JP7444322B1 - Negative electrode materials for lithium ion secondary batteries, negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries - Google Patents

Abstract

The present invention provides a negative electrode material for a lithium ion secondary battery having excellent discharge load characteristics, low temperature charging characteristics, high temperature storage characteristics and pulse charging characteristics, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same. [Solution] The second graphite particles include first graphite particles that meet specific conditions of apparent density and linseed oil absorption, and second graphite particles that meet specific conditions of D0.1 and linseed oil absorption. the first graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is more crystalline than the natural graphite particle. A negative electrode material for lithium ion secondary batteries that is coated with a carbon material with low properties. [Selection diagram] None

Description

The present invention 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.

Lithium ion secondary batteries have been widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs due to their characteristics of being small, lightweight, and high energy density. In recent years, against the backdrop of environmental issues such as global warming caused by _CO2 emissions, clean electric vehicles (EVs) that run solely on batteries, and hybrid electric vehicles (HEVs) that combine a gasoline engine and batteries, etc., have become popular. . Recently, it has also been used for power storage, and its applications are expanding in a wide variety of fields.

The performance of the negative electrode material for a lithium ion secondary battery greatly affects the characteristics of the lithium ion secondary battery. Carbon materials are widely used as negative electrode materials for lithium ion secondary batteries. Carbon materials used for negative electrode materials are broadly classified into graphite and carbon materials with lower crystallinity than graphite (amorphous carbon, etc.). Graphite has a structure in which hexagonal mesh surfaces of carbon atoms are stacked regularly, and when used as a negative electrode material for lithium ion secondary batteries, insertion and desorption reactions of lithium ions proceed from the edges of the hexagonal mesh surfaces, resulting in charging. A discharge occurs.

Amorphous carbon has irregularly stacked hexagonal mesh surfaces or does not have hexagonal mesh surfaces. Therefore, in a negative electrode material using amorphous carbon, insertion and desorption reactions of lithium ions proceed on the entire surface of the negative electrode material. Therefore, it is easier to obtain a lithium ion battery with better input/output characteristics than when graphite is used as the negative electrode material (see, for example, Patent Document 1 and Patent Document 2). On the other hand, since amorphous carbon has lower crystallinity than graphite, its energy density is lower than that of graphite.
Considering the above characteristics of carbon materials, amorphous carbon and graphite are combined to maintain high energy density while improving input/output characteristics, and graphite is coated with amorphous carbon. A negative electrode material has also been proposed in which surface reactivity is reduced and input/output characteristics are improved while maintaining good initial charge/discharge efficiency (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 4-370662 Japanese Patent Application Publication No. 5-307956 International Publication No. 2012/015054

Lithium ion secondary batteries for automotive applications such as EVs and HEVs are required to have high input/output characteristics (that is, excellent discharge load characteristics) in order to charge regenerated energy and discharge power for driving a motor. Furthermore, automobiles are easily affected by outside temperature, and lithium ion secondary batteries are exposed to harsh conditions in summer and winter. Therefore, lithium-ion secondary batteries for automotive applications are required to have both low-temperature charging characteristics and high-temperature storage characteristics. Furthermore, in recent years, lithium ion secondary batteries for automotive applications are required to have pulse charging characteristics in order to shorten charging time.

One aspect of the present disclosure provides a negative electrode material for a lithium ion secondary battery that has excellent discharge load characteristics, low temperature charging characteristics, high temperature storage characteristics, and pulse charging characteristics, a negative electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery using the same. The purpose is to provide batteries.

Specific means for solving the above problem are as follows.
<1> First graphite particles that satisfy the following conditions 1A and 1B,
A second graphite particle that satisfies the following conditions 2A and 2B,
The amount of the second graphite particles is 10% by mass to 55% by mass with respect to the total mass of the graphite particles,
A negative electrode material for a lithium ion secondary battery, wherein the first graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle. .
Condition 1A: The loose apparent density T1 by the standing method is 0.60 g/cc or more, the apparent density T2 by the 30-tap method is 0.80 g/cc or more, and the apparent density T3 by the 250-tap method is 1. 00g/cc or more, and the compression degree value shown by the following formula is 19% or less. Compression degree (%) = [(T2-T1)/T3] x 100
Condition 1B: The linseed oil absorption amount is 40 mL/100 g to 55 mL/100 g. Condition 2A: D0.1 in the volume-based particle size distribution is 5 μm or less. Condition 2B: The linseed oil absorption amount is 55 mL/100 g to 75 mL/100 g. <2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein D10 in the volume-based particle size distribution of the first graphite particles is 7 μm to 13 μm, and D90 is 14 μm to 25 μm.
<3> The negative electrode material for a lithium ion secondary battery according to <1>, wherein D0.1 in the volume-based particle size distribution of the first graphite particles is more than 5 μm.
<4> Further comprising third graphite particles satisfying the following conditions 3A and 3B,
The lithium ion according to <1>, wherein the third graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle. Negative electrode material for secondary batteries.
Condition 3A: In the volume-based particle size distribution, the ratio of the D50 of the third graphite particles to the D50 of the first graphite particles (D50 of the third graphite particles/D50 of the first graphite particles) is in the range of 0.55 to 0.75. Condition 3B: Linseed oil absorption amount is 40 mL/100 g to 55 mL/100 g <5> The amount of the third graphite particles is 10 mass % to 25 mass % based on the total mass of graphite particles, <4> The negative electrode material for lithium ion secondary batteries described above.
<6> A negative electrode for a lithium ion secondary battery, comprising a negative electrode material layer containing the negative electrode material according to any one of <1> to <5>, and a current collector.
<7> A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to <6>, a positive electrode, and an electrolyte.

One aspect of the present disclosure provides a negative electrode material for a lithium ion secondary battery that has excellent discharge load characteristics, low temperature charging characteristics, high temperature storage characteristics, and pulse charging characteristics, a negative electrode for a lithium ion secondary battery using the same, and a lithium ion secondary battery using the same. Batteries can be provided.

It is a figure showing the relationship between oil pressure (t) and electrode density (g/cm ³ ) when pressing a sample electrode. It is a figure showing the relationship between oil pressure (t) and electrode density (g/cm ³ ) when pressing a sample electrode.

Hereinafter, embodiments for implementing the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including elemental steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and they do not limit the present invention.
In this disclosure, the term "step" includes not only a step that is independent from other steps, but also a step that cannot be clearly distinguished from other steps, as long as the purpose of the step is achieved. .
In the present disclosure, numerical ranges indicated using "~" include the numerical values written before and after "~" as minimum and maximum values, respectively.
In the numerical ranges described step by step in this disclosure, the upper limit or lower limit described in one numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. .
Furthermore, in the numerical ranges described in this disclosure, the upper limit or lower limit of the numerical range may be replaced with the values shown in the Examples.
In the present disclosure, unless otherwise specified, the content rate and content of each component in the negative electrode material and composition are as follows: It means the total content rate and amount of the plurality of substances present in the composition.
In the present disclosure, if there are multiple types of particles corresponding to each component in the negative electrode material and composition, unless otherwise specified, the particle size of each component in the negative electrode material and composition is It means the value for a mixture of the plurality of types of particles present in the particle.
In this disclosure, the term "layer" includes cases where the layer is formed in the entire area when observing the area where the layer exists, as well as cases where the layer is formed only in a part of the area. It will be done.
In this disclosure, the term "laminate" refers to stacking layers, and two or more layers may be bonded, or two or more layers may be removable.

<Negative electrode material for lithium ion secondary batteries>
The negative electrode material for lithium ion secondary batteries (hereinafter also simply referred to as negative electrode material) of the present disclosure includes:
First graphite particles that satisfy the following conditions 1A and 1B,
A second graphite particle that satisfies the following conditions 2A and 2B,
The amount of the second graphite particles is 10% by mass to 55% by mass with respect to the total mass of the graphite particles,
The first graphite particle is a secondary particle composed of a plurality of natural graphite particles, and at least a portion of the surface thereof is coated with a carbon material having lower crystallinity than the natural graphite particle.
Condition 1A: The loose apparent density T1 by the standing method is 0.60 g/cc or more, the apparent density T2 by the 30-tap method is 0.80 g/cc or more, and the apparent density T3 by the 250-tap method is 1. 00g/cc or more, and the compression degree value shown by the following formula is 19% or less. Compression degree (%) = [(T2-T1)/T3] x 100
Condition 1B: The linseed oil absorption amount is 40 mL/100 g to 55 mL/100 g. Condition 2A: D0.1 in the volume-based particle size distribution is 5 μm or less. Condition 2B: The linseed oil absorption amount is 55 mL/100 g to 75 mL/100 g. be

As shown in the Examples described below, by using the negative electrode material of the present disclosure, a lithium ion secondary battery with excellent input/output characteristics, low-temperature charging characteristics, high-temperature storage characteristics, and pulse charging characteristics can be obtained.

(First graphite particles)
The loose apparent density T1 of the first graphite particles obtained by the standing method is 0.60 g/cc or more, the apparent density T2 obtained by the 30-tap method is 0.80 g/cc or more, and the apparent density T3 obtained by the 250-tap method is It is 1.00 g/cc or more.

The negative electrode of a lithium ion secondary battery is obtained by drying a coating film formed using a slurry containing a negative electrode material on a current collector such as a copper foil.
In order to increase the energy density of lithium ion secondary batteries, it is necessary to increase the packing density of the negative electrode material in the coating film, in other words, it is necessary to increase the density of the coating film.
As a result of intensive studies by the inventor, it has been found that a good coating film can be formed when the solid content of the slurry used for forming the coating film is sufficiently large, and when the apparent density of the first graphite particles satisfies the above conditions. It has been found that slurry solids contents that are sufficiently high can be achieved.
If the apparent density of the first graphite particles satisfies the above conditions, the variation in film thickness during coating will be small, the amount of binder required to obtain sufficient adhesion strength can be reduced, and the effective capacity can be reduced. The decline tends to be suppressed.

Furthermore, when the apparent density of the first graphite particles satisfies the above conditions, the electrode density of the coating film tends to be high, and the press pressure required to obtain the desired electrode density can be reduced. By lowering the press pressure, the orientation of graphite particles in the direction perpendicular to the thickness direction of the negative electrode is reduced, making it easier to take in and out lithium ions during charging and discharging. As a result, a lithium ion secondary battery with better input/output characteristics such as low temperature charging characteristics and discharge load characteristics tends to be obtained.

The T1 of the first graphite particles is preferably 0.62 g/cc or more, more preferably 0.65 g/cc or more. The upper limit of T1 is not particularly limited, but may be, for example, 0.80 g/cc or less.
The T2 of the first graphite particles is preferably 0.81 g/cc or more, more preferably 0.82 g/cc or more. The upper limit of T2 is not particularly limited, but may be, for example, 1.00 g/cc or less.
The T3 of the first graphite particles is preferably 1.03 g/cc or more, more preferably 1.05 g/cc or more. The upper limit of T3 is not particularly limited, but may be, for example, 1.20 g/cc or less.

The value of the degree of compression calculated from the apparent density of the first graphite particles is 19% or less. When the apparent density of the first graphite particles is within the above range, the value of the degree of compression tends to be small.
In a lithium ion secondary battery, a carbon material serving as a negative electrode material repeatedly expands and contracts during charging and discharging. Therefore, if the adhesion between the carbon material and the current collector is low, the carbon material may peel off from the current collector, resulting in a decrease in charge/discharge capacity and a risk of deterioration in cycle characteristics.
When the degree of compression of the first graphite particles contained in the negative electrode material is 19% or less, the adhesion between the negative electrode material and the current collector tends to improve. Therefore, by using the negative electrode material of this embodiment, even when the carbon material repeatedly expands and contracts due to charging and discharging, the adhesion between the carbon material and the current collector is maintained well, and the high-temperature storage properties and There is a tendency to obtain lithium ion secondary batteries with excellent life characteristics such as cycle characteristics.

The compression degree of the first graphite particles is preferably 18% or less, more preferably 17% or less. The lower limit of the degree of compression is not particularly limited, but may be, for example, 13% or more, or 14% or more.

The linseed oil absorption amount of the first graphite particles is 40 mL/100 g to 55 mL/100 g.
The amount of linseed oil absorbed by graphite particles is an index that indirectly quantifies the voids between the particles, and it can be determined that the larger the value of the amount of linseed oil absorbed, the more voids between the particles.
The amount of linseed oil absorbed by graphite particles is affected by the particle size, particle size distribution, particle shape, tap density, etc. of the graphite particles.
When the linseed oil absorption amount of the first graphite particles is 40 mL/100 g or more, the filling of the negative electrode material does not progress too much, and the thickness of the coating film is less likely to fluctuate due to drying conditions, etc., and when the density of the coating film increases due to pressing. It has the advantage that fluctuations in density are less likely to occur. Furthermore, since the residual stress caused by pressing is small, the negative electrode is less likely to peel off from the current collector, and the input/output characteristics and cycle characteristics tend to be less likely to deteriorate.
The linseed oil absorption amount of the first graphite particles is preferably 41 mL/100 g or more, more preferably 42 mL/100 g or more.

When the linseed oil absorption amount of the first graphite particles is 55 mL/100 g or less, the amount of fine particles relative to the voids between large particles is not too large, and the electrolyte tends to penetrate smoothly. Furthermore, the diffusion resistance of lithium ions is reduced, and overall battery performance, especially continuous charging acceptability (pulse charging characteristics), tends to be less likely to deteriorate.
The linseed oil absorption amount of the first graphite particles is preferably 53 mL/100 g or less, more preferably 50 mL/100 g or less.

The first graphite particles preferably have a D10 in a volume-based particle size distribution of 7 μm to 13 μm, and a D90 of 14 μm to 25 μm.

When the D10 of the first graphite particles is 7 μm or more and the D90 is 14 μm or more, the particles tend to be neither too small nor have a specific surface area too large, and good charge/discharge efficiency and high discharge capacity tend to be obtained.
When the D10 of the first graphite particles is 13 μm or less and the D90 is 25 μm or less, the particles are not too large and deterioration of input/output characteristics such as low temperature charge acceptance and discharge load characteristics tends to be suppressed. In addition, deterioration of life characteristics such as high temperature storage characteristics and cycle characteristics tends to be suppressed.
D10 of the first graphite particles is preferably 7.1 μm to 12.5 μm, more preferably 7.5 μm to 10.0 μm.
D90 of the first graphite particles is preferably 14.5 μm to 24.5 μm, more preferably 15.0 μm to 20.0 μm.

D0.1 in the volume-based particle size distribution of the first graphite particles is preferably larger than 5 μm, more preferably 5.2 μm or more, and even more preferably 5.5 μm or more.
When D0.1 of the first graphite particles is larger than 5 μm, the particles tend to be neither too small nor have a specific surface area too large, and good charge/discharge efficiency and high discharge capacity tend to be obtained.
The upper limit of D0.1 of the first graphite particles is not particularly limited, but may be, for example, 10 μm or less, 8 μm or less, or 7 μm or less.

The D50 of the first graphite particles in a volume-based particle size distribution is preferably 8 μm or more, more preferably 8.5 μm or more, and even more preferably 9 μm or more.

The first graphite particles preferably have a D50 of 20 μm or less in a volume-based particle size distribution, more preferably 19 μm or less, and even more preferably 18 μm or less.

In the present disclosure, D0.1, D10, D50, and D90 of graphite particles have cumulative frequencies of distribution from the small particle side reaching 0.1%, 10%, 50%, and 90%, respectively, in the volume-based particle size distribution. Means the particle size at a point. Volume-based particle size distribution is determined by laser diffraction.

The first graphite particle is a secondary particle composed of a plurality of natural graphite particles, and at least a portion of the surface thereof is coated with a carbon material having lower crystallinity than the natural graphite particle.
At least a part of the surface of the first graphite particle is coated with a carbon material having lower crystallinity than natural graphite particles (hereinafter also referred to as low-crystalline carbon), so that graphite becomes a core material that contributes to charge/discharge reactions. Surface exposure of particles is suppressed. As a result, when a lithium ion secondary battery is produced, the decomposition reaction of the electrolytic solution on the surface of the negative electrode material is suppressed, and a decrease in initial efficiency, cycle characteristics, and pulse charging characteristics tends to be suppressed.

The amount of low crystalline carbon per 100 parts by mass of graphite particles serving as a core material may be, for example, within the range of 1 part by mass to 20 parts by mass, or may be within the range of 1 part by mass to 10 parts by mass. .

The first graphite particles are obtained by subjecting natural graphite particles to processes such as spheroidization and pulverization. Examples of the shape of the first graphite particles include spherical shape and block shape.
Examples of the natural graphite used for producing the first graphite particles include scaly graphite, flaky graphite, and earthy graphite.
It is preferable that the natural graphite used for manufacturing the first graphite particles be highly purified by a purification treatment. The method of purification treatment is not particularly limited, and can be appropriately selected from commonly used purification treatment methods. Examples include flotation, electrochemical treatment, chemical treatment, and the like.

The purity of the natural graphite used for manufacturing the first graphite particles is preferably 99.8% or more (ash content 0.2% or less) on a mass basis, and preferably 99.9% or more (ash content 0.1% or less). It is more preferable that When the purity is 99.8% or more, the safety of the battery is further improved, and the battery performance tends to be further improved. The purity of natural graphite can be calculated, for example, by leaving 100 g of graphite in a furnace at 800° C. in an air atmosphere for 48 hours or more, and then measuring the remaining amount derived from ash.

The method of coating the surface of graphite particles serving as a core material with low crystalline carbon is not particularly limited. For example, the method may include a step of heat-treating a mixture containing graphite particles serving as a core material and a substance that changes into low-crystalline carbon by heating (hereinafter also referred to as a precursor of low-crystalline carbon).
The precursor of low-crystalline carbon is not particularly limited, and examples thereof include pitch, organic polymer compounds, and the like. Examples of pitch include ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt decomposition pitch, pitch made by thermally decomposing polyvinyl chloride, etc., and pitch made by polymerizing naphthalene etc. in the presence of a super strong acid. An example of this is pitch. Examples of the organic polymer compound include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral, and natural substances such as starch and cellulose.
The graphite particles and the low-crystalline carbon precursors used as the core material for producing the first graphite particles may be used alone or in combination of two or more.
The temperature at which the mixture containing graphite particles as a core material and a low-crystalline carbon precursor is heat-treated is not particularly limited, but from the viewpoint of improving the cycle characteristics of a lithium ion secondary battery, the temperature is 900°C to 1500°C. Preferably it is ℃.
In the above method, the content of graphite particles serving as a core material in the mixture before heat treatment is not particularly limited. In order to improve the cycle characteristics of a lithium ion secondary battery, the content of graphite particles serving as a core material is preferably 90% by mass to 99.9% by mass based on the total mass of the mixture.

The specific surface area (N ₂ specific surface area) of the first graphite particles determined by nitrogen adsorption measurement at 77K is not particularly limited, but is preferably 2.5 m ² /g to 5 m ² /g, and 3 m ² It is more preferably from /g to 5m ² /g. If the N ₂ specific surface area of the first graphite particles is within the above range, a good balance of initial charge/discharge efficiency, input/output characteristics, and cycle characteristics of the lithium ion secondary battery tends to be obtained.
The N ₂ specific surface area of the graphite particles is measured by the method described in Examples below.

The R value of the first graphite particles measured by Raman spectroscopy is not particularly limited, but is preferably, for example, 0.2 to 1.0, more preferably 0.2 to 0.8. When the R value of the first graphite particles is 0.2 or more, there are sufficient graphite lattice defects used for taking in and taking out lithium ions, and a decrease in input/output characteristics tends to be suppressed. When the R value of the first graphite particles is less than 1.0, the decomposition reaction of the electrolytic solution is sufficiently suppressed, and a decrease in initial efficiency tends to be suppressed.
In the present disclosure ^, the R value of graphite particles is defined as the intensity ratio ( ^Id / Ig).
The R value of graphite particles is measured by the method described in Examples below.

The amount of CO ₂ adsorbed by the first graphite particles is not particularly limited, but is preferably 0.10 cm ^{3 /} g to 0.40 cm 3 /g, and preferably 0.10 ^{cm 3 /} g to 0.30 cm ³ /g. More preferably, it is 0.10 cm ³ /g to 0.20 cm ³ /g. Since CO ₂ has a high saturated vapor pressure and the kinetic energy of CO ₂ molecules is extremely high, it is difficult to be adsorbed on the basal surface of the graphite skeleton, which has weak interactions. However, it is known that CO ₂ molecules are adsorbed by extremely strong adsorption interactions in the irregularities, ie, ultramicropores, that occur in areas such as lattice defects. On the other hand, it is known that lattice defects have disordered lattices, have polarized dipole moments, and become active sites for redox reactions, which are active in decomposition reactions of electrolyte solutions. If the CO ₂ adsorption amount of the graphite particles is within the above range, it is thought that excessive decomposition reactions of the electrolyte etc. can be suppressed while leaving sites where lithium ions can be intercalated and desorbed between the graphite layers. It will be done. It is also known that the decomposition products of the electrolytic solution form a SEI (Solid Electrolyte Interphase) film on the surface of the active material and thus become a resistance component of the input/output characteristics. Therefore, excellent input/output characteristics and high-temperature storage characteristics can be obtained by controlling the CO ₂ adsorption amount of graphite particles within the above-mentioned range and suppressing excessive side reactions such as electrolyte decomposition.
The amount of CO ₂ adsorbed by graphite particles is measured by the method described in Examples below.

Although the average interplanar spacing d ₀₀₂ of the first graphite particles is not particularly limited, it is preferable that the graphite particles have a range of, for example, 0.335 nm to 0.339 nm. Particularly, from the viewpoint of increasing charge/discharge capacity, d ₀₀₂ is more preferably in the range of 0.335 nm to 0.338 nm, and even more preferably in the range of 0.335 nm to 0.337 nm. When graphite particles having an average interplanar spacing d ₀₀₂ in the range of 0.335 nm to 0.337 nm are used, a good lithium ion secondary battery tends to be obtained with a large charge/discharge capacity of 330 mAh/g to 370 mAh/g.
The average interplanar spacing d ₀₀₂ of graphite particles is measured by the method described in Examples below.

The range of the average circularity of the first graphite particles is not particularly limited, but is preferably, for example, 0.74 or more, and more preferably 0.80 or more.
Since the average circularity of the first graphite particles is 0.74 or more, even if the graphite particles form aggregates due to intermolecular interaction, components such as binder absorbed in the voids between the particles will be localized. There is a tendency for electrodes with excellent adhesion to be obtained. Furthermore, since the localization of the binder is suppressed, an increase in the required amount of the binder is suppressed. As a result, it tends to be possible to suppress a decrease in capacitance and a decrease in input/output characteristics due to an increase in resistance components. Furthermore, a uniform low-crystalline carbon layer is formed on the surface of the graphite particles serving as the core material, and variations in the amount of low-crystalline carbon covering between particles tend to be suppressed. As a result, the inside of the negative electrode can be divided into harder parts and particles (i.e., a large amount of low-crystalline carbon coverage) and softer parts and particles (i.e., a small amount of low-crystalline carbon coverage). suppressed. As a result, the increase in specific surface area due to cracks occurring because the areas with a small amount of low-crystalline carbon coating cannot withstand the load of press treatment, and the decline in high-temperature storage properties due to high activation caused by cracks are suppressed. There is a tendency to
The average circularity of graphite particles is measured by the method described in Examples below.

(Second graphite particles)
The second graphite particles have a D0.1 of 5 μm or less in a volume-based particle size distribution.
When D0.1 of the second graphite particles is 5 μm or less, there are sufficient fine particles derived from the second graphite that fill the voids of the first graphite particles. Therefore, sufficient contact points between particles are ensured, electronic resistance is small, and overall deterioration of battery performance tends to be suppressed.
D0.1 of the second graphite particles is preferably 4.5 μm or less, more preferably 4 μm or less.
The lower limit of D0.1 of the second graphite particles is not particularly limited, but may be, for example, 1 μm or more, or 1.5 μm or more.

The second graphite particles have a linseed oil absorption amount of 55 mL/100 g to 75 mL/100 g.
When the linseed oil absorption amount of the second graphite particles is 55 mL/100 g or more, there are sufficient fine particles derived from the second graphite particles that fill the voids of the first graphite particles. Therefore, sufficient contact points between particles are ensured, electronic resistance is small, and overall deterioration of battery performance tends to be suppressed.
When the linseed oil absorption amount of the second graphite particles is 75 mL/100 g or less, the amount of fine particles derived from the second graphite particles that fill the voids of the first graphite particles is not too large, and the electrolyte can penetrate smoothly. . In addition, the diffusion resistance of lithium ions is small, which tends to suppress deterioration in battery performance in general, especially in continuous charging acceptability (pulse charging characteristics).

The material of the second graphite particles is not particularly limited, and may be natural graphite or artificial graphite.
Examples of natural graphite include natural graphite that can be used as the first graphite particles.
Examples of the artificial graphite include resin materials such as epoxy resins and phenol resins, pitch materials obtained from petroleum, coal, etc., and artificial graphite obtained by firing coke and the like.
The second graphite particles may be in the form of secondary particles formed from a plurality of primary particles.
The second graphite particles may or may not have at least a portion of their surface coated with low-crystalline carbon.

The method for producing the second graphite particles using natural graphite is the same as the method for producing the first graphite particles.
There are no particular restrictions on the method for obtaining artificial graphite. For example, there is a method in which raw materials such as resin, naphthalene, anthracene, phenanthroline, coal tar, and tar pitch are calcined in an inert atmosphere at 800° C. or higher to obtain artificial graphite as a calcined product. In this case, second graphite particles derived from artificial graphite can be produced by pulverizing the obtained fired product using a known method such as a jet mill, vibration mill, pin mill, or hammer mill, and adjusting the particle size. Further, the raw material may be subjected to heat treatment before calcining.

D50 in the volume-based particle size distribution of the second graphite particles is not particularly limited. For example, the D50 of the second graphite particles is preferably 15 μm to 25 μm, more preferably 17 μm to 25 μm. When the D50 of the second graphite particles is 25 μm or less, the discharge capacity, input/output characteristics, and cycle characteristics tend to improve. When the D50 of the second graphite particles is 15 μm or more, the initial charge/discharge efficiency tends to improve.

The specific surface area (N ₂ specific surface area) of the second graphite particles determined by nitrogen adsorption measurement at 77K is not particularly limited, but is preferably 1.7 m ² /g to 5 m ² /g, for example, 2 m ² It is more preferably from /g to 4.5m ² /g. When the N ₂ specific surface area of the second graphite particles is within the above range, a good balance of initial charge/discharge efficiency, input/output characteristics, and cycle characteristics tends to be obtained.

The CO ₂ adsorption amount of the second graphite particles is not particularly limited, but is preferably 0.10 cm ³ /g to 0.40 cm 3 /g, and 0.10 cm ^{3 /} g to 0.30 cm ³ /g, for example. More preferably, it is 0.20 cm ³ /g to ^{0.30 cm 3} /g. When the CO ₂ adsorption amount of the second graphite particles is within the above range, excessive side reactions such as electrolyte decomposition are suppressed, and excellent input/output characteristics and high temperature storage characteristics tend to be obtained.

(Third graphite particles)
The negative electrode material of the present disclosure may include third graphite particles in addition to the first graphite particles and the second graphite particles. By including the third graphite particles in the negative electrode material, a lithium ion secondary battery having high capacity and excellent efficiency when mounted at high density can be obtained.

The third graphite particles have a ratio of D50 of the third graphite particles to D50 of the first graphite particles (D50 of the third graphite particles/D50 of the first graphite particles, hereinafter also referred to as particle size ratio) in the volume-based particle size distribution. ) is in the range of 0.55 to 0.75.
Since the third graphite particles whose particle size ratio is within the above range are finer particles than the first graphite particles (particle size ratio is smaller than 1), they tend to be harder graphite particles than the first graphite particles. be. For this reason, by forming a coating film using a negative electrode material containing third graphite particles, deformation of particles due to press pressure for densification can be further suppressed. As a result, a sufficient permeation path for the electrolyte is ensured, and the electrolyte tends to permeate smoothly.
By setting the particle size ratio of the third graphite particles to 0.55 or more, the coating film does not become too hard, suppressing the tendency for the press pressure required to obtain the desired electrode density to increase, and improving the electrode density. Can be controlled. As a result, the orientation of the graphite particles in the direction perpendicular to the electrode thickness does not become too high, which tends to suppress deterioration in input/output characteristics and deterioration in capacity and efficiency during high-density packaging.
By setting the particle size ratio of the third graphite particles to 0.75 or less, the coating film does not become too soft and springback after pressing (a phenomenon in which it tries to return to the state before pressing) is suppressed, resulting in good electrode density. Can be controlled.
The particle diameter ratio of the third graphite particles is preferably 0.60 to 0.75, more preferably 0.65 to 0.75.

The third graphite particles have a linseed oil absorption of 40 mL/100 g to 55 mL/100 g.
When the linseed oil absorption amount of the third graphite particles is 40 mL/100 g or more, the voids between the particles are not too small and filling does not proceed too much. Therefore, the coating thickness is less likely to change due to drying conditions, etc., and the electrode density is less likely to change even when pressed under high pressure. Furthermore, since the residual stress caused by pressing is small, the negative electrode is difficult to peel off from the current collector. As a result, input/output characteristics and cycle characteristics are maintained well.
When the linseed oil absorption amount of the third graphite particles is 55 mL/100 g or less, the amount of fine particles relative to the spaces between the first graphite particles and the second graphite particles is not too large, and the electrolyte solution penetrates smoothly. In addition, the diffusion resistance of lithium ions is small, and deterioration of battery performance in general, especially in continuous charging acceptability (pulse charging characteristics), is suppressed.
In order to further improve the performance of the lithium ion secondary battery, the linseed oil absorption amount of the third graphite particles is preferably 41 mL/100 g to 55 mL/100 g, more preferably 41 mL/100 g to 50 mL/100 g. .

The third graphite particle is a secondary particle composed of a plurality of natural graphite particles, and at least a portion of the surface thereof is coated with a carbon material having lower crystallinity than the natural graphite particle.
For details and preferred embodiments of the secondary particles consisting of a plurality of natural graphite particles and the coating with low crystalline carbon, the description of the first graphite particles can be referred to.

The contents described above as preferred embodiments of the first graphite particles can be referred to as preferred embodiments of the third graphite particles.

(Mixing ratio of graphite particles)
In the negative electrode material of the present disclosure, the amount of the second graphite particles is 10% by mass to 55% by mass based on the total mass of graphite particles.
The second graphite particles have a wide particle size distribution and include particles larger than the first graphite particles and particles smaller than the first graphite particles. By blending the first graphite particles and the second graphite particles having different particle size distributions, the voids between the particles are mutually filled, and the filling state of the resulting negative electrode coating film can be controlled. That is, in the press step in manufacturing the negative electrode, press force can be applied uniformly to the inside of the coating film. As a result, variations in density in the thickness direction of the coating film are reduced, and the electrolytic solution permeates smoothly. In addition, since the first graphite particles are relatively fine particles and at least a part of the surface is coated with low-crystalline carbon, the second graphite particles (especially the second graphite particles not coated with low-crystalline carbon) It tends to be harder. By blending graphite particles with different hardness, such as the first graphite particle and the second graphite particle, deformation of the particle when pressed under high pressure is suppressed, and a sufficient penetration path for the electrolyte is ensured. This allows the electrolyte to penetrate smoothly.

In the negative electrode material of the present disclosure, the amount of the second graphite particles is 10% by mass or more based on the total mass of the graphite particles, so that there are sufficient fine particles derived from the second graphite particles to fill the voids of the first graphite particles. do. Therefore, sufficient contact points between particles are ensured, electronic resistance is small, and overall deterioration of battery performance is suppressed.
In the negative electrode material of the present disclosure, since the amount of the second graphite particles is 55% by mass or less based on the total mass of the graphite particles, deformation of the particles due to the pressing force of the relatively soft second graphite particles is unlikely to occur. . For this reason, the electrolytic solution permeates smoothly, the diffusion resistance of lithium ions is small, and deterioration of battery performance in general, especially continuous charging acceptability (pulse charging characteristics), tends to be suppressed. Furthermore, the amount of coarse particles derived from the second graphite particles is not too large, and local expansion and contraction due to charging and discharging within the electrode is suppressed. As a result, peeling of the electrode from the current collector is suppressed, and cycle characteristics are maintained favorably.

The amount of the second graphite particles is preferably 15% to 55% by mass, more preferably 20% to 55% by mass, based on the total mass of the graphite particles. It is even more preferable.

When the negative electrode material of the present disclosure includes third graphite particles, the amount of the third graphite particles is preferably 10% by mass to 25% by mass based on the total mass of graphite particles.

When the amount of the third graphite particles contained in the negative electrode material is 10% by mass or more based on the total mass of the graphite particles, fine particles derived from the second graphite particles and fine particles derived from the third graphite particles fill the voids of the first graphite particles. There are sufficient fine particles. Therefore, sufficient contact points between particles are ensured, electronic resistance is small, and overall deterioration of battery performance tends to be suppressed.

When the amount of the tertiary graphite particles contained in the negative electrode material is 25% by mass or less based on the total mass of the graphite particles, the fine particles derived from the second graphite particles and the tertiary graphite particles are not too large, and the penetration of the electrolyte is prevented. It is done smoothly. For this reason, the diffusion resistance of lithium ions is small, and deterioration of battery performance in general, particularly continuous charging acceptability (pulse charging characteristics), tends to be suppressed. Furthermore, the amount of coarse particles derived from the second graphite particles is not too large, and local expansion and contraction due to charging and discharging within the electrode is suppressed. As a result, peeling of the electrode from the current collector is suppressed, and cycle characteristics are maintained favorably.
From the viewpoint of the above-mentioned effects, when the negative electrode material of the present disclosure includes the third graphite particles, the amount of the second graphite particles is preferably 25% by mass to 50% by mass based on the total mass of the graphite particles.

In the present disclosure, the "total mass of graphite particles" means the total mass of the first graphite particles and the second graphite particles when the negative electrode material includes only the first graphite particles and the second graphite particles as graphite particles, and If the material further contains graphite particles that do not fall under the first graphite particles or second graphite particles (for example, third graphite particles), it means the total mass of the first graphite particles, second graphite particles, and graphite particles that do not fall under these. do.

In the negative electrode material of the present disclosure, the total mass of the first graphite particles and the second graphite particles, or the total mass of the first graphite particles, the second graphite particles, and the third graphite particles is 80% by mass or more with respect to the total mass of the graphite particles. The content is preferably 90% by mass or more, and even more preferably 100% by mass.

In the present disclosure, the method of mixing two or more types of graphite particles is not particularly limited. For example, they may be mixed using a powder mixer such as a V-type mixer. Alternatively, two or more types of graphite particles may be mixed together with other materials when preparing the slurry.

The particle size, apparent density, degree of compaction, and linseed oil absorption amount of the negative electrode material (ie, the mixture of graphite particles) are not particularly limited.
For example, D10 in the volume-based particle size distribution of the negative electrode material can be selected from the range of 8 μm to 13 μm, D50 can be selected from the range of 14 μm to 20 μm, and D90 can be selected from the range of 24 μm to 43 μm.
T1 of the negative electrode material may be 0.55 g/cc or more, T2 may be 0.70 g/cc or more, T3 may be 1.00 g/cc or more, and the degree of compression is 21 or less. good.
The linseed oil absorption amount of the negative electrode material can be selected from the range of 45 mL/100 g to 56 mL/100 g.

<Negative electrode for lithium ion secondary batteries>
The negative electrode for a lithium ion secondary battery (hereinafter also referred to as negative electrode) of the present disclosure includes a negative electrode material layer containing the above-described negative electrode material, and a current collector. The negative electrode for a lithium ion secondary battery may include other components as necessary in addition to the negative electrode material layer and current collector containing the negative electrode material described above.

The method for producing the negative electrode is not particularly limited. For example, a method in which a negative electrode material composition and a binder are kneaded together with a solvent to prepare a slurry-like negative electrode material composition, and this is coated on a current collector; Examples include a method of molding it into a shape such as and integrating it with a current collector. Kneading can be performed using a dispersion device such as a stirrer, a ball mill, a super sand mill, a pressure kneader, or the like.

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

The solvent is not particularly limited as long as it can dissolve or disperse the binder. Specific examples include organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and γ-butyrolactone. The content of the solvent may be, for example, 60 parts by mass to 150 parts by mass with respect to 100 parts by mass of the negative electrode material.

The negative electrode material composition may also include a thickener. Examples of the thickener include carboxymethylcellulose or a salt thereof, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, alginic acid or a salt thereof, oxidized starch, phosphorylated starch, casein, and the like. When the negative electrode material composition contains a thickener, the amount thereof is not particularly limited. The content of the thickener may be, for example, 0.1 parts by mass to 5 parts by mass based on 100 parts by mass of the negative electrode material.

The negative electrode material composition may also include a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as natural graphite, artificial graphite, carbon black (acetylene black, thermal black, furnace black, etc.), oxides exhibiting conductivity, nitrides exhibiting conductivity, and the like. When the negative electrode material composition contains a conductive auxiliary material, the amount thereof is not particularly limited. The content of the conductive auxiliary material may be, for example, 0.5 parts by mass to 15 parts by mass based on 100 parts by mass of the negative electrode material.

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

When forming a negative electrode material layer by applying a negative electrode material composition to a current collector, the method is not particularly limited, and metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, Known methods such as a doctor blade method, a comma coat method, a gravure coat method, and a screen printing method can be employed. After applying the negative electrode material composition to the current collector, the solvent contained in the negative electrode material composition 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. Rolling treatment may be performed as necessary. The rolling treatment can be carried out using a flat plate press, a calendar roll, or the like.

When forming a negative electrode material layer by integrating a negative electrode material composition formed into a shape of a sheet, pellet, etc. with a current collector, the method of integration is not particularly limited. For example, it can be carried out using a roll, a flat plate press, or a combination of these means. The pressure during integration is preferably, for example, 1 MPa to 200 MPa.

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

The positive electrode can be obtained by forming a positive electrode material layer on the current collector in the same manner as the method for manufacturing the negative electrode described above. As the current collector, metals such as aluminum, titanium, stainless steel, or alloys can be used in the form of foil, perforated foil, mesh, or the like.

The positive electrode material used to form the positive electrode material layer is not particularly limited. Examples include metal compounds (metal oxides, metal sulfides, etc.) and conductive polymer materials that can be doped with or intercalated with lithium ions. More specifically, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), double oxides thereof (LiCo _x Ni _y Mn _z O ₂ , x+y+z=1), Complex oxide containing additive element M' (LiCo _a Ni _b Mn _c M' _d O ₂ , a+b+c+d=1, M': Al, Mg, Ti, Zr or Ge), spinel type lithium manganese oxide (LiMn ₂ O ₄ ), lithium _vanadium compound, _V2O5 , _VO2 , _MnO2 , _TiO2 , _MoV2O8 , _TiS2 , _V2S5 , _VS2 , _{MoS2 , MoS3 , Cr3O8 , Cr2} Examples include lithium-containing compounds such as O ₅ and olivine-type LiMPO ₄ (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, and porous carbon. The number of positive electrode materials used to form the positive electrode material layer may be one type alone or two or more types.

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

The states of the positive electrode and negative electrode in the lithium ion secondary battery are not particularly limited. For example, it may be in the form of a laminate consisting of a positive electrode, a negative electrode, and a separator placed between the positive electrode and the negative electrode, if necessary. The laminate may be in a spirally wound state or in a state in which a plurality of laminates are further laminated.

The separator is not particularly limited, and for example, resin nonwoven fabric, cloth, microporous film, or a combination thereof can be used. Examples of the resin include those whose main component is polyolefin such as polyethylene and polypropylene. Due to the structure of the lithium ion secondary battery, if the positive electrode and negative electrode do not come into direct contact, a separator may not be used.

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

Since the lithium ion secondary battery of the present disclosure has excellent output characteristics, it is suitable as a large capacity lithium ion secondary battery used in electric vehicles, power tools, power storage devices, and the like. In particular, it is used in electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc., which require charging and discharging with large currents to improve acceleration performance and brake regeneration performance. Suitable as a lithium ion secondary battery.

Hereinafter, the present disclosure will be described in detail based on Examples. However, the present disclosure is not limited to the following examples, and can be implemented with appropriate modifications within the scope without changing the gist thereof.

<Example 1 to Example 5, Comparative Example 1 to Comparative Example 7>
[Preparation of first graphite particles]
Mix 100 parts by mass of spherical natural graphite (secondary particles consisting of a plurality of natural graphite particles) with an average particle diameter of 16 μm and 6 parts by mass of coal tar pitch (softening point 90°C, residual carbon ratio (carbonization ratio) 50%). A mixture was obtained. Next, the mixture was heated to 950°C at a temperature increase rate of 20°C/hour under nitrogen flow and held at 950°C (calcination temperature) for 1 hour to obtain graphite particles coated with low crystalline carbon. Ta. After the obtained graphite particles were crushed with a cutter mill, they were sieved with a 300 mesh sieve, and the portion under the sieve was used as graphite particles (sample number 1).

In the production of graphite particles (sample number 1), graphite particles (sample numbers 2 to 11) were produced by changing the amount of carbon coating or the type of spherical natural graphite used as a raw material.
Regarding the obtained graphite particles (sample numbers 1 to 11), the following methods were used to measure particle diameters (D0.1, D10, D50 and D90), measure _N2 specific surface area, measure oil absorption, and measure R value. Measurement, measurement of CO ₂ adsorption amount, measurement of average interplanar spacing d ₀₀₂ , measurement of circularity, measurement of apparent density, and calculation of degree of compaction were carried out. Table 1 shows the physical property values. The amount of carbon coating (parts by mass) in Table 1 means the amount (parts by mass) of coal tar pitch relative to 100 parts by mass of spherical natural graphite.

[Preparation of second graphite particles]
43 parts by mass of coke powder with an average particle diameter of 10 μm, 18.5 parts by mass of coal tar pitch, 18.5 parts by mass of silicon carbide, and 20 parts by mass of spherical natural graphite with an average particle diameter of 20 μm were mixed and heated at 100°C. A mixture was obtained by stirring for an hour. Next, this mixture was pulverized to a particle size of 25 μm, and the obtained pulverized powder was placed in a mold and formed into a rectangular parallelepiped. The obtained rectangular parallelepiped was heat-treated at 1000°C in a nitrogen atmosphere, and then fired at 2800°C to graphitize the graphitizable components to obtain a graphite molded body. The obtained graphite compact was roughly crushed with a hammer and then crushed with a pin mill to obtain graphite particle powder. Furthermore, sieving was performed using a 300 mesh sieve, and the portion under the sieve was used as graphite particles (sample number 12).
Regarding the obtained graphite particles (sample number 12), particle diameters (D0.1, D10, D50, and D90) and CO ₂ adsorption amount were measured by the following method. Table 1 shows the physical property values.

[Preparation of negative electrode material]
Graphite particles (sample numbers 2 to 11) as the first graphite particles and graphite particles (sample number 12) as the second graphite particles were mixed for 2 hours in a V-type mixer, and Examples 1 to 5 and Comparative Negative electrode materials of Examples 2 to 7 were produced. In the production of each negative electrode material, the blending amount of the second graphite particles was 35% by mass based on the total mass of graphite particles. Further, Comparative Example 1 was a graphite particle (sample number 1) that was not mixed with graphite particles (sample number 12).
Regarding the obtained negative electrode material, measurement of particle diameter (D10, D50, and D90), measurement of apparent density, calculation of degree of compaction, measurement of _N2 specific surface area, and measurement of oil absorption were performed using the following methods. Table 1 shows the physical property values.

[Measurement of particle size]
A dispersion obtained by dispersing a sample in purified water with a surfactant (trade name: Ribonol T/15, Lion Corporation) at a mass ratio of 0.2% was analyzed using a laser diffraction particle size distribution analyzer (SALD-3000J, (Shimadzu Corporation) sample tank. Next, the solution was circulated with a pump while applying ultrasound (pump flow rate was 65% from the maximum value), the amount of water was adjusted so that the absorbance was 0.10 to 0.15, and the volume-based particle size distribution was measured. .
From the obtained volume-based particle size distribution, particle diameters corresponding to D0.1, D10, D50, and D90 of the sample were obtained.

[Measurement of loose apparent density by standing method]
The sample was freely dropped into a graduated cylinder (Tsutsui Rikagaku Kikai Co., Ltd., JIS K-5101 compliant specifications) with a capacity of 30 cm ³ using a funnel with a 500 μm mesh. The sample was overflowed from the graduated cylinder, and the sample was ground with the opening of the graduated cylinder to make the volume of the sample 30 cm ³ . The mass of the graduated cylinder containing the sample was measured, and the mass of the graduated cylinder was subtracted from the measured value to determine the mass of the sample. The loose apparent density (T1) of the sample was calculated using the following formula.
T1={(mass of sample)/(volume of sample: 30cm ³ )}

[Measurement of apparent density by 30 and 250 tap methods]
100 cm ³ of the sample was placed in a graduated flat-bottomed test tube with a capacity of 150 cm ³ (Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-406), and the test tube was capped. The test tube was dropped 30 times from a height of 5 cm, and the mass and volume of the sample were determined. The apparent density (T2) of the sample was calculated by the 30-tap method using the following formula.
T2={(mass of sample)/(volume of sample after 30 taps)}
The apparent density T3 of the sample was measured by the 250-tap method in the same manner as T2 except that the number of drops from a height of 5 cm was changed to 250 times.

[Calculation of compression degree]
The degree of compression of the sample was calculated using the following formula from the measured values of the loose apparent density (T1) of the sample by the standing method, the apparent density (T2) of the 30-tap method, and the apparent density (T3) of the 250-tap method.
Compression degree (%) = [(T2-T1)/T3] x 100

[Measurement of _N2 specific surface area]
The _N2 specific surface area of the sample was determined using a high-speed specific surface area/pore distribution measuring device (FlowSorb III, Shimadzu Corporation), after pretreatment drying (at 200°C for 2 hours or more), and then at liquid nitrogen temperature (77K). Nitrogen adsorption was measured using a single point method and calculated using the BET method.

[Measurement of linseed oil absorption]
The linseed oil absorption of the sample was determined by using dibutyl phthalate (DBP) as a reagent liquid in the method described in JIS K6217-4:2008 "Carbon black for rubber - Basic properties - Part 4: How to determine oil absorption". Instead, linseed oil (Kanto Kagaku Co., Ltd.) was used for measurement.
Specifically, linseed oil was titrated onto the sample using a constant speed buret, and changes in viscosity characteristics were measured using a torque detector. The amount of linseed oil added per unit mass of the sample corresponding to 70% of the maximum torque generated was defined as the linseed oil absorption amount (mL/100g). As a measuring device, an absorption measuring device manufactured by Asahi Research Institute Co., Ltd. was used.

[Measurement of R value]
The R value of a sample is determined by performing Raman spectroscopy under the following conditions, and in the obtained Raman spectra, the intensity ratio of the maximum peak intensity Ig near 1580 cm ^-1 and the maximum peak intensity Id near 1360 cm ^-1 ( Id/Ig).
Raman spectrometry was performed using a laser Raman spectrophotometer (model number: NRS-1000, JASCO Corporation) by irradiating a sample plate with a laser beam, which was set so that the sample was flat. The measurement conditions are as follows.
Laser light wavelength: 532nm
Wavenumber resolution: 2.56cm ^-1
Measurement range: 1180cm ^-1 ~ 1730cm ^-1
Peak research: 0.5°/min

[Measurement of _CO2 adsorption amount]
The CO ₂ adsorption amount of the sample was measured using Belsorp II manufactured by Microtrac Bell Co., Ltd. Further, Belsorp II manufactured by Microtrac Bell Co., Ltd. was used as a pretreatment device. Note that the amount of CO ₂ adsorption was measured at a measurement temperature of 273 K and a relative pressure P/P ₀ =0.98 to 0.99 (P = equilibrium pressure, P ₀ = saturated vapor pressure). The pretreatment was carried out under a vacuum degree of 1 Pa or less, and the temperature was raised to 250°C at a rate of 5°C/min and held for 10 minutes, and then the temperature was raised to 350°C at a rate of 3°C/min and held for 210 minutes. Thereafter, heating was stopped and the mixture was cooled to room temperature. The measured relative pressure for adsorption amount measurement was carried out as shown in Table 2 below.
When the CO ₂ adsorption amount of the standard substance alumina powder (BCR-171, No. 0446, Institute for Reference Materials and Measurements) was measured using the above method, it was 0.40 cm ³ /g.

[Measurement of average spacing d ₀₀₂ ]
The average interplanar spacing d ₀₀₂ of the sample was measured by X-ray diffraction method. Specifically, a sample was filled into a concave portion of a quartz sample holder, set on a measurement stage, and measured using a wide-angle X-ray diffraction device (Rigaku Co., Ltd.) under the following conditions.
Radiation source: CuKα radiation (wavelength = 0.15418 nm)
Output: 40kV, 20mA
Sampling width: 0.010°
Scanning range: 10°~35°
Scan speed: 0.5°/min

[Measurement of average circularity]
The circularity of the sample was measured using a wet flow particle size/shape analyzer (Malvern Panalytical FPIA-3000). The measurement temperature was 25° C., the sample concentration was 10% by mass, and the number of particles counted was 10,000. Additionally, water was used as a dispersion solvent.
Note that before measuring the circularity of the sample, it is preferable to disperse the sample powder in advance. For example, it is possible to disperse the sample using ultrasonic dispersion, a vortex mixer, or the like. The processing conditions are adjusted in consideration of the strength of the sample to be measured in order to suppress the influence of particle disintegration or particle destruction of the sample.

[Preparation of negative electrode]
A sample electrode (negative electrode) was produced using the negative electrode materials produced in Examples and Comparative Examples according to the following procedure.
First, carboxymethyl cellulose (CMC) as a thickener and styrene-butadiene rubber (SBR) as a binder were added to the negative electrode material. The mass ratio of these was negative electrode material:CMC:SBR=98:1:1. Purified water as a dispersion solution was added to this and kneaded to obtain a slurry. A predetermined amount of this slurry was applied substantially evenly and homogeneously onto a rolled copper foil having an average thickness of 10 μm, which is a current collector for the negative electrode (coating amount: 10.0 mg/cm ² ). Thereafter, the electrode density was adjusted to 1.6 g/cm ³ using a roll press to obtain a rolled copper foil with a negative electrode material layer formed on one side. This rolled copper foil was punched out into a disk shape with a diameter of 14 mm to produce a sample electrode (negative electrode). Using the prepared sample electrode, the electrode permeation rate and electrode swelling rate of the electrolyte solution were measured by the following method. The results are shown in Table 3.

[Electrode penetration rate of electrolyte]
Drop 0.02 ml of electrolyte solution (LiPF ₆ /EC+DMC, Kishida Chemical Co., Ltd.) onto the negative electrode coating film of the sample electrode using a microsyringe at room temperature (25°C), and measure the time it takes for the electrolyte solution to disappear from the negative electrode coating film. was measured.

[Electrode swelling rate]
The negative electrode material layer of the sample electrode was immersed in an electrolytic solution (LiPF ₆ /EC+DMC, Kishida Chemical Co., Ltd.) at 70°C for 48 hours, and the change in layer thickness before and after immersion was measured with a micrometer, and the swelling rate was calculated using the following formula. I asked for
Swelling rate (%) = {(Thickness after immersion - Thickness before immersion)/Thickness before immersion} x 100

[Fabrication of lithium ion secondary battery]
The prepared sample electrode (negative electrode), separator, and counter electrode (positive electrode) were placed in a coin-shaped battery container in this order, and an electrolyte was injected to produce a coin-shaped lithium ion secondary battery. As an electrolytic solution, a mixed solvent of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) (the volume ratio of EC:EMC is 3:7) is mixed with 0.5 mass of vinylene carbonate (VC) based on the total amount of the mixed solvent. % and LiPF ₆ was dissolved to a concentration of 1 mol/L. Metallic lithium was used as the counter electrode (positive electrode). As a separator, a microporous polyethylene membrane having a thickness of 20 μm was used. Using the produced lithium ion secondary battery, initial charge/discharge characteristics, low temperature charging characteristics, high temperature storage characteristics, and discharge load characteristics were evaluated by the following methods. The results are shown in Table 3.

(Evaluation of initial charge/discharge characteristics)
The prepared lithium ion secondary battery was charged at a constant current (CC charge) at a current value of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), and then at a constant voltage of 0V until the current value reached 0.02C. Charging (CV charging) was performed. The capacity at this time was defined as the initial charge capacity (CC/CV charge). Next, after a 30-minute rest, constant current discharge (CC discharge) was performed at a current value of 0.2C to 1.5V (V vs. Li/Li ⁺ ). The capacity at this time was defined as the initial discharge capacity.
The value obtained by subtracting the value of the initial discharge capacity from the value of the initial charge capacity was defined as the irreversible capacity, and the ratio of the value of the initial discharge capacity to the value of the initial charge capacity was calculated as the initial efficiency. Note that "C" obtained as a unit of current value means "current value (A)/battery capacity (Ah)".
Irreversible capacity [mAh/g] = (Initial charge capacity) - (Initial discharge capacity)
Initial efficiency [%] = (initial discharge capacity) / (initial charge capacity) x 100

(Evaluation of low temperature charging characteristics)
The prepared lithium ion secondary battery was placed in a constant temperature bath set at 25°C, and constant current charging (CC charging) was performed at a current value of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), and then the current value was Constant voltage charging (CV charging) was performed at 0 V until the voltage reached 0.02C. Next, after a 30-minute rest, constant current discharge (CC discharge) was performed at a current value of 0.2C to 1.5V (V vs. Li/Li ⁺ ). This charging and discharging was defined as one cycle, and a second charging and discharging cycle was performed.
Thereafter, the above-mentioned lithium ion secondary battery was placed in a constant temperature bath set at -30°C, and constant current charging (CC charging) was performed at a current value of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), and then the current value was Constant voltage charging (CV charging) was performed at 0 V until the voltage reached 0.02C.
Low-temperature charging acceptance was determined from the ratio of the CC charging capacity when charging was performed at -30°C to the CC/CV charging capacity when charging was performed at -30°C.
Low temperature charging acceptance [%] = (CC charging capacity at -30°C) / (CC/CV charging capacity at -30°C) x 100

(Evaluation of high temperature storage characteristics)
The prepared lithium ion secondary battery was placed in a constant temperature bath set at 25°C, and charged at a constant current of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), and then the current value was 0.02C. Constant voltage charging was performed at 0V until . Next, after a 30-minute rest, constant current discharge was performed at a current value of 0.2C to 1.5V (V vs. Li/Li ⁺ ). This charging and discharging is considered as one cycle, and after performing the second charging and discharging cycle,
Constant current charging was performed at a current value of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), then constant voltage charging was performed at 0V until the current value reached 0.02C, and the battery was kept at a constant temperature set at 60°C. It was placed in a tank and stored for 5 days.
Thereafter, it was placed in a constant temperature bath set at 25°C, left for 60 minutes, and constant current discharged to 1.5V (V vs. Li/Li ⁺ ) at a current value of 0.2C. Next, charging and discharging were performed under the same conditions as in the first cycle.
The high temperature storage retention rate and high temperature storage recovery rate were calculated from the following equations.
High temperature storage retention rate [%] = (1st cycle discharge capacity at 25 °C after storage at 60 °C for 5 days) / (2nd cycle discharge capacity at 25 °C) × 100
High temperature storage recovery rate [%] = (2nd cycle discharge capacity at 25 °C after storage at 60 °C for 5 days) / (2nd cycle discharge capacity at 25 °C) × 100

(Evaluation of discharge load characteristics)
The prepared lithium ion secondary battery was placed in a constant temperature bath set at 25°C, and charged at a constant current of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), and then the current value was 0.02C. Constant voltage charging was performed at 0V until . Next, after a 30-minute rest, constant current discharge was performed at a current value of 0.2C to 1.5V (V vs. Li/Li ⁺ ). This charging and discharging was defined as one cycle, and a second charging and discharging cycle was performed.
Next, constant current charging is performed at a current value of 0.2C to a voltage of 0V (V vs. Li/Li ⁺ ), then constant voltage charging is performed at 0V until the current value reaches 0.02C, and this battery is charged at a current value of 4C. Constant current discharge was performed to 1.5V (V vs. Li/Li ⁺ ).
The discharge load was calculated from the following formula.
Discharge load [%] = (Discharge capacity obtained at a current value of 4C) / (Discharge capacity in the second cycle obtained at a current value of 0.2C) x 100

[Preparation of negative electrode for evaluating cycle characteristics and pulse charging characteristics]
A sample electrode (negative electrode) was produced using the negative electrode materials produced in Examples and Comparative Examples according to the following procedure.
First, carboxymethyl cellulose (CMC) as a thickener and styrene-butadiene rubber (SBR) as a binder were added to the negative electrode material. The mass ratio of these was negative electrode material/CMC/SBR=98/1/1. Purified water as a dispersion solution was added to this and kneaded to form a slurry. A predetermined amount of this slurry was applied substantially evenly and homogeneously onto a rolled copper foil having an average thickness of 10 μm, which is a current collector for the negative electrode (coating amount: 10.0 mg/cm ² ). Thereafter, the electrode density was adjusted to 1.6 g/cm ³ using a roll press to obtain a rolled copper foil with a negative electrode material layer formed on one side. This rolled copper foil was punched out to a size of 2.5 cm x 12 cm to produce a sample electrode (negative electrode).

[Fabrication of lithium ion secondary battery for evaluating cycle characteristics and pulse charging characteristics]
The fabricated sample electrode (negative electrode) was bent, a bent separator and a counter electrode (positive electrode) were placed in this order, and an electrolyte was injected to fabricate a lithium ion secondary battery. As an electrolytic solution, a mixed solvent of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) (the volume ratio of EC and EMC is 3:7) is mixed with 0.5 of vinylene carbonate (VC) based on the total amount of the mixed solution. % by mass was added and LiPF ₆ was dissolved to a concentration of 1 mol/L. As the counter electrode (positive electrode), an electrode (1.5 cm x 4 cm) with a mass ratio of ternary (Ni, Co, Mn) lithium oxide/conductive material/PVDF (polyvinylidene fluoride) of 90/5/5 is used. did. As a separator, a microporous polyethylene membrane having a thickness of 20 μm was used. Using the produced lithium ion secondary battery, cycle characteristics and pulse charging characteristics were evaluated by the following method. The results are shown in Table 3.

[Evaluation of cycle characteristics]
Using the produced lithium ion secondary battery, cycle characteristics were evaluated as follows.
First, constant current charging was performed at 45° C. with a current value of 2 C and a charge end voltage of 4.2 V, and from when 4.2 V was reached, constant voltage charging was performed at that voltage until the current value reached 0.02 C. After resting for 30 minutes, constant current discharge was performed at 25° C. with a current value of 2 C and a final voltage of 2.7 V, and the discharge capacity was measured (first cycle discharge capacity). The above charging and discharging was defined as one cycle, and 500 cycles were performed, and the discharge capacity was measured after 300 cycles and after 500 cycles. Then, the discharge capacity retention rate (%) was calculated from the following formula.
Discharge capacity maintenance rate [%] = (Discharge capacity after 300 cycles or 500 cycles) / (Discharge capacity at 1st cycle) x 100

[Evaluation of pulse charging characteristics]
The pulse charging characteristics were determined from the Li precipitation state. The prepared lithium ion secondary battery was charged at a constant current of 1 C and a charge end voltage of 4.2 V at 25°C, and from when 4.2 V was reached, constant voltage charging was carried out at that voltage until the current value reached 0.02 C. did. After resting for 30 minutes, constant current discharge was performed at 25° C. with a current value of 1 C and a final voltage of 2.7 V. This charging and discharging was defined as one cycle, and three cycles of charging and discharging were performed.
Next, the above battery was placed in a constant temperature bath set at -30°C, left for 60 minutes, and then charged for 5 seconds at a current value equivalent to 20C. Confirmed by Keyence Corporation (SU3500). It was determined that the pulse charging characteristics were excellent when there was no Li precipitation.

As is clear from the results shown in Table 3, in Examples 1 to 5, in which the graphite particles contained in the negative electrode material satisfy the predetermined conditions, in Comparative Examples 1 to 7, in which the graphite particles contained in the negative electrode material do not satisfy the predetermined conditions. While maintaining high charge/discharge efficiency compared to , it also had excellent low-temperature charging characteristics, high-temperature storage characteristics, discharge load characteristics, and pulse charging characteristics.
The estimated mechanism of performance improvement will be explained below.
The first graphite particles contained in the negative electrode material are relatively fine particles, and the second graphite particles have relatively large (coarse) particles and finer particles (more fine) than the first graphite particles. Therefore, when these graphite particles are blended, the voids between the particles are filled with each other, and the filling state of the resulting negative electrode coating film can be well controlled. The filling state can be controlled by the physical properties of the first graphite particles and the second graphite particles. When the physical properties of the first graphite particles and the second graphite particles satisfy predetermined conditions, press pressure force can be uniformly applied to the inside of the coating film in the press step during production of the negative electrode. Therefore, variations in density are reduced in the thickness direction of the coating film, and the electrolytic solution permeates smoothly. As a result, improved battery performance is achieved. In addition, the hardness of graphite particles, which will be explained below, is also a factor contributing to the improvement of battery performance.

[Evaluation of electrode pressability]
The graphite particles of Sample No. 1, Sample No. 2, Sample No. 3, Sample No. 6, and Sample No. 12 configured in Example 1, Example 2, Example 3, and Comparative Example 2 were used alone, and the same as described above was used. A sample electrode was prepared using the method. Using the sample electrodes, press treatments were carried out at an arbitrary oil pressure (t) with the roll gap of the roll press fixed and varied. Electrode density (g/cm ³ ) was calculated by measuring the thickness of each electrode pressed at each hydraulic pressure, and electrode pressability was evaluated. The results are shown in FIGS. 1 and 2.

As shown in FIGS. 1 and 2, the electrode pressability of Sample No. 1, which is a graphite particle coated with low-crystalline carbon, is higher than that of Sample No. 6, which is a graphite particle that is not coated with low-crystalline carbon. The degree of increase in electrode density with increase in roll press oil pressure is small. Further, when comparing Sample No. 2 and Sample No. 3, which have different particle sizes, Sample No. 3, which has a smaller particle size, has a smaller increase in electrode density than Sample No. 2, and the particles are harder. Furthermore, when comparing sample numbers 1, 2, and 3, which correspond to the first graphite particles, and sample number 12, which corresponds to the second graphite particles, sample numbers 1, 2, and 3 have a higher electrode density than sample number 12. The degree of rise is small and the particles are harder.
The above results show that the hardness of graphite particles can be controlled by coating the graphite particles or by changing the particle diameter of the graphite particles. In other words, by selecting a first graphite particle with a desired hardness and further combining it with a second graphite particle having a different hardness, it is possible to control the hardness of the negative electrode material, and it is possible to control the hardness when pressing the electrode at high pressure. Particle deformation due to pressing force can be suppressed, a permeation path for the electrolyte is secured, and the electrolyte can penetrate smoothly. As a result, it is possible to contribute to improvements in low-temperature charging characteristics, high-temperature storage characteristics, discharge load characteristics, and pulse charging characteristics while maintaining high charge-discharge efficiency.

<Example 6 to Example 9, Comparative Example 8>
Negative electrode materials were produced by using sample number 1 as the first graphite particles and sample number 12 as the second graphite particles, and varying the blending amount of the second graphite particles. Using the obtained negative electrode material, electrode characteristics and battery characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 4.

As shown in Table 4, Examples 1 and 6 to 9, in which the amount of the second graphite particles is 55% by mass or less, have better battery performance than Comparative Example 8, in which the amount of the second graphite particles is more than 55% by mass. They tend to have excellent charge/discharge characteristics. Although the exact reason is unknown, it is thought that the amount of fine particles derived from the second graphite particles filling the voids of the first graphite particles is not too large, allowing smooth penetration of the electrolytic solution. Furthermore, the swelling rate of the electrode due to the electrolytic solution is suppressed, so that the impedance can be kept low.

<Example 10 to Example 12, Comparative Example 9 to Comparative Example 11>
Graphite particles (sample number 13) were produced in the same manner as in the production of graphite particles (sample number 12) except that the D50 of the graphite particles was adjusted to 20 μm.

100 parts by mass of graphite particles (sample number 12) and 6 parts by mass of coal tar pitch (softening point: 90° C., residual carbon ratio (carbonization ratio): 50%) were mixed. Next, the mixture was heated to 950° C. at a rate of 20° C./hour under nitrogen flow and held at 950° C. (calcination temperature) for 1 hour to obtain carbon layer-coated graphite particles. The obtained carbon layer-coated graphite particles were crushed with a cutter mill, and then sieved with a 300 mesh sieve, and the portion under the sieve was used as graphite particles (sample number 14).

Graphite particles (sample number 15) were produced in the same manner as in the production of graphite particles (sample number 12), except that graphitization was carried out in the form of pulverized powder rather than in the form of a molded block.

Graphite particles (sample number 16) were produced in the same manner as in the production of graphite particles (sample number 12) except that the D50 of the graphite particles was adjusted to 27 μm.

In the production of graphite particles (sample number 14), graphite particles (sample number 17) were produced in the same manner except that graphite particles (sample number 13) were used as the graphite particles serving as the core material before carbon layer coating.

Graphite particles (sample number 18) were produced in the same manner as in the production of graphite particles (sample number 16), except that graphitization was carried out in the form of pulverized powder rather than in the form of a molded block.

Negative electrode materials were prepared using Sample No. 1 as the first graphite particles and Samples Nos. 12 to 18 as the second graphite particles, and their physical properties were measured. Furthermore, electrode characteristics and battery characteristics were evaluated in the same manner as in Example 1 using the obtained negative electrode material. The results are shown in Table 5.

As shown in Table 5, Examples 1 and 10 to 12 in which the negative electrode material contains second graphite particles that meet the predetermined conditions are comparative example 9 in which the negative electrode material does not contain the second graphite particles that meet the predetermined conditions. While maintaining high charge/discharge efficiency compared to No. 11, it also had excellent low-temperature charging characteristics, high-temperature storage characteristics, discharge load characteristics, and pulse charging characteristics.

In the following examples, a negative electrode material containing third graphite particles in addition to first graphite particles and second graphite particles was investigated.

<Examples 13 to 19>
Graphite particles having the sample numbers and blending amounts shown in Table 6 were used as first graphite particles, second graphite particles, and third graphite particles, respectively, and these were mixed to produce a negative electrode material. Furthermore, electrode characteristics and battery characteristics were evaluated in the same manner as in Example 1 using the obtained negative electrode material.
In Examples 13 to 19, additional evaluation was carried out when the electrode density was 1.75 g/cm ³ in measuring the electrode penetration rate and evaluating the initial charge/discharge characteristics and cycle characteristics. A negative electrode having an electrode density of 1.75 g/cm ³ was produced by adjusting the oil pressure of the roll press described above. The results are shown in Table 6.

As shown in Table 6, Examples 13 to 19 containing third graphite particles in addition to first graphite particles and second graphite particles had higher charge/discharge rates than Examples 1 and 8 which did not contain third graphite particles. While maintaining efficiency, it also had excellent low-temperature charging characteristics, high-temperature storage characteristics, and discharge load characteristics.
Examples 13 to 19, which include third graphite particles in addition to first graphite particles and second graphite particles, maintain high capacity and efficiency even during high-density mounting (electrode density 1.75 g/cm ³ ), It also had excellent cycle characteristics.

[Measurement of electrode resistance]
Electrode resistance was measured using the negative electrodes (electrode densities: 1.6 g/cm ³ and 1.75 g/cm ³ ) prepared in Example 14, Example 17, Example 19, Example 1, and Example 8. For the measurement, an electrode resistance measurement system (RM2610) manufactured by Hioki Electric Co., Ltd. was used. By using this measurement system, it is possible to separately measure the negative electrode material layer resistance and the interfacial resistance (contact resistance between the current collector and the negative electrode material layer) in the negative electrode. This indicates that the smaller the electrode resistance of the negative electrode, the better the low-temperature charging characteristics, high-temperature storage characteristics, and discharge load characteristics while maintaining high charging and discharging efficiency. The results are shown in Table 7.

As shown in Table 7, the electrode resistances (negative electrode material layer resistance and interfacial resistance) of Examples 14, 17, and 19 containing third graphite particles are the same as those of Examples 1 and 8 containing no third graphite particles. was shown to be lower compared to The above results indicate that electrode resistance can be reduced by adding third graphite particles to the negative electrode material.

Claims (7)

First graphite particles that satisfy the following conditions 1A and 1B,
A second graphite particle that satisfies the following conditions 2A and 2B,
The amount of the second graphite particles is 10% by mass to 55% by mass with respect to the total mass of the graphite particles,
The first graphite particle is a secondary particle consisting of a plurality of natural graphite particles, at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle, and D10 in the volume-based particle size distribution is A negative electrode material for a lithium ion secondary battery , which has a D90 of 7 μm to 13 μm and a D90 of 14 μm to 25 μm .
Condition 1A: The loose apparent density T1 by the standing method is 0.60 g/cc or more, the apparent density T2 by the 30-tap method is 0.80 g/cc or more, and the apparent density T3 by the 250-tap method is 1. 00g/cc or more, and the compression degree value shown by the following formula is 19% or less. Compression degree (%) = [(T2-T1)/T3] x 100
Condition 1B: The linseed oil absorption amount is 40 mL/100 g to 55 mL/100 g. Condition 2A: D0.1 in the volume-based particle size distribution is 5 μm or less. Condition 2B: The linseed oil absorption amount is 55 mL/100 g to 75 mL/100 g. be The negative electrode material for a lithium ion secondary battery according to claim 1, wherein D0.1 in the volume-based particle size distribution of the first graphite particles is more than 5 μm. further comprising third graphite particles satisfying the following conditions 3A and 3B,
The lithium ion according to claim 1, wherein the third graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle. Negative electrode material for secondary batteries.
Condition 3A: In the volume-based particle size distribution, the ratio of the D50 of the third graphite particles to the D50 of the first graphite particles (D50 of the third graphite particles/D50 of the first graphite particles) is in the range of 0.55 to 0.75. Condition 3B: Linseed oil absorption amount is 40 mL/100 g to 55 mL/100 g. The negative electrode material for a lithium ion secondary battery according to claim 3 , wherein the amount of the third graphite particles is 10% by mass to 25% by mass based on the total mass of the graphite particles. First graphite particles that satisfy the following conditions 1A and 1B,
Second graphite particles that satisfy the following conditions 2A and 2B,
Third graphite particles satisfying the following conditions 3A and 3B,
The amount of the second graphite particles is 10% by mass to 55% by mass with respect to the total mass of the graphite particles,
A negative electrode material for a lithium ion secondary battery, wherein the first graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle. .
Condition 1A: The loose apparent density T1 by the standing method is 0.60 g/cc or more, the apparent density T2 by the 30-tap method is 0.80 g/cc or more, and the apparent density T3 by the 250-tap method is 1. 00g/cc or more, and the value of the degree of compression shown by the following formula is 19% or less
Compression degree (%) = [(T2-T1)/T3] x 100
Condition 1B: Linseed oil absorption is 40 mL/100 g to 55 mL/100 g.
Condition 2A: D0.1 in volume-based particle size distribution is 5 μm or less
Condition 2B: Linseed oil absorption is 55 mL/100 g to 75 mL/100 g.
The lithium ion according to claim 1, wherein the third graphite particle is a secondary particle consisting of a plurality of natural graphite particles, and at least a part of the surface is coated with a carbon material having lower crystallinity than the natural graphite particle. Negative electrode material for secondary batteries.
Condition 3A: In the volume-based particle size distribution, the ratio of the D50 of the third graphite particles to the D50 of the first graphite particles (D50 of the third graphite particles/D50 of the first graphite particles) is in the range of 0.55 to 0.75. is
Condition 3B: Linseed oil absorption is 40 mL/100 g to 55 mL/100 g. A negative electrode for a lithium ion secondary battery, comprising a negative electrode material layer containing the negative electrode material according to any one of claims 1 to 5, and a current collector. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 6, a positive electrode, and an electrolyte.