JP5413645B2 - Method for producing negative electrode material for lithium secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery that is used as a negative electrode material for a lithium ion secondary battery used in a site that requires a high capacity, such as a notebook computer, and a method for manufacturing 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, small mobile power sources, batteries for power storage, etc. Yes. Initially, metallic lithium was used as a negative electrode material for lithium secondary batteries. Metallic lithium elutes in the electrolyte as lithium ions during discharge, and lithium ions deposit on the negative electrode surface as metallic lithium during charging, but it is difficult to deposit it in a smooth original state during the deposition. It is easy to deposit in the shape. Since this dendrite has a very strong reaction activity and decomposes the electrolytic solution, there is a problem that the cycle life of charge / discharge is shortened. Furthermore, dendrites may 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. Among them, the graphite material has high lithium ion occlusion and release properties, and since the occlusion and release reaction is performed quickly, the charge and discharge efficiency is high, the theoretical capacity is 372 mAh / g, and the potential during charge and 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 a large amount of current cannot be discharged in a short time, resulting in a problem that the rate characteristic is deteriorated.

  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, Japanese Patent Application Laid-Open No. 4-368778 (Patent Document 1) discloses a carbon negative electrode for a secondary battery in which a surface in contact with an electrolytic solution of carbon serving as an active material is covered with amorphous carbon. It is disclosed.

JP-A-6-267531 (Patent Document 2) includes carbonaceous material (A) particles that satisfy the following condition (1) and organic compound (B) particles that satisfy the following condition (2). After mixing, this is heated to carbonize the organic compound (B), so that the particles of the carbonaceous material (A) are coated with the carbonaceous material (C) that satisfies the following condition (3), An electrode material is disclosed.
(1) The d002 in X-ray wide angle diffraction is 3.37 angstroms or less, the true density is 2.10 g / cm ³ or more, and the volume average particle diameter is 5 μm or more;
(2) The volume average particle size is smaller than the carbonaceous material (A);
(3) In a Raman spectrum analysis using an argon ion laser beam having a d002 of 3.38 angstroms or more and a wavelength of 5145 angstroms in X-ray wide-angle diffraction, a peak P _{A in} the range of 1580 to 1620 cm ⁻¹ and a peak of 1350 to 1370 cm ⁻¹ range has a peak P _B, the ratio R = I _B / I _a of the intensity I _B of P _B with respect to the intensity I _a of the P _a is 0.2 or more.

  Japanese Patent Laid-Open No. 2005-243447 (Patent Document 3) discloses that carbonaceous and / or graphite particles having an average particle diameter of more than 100 nm and not more than 1 μm are mechanochemically treated to hydrophilic graphite particles. A negative electrode material for a lithium ion secondary battery characterized by being adhered is disclosed.

  International Publication WO2007 / 086603 (Patent Document 4) describes graphite powder particles having an average particle diameter D50 of 3 to 10 μm and a standard deviation value of 0.2 μm or less and carbon black in a ratio of 1: 1.5 to 3 0.0 100 parts by weight of the mixed powder mixed at a weight ratio, and after mixing and kneading a pitch from which free carbon has been removed or a pitch having a quinoline insoluble content of less than 1% in a proportion of 30 to 120 parts by weight, non-oxidizing A negative electrode material for a lithium ion secondary battery obtained by firing carbonization at a temperature of 1000 ° C. or higher in a neutral atmosphere or further graphitizing is disclosed.

  Japanese Patent Laid-Open No. 2002-255529 (Patent Document 5) contains at least silicon and carbon around graphite particles having a (002) plane spacing d002 of less than 0.337 nm by X-ray wide angle diffraction. In addition, composite particles having a particle diameter smaller than that of the graphite particles are disposed in a dispersed manner, and the graphite particles and the composite particles are covered with an amorphous carbon film having an interplanar spacing d002 of 0.37 nm or more. The particles are formed by disposing a conductive carbon material around Si fine particles made of crystalline silicon, and covering the Si fine particles and the conductive carbon material with a hard carbon film or a conductive polymer film. A carbonaceous material characterized by this is disclosed.

JP-A-4-368778 (Claims) JP-A-6-267531 (Claims) JP 2005-243447 A (Claims) International Publication No. WO2007 / 086603 (Claims) JP 2002-255529 A (Claims))

  In recent years, with the improvement in performance of mobile phones, notebook computers, etc., where lithium ion secondary batteries are mainly used, the demand for rate characteristics has become more sophisticated, and in lithium ion secondary batteries for hybrid cars and electric vehicles, However, while improving the capacity, further improvement of the input / output characteristics is an essential issue.

  However, in Patent Documents 1 to 5, it has not been possible to satisfy recent high demands, that is, further improvement of rate characteristics and high capacity.

  Accordingly, an object of the present invention is to provide a negative electrode material for a lithium ion secondary battery having excellent input / output characteristics and high reversible capacity. Moreover, the subject of this invention is providing the manufacturing method which can manufacture such a negative electrode material for lithium ion secondary batteries industrially.

  As a result of intensive studies to achieve the above object, the present inventors have (1) covered graphite core particles with carbon fine particles through carbides, so that the carbon fine particles are exposed on the surface. Because it is fixed to the core particle, the surface shape of the particle can be manipulated. (2) Therefore, even with a high-density electrode plate, the lithium ion diffusion path between the electrolyte bulk from the inside of the electrode can be improved, so that excellent output can be achieved. The inventors have found that a negative electrode material for a lithium ion secondary battery having input characteristics and high reversible capacity can be obtained, and completed the present invention.

In the present invention, a negative electrode material for a lithium ion secondary battery having a center line average roughness Ra of 10 to 200 nm is obtained.
A graphite core particle powder having a volume-based median diameter of 5 to 30 μm and a (002) plane spacing d (002) of 0.3360 nm or less and a carbon precursor having a softening point of 70 to 250 ° C. are heated and kneaded. A first step of coating the surface of the graphite core particles with the carbon precursor to obtain a graphite core particle powder coated with the carbon precursor;
A graphite core particle powder coated with the carbon precursor and a carbon fine particle powder having a volume-based median diameter of 0.05 to 5 μm and a (002) plane spacing d (002) of 0.3400 nm or more are mixed. The carbon powder was coated with the carbon precursor by applying mechanical energy to the mixed powder and embedding the carbon fine particles in the carbon precursor of the graphite core powder coated with the carbon precursor. A second step of covering the surface of the graphite core powder and obtaining a graphite core particle powder covered with the carbon fine particles via the carbon precursor;
Third step of obtaining a negative electrode material for a lithium ion secondary battery by firing and carbonizing graphite core particle powder covered with the carbon fine particles through the carbon precursor at 1000 to 1600 ° C. in a non-oxidizing atmosphere. When,
Method for producing a lithium ion secondary battery negative electrode material, characterized in that the applied and provides a.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode material for lithium ion secondary batteries provided with the outstanding input-output characteristic and high reversible capacity can be provided, and such a negative electrode material for lithium ion secondary batteries is industrially used. The manufacturing method which can be manufactured can be provided.

It is typical sectional drawing which shows the graphite nucleus particle | grains coat | covered with this carbon precursor obtained by performing this 1st process. It is typical sectional drawing of the graphite nucleus particle | grains covered with the carbon fine particle through this carbon precursor obtained by performing this 2nd process. It is typical sectional drawing of this negative electrode material for lithium ion secondary batteries obtained by performing this 3rd process. It is a schematic diagram of a Henschel mixer. It is sectional drawing which shows the button type battery for evaluation. It is a SEM photograph of the surface of negative electrode material C1 for lithium ion secondary batteries. It is an enlarged SEM photograph of FIG. It is a SEM photograph of the section of negative electrode material C1 for lithium ion secondary batteries. It is an enlarged SEM photograph of FIG. FIG. 2 is a schematic cross-sectional view showing graphite core particles in which the entire carbon fine particles are completely embedded in a carbon precursor. It is a SEM photograph of the surface of negative electrode material F9 for lithium ion secondary batteries. It is an enlarged SEM photograph of FIG. It is a SEM photograph of the cross section of the negative electrode material F9 for lithium ion secondary batteries. It is a schematic diagram of a hybridizer.

The method for producing a negative electrode material for 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 a surface spacing d (002) of the (002) plane. A graphite core particle powder of 0.3360 nm or less and a carbon precursor having a softening point of 70 to 250 ° C. are heated and kneaded so that the surface of the graphite core particle is coated with the carbon precursor and coated with the carbon precursor. A first step of obtaining a graphite core particle powder,
A graphite core particle powder coated with the carbon precursor and a carbon fine particle powder having a volume-based median diameter of 0.05 to 5 μm and a (002) plane spacing d (002) of 0.3400 nm or more are mixed. By applying mechanical energy to the mixed powder and embedding the carbon fine particles in the carbon precursor of the graphite core particles coated with the carbon precursor, the graphite core powder coated with the carbon precursor A second step of covering the surface with the carbon fine particles and obtaining a graphite core particle powder covered with the carbon fine particles via the carbon precursor;
Third step of obtaining a negative electrode material for a lithium ion secondary battery by firing and carbonizing graphite core particle powder covered with the carbon fine particles through the carbon precursor at 1000 to 1600 ° C. in a non-oxidizing atmosphere. When,
It is a manufacturing method of the negative electrode material for lithium ion secondary batteries which has this.

  The manufacturing method of the present invention will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing graphite core particles coated with the carbon precursor obtained by performing the first step, and FIG. 2 shows the carbon precursor obtained by performing the second step. FIG. 3 is a schematic cross-sectional view of graphite core particles covered with carbon fine particles, and FIG. 3 is a schematic cross-sectional view of the negative electrode material for a lithium ion secondary battery obtained by performing the third step. .

  First, in the first step, the graphite core particle powder and the carbon precursor are heated and kneaded to coat the surface of the graphite core particle 1 with the carbon precursor 2 as shown in FIG. Graphite core particles 3 coated with the body are obtained.

  Next, in the second step, the graphite core particle powder coated with the carbon precursor and the carbon fine particle powder are mixed, and mechanical energy such as shear force and collision force is applied, as shown in FIG. Further, carbon fine particles 4 are embedded in the surface of the carbon precursor 2 of the graphite core particle 3 coated with the carbon precursor, and the surface of the graphite core particle 3 coated with the carbon precursor is covered with the carbon fine particle 4. Covering and obtaining graphite core particles 5 covered with carbon fine particles through a carbon precursor. In the graphite core particles 5 covered with the carbon fine particles via the carbon precursor, a part of the graphite fine particles 4 is embedded in the carbon precursor 2, and the entire carbon particle 4 is not embedded. It exists in the state exposed to the surface of the graphite core particle 5 covered with the carbon fine particles through the carbon precursor.

  Next, in the third step, the graphite core particle powder covered with the carbon fine particles via the carbon precursor is calcined and carbonized in a non-oxidizing atmosphere, so that the carbon fine particles are covered with the carbon precursor. The carbon precursor 2 of the graphite core particles 5 is carbonized to form a carbide, thereby obtaining a negative electrode material 7 for a lithium ion secondary battery as shown in FIG. In the negative electrode material 7 for a lithium ion secondary battery, the carbon fine particles 4 are fixed to the graphite core particles 1 through carbides 6. The negative electrode material 7 for a lithium ion secondary battery is a carbonaceous composite having a core-shell structure in which the graphite core particles 1 (core) are covered with the carbon fine particles 4 (shell). The carbon fine particles 4 are fixed in a state of being exposed on the surface of the negative electrode material 7 for a lithium ion secondary battery.

  In the first step according to the production method of the present invention, the graphite core particle powder and the carbon precursor are heated and kneaded to coat the surface of the graphite core particles with the carbon precursor, In this step, a carbon precursor layer is formed to obtain graphite core particle powder coated with the carbon precursor.

  The graphite core particle powder according to the first step is not particularly limited, and examples thereof include natural graphite or artificial graphite, artificial graphite electrode crushed products, coke, and mixtures thereof. Examples of the shape of the powder include a spherical shape or a scale-like shape, and those that have been previously pulverized, classified, or previously spheroidized may be used. Examples of the artificial graphite related to the graphite core particle powder include artificial graphite having a thermal history of 2500 ° C. or higher. The graphite core particle powder is preferably spherical or scale-like natural graphite or artificial graphite having a thermal history of 2500 ° C. or higher in that the charge / discharge capacity is increased.

  The graphite core 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 volume-based median diameter of the graphite core particle powder is 5 to 30 μm, preferably 5 to 20 μm, and particularly preferably 10 to 15 μm. If the volume-based median diameter of the graphite core particle powder is smaller than the above range, the dispersibility at the time of slurry preparation becomes low, the specific surface area becomes too large, and the self-discharge becomes large. Further, when the volume-based median diameter of the graphite core particle powder is larger than the above range, the capacity retention rate when discharging a large current as a lithium ion secondary battery is lowered. 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) of the graphite core particle powder measured by the X-ray wide angle diffraction method is 0.3360 nm or less, preferably 0.3358 nm or less, particularly preferably 0.3356 nm or less. When the interplanar spacing d (002) of the (002) plane of the graphite core particle powder exceeds the above range, the discharge reversible capacity tends to be small and the energy density tends to be low. In the present invention, a wide angle X-ray diffraction curve is measured by a reflective diffractometer method using a CuKα ray monochromatized with a graphite monochromator, and the interplanar spacing d (002) is determined by using the Gakushin method. It was measured.

  The carbon precursor according to the first step is a substance that is converted into a carbide by calcination and carbonization in the third step, and examples thereof include coal tar, pitch coke, and a phenolic resin. Among these, a pitch from which free carbon is removed or a pitch having a quinoline insoluble content of less than 1% is preferable in that the purity of the negative electrode material is increased.

  The softening point of the carbon precursor is 70 to 250 ° C, particularly preferably 70 to 200 ° C, and more preferably 70 to 150 ° C, as measured by the ring and ball method. When the pitch softening point is less than the above range, the carbon precursor melts due to frictional heat between the particles in the second step, and the graphite core particles or the carbon fine particles are produced. It will be grained. On the other hand, if the softening point of the pitch exceeds the above range, the embedding of the carbon fine particles becomes shallow and the adhesive strength is lowered. 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 carbon precursor preferably has a weight reduction rate after baking carbonization at 1000 ° C. in a non-oxidizing atmosphere of 45% or less, particularly preferably 40% or less, and more preferably 35% or less.

  The mixing amount of the carbon precursor at the time of kneading in the first step is preferably 5 to 50 parts by weight, and preferably 5 to 30 parts by weight with respect to 100 parts by weight of the graphite core particle powder. Particularly preferred is 5 to 20 parts by weight. When the mixing amount of the carbon precursor is less than the above range, it is difficult to uniformly coat the surface of the graphite core particles with the carbon precursor. Further, if the mixing amount of the carbon precursor exceeds the above range, the particles are firmly gathered together, so that it is difficult to crush into individual particles, the particle diameter is likely to increase, and the crushing is performed. Occasionally, the coated carbon precursor layer is cleaved, so that the thickness of the carbon precursor layer on the surface of the graphite core particles tends to be uneven. If the thickness of the carbon precursor layer on the surface of the graphite core particles is non-uniform, the coating of the carbon fine particles becomes non-uniform and the input / output characteristics tend to be low.

  The heating temperature at the time of carrying out heat kneading in the first step is a temperature exceeding the softening point of the carbon precursor, and preferably 20 ° C. or more higher than the softening point of the carbon precursor.

  An example of the heating and kneading operation in the first step is as follows. The graphite core particle powder and the carbon precursor are put into a kneading apparatus, and the temperature in the apparatus container is set to the softening point of the carbon precursor while kneading. The temperature is raised to a predetermined temperature exceeding and kneaded sufficiently while heating. The time for heating and kneading is appropriately selected depending on the capacity of the kneading apparatus, the shape of the kneading blade, the amount of the graphite core particles and the carbon precursor, etc., but usually 5-30 at a temperature exceeding the melting point of the carbon precursor. For minutes. And the graphite core particle powder coat | covered with this carbon precursor is obtained by heat-kneading.

  In the first step, the kneading apparatus for performing the heat-kneading is not particularly limited, and any kneading apparatus such as a kneader or a planetary mixer can be used as long as it can be stirred or kneaded while heating the powder. Examples thereof include a drum rotating mixer such as a drum mixer, a high-speed stirring mixer such as a Henschel mixer, and a high-speed mixer.

  In this way, in the first step, the graphite core particle powder and the carbon precursor are heated and kneaded to coat the surface of the graphite core particles with the carbon precursor, and A carbon precursor layer is formed to obtain graphite core particle powder coated with the carbon precursor.

  The thickness of the carbon precursor coating layer of the graphite core particle powder coated with the carbon precursor obtained in the first step is preferably 0.01 to 0.50 μm, particularly preferably 0.01 to 0.00. 20 μm. When the thickness of the coating layer of the graphite core particle powder coated with the carbon precursor is within the above range, the adhesion between the graphite particles and the carbon fine particles becomes strong, and the graphite particle surface due to expansion / contraction due to repeated charge / discharge The lithium ion secondary battery is less likely to drop out of the battery.

  The volume-based median diameter measured by the laser diffraction method of the graphite core particle powder coated with the carbon precursor obtained in the first step is not particularly limited, but is generally 5 to 30 μm.

  Next, the second step according to the production method of the present invention is performed. In the second step, the graphite core particle powder coated with the carbon precursor and the carbon fine particle powder are mixed, and mechanical energy is applied to the obtained mixed powder to coat with the carbon precursor. By embedding a part of the carbon fine particles in the carbon precursor layer of the graphite core particles, the graphite core particles coated with the carbon precursor are covered with the carbon fine particles, and the carbon fine particles are interposed via the carbon precursor. This is a step of obtaining graphite core particles covered with.

  As shown in FIG. 2, in the graphite core particles covered with the carbon fine particles via the carbon precursor according to the present invention, a part of each particle of the carbon fine particles is embedded in the carbon precursor layer. However, other parts are exposed. That is, the graphite core particles coated with the carbon precursor according to the present invention have a structure in which the entire carbon fine particles 31 are completely embedded in the carbon precursor layer 32 as shown in FIG. Is different.

  Examples of the carbon fine particles according to the second step include carbon black, coke, and pulverized powder of resin carbide. The carbon fine particles are preferably carbon fine particles obtained by thermally decomposing a carbon precursor such as carbon black or thermal black in order to enable fine irregularities.

  The volume-based median diameter of the carbon fine particle powder is 0.05 to 5 μm, preferably 0.05 to 1.00 μm, particularly preferably 0.05 to 0.50 μm. If the volume-based median diameter of the carbon fine particle powder is smaller than the above range, the BET specific surface area of the negative electrode material for a lithium ion secondary battery is increased, and the initial charge loss or self-discharge is increased. If the volume-based median diameter of the carbon fine particle powder is larger than the above range, the area of the adhesion interface with the graphite core particle surface is small and sufficient adhesive strength cannot be obtained, so that the composite particle state cannot be maintained.

  The surface spacing d (002) of the (002) plane measured by the X-ray wide angle diffraction method of the carbon fine particle powder is 0.3400 nm or more, preferably 0.3450 nm or more, particularly preferably 0.3500 nm or more. When the interplanar spacing d (002) of the (002) plane of the carbon fine particle powder is less than the above range, the battery characteristics and behavior of the graphite core particles are dominant, and the input / output characteristics cannot be improved.

The Raman spectrum intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) of the carbon fine particle powder is preferably 0.40 or more, particularly preferably 0.45 to 0.75. When the Raman spectrum intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) of the carbon fine particle powder is in the above range, the input / output characteristics can be further improved. In the present invention, it is appropriate to discuss the disorder of the crystal structure of the particle surface layer using a Raman spectrum. In the present invention, the measurement target is measured with a Raman spectroscopic analyzer (NR1100, manufactured by JASCO Corporation) using an Ar laser with a wavelength of 514.5 nm, and is based on crystal defects on the surface layer, mismatch of the laminated structure, and the like. The spectrum I ₁₃₆₀ in the vicinity of 1360 cm ⁻¹ belonging to the disorder of the crystal structure is divided by the spectrum I ₁₅₈₀ in the vicinity of ₁₅₈₀ cm ⁻¹ belonging to the E _2g type vibration corresponding to the lattice vibration in the carbon hexagonal mesh plane, and the Raman spectrum intensity The ratio R = I ₁₃₆₀ / I ₁₅₈₀ was determined.

BET specific surface area of the carbon fine particles is preferably ^{30 m} 2 / g or less, particularly preferably 7.0~15.0m ² / g. When the BET specific surface area of the carbon fine particles is in the above range, the loss or self-discharge during the initial charge is further reduced. In the present invention, the BET specific surface area is a value measured by the BET method using nitrogen as an adsorbed gas by GEMINI 2375 manufactured by Shimadzu Corporation.

  In the second step, the mixing amount of the carbon fine particle powder is preferably 5 to 20 parts by weight, particularly preferably 5 to 15 parts by weight with respect to 100 parts by weight of the graphite core particle powder coated with the carbon precursor. More preferably, it is 5 to 10 parts by weight. If the mixing amount of the carbon fine particles is less than the above range, it becomes difficult to cover the entire surface of the graphite core particles coated with the carbon precursor, and if it exceeds the above range, the non-graphitic carbon component increases. Thus, the reversible capacity tends to be low.

  In the present invention, the carbon fine particle powder coated with the carbon precursor obtained in the first step is not taken out from the apparatus, and the carbon fine particle powder is further introduced into the apparatus, Two steps can also be performed. In such a case, in the second step, the mixing amount of the carbon fine particle powder is preferably 5 to 25 parts by weight, particularly preferably 100 parts by weight of the graphite core particle powder used in the first step. 5 to 20 parts by weight, more preferably 5 to 15 parts by weight. If the mixing amount of the carbon fine particles is less than the above range, it becomes difficult to cover the entire surface of the graphite core particles coated with the carbon precursor, and if it exceeds the above range, the non-graphitic carbon component increases. Thus, the reversible capacity tends to be low.

  In the second step, the graphite core particle powder coated with the carbon precursor and the carbon fine particle powder are mixed, and mechanical energy is applied to the obtained mixed powder.

  In the second step, using a mix muffler (manufactured by Shinto Kogyo Co., Ltd.), a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.), a high speed mixer, etc., using collisions between particles, compression, friction, shear, Mechanical energy is repeatedly applied to the mixed powder repeatedly from the outside. Thus, with the carbon precursor layer softened, a part of the carbon fine particles is embedded in the carbon precursor layer, and the surface of the graphite core particles covered with the carbon precursor is covered with the carbon fine particles. A graphite core particle powder covered with the carbon fine particles through the carbon precursor is obtained. In the second step, a part of the carbon fine particles are embedded in the carbon precursor layer so that the surface of the graphite core particles is covered with the carbon fine particles. It is necessary to apply mechanical energy to the mixed powder so as to be embedded in the carbon precursor layer in an exposed state. Then, a part of the carbon fine particles is embedded in the carbon precursor layer by selecting the type of apparatus that applies mechanical energy, such as a mix muffler, Henschel mixer, and high-speed mixer, and by selecting the operating conditions. Thus, graphite core particles covered with carbon fine particles are obtained through the carbon precursor. On the other hand, if the mechanical energy applied to the mixed powder is too strong, the entire carbon fine particles are buried in the carbon precursor layer. For example, when a mechanical energy is applied to the mixed powder using a hybridizer (manufactured by Nara Machinery Co., Ltd.) that is a device that applies very strong mechanical energy as in Comparative Example 9, the carbon fine particles are , And completely buried in the carbon precursor layer. Therefore, as shown in FIG. 11, the carbon fine particles are not exposed on the surface of the obtained particles.

  In the second step, the magnitude of mechanical energy when mechanical energy is added to the mixed powder can be defined by, for example, the peripheral speed of the apparatus and the stirring blade. In that case, a mixed muffler, a Henschel mixer, or a high-speed mixer The peripheral speed of the stirring blade is 5 to 150 m / s, preferably 10 to 100 m / s, particularly preferably 20 to 50 m / s. For example, using a mixed muffler, a Henschel mixer or a high-speed mixer, the mixed powder is flowed with a stirring blade having a peripheral speed of 5 to 150 m / s, preferably 10 to 100 m / s, particularly preferably 20 to 50 m / s. By causing particle powders to collide with each other or stirring blades and particle powders, mechanical energy is applied to the mixed powder, and the carbon precursor of graphite core particles coated with the carbon precursor is subjected to the carbon precursor. Part of the microparticles can be embedded.

  In the second step, examples of a method for imparting mechanical energy to the mixed powder include a method using a Henschel mixer 10 (manufactured by Mitsui Mining Co., Ltd.) shown in FIG. The graphite core particle powder coated with the carbon precursor and the carbon fine particle powder are charged into the Henschel mixer 10 shown in FIG. 4, and the upper blade 17 and the lower blade 18 are rotated at a peripheral rotation speed of 5 to 150 m / s. , Preferably 10 to 100 m / s, particularly preferably 20 to 50 m / s, for 5 to 30 minutes. At this time, mechanical energy is applied to the mixed powder put into the Henschel mixer 10 by shearing force, frictional force, compressive force and collision force generated by high-speed rotation of the upper blade 17 and the lower blade 18 having different shapes. Is added. In addition, 11 is an upper cover, 12 is a filter, 13 is a discharge port, 14 is a heat medium circuit, 15 is a main shaft, and 16 is a jacket.

  The temperature inside the Henschel mixer when mechanical energy is added to the mixed powder by a Henschel mixer such as the Henschel mixer 10 shown in FIG. 4 increases due to the application of mechanical energy, but the softening point of the carbon precursor +100 It is preferable to adjust to a temperature of 0 ° C. or lower. When the temperature in the Henschel mixer exceeds the softening point of the carbon precursor + 100 ° C., the carbon precursor melts and elutes from the gaps of the granulated particles, and the eluted carbon precursor enters the Henschel mixer. Since it becomes easy to adhere, regular continuous operation tends to be difficult. In addition, adjusting to the temperature of the carbon precursor softening point + 100 ° C. or lower means, for example, that when the carbon precursor has a softening point of 90 ° C., the temperature inside the Henschel mixer is set to 190 ° C. or lower. is there.

  The rotational peripheral speed of the upper blade 17 and the lower blade 18 when mechanical energy is applied to the mixed powder by a Henschel mixer such as the Henschel mixer 10 shown in FIG. 4 is appropriately adjusted according to the embedding depth of the carbon fine particles. 5 to 150 m / s is preferable. When the rotational peripheral speed of the upper blade 17 and the lower blade 18 is less than 5 m / s, the mechanical energy received by the mixed powder is small, and an effective adhesive strength between the carbon fine particles and the carbon precursor is obtained. Even if it exceeds 150 m / s, the coating efficiency does not change from the case of 150 m / s, and the upper limit is preferably set to 150 m / s in consideration of the maintenance cost, safety, etc. of the apparatus. Further, the treatment time when mechanical energy is added to the mixed powder with the Henschel mixer is preferably 5 to 30 minutes, and particularly preferably 15 to 25 minutes. If the treatment time is less than 5 minutes, the coating efficiency of the carbon fine particles tends to be low, and even if it exceeds 30 minutes, the coverage hardly changes. Therefore, in consideration of productivity, the treatment time is 25 minutes or less. Is particularly preferred. In addition, when the shearing force, frictional force, compressive force, and collision force are too strong and particle breakage occurs, lubricating oil or wax can be added to smooth the friction between the particles.

  In the second step, the remaining carbon ratio of the carbon precursor, the thickness of the carbon precursor layer, the strength of mechanical energy, for example, the upper blade 17 and the lower blade 18 of the Henschel mixer 10 in FIG. The embedding depth of the carbon fine particles can be controlled by adjusting the rotational peripheral speed. In addition, although it is the thickness of this carbon precursor layer, the thickness of this carbon precursor layer can be adjusted by adjusting the mixing amount of this carbon precursor mixed by this 1st process. In the second step, the carbon fine particles are adjusted by adjusting the volume-based median diameter of the carbon fine particles or by adjusting the embedding depth of the carbon fine particles by selecting a device to be used and its operating conditions. The carbon fine particles can be embedded in the carbon precursor of graphite core particles coated with the carbon precursor while being exposed on the surface.

  Next, the third step according to the production method of the present invention is performed. The third step is a step of obtaining a negative electrode material for a lithium ion secondary battery by firing and carbonizing graphite core particle powder covered with carbon fine particles via the carbon precursor in a non-oxidizing atmosphere. .

  In the third step, the calcining carbonization temperature when calcining and carbonizing the graphite core particle powder covered with the carbon fine particles via the carbon precursor is 1000 to 1600 ° C, preferably 1000 to 1400 ° C, particularly preferably. 1000 to 1200 ° C. In the third step, if the calcination carbonization temperature is less than the above range, the low molecular organic unburned content in the carbon precursor remains, and the charge / discharge efficiency of the lithium ion secondary battery is reduced and the cycle characteristics are deteriorated. Happens. Further, in the third step, when the calcining carbonization temperature exceeds the above range, the input / output characteristics are lowered or the discharge reversible capacity is lowered along with the crystal structure change of the carbon fine particles or the carbon precursor carbide. To do.

  In the third step, calcination carbonization is performed in a non-oxidizing atmosphere. The non-oxidizing atmosphere is an inert gas atmosphere such as nitrogen gas, helium gas, argon gas, or the carbon precursor is oxidized and consumed. It is the atmosphere that carbonizes without doing.

  In this way, in the third step, by calcining the graphite core particle powder covered with the carbon fine particles via the carbon precursor, the carbon precursor is carbonized to become a carbide, and the carbon When the precursor becomes a carbide, the carbon fine particles are firmly fixed, and the negative electrode material for a lithium ion secondary battery is obtained.

  After performing the third step, the negative electrode material for a lithium ion secondary battery obtained by performing the third step 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 Nissin Engineering Co., Ltd.), etc. Illustrated. In the classification, the number of revolutions is adjusted as necessary so that the volume median diameter becomes 10 to 40 μm.

  And the negative electrode material for lithium ion secondary batteries of this invention is obtained by performing the manufacturing method of this invention.

The negative electrode material for a lithium ion secondary battery of the present invention has a core-shell structure in which graphite core particles having a volume-based median diameter of 5 to 30 μm are covered with carbon fine particles having a volume-based median diameter of 0.05 to 5 μm. Composite particles,
The carbon fine particles are fixed to the graphite core particles through a carbide obtained by firing and carbonizing the carbon precursor at 1000 to 1600 ° C.,
The centerline average roughness Ra is 10 to 200 nm, the BET specific surface area is 3.0 to 7.0 m ² / g, the (002) plane spacing d (002) is 0.3360 nm or less, and the volume It is a negative electrode material for a lithium ion secondary battery having a median diameter of 10 to 40 μm and a Raman spectral intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) of 0.40 or more.

  The interplanar spacing d (002) of the (002) plane of the graphite core particles is 0.3360 nm or less, preferably 0.3358 nm or less, particularly preferably 0.3356 nm or less. Further, the interplanar spacing d (002) of the (002) plane of the carbon fine particles is 0.3400 nm or more, preferably 0.3450 nm or more, particularly preferably 0.3500 nm or more.

  The carbide obtained by firing and carbonizing graphite core particles, carbon fine particles, a carbon precursor, and a carbon precursor according to the negative electrode material for a lithium ion secondary battery of the present invention at 1000 to 1600 ° C. is a graphite according to the production method of the present invention. This is the same as the carbide obtained by firing and carbonizing the core particles, carbon fine particles, carbon precursor, and carbon precursor at 1000 to 1600 ° C.

  In the negative electrode material for a lithium ion secondary battery of the present invention, the carbon fine particles cover the graphite core particles with the carbon precursor carbide in a state of being exposed on the surface. The negative electrode material for a secondary battery is a carbon composite particle powder having a core-shell structure in which the graphite core particles (core) are covered with the carbon fine particles (shell).

The center line average roughness Ra of the negative electrode material for a lithium ion secondary battery of the present invention is 10 to 200 nm, preferably 50 to 200 nm, and particularly preferably 100 to 200 nm. The centerline average roughness Ra is in the above range, so that a sufficient electrical interparticle contact area is ensured, and even in a high-density electrode plate, the lithium ion diffusion path between the electrolyte bulk from the inside of the electrode is improved. Therefore, the input / output characteristics can be improved and the discharge reversible capacity can be increased. On the other hand, if the center line average roughness Ra is less than the above range, the surface structure does not reflect the structure of the carbon fine particles, and in the high-density electrode plate, the lithium from the inside of the electrode to between the electrolyte bulks An ion diffusion path cannot be secured, resulting in low input / output characteristics. When the center line average roughness Ra exceeds the above range, it is difficult to increase the density of the electrode plate, the battery capacity is reduced, and the electrical interparticle contact area is reduced. The output / input characteristics become lower. The adjustment of the center line average roughness Ra is, for example, the volume-based median diameter of the carbon fine particle powder or the carbon precursor layer when the graphite core particles are coated with the carbon precursor in the first step. This can be achieved by adjusting the strength of mechanical energy applied to the mixed powder by adjusting the thickness or by adjusting the rotational peripheral speed of the Henschel mixer blades in the second step. In the present invention, the center line average roughness Ra is a value calculated by measuring the surface roughness. For example, the height profile of the measurement object is measured with an atomic force microscope with an observation field of view of 4 μm ² . It is obtained as a value obtained by dividing the uneven area from the center line of the cross section curve by the center line length.

The BET specific surface area of the negative electrode material for a lithium ion secondary battery of the present invention is 3.0 to 7.0 m ² / g, preferably 3.0 to 6.0 m ² / g, particularly preferably 3.0 to 5. 0 m ² / g. If the BET specific surface area is less than the above range, the reaction area required for lithium ion desorption / insertion is small, resulting in low input / output characteristics. If the BET specific surface area exceeds the above range, loss during self-discharge and initial charge occurs. growing. The BET specific surface area can be adjusted, for example, by adjusting the volume-based median diameter of the graphite core particles or the thickness of the carbon precursor layer when the carbon precursor is coated on the graphite core particles in the first step. This can be achieved by adjusting the pulverizing conditions such as the rotational speed of the pulverizer and the classification conditions.

  The interplanar spacing d (002) of the (002) plane measured by the X-ray wide angle diffraction method of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 0.3360 nm or less, particularly preferably 0.3358 nm or less, more preferably Is 0.3356 nm or less. When the surface interval d (002) of the (002) plane exceeds the above range, the discharge reversible capacity becomes small.

The Raman spectrum intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) of the negative electrode material for a lithium ion secondary battery of the present invention is preferably 0.40 or more, particularly preferably 0.45 to 0.75. When the Raman spectrum intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) is in the above range, the input / output characteristics are improved. The Raman spectral intensity ratio R (I ₁₃₆₀ / I ₁₅₈₀ ) can be adjusted, for example, by adjusting the rotational peripheral speed of the Henschel mixer blades in the second step, etc. This can be achieved by adjusting the strength, selecting the carbon fine particles, or adjusting the pulverizing conditions such as the number of revolutions of the pulverizer.

  The volume median diameter of the negative electrode material for a lithium ion secondary battery of the present invention is 10 to 40 μm, preferably 10 to 30 μm, particularly preferably 10 to 20 μm. When the volume median diameter is less than the above range, the dispersibility in the liquid during slurry preparation is poor, and when it exceeds the above range, the input / output characteristics are lowered. The volume median diameter can be adjusted, for example, by adjusting the volume-based median diameter of the graphite core particles, pulverization conditions such as the number of revolutions of the pulverizer, and classification conditions.

  In the negative electrode material for a lithium ion secondary battery of the present invention and the negative electrode material for a lithium ion secondary battery obtained by the production method of the present invention, since the carbon fine particles are fixed in a state exposed on the surface, the surface shape of the particles That is, the center line average roughness Ra can be in the above range. Further, since the carbon fine particles having a small particle size are fixed on the surface, the amorphous carbon particles are thinly and uniformly coated. Therefore, while suppressing the specific surface area, the crystallinity of the surface of the graphite core particles can be reduced, and the surface shape of the particles can be controlled. As a result, the negative electrode material for lithium ion secondary batteries of the present invention and the negative electrode material for lithium ion secondary batteries obtained by the production method of the present invention have high input / output characteristics and high discharge reversible capacity. A negative electrode material.

  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 negative electrode material for lithium ion secondary battery>
(First step)
Coal tar pitch (JFE Chemical Corporation, PKQL) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm) , A softening point of 70 ° C.) was heated and kneaded with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) for 10 minutes while maintaining the temperature in the apparatus at 150 to 160 ° C. to obtain powder A1.

(Second step)
Subsequently, furnace black (manufactured by Tokai Carbon Co., Ltd., S-TA, volume-based median diameter 0.7 μm, d (002) = 0.0) was added to a Henschel mixer with respect to 100 parts by weight of spheroidized natural graphite used in the first step. 3620 nm), 20 parts by weight were charged, and while maintaining the temperature in the apparatus at 150 to 160 ° C., treatment was performed at a rotational speed of 100 m / s for 10 minutes to obtain powder B1. When the powder B1 after the second step was observed with a scanning electron microscope, it was confirmed that the surface was covered with furnace black.

(Third process)
The obtained powder B1 was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Subsequently, it is crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material C1 for a lithium ion secondary battery. It was. The physical properties are shown in Table 3. Moreover, although the SEM photograph of the surface and cross section of the negative electrode material C1 for lithium ion secondary batteries is shown in FIGS. 6-9, it is confirmed that the surface of the negative electrode material C1 for lithium ion secondary batteries is covered with furnace black It was done.

<Measurement method for each characteristic>
(1) Volume-based median diameter This is a volume-based median diameter measured by a laser diffraction particle size distribution measuring apparatus (manufactured by Shimadzu Corporation, SALD2000).
(2) d (002) (nm) by X-ray diffraction method
The measurement by the X-ray diffraction method is performed using a Cu (Kα ray) graphite monochromator as a target, a slit as a diverging slit = 1 degree, a light receiving slit = 0.1 mm, and a scattering slit = 1 degree. A surface interval d (002) is obtained.
(3) Specific surface area (m ² / g)
Using a surface area meter (Shimadzu fully automatic surface area measuring device), after performing preliminary drying at 350 ° C. for 30 minutes under nitrogen flow, the relative pressure value of nitrogen relative to atmospheric pressure becomes 0.3. It is a value measured by a nitrogen adsorption BET 10-point method by a gas flow method using a nitrogen-helium mixed gas adjusted accurately as described above.
(4) Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀
Raman spectroscopy using an Ar laser having a wavelength of 514.5 nm (manufactured by JASCO Corporation, NR1100) measured by, attributable to disturbance of the crystal structure due to mismatching of crystal defects and stacking structure of the surface layer 1360 cm ^-1 The spectrum I ₁₃₆₀ in the vicinity is divided by the spectrum I ₁₅₈₀ in the vicinity of ₁₅₈₀ cm ⁻¹ belonging to the E _2g type vibration corresponding to the lattice vibration in the carbon hexagonal mesh plane, and the Raman spectrum intensity ratio R = I ₁₃₆₀ / I ₁₅₈₀ is obtained. It was.
(5) Centerline average roughness The centerline average roughness is a value calculated by surface roughness measurement using an atomic force microscope. The height profile of the object to be measured (single particle) was measured at an observation field of view 4 μm ² , and the center line average roughness Ra was obtained by dividing the uneven area from the center of the cross-sectional curve by the center line length. .

<Creation of lithium ion secondary battery>
(Preparation of slurry)
An appropriate amount of 1 wt% carboxymethylcellulose (CMC) aqueous solution as a thickener was added to 100 parts by weight of the negative electrode material C1 for lithium ion secondary battery obtained as described above, and the mixture was stirred and mixed for 30 minutes. An appropriate amount of 40 wt% styrene-butadiene rubber (SBR) aqueous solution was added as an agent, and the mixture was stirred and mixed 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.

(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. 5 was assembled under an inert atmosphere as an evaluation battery. 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 discharge capacity. Further, the output characteristics of the negative electrode material were examined based on the capacity retention rate when discharged at 10 mA / cm ² from the fully charged state. The results are shown in Table 4.
In FIG. 5, 27 is a negative electrode side stainless cap, 20 is a negative electrode, 21 is a copper foil, 22 is an insulating gasket, 23 is an electrolyte impregnated separator, 24 is a nickel mesh, 25 is a positive electrode side stainless steel cap, and 26 is a positive electrode. is there.

<First loss, initial efficiency and discharge load>
(1) Initial loss The initial loss is a value obtained by subtracting the discharge capacity from the charge capacity at the time of initial charge / discharge. (2) Initial efficiency The initial efficiency is a value (%) obtained by dividing the initial discharge capacity by the initial charge capacity. A larger value is preferable.
(3) Discharge load A discharge load is a discharge capacity at the time of performing a constant current discharge from a fully charged state to 10 V / cm ² at a final voltage of 1.5V. It can be said that the larger this value is, the negative electrode material capable of discharging a large current.
(4) Capacity maintenance ratio The capacity maintenance ratio is a value (%) obtained by dividing the discharge load by the reversible discharge capacity.

(Example 2)
<Manufacture of negative electrode material for lithium ion secondary battery>
(First step)
Coal tar pitch (JFE Chemical Corporation, PKE) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm) , A softening point of 89 ° C.) was heated and kneaded with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) for 10 minutes while maintaining the temperature in the apparatus at 140 to 150 ° C. to obtain powder A2.

(Second step)
Furthermore, with respect to 100 parts by weight of spheroidized natural graphite used in the first step, lamp black (manufactured by Fukuzumi Kasei Co., Ltd., Carbofin GK, volume-based median diameter 0.9 μm, d (002) = 0.3740 nm) ) 20 parts by weight was charged, and the temperature in the apparatus was kept at 140 to 150 ° C., followed by treatment at a rotational speed of 50 m / s for 10 minutes to obtain powder B2. When the powder B2 after the second step was observed with a scanning electron microscope, it was confirmed that the surface was covered with lamp black.

(Third process)
The obtained powder B2 was put into a graphite crucible and calcined at 1600 ° C. in a nitrogen gas atmosphere. Next, it is crushed with a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified with a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material C2 for a lithium ion secondary battery. It was. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
It carried out by the method similar to Example 1 except using the negative electrode material C2 for lithium ion secondary batteries. The results are shown in Table 4.

(Example 3)
<Manufacture of negative electrode material for lithium ion secondary battery>
(First step)
Mesophase pitch (JFE Chemical Co., Ltd., MCP-) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-30, volume-based median diameter is 30.0 μm, d (002) = 0.3355 nm) 50 parts by weight of 150D, softening point 150 ° C. were kneaded with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) for 10 minutes while maintaining the temperature in the apparatus at 190 to 200 ° C. to obtain powder A3.

(Second step)
Furthermore, the non-graphitized coke (trade name LPC-S55, manufactured by Nippon Steel Chemical Co., Ltd., volume-based median diameter 1.8 μm, d (002) is used for Henschel mixer with respect to 100 parts by weight of spheroidized natural graphite used in the first step. ) = 0.422 nm) 5 parts by weight were charged, and while maintaining the temperature in the apparatus at 190 to 200 ° C., the mixture was treated at a rotational speed of 50 m / s for 10 minutes to obtain powder B3. In addition, when the powder B3 after the second step was observed with a scanning electron microscope, it was confirmed that the surface was covered with non-graphitized coke.

(Third process)
The obtained powder B3 was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Next, it is crushed with a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified with a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material C3 for a lithium ion secondary battery. It was. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material C3 for lithium ion secondary batteries was used. The results are shown in Table 4.

Example 4
<Manufacture of negative electrode material for lithium ion secondary battery>
(First step)
Mesophase pitch (JFE Chemical Corporation, MCP-) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm) 250D, softening point 250 ° C.) 10 parts by weight was heated and kneaded with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) for 10 minutes while maintaining the temperature in the apparatus at 270 to 280 ° C. to obtain powder A4.

(Second step)
Subsequently, carbon microspheres (trade name CNS, manufactured by Tokai Carbon Co., Ltd., volume-based median diameter of 0.4 μm, d (002) = 0) with respect to 100 parts by weight of spheroidized natural graphite used in the first step. .3640 nm) was charged at 10 parts by weight, and the temperature in the apparatus was maintained at 270 to 280 ° C., and the mixture was treated at a rotational speed of 100 m / s for 10 minutes to obtain powder B4. When the powder B4 after the second step was observed with a scanning electron microscope, it was confirmed that the surface was covered with carbon microspheres.

(Third process)
The obtained powder B4 was put into a graphite crucible and calcined at 1400 ° C. in a nitrogen gas atmosphere. Next, it is crushed with a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified with a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material C4 for a lithium ion secondary battery. It was. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
It carried out by the same method as Example 1 except using negative electrode material C4 for lithium ion secondary batteries. The results are shown in Table 4.

(Example 5)
<Manufacture of negative electrode material for lithium ion secondary battery>
(First step)
Coal tar pitch (JFE Chemical Corporation, PKQL) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm) , 5 parts by weight with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) was heated and kneaded for 10 minutes while maintaining the temperature in the apparatus at 150 to 160 ° C. to obtain powder A5.

(Second step)
Subsequently, the Henschel mixer was classified into 100 parts by weight of the spheroidized natural graphite used in the first step with Asahi Thermal (trade name Asahi Thermal, manufactured by Asahi Carbon Co., Ltd.) (volume-based median diameter 0.05 μm, d ( 002) = 0.3630 nm) 10 parts by weight were charged, and the temperature in the apparatus was kept at 150 to 160 ° C., and the mixture was treated at a rotational speed of 100 m / s for 10 minutes to obtain a powder B5. In addition, when the powder B5 after the second step was observed with a scanning electron microscope, it was confirmed that the surface was covered with Asahi Thermal.

(Third process)
The obtained powder B5 was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Subsequently, it was crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material C5 for a lithium ion secondary battery. . The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same procedure as in Example 1 was performed except that the negative electrode material C5 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 1)
<Manufacture of negative electrode material for lithium ion secondary battery>
(First step)
Coal tar pitch (JFE Chemical Corporation, PKQL) with respect to 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm) 20 parts by weight of a softening point of 70 ° C. was kneaded with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) for 10 minutes while maintaining the temperature in the apparatus at 150 to 160 ° C. to obtain powder D1.

(Second step)
Subsequently, furnace black (manufactured by Tokai Carbon Co., Ltd., S-TA, volume-based median diameter 0.7 μm, d (002) = 0.0) was added to a Henschel mixer with respect to 100 parts by weight of spheroidized natural graphite used in the first step. 3620 nm) 20 parts by weight were charged, and the mixture was stirred and mixed manually at room temperature without heating to obtain a mixed powder E1.

(Third process)
The obtained mixed powder E1 was put into a graphite crucible and calcined at 1000 ° C. in a nitrogen gas atmosphere. Subsequently, it is crushed by a crushing device (Nisshin Engineering Co., Ltd., Super Rotor) and classified by a classification device (Nisshin Engineering Co., Ltd., turbo classifier) to obtain a negative electrode material F1 for a lithium ion secondary battery. It was. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same procedure as in Example 1 was performed except that the negative electrode material F1 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 2)
<Manufacture of negative electrode material for lithium ion secondary battery>
Instead of 20 parts by weight of coal tar pitch (JFE Chemical Co., Ltd., PKQL, softening point 70 ° C.), a modified product (softening point 300 ° C.) of which mesophase pitch (JFE Chemical Co., Ltd., MCP-250D) is skipped. The negative electrode material F2 for a lithium ion secondary battery was obtained in the same manner as in Example 1 except that. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F2 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 3)
<Manufacture of negative electrode material for lithium ion secondary battery>
Coal tar pitch (JFE Chemical Co., Ltd., PKQL, softening point 70 ° C.) Instead of 20 parts by weight, coal tar is added to coal tar pitch (JFE Chemical Co., Ltd., PKQL) to reduce the softening point (softening) Except for the point being 20 parts by weight), a negative electrode material F3 for a lithium ion secondary battery was obtained in the same manner as in Example 1. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F3 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 4)
<Manufacture of negative electrode material for lithium ion secondary battery>
Instead of 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter is 17.0 μm, d (002) = 0.3355 nm), spheroidized natural graphite (Nippon Graphite Industrial Co., Ltd.) A negative electrode for a lithium ion secondary battery, manufactured in the same manner as in Example 1 except that the product is CGC-35, volume-based median diameter is 35.0 μm, and d (002) = 0.3355 nm) is 100 parts by weight. Material F4 was obtained. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F4 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 5)
<Manufacture of negative electrode material for lithium ion secondary battery>
In place of 20 parts by weight of furnace black (Tokai Carbon Co., Ltd., S-TA, volume-based median diameter 0.7 μm, d (002) = 0.620 nm), a carbonaceous carbon microsphere (manufactured by Tokai Carbon Co., Ltd., trade name GC) A negative electrode material E5 for a lithium ion secondary battery was obtained in the same manner as in Example 1 except that microspheres, volume-based median diameter 6.0 μm, d (002) = 0.3790 nm) were 20 parts by weight. . The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F5 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 6)
<Manufacture of negative electrode material for lithium ion secondary battery>
Furnace Black (manufactured by Tokai Carbon Co., Ltd., S-TA, volume-based median diameter 0.7 μm, d (002) = 0.620 nm) instead of 20 parts by weight Furnace Black (manufactured by Tokai Carbon Co., Ltd., S-TA, volume-based) Example 1 except that 20 parts by weight of graphitized product (volume-based median diameter 0.7 μm, d (002) = 0.3360 nm) having a median diameter of 0.7 μm and d (002) = 0.3620 nm) Thus, a negative electrode material F6 for lithium ion secondary batteries was obtained. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F6 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 7)
<Manufacture of negative electrode material for lithium ion secondary battery>
In the third step, instead of calcining at 1000 ° C. in a nitrogen gas atmosphere, except for calcining at 2800 ° C. in a nitrogen gas atmosphere, the lithium ion secondary A negative electrode material F7 for batteries was obtained. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F7 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 8)
<Manufacture of negative electrode material for lithium ion secondary battery>
Instead of 20 parts by weight of coal tar pitch (JFE Chemical Co., PKQL, softening point 70 ° C.), 1 part by weight of coal tar pitch (JFE Chemical Co., PKQL, softening point 70 ° C.) and the third step Thus, in place of calcination and carbonization at 1000 ° C. in a nitrogen gas atmosphere, the same procedure as in Example 1 was performed except that calcination and carbonization at 2800 ° C. in a nitrogen gas atmosphere. Material F8 was obtained. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F8 for lithium ion secondary batteries was used. The results are shown in Table 4.

(Comparative Example 9)
<Manufacture of negative electrode material for lithium ion secondary battery>
In the second step, a hybridizer (manufactured by Nara Machinery Co., Ltd.) shown in FIG. 14 is used instead of treating for 10 minutes at a rotational speed of 100 m / s while maintaining the temperature in the apparatus at 150 to 160 ° C. with a Henschel mixer. ), While maintaining the temperature in the apparatus at 150 to 160 ° C. for 5 minutes at a rotational speed of 100 m / s, and in the third step, calcination and carbonization at 1000 ° C. in a nitrogen gas atmosphere. A negative electrode material F9 for a lithium ion secondary battery was obtained in the same manner as in Example 1 except that it was calcined at 700 ° C. in a nitrogen gas atmosphere. The physical properties are shown in Table 3. In addition, when the powder B1 after the second step was visually observed, it was confirmed that the surface was not covered with furnace black and was covered with coal tar pitch.
Note that the hybridizer shown in FIG. 14 throws powder into the gap between the drum 46 and the rotating part 48 through the raw material circulation path 42 by rotating the rotating part 48 by adding powder. It is a device that applies mechanical energy to the powder by frictional force, compression force and collision force generated by the difference in rotational speed with the rotating part 48. In FIG. 14, 43 is a stator, 44 is a jacket, 45 is a raw material discharge part, and 47 is a blade.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F9 for lithium ion secondary batteries was used. The results are shown in Table 4. Moreover, although the SEM photograph of the surface and cross section of the negative electrode material F9 for lithium ion secondary batteries is shown in FIGS. 11-13, it was confirmed that furnace black does not exist in the surface of the negative electrode material F9 for lithium ion secondary batteries. It was.

(Comparative Example 10)
<Manufacture of negative electrode material for lithium ion secondary battery>
Instead of 100 parts by weight of spheroidized natural graphite (manufactured by Nippon Graphite Industries Co., Ltd., CGC-15, volume-based median diameter 17.0 μm, d (002) = 0.3355 nm), non-graphitized coke (Nippon Steel Chemical Co., Ltd.) Product name LPC-S55, volume-based median diameter 13.0 μm, d (002) = 3364 nm) calcined carbonized product (volume-based median diameter 13.0 μm, d (002) = 0.3364 nm) And in the third step, instead of firing and carbonizing at 1000 ° C. in a nitrogen gas atmosphere, except performing firing and carbonizing at 800 ° C. in a nitrogen gas atmosphere, the same method as in Example 1, The negative electrode material F10 for lithium ion secondary batteries was obtained. The physical properties are shown in Table 3.

<Creation of lithium ion secondary battery>
The same process as in Example 1 was performed except that the negative electrode material F10 for lithium ion secondary batteries was used. The results are shown in Table 4.

１）炭素前駆体の混合量は、黒鉛核粒子粉末１００重量部に対する重量部である。

1) The mixing amount of the carbon precursor is parts by weight with respect to 100 parts by weight of the graphite core particle powder.

１）炭素微粒子粉末の混合量は、第一工程で用いた黒鉛各粒子粉末１００重量部に対する重量部である。

1) The mixing amount of the carbon fine particle powder is part by weight with respect to 100 parts by weight of each graphite particle powder used in the first step.

  Since Examples 1-5 have a high reversible capacity, discharge load, and capacity retention rate, it can be said that the battery capacity is large and negative electrode materials capable of producing lithium ion secondary batteries having excellent input / output characteristics.

On the other hand, in Comparative Example 1, since the carbon fine particles were not fixed, only the characteristics as a simple mixture were obtained, the initial loss was large, the discharge load, and the capacity retention rate were small.
In Comparative Example 2, since the softening point of the carbon precursor was too high and the carbon fine particles were not fixed uniformly, the surface modification effect of the graphite particles could not be obtained, and the discharge load and capacity retention rate were small.
In Comparative Example 3, since the softening point of the carbon precursor is too low, the R value is small, the carbon fine particles are granulated independently, and the surface of the bare graphite particles is exposed. The capacity maintenance rate was small.
In Comparative Example 4, since the particle diameter of the graphite core particles is too large, the distance that lithium ions move in the particles becomes long, so that the discharge load and the capacity retention rate are extremely small.
In Comparative Example 5, since the particle size of the carbon fine particles was too large, sufficient electrical contact between the composite particles when the electrode plate was made could not be obtained, and the discharge load and capacity retention rate were small.
In Comparative Example 6, since the crystallization degree of the carbon fine particles was too high, the R value was too low, the surface modification effect was not obtained, and the discharge load and the capacity retention rate were small.
In Comparative Example 7, since the firing carbonization temperature was too high, graphite crystallites developed, and as a result, only the same characteristics as graphite particles were obtained.
In Comparative Example 8, since the mixing amount of the carbon precursor is too small, the adhesion strength between the carbon fine particles and the graphite particles becomes insufficient, a structure in a composite particle state cannot be obtained, and only characteristics equivalent to those of the graphite particles alone are obtained. The discharge load and capacity maintenance rate were small.
In Comparative Example 9, since Ra was too small, the discharge load characteristics were low. Moreover, since the calcination carbonization temperature was too low, the initial loss was large.
In Comparative Example 10, since the graphitization degree of the graphite core particles was too low, the reversible capacity was small. Moreover, since the calcination carbonization temperature was too low, the initial loss was large.

DESCRIPTION OF SYMBOLS 1 Graphite core particle 2, 32 Carbon precursor 3 Graphite core particle 4, 31 coated with carbon precursor Carbon fine particle 5 Graphite core particle 6 covered with carbon fine particle through carbon precursor 6 Carbide 7 Through carbide Graphite core particles 27 covered with carbon fine particles Negative electrode side stainless cap 20 Negative electrode 21 Copper foil 22 Insulating gasket 23 Electrolyte impregnated separator 24 Nickel mesh 25 Positive electrode side stainless cap 26 Positive electrode 41 Raw material inlet 42 Raw material circulation path 43 Stator 44 Jacket 45 Material outlet 46 Drum 47 Blade 48 Rotating part

Claims (2)

In order to obtain a negative electrode material for a lithium ion secondary battery having a center line average roughness Ra of 10 to 200 nm,
A graphite core particle powder having a volume-based median diameter of 5 to 30 μm and a (002) plane spacing d (002) of 0.3360 nm or less and a carbon precursor having a softening point of 70 to 250 ° C. are heated and kneaded. A first step of coating the surface of the graphite core particles with the carbon precursor to obtain a graphite core particle powder coated with the carbon precursor;
A graphite core particle powder coated with the carbon precursor and a carbon fine particle powder having a volume-based median diameter of 0.05 to 5 μm and a (002) plane spacing d (002) of 0.3400 nm or more are mixed. By applying mechanical energy to the mixed powder and embedding the carbon fine particles in the carbon precursor of the graphite core particles coated with the carbon precursor, the graphite core powder coated with the carbon precursor A second step of covering the surface with the carbon fine particles and obtaining a graphite core particle powder covered with the carbon fine particles via the carbon precursor;
Third step of obtaining a negative electrode material for a lithium ion secondary battery by firing and carbonizing graphite core particle powder covered with the carbon fine particles through the carbon precursor at 1000 to 1600 ° C. in a non-oxidizing atmosphere. When,
Method for producing a lithium ion secondary battery negative electrode material, characterized in applying. The BET specific surface area of the carbon particles ^{30 m} 2 / g or less, the Raman spectrum intensity ratio _{R (I} 1360 _/ I ₁₅₈₀₎ is a negative electrode for a lithium ion secondary battery according to claim 1, wherein a is 0.40 or more A method of manufacturing the material.

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