JP5821932B2 - Graphite negative electrode material, method for producing the same, and negative electrode for lithium secondary battery and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode material containing graphite, a method for producing the same, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same. Specifically, the present invention relates to a graphite negative electrode material having a high tap density and a small amount of fine powder, a production method thereof, a negative electrode for a lithium secondary battery, and a lithium secondary battery using the graphite negative electrode material.

  In recent years, with the miniaturization of electronic devices, high-capacity secondary batteries are required. In particular, non-aqueous solvent type lithium secondary batteries having higher energy density are attracting attention as compared with nickel / cadmium and nickel / hydrogen batteries. Conventionally, the increase in capacity of the battery has been widely studied, but the performance required for the battery has also been advanced, and further increase in capacity is desired.

  Metals, graphite, and the like have been studied as negative electrode materials for lithium secondary batteries. In recent years, graphite has been widely used in terms of high capacity, high efficiency, and excellent cycle characteristics. Among the demands for higher capacity, particulate graphite having a high tap density is excellent in that the packing density of the active material can be improved. And it is calculated | required to establish the method of manufacturing the negative electrode material containing particulate graphite simply and stably.

  Under these circumstances, Patent Document 1 discloses that bulk mesophase carbon obtained by heat-treating tar or pitch having a free carbon content of 0.3% by weight or less at 400 to 600 ° C. is subjected to high-speed pulverization and / or shear pulverization. It is described that a graphite negative electrode material having a high anisotropy and a discharge capacity of 350 mAh / g or more can be obtained by pulverizing, followed by firing and graphitization.

Further, Patent Document 2 discloses that a bulk mesophase obtained by heat-treating tar or pitch having a free carbon content of 1 wt% or less at 400 to 900 ° C. is pulverized, fired, and graphitized to obtain an interlayer distance d ₀₀₂ . It is described that a graphite negative electrode material having 3360 nm or less, a tap density of 1.2 g / cm ³ or more, and a discharge capacity of 348 to 360 mAh / g can be obtained.

JP 2001-316105 A JP 2002-47006 A

  In increasing the capacity of lithium secondary batteries, not only the packing density of the active material is improved, but excessive reaction with the electrolyte is suppressed, and the amount of fine powder is reduced in order to reduce the irreversible capacity. In order to suppress particle breakage due to rolling, it is important to reduce the average total number of particles contained per gram of graphite negative electrode material.

  However, as described in Patent Documents 1 and 2, the conventional particulate graphite negative electrode material has a high speed when producing particulate graphite having a high tap density in order to improve the packing density of the active material. Since graphite was pulverized by pulverization or the like and then classified to obtain a graphite negative electrode material, there was a problem that a large amount of fine powder was generated by pulverization and classification. Further, the average total number of particles contained per 1 g of the graphite negative electrode material is increased, and this graphite negative electrode material has a problem that the particulate graphite is easily broken in the process of rolling the electrode to increase the density. there were. Furthermore, since the production of these graphite negative electrode materials having a high tap density requires many steps, there is a problem that the cost is high.

  The present invention has been made in view of the above problems. That is, the present invention relates to a graphite negative electrode material for a lithium secondary battery having a high tap density, a small average total number of particles contained per gram and a small amount of fine powder, a method for producing the same, and a lithium secondary battery using the same. An object of the present invention is to provide a negative electrode and a lithium secondary battery.

  The inventors of the present invention have intensively studied to solve the above problems. As a result, the inventors have found a method capable of stably and efficiently producing a graphite negative electrode material having a high tap density, a small average total number of particles contained per gram, and a small amount of fine powder, and completed the present invention.

That is, the present invention uses a pitch raw material having a quinoline insoluble content of 20% by mass or less as a starting material, heat-treating the starting material, spheroidizing the heat-treated material, and spheroidizing material. It is a manufacturing method of the graphite negative electrode material for lithium secondary batteries including the process of baking, and the process of graphitizing the material which finished baking depending on the case.
Moreover, this invention is the graphite negative electrode material for lithium secondary batteries manufactured with the said manufacturing method.
Moreover, this invention is a lithium secondary battery containing the said negative electrode material for lithium secondary batteries.

According to the present invention, a graphite negative electrode material having a high tap density, a small average total number of particles contained per gram, and a small amount of fine powder can be obtained, a high packing density can be achieved, and an irreversible capacity. Therefore, it is possible to realize an excellent lithium secondary battery with a small amount.
In addition, according to the production method of the present invention, the graphite negative electrode material can be produced efficiently and stably, which is very useful industrially.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description, and modifications of the present invention can be implemented without departing from the gist of the present invention.

[1. Production method]
The method for producing a graphite negative electrode material of the present invention uses a pitch raw material having a quinoline insoluble content of 20% by mass or less as a starting material, heat-treats the starting material, spheroidizes the heat-treated material, and spheroidizes. A step of firing the material and optionally a step of graphitizing the material after the firing.

According to the production method of the present invention, the pitch raw material in which the quinoline insoluble content is reduced to 20% by mass or less is selected as a starting material, and this is calcined, and optionally the material after calcining is graphitized Prior to spheroidization, a graphite negative electrode material having a high tap density, a small average total number of particles contained per gram, and a small amount of fine powder can be obtained.
Hereafter, each process of the manufacturing method of this invention is each demonstrated in detail.

(Selection of starting material)
In the present specification, the pitch raw material means a pitch and its equivalent, and means a material that can be graphitized by performing an appropriate treatment.
Examples of the pitch raw material include tar, heavy oil, and pitch.
Specific examples of tar include coal tar and petroleum tar. Specific examples of the heavy oil include catalytic cracked oil, pyrolysis oil, atmospheric residual oil, and vacuum residual oil of petroleum heavy oil. Specific examples of the pitch include coal tar pitch, petroleum pitch, and synthetic pitch. Among these, coal tar pitch containing a large amount of aromatic hydrocarbon is preferable. Any one of these pitch raw materials may be used alone, or two or more thereof may be used in any combination at an arbitrary ratio.

The starting material is the pitch raw material described above, and the quinoline-insoluble content contained in the pitch raw material is 0.000 to 20.000% by mass, preferably 0.001 to 10.000% by mass, and more preferably Is in the range of 0.002 to 7.000% by mass.
The quinoline insoluble matter is submicron unit carbon particles or ultrafine sludge contained in a minute amount in pitch raw materials such as coal tar, and if this is too much, the crystallinity improvement in the graphitization process is significantly inhibited. The discharge capacity after graphitization is significantly reduced. In addition, as a measuring method of a quinoline insoluble matter, the method prescribed | regulated to JISK2425, for example can be used.
As long as the effects of the present invention are not hindered, various thermosetting resins, thermoplastic resins, and the like may be used in combination in addition to the pitch raw material described above as a starting material.

(Heat treatment)
First, heat treatment is performed using the selected pitch raw material as a starting material, and a bulk mesophase (heat treated graphite crystal precursor, hereinafter referred to as “heat treated graphite crystal precursor”), which is a precursor of graphite crystal, is obtained. When this heat treated graphite crystal precursor is pulverized and then reheated such as by firing, a part or all of it is melted. Can be controlled. The volatile component contained in the heat-treated graphite crystal precursor usually includes hydrogen, benzene, naphthalene, anthracene, pyrene and the like.

  The temperature condition during the heat treatment is preferably 400 to 600 ° C, more preferably 450 to 510 ° C. When the temperature of the heat treatment is less than 400 ° C., the amount of volatile components increases, so that it becomes difficult to pulverize the heat-treated graphite crystal precursor safely in the air. On the other hand, when the temperature exceeds 600 ° C., the graphite crystals are excessively developed. Even when the spheroidization treatment is performed later, it is difficult to obtain a graphite negative electrode material having a high tap density.

Further, the heat treatment time is preferably 1 to 48 hours, more preferably 10 to 24 hours. If the heat treatment time is less than 1 hour, it is inappropriate because it is a non-uniform heat treated graphite crystal precursor, while if it exceeds 48 hours, the productivity is not good, the treatment cost is high, and the production is difficult.
Note that the heat treatment may be performed in multiple steps as long as the temperature and the accumulated time of the heat treatment are within the above ranges.

The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen gas or in a volatile atmosphere generated from pitch raw materials.
The apparatus used for the heat treatment is not particularly limited. For example, a shuttle furnace, a tunnel furnace, an electric furnace, an autoclave or other reaction tank, a coker (heat treatment tank for coke production), or the like can be used. During the heat treatment, stirring may be performed in a furnace or the like as necessary.

  The volatile content (VM) of the heat treated graphite crystal precursor obtained by the heat treatment is preferably 4 to 30% by mass, more preferably 5 to 20% by mass. When the volatile content is less than 4% by mass, the particles are crushed into needles during pulverization and the tap density is likely to decrease. When the volatile content exceeds 30% by mass, the volatile content is high, so the pulverization can be safely performed in the atmosphere. It is difficult to do.

(Pulverization)
Next, the heat-treated graphite crystal precursor obtained by heat treatment is pulverized. This is because the heat treatment graphite crystal precursor crystals arranged in the same direction in large units by heat treatment are refined.
Note that normal pulverization refers to an operation of applying force to a substance to reduce its size and adjusting the particle size, particle size distribution, etc. of the substance.

In the pulverization, the particle size of the heat treated graphite crystal precursor after pulverization is preferably 1 to 2000 μm, more preferably 5 to 1000 μm, preferably 5 to 500 μm, more preferably 5 to 200 μm, and particularly preferably 5 to 50 μm. To do. When the particle size is less than 1 μm, the surface of the graphite crystal precursor that has been heat-treated during or after pulverization is oxidized by contact with air, and the improvement in crystallinity during the graphitization process is hindered, resulting in a decrease in discharge capacity after graphitization. May be invited. On the other hand, when the particle size exceeds 5000 μm, the effect of refining by pulverization is reduced and the crystal is easily oriented, the active material orientation ratio of the electrode using the graphite material is lowered, and it is difficult to suppress the electrode expansion during battery charging. .
The particle size refers to, for example, a 50% particle size (d ₅₀ ) obtained from a volume-based particle size distribution by laser diffraction / scattering particle size distribution measurement.

  The apparatus used for pulverization is not particularly limited. Examples of the coarse pulverizer include a jaw crusher, an impact crusher, and a cone crusher. Examples of the intermediate pulverizer include a roll crusher and a hammer mill. Examples of the machine include a turbo mill, a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

(Spheroidization processing)
The heat treated graphite crystal precursor after pulverization is spheroidized. Thereby, the tap density of the graphite particle after baking improves.
In the present specification, the spheroidizing process is a process intentionally performed for the purpose of spheroidizing particles, unlike the pulverizing process for controlling the particle size. Specifically, the spheronization treatment is a process in which mechanical action such as compression, friction, shearing force, etc. including impact of particles as the main component is repeatedly applied to the particles. By performing, it means that the graphite negative electrode material is treated so that at least the average circularity and the average total number of particles per gram have specific values.

  As an apparatus for performing the spheroidizing treatment, for example, an apparatus including a high-speed rotating rotor in which a large number of blades are installed inside a casing can be used. Examples of such an apparatus include hybridization (manufactured by Nara Machinery Co., Ltd.) and the like. Is mentioned. Using this equipment, mechanical treatments such as impact compression, friction, and shear are applied to the ground graphite crystal precursor after pulverization, surface treatment is performed while pulverizing, and classification is performed using an airflow classifier or the like. This operation of repeating a series of operations to be performed an arbitrary number of times is an example of a spheronization process, and the apparatus and operation are not limited to this, and the spheronization process can be performed.

(Baking)
Next, the spheroidized heat-treated graphite crystal precursor is fired. In the present invention, the calcined heat-treated graphite crystal precursor is referred to as a graphite crystal precursor.
Firing is performed in order to completely remove the volatile components of the heat-treated graphite crystal precursor.
The temperature at the time of baking is preferably 800 to 2000 ° C, more preferably 1000 to 1500 ° C. When the temperature is lower than 800 ° C., it is difficult to completely remove volatile components. On the other hand, if the temperature exceeds 2000 ° C., the firing equipment may be expensive.
The holding time for maintaining the temperature in the above range when firing is not particularly limited, but is 30 minutes or longer and 72 hours or shorter.

Firing is performed in an inert gas atmosphere such as nitrogen gas or in a non-oxidizing atmosphere with a gas generated from a heat-treated graphite crystal precursor. In addition, when a graphitization step is necessary, it is possible to directly graphitize without incorporating a firing step in order to simplify the manufacturing process.
Although there is no restriction | limiting in particular as an apparatus used for baking, For example, a shuttle furnace, a tunnel furnace, an electric furnace, a lead hammer furnace, a rotary kiln etc. can be used.

(Graphitization)
If necessary, the calcined graphite crystal precursor may be graphitized next.
Graphitization is performed to improve the crystallinity of the graphite negative electrode material in order to increase the discharge capacity in battery evaluation.
Therefore, graphitization may be performed in accordance with the purpose of using the material, and the graphite negative electrode material of the present invention can be obtained only by firing.
The temperature during graphitization is preferably 2000 to 3200 ° C, more preferably 3000 to 3100 ° C. When the graphitization temperature exceeds 3200 ° C., the reversible capacity of the battery may be reduced, and it is difficult to make a high capacity battery. If the graphitization temperature is less than 2000 ° C., the amount of graphite sublimation tends to increase.
The holding time is not particularly limited when graphitization is performed, but it is usually longer than 1 minute and not longer than 72 hours.

Graphitization is performed in an inert gas atmosphere such as argon gas, or in a non-oxidizing atmosphere by a gas generated from a calcined graphite crystal precursor.
Although there is no restriction | limiting in particular as an apparatus used for graphitization, For example, a resistance heating furnace, an induction heating furnace etc. are mentioned as a direct current furnace, an Atchison furnace, and an indirect electricity supply type.

  In addition, when graphitization is performed or in the previous process, that is, the process from heat treatment to firing, a graphitization catalyst such as Si or B is incorporated into the material (pitch raw material or heat treated graphite crystal precursor), The graphitization catalyst may be brought into contact with the surface of the material.

(Other processing)
In addition, as long as the effects of the invention are not hindered, various processes such as a reclassification process can be performed in addition to the above processes. The reclassification treatment is for removing coarse powder and fine powder so that the particle size after the graphitization treatment after firing is the target particle size.
There are no particular restrictions on the equipment used for the classification process. For example, in the case of dry sieving: rotary sieving, oscillating sieving, rotating sieving, vibrating sieving, dry airflow classifying: gravity classifier, Inertial force classifiers, centrifugal classifiers (classifiers, cyclones, etc.), wet sieving, mechanical wet classifiers, hydraulic classifiers, sedimentation classifiers, centrifugal wet classifiers and the like can be used.

  In the reclassification treatment, when graphitization is performed after firing, the reclassification treatment may be performed after firing, followed by graphitization, or the reclassification treatment may be performed after graphitization after firing. It is possible to omit the reclassification process.

According to the method for producing a graphite negative electrode material of the present invention described above, a graphite negative electrode material having a high tap density, a small average total number per 1 g, and a small amount of fine powder can be produced.
When used as a negative electrode material for a lithium secondary battery, the graphite negative electrode material produced by the method of the present invention realizes an excellent lithium secondary battery with a high packing density and a low irreversible capacity. be able to.
Further, according to the production method of the present invention, a graphite negative electrode material having specific physical properties can be produced efficiently and stably.

[2. Graphite negative electrode material for lithium secondary battery]
The graphite negative electrode material obtained by the above production method satisfies the following physical properties by performing a spheronization treatment.
<Average circularity>
The graphite negative electrode material of the present invention has an average circularity of preferably 0.90 to 0.98, more preferably 0.91 to 0.97.
If the average circularity is less than 0.90, the gap between the particles becomes small, and the load characteristics may be deteriorated. On the other hand, when the average circularity exceeds 0.98, the spheroidizing treatment for repeatedly applying mechanical action such as compression, friction, shearing force and the like including the interaction of particles mainly on the impact force to the particles is performed strongly or for a long time. There is a need to increase the amount of fine powder.

For the average circularity, 0.2 g of a measurement target (here, a graphite negative electrode material) was measured using a flow type particle image analyzer (for example, FPIA manufactured by Simex Industrial Co., Ltd.), polyoxyethylene (20) as a surfactant. After mixing with 50 mL of 0.2% by volume aqueous solution of sorbitan monolaurate and irradiating 28 kHz ultrasonic waves at an output of 60 W for 1 minute, the detection range is specified as 0.6 to 400 μm, and the particle size ranges from 3 to 40 μm. The average value of the circularity given by the following formula (1) measured for the particles.
Circularity = circumference of a circle having the same area as the particle projection area / perimeter of the particle projection image (1)

<Average total number of particles>
In the graphite negative electrode material of the present invention, the average total number of particles is preferably 3 × 10 ⁶ particles / g or less, more preferably 2 × 10 ⁶ particles / g or less, and further preferably 1 × 10 ⁶ particles / g or less. is there.
The average total number of particles refers to the total number of particles present in 1 g of the measurement target, which is obtained when measurement is performed on the number-based circle-equivalent diameter distribution by the flow particle image analysis described above.
When the average total number of these particles is large, in the process of rolling the electrode to increase the density, the particulate graphite negative electrode material is fragile, and when the graphite shape is broken, it tends to generate fine powder. It reacts excessively with the liquid, and the irreversible capacity tends to decrease.

<Ratio of volume-based 90% particle size and 10% particle size (d ₉₀ / d ₁₀ )>
The graphite negative electrode material of the present invention has a ratio (d ₉₀ / d ₁₀ ) of 90% particle size (d ₉₀ ) to 10% particle size (d ₁₀ ) in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement. , Preferably 1.5 to 2.8, more preferably 1.7 to 2.5.
When the ratio of d ₉₀ / d ₁₀ is increased, it indicates that the particle size distribution of the graphite negative electrode material is widened, indicating that there are a large amount of fine powder and coarse powder, especially a large amount of fine powder. _Thus, d 90 _{/ d 10} is greater than 2.8, the number of fine amount, packing density, irreversible capacity tends to decrease. On the other hand, if d ₉₀ / d ₁₀ is less than 1.5, the particle size distribution is too narrow, so that it is difficult to make electrical contact between the particulate graphite, and battery characteristics such as cycle characteristics are likely to deteriorate.
When d ₉₀ / d ₁₀ of the graphite negative electrode material is within the above range, high density packing is possible, and a negative electrode for a lithium secondary battery with a small irreversible capacity can be formed.

<Average particle size based on volume (d ₅₀ )>
The graphite negative electrode material of the present invention has a volume-based average particle diameter of preferably 5 to 60 μm, more preferably 10 to 30 μm.
In this specification, the average particle diameter means a median diameter (d ₅₀ ) in a volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.
When the volume-based average particle diameter is less than 5 μm, the tap density is small, and when the electrode is manufactured, the packing density of the active material is difficult to increase, and it is difficult to obtain a high-capacity battery. On the other hand, if it exceeds 60 μm, uneven coating tends to occur when an electrode is produced by coating.

The volume-based particle size distribution is determined by using a laser diffraction particle size distribution analyzer (for example, LA-700, manufactured by HORIBA, Ltd.), a 2% by volume aqueous solution of polyoxyethylene (20) sorbitan monolaurate as a surfactant ( About 1 ml) is mixed with the graphite negative electrode material, and a value measured using ion-exchanged water as a dispersion medium can be used. The average particle diameter (median diameter) is measured from the volume-based particle size distribution 50% particle diameter (d ₅₀ ), and the ratio (d ₉₀ /) is determined from the 90% particle diameter (d ₉₀ ) and the 10% particle diameter (d ₁₀ ). d ₁₀ ) is measured.

<Minimum particle size (d _min ), maximum particle size (d _max )>
The graphite negative electrode material of the present invention has a minimum particle size (d _min ) of preferably 3.5 μm or more, more preferably 4.0 μm or more, and a maximum particle size (d _max ) of preferably 150.0 μm. Hereinafter, it is more preferably 140.0 μm or less. If the minimum particle size (d _min ) is less than this, it means that the amount of fine powder is large, and this tends to increase the specific surface area and tends to increase the irreversible capacity. Moreover, when the maximum particle size is larger than this, it is difficult to obtain a smooth surface when producing an electrode, and it is difficult to obtain excellent battery characteristics.
The minimum particle size (d _min ) and the maximum particle size (d _max ) are, as with the volume-based average particle size, the volume-based particle size distribution by laser diffraction / scattering particle size distribution measurement using a laser diffraction particle size distribution meter. Can be measured from

<Tap density>
The graphite negative electrode material of the present invention has a tap density of preferably 0.90 to 1.60 g / cm ³ , more preferably 1.00 to 1.50 g / cm ³ . When the tap density is less than 0.90 g / cm ^3, it is difficult to improve the packing density of the active material and it is difficult to obtain a high-capacity battery. On the other hand, when it exceeds 1.60 g / cm ³ , the amount of pores in the electrode decreases, and it is difficult to obtain preferable battery characteristics.

As the tap density, a sieve having an opening of 300 μm is used, and after dropping the graphite material into a 20 cm ³ tapping cell to fill the cell, a powder density measuring instrument (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.) is used. The value obtained by performing tapping with a stroke length of 10 mm 1000 times and measuring the tapping density at that time can be used.

<Surface spacing>
The graphite negative electrode material of the present invention has a (002) plane spacing d ₀₀₂ measured by X-ray diffraction of preferably 0.3450 nm or less, more preferably 0.3410 nm or less.
When exceeding this range, that is, when the crystallinity is inferior, the discharge capacity per unit weight of the active material may be reduced when the electrode is manufactured. On the other hand, the lower limit of the surface spacing d ₀₀₂ as theoretical limit is usually 0.3354nm or more.

Further, the graphite negative electrode material of the present invention, the size Lc ₀₀₂ of the c-axis direction of crystallites measured by X-ray diffraction is preferably 10nm or more, and more preferably 20nm or more. Below this range, the discharge capacity per weight of the active material when an electrode is produced using the graphite material of the present invention may be reduced.
As the interplanar spacing d ₀₀₂ and the crystallite size Lc ₀₀₂ measured by the X-ray diffraction, values measured in accordance with the Gakushin method of the Carbon Materials Society of Japan can be used. In the Gakushin method, values of 100 nm (1000 Å) or more are not distinguished and are all described as “> 1000 (Å)”.

<Other features>
The BET specific surface area of the graphite material of the present invention is not particularly limited, but is preferably 0.2 to 10.0 m ² / g, more preferably 0.3 to 6.0 m ² / g, still more preferably 0.6 to 5 0.0 m ² / g. When the value of the BET specific surface area is less than 0.2 m ² / g, the acceptability of lithium is likely to deteriorate during charging, and lithium is likely to precipitate on the electrode surface, which may cause a safety problem. On the other hand, if it exceeds 10.0 m ² / g, the reactivity with the electrolytic solution increases, gas generation tends to increase, and a preferable battery is difficult to obtain.

  As the specific surface area measured by the BET ratio method, a specific surface area meter (for example, a fully automatic surface area measuring device manufactured by Ritsu Okura) is used, and the measurement object (here, graphite negative electrode material) is 15 minutes at 350 ° C. under nitrogen flow. After the preliminary drying, using a nitrogen helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, the value measured by the nitrogen adsorption BET 6 point method by the gas flow method is Can be used.

[3. Negative electrode]
By forming an active material layer containing the graphite negative electrode material of the present invention as an active material on a current collector, a negative electrode for a lithium secondary battery can be produced.
What is necessary is just to manufacture a negative electrode in accordance with a conventional method. For example, a method in which a binder, a thickener, a conductive material, a solvent, and the like are added to a negative electrode active material to form a slurry, which is applied to a current collector, dried, pressed and densified.
As the negative electrode active material, the graphite negative electrode material of the present invention may be used alone. In addition, a carbon material having a shape or physical property different from that of the graphite negative electrode material of the present invention may be used in combination.

[Mixture of graphite negative electrode material of the present invention and other carbon material]
The graphite negative electrode material of the present invention. (This is referred to as graphite powder (A)) can be used alone as a negative electrode material as it is. Further, two or more types of graphite negative electrode material powders (A) having different physical property values may be used in any combination at any ratio. Furthermore, this negative electrode material, that is, one or more graphite powders (A) may be mixed with another one or two or more carbon materials (B) and used as the negative electrode material.

  When the carbon material (B) is mixed with the graphite powder (A) described above, the mixing ratio of (B) with respect to the total amount of (A) and (B) is preferably 0.1 to 50.0% by mass, more preferably. Is in the range of 1.0 to 40.0 mass%. When the mixing ratio of the carbon material (B) is less than 0.1% by mass, the effect of adding (B) becomes difficult to appear. On the other hand, when it exceeds 50.0 mass%, the characteristic of graphite negative electrode material powder (A) will be impaired and the effect of this invention will become difficult to appear.

  As the carbon material (B), a material selected from natural graphite, artificial graphite, amorphous-coated graphite, resin-coated graphite, and amorphous carbon is used. Any of these materials may be used alone, or two or more of these materials may be used in any combination in any ratio.

As natural graphite, for example, highly purified flaky graphite or spheroidized graphite can be used. The volume-based average particle diameter of natural graphite is preferably in the range of 8 to 60 μm, more preferably 12 to 40 μm. The BET specific surface area of natural graphite is preferably 4.0 to 7.0 m ² / g, more preferably 4.5 to 5.5 m ² / g.

  As the artificial graphite, for example, particles obtained by combining coke powder or natural graphite with a binder, particles obtained by firing and graphitizing single graphite precursor particles in a powder state, and the like can be used.

  As amorphous-coated graphite, for example, natural graphite or artificial graphite coated with an amorphous precursor and fired, or natural graphite or artificial graphite coated with amorphous by CVD can be used.

  As the resin-coated graphite, for example, particles obtained by coating and drying a polymer material on natural graphite or artificial graphite can be used.

  As the amorphous carbon, for example, particles obtained by firing a bulk mesophase, or particles obtained by infusibilizing and firing a carbon precursor can be used.

  When the carbon material (B) is mixed with the graphite powder (A), there is no particular limitation on the selection of the carbon material (B). For example, mixing improves the cycle characteristics and improves the charge acceptance by improving the conductivity. It is possible to select a carbon material (B) that can improve the resistance, reduce the irreversible capacity, and improve the pressability according to the case.

  The apparatus used for mixing the graphite powder (A) and the carbon material (B) is not particularly limited. For example, in the case of a rotary mixer: a cylindrical mixer, a twin cylinder mixer, a double cone mixer Machine, regular cubic mixer, vertical mixer, stationary mixer: spiral mixer, ribbon mixer, Muller mixer, Helical Flight mixer, Pugmill mixer, fluidized mixer A machine or the like can be used.

The density of the negative electrode layer is preferably preferably 1.30 g / cm ³ or more, more preferably 1.40 g / cm ³ or more, more preferably when the 1.60 g / cm ³ or more, than the capacity of the battery increases. Note that the negative electrode layer refers to a layer made of an active material, a binder, a conductive agent, and the like on the current collector, and the density refers to the density at the time of assembling the battery.

  As the binder, any material can be used as long as it is a material that is stable with respect to the solvent and the electrolyte used in manufacturing the electrode. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer. In addition, these may be used individually by 1 type and may be used combining 2 or more types arbitrarily by arbitrary ratios.

  As the thickener, known ones can be arbitrarily selected and used, and examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. In addition, these may be used individually by 1 type and may be used combining 2 or more types arbitrarily by arbitrary ratios.

  Examples of the conductive material include a metal material such as copper or nickel; a carbon material such as graphite or carbon black. In addition, these may be used individually by 1 type and may be used combining 2 or more types arbitrarily by arbitrary ratios.

  Examples of the material of the negative electrode current collector include copper, nickel, and stainless steel. Among these, a copper foil is preferable from the viewpoint of easy processing into a thin film and cost. In addition, these may be used individually by 1 type and may be used combining 2 or more types arbitrarily by arbitrary ratios.

[4. battery]
The graphite negative electrode material of the present invention is useful as a material for battery electrodes. In particular, in a non-aqueous secondary battery such as a positive and negative electrodes capable of occluding and releasing lithium ions, and a lithium secondary battery equipped with an electrolyte, the use of the graphite material of the present invention described above as the negative electrode is extremely Useful. For example, a non-aqueous system comprising a graphite negative electrode material manufactured according to the above method as a negative electrode, and a combination of a metal chalcogenide-based positive electrode for a lithium secondary battery that is normally used and an organic electrolyte mainly composed of a carbonate-based solvent. Secondary batteries have large capacity, small irreversible capacity observed in the initial cycle, high rapid charge / discharge capacity, excellent cycle characteristics, high battery storage and reliability when left at high temperatures, and high efficiency It has excellent discharge characteristics and discharge characteristics at low temperatures.

  There is no particular limitation on the selection of members necessary for the battery configuration, such as the positive electrode and the electrolytic solution constituting such a lithium secondary battery. In the following, materials of members constituting a lithium secondary battery using the graphite material of the present invention are exemplified, but usable materials are not limited to these specific examples.

Examples of the positive electrode include lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide; transition metal oxide materials such as manganese dioxide; and carbonaceous materials such as graphite fluoride. A material capable of inserting and extracting lithium can be used. Specifically, LiFeO ₂ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and their non-stoichiometric compounds, MnO ₂ , TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , P ₂ O ₅ , CrO ₃ , V ₃ O ₃ , TeO ₂ , GeO _{2 and the} like can be used. The manufacturing method in particular of a positive electrode is not restrict | limited, It can manufacture by the method similar to the manufacturing method of said electrode.

  For the positive electrode current collector, for example, it is preferable to use a valve metal or an alloy thereof that forms a passive film on the surface by anodic oxidation in an electrolytic solution. Examples of the valve metal include metals belonging to Group IIIa, IVa, Va, IIIb (Groups 3, 4, 5, 13) and alloys thereof. Specifically, Al, Ti, Zr, Hf, Nb, Ta and alloys containing these metals can be exemplified, and Al, Ti, Ta and alloys containing these metals can be preferably used. . In particular, Al and its alloys are desirable because of their light weight and high energy density.

Any electrolyte such as an electrolytic solution or a solid electrolyte can be used as the electrolyte. Here, the electrolyte refers to all ionic conductors, and both the electrolytic solution and the solid electrolyte are included in the electrolyte.
As the electrolytic solution, for example, a solution obtained by dissolving a solute in a non-aqueous solvent can be used. As the solute, an alkali metal salt, a quaternary ammonium salt, or the like can be used. Specifically, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F _It is preferable to use one or more compounds selected from the group consisting of ₉ SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ .

  Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; cyclic ester compounds such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane; crown ethers, 2- Cyclic ethers such as methyltetrahydrofuran, 1,2-dimethyltetrahydrofuran, 1,3-dioxolane, and tetrahydrofuran; chain carbonates such as diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate can be used. One type of solute and solvent may be selected and used, or two or more types may be mixed and used. Among these, the non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate.

  In addition, the non-aqueous electrolyte solution may include an organic polymer compound in the electrolyte solution, and may be a gel, rubber, or solid sheet solid electrolyte. Specific examples of organic polymer compounds include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; vinyl Insoluble matter of alcohol polymer compound; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer compound such as polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), poly (ω -Methoxyoligooxyethylene methacrylate-co-methyl methacrylate) and the like.

  The material and shape of the separator are not particularly limited. The separator is separated so that the positive electrode and the negative electrode do not come into physical contact with each other, and preferably has high ion permeability and low electrical resistance. The separator is preferably selected from materials that are stable with respect to the electrolyte and excellent in liquid retention. As a specific example, the said electrolyte solution can be impregnated using the porous sheet or nonwoven fabric which uses polyolefin, such as polyethylene and a polypropylene, as a raw material.

The method for producing a lithium secondary battery having at least an electrolytic solution, a negative electrode, and a positive electrode is not particularly limited and can be appropriately selected from commonly employed methods.
In addition to the electrolyte solution, the negative electrode, and the positive electrode, an outer can, a separator, a gasket, a sealing plate, a cell case, and the like can also be used for the lithium secondary battery as necessary.
An example of a method for producing a lithium secondary battery is to place a negative electrode on an outer can, provide an electrolyte and a separator on the outer can, and further place the positive electrode so as to face the negative electrode, and caulk it together with a gasket and a sealing plate. Can be a battery.
The shape of the battery is not particularly limited. For example, a cylinder type in which a sheet electrode and a separator are spiral, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, etc. Can do.

Next, characteristics when a negative electrode for a lithium secondary battery is formed using the graphite negative electrode material of the present invention as an active material will be described.
<Discharge capacity>
In the graphite negative electrode material of the present invention, when this is used as an active material, an active material layer is formed on a current collector, and when used as a negative electrode for a lithium secondary battery, the discharge capacity of the lithium secondary battery is 200 mAh / g. As mentioned above, Preferably it becomes 230 mAh / g or more. When the discharge capacity falls below this range, the battery capacity may be reduced. The higher the discharge capacity, the better. However, the upper limit is usually about 365 mAh / g.

Although there is no restriction | limiting in particular about the measuring method of a specific discharge capacity, It is as follows when a standard measuring method is shown.
First, a negative electrode using a graphite material is prepared. The negative electrode is produced by using a copper foil as a current collector and forming an active material layer on the current collector. The active material layer uses a mixture of graphite material and styrene butadiene rubber (SBR) as a binder resin. The amount of the binder resin is preferably 1% by mass with respect to the weight of the negative electrode. Further, it is preferable that the electrode density is ^{1.30g / cm 3 ~1.95g / cm 3} .

Evaluation of the discharge capacity is performed by preparing a bipolar coin cell using metallic lithium as a counter electrode for the prepared negative electrode and conducting a charge / discharge test thereof.
Although the electrolyte solution of a bipolar coin cell is arbitrary, for example, a mixed solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed so that the volume ratio is DEC / EC = 1/1, or A mixed solution in which ethylene carbonate and ethyl methyl carbonate (EMC) are mixed so that EMC / EC = 1/1 by volume ratio can be used.
Moreover, although the separator used for a bipolar coin cell is also arbitrary, for example, a polyethylene sheet having a thickness of 15 μm to 35 μm can be used.

A charge / discharge test was performed using the bipolar coin cell thus produced, and the discharge capacity was determined. Specifically, the battery is charged to 5 mV with respect to the lithium counter electrode at a current density of 0.2 mA / cm ² , and further charged to a current value of 0.02 mA at a constant voltage of 5 mV. After the doping, a charge / discharge cycle of discharging to 1.5 V with respect to the lithium counter electrode at a current density of 0.4 mA / cm ² was repeated three times, and the discharge value at the third cycle was defined as the discharge capacity.

In addition to the discharge capacity, the following method may be used as a method for examining the characteristics of the graphite negative electrode material of the present invention.
<Irreversible capacity>
The irreversible capacity is a value obtained by subtracting the discharge capacity from the charge capacity in the first cycle of battery charge / discharge. The irreversible capacity is calculated according to the following formula (2).
Irreversible capacity (mAh / g) = initial charge capacity (mAh / g) −initial discharge capacity (mAh / g) (2)

<First charge / discharge efficiency>
The initial charge / discharge efficiency is a value obtained by dividing the discharge capacity by the charge capacity. The initial charge / discharge efficiency is calculated according to the following formula (3).
Charge / discharge efficiency (%) = {(initial discharge capacity (mAh / g) / initial charge capacity (mAh / g)} × 100 (3)

  Examples of the present invention will be described below, but the present invention is not limited to the following examples without departing from the gist thereof.

[Example 1]
A coal tar pitch having a quinoline insoluble content of 0.001% by mass or more and 2% by mass or less is heat-treated in a reaction furnace at 460 ° C. for 10 hours to obtain a molten bulk heat-treated graphite crystal precursor (bulk mesophase). It was. The obtained massive heat-treated graphite crystal precursor was pulverized using an intermediate pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.) to obtain a refined graphite crystal precursor powder having a median diameter of 18 μm. The median diameter is obtained by mixing a 2% by volume aqueous solution (about 1 mL) of polyoxyethylene (20) sorbitan monolaurate, which is a surfactant, with fine heat-treated graphite crystal precursor powder to disperse ion-exchanged water. A value measured on a volume basis using a laser diffraction particle size distribution meter (LA-700 manufactured by Horiba, Ltd.) was used as a medium.
The refined heat-treated graphite crystal precursor powder was subjected to spheronization treatment for 10 minutes using hybridization (manufactured by Nara Machinery Co., Ltd.) as a spheronization apparatus. Then, the obtained powder was put into a container and fired at 1000 ° C. for 1 hour in a nitrogen atmosphere in an electric furnace to obtain a graphite crystal precursor. The graphite crystal precursor after firing was in the form of powder, and almost no melting or fusion was observed.
Further, the calcined graphite crystal precursor powder was transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours using a direct electric furnace to obtain a particulate graphite negative electrode material (graphite negative electrode material of Example 1). It was.

  Using the graphite negative electrode material of Example 1, a lithium secondary battery was produced according to the following method.

<Negative electrode fabrication method>
A graphite material, a carboxymethyl cellulose (CMC) aqueous solution as a thickener, and a styrene-butadiene rubber (SBR) aqueous solution as a binder resin so that CMC and SBR are 1% by mass with respect to the graphite negative electrode material after drying. The mixture was stirred to form a slurry, and this slurry was applied onto the copper foil using a doctor blade. For the coating thickness, the gap was selected so that the electrode basis weight (excluding the copper foil) after drying was 10 mg / cm ² .

This negative electrode was dried at 80 ° C., and then pressed so that the electrode density (excluding the copper foil) was 1.63 ± 0.03 g / cm ³ . A 12.5 mmφ electrode was punched out from the pressed electrode, and the weight of the negative electrode active material (electrode weight−copper foil weight−binder weight) was determined from the weight.

<Method for producing lithium secondary battery>
The negative electrode produced by the above method was vacuum-dried at 110 ° C., and then transferred to a glove box. Under an argon atmosphere, a mixed solution of ethylene carbonate (EC) / diethyl carbonate (DEC) = 1/1 was used as a solvent. A coin battery (lithium secondary battery) was prepared using the 1M-LiPF ₆ electrolyte solution, a polyethylene separator as a separator, and a lithium metal counter electrode as a counter electrode.

[Example 2]
The melt-processed massive heat-treated graphite crystal precursor obtained in the same procedure as in Example 1 was pulverized using an intermediate pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.), and further pulverized (Tsubo Mill manufactured by Matsubo). Was used to obtain a refined heat-treated graphite crystal precursor powder having a median diameter of 17 μm. Thereafter, the spheronization treatment was performed in the same manner as in Example 1, and the obtained powder was put in a container and baked in an electric furnace at 1000 ° C. for 1 hour in a nitrogen atmosphere to obtain a graphite crystal precursor. The graphite crystal precursor not subjected to the graphitization treatment was used as the graphite negative electrode material of Example 2. The graphite crystal precursor after firing was in the form of powder, and almost no melting or fusion was observed.

  Further, using the graphite negative electrode material of Example 2, a lithium secondary battery was produced in the same procedure as in Example 1.

[Comparative Example 1]
In the same manner as in Example 1, a coal tar pitch having a quinoline insoluble content of 0.001% by mass or more and 2% by mass or less was heat-treated in a reaction furnace at 460 ° C. for 10 hours to form a massive block heat-treated graphite crystal. A precursor (bulk mesophase) was obtained. The obtained bulk heat-treated graphite crystal precursor was pulverized using an intermediate pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.), and further pulverized using a pulverizer (Turbo Mill manufactured by Matsubo Co., Ltd.) to refine the median diameter of 17 μm. A graphite crystal precursor powder was obtained. The obtained powder was put into a container without spheroidizing treatment, and baked in an electric furnace at 1000 ° C. for 1 hour in a nitrogen atmosphere to obtain a graphite crystal precursor. The graphite crystal precursor after firing was in the form of powder, and almost no melting or fusion was observed. After firing, the graphite crystal precursor was classified with an airflow classifier (MC-100 manufactured by Seishin Enterprise Co., Ltd.).
After firing, the fired powder was further transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours using a direct current furnace to obtain a particulate artificial graphite negative electrode material (graphite negative electrode material of Comparative Example 1).

[Comparative Example 2]
In Comparative Example 1, a graphite crystal precursor that had not been graphitized after firing at 1000 ° C. for 1 hour was used as the graphite negative electrode material of Comparative Example 2.

The physical properties of the graphite negative electrode materials of Examples 1-2 and Comparative Examples 1-2 were measured as follows. The results are shown in Table 1.
<Average circularity>
Using a flow particle image analyzer (FPIA manufactured by Simex Industrial Co.), 0.2 g of a measurement target (here, a graphite negative electrode material) was added to a polyoxyethylene (20) sorbitan monolaurate as a surfactant in an amount of 0.2 g. After mixing with 50 mL of 2% by volume aqueous solution and irradiating 28 kHz ultrasonic waves at an output of 60 W for 1 minute, the detection range is specified as 0.6 to 400 μm, and based on the numerical values measured for particles in the particle size range of 3 to 40 μm. The average circularity was measured by the following formula (1).
Circularity = circumference of a circle having the same area as the particle projection area / perimeter of the particle projection image (1)
<Average total number of particles>
By flow type particle image analysis, the number-based circle equivalent diameter distribution was measured, and the total number of particles present in 1 g of the measurement object was determined.
<D ₅₀ , d ₉₀ / d ₁₀ , d _min >
Using a laser diffraction particle size distribution analyzer (LA-700, manufactured by HORIBA, Ltd.), a 2% by volume aqueous solution (about 1 ml) of polyoxyethylene (20) sorbitan monolaurate as a surfactant is mixed with the graphite negative electrode material. Then, from the volume-based particle size distribution measured using ion-exchanged water as the dispersion medium, an average particle size (median diameter) of 50% particle size (d ₅₀ ) is obtained, and 90% particle size (d ₉₀ ) and 10% particle size are obtained. These ratios (d ₉₀ / d ₁₀ ) were determined from (d ₁₀ ). Further, the minimum particle diameter (d _min ) was determined from the measurement result.
<Tap density>
Using a sieve with an opening of 300 μm, dropping the graphite material into a 20 cm ³ tapping cell and filling the cell to a full extent, then using a powder density measuring instrument (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.), a stroke length of 10 mm Was tapped 1000 times, and the tapping density at that time was measured.
<BET specific surface area>
Using a specific surface area meter (a fully automated surface area measuring device manufactured by Okura Riken), after subjecting the measurement object to preliminary drying at 350 ° C. for 15 minutes under a nitrogen flow, the value of the relative pressure of nitrogen relative to atmospheric pressure is 0. Using a nitrogen helium mixed gas accurately adjusted to be 3, measurement was performed by a nitrogen adsorption BET 6-point method using a gas flow method.
<Crystallinity (d ₀₀₂ , Lc ₀₀₂ )>
The (002) plane spacing d ₀₀₂ and the crystallite size Lc ₀₀₂ in the c-axis direction were measured by X-ray diffraction.

The discharge capacity, irreversible capacity, and initial charge / discharge efficiency of lithium secondary batteries using the graphite negative electrode materials of Examples 1-2 and Comparative Examples 1-2 were determined. The results are shown in Table 1.
<Measurement method of discharge capacity>
After charging the lithium counter electrode to 5 mV at a current density of 0.2 mA / cm ² , and further charging to a current value of 0.02 mA at a constant voltage of 5 mV, after doping lithium into the negative electrode, 0 The charge / discharge cycle of discharging to 1.5 V with respect to the lithium counter electrode at a current density of 0.4 mA / cm ² was repeated three times, and the discharge value at the third cycle was measured as the discharge capacity.
<Irreversible capacity>
It calculated according to following formula (2).
Irreversible capacity (mAh / g) = initial charge capacity (mAh / g) −initial discharge capacity (mAh / g) (2)
<Charge / discharge efficiency>
It calculated according to following formula (3).
Charge / discharge efficiency (%) = {(initial discharge capacity (mAh / g) / initial charge capacity (mAh / g)} × 100 (3)

As shown in Table 1, when Example 1 subjected to graphitization and Comparative Example 1 are compared, Comparative Example 1 has a large irreversible capacity and a low initial charge / discharge efficiency. On the other hand, Example 1 whose average circularity is 0.90 or more has little irreversible capacity. This is because Example 1 is a graphite negative electrode material with a small amount of fine powder because d ₉₀ / d ₁₀ is in the range of 1.5 to 2.8 and d _min is 3.5 μm or more. In addition, since the average total number of particles per gram of the graphite negative electrode material is small, the particulate graphite negative electrode material is not easily broken in the process of rolling the electrode, and fine powder is not easily generated. It is considered that the amount is small, the excessive reaction between the fine powder and the electrolytic solution can be suppressed, and the irreversible capacity is reduced.
Further, comparing Example 2 and Comparative Example 2 that were fired without graphitization, Comparative Example 2 has a larger irreversible capacity, whereas Example 2 has a smaller irreversible capacity. Furthermore, Example 2 has an average circularity of 0.90 or more, and tends to be filled more densely. In addition, since Example 2 has d ₉₀ / d ₁₀ in the range of 1.5 to 2.8 and d _min is 3.5 μm or more, it is a graphite negative electrode material with a small amount of fine powder. Since the average total number of particles per gram of graphite negative electrode material is also small, the amount of fine powder contained in the negative electrode is small because the particulate graphite negative electrode material is not easily broken and fine powder is not easily generated in the step of rolling the electrode. It is considered that the excessive reaction between the fine powder and the electrolytic solution can be suppressed, and the irreversible capacity is reduced.
In Examples 1 and 2, the tap density is as high as 1.10 g / cm ³ or more, and a high packing density is possible. The BET specific surface area, the interplanar spacing d _002, and the c-axis direction crystallite size Lc _{Since 002} is within the preferred range, an excellent lithium secondary battery with high discharge capacity and low irreversible capacity can be realized.

  Since the present invention has a high tap density and a small amount of fine powder, a high density filling is possible, and a graphite negative electrode material capable of realizing an excellent lithium secondary battery with a high discharge capacity and a low irreversible capacity. Since this negative electrode material can be produced efficiently and stably, it is industrially useful.

Claims (7)

  Including a step of spheroidizing a bulk mesophase obtained by heat-treating a pitch raw material having a quinoline insoluble content of 20% by mass or less by applying mechanical action of compression, friction and shearing force including particle interaction, and A method for producing a graphite negative electrode material for a lithium secondary battery, comprising a step of firing a material after spheronization treatment and graphitizing the material after firing, or a step of directly graphitizing without incorporating a firing step.   The manufacturing method of the graphite negative electrode material for lithium secondary batteries of Claim 1 whose content (VM: Volatile Matter) of bulk mesophase is 4-30 mass%. 3. The method for producing a graphite negative electrode material for a lithium secondary battery according to claim 1, wherein the spheronization treatment is performed so that an average total number of particles of the graphite negative electrode material is 3 × 10 ⁶ particles / g or less.   The manufacturing method of the graphite negative electrode material for lithium secondary batteries of any one of Claims 1-3 whose temperature to bake is 800-2000 degreeC.   The manufacturing method of the graphite negative electrode material for lithium secondary batteries of any one of Claims 1-4 whose volume reference | standard average particle diameter of the bulk mesophase before the process to spheroidize is 5-200 micrometers.   The method for producing a graphite negative electrode material for a lithium secondary battery according to any one of claims 1 to 5, wherein the bulk mesophase is obtained by heat-treating the pitch raw material at a temperature of 400 to 600 ° C.   The manufacturing method of the graphite negative electrode material for lithium secondary batteries of any one of Claims 1-6 whose temperature which graphitizes is 2000-3200 degreeC.