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

Abstract

A negative electrode material for a lithium ion secondary battery, which contains graphite particles and satisfies the following condition: for the graphite particles, when 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 > in a Raman spectrum obtained by Raman spectroscopy is defined as the R value, the R value is greater than the R value; the proportion of particles having R > = 0.2 is 10% by number or more, and the average value of the half-value width of Id in the first 10 spectra of the R value is 60 cm-1 or less.

Description

Technical Field

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

[0002] Lithium-ion secondary batteries have been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smart phones, and tablet PCs, making effective use of their small, lightweight, and high energy density characteristics. In recent years, against the backdrop of environmental issues such as global warming caused by CO2 emissions, electric vehicles such as clean electric vehicles (EVs) that use only batteries for driving, hybrid electric vehicles (HEVs) that combine gasoline engines and batteries, and plug-in hybrid electric vehicles (PHEVs) are becoming popular, and the development of lithium-ion secondary batteries (on-board lithium-ion secondary batteries) as batteries mounted on them is being promoted.

[0003] The performance of the negative electrode material of a lithium ion secondary battery greatly affects the input characteristics of the lithium ion secondary battery. Carbon materials are widely used as materials for negative electrode materials for lithium ion secondary batteries. For example, as materials for obtaining high-density negative electrodes, artificial graphite, spherical natural graphite obtained by spheroidizing scaly natural graphite, and other carbon materials with high crystallinity have been proposed.

[0004] As artificial graphite, for example, Patent Document 1 discloses a negative electrode material for a lithium ion secondary battery comprising composite particles including a plurality of flat graphite particles aggregated or bonded so that their orientation planes are not parallel, and spherical graphite particles.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2015 / 147012 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Due to the rapid growth of the EV market, the demand for negative electrode materials for lithium-ion secondary batteries is increasing. Among them, from the perspective of improving battery performance, it is hoped that the irreversible capacity during the first charge and discharge will be reduced to improve the initial efficiency. In order to improve convenience, there is a strong demand for fast charging, etc., and high-rate charging is required for negative electrode active materials.

[0010] The problem with such high-rate charging is that due to the IR drop when a large current is applied, some lithium ions cannot be inserted into the graphite layers, and lithium metal is easily precipitated on the surface of graphite particles. When lithium metal precipitates in the form of needles, it will pierce the separator and cause an internal short circuit, which may lead to thermal runaway.

[0011] From the above-mentioned viewpoints, it is desired to produce a negative electrode material for a lithium ion secondary battery that can suppress the precipitation of lithium metal and has excellent resistance to lithium (Li) precipitation.

[0012] An object of the present disclosure is to provide a negative electrode material for a lithium ion secondary battery that can produce a lithium ion secondary battery having excellent initial efficiency, can suppress the precipitation of lithium metal, and has excellent resistance to Li precipitation, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery including the negative electrode material.

[0013] Methods for solving problems

[0014] Means for solving the above-mentioned problems include the following aspects.

[0015] <1> A negative electrode material for a lithium ion secondary battery, comprising graphite particles, and satisfying the following conditions: for the graphite particles, a Raman spectrum obtained in Raman spectroscopy measurement at 1580 cm -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range of R is defined as R value, the proportion of particles with 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 top 10 spectra of R value is less than or equal to 60 cm -1 .

[0016] <2> A negative electrode material for a lithium ion secondary battery, comprising graphite particles, and satisfying the following conditions: for the graphite particles, a Raman spectrum obtained in Raman spectroscopy measurement at 1580 cm -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range is defined as the R value, the proportion of particles with R≥0.2 is greater than or equal to 10% by number, and the starting temperature T of the oxidation-based mass reduction reaction of the graphite particles obtained by TG-DTA measurement in a dry air atmosphere is greater than or equal to 700°C.

[0017] <3> like <1> or <2> In the negative electrode material for lithium-ion secondary batteries, the graphite particles include artificial graphite particles.

[0018] <4> like <3> The negative electrode material for lithium-ion secondary battery, wherein the artificial graphite particles are particles obtained by graphitizing a mixture containing a graphitizable aggregate and a graphitizable binder, wherein the binder contains a water-soluble or water-absorbent polymer compound.

[0019] <5> like <1> ~ <4> The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the circularity of the graphite particles is less than or equal to 93%.

[0020] <6> like <1> ~ <5> The negative electrode material for a lithium ion secondary battery according to any one of the claims 1 to 5, wherein the oil absorption of the graphite particles is 40 mL / 100 g to 70 mL / 100 g.

[0021] <7> like <1> ~ <6> The negative electrode material for a lithium ion secondary battery according to any one of the above, wherein the proportion of particles with R ≥ 0.2 in the graphite particles is less than or equal to 80% by number.

[0022] <8> like <1> ~ <7> The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the surface of the graphite particles is not coated with low-crystalline carbon.

[0023] <9> A negative electrode for a lithium ion secondary battery, comprising a negative electrode material layer and a current collector, wherein the negative electrode material layer comprises <1> ~ <8> A negative electrode material for a lithium ion secondary battery according to any one of the above.

[0024] <10> A lithium ion secondary battery comprising <9> The lithium-ion secondary battery comprises a negative electrode, a positive electrode and an electrolyte.

[0025] Effects of the Invention

[0026] The present disclosure can provide a negative electrode material for a lithium ion secondary battery that can produce a lithium ion secondary battery having excellent initial efficiency, can suppress the precipitation of lithium metal, and has excellent resistance to Li precipitation, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery including the negative electrode material. DETAILED DESCRIPTION

[0027] Hereinafter, the mode for implementing the present invention is described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, except for the cases specifically indicated, the constituent elements (including element steps, etc.) are not necessary. The numerical value and its range are also the same and do not limit the present invention.

[0028] In the present disclosure, the term "process" includes not only a process that is independent of other processes, but also a process that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved.

[0029] In the present disclosure, in a numerical range expressed using “to”, the numerical values ​​described before and after “to” are included as the minimum value and the maximum value, respectively.

[0030] In the numerical range recorded in stages in the present disclosure, the upper limit or lower limit recorded in one numerical range can also be replaced by the upper limit or lower limit of the numerical range recorded in other stages. In addition, in the numerical range recorded in the present disclosure, the upper limit or lower limit of the numerical range can also be replaced by the value shown in the embodiment.

[0031] In the present disclosure, each component may include a plurality of equivalent substances. When a plurality of substances equivalent to each component are present in the composition, the content or content of each component refers to the total content or content of the plurality of substances present in the composition unless otherwise specified.

[0032] In the present disclosure, multiple types of particles corresponding to each component may be included. When multiple types of particles corresponding to each component are present in the composition, unless otherwise specified, the particle size of each component refers to a value for a mixture of the multiple types of particles present in the composition.

[0033] In the present disclosure, the term "layer" or "film" includes a case where the layer or film is formed in the entire region or only in a part of the region when observing the region where the layer or film exists.

[0034] In the present disclosure, the term “stacked” means stacking layers, and may be two or more layers combined or two or more layers that can be attached or detached.

[0035] In the present disclosure, the particle size distribution of the negative electrode material can be measured by a laser diffraction particle size distribution measuring device. The average particle size of the particles is the particle size (D50) when the accumulation from the small diameter side reaches 50% in the volume-based particle size distribution. D90 is the particle size when the accumulation from the small diameter side reaches 90% in the volume-based particle size distribution, and D10 is the particle size when the accumulation from the small diameter side reaches 10% in the volume-based particle size distribution.

[0036] 《Negative electrode materials for lithium-ion secondary batteries》

[0037] Hereinafter, regarding the negative electrode material for lithium ion secondary batteries of the present disclosure, the negative electrode material for lithium ion secondary batteries of the first embodiment and the negative electrode material for lithium ion secondary batteries of the second embodiment will be described in order. It should be noted that the present invention is not limited to these embodiments.

[0038] [First embodiment]

[0039] The negative electrode material for a lithium ion secondary battery according to the first embodiment of the present disclosure (hereinafter, also referred to as the negative electrode material) contains graphite particles and satisfies the following conditions: for the graphite particles, a Raman spectroscopic spectrum obtained by Raman spectrometry has a wavelength of 1580 cm -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range of R is defined as R value, the proportion of particles with R ≥ 0.2 (hereinafter also referred to as "the proportion of 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 top 10 spectra of R value is less than or equal to 60 cm -1 .

[0040] By using the negative electrode material of the first embodiment, it is possible to manufacture a lithium ion secondary battery that is excellent in initial efficiency, can suppress the precipitation of lithium metal, and has excellent resistance to lithium (Li) precipitation. The reason for this is, for example, presumably as follows.

[0041] In Raman spectroscopy, at 1580 cm -1 ~1620cm -1 The peak intensity Ig in the range of 1580 cm-1 is identified as a peak corresponding to the graphite crystal structure, for example, -1 Peaks appearing nearby.

[0042] At 1300cm -1 ~1400cm -1 The peak intensity Id in the range of 1360 cm-1 is identified as a peak corresponding to the amorphous structure of carbon. -1 Peaks appearing nearby.

[0043] The graphite particles contained in the negative electrode material meet the following conditions: the ratio of R value as the intensity ratio Id / Ig is greater than or equal to 0.2 to a certain extent, that is, the surface crystallinity of the graphite particles is lower to a certain extent. By lowering the surface crystallinity, the lithium ion secondary battery using the negative electrode material of this embodiment can improve the Li precipitation tolerance without damaging the discharge capacity.

[0044] The average half-value width of Id in the spectrum of the top 10 R values ​​of the graphite particles satisfies that it is less than or equal to 60 cm -1. That is, it means that for graphite particles with low surface crystallinity contained in the negative electrode material, the half-value width of the peak identified as corresponding to the amorphous structure of carbon becomes narrower. It is speculated that the generation of carbon defects is suppressed by the narrower half-value width, and the increase in irreversible capacity during the initial charge caused by the presence of various functional groups in the carbon defects is suppressed. As a result, the lithium-ion secondary battery using the negative electrode material of this embodiment tends to have excellent initial efficiency.

[0045] Regarding the strength ratio Id / Ig, i.e., R value, of the graphite particles contained in the negative electrode material, the ratio of R≥0.2 is greater than or equal to 10% by number. From the viewpoint of Li precipitation resistance of the lithium ion secondary battery, the ratio of R≥0.2 is preferably greater than or equal to 15% by number, and more preferably greater than or equal to 20% by number. By using graphite particles having a ratio of R≥0.2 of greater than or equal to 10% by number, there is a tendency that the input characteristics of the lithium ion secondary battery become good.

[0046] Regarding the R value of the graphite particles, which is the intensity ratio Id / Ig, the ratio of R ≥ 0.2 may be 80% by number or less, or 70% by number or less, from the viewpoint of the initial efficiency of the lithium ion secondary battery.

[0047] The average value of the half-value width of Id in the spectrum of the top 10 R values ​​of the graphite particles contained in the negative electrode material satisfies that it is less than or equal to 60 cm -1 From the perspective of initial efficiency of lithium-ion secondary batteries, it is preferred to satisfy a value less than or equal to 55 cm -1 , preferably less than or equal to 50cm -1 The average value of the half-value width of Id in the top 10 spectra of R value is less than or equal to 60 cm -1 The storage characteristics of the lithium ion secondary battery tend to be improved when the graphite particles are thicker than those of the lithium ion secondary battery.

[0048] The average half-value width of Id in the spectrum of the top 10 R values ​​of the graphite particles can satisfy a value greater than or equal to 20 cm -1 , or greater than or equal to 30cm -1 .

[0049] In the present disclosure, the R value as Id / Ig, the ratio of R≧0.2, and the average value of the half-value width of Id can be measured by the following method.

[0050] The R value of the graphite particles can be determined by measuring the Raman spectroscopic spectrum using a Raman spectrometer (eg, XploRA PLUS, manufactured by Horiba, Ltd.) under the following conditions: At this time, the arithmetic mean value of 400 particles measured is taken as the R value.

[0051] -Raman spectroscopy measurement conditions-

[0052] Laser wavelength: 532nm

[0053] Laser intensity: 100mW or more

[0054] Neutral filter: 1%

[0055] Irradiation intensity: 1mW

[0056] Measuring range: 1000cm -1 ~1800cm -1

[0057] Irradiation time: 30 seconds

[0058] Irradiation area: 1μm 2

[0059] Baseline (D band): 1100cm -1 ~1470cm -1

[0060] Baseline (G band): 1450cm -1 ~1710cm -1

[0061] ·Cumulative number of times for 1 particle: 2 times

[0062] ·Number of particles measured: 400 particles

[0063] By classifying the R values ​​of the 400 particles measured as described above, the ratio (number %) of particles with R ≥ 0.2 and the ratio (number %) of particles with R < 0.2 can be determined.

[0064] The half widths of Id in the top 10 spectra of R values ​​among the 400 particles whose R values ​​were measured as described above were calculated, and their arithmetic mean was taken as the average of the half widths of Id in the top 10 spectra of R values.

[0065] From the viewpoint of Li precipitation resistance of lithium ion secondary batteries, the graphite particles contained in the negative electrode material of the present disclosure preferably include artificial graphite particles. Artificial graphite particles are preferably particles obtained by graphitizing a mixture comprising a graphitizable aggregate and a graphitizable binder. From the viewpoint that the ratio of R ≥ 0.2 is easily satisfied to be greater than or equal to 10% by number and the Li precipitation resistance of lithium ion secondary batteries, the graphitizable binder preferably includes a water-soluble or water-absorbent polymer compound, and more preferably includes an aqueous binder containing a water-soluble or water-absorbent polymer compound.

[0066] The water-soluble or water-absorbing polymer compound is not particularly limited, and may include, for example, at least one selected from the group consisting of starch, amylose, amylopectin, polyacrylic acid, carboxymethyl cellulose, polyvinyl alcohol, and water-soluble proteins.

[0067] By using artificial graphite particles as graphite particles; using a binder comprising a water-soluble or water-absorbent polymer compound when graphitizing a mixture comprising a graphitizable aggregate and a graphitizable binder to manufacture artificial graphite particles; not implementing a treatment of coating the surface of the graphite particles with low-crystalline carbon, etc., it is easy to obtain a negative electrode material that satisfies the numerical conditions of the average value of the half-value width of the aforementioned R value and Id.

[0068] (Average particle size)

[0069] The particle size of the graphite particles at which the accumulation from the smaller diameter side reaches 50% in the volume-based particle size distribution measured by laser diffraction (hereinafter also referred to as “average particle size” or “D50”) may be 5.0 μm to 20.0 μm.

[0070] From the viewpoint of further improving the resistance to Li precipitation, the average particle size of the graphite particles may be 18.0 μm or less, or 17.0 μm or less.

[0071] The average particle size of the graphite particles may be 8.0 μm or more, or 10.0 μm or more.

[0072] The average particle size of the graphite particles can be measured using a laser diffraction particle size distribution measuring apparatus (for example, SALD3100, manufactured by Shimadzu Corporation).

[0073] The method for measuring the average particle size of the graphite particles contained in the negative electrode includes: making a sample electrode, embedding the electrode in epoxy resin, mirror polishing, and observing the electrode cross section with a scanning electron microscope (e.g., KEYENCE Co., Ltd., "VE-7800"); using an ion milling device (e.g., Hitachi High-Tech Co., Ltd., "E-3500") to make an electrode cross section, and measuring it with a scanning electron microscope (e.g., KEYENCE Co., Ltd., "VE-7800"), etc. The average particle size at this time is the median of 100 particle sizes selected at random.

[0074] (D10)

[0075] D10 of the graphite particles may be 0.1 μm to 10.0 μm, or 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.

[0076] D10 of the graphite particles can be measured using a laser diffraction particle size distribution measuring apparatus (for example, SALD3100, manufactured by Shimadzu Corporation).

[0077] (Particle size distribution D90 / 10)

[0078] 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.

[0079] The particle size distribution D90 / D10 can be measured using a laser diffraction particle size distribution measuring apparatus (for example, SALD3100, manufactured by Shimadzu Corporation).

[0080] As a method for measuring the particle size distribution D90 / D10 of graphite particles in a state contained in the negative electrode, there can be cited: making a sample electrode, embedding the electrode in epoxy resin, mirror polishing, and observing the electrode cross section with a scanning electron microscope (e.g., KEYENCE Co., Ltd., "VE-7800"); using an ion milling device (e.g., Hitachi High-Tech Co., Ltd., "E-3500") to make an electrode cross section, and measuring it with a scanning electron microscope (e.g., KEYENCE Co., Ltd., "VE-7800"), etc. The particle size distribution D90 / D10 at this time can be obtained by the following method.

[0081] (1) The area Sn of the mapped particle is determined by using a binarization method or the like (n is a particle-specific number assigned to the selected particle).

[0082] (2) Assuming that the particle is an ideal sphere, the equivalent circle diameter Ln = √Sn / π is calculated from the area Sn.

[0083] (3) Based on the equivalent circle diameter Ln, the volume of the sphere Vn = (4 / 3)π(Ln) 3 .

[0084] (4) Repeat (1) to (3) for the selected 100 particles.

[0085] (5) In a distribution curve with the vertical axis set to 100 volume cumulative % and the horizontal axis set to particle size, the particle size at the point intersecting the horizontal axis at 10% is set to the 10% diameter (D10), and the particle size at the point intersecting the horizontal axis at 90% is set to the 90% diameter (D90), and D90 / D10 can be calculated.

[0086] (Standard deviation of particle size distribution)

[0087] The standard deviation of the particle size distribution of the graphite particles may be 0.18 to 0.40, or 0.25 to 0.35.

[0088] The standard deviation of the particle size distribution can be measured using a laser diffraction particle size distribution measuring apparatus (for example, SALD3100, manufactured by Shimadzu Corporation) based on a frequency distribution curve having a logarithmic scale of particle diameter on the horizontal axis and a particle amount (%) on the vertical axis.

[0089] (I 002 / I 110 )

[0090] When the negative electrode material of the present invention is used to form a negative electrode, from the viewpoint of the input characteristics of a lithium ion secondary battery, the peak intensity (I 002 ) and the peak intensity of the 110 diffraction line (I 110 ) ratio, that is, I 002 / I 110 It may be less than or equal to 700, less than or equal to 600, or less than or equal to 500.

[0091] I 002 / I 110 The lower limit of is not particularly limited and may be greater than or equal to 200.

[0092] I 002 / I 110 It can be obtained by the method described in the examples. 002 / I 110 When the negative electrode is produced, the components other than the graphite particles and their ratios as well as the negative electrode production conditions are the same as the production conditions described in the method for measuring the electrode orientation in the examples.

[0093] (250 tap density)

[0094] From the viewpoint of easily improving the input-output characteristics and energy density of the lithium-ion secondary battery, the 250 tap density of the graphite particles is preferably 0.80 g / cm 3 ~1.20g / cm 3 , more preferably 0.90 g / cm 3 ~1.10g / cm 3 .

[0095] The 250th tap density of graphite particles can be determined, for example, as follows.

[0096] In capacity 150cm 3 100 cm of graphite particle sample powder is placed in a graduated flat-bottomed test tube (e.g., KRS-406 manufactured by Kurachi Scientific Instruments Co., Ltd.) 3, plug the above-mentioned flat-bottomed test tube with a stopper, then drop the flat-bottomed test tube with a scale from a height of 5 cm 250 times, and take the density value calculated from the mass and volume of the sample powder thereafter as the 250-time tap density.

[0097] (Specific surface area)

[0098] The specific surface area of ​​the graphite particles determined by nitrogen adsorption measurement at 77 K is not particularly limited. For example, from the viewpoint of improving rapid charge and discharge performance and suppressing decomposition of the electrolyte, the specific surface area of ​​the graphite particles is preferably 0.2 m 2 / g~6.0m 2 / g, more preferably 1.5m 2 / g~5.0m 2 / g, more preferably 2.0m 2 / g~4.0m 2 / g.

[0099] The specific surface area obtained by nitrogen adsorption measurement at 77 K can be obtained using the BET method from an adsorption isotherm obtained by nitrogen adsorption measurement at 77 K. Specifically, the specific surface area can be obtained by the method described in Examples.

[0100] The specific surface area of ​​graphite particles can be adjusted by particle size distribution, particle structure, etc.

[0101] The specific surface area of ​​graphite particles can be adjusted by coating the graphite particles with low-crystalline carbon or the like, and can also be adjusted by the amount of the aqueous binder when a water-based binder is used as a graphitizable binder. When the particle size is to be reduced, the specific surface area is greatly increased due to the unevenness caused by pulverization, but by coating, the unevenness can be filled with the coating material to make it smooth, thereby adjusting the specific surface area.

[0102] (Circularity)

[0103] From the viewpoint of Li precipitation resistance of a lithium ion secondary battery, the circularity of the graphite particles is preferably 95% or less, more preferably 93% or less, and further preferably 92% or less.

[0104] The circularity of the graphite particles may be greater than or equal to 85%, or greater than or equal to 88%.

[0105] 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 value of 50% (so-called average circularity) may be taken as the circularity.

[0106] (Oil absorption)

[0107] The oil absorption of the graphite particles is preferably 40 mL / 100 g to 70 mL / 100 g, and more preferably 45 mL / 100 g to 60 mL / 100 g.

[0108] The oil absorption of graphite particles is an indicator of the amount of pores present inside and on the surface of the particles and the amount of spaces between the particles.

[0109] It is believed that if the oil absorption of graphite particles is less than or equal to 60mL / 100g, the amount of pores present in the particles and on the particle surface is small, and the contact area with the electrolyte is fully small. In addition, since the interface is small, the amount of the binder when making the negative electrode can be reduced, thus, there is a tendency to reduce resistance and improve battery performance. In addition, since the pores are few, the solvent when the electrode is dried can be reduced, and the cost and environmental aspects of the production line such as the suppression of the equipment involved in drying and electricity are also advantageous.

[0110] When the oil absorption of the graphite particles is greater than or equal to 40 mL / 100 g, there is a tendency to suppress the increase in viscosity of the slurry when mixing with a binder, etc., which is generated when there are too few interparticle spaces. In addition, there is a tendency that the binder is easily appropriately expanded and mixing becomes easy. In addition, it is easy to ensure the interparticle spaces for lithium ion movement.

[0111] In the present disclosure, the oil absorption of graphite particles is measured using linseed oil (e.g. manufactured by Kanto Chemical Co., Ltd.) as a reagent liquid instead of dibutyl phthalate (DBP) in the method described in JIS K6217-4:2017 "Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption".

[0112] Specifically, linseed oil is titrated to 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 a torque of 70% of the maximum torque generated is taken as the oil absorption (mL / 100g). As a measuring instrument, for example, an absorption measuring device (trade name: S-500) manufactured by ASAHISOKEN Co., Ltd. can be used.

[0113] The graphite particles may or may not be treated to be coated with low-crystalline carbon on the surface.

[0114] When the surface of graphite particles is coated with low-crystalline carbon, when a lithium ion secondary battery is constructed, the charging characteristics at low temperatures tend to be further improved.

[0115] On the other hand, when the surface of the graphite particles is not coated with low-crystalline carbon, the graphite particles will crack and peel off during the pressing of the electrode, and there is a tendency that the decomposition activity of the electrolyte is increased and the storage characteristics can be suppressed. In addition, this has the advantage of expanding the degree of freedom of manufacturing conditions. Furthermore, in the negative electrode material disclosed in the present invention, even if low-crystalline carbon is not configured on the surface, the precipitation of lithium metal during charging can be suppressed.

[0116] In the case of artificial graphite particles that are graphitized using a graphitizable binder containing the above-mentioned aqueous binder (for example, an aqueous binder containing a compound that does not contain an aromatic ring, such as starch), it is difficult for compounds that do not contain an aromatic ring, such as starch, to change into graphite. Therefore, there is a tendency for the surface crystallinity of the graphite particles to become lower, and there is a tendency to obtain good charging characteristics at low temperatures even if the treatment of coating the surface of the graphite particles with low crystalline carbon is omitted. Thus, by using the above-mentioned aqueous binder to manufacture artificial graphite particles, it is possible to take into account both the simplification of the process and the improvement of the charging characteristics.

[0117] The R value of the graphite particles may be 0.10 to 0.40 or 0.15 to 0.30. In particular, the graphite particles are preferably not subjected to a surface coating treatment with low-crystalline carbon and have an R value of 0.10 to 0.40, and more preferably 0.15 to 0.30.

[0118] In the present invention, the average interplanar spacing (d 002 ) Carbon materials smaller than 0.340 nm are referred to as graphite.

[0119] In the present disclosure, as described later, a particle in which low-crystalline carbon is arranged on at least a part of the surface of a graphite particle is also referred to as a "graphite particle".

[0120] The average interplanar spacing of graphite crystals (d 002 ) has a theoretical value of 0.3354 nm, and the closer it is to this value, the more graphitization progresses.

[0121] From the perspective of initial charge and discharge efficiency and energy density of lithium-ion secondary batteries, the average interplanar spacing (d 002 ) is preferably less than or equal to 0.33600nm, more preferably less than or equal to 0.33596nm, further preferably less than or equal to 0.33592nm.

[0122] From the above viewpoints, the average interplanar spacing (d 002 ) is preferably 0.3354nm to 0.33600nm, more preferably 0.3354nm to 0.33596nm, and further preferably 0.3354nm to 0.33592nm.

[0123] The average interplanar spacing of graphite particles (d 002 ) can be calculated using the Bragg formula based on the diffraction peak corresponding to the carbon 002 plane that appears near the diffraction angle 2θ of 24° to 27° in the diffraction pattern obtained by irradiating the sample with X-rays (CuKα rays) and measuring the diffraction lines using a goniometer. The average plane spacing (d 002 ) can be measured under the following conditions.

[0124] Radiation source: CuKα radiation (wavelength = 0.15418nm)

[0125] Output power: 40kV, 20mA

[0126] Sampling width: 0.010°

[0127] Scanning range: 10°~35°

[0128] Scanning speed: 0.5° / min

[0129] Bragg type: 2dsinθ=nλ

[0130] Here, d represents the length of one period, θ represents the diffraction angle, n represents the number of reflections, and λ represents the wavelength of X-rays.

[0131] 《Particle structure of graphite particles》

[0132] The graphite particles may include a state in which a plurality of graphite particles are aggregated or bonded (composite particles), or may include composite particles having a structure in which a plurality of flat graphite particles are stacked (hereinafter also referred to as specific composite particles).

[0133] It is believed that specific composite particles can reduce the contact area with the electrolyte inside the particle compared with the composite particles of the structure with the main surface of multiple flat graphite particles toward the random direction, and can effectively suppress the decomposition of the electrolyte. In addition, it is believed that even if pressurization is performed when making the negative electrode, it is not easy to produce deformation or destruction of the particle, and it is easy to ensure the path of the electrolyte between the particles. In addition, the mobile diffusion path of the electrolyte inside the composite particles with the main surface of multiple flat graphite particles toward the random direction is complicated and slow. Therefore, it is believed that even if it is an active material with more particle interfaces, diffusion barriers will be generated and high input-output performance cannot be exerted. Especially under the input-output conditions with high C rate, this tendency is remarkable.

[0134] The flat graphite particles contained in the specific composite particles are non-spherical graphite particles having anisotropic shapes. Examples of the flat graphite particles include graphite particles having scale-like, flaky, partially blocky shapes, and the like.

[0135] Composite particles refer to particles in a state where primary particles are assembled or combined with each other. That is, specific composite particles have a structure in which a plurality of flat graphite particles are overlapped and assembled or combined in a state where the main surfaces are relative to each other. Therefore, a plurality of flat graphite particles overlap in a roughly parallel state to form composite particles. Whether the flat graphite particles are stacked can be confirmed by microscopic observation.

[0136] The state of a plurality of flat graphite particles being assembled or combined refers to the state of two or more flat graphite particles being assembled or combined. Combination refers to the state in which the particles are chemically combined directly or via a carbon material. The so-called assembly refers to the state in which the particles are not chemically combined with each other, but the shape as an aggregate is maintained due to its shape, etc.

[0137] The flat graphite particles can be aggregated or combined via a carbon material. As the carbon material, for example, graphite, carbide, etc. that are graphitized by a graphitizable binder can be cited. From the viewpoint of mechanical strength, it is preferred that two or more flat graphite particles are combined via a carbon material. Whether the flat graphite particles are aggregated or combined can be confirmed, for example, by observation using a scanning electron microscope.

[0138] In order to reduce the composite particle ratio of the structure with the main surface of multiple flat graphite particles facing the random direction, the usage amount of the adhesive is preferably as little as possible. When there is no adhesive, no composite particles are produced. On the other hand, if the adhesive is excessive, more primary particles are produced around the block of the adhesive, that is, an aggregate intermediate coordinated with multiple primary particles will be produced, and the primary particles coordinated to the intermediate are prone to become a state facing each other in an unbalanced manner.

[0139] In order to reduce the block caused by the segregation of tar, pitch etc. as adhesive, a dispersant can be used.By using a dispersant, adhesive is easily evenly dispersed, and there is a tendency that the block of adhesive reduces.Thus it is believed that the effect of reducing the ratio of the composite particles with the structure of the main surface of a plurality of flat graphite particles toward the random direction can be obtained.In addition, the function of adhesive improves, and block formability improves, and the mixing ratio of adhesive can be reduced.As a dispersant, the dispersant that can be used in the operation (b) described later can be enumerated.

[0140] The flat graphite particles and their raw materials are not particularly limited, and examples thereof include artificial graphite, scaly natural graphite, flaky natural graphite, coke, resin, etc. Among them, artificial graphite obtained by graphitizing coke is preferred from the viewpoint of being less deformable and having a low specific surface area.

[0141] When the graphite particles include specific composite particles, all of the graphite particles may be specific composite particles, or a part of the graphite particles may be graphite particles other than the specific composite particles.

[0142] [Second Embodiment]

[0143] The negative electrode material for a lithium ion secondary battery according to the second embodiment of the present disclosure (hereinafter, also referred to as the negative electrode material) contains graphite particles and satisfies the following conditions: for the graphite particles, a Raman spectroscopic spectrum obtained by Raman spectrometry has a wavelength of 1580 cm -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range is defined as the R value, the proportion of particles with R≥0.2 is greater than or equal to 10% by number, and the starting temperature T of the oxidation-based mass reduction reaction of the graphite particles obtained by TG-DTA measurement in a dry air atmosphere is greater than or equal to 700°C.

[0144] By using the negative electrode material of the second embodiment, it is possible to manufacture a lithium ion secondary battery that is excellent in initial efficiency, can suppress the precipitation of lithium metal, and has excellent resistance to lithium (Li) precipitation. The reason for this is, for example, presumably as follows.

[0145] In the negative electrode material of the present embodiment, the following conditions are satisfied, similarly to the negative electrode material of the first embodiment: the ratio of R value as the intensity ratio Id / Ig is greater than or equal to 0.2 to a certain extent, that is, the surface crystallinity of the graphite particles is lowered to a certain extent. By lowering the surface crystallinity, the lithium ion secondary battery using the negative electrode material of the present embodiment can improve the Li precipitation tolerance without damaging the discharge capacity.

[0146] The graphite particles satisfy the starting temperature T of the mass reduction reaction based on oxidation of the graphite particles obtained in the TG-DTA measurement (differential thermal-thermogravimetric simultaneous measurement) in a dry air atmosphere, which is greater than or equal to 700° C. Specifically, using a TG-DTA measuring device, according to the TG curve and the DTA curve, the starting temperature of the mass reduction reaction based on oxidation of the graphite particles (for example, the temperature at which DTA>0) satisfies greater than or equal to 700° C. As a result, in a lithium-ion secondary battery using a negative electrode material, there is a tendency that the initial efficiency is excellent and the precipitation of lithium metal can be suppressed.

[0147] The starting temperature of the mass reduction reaction may be 700°C to 800°C, or 700°C to 750°C.

[0148] When the graphite particles include artificial graphite particles, the starting temperature of the mass reduction reaction tends to be higher. On the other hand, when the graphite particles are natural graphite particles, when a treatment of coating the surface of the graphite particles with low crystalline carbon is implemented, the starting temperature of the mass reduction reaction tends to be lower.

[0149] The configuration described in the section of the negative electrode material of the first embodiment and the configuration described in the section of the negative electrode material for a lithium ion secondary battery of the second embodiment may be combined as appropriate.

[0150] 《Method for producing negative electrode material for lithium-ion secondary battery》

[0151] The method for manufacturing the negative electrode material for lithium ion secondary batteries disclosed in the present invention includes the step of graphitizing coke. In more detail, from the perspective of improving the operability in graphitization treatment, etc., improving the cycle characteristics of lithium ion secondary batteries, etc., the method for manufacturing the negative electrode material for lithium ion secondary batteries disclosed in the present invention preferably includes the following steps (a) to (d). It has:

[0152] (a) a step of obtaining a mixture comprising a graphitizable aggregate (coke) and a graphitizable binder,

[0153] (b) forming the mixture to obtain a formed product,

[0154] (c) a step of graphitizing the molded product to obtain a graphitized product, and

[0155] (d) A step of pulverizing the graphitized product to obtain a pulverized product.

[0156] It should be noted that each step of the above method can be carried out continuously or discontinuously. Each step of the above method can be carried out in the same place or in different places.

[0157] The type of coke used in the above production method is not particularly limited, and examples thereof include petroleum-based or coal-based cokes such as liquid coke, needle coke, mosaic coke, and semi-needle coke having properties intermediate between needle coke and mosaic coke.

[0158] The method for obtaining coke particles (coke particles) is not particularly limited and can be implemented by a known method. The particle size of the coke particles is not particularly limited and can be selected in consideration of the desired particle size and particle structure of the graphite particles. In order to obtain particles with a lower specific surface area, it is preferably pulverized in a raw coke state. Such particles have a tendency to have fewer gaps and cracks caused by cleavage, and the compression load of the graphite particles increases.

[0159] In the manufacturing method disclosed herein, after obtaining a mixture comprising a graphitizable aggregate and a graphitizable binder, the mixture is molded to obtain a molded product. In the manufacturing method disclosed herein, from the viewpoint of Li precipitation resistance of a lithium ion secondary battery, the graphitizable binder preferably comprises a water-soluble or water-absorbent polymer compound, and more preferably comprises an aqueous binder containing a water-soluble or water-absorbent polymer compound.

[0160] By using the above-mentioned aqueous binder, the strength of the molded product is improved, and thus the operability in the subsequent graphitization treatment is also improved. When the strength of the molded product is improved, there is usually a tendency that the graphitized product after the graphitization treatment of the molded product is difficult to crush. However, in the above-mentioned manufacturing method, by using the above-mentioned aqueous binder, the strength of the molded product can be improved, and the graphitized product can be easily crushed.

[0161] The reason why the graphitized material can be easily crushed while improving the strength of the molded product in the above-mentioned production method is presumed to be as follows. It should be noted that the present disclosure is not limited to the following presumption.

[0162] In the above-mentioned manufacturing method, an aqueous binder containing a water-soluble or water-absorbent polymer compound is used, so that the aggregate is incorporated into the binder swollen with water. As a result, the surface of the graphitizable aggregate becomes slippery when the mixture is formed, the mixture is arranged, and the gaps become less. As a result, there is a tendency for the density and strength of the molded product to increase. Furthermore, the gaps between the aggregates are filled with water that is not incorporated into the binder, thereby forming a liquid bridge, and thus the strength of the molded product is improved.

[0163] In the above-mentioned manufacturing method, after the molded product is heat-treated by heating as needed, the molded product is graphitized to obtain a graphitized product. By using an aqueous binder, water evaporates during heat treatment, graphitization, etc. Therefore, the molded product before heat treatment, graphitization, etc. has a high density, but the density of the graphitized product after graphitization decreases. Therefore, the graphitized product can be easily crushed.

[0164] Furthermore, in the above-mentioned manufacturing method, the graphitized material can be easily crushed, and as a result, a crushed material with a small specific surface area can be easily obtained. By using the negative electrode material containing the crushed material with a small specific surface area for the production of a lithium-ion secondary battery, the contact area between the negative electrode material and the electrolyte can be reduced. As a result, the decomposition reaction of the electrolyte is suppressed, and the life of the battery can be extended. As a result, there is a tendency for the lithium-ion secondary battery to have excellent cycle characteristics.

[0165] In the past, when raw coke was used, there were problems such as difficulty in molding and low strength of the molded product, and it was necessary to improve the moldability and strength of the molded product by heat treating the raw coke. On the other hand, in the above-mentioned manufacturing method, even when raw coke is used without heat treatment, a molded product with excellent moldability and high strength can be obtained. Therefore, as a graphitizable aggregate, a material obtained by heat treating raw coke can be used for the formation of a molded product, and raw coke that has not been heat treated can also be used for the formation of a molded product.

[0166] In the above-mentioned manufacturing method, since the strength of the molded product is excellent, it is not necessary to load the mixture into a crucible for graphitization when graphitizing. That is, it is not necessary to use a crucible for graphitization, and the molded product can be graphitized by simply placing it in a graphitization furnace. Therefore, compared with the case of using a crucible for graphitization, there is a tendency that the manufacturing efficiency of the negative electrode material for lithium ion secondary batteries is excellent.

[0167] Generally, by increasing the amount of graphitizable binder, the strength of the molded product can be improved. However, when the amount of graphitizable binder is excessive, the density of the graphitized product is high, and there is a tendency for the graphitized product to be difficult to crush, and the battery characteristics such as the initial charge and discharge efficiency of the negative electrode material are easily reduced. In this embodiment, even if the amount of graphitizable binder is not increased, the strength of the molded product can be improved, and the reduction of battery characteristics caused by excessive use of the binder can also be prevented. Furthermore, by reducing the amount of binder, it is also easy to coat the surface of the crushed product with hard carbon, and there is a tendency to also improve the input characteristics of the lithium ion secondary battery.

[0168] In step (a), a mixture containing a graphitizable aggregate and a graphitizable binder is obtained. The mixing can be carried out at a temperature at which the graphitizable binder softens. Specifically, when the graphitizable binder is asphalt, tar, etc., the temperature can be 50°C to 300°C, and when it is a thermosetting resin, the temperature can be 20°C to 100°C. It should be noted that when the graphitizable binder is an aqueous binder containing a water-soluble or water-absorbent polymer compound, the mixing can be carried out at room temperature or by heating.

[0169] The mixing method is not particularly limited. For example, a method of mixing using a planetary mixer, a kiln mixer, a paddle mixer, etc. is preferred. A kneading machine accompanied by kneading, which is called a mixing mill, etc. can also be used.

[0170] When the graphitizable aggregate is in a particle form, the average particle size (D50) of the graphitizable aggregate is, for example, preferably 5 μm to 40 μm, more preferably 10 μm to 30 μm, and further preferably 10 μm to 25 μm.

[0171] The standard deviation of the particle size distribution of the graphitizable aggregate is, for example, preferably less than or equal to 0.35, more preferably less than or equal to 0.20, further preferably less than or equal to 0.18, and particularly preferably less than or equal to 0.16. By making the standard deviation of the particle size distribution of the above-mentioned aggregate less than or equal to 0.35, the deviation of the particle size of the aggregate can be reduced, and the deviation of the particle size of the obtained crushed material can also be suppressed. By using the negative electrode material of the crushed material with a small deviation in particle size for the production of lithium-ion secondary batteries, the resistance distribution in the negative electrode can be uniformized. As a result, there is a tendency for the rapid charging performance of lithium-ion secondary batteries to improve. Furthermore, by reducing the deviation of the particle size of the aggregate, even if the content or content of the graphitizable binder is reduced, the function as a binder can be appropriately ensured. The standard deviation of the particle size distribution is, for example, a value measured by a laser diffraction method (volume basis).

[0172] The lower limit of the standard deviation of the particle size distribution of the graphitizable aggregate is not particularly limited, and may be, for example, 0.05 or more, or 0.10 or more.

[0173] Examples of a method for adjusting the average particle size of the graphitizable aggregate and the standard deviation of the particle size distribution of the graphitizable aggregate to the above ranges include classification using a sieve, wind classification, wet classification, and the like.

[0174] The graphitizable binder is not particularly limited as long as it is a binder that can be graphitized by graphitization treatment. Specifically, it includes the aforementioned water-based binders, coal-based, petroleum-based, artificial and other asphalts and tars, thermoplastic resins, thermosetting resins, and the like.

[0175] The graphitizable aggregate and the graphitizable binder contained in the mixture may be either one kind or two or more kinds.

[0176] The content of each material in the mixture is not particularly limited. For example, relative to 100 parts by mass of graphitizable aggregate, the content of the graphitizable binder can be 10 parts by mass to 30 parts by mass, or 12 parts by mass to 25 parts by mass, or 14 parts by mass to 20 parts by mass. When the above-mentioned binder is added to a solvent or a dispersion medium and used as a solution or a dispersion, the mass parts of the solvent or the dispersion medium are not included. If the content of the binder is 10 parts by mass or more, there is a tendency to appropriately function as a binder for graphitizable aggregate. If the content of the binder is less than or equal to 30 parts by mass, there is a tendency to fully ensure the amount of fixed carbon in the mixture and excellent yield.

[0177] The graphitizable aggregate and the graphitizable binder contained in the mixture may be either one kind or two or more kinds.

[0178] The mixture may contain other components in addition to the graphitizable aggregate and the graphitizable binder. Examples of other components include aromatic compounds, graphite, dispersants, and graphitization catalysts.

[0179] 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 having a molecular weight of 300 or less.

[0180] Examples of the aromatic compound include naphthalene, methylnaphthalene such as 1-methylnaphthalene and 2-methylnaphthalene, acenaphthene, biphenyl, fluorene, benzopyrene, benzanthracene, dibenzanthracene, dibenzofuran, quinoline, and isoquinoline.

[0181] The aromatic compound contained in the mixture may be only one kind or two or more kinds.

[0182] Among them, as the aromatic compound, methylnaphthalene and naphthalene are preferred from the viewpoint of moldability when forming a molded product.

[0183] When the mixture contains aromatic compounds, the amount thereof is not particularly limited. The content of the aromatic compounds in the mixture is preferably less than or equal to 1% by mass, more preferably less than or equal to 0.5% by mass, and further preferably 0% by mass, relative to the total amount of the mixture.

[0184] The mixture may contain graphite. Examples of graphite include natural graphite and artificial graphite. The graphite is preferably in the form of particles. The mixture may contain only one type of graphite or two or more types.

[0185] From the viewpoint of easily dispersing the components in the mixture in the step (b) described later, the mixture preferably contains a dispersant. By including a dispersant in the mixture, the deviation of the particle size of the pulverized product obtained by pulverizing the graphitized product can be suppressed, and a pulverized product with aligned particle sizes can be easily obtained. As a result, there is a tendency for the rapid charging performance of the lithium ion secondary battery to be improved.

[0186] Furthermore, by including a dispersant in the mixture, the amount of the graphitizable binder can be suppressed, and improvement in battery characteristics such as the initial charge and discharge efficiency of the negative electrode material can be expected.

[0187] There is no particular restriction on the type of dispersant. Specifically, hydrocarbons such as liquid paraffin, paraffin, polyethylene wax, stearic acid, oleic acid, erucic acid, 12-hydroxystearic acid, and other fatty acids, zinc stearate, lead stearate, aluminum stearate, calcium stearate, magnesium stearate and other fatty acid metal salts, stearic acid amide, oleic acid amide, erucic acid amide, methylene bis stearic acid amide, ethylene bis stearic acid amide and other fatty acid amides, stearic acid monoglyceride, stearyl stearate, hardened oil and other fatty acid esters, stearyl alcohol and other higher alcohols, etc. Among them, fatty acids are preferred, and stearic acid is more preferred, from the aspects of not easily affecting the performance of the negative electrode material, being solid at room temperature and therefore easy to handle, melting at the temperature of step (a) and thus evenly dispersing, disappearing in the process until graphitization treatment, and being cheap.

[0188] When the mixture contains a dispersant, the amount thereof is not particularly limited. For example, the content of the dispersant relative to the entire mixture may be 0.1% to 20% by mass, 0.5% to 10% by mass, or 0.5% to 5% by mass.

[0189] From the viewpoint of promoting graphitization of the graphitizable aggregate or binder, the mixture preferably contains a graphitization catalyst. The type of graphitization catalyst is not particularly limited. Specifically, it can be exemplified by substances having a graphitization catalytic effect such as silicon, iron, nickel, titanium, boron, carbides of these substances, oxides of these substances, nitrides of these substances, and the like.

[0190] When the mixture contains a graphitization catalyst, the amount thereof is not particularly limited. For example, the content of the graphitization catalyst relative to the entire mixture may be 0.1% to 50% by mass, 0.5% to 40% by mass, or 0.5% to 30% by mass.

[0191] In step (b), the mixture obtained in step (a) is molded to obtain a molded product. Preferably, the molded product is molded into a predetermined shape by a uniaxial press or the like. By molding in this way, the amount of filling into the graphitization furnace can be increased when the mixture is graphitized to improve productivity, or the effect of the graphitization catalyst can be improved.

[0192] In step (b), there is no particular limitation on the method for molding the mixture. For example, there can be mentioned: a molding method in which the mixture is placed in a container such as a mold and pressurized 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 upper surface, and a metal frame is vibrated and impacted to perform molding; an extrusion molding method in which the mixture is extruded from a nozzle or the like using a transverse press to perform molding, etc.

[0193] In step (b), the density of the obtained molded product is not particularly limited, but is preferably 0.8 g / cm 3 ~1.7g / cm 3 , more preferably 1.0 g / cm 3 ~1.5g / cm 3 , more preferably 1.2 g / cm 3 ~1.5g / cm 3 .

[0194] The fixed carbon amount of the graphitizable binder in the mixture is preferably less than or equal to 20% by mass, more preferably less than or equal to 15% by mass, further preferably less than or equal to 10% by mass, and particularly preferably less than or equal to 5% by mass, relative to 100% by mass of the total of the aggregate and the binder (before graphitization). The lower the fixed carbon amount of the graphitizable binder in the mixture, the higher the coke ratio in the mixture, and there is a tendency for the discharge capacity of the lithium ion secondary battery to increase.

[0195] The lower limit of the fixed carbon content of the graphitizable binder in the mixture is not particularly limited, and may be 0.5% by mass or more, or 1.0% by mass or more, relative to 100% by mass of the total of the aggregate and the binder (before graphitization).

[0196] The molded product obtained in step (b) is preferably subjected to heat treatment before graphitizing the molded product in step (c). By performing the heat treatment, organic components that do not contribute to graphitization contained in the mixture are removed, and there is a tendency to suppress gas generation during graphitization.

[0197] The temperature of the heat treatment is not particularly limited, but is preferably a temperature lower than the temperature of the heat treatment in step (c). For example, the heat treatment can be performed in the range of 500°C to 1000°C.

[0198] In step (c), the molded product obtained in step (b) is graphitized. The method of graphitizing the molded product is not particularly limited as long as the conditions under which the graphitizable components contained in the mixture can be graphitized. For example, a method of heat treating the mixture in an atmosphere that is difficult to oxidize can be cited. The atmosphere that is difficult to oxidize the mixture is not particularly limited, and an inactive atmosphere such as nitrogen and argon, a vacuum, etc. can be cited.

[0199] The temperature of the heat treatment for graphitization may be, for example, greater than or equal to 1500°C, greater than or equal to 2000°C, greater than or equal to 2500°C, or greater than or equal to 2800°C. There is no particular upper limit to the temperature of the heat treatment, and for example, it may be less than or equal to 3200°C. When the temperature of the heat treatment is greater than or equal to 1500°C, there is a tendency for the crystallization to change and graphitization to proceed easily. When the temperature of the heat treatment is greater than or equal to 2000°C, there is a tendency for the development of graphite crystallization to become better. On the other hand, when the temperature of the heat treatment for graphitization is less than or equal to 3200°C, there is a tendency for sublimation of part of the graphite to be suppressed.

[0200] In step (d), the graphitized product obtained in step (c) is pulverized to obtain a pulverized product. The pulverization method is not particularly limited, and it can be carried out by a known method using a jet mill, a vibration mill, a pin mill, a hammer mill, etc. The pulverized product can be adjusted in particle size to a desired size. The method for adjusting the particle size is not particularly limited, and examples thereof include a method using the above-mentioned pulverization device, a method using a sieve, and the like.

[0201] If necessary, the pulverized product obtained in step (d) may be subjected to steps such as (e) disposing low-crystalline carbon on at least a portion of the surface of the pulverized product, (f) mixing the pulverized product with other negative electrode active materials, and the like.

[0202] As a method for configuring low-crystalline carbon on at least a portion of the surface of the pulverized product in step (e), for example, a method of mixing a substance (resin, etc.) that can become low-crystalline carbon by heat treatment with the pulverized product and heat treating the mixture can be cited. If low-crystalline carbon is configured on at least a portion of the surface of the pulverized product, the input-output characteristics such as the rapid charge and discharge characteristics of a lithium-ion secondary battery using the pulverized product as a negative electrode material may be improved.

[0203] [Other processes]

[0204] The method for producing the negative electrode material disclosed in the present invention may include steps other than the above steps.

[0205] For example, the manufacturing method of the negative electrode material may include a process of attaching an organic compound to the surface of a secondary particle after graphitization and performing a heat treatment. By attaching an organic compound to the surface of a secondary particle and performing a heat treatment, the organic compound attached to the surface is converted into low-crystalline carbon. Thus, it is possible to implement a process of coating the surface of the graphite particle with low-crystalline carbon.

[0206] There is no particular limitation on the method for attaching the organic compound to the surface of the secondary particles. For example, there can be mentioned: a wet method in which the secondary particles are dispersed and mixed in a mixed solution in which the organic compound is dissolved or dispersed in a solvent, and then the solvent is removed to attach the secondary particles; a dry method in which mechanical energy is applied to a mixture obtained by mixing the secondary particles and the solid organic compound to attach the secondary particles.

[0207] As long as the organic compound is a substance (carbon precursor) that is converted into low-crystalline carbon by heat treatment, there is no particular limitation. Examples include petroleum-based asphalt, naphthalene, anthracene, phenanthroline, coal tar, phenolic resin, polyvinyl alcohol, etc. The organic compound can be used alone or in combination of two or more.

[0208] The heat treatment temperature when the secondary particles with the organic compound attached to the surface are heat treated is not particularly limited as long as it is a temperature at which the organic compound attached to the surface of the secondary particles is converted into low-crystalline carbon, and is preferably 400° C. to 1500° C. For example, from the viewpoint of improving high temperature resistance, it is more preferably 1000° C. to 1500° C. The heat treatment is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere.

[0209] There is no particular limitation on the method of mixing the pulverized material with other negative electrode active materials in step (f). By mixing the pulverized material with other negative electrode active materials, the desired properties of the lithium ion secondary battery can sometimes be improved compared to the case where only the pulverized material is used as the negative electrode active material. As other negative electrode active materials, graphite particles such as natural graphite and artificial graphite, particles containing elements capable of absorbing and releasing lithium ions, etc. can be cited, but are not limited to these. As elements capable of absorbing and releasing lithium ions, there is no particular limitation, for example, Si, Sn, Ge, In, etc. can be cited.

[0210] The pulverized material obtained in step (f) may include particles in which a plurality of flat graphite particles are aggregated or combined, or may include particles in which a plurality of flat graphite particles are aggregated or combined in a manner in which the main surfaces of the graphite particles are not parallel to each other (hereinafter also referred to as graphite secondary particles).

[0211] If the pulverized product is in the form of graphite secondary particles, when pressing is performed to increase the density of the negative electrode, the negative electrode material particles are suppressed from being oriented toward the current collector, and there is a tendency that a sufficient path for lithium ions to enter and exit the negative electrode material can be ensured.

[0212] Furthermore, by including a plurality of flat graphite particles in a state of aggregation or combination, the influence of the pressure applied during pressing on each graphite particle is reduced due to the gaps between the plurality of flat graphite particles, and there is a tendency that the destruction of the graphite particles, the generation of cracks, etc. are suppressed. As a result, there is a tendency that the Li precipitation resistance of the lithium ion secondary battery is excellent.

[0213] In the present disclosure, "flat graphite particles" refer to non-spherical graphite particles having anisotropic shapes. Examples of flat graphite particles include graphite particles having shapes such as scales, flakes, and partially blocky shapes.

[0214] When the length of the long axis direction of the flat graphite particles is set to A and the length of the short axis direction is set to B, the aspect ratio represented by A / B is preferably 1.2 to 20, and more preferably 1.3 to 10. When the aspect ratio is greater than or equal to 1.2, the contact area between the particles increases, and there is a tendency for the conductivity to be further improved. When the aspect ratio is less than or equal to 20, there is a tendency for the input and output characteristics such as the rapid charge and discharge characteristics of the lithium ion secondary battery to be further improved.

[0215] The aspect ratio is obtained by observing graphite particles under a microscope, randomly selecting 100 graphite particles and measuring their respective A / B, and taking the arithmetic mean of their measured values. In the observation of the aspect ratio, the length A in the major axis direction and the length B in the minor axis direction are measured as follows. That is, in the projected image of the graphite particles observed using a microscope, the tangent a1 and the tangent a2 whose distance is the largest among the two parallel tangents circumscribed to the periphery of the graphite particles are selected, and the distance between the tangent a1 and the tangent a2 is used as the length A in the major axis direction. The tangent b1 and the tangent b2 whose distance is the smallest among the two parallel tangents circumscribed to the periphery of the graphite particles are selected, and the distance between the tangent b1 and the tangent b2 is used as the length B in the minor axis direction.

[0216] In the present disclosure, the "non-parallel principal surface" of the graphite secondary particles refers to that the surface (principal surface) with the largest cross-sectional area of ​​a plurality of flat graphite particles is not aligned in a certain direction. Whether the principal surfaces of a plurality of flat graphite particles are non-parallel to each other can be confirmed by microscopic observation. By a plurality of flat graphite particles being assembled or combined in a state where the principal surfaces are non-parallel to each other, the orientation of the principal surface of the flat graphite particles in the negative electrode can be suppressed, the expansion of the negative electrode accompanying charging can be suppressed, and there is a tendency for the cycle characteristics of the lithium-ion secondary battery to be further improved.

[0217] In addition, the graphite secondary particles may partially include a structure in which a plurality of flat graphite particles are aggregated or bonded so that their main surfaces are parallel to each other.

[0218] From the viewpoint of easy aggregation or combination, the average particle size of the flat graphite particles is, for example, preferably 1 μm to 50 μm, more preferably 1 μm to 25 μm, and further preferably 1 μm to 15 μm. As a method for measuring the average particle size of the flat graphite particles, a method for measuring using a scanning electron microscope can be cited, and the average particle size of the flat graphite particles is, for example, the arithmetic mean of the particle sizes of 100 flat graphite particles.

[0219] Flat graphite particles and raw materials thereof are not particularly limited, and can include artificial graphite, scaly natural graphite, scaly natural graphite, coke, resin, tar, pitch, etc. Among them, the graphite obtained by artificial graphite, natural graphite or coke has high crystallinity and becomes soft particles, so there is a tendency that the high density of the negative electrode becomes easy.

[0220] The negative electrode material may include spherical graphite particles. When the negative electrode material includes spherical graphite particles, the spherical graphite particles themselves have a high density, so there is a tendency that the pressing pressure required to obtain a desired electrode density can be reduced.

[0221] As spherical graphite particles, spherical artificial graphite, spherical natural graphite, etc. can be cited. From the viewpoint of high density of the negative electrode, the spherical graphite particles are preferably high-density graphite particles. Specifically, it is preferred to implement a particle spheroidization process to achieve high tap density spherical natural graphite. Furthermore, the negative electrode material layer containing spherical natural graphite has excellent peel strength, and there is a tendency that it is not easy to peel off from the collector even if it is strongly pressed.

[0222] When the negative electrode material includes spherical graphite particles, the flat graphite particles and spherical graphite particles mentioned above may be included. When the negative electrode material includes the flat graphite particles and spherical graphite particles mentioned above, the ratio of the two is not particularly limited and can be set according to the desired electrode density, the pressure conditions during pressing, the desired battery characteristics, etc.

[0223] In the case where the negative electrode material includes flat graphite particles and spherical graphite particles, there can be mentioned a state where flat graphite particles are mixed with spherical graphite particles, a state where flat graphite particles are combined with spherical graphite particles (hereinafter also referred to as composite particles), etc. As composite particles, for example, there can be mentioned particles in a state where flat graphite particles and spherical graphite particles are combined via carbides of organic matter.

[0224] The composite particles can be produced, for example, by using a mixture containing flat graphite particles or a raw material thereof and spherical graphite particles as the mixture in the step (a).

[0225] 《Negative electrode material composition for lithium-ion secondary batteries》

[0226] The negative electrode material composition for lithium ion secondary battery includes the negative electrode material for lithium ion secondary battery disclosed herein, a binder and a solvent. The negative electrode material composition for lithium ion secondary battery disclosed herein may be in the form of a slurry obtained by kneading the negative electrode material for lithium ion secondary battery, the binder and the solvent together.

[0227] The kneading can be performed using a dispersing device such as a disperser, a planetary mixer, or the like.

[0228] The binder used in the preparation of the negative electrode material composition for lithium ion secondary batteries is not particularly limited. As a binder, styrene-butadiene copolymer (SBR), methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate and other ethylenically unsaturated carboxylic acid esters and acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and other ethylenically unsaturated carboxylic acid homopolymers or copolymers, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polymethacrylonitrile and other ion conductive polymer compounds with large etc. can be cited. When the negative electrode material composition for lithium ion secondary batteries includes a binder, the content of the binder is not particularly limited. For example, relative to a total of 100 parts by mass of the negative electrode material for lithium ion secondary batteries and the binder, it can be 0.5 parts by mass to 20 parts by mass.

[0229] The negative electrode material composition for lithium ion secondary battery may include a thickener. As a thickener, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or its salt, oxidized starch, phosphorylated starch, casein, etc. can be used. When the negative electrode material composition for lithium ion secondary battery includes a thickener, the content of the thickener is not particularly limited. For example, relative to 100 parts by mass of the negative electrode material for lithium ion secondary battery, it can be 0.1 parts by mass to 5 parts by mass.

[0230] The negative electrode material composition for lithium ion secondary battery may include a conductive auxiliary material. As a conductive auxiliary material, carbon materials such as carbon black, graphite, acetylene black, oxides showing conductivity, inorganic compounds such as nitrides showing conductivity, etc. can be cited. When the negative electrode material composition for lithium ion secondary battery includes a conductive auxiliary material, the content of the conductive auxiliary material is not particularly limited. For example, relative to 100 parts by mass of the negative electrode material for lithium ion secondary battery, it can be 0.5 parts by mass to 15 parts by mass.

[0231] 《Negative electrode for lithium-ion secondary batteries》

[0232] The negative electrode for lithium ion secondary battery disclosed in the present invention comprises a negative electrode material layer and a current collector, wherein the negative electrode material layer comprises the negative electrode material for lithium ion secondary battery disclosed in the present invention. In addition to the negative electrode material layer and the current collector containing the negative electrode material for lithium ion secondary battery disclosed in the present invention, the negative electrode for lithium ion secondary battery may also comprise other components as required.

[0233] The negative electrode for a lithium ion secondary battery can be made, for example, by preparing the negative electrode material composition for a lithium ion secondary battery disclosed above and applying it on a collector to form a negative electrode material layer, or by molding the negative electrode material composition for a lithium ion secondary battery into a sheet, particle, or other shape and integrating it with a collector.

[0234] The material of the current collector is not particularly limited, and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc. The state of the current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, etc. In addition, porous materials such as porous metal (foam metal), carbon paper, etc. can also be used as the current collector.

[0235] When the negative electrode material composition for lithium ion secondary battery is applied to the collector to form a negative electrode material layer, the method is not particularly limited, and known methods such as metal mask printing, electrostatic coating, dip coating, spraying, roller coating, scraper, notch wheel coating, gravure coating, screen printing can be used. After the negative electrode material composition for lithium ion secondary battery is applied to the collector, the solvent contained in the negative electrode material composition for lithium ion secondary battery is removed by drying. Drying can be carried out using, for example, a hot air dryer, an infrared dryer, or a combination of these devices. The negative electrode material layer can also be rolled as needed. The rolling process can be carried out by methods such as flat plate pressing and calendering rollers.

[0236] When the negative electrode material composition for lithium ion secondary batteries formed into a sheet, particle, etc. is integrated with the collector to form a negative electrode material layer, the method of integration is not particularly limited. For example, it can be carried out by roller, flat plate pressing or a combination of these means. The pressure when the negative electrode material composition for lithium ion secondary batteries is integrated with the collector is preferably about 1MPa to 200MPa.

[0237] The negative electrode density of the negative electrode material layer is not particularly limited, but is preferably 1.1 g / cm 3 ~1.8g / cm 3 , more preferably 1.1 g / cm 3 ~1.7g / cm 3 , more preferably 1.1 g / cm 3 ~1.6g / cm 3 By setting the negative electrode density to be greater than or equal to 1.1 g / cm 3, so that there is a tendency that the increase in resistance is suppressed and the capacity is increased. By setting it to less than or equal to 1.8 g / cm 3 , so that there is a tendency that the reduction in input characteristics and cycle characteristics is suppressed.

[0238] 《Lithium-ion secondary battery》

[0239] The lithium ion secondary battery of the present disclosure includes the negative electrode for the lithium ion secondary battery of the present disclosure, a positive electrode, and an electrolyte solution.

[0240] The positive electrode can be obtained by forming a positive electrode material layer on a current collector in the same manner as the above-mentioned negative electrode production method. As the current collector, a current collector made of a metal or alloy such as aluminum, titanium, stainless steel, etc. in a foil, perforated foil, mesh, etc. can be used.

[0241] There is no particular limitation on the positive electrode material used to form the positive electrode material layer. Examples of the positive electrode material include metal compounds (metal oxides, metal sulfides, etc.) that can be doped or embedded with lithium ions, conductive polymer materials, etc. More specifically, examples include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and their composite oxides (LiNi x Mn y Co z O2, x+y+z=1), a composite oxide containing an additional element M' (LiNi a Mn b Co c M' d O2, a+b+c+d=1, M': Al, Ti, Zr or Ge), spinel lithium manganese oxide (LiMn2O4), lithium vanadium compounds, 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), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, porous carbon, etc. The positive electrode material can be a single type or two or more types.

[0242] The electrolyte solution is not particularly limited, and for example, an electrolyte solution (so-called organic electrolyte solution) obtained by dissolving a lithium salt as an electrolyte in a non-aqueous solvent can be used.

[0243] Examples of the lithium salt include LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3. The lithium salt may be used alone or in combination of two or more.

[0244] Examples of the non-aqueous solvent include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propane sultone, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3- Oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, triethyl phosphate, etc. The non-aqueous solvent may be one kind alone or two or more kinds.

[0245] The state of the positive electrode and the negative electrode in the lithium ion secondary battery is not particularly limited. For example, the positive electrode and the negative electrode and a separator disposed between the positive electrode and the negative electrode as required may be spirally wound or they may be stacked in a flat plate state.

[0246] The separator is not particularly limited, for example, a resin nonwoven fabric, a cloth, a microporous membrane or a combination thereof can be used. As the resin, a resin having polyolefins such as polyethylene and polypropylene as the main component can be listed. In the case where the positive electrode and the negative electrode do not contact in the structure of the lithium ion secondary battery, a separator may not be used.

[0247] The shape of the lithium ion secondary battery is not particularly limited, and examples thereof include laminated batteries, paper batteries, button batteries, coin batteries, stacked batteries, cylindrical batteries, and square batteries.

[0248] The lithium ion secondary battery of the present disclosure is suitable as a large-capacity lithium ion secondary battery used in electric vehicles, power tools, power storage devices, and the like.

[0249] Example

[0250] Hereinafter, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited to these examples.

[0251] [Example 1]

[0252] As a raw material of graphite particles, green coke (needle coke) derived from petroleum is used.

[0253] The green coke was coarsely pulverized by a hammer mill, the coarsely pulverized product was sieved using a sieve with a mesh size of 3 mm, and the undersize product was sieved using a sieve with a mesh size of 1 mm to recover particles with a particle size of 1 mm to 3 mm.

[0254] The obtained coke particles were pulverized and classified using a roll mill to obtain flat coke particles having a D50 of 10.1 μm. The standard deviation (σ) of the particle size distribution of the coke particles was 0.22.

[0255] 65 parts by mass of the obtained coke particles (90% by mass of fixed carbon), 7 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. The amount of binder in Table 1 was calculated by the ratio (%) of the fixed carbon amount of the binder to the total fixed carbon amount of the aggregate and the binder.

[0256] Next, the obtained mixture was uniaxially pressed at room temperature to a density of less than or equal to 1.3 g / cm 3 , and a molded product was obtained. Next, the obtained molded product was heat treated at 850°C for 8 hours in a nitrogen atmosphere. Then, it was graphitized at 3000°C for 30 hours. Then, the obtained particles were sieved with a 280-mesh sieve to obtain graphite particles as a negative electrode material. Using a laser diffraction particle size distribution measuring device (SALD3100, Shimadzu Corporation), the volume-based particle size distribution of the graphite particles was obtained, and the results showed that D10 was 6.2μm, D50 was 12.2μm, and D90 was 18.9μm.

[0257] [Example 2]

[0258] A mixture was obtained in the same manner as in Example 1 except that flat coke particles having a D50 of 10.5 μm and a standard deviation (σ) of particle size distribution of 0.33 were used. Then, graphite particles as a negative electrode material were obtained in the same manner as in Example 1 using the obtained mixture.

[0259] The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0260] [Example 3]

[0261] A mixture was obtained by kneading 57 parts by mass of the 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 using a kneader to obtain a mixture. The same operation as in Example 1 was performed to obtain a mixture. Then, using the obtained mixture, the same operation as in Example 1 was performed to obtain graphite particles as a negative electrode material.

[0262] The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0263] [Example 4]

[0264] As a raw material for graphite particles, raw coke (mosaic coke) derived from petroleum was used, and flat coke particles were obtained in the same manner as in Example 1. Regarding the coke particles, D50 was 9.1 μm, and the standard deviation (σ) of the particle size distribution was 0.24. Except for using the flat coke particles obtained in Example 4, a mixture was obtained in the same manner as in Example 1. Then, using the obtained mixture, graphite particles as a negative electrode material were obtained in the same manner as in Example 1.

[0265] The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0266] [Comparative Example 1]

[0267] The coke particles obtained in Example 1 were placed in a graphitization box without being mixed with a binder, calcined at 850° C., and after the impurities in the mixture were evaporated, graphitized at 3000° C. The obtained particles were then sieved with a 280-mesh sieve to obtain graphite particles as a negative electrode material.

[0268] The volume-based particle size distribution of the graphite particles was determined in the same manner as in Example 1. The results are shown in Table 1.

[0269] [Comparative Examples 2 to 4]

[0270] Artificial graphite particles having a 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, a treatment of coating the surface of the graphite particles with low-crystalline carbon was performed.

[0271] [Table 1]

[0272]

[0273] The negative electrode materials obtained in each of the Examples and Comparative Examples were used to measure and evaluate the following physical properties.

[0274] (Specific surface area)

[0275] The negative electrode material was filled into the measuring cell, and pre-heated at 200°C while vacuum degassing. The obtained sample was subjected to nitrogen adsorption using a gas adsorption device (ASAP2010, manufactured by Shimadzu Corporation). The obtained sample was subjected to BET analysis using the 5-point method to determine the specific surface area.

[0276] (Tap density)

[0277] In capacity 150cm3 A sample powder of graphite particles was placed in a graduated flat-bottomed test tube (KRS-406, manufactured by Kurachi Scientific Instruments Co., Ltd.) at a depth of 100 cm. 3 The flat-bottomed test tube with scale is plugged with a stopper. The 250 tap density is calculated from the mass and volume of the sample powder after the flat-bottomed test tube with scale is dropped 250 times from a height of 5 cm.

[0278] (R value)

[0279] The R value of the negative electrode material was determined by measuring the Raman spectrum using a Raman spectrometer (XploRA PLUS, manufactured by Horiba, Ltd.) under the following conditions. The arithmetic mean of the measured values ​​of 400 particles was taken as the R value.

[0280] -Raman spectroscopy measurement conditions-

[0281] Laser wavelength: 532nm

[0282] Laser intensity: 100mW or more

[0283] Neutral filter: 1%

[0284] Irradiation intensity: 1mW

[0285] Measuring range: 1000cm -1 ~1800cm -1

[0286] Irradiation time: 30 seconds

[0287] Irradiation area: 1μm 2

[0288] Baseline (D band): 1100cm -1 ~1470cm -1

[0289] Baseline (G band): 1450cm -1 ~1710cm -1

[0290] ·Cumulative number of times for 1 particle: 2 times

[0291] ·Number of particles measured: 400 particles

[0292] (Ratio of particles with R≥0.2 and ratio of particles with R<0.2)

[0293] By classifying the R values ​​of the 400 particles measured as described above, the ratio (number %) of particles with R ≥ 0.2 and the ratio (number %) of particles with R < 0.2 can be determined.

[0294] (Average value of half-value width of Id)

[0295] Among the 400 particles whose R values ​​were measured as described above, the half-value widths of Id in the spectra of the top 10 R values ​​were respectively determined, and then the arithmetic mean thereof was determined.

[0296] (Measurement of Starting Temperature T of Mass Reduction Reaction of Graphite Particles by Oxidation)

[0297] The starting temperature (oxidation reaction starting temperature) T of the mass reduction reaction of the graphite particles contained in the negative electrode material based on oxidation was measured by TG-DTA measurement in a dry air atmosphere. Specifically, the sample was set to about 20 mg, the container was set to a Pt disk, the flow rate of dry air was set to 300 ml / min, and the weight loss and differential thermal analysis were measured from room temperature to 900°C (temperature increase rate 20°C / min). The temperature when DTA>0 was taken as the oxidation reaction starting temperature T.

[0298] (Oil absorption)

[0299] The oil absorption of the negative electrode material is measured using linseed oil (eg manufactured by Kanto Chemical Co., Ltd.) as a reagent liquid instead of dibutyl phthalate (DBP) in the method described in JIS K6217-4:2017 “Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption”.

[0300] 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 a torque of 70% of the maximum torque generated was taken as the oil absorption (mL / 100 g). As a measuring instrument, an absorption measurement device (trade name: S-500) manufactured by ASAHISOKEN Co., Ltd. was used.

[0301] (Circularity)

[0302] The circularity of the negative electrode material was measured using a wet flow particle size and shape analyzer (FPIA-3000 manufactured by Malvern), and the circularity based on the number of particles when the cumulative value was 50% (so-called average circularity) was taken as the circularity.

[0303] (Electrode Orientation)

[0304] A negative electrode for a lithium ion secondary battery was produced as follows, and the electrode orientation was evaluated under the conditions shown below.

[0305] -Manufacturing of negative electrode for lithium-ion secondary battery-

[0306] Graphite particles (97.6 parts by mass), carboxymethyl cellulose (CMC) (1.2 parts by mass), and styrene butadiene rubber (SBR) (1.2 parts by mass) were kneaded to prepare a slurry. The slurry was applied in an amount of 10 g / cm 2 The electrode was coated on the shiny surface of the electrolytic copper foil and pre-dried at 90°C for 2 hours. The electrode density was adjusted to 1.65 g / cm by a roller press. 3 Then, the resulting product was dried at 120° C. for 4 hours in a vacuum atmosphere to perform a curing treatment, thereby forming a negative electrode material layer on the electrolytic copper foil to obtain a negative electrode for a lithium ion secondary battery.

[0307] -Evaluation of electrode orientation-

[0308] The obtained negative electrode for lithium ion secondary battery was formed into a 5 cm wide and 600 cm area. 2 The long strip-shaped sheet is pressed with a roller press at an oil pressure of 4t for the obtained molded product. The linear pressure at this time is 4t / 5cm=0.8t / cm. The pressed negative electrode is placed in an X-ray diffraction measurement cell, and an X-ray diffraction measurement device (X-RAY DIFFRACTIOMETER MultiFlex manufactured by Rigaku Corporation) is used to measure the X-ray diffraction pattern (2θ=25.5°~27.5°, 76.5°~78.5°) using CuKα rays at a scanning speed of 0.25° / min, a tube voltage of 40kV, a tube current of 30mA, a divergence slit of 1°, a scattering slit of 1°, and a light receiving slit of 0.3mm. The peak intensity (I 002 ) and the peak intensity of the 110 diffraction line (I 110 ) ratio, that is, I 002 / I 110 (002 / 110 in Table 2), and this value was used as the electrode orientation.

[0309] (Discharge capacity)

[0310] The lithium ion secondary battery prepared as described above was placed in a thermostatic chamber set at 25°C and charged at a constant current value of 0.2C until the voltage reached 0.005V (V vs. Li / Li + ), then constant voltage charging at 0.005V until the current value reaches 0.02C. Then, after a 30-minute rest, constant current discharge at 0.2C until the voltage reaches 1.5V (V vs. Li / Li + ). Calculate the discharge capacity at this time.

[0311] (Initial efficiency)

[0312] Using the lithium ion secondary battery produced as described above, the initial efficiency was determined by the following procedures (1) to (3).

[0313] (1) Charge at a constant current of 0.2 C to 0.005 V (vs. Li / Li+), and then charge at a constant voltage of 0.005 V until the current value reaches 0.02 C. The capacity at this time is referred to as the initial charge capacity.

[0314] (2) After a rest period of 30 minutes, the battery was discharged at a constant current of 0.2 C to 1.5 V (vs. Li / Li+). The capacity at this time was taken as the initial discharge capacity.

[0315] (3) The initial efficiency was calculated from the charge and discharge capacities calculated in (1) and (2) above using the following (Equation 1).

[0316] Initial efficiency (%) = (initial discharge capacity (mAh) / initial charge capacity (mAh)) × 100 ... (Formula 1)

[0317] (SOC-Li (Li precipitation resistance))

[0318] A lithium ion secondary battery was produced using the negative electrode obtained above, and the Li precipitation resistance was evaluated as follows.

[0319] -Manufacturing of lithium-ion secondary batteries-

[0320] A button cell as a lithium ion secondary battery is prepared using the negative electrode obtained as above, metallic lithium as a counter electrode, a mixed solution of ethylene carbonate / ethyl methyl carbonate (3:7 volume ratio) containing 1M LiPF6 and vinylene carbonate (VC) (1.0 mass %) as an electrolyte, a polyethylene microporous membrane with a thickness of 25 μm as a separator, and a copper plate with a thickness of 250 μm as a spacer.

[0321] - Evaluation of Li precipitation resistance -

[0322] The prepared lithium-ion secondary battery was placed in a thermostatic chamber set at 25°C and charged at a constant current of 0.1C to a voltage of 0.005V (V vs. Li / Li) from the first to the third cycle. + ), then charged at a constant voltage of 0.005V until the current value reached 0.05C. Then, after a 30-minute rest, the battery was discharged at a constant current of 0.2C until the voltage reached 1.5V (V vs. Li / Li +). The discharge capacity of the third cycle is set to 1C in the Li precipitation test. The charging of the fourth cycle is carried out at a current density of 3C at which the discharge capacity of the third cycle is charged for 20 minutes, and the termination condition is set to 1C capacity limit. The first inflection point in the differential curve (dV / dQ, V is voltage, Q is capacitance) of the charging curve of the fourth cycle obtained is used as the starting point of Li precipitation, and the capacity at this time is expressed as a percentage relative to the discharge capacity of the third cycle (or the charging capacity of the fourth cycle set to the same capacity) to evaluate Li precipitation resistance. The results are shown in Table 2. The larger the value of the percentage, the better the Li precipitation resistance.

[0323] (Measurement of DC resistance (DCR))

[0324] The direct current resistance (DCR) of the lithium ion secondary batteries produced in Example 1 and Example 4 was measured to determine the input characteristics of the batteries. The details are as follows.

[0325] The negative electrode obtained above was used, and 94 parts by mass of lithium nickel cobalt manganese oxide (LiNi 0.33 Mn 0.33 Co 0.33 A single-layer laminated full battery (lithium ion secondary battery) is prepared by using a mixed electrode of 3 parts by mass of carbon black, 3 parts by mass of polyvinylidene fluoride, 1 M of LiPF6 in ethylene carbonate / diethyl carbonate (3:7 volume ratio) and vinylene carbonate (VC) (1.0 mass%) as the electrolyte, and a polyethylene microporous membrane with a thickness of 25 μm as the separator.

[0326] The lithium ion secondary battery (single-layer laminated full cell) was placed in a thermostatic chamber set at 25° C. and subjected to three cycles of charge and discharge under the conditions of charge: CC / CV 0.2C 4.2V 0.02C Cut, and discharge: CC 0.2C 2.5V Cut.

[0327] Next, constant current charging was performed at a current value of 0.2C until the SOC reached 50%.

[0328] The lithium ion secondary battery was placed in a thermostatic chamber set at 25°C and charged at constant current for 10 seconds at 1C, 2C, and 3C. The voltage drop (ΔV) at each constant current was measured, and the DC resistance (DCR) was measured using the following formula.

[0329] 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)}

[0330] It was 1.79Ω in Example 1 and 1.68Ω in Example 4. The lower the value of direct current resistance (DCR), the better the input characteristics.

[0331] (Determination of high temperature storage maintenance rate)

[0332] The high temperature storage maintenance rates of the lithium ion secondary batteries produced in Example 1 and Example 4 were determined as follows.

[0333] The lithium-ion secondary battery (single-layer laminated full battery) after the DCR measurement was placed in a thermostatic chamber set at 25°C, and charged at a constant current of 0.2C to a voltage of 4.2V. Then, after a rest of 30 minutes, it was discharged at a constant current of 0.2C to a voltage of 2.5V. Then, it was charged at a constant current of 0.2C to a voltage of 4.2V, and the battery was placed in a thermostatic chamber set at 60°C and stored for 10 days.

[0334] Then, the battery was placed in a thermostatic chamber set at 25°C for 60 minutes and discharged at a constant current of 0.2C until the voltage reached 2.5V (Vvs.Li / Li + ). Then, the battery was charged at a constant current of 0.2C to a voltage of 4.2V, and then, after a rest period of 30 minutes, the battery was discharged at a constant current of 0.2C to a voltage of 2.5V.

[0335] The high temperature storage maintenance rate was calculated according to the following formula.

[0336] High temperature storage retention rate (%) = [(second discharge capacity at 25°C after storage at 60°C for 10 days) / (first discharge capacity at 25°C)] × 100

[0337] The value was 99.0% in Example 1 and 98.7% in Example 4. A higher value of the high-temperature storage maintenance rate indicates better high-temperature storage characteristics.

[0338] [Table 2]

[0339]

[0340] In Table 2, it can be confirmed that the lithium ion secondary battery has excellent initial efficiency and Li precipitation resistance in each example.

[0341] All documents, patent applications, and technical standards described in this specification are incorporated into this specification by reference to the same extent as if each document, patent application, and technical standard was specifically and individually described as being incorporated by reference.

Claims

1. A negative electrode material for a lithium ion secondary battery, comprising graphite particles and satisfying the following conditions: For the graphite particles, the wavelength at 1580 cm in the Raman spectrum obtained by Raman spectroscopy was -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range of R is defined as R value, the proportion of particles with 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 top 10 spectra of R value is less than or equal to 60 cm -1 .

2. A negative electrode material for a lithium ion secondary battery, comprising graphite particles and satisfying the following conditions: For the graphite particles, the wavelength at 1580 cm in the Raman spectrum obtained by Raman spectroscopy was -1 ~1620cm -1 The maximum peak intensity of the range Ig is at 1300cm -1 ~1400cm -1 When the intensity ratio Id / Ig of the maximum peak intensity Id in the range is defined as the R value, the proportion of particles with R≥0.2 is greater than or equal to 10% by number, and the starting temperature T of the oxidation-based mass reduction reaction of the graphite particles obtained by TG-DTA measurement in a dry air atmosphere is greater than or equal to 700°C.

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

4. The negative electrode material for lithium ion secondary battery according to claim 3, wherein The artificial graphite particles are particles obtained by graphitizing a mixture including a graphitizable aggregate and a graphitizable binder, wherein the binder includes a water-soluble or water-absorbing polymer compound.

5. The negative electrode material for lithium ion secondary battery according to any one of claims 1 to 4, wherein The circularity of the graphite particles is less than or equal to 93%.

6. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein The oil absorption of the graphite particles is 40 mL / 100 g to 70 mL / 100 g.

7. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 6, wherein The proportion of the graphite particles with R≥0.2 is less than or equal to 80% by number. 8 . The negative electrode material for a lithium ion secondary battery according to claim 1 , wherein the surface of the graphite particles is not coated with low-crystalline carbon. 9 . A negative electrode for a lithium ion secondary battery, comprising a negative electrode material layer and a current collector, wherein the negative electrode material layer comprises the negative electrode material for a lithium ion secondary battery according to claim 1 . 10 . A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 9 , a positive electrode and an electrolyte.

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