JP7156468B2 - Method for producing negative electrode material for lithium ion secondary battery, and negative electrode material for lithium ion secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a negative electrode material for lithium ion secondary batteries, and a negative electrode material for lithium ion secondary batteries.

Lithium-ion secondary batteries have been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smart phones, and tablet PCs, taking advantage of their characteristics of small size, light weight, and high energy density. In recent years, against the background of environmental problems such as global warming due to _CO2 emissions, clean electric vehicles (EV) that run only on batteries, hybrid electric vehicles (HEV) that combine a gasoline engine and batteries, and plug-in hybrid electric vehicles have become popular. (PHEV) and the like are becoming widespread, and lithium ion secondary batteries (vehicle lithium ion secondary batteries) are used as batteries mounted in EVs, HEVs, PHEVs, and the like. Recently, lithium ion secondary batteries have also been used for power storage, and the applications of lithium ion secondary batteries are expanding in a wide variety of fields.

The performance of the negative electrode material of the lithium ion secondary battery greatly affects the output characteristics of the lithium ion secondary battery. Carbon materials are widely used as materials for negative electrode materials for lithium ion secondary batteries. Carbon materials used for negative electrode materials are roughly classified into graphite and carbon materials having a lower crystallinity than graphite (such as amorphous carbon). Graphite has a structure in which hexagonal mesh planes of carbon atoms are regularly stacked, and when used as a negative electrode material for a lithium ion secondary battery, lithium ion insertion reaction and desorption reaction proceed from the end of the hexagonal mesh plane, Charging and discharging are performed.

Amorphous carbon has irregular lamination of hexagonal mesh planes or no hexagonal mesh planes. In a negative electrode material using amorphous carbon, lithium ion intercalation reaction and deintercalation reaction proceed over the entire surface of the negative electrode material. Therefore, it is easier to obtain a lithium ion battery with better output characteristics than when graphite is used as the negative electrode material (see, for example, Patent Documents 1 and 2). On the other hand, since amorphous carbon has lower crystallinity than graphite, its energy density is lower than that of graphite.
Further, Patent Document 3 proposes improving the initial efficiency by adjusting the micropore volume to a specific range.

JP-A-4-370662 JP-A-5-307956 WO2012/090728

Considering the characteristics of the carbon material, it contains composite particles coated with amorphous carbon and graphite, and maintains high energy density while reducing surface reactivity to maintain good initial charge-discharge efficiency and output. A negative electrode material with improved properties has also been proposed. However, from the background as described above, there is a demand for a negative electrode material that realizes further improvement in the output characteristics of lithium ion secondary batteries. In addition, lithium ion secondary batteries for vehicles such as EVs, HEVs, and PHEVs are required to have high-temperature storage characteristics.
Further, as described in Patent Document 3, conventionally, there is a trade-off relationship between the initial efficiency and the micropore capacity, and it has been difficult to achieve both charging characteristics and initial efficiency.

The present invention has been made in view of the above circumstances, and manufactures a negative electrode material for a lithium ion secondary battery that can produce a negative electrode for a lithium ion secondary battery that is excellent in input characteristics, output characteristics, high temperature storage characteristics, and initial efficiency. The purpose is to provide a method.

The present inventors made intensive studies to achieve the above object, and as a result, arrived at the present invention. That is, one form of the present invention includes the following aspects.

<1> A step of preparing an activated carbonaceous material A that has been treated to increase the BET specific surface area of the carbonaceous material A by 2% to 50%;
obtaining a mixture by mixing the activated carbonaceous material A and a carbonaceous material precursor from which a carbonaceous material B different from the carbonaceous material A is obtained;
a step of heat-treating the mixture to obtain a fired product;
A method for producing a negative electrode material for a lithium ion secondary battery having

<2> The negative electrode material for a lithium ion secondary battery according to <1>, wherein the step of obtaining the baked product is a step of setting the BET specific surface area of the baked product to 0.5 m ² /g to 10 m ² /g. Production method.

<3> The method for producing a negative electrode material for a lithium ion secondary battery according to <1> or <2>, wherein the heat treatment is performed at a temperature of 700°C to 1500°C.

<4> The negative electrode material for a lithium ion secondary battery according to any one of <1> to <3>, wherein the crystallinity of the carbonaceous material B is lower than the crystallinity of the activated carbonaceous material A. Production method.

<5> Containing a carbonaceous substance AA and a carbonaceous substance B different from the carbonaceous substance AA,
A negative electrode material for a lithium ion secondary battery, wherein the ratio of the BET specific surface area after heat treatment to the BET specific surface area before heat treatment is 2.5 or more when heat treated at 600° C. for 30 minutes in an air atmosphere.

INDUSTRIAL APPLICABILITY According to the present invention, there are provided a negative electrode material for lithium ion secondary batteries that is excellent in input characteristics, output characteristics, high temperature storage characteristics and initial efficiency, and a method for producing a negative electrode material for lithium ion secondary batteries capable of producing the same. .

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present invention.

In the present disclosure, the term "process" includes a process that is independent of other processes, and even if the purpose of the process is achieved even if it cannot be clearly distinguished from other processes. .
In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . Moreover, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In the present disclosure, each component may contain multiple types of applicable substances. When there are multiple types of substances corresponding to each component in the negative electrode material or composition, the content rate or content of each component is the ratio of the multiple types of substances present in the negative electrode material or composition, unless otherwise specified. It means the total content rate or content.
Particles corresponding to each component in the present disclosure may include a plurality of types. When a plurality of types of particles corresponding to each component are present in the negative electrode material or composition, the particle diameter of each component is the same as that of the mixture of the plurality of types of particles present in the negative electrode material or composition, unless otherwise specified. means value.
In the present disclosure, the term "layer" includes not only the case where the layer is formed in the entire region when observing the region where the layer exists, but also the case where it is formed only in part of the region. included.
In the present disclosure, the term "laminate" indicates stacking layers, and two or more layers may be bonded, or two or more layers may be detachable.

<Method for producing negative electrode material for lithium ion secondary battery>
The method for producing a negative electrode material for a lithium ion secondary battery according to the present disclosure includes the step of preparing an activated carbonaceous material A that has been subjected to a treatment to increase the BET specific surface area of the carbonaceous material A by 2% to 50%; obtaining a mixture by mixing the activated carbonaceous material A and a carbonaceous material precursor that is a source of a carbonaceous material B different from the carbonaceous material A; and heat-treating the mixture to obtain a fired product. and obtaining.
The method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure may include other steps as necessary.

By using a negative electrode material for a lithium ion secondary battery produced by the method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure, a lithium ion secondary battery having excellent input characteristics, output characteristics, high temperature storage characteristics and initial efficiency It becomes possible to manufacture a negative electrode for
Hereinafter, each step included in the method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure, materials used, and the like will be described in detail.

<Step of preparing activated carbonaceous substance A>
In the step of preparing the activated carbonaceous material A, the activated carbonaceous material A, which has been treated to increase the BET specific surface area of the carbonaceous material A by 2% to 50%, is prepared. The treatment for increasing the BET specific surface area of carbonaceous material A is not particularly limited.
Examples of the treatment for increasing the BET specific surface area of the carbonaceous material A include heat treatment in an atmosphere containing CO ₂ gas, water vapor, O ₂ gas, etc., mechanical treatment, and the like. From the viewpoint of controlling the particle size of the activated carbonaceous material A, controlling the surface state of the activated carbonaceous material A, etc., it is preferable to perform the heat treatment in an atmosphere in which O ₂ gas exists (for example, in an air atmosphere).

Appropriate processing temperatures vary depending on the gas atmosphere used, processing time, and the like. For example, in the case of treatment in an air atmosphere, the heat treatment temperature is preferably 100°C to 600°C, more preferably 150°C to 600°C. Within this temperature range, the specific surface area of the activated carbonaceous material A can be increased without burning the carbonaceous material A.
The heat treatment time varies depending on the heat treatment temperature, the type of carbon material, etc., but is preferably 0.5 hours to 24 hours, more preferably 1 hour to 6 hours. Within this time, the specific surface area of the activated carbonaceous material A can be effectively increased. Furthermore, when heat treatment is performed in an atmosphere in which _O.sub.2 gas exists, the content of _O.sub.2 gas is preferably 1% by volume to 30% by volume. Within this range, there is a tendency that the specific surface area of the activated carbonaceous material A can be effectively increased.

When the gas atmosphere used is a CO ₂ gas atmosphere, the heat treatment temperature is preferably 600°C to 1000°C, more preferably 700°C to 900°C. The heat treatment time varies depending on the heat treatment temperature and the type of carbon material, but is preferably 0.5 hours to 24 hours, more preferably 1 hour to 6 hours.

In the present disclosure, the BET specific surface area is calculated by the BET method by measuring nitrogen adsorption at liquid nitrogen temperature (77K) by the multipoint method.
When measuring the BET specific surface area, it is considered that the water adsorbed in the sample surface and structure affects the gas adsorption capacity, so it is preferable to first perform a pretreatment to remove water by heating. .
In the pretreatment, for example, a measurement cell containing 0.05 g of a measurement sample is evacuated to 10 Pa or less by a vacuum pump, heated at 110° C., held for 3 hours or longer, and then kept in a reduced pressure state. Cool naturally to room temperature (25°C). After this pretreatment, the evaluation temperature may be set to 77 K, and the evaluation pressure range may be set to less than 1 relative pressure (equilibrium pressure with respect to saturated vapor pressure).

In the step of preparing the activated carbonaceous material A, the increase rate of the BET specific surface area of the activated carbonaceous material A with respect to the carbonaceous material A is 2% to 50%, and may be 5% to 50%. If the rate of increase in the BET specific surface area of the activated carbonaceous material A relative to that of the carbonaceous material A is less than 2%, the input characteristics tend to improve only slightly. When the rate of increase in the BET specific surface area of the activated carbonaceous material A relative to that of the carbonaceous material A exceeds 50%, the initial efficiency and high-temperature storage characteristics tend to deteriorate.

The carbonaceous material A used in the step of preparing the activated carbonaceous material A is not particularly limited.
Examples of the carbonaceous substance A include carbon materials such as artificial graphite, natural graphite, graphitized mesophase carbon, graphite such as graphitized carbon fiber, low-crystalline carbon, amorphous carbon, and mesophase carbon.
From the viewpoint of increasing the charge/discharge capacity, the carbonaceous substance A preferably contains graphite. The shape of graphite is not particularly limited, and may be scaly, spherical, massive, fibrous, or the like. From the viewpoint of obtaining a high tap density, it is preferably spherical.
When the carbonaceous substance A is spherical natural graphite, the volume average particle diameter (D ₅₀ ) of the carbonaceous substance A is preferably 5 μm to 30 μm, more preferably 6 μm to 25 μm, and 7 μm to 20 μm. is more preferred.
When the carbonaceous substance A is artificial graphite, the volume average particle diameter (D ₅₀ ) of the carbonaceous substance A is preferably 8 μm to 40 μm, more preferably 10 μm to 35 μm, and 12 μm to 30 μm. is more preferred.

When the carbonaceous substance A is spherical natural graphite, the BET specific surface area of the carbonaceous substance A is preferably 5 m ² /g to 15 m ² /g, more preferably 6 m ² /g to 13 m ² /g. It is more preferably 7 m ² /g to 11 m ² /g.
When the carbonaceous substance A is artificial graphite, the BET specific surface area of the carbonaceous substance A is preferably 1 m ² /g to 10 m ² /g, more preferably 2 m ² /g to 8 m ² /g. , 3 m ² /g to 7 m ² /g.

When the carbonaceous material A is spherical natural graphite, the BET specific surface area of the activated carbonaceous material A is preferably 5 m ² /g to 23 m ² /g, and more preferably 6 m ² /g to 20 m ² /g. is more preferred, and 7 m ² /g to 15 m ² /g is even more preferred.
When the carbonaceous substance A is artificial graphite, the BET specific surface area of the activated carbonaceous substance A is preferably 1 m ² /g to 13 m ² /g, more preferably 2 m ² /g to 12 m ² /g. More preferably, it is 3 m ² /g to 10 m ² /g.

In the method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure, a commercially available activated carbonaceous material A can be purchased and prepared.

The artificial graphite may be, for example, graphite particles (hereinafter referred to as “massive graphite particles”) in which a plurality of flattened particles are aggregated or combined so that the orientation planes (principal planes) are non-parallel. Whether or not massive graphite particles are contained can be confirmed by observation with a scanning electron microscope (SEM).

A flattened particle means a particle having a long axis and a short axis, and is not perfectly spherical. For example, those having shapes such as scaly, scaly, and partly lumpy are included. In the massive graphite particles, that the main surfaces of a plurality of flattened particles are non-parallel means that the surfaces (main surfaces) of the flattened graphite particles with the largest cross-sectional area are not aligned in a certain direction.

Also, in massive graphite particles, flat particles are aggregated or bound together. It refers to the state of being bound to Aggregation refers to a state in which particles are not chemically bonded to each other, but maintain their aggregate shape due to their shape or the like. In the present invention, from the viewpoint of mechanical strength, it is preferable that they are bonded.
In one massive graphite particle, the number of aggregated or bonded flat particles is not particularly limited, but is preferably 3 or more, more preferably 5 to 20, and 5 to 15. It is even more preferable to have

-Method for producing massive graphite particles-
The method for producing the massive graphite particles is not particularly limited as long as a predetermined structure is formed. For example, 1% by mass to 50% by mass of a graphitization catalyst is added to the total amount of graphitizable aggregate or graphite and a graphitizable binder (organic binder), mixed, fired, and then pulverized. can be obtained by As a result, pores are generated after the graphitization catalyst is removed, and good properties are imparted to the massive graphite particles. In addition, the aggregated graphite particles can be adjusted to have a desired structure by appropriately selecting a mixing method of graphite or aggregate and a binder, adjustment of a mixing ratio such as an amount of binder, and pulverization conditions after sintering.

As the aggregate that can be graphitized, for example, coke powder, resin carbide, etc. can be used, but there is no particular limitation as long as it is a powder material that can be graphitized. Among them, coke powder that is easily graphitized such as needle coke is preferable. As graphite, for example, natural graphite powder, artificial graphite powder, etc. can be used, but there is no particular limitation as long as it is in powder form. The volume average particle size of the graphitizable aggregate or graphite is preferably smaller than the volume average particle size of the massive graphite particles, more preferably 2/3 or less of the volume average particle size of the massive graphite particles. Also, the graphitizable aggregate or graphite is preferably flat particles.

When graphitizable aggregates or graphite are flat particles, spherical graphite particles such as spherical natural graphite may be used in combination.
The degree of circularity is preferably 0.60 to 0.95, more preferably 0.65 to 0.95, and even more preferably 0.70 to 0.95, from the viewpoint of grain orientation control.
Here, the degree of circularity is defined as the perimeter of a circle calculated from the circle-equivalent diameter, which is the diameter of a circle having the same area as the projected area of the graphite particle, and the perimeter measured from the projected image of the graphite particle (contour line is a numerical value obtained by dividing by the length of ) and is obtained by the following formula. The degree of circularity is 1.00 for a perfect circle.
Circularity = (perimeter of equivalent circle)/(perimeter of particle cross-sectional image)
Specifically, the circularity is obtained by observing an image magnified 1000 times with a scanning electron microscope, arbitrarily selecting 10 graphite particles, measuring the circularity of each particle, and calculating the arithmetic average value. is the average circularity The degree of circularity, the perimeter of the equivalent circle, and the perimeter of the projected image of the particle can be determined by commercially available image analysis software.

As the graphitization catalyst, for example, metals such as iron, nickel, titanium, silicon and boron, semimetals, carbides and oxides thereof can be used. Among these, carbides or oxides of silicon or boron are preferred. The amount of these graphitization catalysts added is preferably in the range of 1% by mass to 50% by mass, more preferably in the range of 5% by mass to 40% by mass, still more preferably from 5% by mass to The range is 30% by mass. If it is 1% by mass or more, it tends to suppress the increase in the aspect ratio and specific surface area of the massive graphite particles and improve the development of graphite crystals. Each is preferred because it tends not to impair the properties.

The binder (organic binder) is not particularly limited as long as it can be graphitized by firing. Examples include organic materials such as tar, pitch, thermosetting resins, and thermoplastic resins. Further, the binder is preferably added in an amount of 5% by mass to 80% by mass, more preferably 10% by mass to 80% by mass, and 15% by mass to 80% by mass of the flat graphitizable aggregate or graphite. More preferably, it is added in mass %. By setting the amount of the binder added to an appropriate amount, it tends to be possible to suppress the aspect ratio or the specific surface area of the produced massive graphite particles from becoming too large.
The method of mixing the graphitizable aggregate or graphite with the binder is not particularly limited and may be carried out using a kneader or the like, but mixing at a temperature above the softening point of the binder is preferred. Specifically, when the binder is pitch, tar, etc., the temperature is preferably 50°C to 300°C, and when the binder is a thermosetting resin, a thermoplastic resin, etc., the temperature is preferably 20°C to 100°C. .

Next, the above mixture is fired and graphitized. The mixture may be formed into a predetermined shape before this treatment. Further, after molding, the material may be pulverized before graphitization to adjust the particle size, and then graphitization may be performed. The firing is preferably carried out under conditions in which the mixture is not easily oxidized, and examples thereof include a method of firing in a nitrogen atmosphere, an argon gas atmosphere, or in vacuum. The graphitization temperature is preferably 2000°C or higher, more preferably 2500°C or higher, and even more preferably 2800°C to 3200°C.
When the graphitization temperature is 2000° C. or higher, the graphite crystals are well developed, and the discharge capacity tends to be improved. In addition, there is a tendency that the added graphitization catalyst can be suppressed from remaining in the produced massive graphite particles. If the graphitization catalyst remains in the massive graphite particles, the discharge capacity may decrease, so it is preferable to suppress the remaining graphitization catalyst. On the other hand, if the graphitization temperature is 3200° C. or less, it tends to be possible to suppress the sublimation of graphite.

If the particle size is not adjusted before graphitization, it is preferable to pulverize the graphitized material obtained by the graphitization treatment so as to have a desired volume average particle size. The method of pulverizing the graphitized material is not particularly limited, but known methods such as jet mills, vibration mills, pin mills and hammer mills can be used. Through the production method described above, graphite particles in which a plurality of flattened particles are aggregated or combined so that their main surfaces are non-parallel, that is, massive graphite particles can be obtained.
Furthermore, Japanese Patent No. 3285520, Japanese Patent No. 3325021, etc. can be referred to for details of the above manufacturing method.
In addition, the surfaces of the obtained massive graphite particles may be coated with low-crystalline carbon.

<Step of obtaining a mixture>
In the step of obtaining the mixture, the activated carbonaceous material A and a carbonaceous material precursor from which the carbonaceous material B different from the carbonaceous material A is derived are mixed.

From the viewpoint of improving input/output characteristics, the carbonaceous substance B preferably contains at least one of crystalline carbon and amorphous carbon. For example, it is a carbonaceous substance obtained from an organic compound that can be converted to carbonaceous by heat treatment (hereinafter, a carbonaceous substance precursor that is a source of carbonaceous substance B is also referred to as a precursor of carbonaceous substance B). is preferred. Specific examples of the carbonaceous substance B include carbon materials such as low-crystalline carbon, amorphous carbon, and mesophase carbon.

Precursors of the carbonaceous substance B are not particularly limited, and include pitch, organic polymer compounds, and the like. Examples of pitch include ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt cracked pitch, pitch produced by thermally decomposing polyvinyl chloride, etc., pitch produced by polymerizing naphthalene in the presence of super strong acid, etc. is mentioned.
Examples of organic polymer compounds include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate and polyvinyl butyral, and natural substances such as starch and cellulose.

When pitch is used as a precursor of the carbonaceous substance B, the softening point of the pitch is preferably 70°C to 250°C, more preferably 75°C to 150°C, and 80°C to 120°C. is more preferred.
The softening point of the pitch is a value determined by the tar pitch softening point measuring method (ring and ball method) described in JIS K 2425:2006.
The residual carbon content of the precursor of the carbonaceous substance B is preferably 5% by mass to 80% by mass, more preferably 10% by mass to 70% by mass, and 20% by mass to 60% by mass. is more preferred. A method for measuring the residual coal rate will be described later.

The mixture may contain other particulate carbonaceous substance B (carbonaceous particles) in addition to the precursor of carbonaceous substance B, if necessary. When the mixture includes carbonaceous particles together with a precursor of carbonaceous material B, the carbonaceous material B and the carbonaceous particles formed from the precursor of carbonaceous material B may be the same or different.
Carbonaceous particles used as the other carbonaceous substance B are not particularly limited, and examples thereof include particles of acetylene black, oil furnace black, ketjen black, channel black, thermal black, earthy graphite, and the like.

In the step of obtaining the mixture, the content of the activated carbonaceous substance A and the precursor of the carbonaceous substance B in the mixture is not particularly limited. From the viewpoint of input/output characteristics, the content of the precursor of the carbonaceous material B is such that the content of the carbonaceous material B in the total mass of the negative electrode material for a lithium ion secondary battery is 0.1% by mass or more. It is preferably 0.5% by mass or more, more preferably 1% by mass or more. From the viewpoint of suppressing a decrease in capacity, the content of the precursor of the carbonaceous substance B is such that the content of the carbonaceous substance B in the total mass of the negative electrode material for a lithium ion secondary battery is 30% by mass or less. The amount is preferably 20% by mass or less, more preferably 10% by mass or less.

In the step of obtaining the mixture, the method of preparing the mixture containing the activated carbonaceous substance A and the precursor of the carbonaceous substance B is not particularly limited. For example, a method of mixing the precursors of activated carbonaceous substance A and carbonaceous substance B with a solvent and then removing the solvent (wet mixing), a method of mixing precursors of activated carbonaceous substance A and carbonaceous substance B into powder, A method of mixing in a state (powder mixing) and a method of mixing precursors of activated carbonaceous substance A and carbonaceous substance B while applying mechanical energy (mechanical mixing) can be mentioned.

The mixture containing the activated carbonaceous material A and the precursor of the carbonaceous material B is preferably in a composite state. A composite state means a state in which each material is physically or chemically in contact with each other.

<Step of obtaining fired product>
In the step of obtaining the fired product, the mixture is heat-treated to obtain the fired product.
The heat treatment temperature when heat-treating the mixture containing the activated carbonaceous material A and the precursor of the carbonaceous material B is not particularly limited. For example, the heat treatment is preferably performed under temperature conditions of 700°C to 1500°C, more preferably under temperature conditions of 750°C to 1300°C, and further preferably under temperature conditions of 800°C to 1200°C. is more preferred. From the viewpoint of sufficiently advancing the carbonization of the precursor of the carbonaceous substance B, the heat treatment is preferably performed at a temperature of 700°C or higher, and from the viewpoint of improving the input characteristics, the heat treatment is performed at a temperature of 1500°C or lower. It is preferably carried out under conditions. Also, if the heat treatment temperature is within the above range, the initial efficiency and input/output characteristics tend to improve. The heat treatment temperature may be constant or may vary from the beginning to the end of the heat treatment.
The treatment time for the heat treatment of the mixture containing the activated carbonaceous material A and the precursor of the carbonaceous material B varies as appropriate depending on the type of the precursor of the carbonaceous material B used. For example, when coal tar pitch with a softening point of 100° C. (±20° C.) is used as the precursor of the carbonaceous substance B, it is preferable to raise the temperature up to 400° C. at a rate of 10° C./min or less. Further, the total heat treatment time including the heating process is preferably 2 hours to 18 hours, more preferably 3 hours to 15 hours, and even more preferably 4 hours to 12 hours.

The atmosphere in which the mixture containing the activated carbonaceous substance A and the precursor of the carbonaceous substance B is heat-treated is not particularly limited as long as it is an inert gas atmosphere such as nitrogen gas or argon gas, and from an industrial point of view. A nitrogen gas atmosphere is preferred.

The step of obtaining the fired product is preferably a step of setting the BET specific surface area of the fired product to 0.5 m ² /g to 10 m ² /g, more preferably 1 m ² /g to 8 m ² /g. More preferably, it is a step of 2 m ² /g to 6 m ² /g.
The BET specific surface area of the baked product refers to the BET specific surface area of the baked product after pulverization, which will be described later.
The BET specific surface area of the fired product tends to decrease by raising the treatment temperature when heat-treating the mixture. By lowering the treatment temperature when heat-treating the mixture, the BET specific surface area of the baked product tends to increase.

The crystallinity of the carbonaceous material B is preferably lower than the crystallinity of the activated carbonaceous material A. Since the crystallinity of the carbonaceous material B is lower than that of the activated carbonaceous material A, the input characteristics tend to be improved.
The degree of crystallinity of the activated carbonaceous material A and the carbonaceous material B can be determined, for example, based on observation results with a transmission electron microscope (TEM).
Also, the baked product obtained in the step of obtaining the baked product may be pulverized with a cutter mill, a phaser mill, a juicer-mixer, or the like. Moreover, you may sift the crushed baked material.

<Negative electrode material for lithium ion secondary battery>
The negative electrode material for a lithium ion secondary battery of the present disclosure contains a carbonaceous substance AA and a carbonaceous substance B different from the carbonaceous substance AA, and when heat-treated at 600 ° C. for 30 minutes in an air atmosphere, the above The negative electrode material for a lithium ion secondary battery has a ratio of the BET specific surface area after heat treatment to the BET specific surface area before heat treatment (after heat treatment/before heat treatment) of 2.5 or more.

The negative electrode material for a lithium ion secondary battery of the present disclosure may be, for example, in a form in which the carbonaceous substance B is present on at least part of the surface of particles containing the carbonaceous substance AA. Whether or not the carbonaceous substance B exists on the surface of the particles containing the carbonaceous substance AA can be confirmed by observation with a transmission electron microscope.

The negative electrode material for lithium ion secondary batteries of the present disclosure may be produced by the method for producing a negative electrode material for lithium ion secondary batteries of the present disclosure. However, the negative electrode material for a lithium ion secondary battery of the present disclosure is not limited to that produced by the production method of the present disclosure.
The particles containing the carbonaceous material AA are the activated carbonaceous material A when the negative electrode material for a lithium ion secondary battery is produced by the production method of the present disclosure. However, in the negative electrode material for a lithium ion secondary battery of the present disclosure, the particles containing the carbonaceous substance AA may not be subjected to the activation treatment described above.

Examples of the carbonaceous substance AA include carbon materials such as artificial graphite, natural graphite, graphitized mesophase carbon, graphite such as graphitized carbon fiber, low-crystalline carbon, amorphous carbon, and mesophase carbon. Examples of the artificial graphite as the carbonaceous substance AA include those described for the carbonaceous substance A, and preferred embodiments are also the same.

Examples of the carbonaceous substance B include those described in the above-described production method, and the same applies to preferred forms.

For example, a negative electrode material for a lithium ion secondary battery is present on particles containing carbonaceous material AA as nuclei (for example, activated carbonaceous material A) and at least part of the surface of particles containing carbonaceous material AA. , and a carbonaceous substance B having a lower crystallinity than the carbonaceous substance AA (also referred to as “negative electrode material X for a lithium ion secondary battery”), the types of the carbonaceous substance AA and the carbonaceous substance B are carbon It is not particularly limited as long as it satisfies the condition that the crystallinity of the carbonaceous substance B is lower than that of the carbonaceous substance AA.

The negative electrode material X for a lithium ion secondary battery has a carbonaceous material B having a lower crystallinity than the carbonaceous material AA on at least part of the surface. When this negative electrode material for a lithium ion secondary battery is heat-treated at 600° C. for 30 minutes in an air atmosphere (hereinafter also referred to as “heat treatment X”), the carbonaceous substance B existing on the surface is removed.
That is, when the BET specific surface area is measured after the heat treatment X is performed, the BET specific surface area related to the surface state of the particles containing the carbonaceous substance AA can be obtained. For example, in the case of the negative electrode material for a lithium ion secondary battery manufactured by the manufacturing method of the present disclosure, after performing the heat treatment X, the BET specific surface area related to the surface state of the activated carbonaceous material A is obtained.

The ratio of the BET specific surface area (2) of the negative electrode material for lithium ion secondary batteries after heat treatment X to the BET specific surface area (1) of the negative electrode material for lithium ion secondary batteries before heat treatment X [(2 )/(1)] is 2.5 or more, preferably 3.0 or more, more preferably 3.5 or more, and 3.8 or more from the viewpoint of input characteristics. More preferred.
The BET specific surface area ratio [(2)/(1)] is preferably 6.0 or less, more preferably 5.5 or less, and 5.3 from the viewpoint of initial efficiency and high-temperature storage characteristics. It is more preferably 5.0 or less, particularly preferably 5.0 or less.

The BET specific surface area (1) of the negative electrode material for lithium ion secondary batteries before heat treatment X is preferably 0.5 m ² /g to 10 m ² /g from the viewpoint of input characteristics and storage characteristics, and 1 m ² /g to 8 m ² /g, more preferably 2 m ² /g to 6 m ² /g.

The BET specific surface area (2) of the negative electrode material for lithium ion secondary batteries after heat treatment X is appropriately set according to the volume average particle diameter (D ₅₀ ), type, etc. of the negative electrode material for lithium ion secondary batteries. is preferred. From the viewpoint of input characteristics, initial efficiency, and high-temperature storage characteristics, for example, it is preferably 1 m ² /g to 35 m ² /g, more preferably 2 m ² /g to 35 m ² /g, and 4 m ² /g. more preferably 5 m ² /g to 30 m ² /g, most preferably 5 m ² /g to ²⁰ m ² /g.

When the carbonaceous material AA is spherical natural graphite, the BET specific surface area (2) after the heat treatment X is preferably 5 m ² /g to 30 m ² /g, more preferably 6 m ² /g to 26 m ² /g. and more preferably 7 m ² /g to 20 m ² /g.
When the carbonaceous material AA is artificial graphite, the BET specific surface area (2) after the heat treatment X is preferably 1 m ² /g to 17 m ² /g, more preferably 2 m ² /g to 16 m ² /g. more preferably 3 m ² /g to 13 m ² /g.

The content of the carbonaceous substance AA (for example, the activated carbonaceous substance A) and the content of the carbonaceous substance B in the negative electrode material for a lithium ion secondary battery are not particularly limited. From the viewpoint of improving the input/output characteristics, the content of the carbonaceous material B in the total mass of the negative electrode material for lithium ion secondary batteries is preferably 0.1% by mass or more, and is preferably 0.5% by mass or more. It is more preferable that the content is 1% by mass or more. From the viewpoint of suppressing a decrease in capacity, the content of the carbonaceous substance B in the total mass of the negative electrode material for a lithium ion secondary battery is preferably 30% by mass or less, more preferably 20% by mass or less. It is preferably 10% by mass or less, and more preferably 10% by mass or less. As the carbonaceous substance B, when carbonaceous particles are used in addition to the carbonaceous substance B formed by heat treatment of the precursor of the carbonaceous substance B, the content of the carbonaceous substance B is the total of both. refers to the content of

The content of the carbonaceous material B in the negative electrode material for a lithium ion secondary battery, when calculated from the amount of the precursor of the carbonaceous material B, is the amount of the precursor of the carbonaceous material B and its residual carbon rate (mass% ) can be calculated by multiplying The carbon residue rate of the precursor of carbonaceous material B is determined by the precursor of carbonaceous material B alone (or the precursor of carbonaceous material B and carbonaceous material AA (for example, activated carbonaceous material A) at a predetermined ratio. in the state of the mixture) is heat-treated at a temperature at which the precursor of the carbonaceous material B can change to carbonaceous, and the mass of the precursor of the carbonaceous material B before the heat treatment and the precursor of the carbonaceous material B after the heat treatment are It can be calculated from the mass of the carbonaceous substance B derived. The mass of the precursor of the carbonaceous material B before the heat treatment and the mass of the carbonaceous material B derived from the precursor of the carbonaceous material B after the heat treatment can be determined by thermogravimetric analysis or the like.

The average interplanar spacing d ₀₀₂ of the negative electrode material for a lithium ion secondary battery determined by X-ray diffraction is preferably 0.340 nm or less. When the average interplanar spacing d ₀₀₂ is 0.340 nm or less, the lithium ion secondary battery tends to be excellent in both initial efficiency and energy density.
The value of the average interplanar spacing d ₀₀₂ is 0.3354 nm, which is the theoretical value for graphite crystals, and the closer to this value, the higher the energy density tends to be.

The average interplanar spacing d ₀₀₂ of the negative electrode material for lithium ion secondary batteries is obtained by irradiating a sample that is a negative electrode material for lithium ion secondary batteries with X-rays (CuKα rays) and measuring the diffraction line with a goniometer. From the profile, it can be calculated using Bragg's equation from the diffraction peak corresponding to the carbon 002 plane that appears around the diffraction angle 2θ=24° to 27°.

The value of the average interplanar spacing d ₀₀₂ of the negative electrode material for lithium ion secondary batteries tends to decrease, for example, by increasing the temperature of the heat treatment when producing the negative electrode material for lithium ion secondary batteries. Therefore, the average interplanar spacing d ₀₀₂ of the negative electrode material can be controlled by adjusting the temperature of the heat treatment when producing the negative electrode material for the lithium ion secondary battery.

(R value of Raman spectroscopy)
The R value of Raman spectroscopic measurement of the negative electrode material for lithium ion secondary batteries is preferably 0.1 to 1.0, more preferably 0.2 to 0.8, and 0.3 to 0.7. is more preferable. When the R value is 0.1 or more, graphite lattice defects used for intercalation and deintercalation of lithium ions are sufficiently present, and deterioration of input/output characteristics tends to be suppressed. When the R value is 1.0 or less, the decomposition reaction of the electrolytic solution is sufficiently suppressed, and the decrease in initial efficiency tends to be suppressed.

The R value is defined as the intensity ratio (Id/Ig) between the maximum peak intensity Ig near 1580 cm ^{−1 and the maximum peak intensity Id near 1360 cm −1 in} the Raman spectroscopic spectrum obtained by Raman spectroscopic measurement. Here, the peak appearing around 1580 cm ⁻¹ is usually a peak identified as corresponding to the graphite crystal structure, and means a peak observed at, for example, 1530 cm ⁻¹ to 1630 cm ⁻¹ . Also, the peak appearing around 1360 cm ⁻¹ is usually identified as corresponding to the amorphous structure of carbon, and means, for example, the peak observed at 1300 cm ⁻¹ to 1400 cm ⁻¹ .

In the present disclosure, Raman spectroscopic measurement is performed using a laser Raman spectrophotometer (model number: NRS-1000, JASCO Corporation), and an argon laser beam is applied to a sample plate on which a negative electrode material for a lithium ion secondary battery is set to be flat. is irradiated and measured. The measurement conditions are as follows.
Argon laser light wavelength: 532 nm
Wavenumber resolution: 2.56 cm ^-1
Measurement range: 1180 cm ^-1 to 1730 cm ^-1
Peak research: background subtraction

The volume average particle diameter (D ₅₀ ) of the negative electrode material for lithium ion secondary batteries is preferably 1 μm to 40 μm, more preferably 3 μm to 30 μm, even more preferably 5 μm to 25 μm.
When the volume average particle size of the negative electrode material for lithium ion secondary batteries is 1 μm or more, sufficient tap density and good coatability when used as a negative electrode material composition for lithium ion secondary batteries tend to be obtained. be. On the other hand, when the volume average particle diameter of the negative electrode material for lithium ion secondary batteries is 40 μm or less, the diffusion distance of lithium from the surface to the inside of the negative electrode material for lithium ion secondary batteries does not become too long, and the input/output characteristics are improved. It tends to be well maintained.

The volume average particle diameter (D ₅₀ ) of the negative electrode material for lithium ion secondary batteries is the cumulative 50% when the volume cumulative distribution curve is drawn from the small diameter side in the particle size distribution of the negative electrode material for lithium ion secondary batteries. It is the particle diameter when it becomes. The volume average particle diameter (D ₅₀ ) can be measured, for example, by dispersing the negative electrode material for a lithium ion secondary battery in purified water containing a surfactant, and using a laser diffraction particle size distribution analyzer (for example, Shimadzu Corporation, SALD- 3000 J).

The BET specific surface area of the negative electrode material for lithium ion secondary batteries is preferably 0.5 m ² /g to 10 m ² /g, more preferably 1 m ² /g to 8 m ² /g, and 2 m ² /g. More preferably, it is between g and 6 m ² /g. If the BET specific surface area is within the above range, there is a tendency to obtain a good balance between input/output characteristics and initial efficiency.

Since the negative electrode material for lithium ion secondary batteries of the present disclosure is excellent in high temperature storage characteristics, it is used in electric vehicles (EV), plug-in hybrid electric vehicles (PHEV), hybrid electric vehicles (HEV), power tools, power storage devices, etc. It is suitable as a negative electrode material for large-capacity lithium ion secondary batteries to be used. In particular, it is suitable as a negative electrode material for lithium ion secondary batteries used in EVs, PHEVs, HEVs, etc., which are required to be adapted to various environments.

<Negative electrode for lithium ion secondary battery>
The negative electrode for lithium ion secondary batteries of the present disclosure includes a negative electrode material layer containing the negative electrode material for lithium ion secondary batteries of the present disclosure, and a current collector. The negative electrode for lithium ion secondary batteries may contain, if necessary, other components in addition to the negative electrode material layer and current collector containing the negative electrode material for lithium ion secondary batteries of the present disclosure.

For the lithium ion secondary battery negative electrode, for example, a lithium ion secondary battery negative electrode material and a binder are kneaded together with a solvent to prepare a slurry negative electrode material composition for a lithium ion secondary battery, which is then used as a current collector. A negative electrode material layer is formed by coating it on the body, or the negative electrode material composition for lithium ion secondary batteries is formed into a shape such as a sheet or pellet and integrated with a current collector. It can be produced by Kneading can be performed using a dispersing device such as a stirrer, ball mill, super sand mill, pressure kneader, or the like.

The binder used for preparing the negative electrode material composition for lithium ion secondary batteries is not particularly limited. Binders include ethylenically unsaturated carboxylic acid esters such as styrene-butadiene copolymer (SBR), methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate. And homopolymers or copolymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, poly Polymer compounds with high ion conductivity such as acrylonitrile and polymethacrylonitrile can be used. When the negative electrode material composition for lithium ion secondary batteries contains a binder, the content of the binder is not particularly limited. For example, it may be 0.5 parts by mass to 20 parts by mass with respect to a total of 100 parts by mass of the negative electrode material for a lithium ion secondary battery and the binder.

The negative electrode material composition for lithium ion secondary batteries may contain a thickener. Carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or its salts, oxidized starch, phosphorylated starch, casein and the like can be used as thickeners. When the negative electrode material composition for lithium ion secondary batteries contains a thickener, the content of the thickener is not particularly limited. For example, it may be 0.1 to 5 parts by mass with respect to 100 parts by mass of the negative electrode material for lithium ion secondary batteries.

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

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. Porous materials such as porous metal (foamed metal), carbon paper, and the like can also be used as current collectors.

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

When the negative electrode material composition for a lithium ion secondary battery molded into a sheet, pellet, or the like is integrated with a current collector to form a negative electrode material layer, the integration method is not particularly limited. For example, it can be carried out by a roll, flat plate press, or a combination of these means. The pressure when the negative electrode material composition for a lithium ion secondary battery is integrated with the current collector is preferably, for example, about 1 MPa to 200 MPa.

The negative electrode density of the negative electrode material layer is not particularly limited. For example, it is preferably 1.1 g/cm ³ to 1.8 g/cm ³ , more preferably 1.2 g/cm ³ to 1.7 g/cm ³ , and 1.3 g/cm ³ to 1.8 g/cm 3 . More preferably 6 g/cm ³ . When the negative electrode density is 1.1 g/cm ³ or more ^, an increase in electrical resistance is suppressed and the capacity tends to increase. Decrease tends to be suppressed.

<Lithium ion secondary battery>
A lithium ion secondary battery of the present disclosure includes a negative electrode for a lithium ion secondary battery, a positive electrode, and an electrolytic solution.

A positive electrode can be obtained by forming a positive electrode material layer on a current collector in the same manner as in the method for producing the negative electrode described above. As the current collector, a metal or alloy such as aluminum, titanium, or stainless steel in the form of foil, foil with holes, mesh, or the like can be used.

The positive electrode material used for forming the positive electrode layer is not particularly limited. Examples of positive electrode materials include metal compounds (metal oxides, metal sulfides, etc.) capable of doping or intercalating lithium ions, conductive polymer materials, and the like. More specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), their composite oxides (LiCo _x Ni _{y Mnz} O ₂ , x + y + z = 1), Multiple 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} compounds, _V2O5 , _V6O13 , _VO2 , _MnO2 , _TiO2 , _{MoV2O8 , TiS2 , V2S5} , _VS2 , _MoS2 , _MoS3 , _Cr3 metal compounds such as O ₈ , Cr ₂ 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 positive electrode material may be used singly or in combination of two or more.

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

The states of the positive electrode and the negative electrode in the lithium ion secondary battery are not particularly limited. For example, the positive electrode, the negative electrode, and, if necessary, the separator disposed between the positive electrode and the negative electrode may be spirally wound, or may be stacked in a plate shape.

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

The shape of the lithium ion secondary battery is not particularly limited. For example, laminate-type batteries, paper-type batteries, button-type batteries, coin-type batteries, laminated-type batteries, cylindrical-type batteries, and square-type batteries can be used.

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 (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc., which require high-current charging and discharging in order to improve acceleration performance and brake regeneration performance. It is suitable as a lithium ion secondary battery.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

<Example 1>
(1) Preparation of negative electrode material 100 g of spherical natural graphite (volume average particle diameter: 10 μm) as carbonaceous material A was placed in an alumina crucible with a volume of 2.25 L and left at a constant temperature of 500 ° C. for 3 hours in an air atmosphere. did.
100 parts by mass of the obtained activated carbonaceous material A and 10 parts by mass of coal tar pitch (softening point: 98°C, residual carbon content: 50% by mass) as a precursor of the carbonaceous material B were powdered. A mixture was obtained by mixing. Next, the mixture was heat-treated to produce a baked product in which the carbonaceous material B adhered to the surface of the activated carbonaceous material A. The heat treatment was carried out by raising the temperature from 25° C. to 1000° C. at a heating rate of 200° C./hour under nitrogen flow, and holding at 1000° C. for 1 hour. The fired material in which the carbonaceous material B adheres to the surface of the activated carbonaceous material A is pulverized with a cutter mill and sieved with a 300-mesh sieve, and the under-sieved material is used as a negative electrode material for lithium ion secondary batteries (negative electrode material).

The BET specific surface area of the carbonaceous material A, the BET specific surface area of the activated carbonaceous material A, the volume average particle size (D ₅₀ ) of the negative electrode material, and the BET specific surface area of the negative electrode material were measured by the methods shown below. Also, based on the BET specific surface area of carbonaceous material A and the BET specific surface area of activated carbonaceous material A, the rate of increase in BET specific surface area of activated carbonaceous material A with respect to carbonaceous material A [((activated carbonaceous material BET specific surface area of substance A−BET specific surface area of carbonaceous substance A)/BET specific surface area of carbonaceous substance A)×100 (%)] was calculated. Table 1 shows the results.

[Measurement of BET specific surface area]
The BET specific surface area is measured by the BET method by measuring nitrogen adsorption at liquid nitrogen temperature (77 K) by the multipoint method using a specific surface area / pore size distribution measuring device (Flow Soap II 2300, Tokai Riki Co., Ltd.). Calculated.

[Measurement of volume average particle diameter (D ₅₀ )]
A dispersion obtained by dispersing a sample together with a surfactant in purified water was placed in a sample tank of a laser diffraction particle size distribution analyzer (SALD-3000J, Shimadzu Corporation). Next, the dispersion liquid was circulated with a pump while applying ultrasonic waves, and the volume cumulative 50% particle diameter of the obtained particle size distribution was defined as the volume average particle diameter (D ₅₀ ).

(2) Preparation of lithium ion secondary battery An aqueous solution (CMC concentration: 2% by mass) of CMC (carboxymethyl cellulose, Daiichi Kogyo Seiyaku Co., Ltd., Cellogen WS-C) as a thickener is added to 98 parts by mass of the negative electrode material. , and CMC were added so that the solid content was 1 part by mass, and kneaded for 10 minutes. Then, purified water was added in several portions so that the total solid content concentration of the negative electrode material and CMC was 45% by mass to 60% by mass, and the mixture was kneaded for 10 minutes. Subsequently, an aqueous dispersion of SBR (styrene-butadiene copolymer, BM400-B, Nippon Zeon Co., Ltd.) as a binder (SBR concentration: 40% by mass) was added so that the solid content of SBR was 1 part by mass. , and mixed for 10 minutes to prepare a paste-like negative electrode material composition for a lithium ion secondary battery (negative electrode material composition). Next, the negative electrode material composition is applied to an electrolytic copper foil having a thickness of 11 μm with a comma coater whose clearance is adjusted so that the coating amount per unit area is 10.0 mg/cm ² to form a negative electrode material layer. did. After that, the negative electrode density was adjusted to 1.5 g/cm ³ by hand pressing. The electrodeposited copper foil on which the negative electrode material layer was formed was punched out into a disk shape with a diameter of 14 mm to prepare a sample electrode (negative electrode).

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 electrolytic solution was injected to produce a coin-shaped lithium ion secondary battery. As the electrolyte, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the volume ratio of EC and EMC was 3:7) to a concentration of 1.0 mol/L. It was used. LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode. It was designed so that the initial negative electrode capacity/initial positive electrode capacity=1.2.
A polyethylene microporous membrane having a thickness of 20 μm was used as the separator. The produced lithium ion secondary battery was CC-charged to 4.2 V at a current value corresponding to 0.2 CA and then CV-charged to 0.02 CA. After that, the battery was rested for 30 minutes, discharged to 2.7 V at a current value corresponding to 0.2 CA, and rested for 30 minutes. This series of steps was defined as one cycle, and this cycle was repeated three times for initialization. Initial efficiency, input characteristics, output characteristics and high temperature storage characteristics were evaluated by the following methods using the initialized lithium ion secondary battery. Table 1 shows the results obtained.

[Evaluation of initial efficiency]
(1) Charge to 0 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA, and then charge at a constant voltage of 0 V until the current value reaches 0.02 CA. The capacity at this time was defined as the initial charge capacity.
(2) After resting for 30 minutes, the battery was discharged to 1.5 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA. The capacity at this time was defined as the initial discharge capacity.
(3) From the charge/discharge capacities determined in (1) and (2) above, the initial efficiency was determined using the following (Equation 1).
Initial efficiency (%) = (initial discharge capacity (mAh)/initial charge capacity (mAh)) x 100 (Formula 1)

[Evaluation of output characteristics]
(1) Charge to 0 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA, and then charge at a constant voltage of 0 V until the current value reaches 0.02 CA.
(2) After 30 minutes of rest time, the battery was discharged to 1.5 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA.
(3) (1) and (2) were repeated, and the discharge capacity at this time was defined as "discharge capacity 1" (mAh).
(4) After a rest period of 30 minutes, the battery was charged to 0 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA, and then charged at a constant voltage of 0 V until the current value reached 0.02 CA.
(5) After a rest period of 30 minutes, the battery was discharged to 1.5 V (vs. Li/Li ⁺ ) at a constant current of 3 CA, and the discharge capacity at this time was defined as "discharge capacity 2" (mAh).
(6) From the discharge capacities obtained in (3) and (5), output characteristics were obtained using the following (Equation 2).
Output characteristics (%) = (discharge capacity 2 (mAh)/discharge capacity 1 (mAh)) x 100 (Formula 2)

[Evaluation of input characteristics]
(1) The battery was charged to 4.2 V at a constant current of 0.2 CA, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 CA. The charge capacity at this time was defined as "charge capacity 1" (mAh).
(2) After 30 minutes of rest time, it was discharged to 2.7 V at a constant current of 0.2 CA.
(3) Charged to 4.2 V at a constant current of 3 CA after a rest period of 30 minutes. The charge capacity at this time was defined as "charge capacity 2" (mAh).
(4) From the discharge capacities obtained in (1) and (3), input characteristics were obtained using the following (Equation 3).
Input characteristics (%) = (charge capacity 2 (mAh)/charge capacity 1 (mAh)) x 100 (Formula 3)

[Evaluation of high temperature storage characteristics]
(1) Charged to 0 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA, and then performed constant voltage charge at 0 V until the current value reached 0.02 CA.
(2) After 30 minutes of rest time, the battery was discharged to 1.5 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA.
(3) After resting for 30 minutes, it was charged to 0 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA. The charge capacity (mAh) at this time was measured.
(4) The battery of (3) was left at 60° C. for 5 days.
(5) Discharge to 1.5 V (vs. Li/Li ⁺ ) at a constant current of 0.2 CA. The discharge capacity (mAh) at this time was measured.
(6) From the charge capacity obtained in (3) and the discharge capacity obtained in (5), high-temperature storage characteristics were determined using the following (Equation 4).
High temperature storage characteristics (%) = (discharge capacity (mAh)/charge capacity (mAh)) x 100 (Formula 4)

<Example 2>
Evaluation was carried out in the same manner as in Example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material A was set to 300°C. Table 1 shows the results obtained.

<Example 3>
Evaluation was carried out in the same manner as in Example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material A was set to 400°C. Table 1 shows the results obtained.

<Example 4>
Evaluation was carried out in the same manner as in Example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material A was set to 600°C. Table 1 shows the results obtained.

<Example 5>
Evaluation was carried out in the same manner as in Example 1, except that the treatment atmosphere for the carbonaceous substance A was _CO2 and the treatment temperature (activation treatment temperature) was 900°C. Table 1 shows the results obtained.

<Example 6>
Evaluation was carried out in the same manner as in Example 1, except that spherical natural graphite (volume average particle size: 16 μm) was used as the carbonaceous substance A. Table 1 shows the results obtained.

<Example 7>
Evaluation was carried out in the same manner as in Example 1, except that spherical natural graphite (volume average particle size: 20 μm) was used as the carbonaceous substance A. Table 1 shows the results obtained.

<Example 8>
50 parts by mass of coke powder with an average particle size of 8 μm, 20 parts by mass of tar pitch, 20 parts by mass of silicon carbide, and 10 parts by mass of spherical natural graphite with an average particle size of 20 μm (circularity 0.92) were mixed and heated to 100 ° C. for 1 hour to obtain a mixture. Next, this mixture was pulverized to an average particle size of 18 μm, and the obtained pulverized powder was put into a mold and molded into a rectangular parallelepiped. The resulting rectangular parallelepiped was heat-treated at 1000° C. in a nitrogen atmosphere and then fired at 2800° C. to graphitize the graphitizable components. The obtained graphite compact was pulverized to an average particle size of 18 μm to prepare graphite particles. When the obtained graphite particles were observed with an SEM, it was found that a plurality of flattened particles were included in the graphite particles in which the orientation planes (principal planes) were non-parallel and aggregated or combined. 100 g of the obtained graphite particles were placed in an alumina crucible with a volume of 2.25 L, and allowed to stand at a constant temperature of 500° C. for 3 hours in an air atmosphere. The BET specific surface area of the obtained carbonaceous material A (activated carbonaceous material A) was measured.
100 parts by mass of the activated carbonaceous material A and 2 parts by mass of coal tar pitch (softening point: 98° C., residual carbon content: 50% by mass) as a precursor of the carbonaceous material B are powder-mixed. A mixture was obtained. Next, the mixture was heat-treated to produce a baked product in which the carbonaceous material B adhered to the surface of the activated carbonaceous material A. The heat treatment was carried out by raising the temperature from 25° C. to 1000° C. at a heating rate of 200° C./hour under nitrogen flow, and holding at 1000° C. for 1 hour. The fired material in which the carbonaceous material B adheres to the surface of the activated carbonaceous material A is pulverized with a cutter mill and sieved with a 300-mesh sieve, and the under-sieved material is used as a negative electrode material for lithium ion secondary batteries (negative electrode material).
Evaluation was carried out in the same manner as in Example 1 using the obtained negative electrode material. Table 1 shows the results obtained.

<Example 9>
40 parts by mass of coke powder with an average particle size of 8 µm, 25 parts by mass of tar pitch, 5 parts by mass of silicon carbide with an average particle size of 48 µm, and 20 parts by mass of coal tar were mixed and stirred at 200°C for 1 hour. Then, the mixture was fired at 2800° C. in a nitrogen atmosphere and pulverized to prepare graphite particles having an average particle size of 20 μm. When the obtained graphite particles were observed with an SEM, it was found that a plurality of flattened particles were included in the graphite particles in which the orientation planes (principal planes) were non-parallel and aggregated or combined. 100 g of the obtained graphite particles were placed in an alumina crucible with a volume of 2.25 L, and allowed to stand at a constant temperature of 500° C. for 3 hours in an air atmosphere. The BET specific surface area of the obtained carbonaceous material A (activated carbonaceous material A) was measured.
Using the obtained activated carbonaceous material A, a negative electrode material (negative electrode material) for a lithium ion secondary battery was obtained in the same manner as in Example 8.
Evaluation was carried out in the same manner as in Example 1 using the obtained negative electrode material. Table 1 shows the results obtained.

<Example 10>
The procedure was the same as in Example 1, except that carbonaceous substance A was heated to 700° C. in a nitrogen gas atmosphere, and then a gas obtained by flowing nitrogen gas into water heated to 80° C. at a flow rate of 100 cc/min was blown for 3 hours. evaluation was carried out. Table 1 shows the results obtained.

<Comparative Example 1>
Evaluation was carried out in the same manner as in Example 1, except that the carbonaceous material A was not heat-treated (activated). Table 1 shows the results obtained.

<Comparative Example 2>
Evaluation was carried out in the same manner as in Example 1, except that the carbonaceous material A was heat-treated in a nitrogen atmosphere. Table 1 shows the results obtained.

<Comparative Example 3>
Evaluation was carried out in the same manner as in Example 1, except that the carbonaceous material A was heat-treated at 200°C. Table 1 shows the results obtained.

<Comparative Example 4>
Evaluation was carried out in the same manner as in Example 1, except that the carbonaceous material A was heat-treated at 800°C. Table 1 shows the results obtained.

As shown in the results of Table 1, the lithium-ion secondary batteries produced using the negative electrode materials of Examples had better input characteristics, It can be seen that it is excellent in any of the items of output characteristics, high temperature storage characteristics, and initial efficiency, and exhibits characteristics equivalent to those of the comparative examples in other items.

The negative electrode materials of Examples 1 and 6 to 8 and Comparative Examples 1 and 4 were subjected to heat treatment X at 600° C. for 30 minutes in an air atmosphere. The BET specific surface area (2) of the negative electrode material after this heat treatment X was measured by the method described above. A ratio of the BET specific surface area (2) after the heat treatment X to the BET specific surface area (1) before the heat treatment X [(2)/(1)] was calculated. Table 2 shows the results.

Claims (6)

It contains a carbonaceous substance AA and a carbonaceous substance B different from the carbonaceous substance AA, and the carbonaceous substance AA is spherical natural graphite or a plurality of flattened graphite particles whose orientation planes are non-parallel. A negative electrode material for a lithium ion secondary battery, which is graphite particles in which particles are aggregated or bound,
When the carbonaceous material AA is the spherical natural graphite, the volume average particle size of the negative electrode material for a lithium ion secondary battery is 16.7 μm or less,
When the negative electrode material for a lithium ion secondary battery is heat-treated at 600° C. for 30 minutes in an air atmosphere, the ratio of the BET specific surface area after the heat treatment to the BET specific surface area before the heat treatment is 2.5 or more. Anode material for lithium-ion secondary batteries. 2. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the BET specific surface area after the heat treatment is 1 m ² /g to 35 m ² /g. 3. The negative electrode material for a lithium ion secondary battery according to claim 1, wherein the BET specific surface area before heat treatment is 0.5 m ² /g to 10 m ² /g. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the content of the carbonaceous material B in the total mass of the negative electrode material for lithium ion secondary batteries is 0.1% by mass or more. negative electrode material. 5. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the average interplanar spacing d ₀₀₂ obtained by X-ray diffraction method is 0.340 nm or less. 6. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5, having an R value measured by Raman spectroscopy of 0.1 to 1.0.