JP6981471B2 - A method for manufacturing a negative electrode material for a lithium ion secondary battery, and a negative electrode material for a lithium ion secondary battery. - Google Patents

Description

The present invention relates to a method for manufacturing a negative electrode material for a lithium ion secondary battery and a negative electrode material for a lithium ion secondary battery.

Lithium-ion secondary batteries have been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smartphones, and tablet PCs because of their small size, light weight, and high energy density. In recent years, _{against the background of environmental problems such as global warming due to CO 2} emissions, clean electric vehicles (EVs) that run only on batteries, hybrid electric vehicles (HEVs) that combine gasoline engines and batteries, and plug-in hybrid electric vehicles. (PHEV) and the like have become widespread, and lithium ion secondary batteries (vehicle-mounted lithium ion secondary batteries) are used as batteries mounted on 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 various 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. A carbon material is widely used as a material for a negative electrode material for a lithium ion secondary battery. The carbon material used for the negative electrode material is roughly classified into graphite and a carbon material having a lower crystallinity than graphite (amorphous carbon or the like). Graphite has a structure in which hexagonal network surfaces of carbon atoms are regularly laminated, and when it is 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 network surface. Charging and discharging are performed.

Amorphous carbon has an irregular stacking of hexagonal mesh surfaces or has no hexagonal mesh surface. In the negative electrode material using amorphous carbon, the insertion reaction and the desorption reaction of lithium ions proceed on the entire surface of the negative electrode material. Therefore, it is easy to obtain a lithium ion battery having excellent output characteristics as compared with the case where graphite is used as the negative electrode material (see, for example, Patent Document 1 and Patent Document 2). On the other hand, amorphous carbon has a lower crystallinity than graphite, so its energy density is lower than that of graphite.
Further, Patent Document 3 proposes improvement of initial efficiency by adjusting the micropore capacity to a specific range.

Japanese Unexamined Patent Publication No. 4-370662 Japanese Unexamined Patent Publication No. 5-307956 International Publication No. 2012/090728

Considering the characteristics of carbon material, it contains composite particles coated with graphite coated with amorphous carbon, and while maintaining high energy density, it reduces surface reactivity to maintain good initial charge / discharge efficiency and output. Negative electrode materials with enhanced characteristics have also been proposed. However, from the background as described above, there is a demand for a negative electrode material that can further improve the output characteristics of the lithium ion secondary battery. In addition, in-vehicle lithium ion secondary batteries such as EVs, HEVs, and PHEVs are also 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 the charging characteristics and the 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 capable of manufacturing a negative electrode for a lithium ion secondary battery excellent in input characteristics, output characteristics, high temperature storage characteristics and initial efficiency. The purpose is to provide a method.

The present inventors have arrived at the present invention as a result of diligent studies to achieve the above object. That is, one embodiment of the present invention includes the following aspects.

<1> A step of preparing the activated carbonaceous substance A which has been treated to increase the BET specific surface area by 2% to 50% with respect to the carbonaceous substance A.
A step of mixing the activated carbonaceous substance A and a carbonic substance precursor that is a source of the carbonic substance B different from the carbonic substance A to obtain a mixture.
The step of heat-treating the mixture to obtain a fired product, and
A method for manufacturing a negative electrode material for a lithium ion secondary battery.

<2> Step of obtaining the fired product, a BET specific surface area of the fired product is a step to ^{0.5m 2 / g~10m 2 / g <} 1> negative electrode material for a lithium ion secondary battery according to 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 under a temperature condition 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 carbonic substance B is lower than the crystallinity of the activated carbonic substance A. Production method.

<5> A carbon substance AA and a carbon substance B different from the carbon substance AA are contained.
A negative electrode material for a lithium ion secondary battery in which 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 when the heat treatment is performed at 600 ° C. for 30 minutes in an air atmosphere.

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

Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to the numerical values and their ranges, and does not limit the present invention.

In the present disclosure, the term "process" includes, in addition to a process independent of other processes, the process as long as the purpose of the process is achieved even if it cannot be clearly distinguished from the other process. ..
In the present disclosure, the numerical range indicated by using "~" includes the numerical values before and after "~" as the minimum value and the maximum value, respectively.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. .. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.
In the present disclosure, each component may contain a plurality of applicable substances. When a plurality of substances corresponding to each component are present in the negative electrode material or composition, the content or content of each component shall be the content of the plurality of substances present in the negative electrode material or composition unless otherwise specified. It means the total content or content.
In the present disclosure, a plurality of types of particles corresponding to each component may be contained. When a plurality of particles corresponding to each component are present in the negative electrode material or composition, the particle size of each component is the mixture of the plurality of particles present in the negative electrode material or composition unless otherwise specified. Means a value.
In the present disclosure, the term "layer" refers to the case where the layer is formed in the entire region when the region is observed, and also when the layer is formed only in a part of the region. included.
In the present disclosure, the term "laminated" refers to stacking layers, and two or more layers may be bonded or the two or more layers may be removable.

<Manufacturing method of negative electrode material for lithium ion secondary battery>
The method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure includes a step of preparing an activated carbonaceous substance A which has been treated to increase the BET specific surface area by 2% to 50% with respect to the carbonaceous substance A. A step of mixing the activated carbonaceous substance A and a carbonic substance precursor that is a source of the carbonic substance B different from the carbonic substance A to obtain a mixture, and a step of heat-treating the mixture to obtain a fired product. It has a step of obtaining and.
The method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure may include other steps, if necessary.

A lithium ion secondary battery excellent in input characteristics, output characteristics, high temperature storage characteristics and initial efficiency by using the negative electrode material for a lithium ion secondary battery manufactured by the method for manufacturing a negative electrode material for a lithium ion secondary battery of the present disclosure. Negative electrode can be manufactured.
Hereinafter, each process included in the method for manufacturing 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 substance A, the activated carbonaceous substance A which has been treated to increase the BET specific surface area by 2% to 50% with respect to the carbonic substance A is prepared. The treatment for increasing the BET specific surface area of the carbonaceous substance A is not particularly limited.
Examples of the treatment for increasing the BET specific surface area of the carbonaceous substance A include _{heat treatment in an atmosphere in which CO 2} gas, water vapor, O ₂ gas and the like are present, and mechanical treatment. From the viewpoint of controlling the particle size of the activated carbonaceous substance A, controlling the surface state of the activated carbonaceous substance A, and the like, _{it is preferable to perform heat treatment in an atmosphere in which O 2} gas is present (for example, in an air atmosphere).

The appropriate treatment temperature varies depending on the gas atmosphere used, the treatment 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, it is possible to increase the specific surface area of the activated carbonaceous substance A without burning the carbonic substance A.
The heat treatment time varies depending on the heat treatment temperature, the type of carbon material, and the like, but is preferably 0.5 hours to 24 hours, and more preferably 1 hour to 6 hours. Within this time, it is possible to effectively increase the specific surface area of the activated carbonaceous substance A. Further, when the heat treatment is performed in an atmosphere in which _{O 2 gas is present, the content of O 2} gas is preferably 1% by volume to 30% by volume. Within this range, the specific surface area of the activated carbonaceous substance A tends to be effectively increased.

Further, the heat treatment temperature when the gas atmosphere used is a CO ₂ gas atmosphere 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 a liquid nitrogen temperature (77K) by a multi-point method.
When measuring the BET specific surface area, it is considered that the water adsorbed on the sample surface and structure affects the gas adsorption capacity. Therefore, it is preferable to first perform a pretreatment for removing water by heating. ..
In the pretreatment, for example, the measurement cell in which 0.05 g of the measurement sample is charged is depressurized to 10 Pa or less with a vacuum pump, then heated at 110 ° C. and held for 3 hours or more, and then kept in the depressurized state. Let it cool naturally to room temperature (25 ° C). After performing this pretreatment, the evaluation temperature may be 77K, and the evaluation pressure range may be measured as a relative pressure (equilibrium pressure with respect to saturated vapor pressure) of less than 1.

In the step of preparing the activated carbonaceous substance A, the rate of increase in the BET specific surface area of the activated carbonaceous substance A with respect to the carbonic substance A is 2% to 50%, and may be 5% to 50%. When the rate of increase in the BET specific surface area of the activated carbonaceous substance A with respect to the carbonaceous substance A is less than 2%, the input characteristics tend to be slightly improved. When the rate of increase in the BET specific surface area of the activated carbonaceous substance A with respect to the carbonaceous substance A exceeds 50%, the initial efficiency and the high temperature storage property tend to deteriorate.

The carbonaceous substance A used in the step of preparing the activated carbonaceous substance A is not particularly limited.
Examples of the carbonaceous substance A include artificial graphite, natural graphite, graphitized mesophase carbon, graphite such as graphitized carbon fiber, and carbon materials such as 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 examples thereof include scaly, spherical, lumpy, and fibrous shapes. 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 size (D ₅₀ ) of the carbonic substance A is preferably 5 μm to 30 μm, more preferably 6 μm to 25 μm, and 7 μm to 20 μm. Is even more preferable.
When the carbonaceous substance A is artificial graphite, the volume average particle size (D ₅₀ ) of the carbonic substance A is preferably 8 μm to 40 μm, more preferably 10 μm to 35 μm, and 12 μm to 30 μm. Is even more preferable.

If the carbon material A is a spherical natural graphite, BET specific surface area of the carbon material A ^is preferably 5m ² / g~15m 2 / ^g, more to be 6m ² / g~13m 2 / g ^preferably, further preferably 7m ² / g~11m 2 / g.
If the carbon material A is artificial graphite, BET specific surface area of the carbon material A ^is preferably 1m ² / g~10m 2 / ^g, more preferably 2m ² / g~8m 2 / g , further preferably ^{3m 2} / ^g~7m 2 / g.

If the carbon material A is a spherical natural graphite, BET specific surface area of the activated carbon material ^A, it is 5m ² / g~23m 2 / g is ^preferable, 6m ² / ^g~20m 2 / g it is more ^preferable, further preferably 7m ² / g~15m 2 / g.
If the carbon material A is artificial graphite, BET specific surface area of the activated carbon material A ^is preferably 1m ² / g~13m 2 / ^g, it is 2m ² / g~12m 2 / g more ^preferably, further preferably 3m ² / g~10m 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 substance A can be purchased and prepared.

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

Flat particles are particles having a major axis and a minor axis, and are not completely spherical. For example, scaly, scaly, and some lumpy shapes are included in this. In the massive graphite particles, the fact that the main surfaces of the plurality of flat particles are non-parallel means that the surfaces (main surfaces) having the largest cross-sectional area of the flat graphite particles are not aligned in a certain direction.

Further, in the massive graphite particles, the flat particles are aggregated or bonded, but the bonding means that the particles are chemically bonded to each other through carbonaceous substances in which organic binders such as tar and pitch are carbonized. It means the state of being connected to. Further, the aggregate means a state in which the particles are not chemically bonded to each other, but the shape as an aggregate is maintained due to the shape or the like. In the present invention, those bonded are preferable from the viewpoint of mechanical strength.
The number of aggregated or bonded flat particles in one lump graphite particle is not particularly limited, but is preferably 3 or more, more preferably 5 to 20, and 5 to 15. It is more preferable to have.

-Manufacturing method of 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 graphitizing catalyst is added to the total amount of graphitizable aggregate or graphite and graphitizable binder (organic binder), mixed, fired, and then pulverized. It can be obtained by doing. As a result, pores are generated after the graphitization catalyst is removed, and good properties are imparted as massive graphite particles. Further, the lump graphite particles can be adjusted to a desired configuration by appropriately selecting a mixing method of graphite or aggregate and a binder, adjustment of a mixing ratio such as a binder amount, pulverization conditions after firing, and the like.

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

When graphitizable aggregate or graphite is flat particles, spherical graphite particles such as spherical natural graphite may be used in combination.
The 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 controlling particle orientation.
Here, the circularity is the perimeter as a circle calculated from the diameter equivalent to a circle, which is the diameter of a circle having the same area as the projected area of the graphite particles, and the perimeter measured from the projected image of the graphite particles (contour line). It is a numerical value obtained by dividing by (the length of), and is calculated by the following formula. The circularity is 1.00 in a perfect circle.
Circularity = (perimeter of equivalent circle) / (perimeter of particle cross-sectional image)
Specifically, the circularity is calculated by observing an image magnified at a magnification of 1000 times with a scanning electron microscope, arbitrarily selecting 10 graphite particles, measuring the circularity of each particle, and calculating the arithmetic mean value. The average circularity to be made. The circularity, the perimeter of the equivalent circle, and the perimeter of the projected image of the particles can be obtained by commercially available image analysis software.

As the graphitization catalyst, for example, a metal or metalloid such as iron, nickel, titanium, silicon, or boron, and a graphitization catalyst such as carbides or oxides thereof can be used. Of 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, and further preferably in the range of 5% by mass to 5% by mass with respect to the obtained massive graphite particles. It is in the range of 30% by mass. If it is 1% by mass or more, the increase in the aspect ratio and the specific surface area of the massive graphite particles tends to be suppressed to improve the development of graphite crystals, while if it is 50% by mass or less, it is easy to mix uniformly. Each is preferable because the sex tends not to be impaired.

The binder (organic binder) is not particularly limited as long as it can be graphitized by firing, and examples thereof include organic materials such as tar, pitch, thermosetting resin, and thermoplastic resin. 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, based on the flat graphitizable aggregate or graphite. It is more preferable to add% by mass. By setting the amount of the binder added to an appropriate amount, it tends to be possible to prevent the aspect ratio or the specific surface area of the produced massive graphite particles from becoming too large.
The method for mixing graphitizable aggregate or graphite and binder is not particularly limited and is carried out using a kneader or the like, but it is preferable to mix at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, the temperature is preferably 50 ° C to 300 ° C, and when the binder is a thermosetting resin, a thermoplastic resin or the like, the temperature is preferably 20 ° C to 100 ° C. ..

Next, the above mixture is calcined and graphitized. Before this treatment, the mixture may be formed into a predetermined shape. Further, it may be pulverized after molding and before graphitization, the particle size may be adjusted, and then graphitization may be performed. The firing is preferably performed under conditions in which the mixture is difficult to oxidize, and examples thereof include a method of firing in a nitrogen atmosphere, an argon gas atmosphere, or a 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 development of graphite crystals tends to be good and the discharge capacity tends to be improved. Further, the added graphitization catalyst tends to 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 that the residue is suppressed. On the other hand, if the graphitization temperature is 3200 ° C. or lower, the sublimation of graphite tends to be suppressed.

When the particle size is not adjusted before graphitization, it is preferable to pulverize the graphitized product obtained by the graphitization treatment so as to have a desired volume average particle size. The method for pulverizing the graphitized product is not particularly limited, but a known method such as a jet mill, a vibration mill, a pin mill, or a hammer mill can be used. By going through the production method shown above, it is possible to obtain graphite particles in which a plurality of flat particles are aggregated or bonded so that the main surfaces are non-parallel, that is, massive graphite particles.
Further, for details of the above-mentioned manufacturing method, Japanese Patent No. 3285520, Japanese Patent No. 332521, and the like can also be referred to.
Further, the surface of the obtained massive graphite particles may be coated with low crystalline carbon.

<Step to obtain a mixture>
In the step of obtaining the mixture, the activated carbonaceous substance A and the carbonaceous substance precursor which is the source of the carbonic substance B different from the carbonic substance A are mixed.

From the viewpoint of improving the 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 into a carbonaceous substance by heat treatment (hereinafter, the carbonaceous substance precursor that is the source of the carbonic substance B is also referred to as a precursor of the carbonic substance B). Is preferable. Specific examples of the carbonaceous substance B include carbon materials such as low crystalline carbon, amorphous carbon, and mesophase carbon.

The precursor of the carbonaceous substance B is not particularly limited, and examples thereof include pitches and organic polymer compounds. The pitches include ethylene heavy end pitch, crude oil pitch, coal tar pitch, asphalt decomposition pitch, pitch produced by thermally decomposing polyvinyl chloride, etc., pitch produced by polymerizing naphthalene, etc. in the presence of super strong acid, etc. Can be mentioned.
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.

When the pitch is used as the 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 even more preferable.
The softening point of the pitch means a value obtained by the softening point measuring method (ring ball method) of the tar pitch 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 even more preferable. The method for measuring the residual coal rate will be described later.

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

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

In the step of obtaining the mixture, the method for preparing the mixture containing the activated carbonaceous substance A and the precursor of the carbonic substance B is not particularly limited. For example, a method of mixing the precursors of the activated carbonaceous substance A and the carbonaceous substance B with the solvent and then removing the solvent (wet mixing), the precursors of the activated carbonaceous substance A and the carbonic substance B are powdered. Examples thereof include a method of mixing in a state (powder mixing) and a method of mixing activated carbonaceous substance A and precursors of carbonic substance B while applying mechanical energy (mechanical mixing).

The mixture containing the activated carbonaceous substance A and the precursor of the carbonic substance B is preferably in a composite state. The compounded state means that the respective materials are in physical or chemical contact.

<Process to obtain fired product>
In the step of obtaining a calcined product, the mixture is heat-treated to obtain a calcined product.
The heat treatment temperature at the time of heat-treating the mixture containing the activated carbonaceous substance A and the precursor of the carbonic substance B is not particularly limited. For example, the heat treatment is preferably performed under a temperature condition of 700 ° C. to 1500 ° C., more preferably performed under a temperature condition of 750 ° C. to 1300 ° C., and is performed under a temperature condition of 800 ° C. to 1200 ° C. Is even more preferred. From the viewpoint of sufficiently advancing the carbonization of the precursor of the carbonaceous substance B, the heat treatment is preferably performed under a temperature condition 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. Further, when the heat treatment temperature is within the above range, the initial efficiency and the input / output characteristics tend to be improved. The heat treatment temperature may be constant or may change from the start to the end of the heat treatment.
The treatment time when heat-treating a mixture containing the activated carbonaceous substance A and the precursor of the carbonic substance B varies appropriately depending on the type of the precursor of the carbonic substance B used. For example, when a coal tar pitch having 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. The total heat treatment time including the temperature raising process is preferably 2 hours to 18 hours, more preferably 3 hours to 15 hours, and further preferably 4 hours to 12 hours.

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

Obtaining a baked product, it is preferable that the BET specific surface area of the fired product is a step to 0.5m ² / g~10m ² / ^g, a step of the 1m ² / g~8m 2 / g More preferably, it is a step of making ^{2 m 2 / g to 6 m 2 / g.}
The BET specific surface area of the fired product means the BET specific surface area of the fired product after crushing, which will be described later.
By increasing the treatment temperature when the mixture is heat-treated, the BET specific surface area of the fired product tends to decrease. By lowering the treatment temperature when the mixture is heat-treated, the BET specific surface area of the fired product tends to increase.

The crystallinity of the carbonic substance B is preferably lower than the crystallinity of the activated carbonaceous substance A. Since the crystallinity of the carbonaceous substance B is lower than the crystallinity of the activated carbonaceous substance A, the input characteristics tend to be improved.
The high and low crystallinity of the activated carbonaceous substance A and the carbonic substance B can be determined, for example, based on the observation results by a transmission electron microscope (TEM).
Further, the fired product obtained in the step of obtaining the fired product may be crushed by a cutter mill, a phaser mill, a juicer mixer or the like. Further, the crushed fired product may be sieved.

<Negative electrode material for lithium-ion secondary batteries>
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-mentioned A negative electrode material for a lithium ion secondary battery in which the ratio of the BET specific surface area after the heat treatment (after heat treatment / before heat treatment) to the BET specific surface area before heat treatment is 2.5 or more.

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

The negative electrode material for a lithium ion secondary battery of the present disclosure may be manufactured by the method for manufacturing a negative electrode material for a lithium ion secondary battery of the present disclosure. However, the negative electrode material for a lithium ion secondary battery of the present disclosure is not limited to the one manufactured by the manufacturing method of the present disclosure.
When the negative electrode material for a lithium ion secondary battery is produced by the production method of the present disclosure, the particles containing the carbonaceous substance AA are the activated carbonaceous substance A. However, in the negative electrode material for a lithium ion secondary battery of the present disclosure, the particles containing the carbonaceous substance AA do not have to be subjected to the above-mentioned activation treatment.

Examples of the carbonaceous substance AA include graphite such as artificial graphite, natural graphite, graphitized mesophase carbon and graphitized carbon fiber, and carbon materials such as low crystalline carbon, amorphous carbon and mesophase carbon. As the artificial graphite as the carbonaceous substance AA, the one described in the carbonic substance A can be mentioned, and the same applies to the preferred embodiment.

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

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

The negative electrode material X for a lithium ion secondary battery has a carbonaceous substance B having a lower crystallinity than the carbonic substance AA on at least a part of the surface thereof. 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 present 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, the BET specific surface area related to the surface state of the activated carbonaceous substance A can be obtained after the heat treatment X.

The ratio of the BET specific surface area (2) of the negative electrode material for the lithium ion secondary battery after the heat treatment X to the BET specific surface area (1) of the negative electrode material for the lithium ion secondary battery before the 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 ratio of BET specific surface area [(2) / (1)] is preferably 6.0 or less, more preferably 5.5 or less, from the viewpoint of initial efficiency and high temperature storage characteristics. It is more preferably less than or equal to, and particularly preferably 5.0 or less.

BET specific surface area of the negative electrode material for a lithium ion secondary battery before performing the heat treatment X (1) is preferably from the viewpoint of the input characteristics and storage ^{characteristics,} it is ^{0.5m 2 / g~10m 2 / g,} 1m more preferably ² / ^{g~8m 2} / ^g, further preferably 2m ² / g~6m 2 / g.

The BET specific surface area (2) of the negative electrode material for the lithium ion secondary battery after the heat treatment X is _{appropriately set according to the volume average particle diameter (D 50} ), the type, etc. of the negative electrode material for the lithium ion secondary battery. Is preferable. Input characteristics, in terms of initial efficiency and high-temperature storage characteristics, for ^example, is preferably 1m ² / g~35m 2 / ^g, more preferably ^{2m 2 / g~35m 2 / g,} 4m 2 / more preferably g~35m is ² / ^g, particularly preferably from 5m ² / g~30m 2 / ^g, it is highly preferably 5m ² / g~20m 2 / g.

If the carbon material AA is spherical natural graphite, BET specific surface area after the heat treatment X (2) ^is preferably ^{5m 2 / g~30m 2 / g,} 6m 2 / g~26m 2 / g more ^preferably, further preferably 7m ² / g~20m 2 / g.
If the carbon material AA is artificial graphite, BET specific surface area after the heat treatment X (2) ^is preferably 1m ² / g~17m 2 / ^g, with 2m ² / g~16m 2 / g more preferably ^in, further preferably 3m ² / g~13m 2 / g.

The content of the carbonaceous substance AA (for example, the activated carbonaceous substance A) and the content of the carbonic substance B in the negative electrode material for the lithium ion secondary battery are not particularly limited. From the viewpoint of improving the input / output characteristics, the content of the carbonaceous substance B in the total mass of the negative electrode material for the lithium ion secondary battery is preferably 0.1% by mass or more, preferably 0.5% by mass or more. It is more preferably present, and further preferably 1% by mass or more. From the viewpoint of suppressing the decrease in capacity, the content of the carbonaceous substance B in the total mass of the negative electrode material for the 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. When carbonaceous particles are used in combination with the carbonic substance B formed by the heat treatment of the precursor of the carbonic substance B, the content of the carbonic substance B is the total of both. Refers to the content rate of.

When the content of the carbonaceous substance B in the negative electrode material for a lithium ion secondary battery is calculated from the amount of the precursor of the carbonic substance B, the residual carbon content (mass%) is added to the amount of the precursor of the carbonic substance B. ) Can be calculated. The residual carbon content of the precursor of the carbon substance B is such that the precursor of the carbon substance B is used alone (or a predetermined ratio of the precursor of the carbon substance B and the carbon substance AA (for example, the activated carbon substance A)). The precursor of the carbonaceous substance B is heat-treated at a temperature at which it can change to carbonaceous material (in the state of a mixture of the above), and the mass of the precursor of the carbonaceous substance B before the heat treatment and the precursor of the carbonic substance B after the heat treatment are obtained. It can be calculated from the mass of the derived carbonaceous substance B. The mass of the precursor of the carbonaceous substance B before the heat treatment and the mass of the carbonic substance B derived from the precursor of the carbonic substance B after the heat treatment can be determined by thermal weight analysis or the like.

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

Mean spacing d ₀₀₂ of the negative electrode material for a lithium ion secondary battery, diffraction X-ray irradiation of (CuKa radiation) but the sample is a negative electrode material for a lithium ion secondary battery, obtained by measuring the diffraction lines by goniometer From the profile, it can be calculated using Bragg's equation from the diffraction peak corresponding to the carbon 002 surface appearing in the vicinity of the diffraction angle 2θ = 24 ° to 27 °.

The value of the average surface spacing _d002 of the negative electrode material for a lithium ion secondary battery tends to be small, for example, by increasing the temperature of the heat treatment when producing the negative electrode material for a lithium ion secondary battery. _{Therefore, the average surface 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 the Raman spectroscopic measurement of the negative electrode material for a lithium ion secondary battery 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 insertion and desorption 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.

R value, in the Raman spectrum obtained in the Raman spectrometry, to define the intensity Ig of the maximum peak in the vicinity of 1580 cm ^-1, the intensity ratio of the intensity Id of the maximum peak around 1360 cm ^-1 and (Id / Ig). Here, the peak appearing near 1580 cm ^-1, generally a peak identified as corresponding to the graphite crystal structure, means a peak observed for example ^{1530cm -1 ~1630cm} -1. Further a peak appearing near 1360 cm ^-1, generally a peak identified as corresponding to the amorphous structure of the carbon, means a peak observed for example ^{1300cm -1 ~1400cm} -1.

In the present disclosure, the Raman spectroscopy is performed by using a laser Raman spectrophotometer (model number: NRS-1000, Nippon Spectroscopy Co., Ltd.) on a sample plate in which the negative electrode material for a lithium ion secondary battery is set flat. Is irradiated and the measurement is performed. The measurement conditions are as follows.
Wavelength of argon laser light: 532 nm
Wavenumber resolution: 2.56 cm ^-1
Measuring range: 1180 cm ^{-1 to} 1730 ^{cm -1}
Peak Research: Background Removal

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

The volume average particle size (D ₅₀ ) of the negative electrode material for lithium ion secondary batteries is 50% cumulative 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 size when it becomes. The volume average particle size (D ₅₀ ) is determined by, for example, a laser diffraction type particle size distribution measuring device (for example, Shimadzu Corporation, SALD-) in which a negative electrode material for a lithium ion secondary battery is dispersed in purified water containing a surfactant. It can be measured at 3000J).

BET specific surface area of the negative electrode material for a lithium ion secondary battery ^is preferably 0.5m ² / g~10m 2 / ^g, more preferably ^{1m 2 / g~8m 2 / g,} 2m 2 / It is more preferably g to 6 m ^{2 / g.} When the BET specific surface area is within the above range, a good balance between input / output characteristics and initial efficiency tends to be obtained.

Since the negative electrode material for a lithium ion secondary battery of the present disclosure has excellent high temperature storage characteristics, it can be 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 a large-capacity lithium ion secondary battery used. In particular, it is suitable as a negative electrode material for a lithium ion secondary battery used in EVs, PHEVs, HEVs and the like, which are required to be applied in various environments.

<Negative electrode for lithium-ion secondary battery>
The negative electrode for a lithium ion secondary battery of the present disclosure includes a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery of the present disclosure, and a current collector. The negative electrode for a lithium ion secondary battery may include a negative electrode material layer and a current collector including the negative electrode material for a lithium ion secondary battery of the present disclosure, and other components as necessary.

For the negative electrode for a lithium ion secondary battery, for example, a negative electrode material for a lithium ion secondary battery and a binder are kneaded together with a solvent to prepare a slurry negative negative material composition for a lithium ion secondary battery, and the current is collected. It can be manufactured by applying it on the body to form a negative electrode material layer, or the negative electrode material composition for a lithium ion secondary battery is formed into a sheet-like or pellet-like shape and integrated with the current collector. It can be made by. Kneading can be performed using a disperser such as a stirrer, a ball mill, a super sand mill, or a pressure kneader.

The binder used for preparing the negative electrode material composition for a lithium ion secondary battery is not particularly limited. Examples of the binder 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. Examples thereof include polymer compounds having high ionic conductivity such as acrylonitrile and polymethacryliconitrile. When the negative electrode material composition for a lithium ion secondary battery contains a binder, the content of the binder is not particularly limited. For example, the amount may be 0.5 parts by mass to 20 parts by mass with respect to 100 parts by mass in total of the negative electrode material for the lithium ion secondary battery and the binder.

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

The negative electrode material composition for a lithium ion secondary battery may contain a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as carbon black, graphite, and acetylene black, oxides exhibiting conductivity, and inorganic compounds such as nitrides exhibiting conductivity. When the negative electrode material composition for a lithium ion secondary battery 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 a lithium ion secondary battery.

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, a porous material such as porous metal (foamed metal), carbon paper, or the like can also be used as a current collector.

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 the metal mask printing method, electrostatic coating method, dip coating method, and spray coating method are not particularly limited. A known method such as a method, a roll coating method, a doctor blade method, a comma coating method, a gravure coating method, or a screen printing method can be adopted. After the negative electrode material composition for a lithium ion secondary battery is applied to the current collector, the solvent contained in the negative electrode material composition for a lithium ion secondary battery 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 rolled. The rolling process 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 formed in the shape of a sheet, pellet or the like is integrated with the current collector to form the negative electrode material layer, the method of integration is not particularly limited. For example, it can be performed by a roll, a flat plate press, or a combination of these means. The pressure at which 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 ^{1.1g / cm 3 ~1.8g / cm 3} , more preferably from ^{1.2g / cm 3 ~1.7g / cm 3} , 1.3g / cm 3 ~1. It is more preferably 6 g / cm ^3. By setting the negative electrode density to 1.1 g / cm ³ or more, the increase in electrical resistance tends to be suppressed and the capacity tends to increase, ^{and by setting it to 1.8 g / cm 3} or less, the input / output characteristics and cycle characteristics The decline tends to be suppressed.

<Lithium-ion secondary battery>
The 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.

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

The positive electrode material used for forming the positive electrode material layer is not particularly limited. Examples of the positive electrode material include metal compounds (metal oxides, metal sulfides, etc.) capable of doping or intercalating lithium ions, conductive polymer materials, and the like. More specifically, the lithium cobaltate (LiCoO _2), lithium nickelate (LiNiO _2), lithium manganate (LiMnO _2), these mixed oxide _{(LiCo x Ni y Mn z O} 2, x + y + z = 1), 'mixed oxide containing _{(LiCo a Ni b Mn c M} ' added element _{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, V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Cr ₃ Examples thereof include 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 one kind alone or two or more kinds.

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.
Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF _{6 , LiBF 4} , LiSO ₃ CF _{3 and the} like. The lithium salt may be used alone or in combination of two or more.
Examples of the non-aqueous solvent include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propanesulton, 3-methylsulfolane, and 2,4-dimethylsulfolane. 3-Methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, butylmethyl carbonate, ethylpropyl carbonate, butylethyl carbonate, dipropyl carbonate, 1, Examples thereof include 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrachloride, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethylphosphate ester, triethylphosphate ester 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 and the negative electrode and the separator arranged between the positive electrode and the negative electrode may be spirally wound or laminated as a flat plate.

The separator is not particularly limited, and for example, a non-woven fabric made of resin, a cloth, a micropore film, or a combination thereof can be used. Examples of the resin include those containing polyolefins such as polyethylene and polypropylene as main components. Due to the structure of the lithium ion secondary battery, if the positive electrode and the negative electrode do not come into direct contact with each other, the separator may not be used.

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

Since the lithium ion secondary battery of the present disclosure is excellent in 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 are required to be charged and discharged with a large current in order to improve acceleration performance and brake regeneration performance. It is suitable as a lithium ion secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, 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 substance A is placed in an alumina crucible having a volume of 2.25 L and allowed to stand in an air atmosphere at a constant temperature of 500 ° C. for 3 hours. did.
100 parts by mass of the obtained activated carbonaceous substance 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 carbonic substance B are powdered. Mixing gave a mixture. Next, the mixture was heat-treated to prepare a fired product in which the carbonaceous substance B was attached to the surface of the activated carbonaceous substance 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 the temperature at 1000 ° C. for 1 hour. The calcined product on which the carbonaceous substance B adheres to the surface of the activated carbonaceous substance A is crushed by a cutter mill, sieved by a 300 mesh sieve, and the portion under the sieve is used as a negative electrode material for a lithium ion secondary battery (negative electrode). Material).

By the method shown below, the BET specific surface area of the carbon material A, a BET specific surface area of the activated carbon material A, the measurement of the volume average particle diameter (D ₅₀₎ and a BET specific surface area of the negative electrode material of the negative electrode material was performed. Further, based on the BET specific surface area of the carbonaceous substance A and the BET specific surface area of the activated carbonaceous substance A, the rate of increase in the BET specific surface area of the activated carbonaceous substance A with respect to the carbonic substance A [((activated carbonaceousness). 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. The results are shown in Table 1.

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

[Measurement of volume average particle diameter (D _50)]
A dispersion in which the sample was dispersed in purified water together with a surfactant was placed in a sample water tank of a laser diffraction type particle size distribution measuring device (SALD-3000J, Shimadzu Corporation). Next, the dispersion was circulated by a pump while applying ultrasonic waves, and the volume cumulative 50% particle size of the obtained particle size distribution was taken as the volume average particle size (D ₅₀ ).

(2) Preparation of Lithium Ion Secondary Battery An aqueous solution of CMC (carboxymethyl cellulose, Dai-ichi Kogyo Seiyaku Co., Ltd., Cellogen WS-C) (CMC concentration: 2% by mass) was added to 98 parts by mass of the negative electrode material as a thickener. , CMC was added so that the solid content was 1 part by mass, and kneading was performed for 10 minutes. Next, purified water was added in several portions so that the total solid content concentration of the negative electrode material and the CMC was 45% by mass to 60% by mass, and kneading was performed for 10 minutes. Subsequently, an aqueous dispersion (SBR concentration: 40% by mass) of SBR (styrene-butadiene copolymer, BM400-B, ZEON CORPORATION) was used as a binder so that the solid content of SBR was 1 part by mass. In addition, the mixture was 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. Then, the negative electrode density was adjusted to 1.5 g / cm ^{3 by hand pressing.} The electrolytic copper foil on which the negative electrode material layer was formed was punched into a disk shape having 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-type battery container in this order, and an electrolytic solution was injected to prepare a coin-type lithium-ion secondary battery. The electrolytic solution is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (volume ratio of EC and EMC is 3: 7) in which LiPF ₆ is dissolved at a concentration of 1.0 mol / L. It was used. As the positive electrode, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used. It was designed so that the initial negative electrode capacity / initial positive electrode capacity = 1.2.
As the separator, a polyethylene micropore membrane having a thickness of 20 μm was used. The prepared lithium ion secondary battery was CC-charged to 4.2 V with a current value equivalent to 0.2 CA, and then CV-charged to 0.02 CA. After that, it was paused for 30 minutes, discharged to 2.7 V with a current value equivalent to 0.2 CA, and paused for 30 minutes. This series of steps was set as one cycle, and this was repeated for three cycles to initialize. Initial efficiency, input characteristics, output characteristics, and high-temperature storage characteristics were evaluated by the following methods using an initialized lithium-ion secondary battery. The results obtained are shown in Table 1.

[Evaluation of initial efficiency]
(1) Charging was performed to 0 V (vs. Li / Li ⁺ ) with a constant current of 0.2 CA, and then constant voltage charging was performed at 0 V until the current value reached 0.02 CA. The capacity at this time was taken as the initial charge capacity.
(2) After a rest time of 30 minutes, discharge was performed to ^{1.5 V (vs. Li / Li +) with a constant current of 0.2 CA.} The capacity at this time was taken as the initial discharge capacity.
(3) From the charge / discharge capacities obtained in (1) and (2) above, the initial efficiency was obtained using the following (Equation 1).
Initial efficiency (%) = (Initial discharge capacity (mAh) / Initial charge capacity (mAh)) × 100 ... (Equation 1)

[Evaluation of output characteristics]
(1) Charging was performed to 0 V (vs. Li / Li ⁺ ) with a constant current of 0.2 CA, and then constant voltage charging was performed at 0 V until the current value reached 0.02 CA.
(2) After a rest time of 30 minutes, the battery was discharged to ^{1.5 V (vs. Li / Li +) with a constant current of 0.2 CA.}
(3) (1) and (2) were performed again, and the discharge capacity at this time was set to "discharge capacity 1" (mAh).
(4) After a pause of 30 minutes, ^{charging was performed to 0 V (vs. Li / Li +} ) with a constant current of 0.2 CA, and then constant voltage charging was performed at 0 V until the current value reached 0.02 CA.
(5) After a pause time of 30 minutes, the battery ^{was discharged to 1.5 V (vs. Li / Li +} ) with a constant current of 3CA, and the discharge capacity at this time was set to "discharge capacity 2" (mAh).
(6) From the discharge capacities obtained in (3) and (5), the output characteristics were obtained using the following (Equation 2).
Output characteristics (%) = (discharge capacity 2 (mAh) / discharge capacity 1 (mAh)) × 100 ... (Equation 2)

[Evaluation of input characteristics]
(1) Charging was performed to 4.2 V with a constant current of 0.2 CA, and then constant voltage charging was performed with 4.2 V until the current value reached 0.02 CA. The charging capacity at this time was set to "charging capacity 1" (mAh).
(2) After a rest time of 30 minutes, the battery was discharged to 2.7 V with a constant current of 0.2 CA.
(3) After a 30-minute rest period, the battery was charged to 4.2 V with a constant current of 3CA. The charging capacity at this time was set to "charging capacity 2" (mAh).
(4) From the discharge capacities obtained in (1) and (3), the input characteristics were obtained using the following (Equation 3).
Input characteristics (%) = (Charging capacity 2 (mAh) / Charging capacity 1 (mAh)) × 100 ... (Equation 3)

[Evaluation of high temperature storage characteristics]
(1) Charging was performed to 0 V (vs. Li ^/ Li +) with a constant current of 0.2 CA, and then constant voltage charging was performed at 0 V until the current value reached 0.02 CA.
(2) After a rest time of 30 minutes, the battery was discharged to ^{1.5 V (vs. Li / Li +) with a constant current of 0.2 CA.}
(3) After a rest time of 30 minutes, the battery was charged to ^{0 V (vs. Li / Li +) with 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) The battery was discharged to 1.5 V (vs. Li / Li ^{+) with 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), the high temperature storage characteristics were determined using the following (Equation 4).
High temperature storage characteristic (%) = (discharge capacity (mAh) / charge capacity (mAh)) × 100 ... (Equation 4)

<Example 2>
The evaluation was carried out in the same manner as in Example 1 except that the heat treatment temperature (activation treatment temperature) of the carbonaceous substance A was set to 300 ° C. The results obtained are shown in Table 1.

<Example 3>
The evaluation was carried out in the same manner as in Example 1 except that the heat treatment temperature (activation treatment temperature) of the carbonaceous substance A was set to 400 ° C. The results obtained are shown in Table 1.

<Example 4>
The evaluation was carried out in the same manner as in Example 1 except that the heat treatment temperature (activation treatment temperature) of the carbonaceous substance A was set to 600 ° C. The results obtained are shown in Table 1.

<Example 5>
The evaluation was carried out in the same manner as in Example 1 except that the treatment atmosphere of the carbonaceous substance A was set to CO ₂ and the treatment temperature (activation treatment temperature) was set to 900 ° C. The results obtained are shown in Table 1.

<Example 6>
The evaluation was carried out in the same manner as in Example 1 except that spherical natural graphite (volume average particle diameter: 16 μm) was used as the carbonaceous substance A. The results obtained are shown in Table 1.

<Example 7>
The evaluation was carried out in the same manner as in Example 1 except that spherical natural graphite (volume average particle diameter: 20 μm) was used as the carbonaceous substance A. The results obtained are shown in Table 1.

<Example 8>
50 parts by mass of coke powder having 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 (circularity 0.92) having an average particle size of 20 μm are mixed and 100 ° C. The mixture was stirred for 1 hour to obtain a mixture. Next, this mixture was pulverized to an average particle diameter of 18 μm, and the obtained pulverized powder was placed in a mold and molded into a rectangular parallelepiped. The obtained rectangular parallelepiped was heat-treated at 1000 ° C. in a nitrogen atmosphere and then calcined at 2800 ° C. to graphitize the graphitizable components. The obtained graphite compact was pulverized to an average particle diameter of 18 μm to prepare graphite particles. When the obtained graphite particles were observed by SEM, a plurality of flat particles were contained, and graphite particles were aggregated or bonded so that the orientation planes (main planes) were non-parallel. 100 g of the obtained graphite particles were placed in an alumina crucible having a volume of 2.25 L, and allowed to stand in an air atmosphere at a constant temperature of 500 ° C. for 3 hours. The BET specific surface area of the obtained carbonaceous substance A (activated carbonaceous substance A) was measured.
A powder mixture of 100 parts by mass of activated carbonaceous substance A and 2 parts by mass of coal tar pitch (softening point: 98 ° C., residual carbon content: 50% by mass) as a precursor of carbonic substance B is mixed. A mixture was obtained. Next, the mixture was heat-treated to prepare a fired product in which the carbonaceous substance B was attached to the surface of the activated carbonaceous substance 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 the temperature at 1000 ° C. for 1 hour. The calcined product on which the carbonaceous substance B adheres to the surface of the activated carbonaceous substance A is crushed by a cutter mill, sieved by a 300 mesh sieve, and the portion under the sieve is used as a negative electrode material for a lithium ion secondary battery (negative electrode). Material).
The evaluation was carried out in the same manner as in Example 1 using the obtained negative electrode material. The results obtained are shown in Table 1.

<Example 9>
40 parts by mass of coke powder having an average particle size of 8 μm, 25 parts by mass of tar pitch, 5 parts by mass of silicon carbide having 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, it was calcined at 2800 ° C. in a nitrogen atmosphere and then pulverized to prepare graphite particles having an average particle size of 20 μm. When the obtained graphite particles were observed by SEM, a plurality of flat particles were contained, and graphite particles were aggregated or bonded so that the orientation planes (main planes) were non-parallel. 100 g of the obtained graphite particles were placed in an alumina crucible having a volume of 2.25 L, and allowed to stand in an air atmosphere at a constant temperature of 500 ° C. for 3 hours. The BET specific surface area of the obtained carbonaceous substance A (activated carbonaceous substance A) was measured.
Using the obtained activated carbonaceous substance A, a negative electrode material (negative electrode material) for a lithium ion secondary battery was obtained in the same manner as in Example 8.
The evaluation was carried out in the same manner as in Example 1 using the obtained negative electrode material. The results obtained are shown in Table 1.

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

<Comparative Example 1>
The evaluation was carried out in the same manner as in Example 1 except that the carbonaceous substance A was not heat-treated (activated). The results obtained are shown in Table 1.

<Comparative Example 2>
The evaluation was carried out in the same manner as in Example 1 except that the carbonaceous substance A was heat-treated in a nitrogen atmosphere. The results obtained are shown in Table 1.

<Comparative Example 3>
The evaluation was carried out in the same manner as in Example 1 except that the carbonaceous substance A was heat-treated at 200 ° C. The results obtained are shown in Table 1.

<Comparative Example 4>
The evaluation was carried out in the same manner as in Example 1 except that the carbonaceous substance A was heat-treated at 800 ° C. The results obtained are shown in Table 1.

As shown in the results of Table 1, the lithium ion secondary battery manufactured by using the negative electrode material of the example has the input characteristics, as compared with the lithium ion secondary battery manufactured by using the negative electrode material of the comparative example. It can be seen that any of the items of output characteristics, high temperature storage characteristics and initial efficiency is excellent, and the other items show the same characteristics as the comparative example.

The negative electrode materials of Examples 1, 6 to 8 and Comparative Examples 1 and 4 were heat-treated 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 above method. The ratio [(2) / (1)] of the BET specific surface area (2) after the heat treatment X to the BET specific surface area (1) before the heat treatment X was calculated. The results are shown in Table 2.

Claims (4)

A step of preparing the activated carbonaceous substance A which has been treated to increase the BET specific surface area by 2% to 50% with respect to the carbonaceous substance A, and
A step of mixing the activated carbonaceous substance A and a carbonic substance precursor that is a source of the carbonic substance B different from the carbonic substance A to obtain a mixture.
The step of heat-treating the mixture to obtain a fired product, and
Have,
The carbonaceous substance A is a spherical natural graphite or graphite particles in which a plurality of flat particles are aggregated or bonded so that the orientation planes are non-parallel. Manufacture of a negative electrode material for a lithium ion secondary battery. Method. Wherein the step of obtaining a calcined product, the production method of the negative electrode material for a lithium ion secondary battery according to BET specific surface area of the fired product to claim 1 is a process to 0.5m 2 ^/ g~10m 2 ^{/ g.} The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the heat treatment is performed under a temperature condition of 700 ° C to 1500 ° C. Crystallinity of the carbon material B is, the activated carbon material A manufacturing how the negative electrode material for a lithium ion secondary battery according to any one of lower claims 1 to 3 than the crystalline ..