. + Constant current discharge was performed up to 3C. The discharge capacity of the third cycle was set to 1C in the Li deposition test. The fourth cycle of charging was performed at a current density of 3C to charge the discharge capacity of the third cycle in 20 minutes, with the termination condition being a 1C capacity restriction. The first inflection point in the differential profile of the obtained fourth cycle charging curve (dV / dQ, where V is voltage and Q is capacitance) was taken as the Li deposition start point, and the capacity at this time was expressed as a percentage of the discharge capacity of the third cycle (or the charging capacity of the fourth cycle set to the same capacity), and the Li deposition resistance was evaluated. The results are shown in Table 2. The larger the percentage value, the better the Li deposition resistance.

[0172] (Measurement of DC resistance (DCR)) The DC resistance (DCR) of the lithium-ion secondary batteries fabricated in Example 1 and Example 4 was measured to determine the input characteristics of these batteries. Specifically, the results are as follows: Using the negative electrode obtained above, lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode. 0.33 Mn 0.33 Co 0.33 A single-layer laminate full cell (lithium-ion secondary battery) was fabricated using a composite electrode containing 94 parts by mass of O2, 3 parts by mass of carbon black, and 3 parts by mass of polyvinylidene fluoride; a mixture of ethylene carbonate / diethyl carbonate (3:7 volume ratio) containing 1 M LiPF6 and vinylene carbonate (VC) (1.0% by mass) as the electrolyte; and a 25 μm thick polyethylene microporous membrane as the separator. The above lithium-ion secondary battery (single-layer laminated full cell) was placed in a constant temperature bath set to 25°C, and three charge-discharge cycles were performed under the following conditions: Charging: CC / CV 0.2C 4.2V 0.02C Cut, Discharging: CC 0.2C 2.5V Cut. Next, constant current charging was performed at a current value of 0.2C until the State of Charge (SOC) reached 50%. Furthermore, the lithium-ion secondary battery was placed in a constant temperature bath set to 25°C, and constant current charging was performed for 10 seconds each under conditions of 1C, 2C, and 3C. The voltage drop (ΔV) for each constant current was measured, and the DC resistance (DCR) was measured using the following formula. DCR[Ω] = {(2C voltage drop ΔV - 1C voltage drop ΔV) + (3C voltage drop ΔV - 2C voltage drop ΔV)} / {(3C control current value I - 2C control current value I) + (2C control current value I - 1C control current value I)} In Example 1, the value was 1.79Ω, and in Example 4, it was 1.68Ω. This indicates that a lower DC resistance (DCR) value indicates better input characteristics.

[0173] (Measurement of high-temperature storage retention rate) The high-temperature storage retention rates of the lithium-ion secondary batteries prepared in Example 1 and Example 4 were determined. Specifically, the results are as follows: After the DCR measurement described above, the lithium-ion secondary battery (single-layer laminated full cell) was placed in a constant-temperature bath set to 25°C and charged with a constant current of 0.2C until the voltage reached 4.2V. Then, after a 30-minute rest period, it was discharged with a constant current of 0.2C until the voltage reached 2.5V. After this, it was charged with a constant current of 0.2C until the voltage reached 4.2V, and the battery was placed in a constant-temperature bath set to 60°C and stored for 10 days. Afterward, place it in a constant temperature bath set to 25°C and leave it for 60 minutes, then set the voltage to 2.5V (V vs. Li / Li) with a current of 0.2C. + Constant current discharge was performed until the voltage reached 4.2V at a current of 0.2C. Then, after a 30-minute rest period, constant current discharge was performed again at a current of 0.2C until the voltage reached 2.5V. The high-temperature storage retention rate was calculated using the following formula. High-temperature storage retention rate (%) = [(Discharge capacity at 25°C after 10 days of storage at 60°C) / (Discharge capacity at 25°C)] × 100 In Example 1, the retention rate was 99.0%, and in Example 4, it was 98.7%. A higher value for the high-temperature storage retention rate indicates superior high-temperature storage characteristics.

[0174] [Table 2]

[0175] Table 2 shows that each example demonstrated a tendency towards superior initial efficiency and resistance to Li deposition in lithium-ion secondary batteries.

[0176] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. Contains graphite particles, The aforementioned graphite particles, in the Raman spectral spectrum obtained by Raman spectroscopy, showed a value of 1580 cm⁻¹. －１ ~1620cm －１ The maximum peak intensity Ig within the range and 1300 cm －１ ~1400cm －１ For the R value, which is the intensity ratio Id / Ig of the maximum peak intensity Id within the range, the proportion of particles with R ≥ 0.2 is 10% or more, and the average half-width of Id in the top 10 R-value spectra is 60 cm². －１ The following conditions must be met: A negative electrode material for lithium-ion secondary batteries that satisfies at least one of the following conditions (1) to (3). (1) The circularity of the graphite particles is 93% or less. (2) The amount of oil absorbed by the graphite particles is 40 mL / 100 g to 70 mL / 100 g. (3) The proportion of graphite particles in which R ≥ 0.2 is 80 percent or less.

2. Contains graphite particles, The graphite particles have a ratio R value that is the intensity ratio Id / Ig of the intensity Ig of the maximum peak in the range of 1580 cm －１ to 1620 cm －１ and the intensity Id of the maximum peak in the range of 1300 cm －１ to 1400 cm －１ such that the proportion of particles with R ≧ 0.2 is 10% or more by number, and the starting temperature T of the mass reduction reaction due to oxidation of the graphite particles obtained by TG-DTA measurement in a dry air atmosphere satisfies T ≧ 700°C, A negative electrode material for lithium-ion secondary batteries that satisfies at least one of the following conditions (1) to (3). (1) The circularity of the graphite particles is 93% or less. (2) The amount of oil absorbed by the graphite particles is 40 mL / 100 g to 70 mL / 100 g. (3) The proportion of graphite particles in which R ≥ 0.2 is 80 percent or less.

3. The negative electrode material for a lithium-ion secondary battery according to claim 1 or claim 2, wherein the graphite particles include artificial graphite particles.

4. The artificial graphite particles are particles obtained by graphitizing a mixture containing a graphitizable aggregate and a graphitizable binder, wherein the binder contains a polymer compound that is water-soluble or water-absorbent.

5. The negative electrode material for a lithium-ion secondary battery according to claim 1 or claim 2, wherein the surface of the graphite particles is not subjected to a coating of low-crystallinity carbon.

6. 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 described in claim 1 or claim 2, and a current collector.

7. A lithium-ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, as described in claim 6.

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