JP2009158105A - Method for producing composite carbon material for negative electrode material of lithium ion secondary battery - Google Patents

Abstract

To provide a composite carbon material for a negative electrode material of a low-resistance lithium ion secondary battery while maintaining high energy density (high filling density, high reversible capacity), high initial efficiency, and excellent charge / discharge cycle characteristics. To do.
A graphite particle powder having a volume-based median diameter of 5 to 30 μm and an average lattice spacing d (002) of 0.3360 nm or less and a pitch having a softening point of 70 to 250 ° C. are heat-kneaded, The surface of the graphite particles is coated with a coating layer composed of the pitch, and then the obtained graphite particle powder having the coating layer is coated with copper particles having a particle diameter of 0.01 to 1.5 μm. 1 to 240 parts by weight in terms of copper atoms is fixed to 100 parts by weight of the particles, and then the graphite particle powder having a coating layer to which the obtained copper particles are fixed is 800 to 2150 ° C. in a non-oxidizing atmosphere. A method for producing a composite carbon material for a negative electrode material of a lithium ion secondary battery, characterized by firing and carbonizing.
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Description

  The present invention relates to a composite carbon material for a negative electrode material of a lithium ion secondary battery used as a negative electrode material of a lithium ion secondary battery used in a site requiring high capacity, such as a notebook computer, and a method for producing the same.

  Lithium secondary batteries using organic electrolytes of lithium salts as non-aqueous electrolyte secondary batteries are lightweight and have high energy density, and are expected as power sources for small electronic devices or power storage batteries. The demand for rapid charging / discharging has become more advanced as the performance of mobile phones and notebook computers, etc., where batteries are mainly used, has improved, and the improvement of output characteristics is an important issue for lithium-ion secondary batteries for hybrid cars and electric vehicles. It has become.

  Initially, metallic lithium was used as the negative electrode material for lithium secondary batteries, but metallic lithium eluted into the electrolyte as lithium ions during discharge, and when lithium ions were deposited on the negative electrode surface as metallic lithium during charging. It is difficult to deposit in a smooth and original state, and it tends to deposit in a dendritic form. Since this dendrite has extremely strong activity, the electrolyte solution is decomposed, so that the battery performance is lowered and the charge / discharge cycle life is shortened. Furthermore, there is a risk that dendrites grow and reach the positive electrode, causing both electrodes to short-circuit.

  In order to remedy this drawback, it has been proposed to use a carbon material instead of metallic lithium. A carbon material is suitable as a negative electrode material because there is no problem of precipitation in the form of dendrites upon occlusion and release of lithium ions. That is, the carbon material has high lithium ion storage / release properties, and since the storage / release reaction is performed quickly, the charge / discharge efficiency is high, the theoretical capacity is 372 mAh / g, and the potential during charge / discharge is also high. There is an advantage that a high voltage battery is obtained which is almost equal to metallic lithium.

  However, in the case of a graphite material having a high degree of graphitization and a highly developed hexagonal network structure, the capacity is large and the initial efficiency is as high as 90% or more, but the potential curve during discharge is flat. Therefore, it is difficult to determine the end point of discharge, and it is difficult to discharge a large amount of current in a short time, resulting in poor rate characteristics.

  Therefore, by improving the properties of the carbon material centering on the graphite material, for example, a carbon material having a multilayer structure in which the surface of the graphite material having a high degree of graphitization is coated with a carbonaceous material having a low degree of graphitization, or the degree of graphitization Attempts have been made to eliminate these difficulties by combining a high-graphite graphite material and a carbonaceous material having a low graphitization degree, and many proposals have been made.

For example, in Japanese Patent Laid-Open No. 10-334915 (Patent Document 1), (Claim 1) mechanical energy is set so that the apparent density ratio before and after the treatment is 1.1 or more and the median diameter ratio before and after the treatment is 1 or less. Non-aqueous secondary battery electrode characterized by containing treated carbonaceous or graphite particles, (Claim 2) Interlayer distance (d002) of carbonaceous or graphite particles before treatment is 0.34 nm or less The electrode for a non-aqueous secondary battery according to claim 1, wherein the crystallite size (Lc) is 30 nm or more and the true density is 2.25 g / cc or more, (Claim 3) Carbonaceous material after treatment or the median diameter of the graphite particles is a 5 to 50 [mu] m, BET method specific surface area, 25 m ² / g or less, 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 in the argon ion laser Raman spectrum Half-value width of the R value is 0.5 or less and 1580 cm ^-1 peak is the peak intensity ratio is 26cm ^-1 or less, an apparent density of claim 1 or 2, wherein the at 0.5 g / cc or more An electrode for a non-aqueous secondary battery, (Claim 4) A multi-layer structure carbon material obtained by carbonizing the organic compound after mixing the treated carbonaceous or graphite particles according to claims 1 to 3 with the organic compound. An electrode for a non-aqueous secondary battery is disclosed.

JP-A-11-054123 (Patent Document 2) discloses the following characteristics as a negative electrode material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery:
(1) The surface spacing (d002) of (002) planes by wide-angle X-ray diffraction method is less than 3.37 mm, and the crystallite size (Lc) in the C-axis direction is at least 1000 mm (2) Argon ion laser Raman spectrum and the half value width of a and 1580 cm ^-1 peak R value is 0.3 or less 24cm ^-1 or less (3) average particle size is the peak intensity ratio of 1360 cm ^-1 to the peak intensity of 1580 cm ^-1 is in 10~30μm of The average value of the thickness of the thinnest part is at least 3 μm or more and the average particle size or less (4) The specific surface area by the BET method is 3.5 m ² / g or more and 10.0 m ² / g or less (5) The tapping density is 0.5 g / Cc to 1.0 g / cc or less (6) Lumped graphite powder having an X-ray diffraction peak intensity ratio of (110) / (004) by a wide-angle X-ray diffraction method of 0.015 or more is used as a nucleus, and the nucleus Non-aqueous electrolyte secondary using a carbonaceous powder having a multi-layer structure in which a carbon precursor is coated on the surface of the substrate and then fired in a temperature range of 700 to 2800 ° C. in an inert gas atmosphere to form a surface layer of the carbonaceous material. A battery is disclosed.

  However, since the tapping density is low, the rate characteristic can be improved, but the electrode plate density is small, and the battery capacity per volume cannot be increased.

  In addition, JP 2004-031038 A (Patent Document 3) and JP 2004-179015 A (Patent Document 4) both have a binder pitch formed on an approximately spherical granulated product using a binder in advance. A negative electrode material obtained by firing after impregnation and coating is disclosed.

However, these have a problem that the charge capacity cannot be increased because the tap density cannot be increased (up to about 0.95 g / cm ³ ) because the granulated molded body is covered with pitch.

  Japanese Patent Laying-Open No. 2005-302725 (Patent Document 5) discloses (Claim 34) a step of assembling a carbon material into a sphere or a similar sphere by a mechanical mechanical pulverization process and simultaneously assembling into a primary stable structure. And using a dusting machine that imparts friction and shear forces between the surfaces, the fine carbon powder particles produced in the spheronization or similar spheronization process have a secondary stable structure on the surface of the carbon material. Disclosed is a method for producing a negative electrode active material for a lithium secondary battery, comprising the steps of assembling and heat treating the assembly.

  However, the material obtained by this method has a problem that there are many voids remaining inside, and it is difficult to increase the density of the electrode plate when filling as a negative electrode active material.

  JP-A-8-69797 (Patent Document 6) discloses a carbon material for a lithium secondary battery in which copper plating fine particles are attached to the surface of the carbon material, and the carbon for the lithium secondary battery. A method for producing a carbon material for a lithium secondary battery obtained by copper plating on a carbon material, in particular, displacement plating or reduction plating is disclosed.

  However, in this copper plating method, since the copper particles are likely to be deposited on the battery reaction-active edge surface, the copper particles inhibit the entry and exit of lithium ions into the graphite particles, so that there is a problem that the battery reaction is lowered. . In addition, the copper plating method has a problem of poor productivity.

Japanese Patent Laid-Open No. 10-334915 (Claims) JP-A-11-054123 (Claims) JP 2004-031038 A (Claims) JP-A-2004-179015 (Claims) Japanese Patent Laying-Open No. 2005-302725 (Claims) JP-A-8-69797 (Claims)

  That is, in order to obtain a material having a high energy density, a small initial irreversible capacity, excellent cycle characteristics, and excellent charge / discharge characteristics at a large current, copper graphite particles that do not hinder the entry and exit of lithium ions into the graphite particles There is a demand for an adhesion method to copper, and further, a method for adhesion of copper having excellent productivity to graphite particles is desired.

  Accordingly, an object of the present invention is to provide a composite for a negative electrode material of a low-resistance lithium ion secondary battery while maintaining high energy density (high filling density, high reversible capacity), high initial efficiency, and excellent charge / discharge cycle characteristics. It is to provide a carbon material.

  As a result of intensive studies to achieve the above object, the inventors of the present invention formed a coating layer made of pitch on the surface of the graphite particles, and then fixed the copper particles on the coating layer, thereby achieving a high energy density. The present inventors have found that a composite carbon material for a negative electrode material of a low-resistance lithium ion secondary battery can be obtained while maintaining high initial efficiency and excellent charge / discharge cycle characteristics.

That is, in the present invention, a graphite particle powder having a volume-based median diameter of 5 to 30 μm and an average lattice spacing d (002) of 0.3360 nm or less and a pitch having a softening point of 70 to 250 ° C. are heat-kneaded. A first step of coating the surface of the graphite particles with a coating layer comprising the pitch to obtain a graphite particle powder having the coating layer;
A step of fixing copper particles having a particle diameter of 0.01 to 1.5 μm to the graphite particle powder having the coating layer to obtain a graphite particle powder having a coating layer to which the copper particles are fixed. A second step in which the fixed amount is 1 to 240 parts by weight in terms of copper atoms with respect to 100 parts by weight of the graphite particle powder having the coating layer;
A third step of obtaining a composite carbon material for a negative electrode material of a lithium ion secondary battery by firing and carbonizing a graphite particle powder having a coating layer to which the copper particles are fixed at 800 to 2150 ° C. in a non-oxidizing atmosphere; ,
The manufacturing method of the composite carbon material for negative electrode materials of a lithium ion secondary battery characterized by having.

  According to the present invention, a composite carbon material for a negative electrode material of a low-resistance lithium ion secondary battery while maintaining high energy density (high packing density, high reversible capacity), high initial efficiency, and excellent charge / discharge cycle characteristics. Can be provided. Therefore, conductivity can be ensured without applying pressure that impedes immersion, so high energy density (high filling density, high reversible capacity), high initial efficiency, and excellent charge / discharge cycle characteristics. It is possible to improve the rate characteristics of the composite carbon material for the negative electrode material of the lithium ion secondary battery while maintaining the above.

The method for producing a composite carbon material for a negative electrode material of a lithium ion secondary battery of the present invention (hereinafter also referred to as the production method of the present invention) has a volume-based median diameter of 5 to 30 μm and an average lattice spacing d (002). A graphite particle powder having a coating layer composed of a pitch of 0.3360 nm or less and a pitch having a softening point of 70 to 250 ° C. A first step of obtaining particle powder;
A step of fixing copper particles having a particle diameter of 0.01 to 1.5 μm to the graphite particle powder having the coating layer to obtain a graphite particle powder having a coating layer to which the copper particles are fixed. A second step in which the fixed amount is 1 to 240 parts by weight in terms of copper atoms with respect to 100 parts by weight of the graphite particle powder having the coating layer;
A third step of obtaining a composite carbon material for a negative electrode material of a lithium ion secondary battery by firing and carbonizing a graphite particle powder having a coating layer to which the copper particles are fixed at 800 to 2150 ° C. in a non-oxidizing atmosphere; ,
It is a manufacturing method of the composite carbon material for negative electrode materials of the lithium ion secondary battery which has this.

  In the first step according to the production method of the present invention, the graphite particle powder and the pitch are heated and kneaded to coat the surface of the graphite particles with the coating layer made of the pitch. This is a step of obtaining a graphite particle powder having a layer.

  The graphite particle powder according to the first step is a graphite particle powder having a volume-based median diameter of 5 to 30 μm and an average lattice spacing d (002) of 0.3360 nm or less.

  The graphite particle powder is not particularly limited, and examples thereof include natural graphite or artificial graphite, a crushed product of an artificial graphite electrode, coke, and a mixture thereof. The shape of the graphite particle powder is spherical or A scale-like thing is mentioned, What was pulverized beforehand, what was classified, and what was spheroidized beforehand may be used.

  The graphite particle powder is obtained, for example, by pulverizing and classifying natural graphite, artificial graphite, a pulverized product of artificial graphite electrode, coke or the like using a pulverizer such as a roller mill or an impact pulverizer.

  The graphite particle powder may be spheroidized in advance, and as a method of spheroidizing, for example, non-spherical graphite particles such as flaky graphite may be converted into a high-speed air current using a hybridization system. Examples of the medium impact method include a method of spheroidizing by collision of particles, wear and compression. Examples of the graphite particle powder that has been spheroidized in advance include spheroidized graphite manufactured by Chuetsu Graphite Industries Co., Ltd.

  The volume-based median diameter of the graphite particle powder is 5 to 30 μm, preferably 5 to 25 μm, particularly preferably 5 to 20 μm. When the volume-based median diameter of the graphite particle powder is larger than the above range, when a large current is discharged as a lithium ion secondary battery, the intragranular diffusion distance of lithium ions becomes long, and the output characteristics tend to be low. When preparing a negative electrode of a lithium ion secondary battery, it is difficult to make the film thickness thin and uniform during coating of the active material, and output characteristics per volume are likely to be low. Further, if the volume-based median diameter of the graphite particle powder is smaller than the above range, the specific surface area becomes too large and the initial irreversible capacity tends to increase. In the present invention, the volume-based median diameter is a value measured by a laser diffraction type particle size distribution measuring apparatus (SALD 2000 manufactured by Shimadzu Corporation), and is a median diameter based on volume.

  The (002) plane spacing d (002) measured by X-ray wide angle diffraction method of the graphite particle powder is 0.3360 nm or less, preferably 0.3358 nm or less, particularly preferably 0.3354 to 0.3356 nm. . When the interplanar spacing d (002) of the (002) plane measured by the X-ray wide angle diffraction method of the graphite core particle powder exceeds the above range, the discharge reversible capacity becomes less than 330 mAh / g. In the present invention, a CuKα ray monochromatized with a graphite monochromator is used to measure a wide-angle X-ray diffraction curve by a reflective diffractometer method, and the interplanar spacing d (002) is determined using a Gakushin method. Was measured.

  The aspect ratio of the graphite particle powder is preferably 1.0 to 2.0. When the aspect ratio of the graphite particle powder is 2.0 or less, the filling property in the negative electrode of the lithium ion secondary battery becomes high, which is preferable in terms of excellent charge / discharge capacity.

  The pitch according to the first step is a pitch having a softening point of 70 to 250 ° C. The pitch is not particularly limited, and coal tar pitch, petroleum pitch, organic synthetic pitch obtained by polycondensation of condensed polycyclic aromatic hydrocarbon compounds, and polycondensation of heteroatom-containing condensed polycyclic aromatic hydrocarbon compounds. Examples include organic synthetic pitches obtained, and among these, coal tar pitch is preferable.

  The softening point of the pitch is 70 to 250 ° C., preferably 70 to 150 ° C., particularly preferably 70 to 90 ° C. as measured by the ring and ball method. If the softening point of the pitch is less than the above range, in the second step, the pitch melt adheres to the inner wall of the apparatus, causing a problem that continuous operation cannot be performed. Since the softened state of the resin deteriorates, the dispersibility deteriorates, and spheroidization becomes difficult in the second step. Moreover, you may use the pitch which adjusted the softening point to the said range by mixing 2 or more types of pitches from which a softening point differs, or adding tar.

  The pitch is preferably a pitch obtained by removing free carbon by a method such as filtration or a quinoline insoluble content of less than 1% in that the initial charge / discharge loss as the negative electrode material is reduced.

The blending amount of the pitch at the time of heat-kneading in the first step is appropriately selected, but is preferably 5 to 40 parts by weight, and 10 to 30 parts by weight with respect to 100 parts by weight of the graphite particle powder. It is particularly preferable to use 15 to 25 parts by weight.
When the blending amount of the pitch is less than the above range, it is difficult to uniformly coat the pitch on the surface of the graphite particles, and a fine portion of the particle size distribution is increased, which tends to be broad.
Further, if the blending amount of the pitch exceeds the above range, the particles are excessively aggregated, so that it becomes difficult to crush individual granulated particles one by one, and the particle diameter of the composite carbon material becomes large. Further, the thickness of the coating layer becomes non-uniform, and the powder of the pitch alone exists. In addition, since a coarse lump is formed, the composite carbon material needs to be pulverized, and the initial charge / discharge loss increases as battery characteristics. Further, in the second step, the excess pitch adheres to the inside of the apparatus, so that a problem that makes continuous operation difficult is likely to occur.

  An example of the operation of the heat-kneading operation in the first step is as follows. The graphite particle powder and the pitch are put into a kneading apparatus, and the temperature in the apparatus container exceeds a predetermined softening point of the pitch while kneading. The temperature is raised to a temperature and kneaded sufficiently while heating. And after heat-kneading, it cools to room temperature and obtains the graphite particle powder which has this coating layer.

  The heating temperature at the time of heat kneading in the first step is a temperature exceeding the softening point of the pitch, and preferably 20 ° C. or more higher than the softening point of the pitch. In addition, the time for performing the heat kneading in the first step is appropriately selected depending on the capacity of the kneading apparatus, the shape of the kneading blade, the amount of the graphite particle powder and the pitch, etc., but at a temperature exceeding the melting point of the pitch. Usually 10 minutes to 2 hours.

  The kneading apparatus for performing heat kneading in the first step is not particularly limited as long as it can normally stir or knead while heating the powder, and is provided with a mixer, a kneader, and a pressure lid. A pressure kneader may be used.

  In the first step, it is preferable that a meltable organic substance is further added to the graphite particle powder and the pitch, and the graphite particle powder, the pitch, and the meltable organic substance are heated and kneaded. In the first step, when the graphite particle powder and the pitch are heated and mixed, the pitch needs to be in a low-viscosity molten state. Therefore, the fusible organic substance reduces the viscosity of the pitch. Used for.

  The fusible organic substance refers to an organic substance having a viscosity at a heating temperature of 20 Pa · s or less at the time of heating and kneading in the first step, and as the fusible organic substance, synthetic oil, natural oil, stearic acid, synthetic wax, Examples include natural wax. The meltable organic matter preferably has a volatile content of 50% or more when heated to 400 ° C. in air, and a residual carbon ratio of 3% or less when heated to 800 ° C. in an inert atmosphere. is there. Since the fusible organic substance is used in the first step to reduce the viscosity of the pitch, the fusible organic substance preferably has a low molecular weight, and excessive graphite particles are pulverized during heating and kneading. Those that prevent it are preferred. In addition, the fusible organic substance also acts as a lubricant in the second step, and has an effect of preventing the granulated powder from being pulverized. In addition, when considering the production aspect, the fusible organic substance also has an effect of suppressing metal wear of the apparatus and an effect of suppressing adhesion of pitch to the inside of the apparatus. Further, in the third step, when the graphite particle powder having the coating layer to which the copper particles are fixed is calcined and carbonized, the fusible organic substance contained in the graphite particles having the coating layer to which the copper particles are fixed The effect of expelling oxygen around the graphite particle powder having a coating layer on which the copper particles are fixed, or the reaction between the fusible organic substance and oxygen to lower the oxygen concentration by the gas pressure at the time of vaporization There is also. Therefore, the fusible organic substance is preferably an organic substance that volatilizes 50% or more when heated to 400 ° C. in air, from the viewpoint of increasing the reversible capacity. In addition, since the remaining carbon content in the meltable organic matter lowers the reversible capacity, it is desirable that the remaining coal rate is as low as possible. Therefore, the meltable organic matter was heated to 800 ° C. in an inert atmosphere. It is preferable that the remaining charcoal rate at the time is 3% or less. In addition, this inert atmosphere refers to the atmosphere of inert gas, such as nitrogen gas, helium gas, and argon gas.

  The blending amount of the meltable organic material is preferably 1 to 30 parts by weight, particularly preferably 3 to 20 parts by weight with respect to 100 parts by weight of the graphite particle powder. If the blending amount of the fusible organic material is less than the above range, when mechanochemical treatment is performed in the second step, fine powder due to impact is likely to be generated, and the initial irreversible capacity is likely to increase. When the copper particles are adhered by the liquid phase method in the second step, the adsorption effect of copper ions is likely to be hindered, and either the mechanochemical treatment or the copper particles are adhered by the liquid phase method. In addition, the copper particles are easily peeled off from the carbon material after calcination carbonization.

In the first step, as a method of heat-kneading the graphite particle powder, the pitch, and the meltable organic material,
(I) A method in which the graphite particle powder and the meltable organic substance are first heat-kneaded and then the pitch is added and heat-kneaded (ii) The graphite particle powder and the pitch are first heat-kneaded, A method of adding and kneading the meltable organic substance (iii) A method of heating and kneading the graphite particle powder, the pitch and the meltable organic substance,
Etc. Among these, the methods (i) and (iii) are preferable in that excessive pulverization of the graphite particle powder can be prevented.

  Thus, in the first step, the graphite particle powder and the pitch are heated and kneaded to coat the particle surface of the graphite particles with the coating layer made of the pitch, and the coating layer A graphite particle powder having Preferably, in the first step, the graphite particle powder, the pitch, and the fusible organic substance are heated and kneaded to coat the surface of the graphite particles with the pitch and the fusible organic substance. The layer is coated to obtain a graphite particle powder having the coating layer.

  The volume-based median of the graphite particle powder having the coating layer obtained by the first step is not particularly limited, but preferably the volume-based median diameter measured by a laser diffraction method is approximately 10 to 40 μm.

  Next, the second step according to the production method of the present invention is performed. In the second step, the copper particles having a particle diameter of 0.01 to 1.5 μm are fixed to the coating layer of the graphite particle powder having the coating layer, and the graphite having the coating layer to which the copper particles are fixed. This is a step of obtaining particle powder.

  In the second step, the particle diameter of the copper particles fixed to the graphite particle powder having the coating layer is 0.01 to 1.5 μm. That is, the particle diameter of the copper particles fixed to the coating layer of the graphite particle powder having the coating layer fixed with the copper particles obtained by performing the second step is 0.01 to 1.5 μm. . When the particle diameter of the copper particles fixed to the coating layer of the graphite particle powder having the coating layer to which the copper particles are fixed is in the above range, the reversible capacity is increased.

  In the second step, the fixed amount of the copper particles fixed to the graphite particle powder having the coating layer is 1 to 240 parts by weight in terms of copper atoms with respect to 100 parts by weight of the graphite particle powder having the coating layer. The amount is preferably 10 to 150 parts by weight, particularly preferably 20 to 100 parts by weight, and still more preferably 30 to 50 parts by weight. When the fixed amount of the copper particles fixed to the graphite particle powder having the coating layer is less than the above range, it becomes difficult to impart sufficient conductivity. Since the graphite particle powder having the coating layer is covered, the battery reaction is hindered.

  The first embodiment of the second step is a method of attaching the copper particles to the surface of the coating layer of graphite particle powder having the coating layer by a liquid phase method.

  In the liquid phase method according to the first embodiment of the second step, the graphite particle powder having the coating layer is added to an aqueous solution of a copper salt, and the graphite particle powder having the coating layer is added using a stirrer or the like. The aqueous solution of the copper salt to which is added is stirred, and then the obtained slurry or wet cake is dried, followed by heat treatment at a temperature equal to or higher than the decomposition temperature of the copper salt, and the graphite having the coating layer This is done by decomposing the copper salt adhering to the particle powder.

  In the liquid phase method, first, graphite particle powder having the coating layer is added to an aqueous solution of copper salt, and the aqueous solution of copper salt to which the graphite particle powder having the coating layer is added using a stirrer or the like. Stir. As a result, the copper ions in the aqueous solution are ion-exchanged with ions of different atoms such as hydrogen ions existing in the pitch constituting the coating layer, and the copper ions adhere to the pitch.

  The copper salt according to the liquid phase method is not particularly limited as long as it contains a copper ion. For example, copper sulfate, copper nitrate (II), copper chloride (II), copper acetate (I), acetic acid Copper (II) etc. are mentioned. Although the copper salt has a decomposition temperature of 350 ° C. or lower, the arrangement of benzene rings inside the pitch does not proceed during the heat treatment in the liquid phase method. When firing and carbonizing at a temperature, the pitch is preferred in that it is likely to be amorphous. Specifically, for example, copper sulfate, copper nitrate (II), copper chloride (II), copper acetate (I), acetic acid Copper (II) is preferred.

  In the liquid phase method, the amount of copper in the aqueous solution of copper salt is 1 to 240 parts by weight in terms of copper atom with respect to 100 parts by weight of graphite particle powder having the coating layer added to the aqueous solution of copper salt, Preferably it is 10-150 weight part, Most preferably, it is 20-100 weight part, More preferably, it is 30-50 weight part. If the amount of copper in the aqueous solution of the copper salt is less than the above range, it becomes difficult to impart sufficient electrical conductivity, and if the amount exceeds the above range, the graphite particles have a graphite particle powder having the coating layer. Since it covers, battery reaction is inhibited.

  In the liquid phase method, when stirring the aqueous solution of the copper salt to which the graphite particle powder having the coating layer is added, the temperature of the aqueous solution of the copper salt is not particularly limited, but is preferably 50 ° C. or less, particularly preferably. Is 20 to 30 ° C., and the stirring time is not particularly limited, but is usually 3 minutes to 30 minutes.

In the liquid phase method, the obtained slurry or wet cake is then dried and subsequently heat-treated at a temperature equal to or higher than the decomposition temperature of the copper salt, and the copper adhered to the graphite particle powder having the coating layer. Decomposes salt. As a result, X of the copper salt, for example, CuX or CuX ₂ (wherein X represents an anion) is thermally decomposed and gasified, and the copper particles are converted into copper particles to form graphite particles having the coating layer. It is fixed to the surface of the coating layer of powder.

  In the liquid phase method, when the heat treatment is performed, the temperature of the heat treatment is not particularly limited as long as it is equal to or higher than the decomposition temperature of the copper salt, and the time of the heat treatment is not particularly limited. The temperature and time required for X to thermally decompose and copper ions to become copper particles are appropriately selected.

  In the liquid phase method, a graphite particle powder having a coating layer on which the copper particles are fixed is obtained by performing the heat treatment.

  In the graphite particle powder having the coating layer to which the copper particles are fixed, the particle size of the copper particles fixed to the coating layer is 0.01 to 1.5 μm, but the liquid phase method is performed. Thus, the particle diameter of the copper particles fixed to the surface of the coating layer is usually 0.01 to 1.5 μm. When the particle diameter of the copper particles fixed to the coating layer is in the above range, the reversible capacity is increased. When the copper particles are fixed to the coating layer by the liquid phase method, the particle diameter of the copper particles fixed to the surface of the coating layer is obtained by observation with a scanning electron microscope (SEM).

  The second embodiment of the second step is a method of embedding the copper particles in the coating layer of the graphite particle powder having the coating layer by mechanochemical treatment.

  In the mechanochemical treatment according to the second embodiment of the second step, the graphite particle powder having the coating layer and the copper particle powder for mechanochemical treatment are mixed, and the obtained mixed powder is subjected to friction and compression. Then, it is performed by applying mechanical energy to the mixed powder. Mechanical powder is applied to the mixed powder, and the graphite particle powder having the coating layer and the copper particles for mechanochemical treatment are repeatedly contacted, collided and rubbed, so that the coating layer is softened, and the coating The copper particles for mechanochemical treatment are embedded in the coating layer of graphite particles having a layer, and the copper particles are fixed to the coating layer. In the mechanochemical treatment, graphite fine particles may be produced by friction and compression of the graphite particles. In such a case, the graphite fine particles are also embedded in the coating layer.

  As the copper particle powder for mechanochemical treatment, copper having a particle diameter of 0.01 to 1.5 μm is used, and preferably does not contain a metal alloying with lithium as an impurity. When the particle diameter of the copper particle powder for mechanochemical treatment is in the above range, the reversible capacity is increased. The copper particle powder for mechanochemical treatment is preferably copper having a purity of 3N or more, but is not limited thereto. The granular copper particles are prepared using a suitable pulverizer, but those pulverized in an inert gas atmosphere are preferred so as not to be oxidized during the pulverization.

  In the mechanochemical treatment, the mixing amount of the copper particle powder for mechanochemical treatment is preferably 1 to 240 parts by weight, particularly preferably 10 to 150 parts by weight with respect to 100 parts by weight of the graphite particle powder having the coating layer. More preferably, it is 20-100 weight part, More preferably, it is 30-50 weight part. When the mixing amount of the copper particle powder for mechanochemical treatment is less than the above range, it becomes difficult to impart sufficient conductivity, and when the mixing amount exceeds the above range, the graphite particle powder in which the copper particle has the coating layer. Battery reaction is hindered.

  As a method for applying mechanical energy to the mixed powder in the mechanochemical treatment, for example, a mechanofusion system (manufactured by Hosokawa Micron Co., Ltd.), a hybridizer (manufactured by Nara Machinery Co., Ltd.) or the like is used. Can be repeatedly rubbed and compressed, and mechanical energy can be continuously applied to the mixed powder from the outside. Thereby, the copper particles for mechanochemical treatment are embedded in the coating layer of the graphite particle powder having the coating layer.

  A device for friction and compression of the mixed powder, that is, a specific device for applying mechanical energy from the outside is not limited to the above device, and can mix and compress the mixed powder. If it is.

  More specifically, examples of a method for imparting mechanical energy to the mixed powder include a method using a hybridizer (manufactured by Nara Machinery Co., Ltd.) shown in FIG. In the hybridizer shown in FIG. 1, the graphite particle powder having the coating layer and the copper particle powder for mechanochemical treatment are introduced from the raw material inlet 1, and the rotating portion 8 is rotated at a peripheral rotation speed of 20 to 100 m / Rotate for 1 to 3 minutes at s. At this time, the drum 6 and the rotation with respect to the mixed powder of the graphite particle powder having the coating layer and the copper particle powder for mechanochemical treatment introduced into the gap between the drum 6 and the rotating portion 8 through the raw material circulation path 2. Mechanical energy is applied to the mixed powder by frictional force, compressive force, and impact force generated by the difference in rotational speed with the part 8. In addition, 3 is a stator, 4 is a jacket, 5 is a raw material discharge | emission part, 7 is a braid | blade.

  The temperature inside the hybridizer when mechanical energy is applied to the mixed powder by the hybridizer shown in FIG. 1 increases due to the application of mechanical energy, but the softening point of the pitch according to the first step It is preferable to adjust the temperature below + 20 ° C. When the temperature in the hybridizer exceeds the softening point of the pitch + 20 ° C., the pitch is melted and eluted from the gaps between the granulated particles, and the eluted pitch tends to adhere to the inside of the hybridizer. Regular continuous operation tends to be difficult.

  The rotational peripheral speed of the rotating part 8 when mechanical energy is applied to the mixed powder by the hybridizer shown in FIG. 1 is preferably 20 to 100 m / s. When the rotational peripheral speed of the rotating part 8 is less than 20 m / s, the mechanical energy received by the mixed powder is small, and the copper particle powder for mechanochemical treatment and the fine particle fragments of the graphite are difficult to be embedded. Even if it exceeds 100 m / s, there is no significant difference in the performance of the composite carbon material for the negative electrode material of the lithium ion secondary battery from the case of 100 m / s, and the upper limit is 100 m in consideration of cost, device safety, etc. / S is preferable. The treatment time when mechanical energy is applied to the mixed powder with the hybridizer is preferably 30 seconds to 5 minutes, particularly preferably 1 minute to 3 minutes. When the treatment time is less than 30 seconds, embedding is difficult to occur, and even when it exceeds 5 minutes, the physical properties of the carbon particle powder for a lithium ion secondary battery negative electrode material hardly change. The time is particularly preferably 2 minutes or less.

  Further, in the mechanochemical treatment, when the frictional force and compressive force to the mixed powder are too strong and the graphite particles having the coating layer are destroyed, the first step is performed to reduce wear. It is possible to add the meltable organic matter according to the above. At that time, the amount of the meltable organic substance to be charged is appropriately determined in consideration of cost and processing time.

  When performing the mechanochemical treatment, by setting the particle diameter of the copper particle powder for mechanochemical treatment to 0.01 to 1.5 μm, the particle diameter of the copper particles fixed to the coating layer is It can be set to 0.01 to 1.5 μm.

  Thus, by performing this 2nd process, the graphite particle powder which has a coating layer to which this copper particle was fixed is obtained.

  Next, the third step according to the production method of the present invention is performed. In the third step, the graphite particle powder having the coating layer to which the copper particles are fixed is calcined and carbonized at 800 to 2150 ° C. in a non-oxidizing atmosphere, and the composite carbon material for a negative electrode material of a lithium ion secondary battery It is the process of obtaining.

  In the third step, the calcining carbonization temperature when calcining the graphite particle powder having the coating layer on which the copper particles are fixed is 800 to 2150 ° C, preferably 900 to 2000 ° C, particularly preferably 1000 to 1200 ° C. It is. In the third step, if the calcination carbonization temperature is less than the above range, the low molecular organic unburned portion remains in the pitch, and the charge / discharge efficiency of the lithium ion secondary battery is deteriorated and the cycle characteristics are deteriorated. In addition, when the meltable organic material is used, the volatilization of the meltable organic material becomes insufficient, and the charge / discharge efficiency of the lithium ion secondary battery is lowered and the cycle characteristics are deteriorated. Further, in the third step, when the firing carbonization temperature exceeds the above range, graphitization of the carbide layer proceeds, leading to a decrease in rate characteristics, and in addition, dissolution of copper occurs and the battery exists in the carbon material. Fills the active pores of the reaction.

  Thus, in the third step, the graphite particle powder having the coating layer to which the copper particles are fixed is calcined and carbonized, so that the pitch constituting the coating layer is carbonized to become a carbide layer. The composite carbon material for the negative electrode material of the lithium ion secondary battery of the invention is obtained. When the fusible organic material is used, in the third step, the pitch is carbonized and the fusible organic material is volatilized from the graphite particles having the coating layer to which the copper particles are fixed.

  After performing the third step, the obtained composite carbon material powder for negative electrode material of the lithium ion secondary battery can be crushed or classified as necessary. The crushing device for performing the crushing is not particularly limited, and devices such as a turbo mill (manufactured by Matsubo Co., Ltd.), a quick mill (manufactured by Seishin Enterprise Co., Ltd.), a super rotor (manufactured by Nisshin Engineering Co., Ltd.), etc. Illustrated. In the classification, the composite carbon material for the negative electrode material of the lithium ion secondary battery can be adjusted to a minimum particle diameter of 1 μm or more, a maximum particle diameter of 55 μm or less, and a volume-based median diameter of 5 to 30 μm.

Thus, the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by performing the production method of the present invention is:
The graphite particles, and the carbide layer formed on the surface of the graphite particles,
In the carbide layer, the copper particles having a particle diameter of 0.01 to 1.5 μm are embedded,
It is a composite carbon material for a negative electrode material of a lithium ion secondary battery.

The particle diameter aspect ratio of the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by the production method of the present invention is preferably 1.0 to 2.0, particularly preferably 1.0 to 1.6, and further preferably. 1.0 to 1.3. When the particle diameter aspect ratio of the composite carbon material is within the above range, the chargeability at the negative electrode and the balance containing the electrolytic solution are balanced and the charge / discharge capacity is increased. When the particle diameter aspect ratio of the composite carbon material is larger than 2.0, the graphite layer direction is likely to be oriented parallel to the substrate when the active material layer is applied, and the active material layer is easily peeled off from the substrate. Deteriorating defects occur.
The adjustment of the particle diameter aspect ratio of the composite carbon material is carried out under the conditions of heating and kneading in the first step, friction or compression conditions in the mechanochemical treatment, for example, the rotational speed in the hybridizer, It becomes possible by selecting the graphite particle powder and the pitch. In the present invention, in SEM (scanning electron microscope) observation, 100 particles are arbitrarily selected from the composite carbon material for a negative electrode material, and an average value of values obtained by dividing the longest diameter of the particles by the minimum diameter, The particle diameter is the aspect ratio.

The tapping density of the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by the production method of the present invention is preferably 1.0 to 1.3 g / cm ³ .

The BET specific surface area of the composite carbon material for a negative electrode material of a lithium ion secondary battery obtained by the production method of the present invention is preferably 1.5 to ⁵ m ² / g. If the BET specific surface area of the composite carbon material is less than the above range, the reaction area required for lithium ion desorption / insertion is small, so it is difficult to maintain output characteristics. Becomes too large, and a large loss is likely to occur during the initial charge. The specific surface area of the composite carbon material is adjusted by adjusting the thickness of the coating layer to be coated in the first step, the friction or compression conditions in the mechanochemical treatment, for example, the rotational speed of the hybridizer, and the third step. It can be performed by performing pulverization using a pulverizer after adjustment, adjusting the pulverization conditions, performing classification after performing the third step, adjusting the classification conditions, and the like. The BET specific surface area is a value calculated by the BET 10-point method using N ₂ gas. In the present invention, the nitrogen adsorption specific surface area is large after performing preliminary drying at 350 ° C. for 30 minutes under a nitrogen flow with respect to the measurement object using a surface area meter (manufactured by Shimadzu Corporation, fully automatic surface area measuring device). This is a value measured by a nitrogen adsorption BET 10-point method using a gas flow method using a nitrogen-helium mixed gas accurately adjusted so that the value of the relative pressure of nitrogen with respect to atmospheric pressure is 0.3.

  The volume-based median diameter D50 of the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by the production method of the present invention is preferably 5 to 30 μm, particularly preferably 10 to 25 μm, and further preferably 10 to 20 μm. When the volume-based median diameter of the composite carbon material is less than 5 μm, dispersion in the liquid during slurry preparation tends to be poor, and the specific surface area becomes small. On the other hand, when the volume-based median diameter of the composite carbon material exceeds 30 μm, when a large current is discharged as a lithium ion secondary battery, the intragranular diffusion distance of lithium ions becomes long and the output characteristics tend to be low. In addition, the thickness of the active material applied is limited, and when designing an electrode structure with excellent output characteristics, it is difficult to apply a thin and uniform active material layer. In the present invention, the volume-based median diameter is a median diameter measured by a laser diffraction method, and is a median diameter measured by SALD manufactured by Shimadzu Corporation. The volume-based median diameter is adjusted by adjusting the particle diameter of the graphite particle powder and the blending amount of the pitch in the first step, and pulverizing using a pulverizer after performing the third step. It is possible to adjust the pulverization conditions, perform classification after performing the third step, and adjust the classification conditions.

  In the composite carbon material for a negative electrode material of a lithium ion secondary battery obtained by the production method of the present invention, the interplanar spacing d (002) of the (002) plane of the graphite crystallite obtained by the X-ray diffraction method for the crystallinity inside the particles. It is reasonable to discuss in terms of The interlayer distance of the d (002) plane of the graphite crystallite of the composite carbon material for the negative electrode material of the lithium ion secondary battery obtained by the production method of the present invention is preferably 0.3500 nm or less, particularly preferably 0.3358 nm or less, More preferably, it is 0.3354-0.3358 nm. When the interlayer distance on the d (002) plane of the graphite crystallites exceeds the above range, the discharge reversible capacity tends to be small. Natural graphite shows a value close to 0.3354 nm of ideal graphite, and graphitizable coke can be made 0.3400 nm or less by performing heat treatment at 2800 ° C. or higher. In the present invention, the interlayer distance of the d (002) plane of the graphite crystallite is such that CuKα rays are used as an X-ray source, high-purity silicon is used as a standard material, and the peak position of the diffraction pattern on the (002) plane is half It is a value calculated from the price range based on the Gakushin method.

In the present invention, it is appropriate to discuss the disorder of the crystal structure of the particle surface layer of the composite carbon material for the negative electrode material of the lithium ion secondary battery using a Raman spectrum. In the composite carbon material for a negative electrode material of a lithium ion secondary battery obtained by the production method of the present invention, the intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ of the Raman spectrum is preferably 0.60 or less. In the present invention, the composite carbon material for the negative electrode material of the lithium ion secondary battery is measured with a Raman spectroscopic analyzer (NR1100, manufactured by JASCO Corporation) using an Ar laser with a wavelength of 514.5 nm. the spectrum _{I 1360} of 1360 cm ^-1 vicinity attributable to disturbance of the crystal structure due to mismatching of crystal defects and stacking structure, the 1580 cm ^-1 vicinity attributable to _{E 2 g} vibration corresponding to the lattice vibration of the carbon hexagonal net plane By dividing by the spectrum I ₁₅₈₀ , the Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ was determined. The intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ of the Raman spectrum is adjusted by adjusting the graphite particle powder in the first step, the pitch, the friction or compression conditions in the mechanochemical treatment, such as the rotational speed of the hybridizer. This is possible by selecting.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Example 1
<Manufacture of composite carbon material for negative electrode material of lithium ion secondary battery>
(First step)
For 100 parts by weight of spherical natural graphite having an average particle diameter of 13 μm and an average lattice spacing d (002) of graphite crystallites of 0.3355 nm, 70% is obtained as a fusible organic substance when heated to 400 ° C. in the air. Volatilized and mixed with 5 parts by weight of molten mechanical oil having a residual carbon ratio of 0.6% when heated to 800 ° C in an inert atmosphere, and after kneading by heating at 150 ° C for 30 minutes, 30 parts by weight of coal tar pitch (softening point: 89 ° C.) was added to 100 parts by weight of spherical natural graphite, and further kneaded at 150 ° C. for 30 minutes, and then cooled to 25 ° C. to obtain Powder A.

(Second step)
Next, 100 parts by weight of the obtained powder A and 40 parts by weight of a copper powder having a particle diameter of 0.1 to 0.5 μm prepared by a ball mill (manufactured by Fritsch Co., Ltd., P-7) are mixed in the hybridizer apparatus. , While maintaining the maximum temperature in the apparatus at 75 ° C. ± 5 ° C., it was processed at a rotational speed of 8000 rpm (rotational peripheral speed: 100 m / s) for 3 minutes, and the powder was taken out of the apparatus and cooled to 25 ° C. A powder B1 was obtained.
In addition, the particle diameter of the copper powder before throwing is the range of the particle diameter measured by the laser diffraction type particle size distribution measuring apparatus (SALD 2000 manufactured by Shimadzu Corporation).

(3rd process, crushing, classification)
The obtained powder B1 was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Next, it is crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor), classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier), and composite carbon for negative electrode material of a lithium ion secondary battery. Material C1 was obtained.

<Production and performance evaluation of lithium ion secondary batteries>
(Preparation of slurry)
An appropriate amount of 1 wt% carboxymethylcellulose (CMC) aqueous solution is added as a thickener to 100 parts by weight of the composite carbon material C1 for negative electrode material of the lithium ion secondary battery obtained as described above, and stirred for 30 minutes. After mixing, an appropriate amount of 40 wt% styrene-butadiene rubber (SBR) aqueous solution was added as a binder and stirred for 5 minutes to prepare a negative electrode mixture paste.

(Production of working electrode)
The obtained negative electrode mixture paste was applied onto a copper foil (current collector) having a thickness of 18 μm and heated to 130 ° C. in a vacuum to completely evaporate the solvent. The obtained sheet was rolled with a roller press so that the electrode plate density was 1.5 g / cc, and punched with a punch to obtain a working electrode. The sheet resistance was measured with respect to the working electrode using a surface resistance meter Loresta manufactured by Mitsubishi Oil Chemical Co., Ltd. The results are shown in Table 1.

(Preparation of counter electrode)
Under an inert atmosphere, a lithium metal foil was punched into a nickel mesh (current collector) punched out with a punch to obtain a counter electrode.

(Preparation of reversible discharge capacity button type battery)
Using the above working electrode and counter electrode, a button type battery shown in FIG. 2 as an evaluation battery was assembled in an inert atmosphere. As the electrolytic solution, a 1: 1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1 mol / dm ³ of the lithium salt LiPF ₆ was dissolved was used. Charging current density 0.2 mA / cm ^2, after finishing the constant current charging at a final voltage 5 mV, holding a constant potential to the lower limit current 0.02 mA / cm ^2. The discharge was a constant current discharge to a final voltage of 1.5 V at a current density of 0.2 mA / cm ² , and the discharge capacity after the end of 5 cycles was defined as a reversible capacity. Further, the difference between the initial charge capacity and the initial discharge capacity at that time was defined as loss, and the ratio obtained by dividing the initial discharge capacity by the initial charge capacity was defined as the initial efficiency. For the rate characteristics, the discharge capacity after the end of 5 cycles when charging / discharging at 10 mA / cm ² was examined as the discharge load. The results are shown in Table 1. In FIG. 2, 9 is a negative electrode side stainless steel cap, 10 is a negative electrode, 11 is a copper foil, 12 is an insulating gasket, 13 is an electrolyte-impregnated separator, 14 is a nickel mesh, 15 is a positive electrode side stainless steel cap, and 16 is a positive electrode.

(Production of button-type battery for cycle durability evaluation)
Change the counter electrode to lithium cobalt oxide and assemble a button-type battery in the same manner as above, and repeatedly charge and discharge between 4.1 V and 3.0 V at 20 ° C. and a current density of 0.2 C 100 times. Thereafter, the cycle capacity retention rate was examined. The measurement results are shown in Table 1.

(Example 2)
(First step)
A powder A was obtained in the same manner as in Example 1.

(Second step)
In the first step, copper (II) nitrate trihydrate adjusted to 40 parts by weight in terms of copper atoms with respect to 100 parts by weight of the powder A in a kneader containing the powder A after cooling. Was added and stirred at room temperature (25 ° C.) for 1 hour. After stirring, the aqueous copper nitrate solution mixed with the powder A was taken out of the apparatus and subjected to heat treatment for 1 hour in a drier kept at 170 ° C. to obtain a powder B2.

(3rd process, crushing, classification)
A composite carbon material C2 for a negative electrode material of a lithium ion secondary battery was obtained in the same manner as in Example 1 except that powder B2 was used instead of powder B1. When observed 200,000 times by SEM, the particle diameter of the copper particles adhering to the composite carbon material C2 for a negative electrode material of the lithium ion secondary battery was 0.01 to 0.05 μm.
In addition, as for the particle diameter of the copper particle adhering to the composite carbon material C2 for negative electrode materials of the lithium ion secondary battery, 100 copper particles were arbitrarily selected by SEM (scanning electron microscope) observation. The longest diameter X and the minimum diameter Y were measured, and the average value ((X + Y) / 2) of the longest diameter X and the minimum diameter Y was defined as the particle diameter of each copper particle.

<Production and performance evaluation of lithium ion secondary batteries>
It replaced with the composite carbon material C1 for negative electrode materials of a lithium ion secondary battery, and it carried out by the method similar to Example 1 except setting it as the composite carbon material C2 for negative electrode materials of a lithium ion secondary battery. The results are shown in Table 1.

(Example 3)
Instead of introducing an aqueous solution of copper nitrate (II) trihydrate adjusted to be 40 parts by weight in terms of copper atoms with respect to 100 parts by weight of powder A, copper atoms were added to 100 parts by weight of powder A. The same procedure as in Example 2 was performed, except that an aqueous solution of copper nitrate (II) trihydrate adjusted to 1 part by weight was added. The results are shown in Table 1.

Example 4
Instead of introducing an aqueous solution of copper nitrate (II) trihydrate adjusted to be 40 parts by weight in terms of copper atoms with respect to 100 parts by weight of powder A, copper atoms were added to 100 parts by weight of powder A. The same procedure as in Example 2 was performed, except that an aqueous solution of copper nitrate (II) trihydrate adjusted to 240 parts by weight was added. The results are shown in Table 1.

(Example 5)
Instead of putting 40 parts by weight of copper powder with a particle size of 0.1 to 0.5 μm into the hybridizer device, 40 parts by weight of copper powder with a particle size of 0.1 to 1 μm is put into the hybridizer device. Except that, it was performed in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
<Manufacture of composite carbon material for negative electrode material of lithium ion secondary battery>
(First step)
A powder A was obtained in the same manner as in Example 1.

(Baking, crushing, classification)
The obtained powder A was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Next, it is crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor), classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier), and composite carbon for negative electrode material of a lithium ion secondary battery. Material D1 was obtained.

<Production and performance evaluation of lithium ion secondary batteries>
It replaced with the composite carbon material C1 for negative electrode materials of a lithium ion secondary battery, and it carried out by the method similar to Example 1 except setting it as the composite carbon material D1 for negative electrode materials of a lithium ion secondary battery. The results are shown in Table 1.

(Comparative Example 2)
Instead of introducing an aqueous solution of copper nitrate (II) trihydrate adjusted to be 40 parts by weight in terms of copper atoms with respect to 100 parts by weight of powder A, copper atoms were added to 100 parts by weight of powder A. The same procedure as in Example 2 was performed, except that an aqueous solution of copper nitrate (II) trihydrate adjusted to 0.5 parts by weight was added. The results are shown in Table 1.

(Comparative Example 3)
Instead of introducing an aqueous solution of copper nitrate (II) trihydrate adjusted to be 40 parts by weight in terms of copper atoms with respect to 100 parts by weight of powder A, copper atoms were added to 100 parts by weight of powder A. The same procedure as in Example 2 was performed, except that an aqueous solution of copper nitrate (II) trihydrate adjusted to 500 parts by weight was added. The results are shown in Table 1.

(Comparative Example 4)
Instead of putting 40 parts by weight of copper powder having a particle diameter of 0.1 to 0.5 μm into the hybridizer apparatus, 40 parts by weight of copper powder having a particle diameter of 1.7 to 3.0 μm is put into the hybridizer apparatus. The same method as in Example 1 was carried out except that it was added to. The results are shown in Table 1.

  From Table 1 and Table 2, in Comparative Example 1 without addition of copper, the potential drop during charging / discharging with a large current is large and reaches the end-of-discharge battery immediately, so the value of the discharge load is significantly reduced. . The same applies when the amount of copper particles added is small as in Comparative Example 2. On the contrary, as in Comparative Example 3, when the amount of the fixed copper particles is excessive, the battery reaction is remarkably inhibited, so that the reversible capacity is remarkably lowered. Further, as in Comparative Example 4, when the particle diameter of the copper particles is too large, the reversible capacity is remarkably reduced because the destruction of the graphite particles is promoted at the time of compounding and the crystallinity of the graphite particles is remarkably lowered.

It is a schematic diagram of a hybridizer. It is sectional drawing of the battery for evaluation of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material inlet 2 Raw material circulation path 3 Stator 4 Jacket 5 Raw material outlet 6 Drum 7 Blade 8 Rotating part 9 Negative side stainless cap 10 Negative electrode 11 Copper foil 12 Insulating gasket 13 Electrolyte impregnation separator 14 Nickel mesh 15 Positive side stainless cap 16 Positive electrode

Claims (2)

A graphite particle powder having a volume-based median diameter of 5 to 30 μm and an average lattice spacing d (002) of 0.3360 nm or less and a pitch having a softening point of 70 to 250 ° C. are heat-kneaded, and the surface of the graphite particles Coating a coating layer comprising the pitch to obtain a graphite particle powder having the coating layer;
A step of fixing copper particles having a particle diameter of 0.01 to 1.5 μm to the graphite particle powder having the coating layer to obtain a graphite particle powder having a coating layer to which the copper particles are fixed. A second step in which the fixed amount is 1 to 240 parts by weight in terms of copper atoms with respect to 100 parts by weight of the graphite particle powder having the coating layer;
A third step of obtaining a composite carbon material for a negative electrode material of a lithium ion secondary battery by firing and carbonizing a graphite particle powder having a coating layer to which the copper particles are fixed at 800 to 2150 ° C. in a non-oxidizing atmosphere; ,
The manufacturing method of the composite carbon material for negative electrode materials of a lithium ion secondary battery characterized by having.   The method for producing a composite carbon material for a negative electrode material for a lithium ion secondary battery according to claim 1, wherein in the second step, the copper particles are fixed by a liquid phase method or a mechanochemical treatment.

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