JP5081375B2 - Negative electrode material for lithium secondary battery, production method thereof, 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 for a lithium secondary battery comprising a graphite composite mixed powder, a method for producing the same, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same. Specifically, when used at a high electrode density, it is possible to obtain a lithium secondary battery having a large discharge capacity, high charge / discharge efficiency, excellent load characteristics, and small electrode expansion during charging. The present invention relates to a negative electrode material, a method for producing the same, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.

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

Particulate materials such as metals and graphite have been studied as negative electrode materials for lithium secondary batteries. In particular, as the capacity of batteries further increases, negative electrode materials that can be used at higher electrode densities (for example, 1.6 g / cm ³ or more) are desired.

  Graphite negative electrode particles are known as a negative electrode material excellent in capacity increase. However, the graphite negative electrode particle is not a perfect spherical shape but a flat shape particle such as a scaly shape. Further, in the flat particle, the graphite crystal plane direction is often parallel to the flat shape of the particle. . In such a case, if the press pressure is increased in order to obtain a higher electrode density, the flat graphite negative electrode particles are easily aligned in parallel to the current collector, and the entire electrode is aligned. The electrode tends to expand due to the formation of a graphite intercalation compound with lithium. When the electrode expands, there is a problem in that the amount of active material that can be filled per unit volume of the electrode active material decreases, and as a result, the battery capacity decreases.

In order to solve these problems, it has been studied to use a composite carbon material obtained by mixing graphite and pitch and firing.
In Patent Document 1, a high-crystalline scale-like natural graphite or quiche graphite and pitch or resin are mixed, pulverized, carbonized, graphitized and combined to improve the defects of natural graphite, and the initial charge / discharge efficiency is improved. It is described that a graphite negative electrode material that is high, excellent in cycle characteristics, high capacity, and excellent coatability is obtained.

  Patent Document 2 discloses that high-capacitance of graphite is obtained by melting and mixing a graphite powder with good orientation and a mesophase pitch having a softening point of 250 to 400 ° C., and then comminuting and comminuting. It is described that a negative electrode material having high battery efficiency and high bulk density can be obtained by incorporating both characteristics such as good characteristics and good handleability of mesophase pitch. As the graphite powder, natural graphite, artificial graphite and the like are used, but no particular attention has been paid to the shape of the graphite particles represented by the aspect ratio.

  Another problem when using higher electrode density is that the graphite negative electrode material is broken and more reactive surfaces with the electrolyte are exposed, resulting in greater reaction with the electrolyte and charge / discharge. It is mentioned that efficiency becomes easy to fall.

  Furthermore, when the electrode is used at a higher electrode density, the particles are liable to be crushed, so that the space for lithium ions in the electrode is reduced, the lithium ion permeability is deteriorated, and the load characteristics are deteriorated. Such a problem is more likely to occur as the particles are flatter.

  Therefore, in order to further increase the capacity of the lithium secondary battery, not only the capacity of the active material but also a negative electrode material that can be used at a higher electrode density is desired. Even at a high electrode density, expansion during battery charging is desired. There is a strong demand to suppress the above, maintain charge / discharge efficiency, and maintain load characteristics.

  On the other hand, Patent Document 3 discloses that a graphite core material (A) and a graphite material are obtained by melt-kneading pitch and scale-like natural graphite, compounding and mechanochemical treatment, followed by graphitization. A spherical or ellipsoidal composite in which the graphite layer (C) is present on the outer surface of the composite particles made of the coating material (B) and the order of crystallinity is (A)> (B)> (C) It is described that, by obtaining a graphite material, an increase in irreversible capacity, a high rate characteristic, and a decrease in cycle characteristics can be improved even at a high density. Further, the reactivity with the electrolytic solution is controlled by forming a graphite layer (C) by mechanochemical treatment, and the graphite coating material (B) is densely contained in the graphite core material (A). Therefore, it is described that the composite particles are not broken even at a high density and the above-described excellent characteristics are exhibited.

JP 2000-182617 A JP 2002-373656 A JP 2003-173778 A

  The composite graphite negative electrode material described in Patent Document 1 uses highly crystalline scaly natural graphite or the like as a raw material for composite with pitch or the like. Because of the scaly shape, the graphite is easily oriented in the direction parallel to the electrode surface in the electrode active material particles, and the active material particles themselves are also easily flattened. Therefore, it was easy to cause expansion in the electrode thickness direction during battery charging. Moreover, the lithium ion permeability was poor, and the battery capacity, charge / discharge efficiency, and load characteristics were insufficient.

  In addition, the graphite-based negative electrode material described in Patent Document 2 is a composite of mesophase, which is usually flat graphite, but does not focus on the flatness of graphite, and as in Patent Document 1, as a result The graphite orientation in the composite powder and the electrode was easy to align, which was insufficient in terms of suppressing the expansion of the electrode at a high electrode density.

  On the other hand, according to the technique described in Patent Document 3, by using the spherical and dense hard material as described above, characteristics at a higher electrode density are improved as compared with the techniques described in Patent Documents 1 and 2. I think that the.

  However, because it is integrated with the graphite coating material (B), it is difficult to control the thickness of the graphite layer (C) on the outer surface, and it is difficult to exhibit stable battery characteristics. It was. In addition, since it is composed only of a spherical dense hard material, there is a problem that it is difficult to increase the filling rate of the negative electrode material in the electrode, and it is difficult to achieve a higher electrode density. In addition, from the viewpoint of industrial production, there is a problem that the manufacturing process is complicated and the cost is high.

Further, it is described that the low crystalline surface layer (C) is coated without peeling from the core material, and that the BET specific surface area is preferably 1 m ² / g or less, but the BET specific surface area is reduced. Lithium acceptance at the time of charging deteriorated, and the charging capacity was insufficient.

  The present invention has been made in view of the above problems. That is, the present invention is a graphite-based negative electrode material for a lithium secondary battery, and when used at a high electrode density, has a large discharge capacity, high charge / discharge efficiency, excellent load characteristics, and at the time of charging. An object of the present invention is to provide an excellent negative electrode material capable of obtaining a lithium secondary battery with small electrode expansion, a method for producing the same, and a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.

  The inventors of the present invention have intensively studied a graphite-based negative electrode material for a lithium secondary battery. As a result, by using as a negative electrode material a graphite composite powder containing a graphite having an aspect ratio within a predetermined range and a graphite composite powder in which a graphite having a different orientation from the composite is combined, and an artificial graphite powder, It has been found that a high-performance lithium secondary battery can be stably and efficiently manufactured at a high electrode density, with a high discharge capacity, high charge / discharge efficiency, excellent load characteristics, and low electrode expansion during charging. The present invention has been completed.

That is, the gist of the present invention is that the graphite (D) having an aspect ratio of 1.2 or more and 4.0 or less and the graphite (E) having a different orientation from the graphite (D) are combined. composite powder and (a), provided with a graphite composite mixture powder consisting of a human granulated graphite powder (B) (C), the artificial graphite powder (B) is not encompass the graphite (D) is alone A lithium secondary battery, characterized in that it is any of the artificial graphite particles produced by the method described above or the artificial graphite particles obtained by granulating only the graphite (E) without containing the graphite (D). It exists in the negative electrode material.

Another gist of the present invention is a method for producing the above-described negative electrode material for a lithium secondary battery, comprising a graphite crystal precursor obtained by heat-treating a pitch raw material having a quinoline insoluble content of 3% by weight or less. and pulverized product, an aspect ratio of 1.2 or more and 4.0 or less, a tap density of 0.7 g / cm ³ or more, by mixing graphite and (D) is 1.35 g / cm ³ or less, wherein After heat treatment A for fixing the graphite (D) and the refined particles of the graphite crystal precursor in contact with each other in a non-oriented state, the heat treatment B for pulverizing, firing and graphitizing is performed . The present invention resides in a method for producing a negative electrode material for a lithium secondary battery, wherein the graphite composite mixed powder (C) is prepared .

Another gist of the present invention is as follows.
A method for producing a negative electrode material for a lithium secondary battery as described above, wherein a pitch raw material having a quinoline insoluble content of 3 wt% or less, an aspect ratio of 1.2 or more and 4.0 or less, and a tap density of 0.00. While producing a graphite composite powder (A) from a graphite (D) of 7 g / cm ³ or more and 1.35 g / cm ³ or less, an artificial graphite powder (B) is produced from a pitch raw material. A method for producing a negative electrode material for a lithium secondary battery, comprising: preparing a graphite composite mixed powder (C) by mixing the graphite composite powder (A) and the artificial graphite powder (B). Exist.

  Another gist of the present invention includes a current collector and an active material layer formed on the current collector, and the active material layer contains the above-described negative electrode material for a lithium secondary battery. It exists in the negative electrode for lithium secondary batteries characterized by the above-mentioned.

  Another gist of the present invention is a lithium secondary battery comprising a current collector and an active material layer formed on the current collector, wherein the active material layer is produced by the above-described production method. The negative electrode for lithium secondary batteries is characterized by containing a negative electrode material for a battery.

  Another aspect of the present invention is a lithium battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is the above-described negative electrode for a lithium secondary battery. It exists in a secondary battery.

According to the negative electrode material for a lithium secondary battery of the present invention, when used at a high electrode density (for example, 1.6 g / cm ³ or more), the discharge capacity is large, the charge / discharge efficiency is high, the load characteristics are excellent, and An excellent lithium secondary battery with small electrode expansion during charging can be realized.
In addition, according to the method for producing a negative electrode material for a lithium secondary battery of the present invention, the negative electrode material for a lithium secondary battery can be efficiently and stably produced, 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 can be arbitrarily modified and implemented without departing from the gist of the present invention.
[1. Negative electrode material for lithium secondary battery]

  The negative electrode material for a lithium secondary battery of the present invention has a graphite (D) having an aspect ratio of 1.2 or more and 4.0 or less and a graphite (E) having a different orientation from the graphite (D). Graphite composite mixed powder (C) composed of composite graphite composite powder (A) and artificial graphite powder (B), or composed of this graphite composite mixed powder (C) and natural graphite powder (G) A graphite composite mixed powder (F) is provided.

The high capacity of the battery was achieved by graphite (D), (E) and artificial graphite powder (B) having high crystallinity. The presence of both graphite (D) combined with graphite (E) and artificial graphite powder (B) makes it possible to simultaneously improve battery efficiency and suppress electrode expansion during charging. It was. Furthermore, by combining the graphite (D) having a specified aspect ratio, it was possible to produce a specified graphite composite powder (A), and high load characteristics were obtained.
Hereinafter, (A) to (G) will be described.

[1-1. Graphite (D)]
The type of graphite (D) is not particularly limited as long as it satisfies the orientation requirements described later. Examples include natural graphite and artificial graphite. Examples of natural graphite include scaly graphite, scaly graphite, and soil graphite. Examples of the artificial graphite include graphite particles such as mesocarbon microbeads, carbon fibers, coke, needle coke, and high-density carbon material, which are produced by heat-treating a pitch raw material.

  The shape of the graphite (D) is not particularly limited. Examples include lumps, spheres, and ellipses. However, it is preferable that the particles have a shape close to a sphere. Specifically, the aspect ratio needs to satisfy the following regulations.

<Aspect ratio>
The aspect ratio of the graphite (D) is usually 1.2 or more, preferably 1.5 or more, and usually 4.0 or less, preferably 3.0 or less. If the aspect ratio is less than this range, the anisotropy is small, so that the shape is close to a sphere or a cube, and it is difficult to increase the packing density of the electrode after pressing. On the other hand, when the above range is exceeded, the active material is easily oriented on the electrode surface, and it is difficult to increase the load characteristics at a high electrode density. Alternatively, electrode expansion during battery charging when the battery is manufactured increases, and it is difficult to increase the battery capacity per unit volume of the electrode.

  In addition, the measurement of the aspect ratio of the graphite (D) is carried out using a negative electrode material before negative electrode production using a negative electrode material powder dispersed on a flat plate and directly embedded in a resin, or using a negative electrode material. About the manufactured negative electrode, it can carry out in the following procedures using the negative electrode.

  The resin embedding of the negative electrode material or the negative electrode is polished parallel to the flat plate, a cross-sectional photograph thereof is taken, and the major axis of the graphite (D) cross section is measured by 50 or more points by image analysis of the photographed photograph. To do. In addition, the resin-embedded material of the negative electrode material or the negative electrode is polished and polished perpendicularly to the flat plate, a cross-sectional photograph thereof is taken, and the short diameter of the graphite (D) cross-section is analyzed by image analysis of the photographed photograph. 50 or more (particle thickness) is measured. An average value is obtained for each of the measured major axis and minor axis, and the ratio of the average major axis to the average minor axis is defined as an aspect ratio (major axis / minor axis). The particles embedded in the resin or made into an electrode plate usually tend to be aligned so that the thickness direction of the particle is perpendicular to the flat plate, and thus the major axis and minor axis characteristic of the particle are obtained by the above method. I can do it.

  In addition, generally the cross-sectional photograph of particle | grains is image | photographed using a scanning electron microscope (Scanning Electron Microscope: SEM). However, when the shape of the graphite (D) cannot be specified by the SEM photograph, a sectional photograph is taken in the same manner as described above using a polarizing microscope or a transmission electron microscope (TEM). Since the graphite (D) is different in orientation from the graphite (E), the shape of the graphite (D) can be specified by confirming the orientation using a polarizing microscope photograph or a TEM photograph. Therefore, the aspect ratio can be obtained by performing the same image analysis as described above.

  The method for obtaining the graphite (D) having an aspect ratio in the above range is not particularly limited. For example, particles having repeated mechanical actions such as compression, friction, shearing force, etc., including interaction of particles mainly with impact force. It is preferable to use an apparatus given in the above. Specifically, it has a rotor with a large number of blades installed inside the casing, and when the rotor rotates at high speed, mechanical action such as impact compression, friction, shearing force, etc. is applied to the carbon material introduced inside. An apparatus that provides a surface treatment is preferable. Moreover, it is preferable to have a mechanism that repeatedly gives mechanical action by circulating the carbon material. An example of a preferred apparatus is a hybridization system manufactured by Nara Machinery Co., Ltd.

<Orientation>
As the graphite (D), for example, highly crystalline graphite, which originally has a single orientation plane, is partially made into a state having different orientations by mechanical energy treatment or the like.
As a method for confirming the orientation of the graphite (D), observation with a polarizing microscope can be given. This utilizes the fact that when light emitted from one light source enters an anisotropic body with an anisotropic crystal structure direction, the light changes in a limited vibration direction. A single color or several colors are observed, and the orientation of the particles can be observed due to the difference.

<Tap density>
The tap density of the graphite (D) is not particularly limited, but is usually 0.70 g / cm ³ or more, preferably 0.80 g / cm ³ or more, more preferably 0.90 g / cm ³ or more, and usually 1. 35 g / cm ³ or less, preferably 1.20 g / cm ³ or less. When the tap density is below this range, it is difficult to increase the packing density of the active material and it is difficult to obtain a high-capacity battery. On the other hand, if it exceeds this range, the amount of pores in the electrode decreases, and it is difficult to obtain favorable battery characteristics.

As the tap density, for example, a sieve having an opening of 300 μm is used, and after a measurement object (here, graphite (D)) is dropped into a 20 cm ³ tapping cell and the cell is fully filled, a powder density measuring device A value obtained by performing tapping with a stroke length of 10 mm 1000 times (for example, a tap denser manufactured by Seishin Enterprise Co., Ltd.) and measuring the tapping density at that time can be used.

<BET specific surface area>
The BET specific surface area of the graphite (D) is not particularly limited, but is usually 3.0 m ² / g or more, preferably 4.0 m ² / g or more, and usually 10.0 m ² / g or less, preferably The range is 8.0 m ² / g or less. When the value of the BET specific surface area is less than the lower limit of this range, when used as a negative electrode material, the acceptability of lithium tends to deteriorate during battery charging, and lithium tends to precipitate on the electrode surface, which is not preferable for safety. On the other hand, if the value of the BET specific surface area exceeds the upper limit of this range, the reactivity with the electrolytic solution increases when the negative electrode material is formed, gas generation tends to increase, and a preferable battery is difficult to obtain.

  As a BET specific surface area, a surface area meter (for example, a fully automatic surface area measuring device manufactured by Ritsu Okura) is used, and preliminary drying is performed at 350 ° C. for 15 minutes under a nitrogen flow with respect to a measurement target (here, graphite (D)). Thereafter, a value measured by a nitrogen adsorption BET one-point method using a gas flow method can be used using a nitrogen helium mixed gas that is accurately adjusted so that the relative pressure value of nitrogen with respect to atmospheric pressure is 0.3.

<Volume standard average particle size>
The volume-based average particle diameter of the graphite (D) is not particularly limited, but is usually 1.0 μm or more, preferably 6.0 μm or more, and usually 60 μm or less, preferably 30 μm or less. If the volume-based average particle size is below this range, the graphite (D) is likely to aggregate, and it becomes difficult to mix with the graphite crystalline precursor in the production process described later, and the resulting graphite composite powder (A ) Tends to be inhomogeneous. On the other hand, if the volume-based average particle diameter exceeds this range, uneven coating tends to occur when an electrode is produced by coating as a negative electrode material.

  As the volume-based average particle size, a 2% by volume aqueous solution (about 1 ml) of polyoxyethylene (20) sorbitan monolaurate as a surfactant is mixed with a measurement target (here, graphite (D)), and ion exchange is performed. A value obtained by measuring a volume-based average particle diameter (median diameter) with a laser diffraction particle size distribution meter (for example, LA-700 manufactured by Horiba, Ltd.) using water as a dispersion medium can be used.

<Surface spacing, etc.>
Plane spacing d ₀₀₂ of (002) plane graphite measured by X-ray diffraction (D) is not particularly limited, normally less than 0.3360 nm, preferably in the range of less 0.3358Nm. When the value of the interplanar distance d ₀₀₂ exceeds this range, that is, when the crystallinity is inferior, the discharge capacity per unit weight of the active material tends to be small when the electrode is manufactured. On the other hand, the lower limit of the interplanar spacing d002 is usually 0.3354 nm or more as a theoretical limit.

Further, the crystallite size Lc _{004 in} the c-axis direction of the graphite (D) measured by X-ray diffraction is not particularly limited, but is usually in the range of 90 nm or more, preferably 100 nm or more. If the crystallite size Lc ₀₀₄ is below this range, the discharge capacity per active material weight tends to be small when the electrode is manufactured.

As the interplanar spacing d ₀₀₂ and the crystallite size Lc ₀₀₄ measured by the above 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 exceeding 100 nm (1000 Å) are not distinguished and are all described as “> 1000 (Å)”.

[1-2. Graphite (E)]
The type of graphite (E) is not particularly limited as long as the orientation is different from that of graphite (D). As an example, artificial graphite produced by high-temperature heat treatment of pitch raw material can be cited.

<Orientation>
Graphite (E) is different in orientation from graphite (D). “Different orientation” means that when the powder is observed with a polarizing microscope, the pattern of the anisotropic unit of the optically anisotropic structure, that is, the size, direction, number, etc. of the anisotropic unit is visually observed. When compared, it means that at least one of the size, direction, number, and the like is different. For example, among graphite (D) and graphite (E), when one graphite has crystal orientation in one direction and the other graphite has random crystal orientation, For example, D) and graphite (E) both have crystal orientation in one direction, and the directions are different.
When one or both of the graphite (D) and the graphite (E) is not a single crystal but an aggregate of a plurality of crystals, the unit of the aggregate is defined as one region, and the optical What is necessary is just to contrast the aggregate patterns of anisotropic units of anisotropic texture.

  Specifically, as a method for confirming the orientation of the graphite (E), the same method as in the case of the graphite (D) can be used.

<Surface spacing>
Plane spacing d ₀₀₂ of (002) plane graphite measured by X-ray diffraction (E) is not particularly limited, normally less than 0.3360 nm, preferably in the range of less 0.3358Nm. When the value of the interplanar distance d ₀₀₂ exceeds this range, that is, when the crystallinity is inferior, the discharge capacity per unit weight of the active material tends to be small when the electrode is manufactured. Meanwhile, the lower limit of the surface spacing d ₀₀₂ of, as a theoretical limit is usually 0.3354nm or more. The interplanar spacing _d002 is measured by the same method as in the case of the graphite (D).

Further, the crystallite size Lc _{004 in} the c-axis direction of the graphite (E) measured by X-ray diffraction is not particularly limited, but is usually 90 nm or more, preferably 100 nm or more. If the crystallite size Lc004 is below this range, the discharge capacity per active material weight tends to be small when an electrode is manufactured. The crystallite size Lc ₀₀₄ is measured by the same method as in the case of the graphite (D).

[1-3. Graphite composite powder (A)]
The graphite composite powder (A) is a composite of the above-mentioned graphite (D) and graphite (E). Composite means that graphite (E) covers and / or bonds graphite (D).

<Composite form>
The form of the composite of the graphite (D) and the graphite (E) in the graphite composite powder (A) is not particularly limited, but specific examples include the following forms.
I) A form in which the entire surface or a part of the graphite (D) is coated with the graphite (E).
II) A form in which graphite (E) is bound to the whole or part of the surface of graphite (D), and two or more graphites (D) and graphite (E) are combined.
III) A form in which the above I) and II) are mixed in an arbitrary ratio.

<Shape>
The shape of the graphite composite powder (A) is not particularly limited. Examples include a spherical shape, an elliptical shape, a massive shape, and the like. However, it is preferable that the particles have a shape close to a sphere. Specifically, it is preferable that the aspect ratio satisfies the following regulations.

<Aspect ratio>
The aspect ratio of the graphite composite powder (A) is not particularly limited, but is usually 1.1 or more, preferably 1.3 or more, and usually 4.0 or less, preferably 3.0 or less. If the aspect ratio is less than this range, the anisotropy is small, so that the shape is close to a sphere or a cube, and it is difficult to increase the packing density of the electrode after pressing. On the other hand, when the above range is exceeded, the active material is easily oriented on the electrode surface, and it is difficult to increase the load characteristics at a high electrode density. Alternatively, electrode expansion during battery charging when the battery is manufactured increases, and it is difficult to increase the battery capacity per unit volume of the electrode.

The aspect ratio of the graphite composite powder (A) can be measured by the following procedure as in the case of the graphite (D).
The resin embedding of the negative electrode material or the negative electrode is polished in parallel to the flat plate, a cross-sectional photograph thereof is taken, and the major axis of the cross section of the graphite composite powder (A) is determined by image analysis of the photographed photograph. Measure above. Also, the resin-embedded material of the negative electrode material or the negative electrode is polished and polished perpendicularly to the flat plate, a cross-sectional photograph thereof is taken, and an analysis of the photographed photograph shows that the cross section of the graphite composite powder (A) Measure 50 or more of the minor diameter (particle thickness). An average value is obtained for each of the measured major axis and minor axis, and the ratio of the average major axis to the average minor axis is defined as an aspect ratio (major axis / minor axis).
In addition, although the cross-sectional photograph of particle | grains may be image | photographed with any of SEM, a polarizing microscope, and TEM, in the case of graphite composite powder (A), it image | photographs normally using SEM.

<Tap density>
The tap density of the graphite composite powder (A) is not particularly limited, but is usually 0.80 g / cm ³ or more, especially 0.90 g / cm ³ or more, and usually 1.35 g / cm ³ or less, especially 1.30 g. A range of not more than / cm ³ is preferable. When the tap density is below this range, 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 this range, the amount of pores in the electrode decreases, and it is difficult to obtain favorable battery characteristics. The tap density is measured by the same method as in the case of the graphite (D).

<BET specific surface area>
The BET specific surface area of the graphite composite powder (A) is not particularly limited, but is usually 0.8 m ² / g or more, especially 2.0 m ² / g or more, and usually 5.5 m ² / g or less, especially 4. A range of 0 m ² / g or less is preferred. If the BET specific surface area is less than the lower limit of this range, the lithium acceptability tends to deteriorate during charging, and lithium tends to precipitate on the electrode surface, which is not preferable for safety. On the other hand, if the upper limit of this range is exceeded, the reactivity between the negative electrode and the electrolyte increases, gas generation tends to increase, and a preferable battery is difficult to obtain. The BET specific surface area is measured by the same method as in the case of the above-mentioned graphite (D).

<Volume standard average particle size>
The volume-based average particle diameter of the graphite composite powder (A) is not particularly limited, but is usually in the range of 6.0 μm or more, particularly 10.0 μm or more, and usually 80.0 μm or less, especially 40.0 μm or less. Below this range, the tap density as the graphite composite mixed powder (C) becomes small, so that 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 this range, uneven coating tends to occur when an electrode is produced by coating as a graphite composite mixed powder (C). The volume-based average particle diameter is measured by the same method as in the case of the graphite (D).

<Ratio of graphite (D) contained in graphite composite powder (A)>
The ratio of the graphite (D) contained in the graphite composite powder (A) is a value of the weight ratio of the graphite (D) to the graphite composite powder (A) and is usually 30% by weight or more, preferably 40% by weight. Above, more preferably 50% by weight or more, and usually 97% by weight or less, preferably 90% by weight or less, more preferably 83% by weight or less. If the ratio of the graphite (D) is below this range, the ratio of the graphite (E) is relatively increased, so that it is difficult to increase the packing density when the electrode is used, and an excessive press load is required and the graphite (D). It is difficult to obtain the advantage of compounding. On the other hand, if the ratio of the graphite (D) exceeds this range, the reactivity with the electrolyte increases when the electrode is used, and gas generation tends to increase, and the advantage of being combined with the graphite (E) can be obtained. hard.

[1-4. Artificial graphite powder (B)]
The kind of artificial graphite powder (B) is not particularly limited. Examples include artificial graphite produced by heat-treating a pitch material at high temperature.

  Specifically, the artificial graphite powder (B) includes (i) artificial graphite particles produced alone, and (ii) the graphite (D) and the graphite (E) having different orientation from the graphite (D). Any of the artificial graphite particles obtained by granulating only the graphite (E) without containing the graphite (D) may be used. In the case of (ii), the graphite (E) and the artificial graphite powder (B) are produced from the same raw material at a time, which is advantageous from the viewpoint of ease of production.

  The artificial graphite powder (B) has a high crystallinity and is characterized in that it does not include a portion with different orientation such as graphite particles. Therefore, using a polarizing microscope or a TEM, according to the same procedure as in the case of graphite (D), the negative electrode material before the negative electrode production, the cross-sectional photograph of the negative electrode material powder, for the negative electrode manufactured using the negative electrode material The artificial graphite powder (B) can be distinguished from the graphite composite powder (A) by taking a cross-sectional photograph of the negative electrode material powder present in the negative electrode cross section and confirming its orientation.

  The shape of the artificial graphite powder (B) is not particularly limited. Examples include lumps, spheres, ellipses, flakes, fibers, and the like. Of these, a block shape, a spherical shape, and an elliptical shape are preferable.

<BET specific surface area>
The BET specific surface area of the artificial graphite powder (B) is not particularly limited, but is usually 0.3 m ² / g or more, particularly 0.5 m ² / g or more, more preferably 0.6 m ² / g or more, and usually 3. A range of 0 m ² / g or less, particularly 2.8 m ² / g or less, and further 2.0 m ² / g or less is preferable. When the BET specific surface area is below the lower limit of this range, the lithium acceptability is deteriorated during charging, and lithium is liable to precipitate on the electrode surface, which is not preferable for safety. On the other hand, when the upper limit is exceeded, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery is difficult to obtain. The BET specific surface area is measured by the same method as in the case of the above-mentioned graphite (D).

<Volume standard average particle size>
The volume-based average particle diameter of the artificial graphite powder (B) is not particularly limited, but is usually 3 μm or more, preferably 5 μm or more, more preferably 6 μm or more, and usually 30 μm or less, particularly preferably 20 μm or less. If the volume-based average particle size is less than this range, the tap density as the graphite composite mixed powder (C) becomes small. Therefore, it is difficult to increase the packing density of the active material when the electrode is manufactured, and the high-capacity battery Hard to get. On the other hand, if it exceeds this range, uneven coating tends to occur when an electrode is produced by coating as a negative electrode material. The volume-based average particle diameter is measured by the same method as in the case of the graphite (D).

<Tap density>
The tap density of artificial graphite powder (B) is not particularly limited, usually 0.90 g / cm ³ or more and preferably 1.10 g / cm ³ or more and usually 1.35 g / cm ³ or less, preferably 1.30 g / A range of cm ³ or less is preferred. When the tap density is below this range, 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 this range, the amount of pores in the electrode decreases, and it is difficult to obtain favorable battery characteristics. The tap density is measured by the same method as in the case of the graphite (D).

<Surface spacing>
Plane spacing d ₀₀₂ of (002) plane of the artificial graphite powder (B) measured by X-ray diffraction is not particularly limited, normally less than 0.3360 nm, among others 0.3358nm preferably in the following range. When exceeding this range, that is, when the crystallinity is inferior, the discharge capacity per unit weight of the active material tends to be small when the electrode is manufactured. Meanwhile, the lower limit of the surface spacing d ₀₀₂ of, as a theoretical limit is usually 0.3354nm or more. The interplanar spacing _d002 is measured by the same method as in the case of the graphite (D).

The crystallite size Lc _{004 in} the c-axis direction of the artificial graphite powder (B) measured by X-ray diffraction is not particularly limited, but is usually 90 nm or more, preferably 100 nm or more. Below this range, the discharge capacity per active material weight when the electrode is manufactured tends to be small. The crystallite size Lc ₀₀₄ is measured by the same method as in the case of the graphite (D).

[1-5. Graphite composite mixed powder (C)]
The graphite composite mixed powder (C) is in a state where the graphite composite powder (A) and the artificial graphite powder (B) are mixed.

<Tap density>
The tap density of the graphite composite mixed powder (C) is not particularly limited, but is usually 0.8 g / cm ³ or more, particularly 0.9 g / cm ³ or more, more preferably 1.0 g / cm ³ or more, and usually 1 .4g / cm ³ or less, preferably 1.35 g / cm ³ or less, more 1.3 g / cm ³ is preferably in a range of about. When the tap density is below this range, 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 this range, the amount of pores in the electrode decreases, and it is difficult to obtain favorable battery characteristics. The tap density is measured by the same method as in the case of the graphite (D).

<BET specific surface area>
The BET specific surface area of the graphite composite mixed powder (C) is not particularly limited, but is usually 1 m ² / g or more, particularly 1.5 m ² / g or more, more preferably 1.8 m ² / g or more, and usually 5 m ^2. / G or less, in particular, a range of 3.5 m ² / g or less, more preferably 3 m ² / g or less. Below the lower limit, the acceptability of lithium is likely to deteriorate during charging, and lithium is likely to precipitate on the electrode surface, which is not preferable for safety. If the upper limit is exceeded, the reactivity with the electrolyte increases, gas generation tends to increase, and a preferable battery is difficult to obtain. The BET specific surface area is measured by the same method as in the case of the above-mentioned graphite (D).

<Surface spacing, etc.>
Plane spacing d ₀₀₂ of (002) plane of graphite composite mixture powder is measured by X-ray diffraction (C) is not particularly limited, normally less than 0.3360 nm, among others 0.3358nm preferably in the following range. When exceeding this range, that is, when the crystallinity is inferior, the discharge capacity per unit weight of the active material tends to be small when the electrode is manufactured. Meanwhile, the lower limit of the surface spacing d ₀₀₂ of, as a theoretical limit is usually 0.3354nm or more. The interplanar spacing _d002 is measured by the same method as in the case of the graphite (D).

The size Lc ₀₀₄ of the crystallites in the c-axis direction of the graphite complex mixed powder (C) measured by X-ray diffraction is not particularly limited, but is usually 90 nm or more, preferably 100 nm or more. Below this range, the discharge capacity per weight of active material tends to be small when an electrode is produced using the graphite composite mixed powder (C) of the present invention. The crystallite size Lc ₀₀₄ is measured by the same method as in the case of the graphite (D).

<Ratio of graphite composite powder (A) contained in graphite composite mixed powder (C)>
The ratio of the graphite composite powder (A) contained in the graphite composite mixed powder (C) is usually 35% by weight or more, preferably the weight ratio of the graphite composite powder (A) to the graphite composite mixed powder (C). Is 50% by weight or more, more preferably 55% by weight or more, and usually 98% by weight or less, preferably 90% by weight or less, more preferably 86% by weight or less. If the weight ratio of the graphite composite powder (A) is less than this range, the proportion of the artificial graphite powder (B) is relatively increased, so that it is difficult to increase the packing density when an electrode is used, and an excessive press load is required. It is difficult to obtain the advantage of mixing artificial graphite powder (B). On the other hand, if it exceeds this range, the ratio of the graphite composite powder (A) is too large, and the electrode coatability may be impaired.

<Volume standard average particle size>
The volume-based average particle diameter of the graphite composite mixed powder (C) is not particularly limited, but is usually 5 μm or more, preferably 8 μm or more, and usually 60 μm or less, preferably 30 μm or less. If it falls below this range, the tap density becomes small. Therefore, when the electrode is manufactured, it is difficult to increase the packing density of the active material, and it is difficult to obtain a high-capacity battery. On the other hand, if it exceeds this range, uneven coating tends to occur when an electrode is produced by coating. The volume-based average particle diameter is measured by the same method as in the case of the graphite (D).

  In addition, when obtaining data such as tap density, specific surface area, and particle size of the graphite composite powder (A) and artificial graphite powder (B) contained in the graphite composite mixed powder (C), Follow the method.

  When obtaining a graphite composite mixed powder (C) by the same manufacturing method using the same raw material, a plurality of types of graphite composite mixed powders in which only the mixing ratio of the graphite composite powder (A) and the artificial graphite powder (B) is changed ( C), and by measuring data such as tap density, specific surface area, and particle size of the graphite composite mixed powder (C) of each blending ratio, the graphite composite powder (A ) Data such as the tap density, specific surface area, and particle size of the simple substance and artificial graphite powder (B) can be obtained.

[1-6. Graphite composite mixed powder (F) and natural graphite powder (G)]
Next, the graphite composite mixed powder (F) will be described. In addition to each component of said graphite composite mixed powder (C), graphite composite mixed powder (F) is further provided with natural graphite powder (G). The natural graphite powder (G) is used for the purpose of controlling the BET specific surface area of the negative electrode material, improving the electrode pressability, improving the discharge capacity, and reducing the cost.

The kind of natural graphite powder (G) is not particularly limited. Examples of natural graphite include scaly graphite, scaly graphite, and earthy graphite.
Further, the shape of the natural graphite powder (G) is not particularly limited. Specific examples include a lump shape, a spherical shape, an ellipse shape, a flake shape, and a fiber shape.

<BET specific surface area>
The BET specific surface area of the natural graphite powder (G) is not particularly limited, but is usually 3.0 m ² / g or more, preferably 3.5 m ² / g or more, more preferably 4.0 m ² / g or more, and usually The range is 10 m ² / g or less, preferably 8.0 m ² / g or less, more preferably 7.0 m ² / g or less. When the value of the BET specific surface area is below the lower limit of this range, the effect of controlling the BET specific surface area of the graphite composite mixed powder (F) decreases, which is not preferable. On the other hand, if the value of the BET specific surface area exceeds the upper limit of this range, the safety is lowered, which is not preferable. The BET specific surface area is measured by the same method as in the case of the above-mentioned graphite (D).

<Volume standard average particle size>
The volume-based average particle diameter of the natural graphite powder (G) is not particularly limited, but is usually 5 μm or more, preferably 10 μm or more, and usually 40 μm or less, preferably 30 μm or less. Below this range, when the graphite composite powder (F) is used, the tap density becomes small. Therefore, it is difficult to increase the packing density of the active material during the production of the electrode, and it is difficult to obtain a high-capacity battery. On the other hand, if it exceeds this range, uneven coating tends to occur when an electrode is produced by coating as a negative electrode material. The volume-based average particle diameter is measured by the same method as in the case of the graphite (D).

<Ratio of graphite composite mixed powder (C) in graphite composite mixed powder (F)>
The ratio of the graphite composite mixed powder (C) in the graphite composite mixed powder (F) is usually 20% by weight or more, preferably 30% by weight or more, more preferably 40% by weight or more, based on the total weight. Usually, it is 90 weight% or less, Preferably it is 80 weight% or less, More preferably, it is the range of 70 weight% or less. If the ratio of the graphite composite mixed powder (C) is below the lower limit of this range, the excellent battery characteristics brought about by the graphite composite mixed powder (C) cannot be exhibited, which is not preferable. On the other hand, if it exceeds the upper limit of this range, the electrode pressability is hardly improved, which is not preferable.

[1-7. Others]
Hereinafter, the graphite composite mixed powder (C) is referred to as “the negative electrode material (I) of the present invention” and the graphite composite mixed powder (F) is referred to as “the negative electrode material (II) of the present invention” as appropriate. Shall. Further, when the graphite composite mixed powder (C) and the graphite composite mixed powder (F) are not particularly distinguished, they are referred to as “the negative electrode material of the present invention”.

<Active material orientation ratio when electrode is formed>
The negative electrode material of the present invention preferably has the following characteristics when a negative electrode for a lithium secondary battery is produced using this as an active material.

That is, a negative electrode material of the present invention as an active material, the electrode density 1.63 ± 0.05g / cm ^3, i.e., the electrodes so that the 1.58 g / cm ³ or more 1.68 g / cm ³ within the following ranges The active material orientation ratio of the electrode is usually 0.07 or more, especially 0.09 or more, more preferably 0.10 or more, and usually 0.20 or less, especially 0.18 or less, and further 0. It is preferable that it is in the range of .16 or less. Below the above range, electrode expansion during battery charging when a battery is produced increases, making it difficult to increase the battery capacity per unit volume of the electrode. On the other hand, if it exceeds the above range, the crystallinity of the active material when the battery is produced becomes low, and it becomes difficult to increase the discharge capacity of the battery or increase the packing density of the electrode after pressing.

Here, the active material orientation ratio of the electrode is an index representing the degree of orientation of the hexagonal network surface of the graphite crystal with respect to the thickness direction of the electrode. A larger orientation ratio represents a state in which the directions of the graphite crystal hexagonal planes of the particles are not aligned.
A specific procedure for measuring the active material orientation ratio of the electrode is as follows.

(1) Formation of electrodes:
A negative electrode material, a CMC (carboxymethylcellulose) aqueous solution as a thickener, and an SBR (styrene butadiene rubber) aqueous solution as a binder resin, with respect to the total weight after drying of the mixture of the negative electrode material, CMC and SBR, Mix and stir so that each SBR is 1% by weight to form a slurry. Next, the slurry is applied onto a copper foil having a thickness of 18 μm using a doctor blade. For the coating thickness, the gap is selected so that the electrode basis weight (excluding the copper foil) after drying is 10 mg / cm ² . After drying this electrode at 80 ° C., pressing is performed so that the electrode density (excluding the copper foil) is 1.63 ± 0.05 g / cm ³ .

(2) Measurement of active material orientation ratio About the electrode after a press, the active material orientation ratio of an electrode is measured by X-ray diffraction. Although a specific method is not particularly limited, as a standard method, a chart of (110) plane and (004) plane of graphite is measured by X-ray diffraction, and an asymmetric Pearson VII is used as a profile function for the measured chart. The peak separation is performed by using the fitting, and the integrated intensity of the peaks on the (110) plane and the (004) plane is calculated. From the obtained integrated intensity, a ratio represented by (110) area intensity / (004) area intensity is calculated and defined as the active material orientation ratio of the electrode.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
-Target: Cu (Kα ray) graphite monochromator-Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree-Measurement range and step angle / measurement time:
(110) plane: 76.5 degrees ≦ 2θ ≦ 78.5 degrees 0.01 degrees / 3 seconds (004) plane: 53.5 degrees ≦ 2θ ≦ 56.0 degrees 0.01 degrees / 3 seconds Sample preparation: Fix the electrode to the glass plate with double-sided tape with a thickness of 0.1 mm For the electrode formed to have an electrode density of 1.63 ± 0.05 g / cm ³ by the above method, the active material orientation ratio by X-ray diffraction is Can be sought.

<Discharge capacity when using a lithium secondary battery>
The negative electrode material of the present invention preferably has the following characteristics when a lithium secondary battery is produced using this as an active material for the negative electrode.
That is, when a negative electrode material of the present invention is used as an active material to form an active material layer on a current collector and used as a negative electrode of a lithium secondary battery, the discharge capacity of the lithium secondary battery is usually 345 mAh / g or more. Especially, it is preferable that it exists in the range of 350 mAh / g or more. When the discharge capacity falls below this range, the battery capacity tends to decrease. 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, an electrode using a negative electrode material is prepared. The 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 a negative electrode material and styrene butadiene rubber (SBR) as a binder resin. The amount of the binder resin is 1% by weight with respect to the weight of the electrode. The electrode density is 1.45 g / cm ³ or more and 1.95 g / cm ³ or less.

Evaluation of the discharge capacity is performed by preparing a bipolar coin cell using metallic lithium as a counter electrode and performing a charge / discharge test on the prepared electrode.
The electrolyte solution of the two-pole coin cell is arbitrary. For example, a mixture in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed so that the volume ratio is DEC / EC = 1/1 to 7/3. A liquid or a mixed liquid in which ethylene carbonate and ethyl methyl carbonate (EMC) are mixed so that EMC / EC = 1/1 to 7/3 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 is performed using the bipolar coin cell thus produced, and the discharge capacity is obtained. 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 is repeated three times, and the discharge value at the third cycle is defined as the discharge capacity.

[2. Method for producing negative electrode material for lithium secondary battery]
[Production Method of Graphite Composite Mixed Powder (C)]
The negative electrode material (I) of the present invention, that is, the graphite composite mixed powder (C), is a graphite composite in which the graphite (D) and the graphite (E) having a different orientation from the graphite (D) are combined. The powder (A) and the artificial graphite powder (B) are contained, but this graphite composite mixed powder (C) is different from the conventional composite graphite powder production, and the following materials and production conditions: Can be obtained by selection.

  That is, as the graphite (D), selecting a material having the aspect ratio defined above, a pitch raw material that is a precursor of the graphite (E), or a heat-treated and pulverized pitch raw material, Mixing and heat treatment can be mentioned.

The reason why the graphite composite mixed powder (C) is obtained by selecting the above materials and production conditions is considered as follows.
That is, by using the graphite (D) having an aspect ratio in the range of 1.2 or more and 4.0 or less, the obtained graphite composite powder (A) also has a specified aspect ratio. Further, in the graphite composite powder (A) particles, the graphite (D) is coated or bound to the graphite (E) having different orientation and is bonded in a random orientation direction.

  Specifically, the graphite composite mixed powder (C) can be obtained by the following two production methods and the like.

(Manufacturing method 1)
A pulverized graphite crystal precursor obtained by pitch heat-treating a pitch raw material having a quinoline insoluble content of 3.0% by weight or less, an aspect ratio of 1.2 to 4.0, and a tap density of 0.7 g / cm. ^{3 and not} less than 1.35 g / cm ³ of graphite (D) are mixed and subjected to heat treatment A, then pulverized and heat treatment B is performed.

  That is, a graphite crystal precursor, which is a raw material for graphite (E) and artificial graphite powder (B), and graphite (D) are mixed at a predetermined ratio, subjected to heat treatment A, pulverized, and further heat treated. By performing B (firing and graphitization), a graphite composite mixed powder (C) is produced.

  In addition, it is preferable to use a graphite crystal precursor having a volatile content of usually 5% by weight or more and 20% by weight or less. By using a graphite crystal precursor having a volatile content within this range, the graphite (D) and the graphite (E) are composited by the heat treatment A, so that the graphite composite having the physical properties specified above. A mixed powder (C) can be obtained. Moreover, the active material orientation ratio of the negative electrode formed with the graphite composite mixed powder (C) as an active material also satisfies the above range, which is preferable.

(Manufacturing method 2)
A pitch raw material having a quinoline insoluble content of 3% by weight or less, and a graphite having an aspect ratio of 1.2 or more and 4.0 or less and a tap density of 0.7 g / cm ³ or more and 1.35 g / cm ³ or less. From the quality (D), a graphite composite powder (A) is produced. Separately, artificial graphite powder (B) is produced from a graphite crystal precursor in the same manner as in production method 1. A graphite composite mixed powder (C) is prepared by mixing the graphite composite powder (A) thus obtained and the artificial graphite powder (B) independently.

In particular, a graphite composite obtained by using a pitch raw material that is liquefied by heat treatment or a solvent and having a graphite (E) content of 3% by weight to 70% by weight with respect to the graphite composite powder (A). By mixing powder (A) and artificial graphite powder (B) obtained from a graphite precursor separately from this, graphite composite mixed powder (C) having the physical properties specified above is obtained. Can do.
Hereinafter, the production method 1 and the production method 2 will be described in detail.

[2-1. Manufacturing method 1]
First, the manufacturing method 1 is demonstrated.
First, a method for producing a bulk mesophase (preliminarily heat-treated graphite crystal precursor, hereinafter referred to as “heat-treated graphite crystal precursor” as appropriate), which is a precursor of graphite crystal, is preliminarily treated with heat.

<Starting material>
Pitch raw materials are used as starting materials for the graphite (E) and the artificial graphite powder (B) contained in the graphite composite mixed powder (C) of the present invention. In the present specification, the “pitch raw material” refers to a pitch and the same, and can be graphitized by performing an appropriate treatment. As a specific example of pitch raw material, tar, heavy oil, pitch, or the like can be used. 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 is preferable because of its high aromaticity. Any one of these pitch raw materials may be used alone, or two or more thereof may be used in any combination and ratio.

Further, the content of the quinoline insoluble component in the pitch raw material is not particularly limited, but is usually 3.0% by weight or less, preferably 1.0% by weight or less, more preferably 0.02% by weight or less. Use one that is in range. Quinoline-insoluble matter is submicron carbon particles or ultrafine sludge contained in trace amounts in coal tar. If this amount is too large, crystallinity improvement during graphitization will be significantly inhibited, and discharge after graphitization will occur. It causes a significant decrease in capacity. In addition, as a measuring method of a quinoline insoluble matter, the method prescribed | regulated to JISK2425, for example can be used.
In addition to the above pitch raw materials, various thermosetting resins and thermoplastic resins may be used in combination as long as the effects of the present invention are not hindered.

<Production of heat-treated graphite crystal precursor>
The pitch raw material selected from the above is preheated to obtain a heat treated graphite crystal precursor. This prior heat treatment is referred to as pitch heat treatment. After this heat treated graphite crystal precursor is pulverized, mixed with graphite (D), and then heat treated A, part or all of it melts, but here the volatile content is adjusted by prior heat treatment. By setting, the molten state can be appropriately 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 pitch heat treatment is not particularly limited, but is usually in the range of 300 ° C. or higher, preferably 450 ° C. or higher, and usually 550 ° C. or lower, preferably 510 ° C. or lower. If the temperature of the heat treatment is below this range, the amount of volatile components increases, making it difficult to pulverize safely in the air. On the other hand, if the temperature exceeds the upper limit, part or all of the heat treated graphite crystal precursor does not melt during heat treatment A. It is difficult to obtain composite particles of graphite (D) and heat-treated graphite crystal precursor (graphite composite powder (A)).

The time for performing the pitch heat treatment is not particularly limited, but is usually 1 hour or longer, preferably 10 hours or longer, and usually 48 hours or shorter, preferably 24 hours or shorter. If the heat treatment time is less than this range, it becomes a non-uniform heat treated graphite crystal precursor, which is not preferable for production. On the other hand, if it exceeds the upper limit, the productivity is poor and the processing cost is high, which is also not preferable.
Note that the heat treatment may be performed in a plurality of times as long as the temperature and cumulative time of the heat treatment are within the above ranges.

When the pitch heat treatment is performed, it is performed in an inert gas atmosphere such as nitrogen gas or in a volatile matter atmosphere generated from the pitch raw material.
Although there is no restriction | limiting in particular as an apparatus used for pitch heat processing, For example, reaction tanks, such as a shuttle furnace, a tunnel furnace, an electric furnace, an autoclave, a coker (heat processing tank of coke manufacture), etc. can be used.
During the pitch heat treatment, stirring may be performed as necessary.

<Volatile content of heat treated graphite crystal precursor>
The volatile content of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited, but is usually 5% by weight or more, preferably 6% by weight or more, and usually 20% by weight or less, preferably 15% by weight or less. If the volatile content is below the above range, the volatile content is large, so that it is difficult to pulverize safely in the atmosphere. On the other hand, if the volatile content exceeds the upper limit, part or all of the graphite crystal precursor does not melt during heat treatment A, It is difficult to obtain composite particles (graphite composite powder (A)) of (D) and heat-treated graphite crystal precursor. In addition, as a measuring method of a volatile matter, the method prescribed | regulated to JISM8812 can be used, for example.

<Softening point of heat-treated graphite crystal precursor>
The softening point of the graphite crystal precursor obtained by pitch heat treatment is not particularly limited, but is usually 250 ° C. or higher, preferably 300 ° C. or higher, more preferably 370 ° C. or higher, and usually 470 ° C. or lower, preferably 450 ° C. or lower. More preferably, it is set as the range of 430 degrees C or less. Below the lower limit, the carbonization yield of the graphite crystal precursor after the heat treatment is low and it is difficult to obtain a uniform mixture with the graphite (D), and when above the upper limit, part of the graphite crystal precursor during heat treatment A or All of them are not melted, and it is difficult to obtain composite particles (graphite composite powder (A)) of graphite (D) and heat-treated graphite crystal precursor. As a softening point, a sample molded to a thickness of 1 mm by a tablet molding machine was used, using a thermomechanical analyzer (for example, TMA4000 manufactured by Bruker AEX Co., Ltd.), under a nitrogen flow, a heating rate of 10 ° C./min. A value measured by the penetration method can be used under the conditions of a needle tip shape of 1 mmφ and a load of 20 gf.

<Pulverization of heat treated graphite crystal precursor>
Next, the graphite crystal precursor obtained by the pitch heat treatment is pulverized. In order to refine the graphite crystal precursor crystals that are aligned in the same direction in large units by heat treatment and / or to make the mixing (mixing) of graphite (D) and heat treated graphite crystal precursor uniform. It is.

  The pulverization of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited, but the particle size of the graphite crystal precursor after pulverization is usually 1 μm or more, preferably 5 μm or more, and usually 10 mm or less, preferably 5 mm or less. It is preferably performed so that the thickness is 500 μm or less, more preferably 200 μm or less, and particularly preferably 50 μm or less. If 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, inhibiting the improvement of crystallinity during the graphitization process, and reducing the discharge capacity after graphitization. There is a risk of inviting. On the other hand, when the particle size exceeds 10 mm, the effect of refining by pulverization is reduced and the crystals are easily oriented, and the graphite (E) and / or the artificial graphite powder (B) is easily oriented, and the graphite composite mixed powder ( The active material orientation ratio of the electrode using C) becomes low, and it becomes difficult to suppress electrode expansion during battery charging. And / or, since the particle size difference between the graphite (D) and the heat-treated graphite crystal precursor is large, uniform mixing is difficult, and the composite is likely to be non-uniform.

  There are no particular restrictions on the apparatus used for pulverization, but examples include a coarse pulverizer such as a shearing mill, jaw crusher, impact crusher, and cone crusher, and an intermediate pulverizer includes a roll crusher and a hammer mill. Examples of the fine pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

<Method for Producing Graphite Composite Mixed Powder (C)>
By mixing graphite (D) and heat treated graphite crystal precursor (raw material of graphite (E) and artificial graphite powder (B)) at a predetermined ratio, heat treatment A, pulverization, heat treatment B (firing, graphitization) A graphite composite mixed powder (C) is prepared.

<Mixing ratio of graphite (D) and heat-treated graphite crystal precursor>
The mixing ratio of the graphite (D) and the heat-treated graphite crystal precursor performed before the heat treatment A is not particularly limited, but the ratio of the graphite (D) to the mixture is usually 20% by weight or more, preferably 30% by weight or more. More preferably, it is 40% by weight or more, usually 80% by weight or less, preferably 70% by weight or less. Below the lower limit, the ratio of the graphite (E) and / or artificial graphite powder (B) in the graphite composite mixed powder (C) increases, so that it is difficult to increase the packing density when an electrode is used, and an excessive press load is applied. It is difficult to obtain the required effect of combining graphite (D). Exceeding the upper limit may increase the exposure of the graphite (D) surface in the graphite composite powder (A) and increase the specific surface area of the graphite composite mixed powder (C), which is not preferable in terms of powder properties. .

<Mixed>
There are no particular restrictions on the apparatus used when mixing the graphite (D) and the heat-treated graphite crystal precursor adjusted to a predetermined particle size. For example, a V-type mixer, a W-type mixer, a container variable type mixer, A kneader, a drum mixer, a shear mixer, etc. are mentioned.

<Heat treatment A>
Next, heat treatment A is applied to the mixture of the graphite (D) and the heat treated graphite crystal precursor. This is because, by remelting or fusing the pulverized heat-treated graphite crystal precursor, the graphite (D) and the refined heat-treated graphite crystal precursor particles are fixed in contact in a non-oriented state. Thereby, the mixture of the graphite (D) and the heat-treated graphite crystal precursor is not a simple particle mixture but a more uniform composite mixture (hereinafter referred to as “graphite composite mixture” as appropriate).

  The temperature condition of the heat treatment A is not particularly limited, but is usually 300 ° C. or higher, preferably 400 ° C. or higher, more preferably 450 ° C. or higher, and usually 650 ° C. or lower, preferably 600 ° C. or lower. If the temperature of the heat treatment A is lower than the above range, a large amount of volatile components remain in the material after the heat treatment A, so that there is a possibility that the powders will be fused together during the firing or graphitization process, It is necessary and not preferable. On the other hand, if it exceeds the above range, the remelted component may be broken into needles at the time of pulverization, leading to a decrease in tap density, which is not preferable.

  The time for performing the heat treatment A is not particularly limited, but is usually 5 minutes or more, preferably 20 minutes or more, and usually 3 hours or less, preferably 2 hours. If the time during which the heat treatment A is performed is less than the above range, the volatile matter becomes non-uniform, causing fusion during firing or graphitization, which is not preferable, and exceeding it is also not preferable because the productivity is low and the processing cost increases.

The heat treatment A is performed in an inert gas atmosphere such as nitrogen gas or in a volatile matter atmosphere generated from a heat treated graphite crystal precursor refined by pulverization.
Although there is no restriction | limiting in particular in the apparatus used for the heat processing A, For example, a shuttle furnace, a tunnel furnace, an electric furnace etc. can be used.

<Pulverization of heat treated graphite crystal precursor and alternative treatment for heat treatment A>
By the way, as an alternative to the pulverization and heat treatment A described above, a heat treatment graphite crystal precursor can be refined and non-oriented, for example, a temperature at which the heat treated graphite crystal precursor is melted or softened. It is possible to mix with graphite (D) and perform heat treatment while performing a process of applying mechanical energy in the region.

  The heat treatment as this alternative treatment is not particularly limited, but is usually performed at 200 ° C. or higher, preferably 250 ° C. or higher, and usually 450 ° C. or lower, preferably 400 ° C. or lower. If the temperature condition falls below the above range, the graphite crystal precursor during the alternative treatment is not sufficiently melted and softened, and it becomes difficult to make a composite with the graphite (D). Moreover, when it exceeds, heat processing will advance rapidly, and particles, such as artificial graphite powder (B), will break into a needle shape at the time of a grinding | pulverization, and it will be easy to cause the fall of a tap density.

  The treatment time is not particularly limited, but is usually 30 minutes or longer, preferably 1 hour or longer, and usually 24 hours or shorter, preferably 10 hours or shorter. If the treatment time is less than the above range, the graphite crystal precursor subjected to the substitution treatment becomes non-uniform, which is not preferable in production. Moreover, when it exceeds, productivity will worsen and processing cost will become high and is unpreferable.

This alternative treatment is usually performed in an inert atmosphere such as nitrogen gas or an oxidizing atmosphere such as air. However, when the treatment is performed in an oxidizing atmosphere, it may be difficult to obtain high crystallinity after graphitization. Therefore, it is necessary to prevent the infusibilization with oxygen from proceeding excessively. Specifically, the oxygen amount in the graphite crystal precursor after the alternative treatment is usually 8% by weight or less, preferably 5% by weight or less.
Moreover, there is no restriction | limiting in particular as an apparatus used for an alternative process, For example, a mixer, a kneader, etc. can be used.

<Crushing>
Next, the graphite composite mixture subjected to the heat treatment A is pulverized. This is because the mass of the graphite composite mixture that has been composited with the graphite (D) by the heat treatment A and melted or fused in a state in which the structure has been refined and non-oriented is pulverized to the target particle size.

  The particle size of the graphite composite mixture after pulverization is not particularly limited, but is usually 6 μm or more, preferably 9 μm or more, and usually 65 μm or less, preferably 35 μm or less. If the particle size is less than the above range, the tap density of the graphite composite negative electrode material C becomes small. Therefore, when the electrode is used, it is difficult to increase the packing density of the active material and it is difficult to obtain a high-capacity battery. On the other hand, when the above range is exceeded, uneven coating tends to occur when an electrode is produced by coating as the graphite composite negative electrode material C, which is not preferable.

  There are no particular restrictions on the apparatus used for pulverization. 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 thereof include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

<Heat treatment B: Firing>
Heat treatment B refers to firing and graphitization. Hereinafter, the firing will be described. However, the firing can be omitted.
The graphite composite mixture pulverized by pulverization is fired. This is because the volatile matter of the graphite composite mixture is removed by firing in order to suppress the fusion of the graphite composite mixture during graphitization.

The temperature condition for performing the baking is not particularly limited, but is usually 600 ° C. or higher, preferably 1000 ° C. or higher, and usually 2400 ° C. or lower, preferably 1300 ° C. or lower. If the temperature condition is below the above range, the graphite composite mixture is liable to cause powder fusion during graphitization, which is not preferable. On the other hand, if it exceeds the above range, the firing equipment is expensive, which is not preferable.
The holding time for keeping the temperature condition in the above range when firing is not particularly limited, but is usually 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 the re-pulverized graphite composite mixture. In addition, for simplification of the manufacturing process, it is possible to directly graphitize without incorporating a firing 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.

<Heat treatment B: Graphitization>
Next, graphitization is performed on the fired graphite composite mixture. This is to improve the crystallinity in order to increase the discharge capacity in battery evaluation. Graphitized composite powder (C) (the negative electrode material (I) of the present invention) can be obtained.

  The temperature condition for graphitization is not particularly limited, but is usually 2800 ° C. or higher, preferably 3000 ° C. or higher, and usually 3200 ° C. or lower, preferably 3100 ° C. or lower. If it exceeds the above range, the reversible capacity of the battery may be reduced, and it is difficult to make a high capacity battery. Moreover, if it exceeds the above range, the amount of graphite sublimation tends to increase, which is not preferable.

The holding time during graphitization is not particularly limited, but is usually longer than 0 minutes and not longer than 24 hours.
The graphitization is performed in an inert gas atmosphere such as argon gas, or in a non-oxidizing atmosphere with a gas generated from the calcined graphite composite mixture.

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.
Note that graphite such as Si or B is formed in or on the surface of the material (graphite (D), pitch raw material or graphite crystal precursor) during the graphitization treatment or in the previous steps, that is, the steps from heat treatment to firing. A crystallization catalyst may be added.

[Production Method 2]
Next, manufacturing method 2 will be described.

<Method for Producing Graphite Composite Powder (A)>
The above-mentioned pitch raw material and graphite (D) are mixed at an arbitrary ratio, and heat treatment B is performed to produce a graphite composite powder (A).

<Method for producing artificial graphite powder (B)>
The pitch raw material is subjected to pitch heat treatment in the same manner as in production method 1 to obtain a graphite crystal precursor. The graphite crystal precursor may be powdered by performing the above-described medium pulverizer and fine pulverization step.
Further, the graphite crystal precursor is pulverized and subjected to heat treatments A and B to produce artificial graphite powder (B). However, pulverization and heat treatment can be performed in any order, and heat treatment A may be omitted.

<Mixed>
The graphite composite powder (A) and the artificial graphite powder (B) are mixed using any apparatus used in the “mixing” of the production method 1.
The ratio of the graphite composite powder (A) to the artificial graphite powder (B) is usually a value of the weight ratio of the artificial graphite powder (B) to the total amount of the graphite composite powder (A) and the artificial graphite powder (B). It is 2% by weight or more, preferably 10% by weight or more, more preferably 14% by weight or more, and usually 65% by weight or less, preferably 50% by weight or less, more preferably 45% by weight or less. If it falls below this range, the proportion of the artificial graphite powder (B) increases, so that it is difficult to increase the packing density when it is used as an electrode, and an excessive press load is required and it is difficult to obtain the advantage of mixing the artificial graphite powder (B). On the other hand, if it exceeds this range, the ratio of the graphite composite powder (A) is too large, and the electrode coatability may be impaired.

<Other processing>
In addition, various processes such as a classification process can be performed in addition to the above processes as long as the effects of the invention are not hindered. The classification treatment is for removing coarse powder and fine powder so that the particle size after graphitization treatment becomes a 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.
The classification treatment may be performed immediately after the pulverization after the heat treatment A, or may be performed at other timing, for example, after the calcination after the pulverization, or after the graphitization. Furthermore, the classification process itself can be omitted. However, from the viewpoint of reducing the BET specific surface area of the graphite composite mixed powder (C) and the productivity, it is preferable to perform the classification treatment immediately after the pulverization after the heat treatment A.

[Processing after production of graphite composite mixed powder (C)]
For the graphite composite mixed powder (C) produced by the above procedure, it was produced separately for the purpose of controlling the BET specific surface area of the negative electrode material, improving the electrode pressability, improving the discharge capacity, and reducing the cost. Artificial graphite powder or natural graphite powder may be added and mixed. When the artificial graphite powder is added, this can be regarded as a part of the artificial graphite powder (B) which is a component of the graphite composite mixed powder (C). On the other hand, when natural graphite powder is added, this functions as the above-mentioned natural graphite powder (G), and the mixed powder as a whole functions as the above-mentioned graphite composite mixed powder (F).

[3. Negative electrode for lithium secondary battery]
By forming an active material layer containing the 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. In addition to the negative electrode material of the present invention, other active materials can be used in combination.

The density of the negative electrode layer is usually 1.45 g / cm ³ or more, preferably 1.55 g / cm ³ or more, and more preferably 1.6 g / cm ³ or more, because the battery capacity 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 use 2 or more types together by arbitrary combinations and 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 use 2 or more types together by arbitrary combinations and 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 use 2 or more types together by arbitrary combinations and ratios.

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

[4. Lithium secondary battery]
The negative electrode material of the present invention is useful as a material for battery electrodes. In particular, it is extremely useful to use the negative electrode material of the present invention described above for a negative electrode in a non-aqueous secondary battery such as a positive and negative electrodes capable of inserting and extracting lithium ions, and a lithium secondary battery including an electrolyte. is there. For example, a negative electrode is produced using the negative electrode material of the present invention, and a non-aqueous secondary material constituted by combining 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. The battery has a large capacity, a small irreversible capacity observed in the initial cycle, a high rapid charge / discharge capacity, excellent cycle characteristics, high battery storage and reliability when left at high temperatures, and high efficiency discharge characteristics. In addition, it has excellent 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. Below, the material of the member which comprises the lithium secondary battery using the negative electrode material of this invention is illustrated, However, The material which can be used is 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 IIIb, Group IVa, and Group Va in the short-period periodic table, 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 kind of solute and solvent may be selected and used, or two or more kinds may be mixed and used. Among these, the non-aqueous solvent preferably contains a cyclic carbonate and a chain carbonate.

  Further, the non-aqueous electrolyte solution may include an organic polymer compound in the electrolyte solution, and may be a gel-like, rubber-like, or solid sheet-like 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 manufacturing a lithium secondary battery is to place a negative electrode on an outer can, provide an electrolyte and a separator on the can, and further place a 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.

[Estimated reason why the negative electrode material of the present invention becomes an active material exhibiting excellent battery performance]
Reasons for obtaining a battery having a high discharge capacity, high charge / discharge efficiency, excellent load characteristics, and low electrode expansion during charging when the negative electrode material of the present invention is used as a negative electrode active material at a high electrode density Is not necessarily clear, but is estimated as follows.

  The negative electrode material (I) of the present invention, that is, the graphite composite mixed powder (C) has high crystallinity, and has a graphite (D) having an aspect ratio in the above specified range. Excellent characteristics. Moreover, the increase in a specific surface area is suppressed by having graphite (E) from which this graphite (D) and orientation differ, and charge / discharge efficiency is high. Furthermore, since these graphite (D) and graphite (E) are compounded, the active material orientation ratio is high and the expansion is small.

  In addition, the negative electrode material (II) of the present invention, that is, the graphite composite mixed powder (F), in addition to the above-mentioned graphite composite mixed powder (C), further includes a natural graphite powder (G). It is preferable because it enables more precise control of powder physical properties and is excellent in load characteristics and cycle life.

Here, in particular, the advantages of the present invention will be considered in comparison with the technique described in Patent Document 3.
In the composite graphite material described in Patent Document 3, since the outer surface graphite layer (C) is integrated with the graphite coating material (B), the thickness of the outer surface graphite layer (C) is reduced. There is a problem that it is difficult to control and it is difficult to exert stable battery characteristics. In addition, since it is composed only of a spherical dense hard material, there is a problem that it is difficult to increase the filling rate of the negative electrode material in the electrode, and it is difficult to achieve a higher electrode density. In addition, from the viewpoint of industrial production, there is a problem that the manufacturing process is complicated and the cost is high. Further, it is described that the low crystalline surface layer (C) is coated without peeling from the core material, and that the BET specific surface area is preferably 1 m ² / g or less, but the BET specific surface area is reduced. Lithium acceptance at the time of charging deteriorated, and the charging capacity was insufficient.

  On the other hand, in the present invention, since the artificial graphite powder (B) is present in the spherical, ellipsoidal, and massive graphite composite powder (A), it is easy to increase the filling rate of the negative electrode material in the electrode, and the electrode density is higher. It is possible to control the BET specific surface area by changing the combination of the graphite composite powder (A) having a high BET specific surface area and the artificial graphite powder (B) having a low BET specific surface area. Become.

  EXAMPLES Examples of the present invention will be described below. However, the present invention is not limited to the following examples, and can be implemented with arbitrary modifications without departing from the gist thereof.

[Example 1]
A coal tar pitch having a quinoline insoluble content of 0.05% by weight or less was heat-treated in a reaction furnace at 460 ° C. for 10 hours to obtain a meltable massive heat-treated graphite crystal precursor having a softening point of 385 ° C. In addition, the value measured by the above-mentioned method was used for the value of the softening point.
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 fine pulverizer (Tsubo Mill manufactured by Matsubo Co., Ltd.) to give a median diameter of 17 μm. A refined graphite crystal precursor powder was obtained. In addition, the value measured by the method described above was used as the median diameter value.

Natural graphite having a median diameter of 17 μm, an aspect ratio of 1.9, and a tap density of 1.0 g / cm ³ is added to the above-mentioned fine graphite crystal precursor powder with respect to the total weight of the fine graphite crystal precursor powder and natural graphite. 50% by weight was mixed to obtain a mixed powder of graphite (D) and heat-treated graphite crystal precursor. In addition, the value measured by the method described above was used as the value of the aspect ratio.

The mixed powder of the heat treated graphite crystal precursor was packed in a metal container, and heat treatment A was performed in a box-shaped electric furnace at 540 ° C. for 2 hours under a nitrogen gas flow. During the heat treatment A, the refined graphite crystal precursor powder melted and became a lump of a mixture of the heat treated graphite crystal precursor uniformly compounded with natural graphite.
The mass of the solidified graphite crystal precursor mixture thus solidified is pulverized with a crusher (Roll jaw crusher manufactured by Yoshida Seisakusho), and further pulverized with a fine pulverizer (Turbo Mill manufactured by Matsubo) to obtain a powder having a median diameter of 18.5 μm. Obtained.

The obtained powder was put into a container and baked in an electric furnace at 1000 ° C. for 1 hour in a nitrogen atmosphere. After firing, it was in the form of a powder, and almost no melting or fusion was observed.
Further, the calcined powder was transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours under an inert atmosphere using a direct electric furnace to obtain a graphite composite mixed powder (C) (negative electrode material of Example 1). Obtained.

When the physical properties of the obtained negative electrode material of Example 1 were measured, the median diameter was 17.5 μm, the tap density was 1.2 g / cm ³ , and the BET specific surface area was 2.3 m ² / g.

  Further, according to the procedure described above, the negative electrode of Example 1 was obtained by taking a cross-sectional photograph of the graphite composite mixed powder (C) using a polarizing microscope and selecting the graphite composite powder (A) having different orientation. The graphite composite powder (A) in the material was specified. As a result, the proportion of the graphite composite powder (A) contained in the negative electrode material (graphite composite mixed powder (C)) of Example 1 was 55% by weight, and the proportion of the artificial graphite powder (B) was 45% by weight. It was.

  Furthermore, when the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured, the graphite composite powder (A) had a median diameter of 19.5 μm and an aspect ratio of 1.2. The artificial graphite powder (B) had a median diameter of 8.5 μm.

The measured crystallinity of the negative electrode material of Example 1 by X-ray diffraction method, it was _{d 002 = 0.3357nm, Lc 004>} 1000Å (100nm).

Furthermore, using the negative electrode material of Example 1, an electrode having an electrode density of 1.63 ± 0.05 g / cm ³ was prepared according to the following method, and the active material orientation ratio of the electrode was determined to be 0.17. It was.

Moreover, using the negative electrode material of Example 1, a lithium secondary battery was produced according to the following method, and the discharge capacity, charge / discharge efficiency, and load characteristics were measured. Similarly, a lithium secondary battery was prepared, disassembled in a charged state, and the thickness of the electrode was measured to measure the charge expansion coefficient.
The evaluation results of the physical properties of the negative electrode material of Example 1 are shown in Tables 1 to 3.

<Electrode production method>
A negative electrode material, a CMC aqueous solution as a thickener, and an SBR aqueous solution as a binder resin were mixed and stirred so that CMC and SBR were 1% by weight with respect to the dried negative electrode material, respectively. This slurry was applied onto a copper foil. 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 .

The electrode was dried at 80 ° C. and then pressed so that the electrode density (excluding copper foil) was 1.73 ± 0.05 g / cm ³ . A 12 mmφ electrode was punched from the pressed electrode, and the weight of the negative electrode active material (electrode weight−copper foil weight−binder resin weight) was determined from the weight.

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

<Measurement method of discharge capacity>
The lithium counter electrode is charged to 5 mV at a current density of 0.2 mA / cm ² , further charged to a current value of 0.02 mA at a constant voltage of 5 mV, and the negative electrode is doped with lithium. A charge / discharge cycle of discharging to 1.5 V with respect to the lithium counter electrode at a current density of 4 mA / cm ² was repeated three times, and the discharge value at the third cycle was measured as the discharge capacity.

<Calculation method of charge / discharge efficiency>
Calculated according to:
-Electrode density 1.73 ± 0.05 g / cm ³
Charge / discharge efficiency (%) = {initial discharge capacity (mAh / g) / initial charge capacity (mAh / g)} × 100

<Measurement method of charge expansion coefficient>
In the measurement of the discharge capacity, after 3 cycles of charge and discharge, the charge termination condition of the 4th cycle was performed with a constant capacity charge of 300 mAh / g. The charged coin battery was disassembled so as not to be short-circuited in the argon glove box, the electrode was taken out, and the thickness of the electrode during charging (excluding the copper foil) was measured. Based on the following formula, the charge expansion coefficient was determined based on the thickness of the press electrode (excluding the copper foil) before battery preparation.
{(Charge electrode thickness−Press electrode thickness) / Press electrode thickness} × 100 = Charge expansion coefficient (%)

<Calculation method of load characteristics>
-Electrode density 1.73 ± 0.05 g / cm ³
· 2C discharge capacity (mAh / g): 7.0mA / cm 2 current density at discharge discharge capacity · 0.2 C discharge capacity when the (mAh / g): was discharged at a current density of 0.7 mA / cm ² Discharge capacity / load characteristics (%) = {2C discharge capacity (mAh / g) /0.2C discharge capacity (mAh / g)} × 100

[Example 2]
The massive graphite crystal precursor mixture obtained in the same procedure as in Example 1 was pulverized with a coarse crusher (roll jaw crusher manufactured by Yoshida Seisakusho), and then pulverized using a pulverizer (Dalton hammer mill). A refined graphite crystal precursor powder having a median diameter of 21.0 μm, which was sieved using a sieve having an opening of 45 μm, was obtained. Thereafter, the treatment after the baking treatment was performed in the same procedure as in Example 1 to obtain a graphite composite mixed powder (C) (negative electrode material of Example 2).

The physical properties of the negative electrode material obtained in Example 2 were measured in the same manner as in Example 1. The median diameter was 20.0 μm, the tap density was 1.20 g / cm ³ , and the BET specific surface area was 1.8 m ² / g. It was. Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, d ₀₀₂ = 0.3357 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Example 2 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 60% by weight, and the artificial graphite powder (B) was 40% by weight. Furthermore, the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured. The graphite composite powder (A) had a median diameter of 22.3 μm and an aspect ratio of 1.8. The artificial graphite powder (B) had a median diameter of 7.1 μm.

  About the negative electrode material of Example 2, the polarization microscope photograph (magnification 1500 times) of the graphite composite powder (A) portion in the particle cross section of the graphite composite mixed powder (C) after the graphitization step is shown in FIG. ). Moreover, the schematic diagram showing the shape of the graphite (D) and the graphite (E) in the particle | grain cross section of Fig.1 (a) is shown in FIG.1 (b). However, this photograph is for explaining “different orientation”, and the particles of the graphite composite mixed powder (C) of Example 2 are not limited thereto. The portion corresponding to the graphite (D) on the center side of the particles spreads over a wide area of the same color. On the other hand, the portion corresponding to the outer graphite (E) has a plurality of small regions of anisotropic units of various colors, and the graphite (D) is an anisotropic unit of an optically anisotropic structure. The pattern is different.

Moreover, when the negative electrode material of Example 2 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.15.
Furthermore, using the negative electrode material of Example 2, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 2 are shown in Tables 1 to 3.

[Example 3]
In the method for producing the negative electrode material of Example 2, the amount of natural graphite (median diameter 17.0 μm, aspect ratio 1.9, tap density 1.0 g / cm ³ ) mixed with the refined graphite crystal precursor powder was reduced. The graphite composite mixed powder (C) (the negative electrode material of Example 3) was processed in the same procedure as in Example 2 except that the total weight of the graphite oxide crystal precursor powder and natural graphite was 30% by weight. )

The physical properties of the negative electrode material obtained in Example 3 were measured in the same manner as in Example 1. The median diameter was 17.5 μm, the tap density was 1.16 g / cm ³ , and the BET specific surface area was 2.5 m ² / g. It was. Further, when the crystallinity was measured by X-ray diffractometry in the same manner as in Example 1, d ₀₀₂ = 0.3356 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Example 3 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 73% by weight, and the artificial graphite powder (B) was 27% by weight. Furthermore, when the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured, the graphite composite powder (A) had a median diameter of 19.5 μm and an aspect ratio of 1.8. The artificial graphite powder (B) had a median diameter of 5.2 μm.

Moreover, when the negative electrode material of Example 3 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.10.
Furthermore, using the negative electrode material of Example 3, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 3 are shown in Tables 1 to 3.

[Example 4]
In the method for producing the negative electrode material of Example 2, natural graphite having a median diameter of 21.0 μm, an aspect ratio of 2.4, and a tap density of 0.9 g / cm ³ was used as the natural graphite mixed with the refined graphite crystal precursor powder. Was mixed in the same procedure as in Example 2 except that 50% by weight was mixed with respect to the total weight of the refined graphite crystal precursor powder and natural graphite, and the graphite composite mixed powder (C) (of Example 4) Negative electrode material) was obtained.

The physical properties of the negative electrode material obtained in Example 4 were measured in the same manner as in Example 1. The median diameter was 22.0 μm, the tap density was 1.10 g / cm ³ , and the BET specific surface area was 1.7 m ² / g. It was. Further, when the crystallinity was measured by X-ray diffractometry in the same manner as in Example 1, d ₀₀₂ = 0.3356 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Example 4 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 58% by weight, and the artificial graphite powder (B) was 42% by weight. Furthermore, the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured. The graphite composite powder (A) had a median diameter of 23.0 μm and an aspect ratio of 2.9. The artificial graphite powder (B) had a median diameter of 10.2 μm.

Moreover, when the negative electrode material of Example 4 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.08.
Furthermore, using the negative electrode material of Example 4, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 4 are shown in Tables 1 to 3.

[Example 5]
Except that a material pitch having a softening point of 430 ° C. was used, the same procedure as in Example 2 was used to obtain a graphite composite mixed powder (C) (negative electrode material of Example 5).

The physical properties of the negative electrode material obtained in Example 5 were measured in the same manner as in Example 1. The median diameter was 18.0 μm, the tap density was 1.16 g / cm ³ , and the BET specific surface area was 2.4 m ² / g. It was. Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, d ₀₀₂ = 0.3357 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Example 5 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 53% by weight, and the artificial graphite powder (B) was 47% by weight. Furthermore, when the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured, the graphite composite powder (A) had a median diameter of 19.8 μm and an aspect ratio of 1.4. The artificial graphite powder (B) had a median diameter of 7.9 μm.

Moreover, when the negative electrode material of Example 5 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.10.
Furthermore, using the negative electrode material of Example 5, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 5 are shown in Tables 1 to 3.

[Example 6]
In the method for producing the negative electrode material of Example 2, Example 2 was performed except that the ground heat-treated graphite crystal precursor was not pulverized and natural graphite was mixed with the graphite crystal precursor having a median diameter of 60 μm. The same procedure was followed to obtain a graphite composite mixed powder (C) (negative electrode material of Example 6).

The physical properties of the negative electrode material obtained in Example 6 were measured in the same manner as in Example 1. The median diameter was 18.0 μm, the tap density was 1.22 g / cm ³ , and the BET specific surface area was 1.9 m ² / g. It was. Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, d ₀₀₂ = 0.3357 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Example 6 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 52% by weight, and the artificial graphite powder (B) was 48% by weight. Furthermore, the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured. The graphite composite powder (A) had a median diameter of 19.3 μm and an aspect ratio of 2.1. The artificial graphite powder (B) had a median diameter of 7.0 μm.

Moreover, when the negative electrode material of Example 6 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.09.
Furthermore, using the negative electrode material of Example 6, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 6 are shown in Tables 1 to 3.

[Example 7]
Example 7 was manufactured by manufacturing method 2.
Natural graphite (median diameter 17.0 μm, aspect ratio 1.9, tap density 1.0 g / cm ³ ) powder 23% by weight used in Example 1 and 77% by weight petroleum heavy oil were mixed, and 1000 ° C. The powder fired in step 1 was placed in a graphite crucible and graphitized at 3000 ° C. for 5 hours using a direct electric furnace to obtain a graphite composite powder (A). When the physical properties of the obtained graphite composite powder (A) were measured, the median diameter was 18.5 μm, the aspect ratio was 2.3, and the tap density was 1.1 g / cm ³ .

  Further, a coal tar pitch having a quinoline insoluble content of 0.05% by weight or less similar to that in Example 1 was heat-treated at 460 ° C. for 10 hours in a reaction furnace, and a meltable bulk heat-treated graphite crystal precursor (bulk mesophase ) The obtained massive heat-treated graphite crystal precursor was pulverized using an intermediate pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.) and further pulverized using a fine pulverizer (Tsubo Mill manufactured by Matsubo). A refined graphite crystal precursor powder having a median diameter of 17.0 μm was obtained.

This graphite crystal precursor powder was packed in a metal container and reheated at 540 ° C. for 2 hours in a box-shaped electric furnace under nitrogen gas flow. During reheating, the refined graphite crystal precursor powder became a mass of melted and solidified graphite crystal precursor (bulk mesophase).
The solidified graphite crystal precursor lump is re-pulverized with a crusher (Roll jaw crusher manufactured by Yoshida Seisakusho) and further pulverized with a fine pulverizer (Matsubo turbo mill), and then a wind classifier (Seishin Enterprise Co., Ltd.). Classification using OMC-100) was performed to obtain a powder having a median diameter of 15.3 μm.

The obtained powder was put into a container and baked in an electric furnace at 1000 ° C. for 1 hour in a nitrogen atmosphere.
Further, the fired powder was transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours using a direct electric furnace to obtain artificial graphite powder (B). When the physical properties of the obtained artificial graphite powder (B) were measured, the median diameter was 15.5 μm.

  50% by weight of the graphite composite powder (A) obtained by the above procedure and 50% by weight of the artificial graphite powder (B) were mixed to obtain a graphite composite mixed powder (C) (negative electrode material of Example 7). Obtained.

The physical properties of the negative electrode material obtained in Example 7 were measured in the same manner as in Example 1. The median diameter was 15.0 μm, the tap density was 1.15 g / cm ³ , and the BET specific surface area was 1.4 m ² / g. It was. Further, when the crystallinity was measured by X-ray diffractometry in the same manner as in Example 1, d ₀₀₂ = 0.3356 nm and Lc ₀₀₄ > 1000 Å (100 nm).

Moreover, when the negative electrode material of Example 7 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio of the electrode was calculated | required, it was 0.07.
Furthermore, using the negative electrode material of Example 7, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion coefficient were measured.
The evaluation results of the physical properties of the negative electrode material of Example 7 are shown in Tables 1 to 3.

[Example 8]
50 wt% of natural graphite powder (G) (median diameter 18.2 μm, aspect ratio 10.1 and tap density 0.41 g / cm ³ ) was added to the graphite composite mixed powder (C) produced in the same manner as in Example 1. The mixed graphite composite mixed powder (F) was used as the negative electrode material of Example 8.

[Example 9]
30% by weight of natural graphite powder (G) (median diameter 18.2 μm, aspect ratio 10.1, tap density 0.41 g / cm ³ ) was added to the graphite composite mixed powder (C) produced in the same manner as in Example 1. The mixed graphite composite mixed powder (F) was used as the negative electrode material of Example 9.

[Example 10]
50 wt% of natural graphite powder (G) (median diameter 23.0 μm, aspect ratio 2.3, tap density 0.98 g / cm ³ ) was added to the graphite composite mixed powder (C) produced in the same manner as in Example 1. The mixed graphite composite mixed powder (F) was used as the negative electrode material of Example 10.

  The physical properties of the negative electrode materials of Examples 8, 9, and 10 were measured in the same manner as in Example 1. The evaluation results of the negative electrode materials of Examples 8, 9, and 10 are shown in Tables 1 to 3. Note that the negative electrode material graphite (D), graphite composite powder (A), artificial graphite powder (B), and graphite composite mixed powder (C) of these examples all have the same physical properties as in Example 1. is there.

[Comparative Example 1]
Comparative Example 1 was the same method as Example 7, but used graphite (D) without covering it with graphite (E).
The natural graphite (median diameter 17.0 μm, aspect ratio 1.9, tap density 1.0 g / cm ³ ) powder used in Example 1 was placed in a graphite crucible and directly at 3000 ° C. for 5 hours using a current furnace. Graphitized to obtain graphite powder (A ′) derived from natural graphite. This corresponds to a powder of graphite (D) not coated with graphite (E). The obtained graphite powder (A ′) had a median diameter of 16.8 μm.

Furthermore, artificial graphite powder (B) was obtained by the following procedure.
A coal tar pitch having a quinoline insoluble content of 0.05% by weight or less as in Example 1 was heat-treated in a reaction furnace at 460 ° C. for 10 hours to obtain a melted bulk heat-treated graphite crystal precursor (bulk mesophase). Obtained. The obtained massive heat-treated graphite crystal precursor was pulverized using an intermediate pulverizer (Orient Mill manufactured by Seishin Enterprise Co., Ltd.) and further pulverized using a fine pulverizer (Tsubo Mill manufactured by Matsubo). A refined graphite crystal precursor powder having a median diameter of 17 μm was obtained. This graphite crystal precursor powder was packed in a metal container and reheated at 540 ° C. for 2 hours in a box-shaped electric furnace under nitrogen gas flow. During reheating, the refined graphite crystal precursor powder became a mass of melted and solidified graphite crystal precursor (bulk mesophase). The solidified graphite crystal precursor lump is re-pulverized with a crusher (Roll jaw crusher manufactured by Yoshida Seisakusho) and further pulverized with a fine pulverizer (Matsubo turbo mill), and then a wind classifier (Seishin Enterprise Co., Ltd.). Classification using OMC-100) was performed to obtain a powder having a median diameter of 13.5 μm. The obtained powder was put into a container and baked in an electric furnace at 1000 ° C. for 1 hour in a nitrogen atmosphere. After firing, it was in the form of a powder, and almost no melting or fusion was observed. Further, the fired powder was transferred to a graphite crucible and graphitized at 3000 ° C. for 5 hours using a direct electric furnace to obtain artificial graphite powder (B). The median diameter of this powder was 12.0 μm.

  50% by weight of graphite powder (A ′) obtained by the above procedure and 50% by weight of artificial graphite powder (B) are mixed to obtain a graphite composite mixed powder (C) (negative electrode material of Comparative Example 1). It was.

The physical properties of the obtained negative electrode material of Comparative Example 1 were measured in the same manner as in Example 1. The median diameter was 16.0 μm, the tap density was 1.20 g / cm ³ , and the BET specific surface area was 2.1 m ² / g. . Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, d ₀₀₂ = 0.3357 nm and Lc ₀₀₄ > 1000 Å (100 nm).

Moreover, it was 0.06 when the electrode was produced in the same procedure as Example 1 using the negative electrode material of the comparative example 1, and the active material orientation ratio of the electrode was calculated | required.
Further, using the negative electrode material of Comparative Example 1, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion were measured.
The evaluation results of the physical properties of the negative electrode material of Comparative Example 1 are shown in Tables 1 to 3.

[Comparative Example 2]
In the production procedure of the negative electrode material of Example 2, the natural graphite mixed with the graphite crystal precursor was used except that one having a median of 20.0 μm, an aspect ratio of 10.5, and a tap density of 0.4 g / cm ³ was used. A graphite composite mixed powder (C) (negative electrode material of Comparative Example 2) was obtained by the same procedure as in Example 2.

The physical properties of the obtained negative electrode material of Comparative Example 2 were measured in the same manner as in Example 1. The median diameter was 20.3 μm, the tap density was 0.62 g / cm ³ , and the BET specific surface area was 2.1 m ² / g. . Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, it was d ₀₀₂ = 0.3356 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Comparative Example 2 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 54% by weight, and the artificial graphite powder (B) was 46% by weight. Furthermore, when the physical properties of each of the graphite composite powder (A) and the artificial graphite powder (B) were measured, the graphite composite powder (A) had a median diameter of 19.0 μm and an aspect ratio of 13.2. The artificial graphite powder (B) had a median diameter of 7.5 μm.

Moreover, when the negative electrode material of the comparative example 2 was used and the electrode was produced in the procedure similar to Example 1, and the active material orientation ratio was calculated | required, it was 0.04.
Further, using the negative electrode material of Comparative Example 2, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion were measured.
The evaluation results of the physical properties of the negative electrode material of Comparative Example 2 are shown in Tables 1 to 3.

[Comparative Example 3]
In the production procedure of the negative electrode material in Example 2, the natural graphite mixed with the graphite crystal precursor was used except that one having a median of 24.0 μm, an aspect ratio of 25.1, and a tap density of 0.3 g / cm ³ was used. A graphite composite mixed powder (C) (negative electrode material of Comparative Example 2) was obtained by the same procedure as in Example 2.

The physical properties of the obtained negative electrode material of Comparative Example 3 were measured in the same manner as in Example 1. The median diameter was 23.1 μm, the tap density was 0.51 g / cm ³ , and the BET specific surface area was 1.7 m ² / g. . Further, when the crystallinity was measured by the X-ray diffraction method in the same manner as in Example 1, it was d ₀₀₂ = 0.3356 nm and Lc ₀₀₄ > 1000 Å (100 nm).

  Further, when the ratio of the graphite composite powder (A) and the artificial graphite powder (B) in the negative electrode material (graphite composite mixed powder (C)) of Comparative Example 3 was measured in the same manner as in Example 1, graphite was measured. The composite powder (A) was 57% by weight, and the artificial graphite powder (B) was 43% by weight. Furthermore, when the physical properties of the graphite composite powder (A) and the artificial graphite powder (B) were measured, the graphite composite powder (A) had a median diameter of 25.2 μm and an aspect ratio of 22.3. The artificial graphite powder (B) had a median diameter of 7.8 μm.

Moreover, when the electrode was produced in the same procedure as Example 1 using the negative electrode material of the comparative example 3, and the active material orientation ratio was calculated | required, it was 0.03.
Furthermore, using the negative electrode material of Comparative Example 3, a lithium secondary battery was produced in the same procedure as in Example 1, and the discharge capacity, charge / discharge efficiency, load characteristics, and charge expansion were measured.
The evaluation results of the physical properties of the negative electrode material of Comparative Example 3 are shown in Tables 1 to 3.

[Comparative Example 4]
To the natural graphite (median diameter 17.0 μm, aspect ratio 1.9, tap density 1.0 g / cm ³ ) powder used in Example 1, the same graphite crystal precursor powder as that used in Example 1 was used. 50% by weight was mixed with respect to the total weight of the refined graphite crystal precursor powder and natural graphite to obtain a mixed powder of graphite (D) and graphite crystal precursor. In addition, the value of the aspect ratio obtained by the method described above was obtained. In the same manner as in Example 1, this powder was subjected to heat treatment A, pulverization, firing and graphitization to obtain a negative electrode material of Comparative Example 4.

[Comparative Example 5]
To the mixed powder of the graphite (D) obtained in Comparative Example 4 and the graphite crystal precursor, a phenol resin solution diluted to 50% by weight with a commercially available methanol solvent was further added to the total weight of the mixed powder. 5% by weight. In the same manner as in Example 1, the powder was subjected to heat treatment A, pulverization, firing, and graphitization to obtain a negative electrode material of Comparative Example 5.

The physical properties of the obtained negative electrode materials of Comparative Examples 4 and 5 were measured in the same manner as in Example 1.
The evaluation results of the physical properties of the negative electrode materials of Comparative Examples 4 and 5 are shown in Tables 1 to 3. In Comparative Examples 4 and 5, the component corresponding to the artificial graphite powder (B) is not used, and the graphite composite powder (A) is used as a negative electrode material as it is. Therefore, the tap density, particle size, and specific surface area values of the graphite composite powders (A) of Comparative Examples 4 and 5 are the same as the tap density, particle size, and specific surface area values of the negative electrode material (in Table 1, ( (*) And values are omitted.)

  In addition, in the column of “Presence / absence of compounding” in Tables 1 to 3 above, “○” indicates that the graphite composite powder (A) and the artificial graphite powder (B) are simultaneously manufactured, and these are separately manufactured and mixed. Is indicated by the notation “mixed”.

  Looking at the results in Tables 1 to 3, the negative electrode material of Comparative Example 1 is composed of graphite (D) and artificial graphite powder (B) not coated or bound with graphite (E). Since it is not compounded, the electrode orientation ratio is low. As a result, the charge expansion coefficient of the electrode has become extremely high.

  In the negative electrode materials of Comparative Examples 2 and 3, since the aspect ratio of the graphite (D) exceeds the specified value of the present invention, the obtained negative electrode material has an electrode orientation ratio significantly lower than the specified range of the present invention. As a result, the charge expansion coefficient of any electrode has become extremely high. Moreover, charging / discharging efficiency is low and load characteristics are also low.

  In the negative electrode materials of Comparative Examples 4 and 5, there are no particles corresponding to the artificial graphite powder (B) of the present invention. As a result, sufficient battery capacity is not obtained, and the charge expansion coefficient of the electrode is also increased.

  On the other hand, in the negative electrode materials of Examples 1 to 7, all of the tap density, crystallinity, and electrode orientation satisfy the specified range of the present invention. And the battery produced using these negative electrode materials has high discharge capacity, and the charge expansion coefficient of the electrode is also suppressed low.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2004-035207) for which it applied on February 12, 2004, The whole is used by reference.

According to the negative electrode material for a lithium secondary battery of the present invention, when used at a high electrode density (for example, 1.6 g / cm ³ or more), the discharge capacity is large, the charge / discharge efficiency is high, the load characteristics are excellent, and Since an excellent lithium secondary battery with small electrode expansion at the time of charging can be realized, it can be suitably used in various fields such as an electronic device in which the lithium secondary battery is used.

  Further, according to the method for producing a negative electrode material for a lithium secondary battery of the present invention, the negative electrode material for a lithium secondary battery can be produced efficiently and stably. The value is great.

(A) is a polarizing microscope photograph (1500 times magnification) of the graphite composite powder (A) portion in the particle cross section of the graphite composite mixed powder (C) after the graphitization step of the negative electrode material of Example 2. (B) is a schematic diagram showing the shapes of graphite (D) and graphite (E) in the particle cross section of (a).

Claims (17)

Graphite aspect ratio of 1.2 to 4.0 and (D) and the graphite orientation different graphite and (D) (E) graphite composite powder complexed (A), human Comprising graphite composite powder (C) composed of graphite powder (B) ,
In the artificial graphite powder (B), only the graphite (E) is granulated without containing the artificial graphite particles or the graphite (D) produced alone, which does not include the graphite (D). A negative electrode material for a lithium secondary battery, which is any one of the obtained artificial graphite particles . The negative electrode material for a lithium secondary battery according to claim 1, wherein the graphite (D) is natural graphite. The graphite composite mixed powder (C) has a tap density of 0.8 g / cm ³ or more, a BET specific surface area of 1 m ² / g or more and 5 m ² / g or less, and a (002) plane by X-ray diffraction. Interval d ₀₀₂
3. The negative electrode material for a lithium secondary battery according to claim 1, wherein is 0.3360 nm or less. The negative electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein the aspect ratio of the graphite composite powder (A) is 1.1 or more and 4.0 or less. The tap density of the graphite composite powder (A) is 0.80 g / cm ³ or more and 1.35 g / cm ³ or less, and the BET specific surface area is 0.8 m ² / g or more and 5.5 m ² / g or less. 5. The negative electrode material for a lithium secondary battery according to claim 1, wherein the volume-based average particle size is 6 μm or more and 80 μm or less. The artificial graphite powder (B) has a BET specific surface area of 0.3 m ² / g or more and 3 m ² / g or less, and a volume-based average particle size of 3 μm or more and 30 μm or less. The negative electrode material for a lithium secondary battery according to any one of 5. The lithium secondary battery according to any one of claims 1 to 6, wherein the ratio of the graphite (D) to the graphite composite powder (A) is 30 wt% or more and 97 wt% or less. Negative electrode material. 8. The lithium according to claim 1, wherein the ratio of the graphite composite powder (A) to the graphite composite mixed powder (C) is 35% by weight or more and 98% by weight or less. Negative electrode material for secondary batteries. The negative electrode for a lithium secondary battery according to any one of claims 1 to 8, wherein the graphite (E) and the artificial graphite powder (B) are produced from the same raw material. material. A natural graphite powder (G) is further provided, and the ratio of the graphite composite mixed powder (C) to the total amount of the graphite composite mixed powder (C) and the natural graphite powder (G) is 20 wt% or more and 90 wt% or less. It exists, The negative electrode material for lithium secondary batteries as described in any one of Claims 1-9 characterized by the above-mentioned. 11. The active material orientation ratio of an electrode formed using the negative electrode material as an active material at an electrode density of 1.63 ± 0.05 g / cm ³ is 0.07 or more. 11. The negative electrode material for lithium secondary batteries as described in the paragraph. The negative electrode material for a lithium secondary battery according to any one of claims 1 to 11, wherein a discharge capacity of the lithium secondary battery produced using the negative electrode material is 345 mAh / g or more. A method for producing a negative electrode material for a lithium secondary battery according to any one of claims 1 to 9, 11, and 12,
A pulverized graphite crystal precursor obtained by heat-treating a pitch raw material having a quinoline insoluble content of 3 wt% or less, an aspect ratio of 1.2 to 4.0, and a tap density of 0.7 g / The graphite (D) which is not less than cm ^{3 and not} more than 1.35 g / cm ³ is mixed, and the graphite (D) and the refined particles of the graphite crystal precursor are fixed in contact in a non-oriented state. after the heat treatment a to reduction, milled and heat-treated B subjected to firing and graphitization
A method for producing a negative electrode material for a lithium secondary battery, characterized in that a graphite composite mixed powder (C) is prepared . A method for producing a negative electrode material for a lithium secondary battery according to any one of claims 1 to 9, 11, and 12,
A pitch raw material having a quinoline insoluble content of 3% by weight or less, and a graphite having an aspect ratio of 1.2 or more and 4.0 or less and a tap density of 0.7 g / cm ³ or more and 1.35 g / cm ³ or less. While producing graphite composite powder (A) from quality (D), artificial graphite powder (B) is produced from pitch raw material, and obtained graphite composite powder (A) and artificial graphite powder (B) A method for producing a negative electrode material for a lithium secondary battery, wherein the mixed powder of graphite composite (C) is prepared by mixing . A current collector and an active material layer formed on the current collector;
A negative electrode for a lithium secondary battery, wherein the active material layer contains the negative electrode material for a lithium secondary battery according to any one of claims 1 to 12. A current collector and an active material layer formed on the current collector;
A negative electrode for a lithium secondary battery, wherein the active material layer contains a negative electrode material for a lithium secondary battery produced by the production method according to claim 13 or 14. A positive and negative electrode capable of inserting and extracting lithium ions, and an electrolyte,
A lithium secondary battery, wherein the negative electrode is a negative electrode for a lithium secondary battery according to claim 15 or 16.