WO2013058348A1 - リチウムイオン電池用電極材料の製造方法 - Google Patents
リチウムイオン電池用電極材料の製造方法 Download PDFInfo
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- WO2013058348A1 WO2013058348A1 PCT/JP2012/077038 JP2012077038W WO2013058348A1 WO 2013058348 A1 WO2013058348 A1 WO 2013058348A1 JP 2012077038 W JP2012077038 W JP 2012077038W WO 2013058348 A1 WO2013058348 A1 WO 2013058348A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/78—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by stacking-plane distances or stacking sequences
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C—CHEMISTRY; METALLURGY
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- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a method for producing an electrode material for a lithium ion battery.
- lithium ion secondary batteries As a power source for portable devices, lithium ion secondary batteries have become almost mainstream because of their large energy density and long cycle life. Mobile devices and the like have diversified functions and have increased power consumption. Therefore, the lithium ion secondary battery is required to further increase its energy density and at the same time improve the charge / discharge cycle characteristics. Recently, there has been an increasing demand for high-power, large-capacity secondary batteries such as electric tools such as electric drills and hybrid vehicles. Conventionally, lead secondary batteries, nickel cadmium secondary batteries, and nickel metal hydride secondary batteries have been mainly used in this field. However, expectations for high-density lithium-ion secondary batteries that are small and light are high. A lithium ion secondary battery having excellent current load characteristics is demanded.
- the main required characteristics are long-term cycle characteristics over 10 years and large current load characteristics for driving high-power motors.
- a high volumetric energy density is required to extend the cruising range, which is harsh compared to mobile applications.
- the lithium ion secondary battery uses a metal oxide such as lithium cobaltate or lithium manganate as a positive electrode active material or a composite oxide thereof, a lithium salt as an electrolyte, and a graphite as a negative electrode active material. Carbonaceous materials such as are used.
- the graphite used for the negative electrode active material includes natural graphite and artificial graphite.
- Natural graphite is generally inexpensive and has the advantage of high capacity due to its high crystallinity. However, since the shape is scaly, when it is made into a paste together with a binder and applied to a current collector, natural graphite is oriented in one direction. When charged with such an electrode, the electrode expands in only one direction, and the performance as an electrode, such as current characteristics and cycle life, is reduced. Although spheroidized natural graphite obtained by granulating natural graphite to make a sphere has been proposed, the spheroidized natural graphite is crushed and oriented by pressing at the time of electrode production.
- Japanese Patent No. 3534391 (US Pat. No. 6,632,569; Patent Document 1) and the like propose a method of coating artificial carbon on the surface of natural graphite processed into a spherical shape.
- the material produced by this method can handle the high capacity, low current, and medium cycle characteristics required by mobile applications, etc., but demands such as the large current and long cycle characteristics of large batteries as described above. It is very difficult to meet.
- Natural graphite has many metal impurities such as iron, and has a problem in terms of quality stability.
- artificial graphite examples include mesocarbon microsphere graphitized products described in JP-A-4-190555 (Patent Document 2) and the like. This is a well-balanced negative electrode material that can achieve high-capacity, high-current batteries, but the long-term cycle characteristics required for large batteries such as the conductive contacts between electrode powders tend to deteriorate. Is difficult to achieve.
- a carbon raw material powder is filled in a graphite crucible and graphitized in an Atchison furnace (Patent No. 3838618 (US Pat. No. 6,783747); Patent Document 4).
- Carbon raw material powder is formed into a fixed shape using a binder such as pitch or polymer, graphitized in an Atchison furnace, and then the formed body is crushed (Patent Document 3).
- Carbon raw material powder is put into a graphite material container and heated by a heater as a heat source to be graphitized.
- the carbon raw material powder or its molded body is moved in a space heated by a heater.
- Japanese Patent No. 3534391 (US Pat. No. 6,632,569) Japanese Patent Laid-Open No. 4-190555 Japanese Patent No. 3361510 (European Patent No. 0918040) Japanese Patent No. 3838618 (US Pat. No. 6,783,747)
- an object of the present invention is to provide a method capable of producing a graphite material for a high-quality negative electrode for a lithium ion secondary battery having a low level of impurities and excellent stability with high productivity and low cost. .
- the present invention relates to a method for producing an electrode material for lithium ion batteries according to the following [1] to [12].
- a method for producing an electrode material for a lithium ion battery including a step of generating heat by directly passing an electric current through the carbon material and graphitizing, wherein the carbon material 1 before graphitization has a density of 1.4 g / cm 3.
- the compacted powder resistance is 0.3 ⁇ cm or less
- the angle of repose is 20 ° or more and 50 ° or less
- the D90 in the volume-based particle size distribution measured by the laser diffraction method is 120 ⁇ m or less.
- the carbon material 2 of (002) has an average interplanar spacing d002 of 0.3354 nm or more and 0.3450 nm or less by X-ray diffraction, and the carbon material 1 heat-treated the organic carbon material at 800 ° C. or more and 1500 ° C. or less.
- the manufacturing method of the electrode material for lithium ion batteries which is pulverized later. [2] (Consolidated powder resistance when the graphitized carbon material 2 is compressed to a density of 1.4 g / cm 3 ) / (The carbon material 1 before graphitization is compressed to a density of 1.4 g / cm 3 2.
- the method of the present invention it is possible to produce a graphite material that can be used for a high-quality lithium-ion battery electrode material that is less contaminated with impurities and excellent in stability, with high productivity and low cost. Further, when the obtained graphite material is used for a negative electrode for a lithium ion secondary battery, insertion and release of lithium ions on the surface of the material can be performed more smoothly, so that the input / output characteristics and cycle life are excellent.
- Example 2 is an SEM photograph of the graphite material obtained in Example 1.
- the pulverized surface (edge portion) is easily exposed and the specific surface area is increased, side reactions with the electrolyte increase when used as a negative electrode.
- the amount exceeds 20% by mass the binding between the graphitized particles increases, which affects the yield.
- the heating loss of the organic carbon raw material is in the above range, the surface of the obtained graphite material is stabilized, and side reactions with the electrolytic solution are reduced when used as a negative electrode. The reason for this is thought to be that the exposed edge portion crystals are reconstructed and stabilized by graphitization after carbonization and the particle surface becomes smooth due to the components that volatilize when heated at 300-1200 ° C. It is done.
- the heating loss can be measured by using a commercially available apparatus capable of simultaneous differential heat-thermogravimetric measurement (TG-DTA) at a heating rate of 10 ° C./min.
- TGDTAw6300 manufactured by Seiko Instruments Inc.
- argon gas is flowed at 200 ml / min, 300 at 10 ° C./min.
- the temperature is raised from 1200C to 1200C and measured.
- ⁇ -alumina manufactured by Wako Pure Chemical Industries, Ltd. was used at 1500 ° C. for 3 hours in advance to remove volatile components.
- the organic carbon raw material having such a heat loss is preferably selected from, for example, petroleum pitch, coal pitch, coal coke, petroleum coke, and mixtures thereof. Of these, petroleum coke is more preferable. Further, the organic carbon raw material is preferably non-needle-like, and particularly preferably non-needle-like coke not subjected to heat treatment.
- Petroleum coke is a black, porous solid residue obtained by cracking or cracking distillation of petroleum or bituminous oil. Petroleum coke is classified into fluid coke and delayed coke depending on the method of coking. However, fluid coke is in the form of powder and is not used for much as it is used for refinery's own fuel. In general, petroleum coke is called delayed coke. There are two types of delayed coke: raw coke and calcined coke. Raw coke is the raw coke collected from the coking apparatus, and the calcined coke is further baked to remove volatile components. Since raw coke has a high possibility of causing a dust explosion, in order to obtain fine-particle petroleum coke, raw coke was calcined to remove volatile components and then pulverized. Conventionally, calcined coke has generally been used for electrodes and the like. Since raw coke has less ash than coal coke, it is used only for carbon materials, casting coke and alloy iron coke in the carbide industry.
- sulfur in the organic carbon raw material is preferable. Sulfur is volatilized during the graphitization process, and has the adverse effect of bumping the carbon material and roughening the surface after graphitization.
- the sulfur content in the organic carbon raw material is preferably 3% by mass or less, and more preferably 2% by mass or less.
- the organic carbon material preferably has an average coefficient of thermal expansion (CTE) of 30 to 100 ° C. of 4.0 ⁇ 10 ⁇ 6 / ° C. or more and 6.0 ⁇ 10 ⁇ 6 / ° C. or less.
- the CTE of the carbon raw material can be measured by the following method, for example. First, 500 g of the carbon raw material is pulverized to 28 mesh or less with a vibration mill. This sample is sieved and mixed in a ratio of 28 to 60 mesh 60 g, 60 to 200 mesh 32 g, 200 mesh or less 8 g to make the total amount 100 g.
- 100 g of this blended sample is put in a stainless steel container, 25 g of binder pitch is added, and the mixture is heated and uniformly mixed in an oil bath at 125 ° C. for 20 minutes.
- the mixture is cooled and pulverized with a vibration mill to reduce the total amount to 28 mesh or less.
- 30 g of the sample is placed in a pressure molding machine at 125 ° C., and pressed at a gauge pressure of 450 kg / cm 2 for 5 minutes to be molded.
- the molded product is placed in a magnetic crucible, heated from room temperature to 1000 ° C. in a firing furnace in 5 hours, and held at 1000 ° C. for 1 hour to cool.
- This fired product is cut into 4.3 ⁇ 4.3 ⁇ 20.0 mm with a precision cutting machine to obtain a test piece.
- the test piece is subjected to thermal expansion measurement at 30 to 100 ° C. with a TMA (thermomechanical analyzer), for example, TMA / SS 350 manufactured by Seiko Electronics, and CTE is calculated.
- TMA thermomechanical analyzer
- the carbon material 1 before graphitization can be obtained, for example, by subjecting the organic carbon raw material to heat treatment at 800 ° C. or more and 1500 ° C. or less and then pulverizing.
- the carbon material 1 before graphitization preferably has a low resistance because an electric current flows directly through the carbon material during graphitization.
- the compacted powder resistance value when compressed to a density of 1.4 g / cm 3 is set to 0.4 ⁇ cm or less.
- preliminary low temperature heat treatment is performed at 800 ° C. to 1500 ° C. to increase the carbonization degree.
- the preferred heat treatment temperature is 900 to 1300 ° C., although it varies depending on the type of organic carbon raw material used and the graphitization conditions in the next step. From the viewpoint of productivity, the temperature of the heat treatment should be lowered as much as possible, but if it is too low, the resistance will not be lowered sufficiently.
- D90 is preferably 120 ⁇ m or less, more preferably D90 is 80 ⁇ m or less, and still more preferably D90 is 70 ⁇ m or less in a volume-based particle size distribution measured by a laser diffraction method.
- the D50 average particle size
- the D50 is preferably classified so as to be 30 ⁇ m or less, more preferably 4 ⁇ m or more and 25 ⁇ m or less.
- the average particle size is large, there are merits such as increased stability with the electrolytic solution and easy coating, but conversely, the high current characteristics proceed in a bad direction and the electrode density is difficult to increase. Conversely, if it is small, side reactions tend to occur during charge and discharge.
- the particle size of the powder can be measured with a laser scattering / diffraction particle size distribution analyzer (CILAS).
- the aspect ratio (long axis length / short axis length) of the carbon material 1 before graphitization is preferably 6 or less, and more preferably 1 or more and 5 or less. If the aspect ratio is too large, it is difficult to control the current distribution during graphitization, and there are disadvantages in terms of coating properties and stability when used as the negative electrode of a battery.
- the aspect ratio can be obtained from an optical microscope image. For simplicity, the measurement may be performed by image analysis using an FPIA 3000 manufactured by Sysmex.
- the repose angle of the carbon material 1 before graphitization is preferably 20 ° or more and 50 ° or less.
- the angle of repose is less than 20 °, the fluidity of the carbon material 1 increases, so that the powder may be scattered during filling of the furnace body or the powder may be ejected during energization.
- the angle of repose exceeds 50 °, the fluidity of the carbon material 1 is lowered, so that the filling property in the furnace body is lowered and the productivity is lowered, and the energization resistance of the whole furnace may be extremely increased.
- a more preferred angle of repose has a lower limit of 30 ° and an upper limit of 45 °. The angle of repose can be measured using a tap denser.
- the carbon material 1 before graphitization has a compressibility ((hardened bulk density ⁇ relaxed bulk density) ⁇ 100 / relaxed bulk density) calculated from the loose bulk density (0 times tapping) and the hardened bulk density (tap density). It is preferably ⁇ 50%. If it exists in this range, when producing the electrode slurry knead
- the loose bulk density is a density obtained by dropping 100 g of a sample from a height of 20 cm onto a measuring cylinder and measuring the volume and mass without applying vibration.
- the solid bulk density is a density obtained by measuring the volume and mass of 100 g of powder tapped 400 times using a cantachrome auto tap. These are measurement methods based on ASTM B527 and JIS K5101-12-2, and the drop height of the auto tap in the tap density measurement was 5 mm.
- (2) Graphitization Graphitization is performed by causing a current to flow directly through the carbon material 1 to generate heat.
- a rectangular parallelepiped furnace body made of ceramic bricks and having an open top can be used.
- the length in the longitudinal direction as viewed from the opening direction is set to about twice or more than the length in the short direction, and electrodes for energization are arranged on both inner sides of the longitudinal direction.
- Carbon material is put into this furnace and graphitized by heat generated by energization.
- heat is uniformly applied to the carbon material, so that there is an advantage that no agglomeration occurs during graphitization.
- a graphite material with few impurities can be obtained because the temperature distribution is uniform and there is no trapping part for impurity volatilization.
- the graphitization treatment is preferably performed in an atmosphere in which the carbon material is not easily oxidized.
- a method of performing a heat treatment in an inert gas atmosphere such as nitrogen, or a method of providing a layer that barriers oxygen on a surface in contact with air can be given.
- the barrier layer include a method of separately providing a carbon plate or a carbon powder layer and consuming oxygen.
- the lower limit of the graphitization temperature is usually 2000 ° C., preferably 2500 ° C., more preferably 2900 ° C., and most preferably 3000 ° C.
- the upper limit of the graphitization temperature is not particularly limited, but is preferably 3200 ° C. from the viewpoint that a high discharge capacity is easily obtained.
- a graphitization cocatalyst such as a boron compound such as B 4 C or a silicon compound such as SiC can be added in order to increase the heat treatment efficiency and productivity of graphitization.
- the blending amount is preferably 10 to 100,000 ppm by mass in the carbon material.
- Graphitization is performed so that the average interplanar spacing d002 of the (002) plane by the X-ray diffraction method of the carbon material 2 after graphitization is in the range of 0.3354 nm or more and 0.3450 nm or less. Preferably, it is performed until d002 becomes 0.3360 nm or more and 0.3370 nm or less.
- d002 can be measured by a known method using a powder X-ray diffraction (XRD) method (Inayoshi Noda, Michio Inagaki, Japan Society for the Promotion of Science, 117th Committee Material, 117-71-A-1 (1963). ), Michio Inagaki et al., Japan Society for the Promotion of Science, 117th Committee Materials, 117-121-C-5 (1972), Michio Inagaki, “Carbon”, 1963, No. 36, pages 25-34).
- XRD powder X-ray diffraction
- Graphitization is performed by (consolidated powder resistance when the graphitized carbon material 2 is compressed to a density of 1.4 g / cm 3 ) / (carbon material 1 before graphitization to a density of 1.4 g / cm 3 . It is preferable to carry out such that the compacted powder resistance when compressed) ⁇ 0.5.
- a uniform current distribution can be obtained from the beginning of energization, and graphitization can be performed with a uniform temperature distribution. This range can be adjusted by selecting the organic carbon raw material or carbon material 1 or selecting the graphitization conditions.
- Graphite Material for Electrode Material for Lithium Ion Battery Graphite material obtained by graphitizing the carbon material (carbon material after graphitization) has a peak intensity (I D) in the vicinity of 1360 cm ⁇ 1 measured by Raman spectroscopy. ) And the peak intensity (I G ) in the vicinity of 1580 cm ⁇ 1 , the intensity ratio I D / I G (R value) is preferably 0.01 or more and 0.2 or less. When the R value is greater than 0.2, many highly active edge portions are exposed on the surface, and many side reactions are likely to occur during charge and discharge. On the other hand, if it is less than 0.01, the barrier to the entry and exit of lithium is increased, and the input / output characteristics are liable to deteriorate.
- the laser Raman R value is measured using NRS3100 manufactured by JASCO Corporation under the conditions of an excitation wavelength of 532 nm, an incident slit width of 200 ⁇ m, an exposure time of 15 seconds, a total of 2 times, and a diffraction grating of 600 lines / mm.
- the graphite material preferably has an average coefficient of thermal expansion (CTE) of 30 ° C. to 100 ° C. of 4.0 ⁇ 10 ⁇ 6 / ° C. to 5.0 ⁇ 10 ⁇ 6 / ° C.
- the coefficient of thermal expansion is used as one of the indexes indicating the acicularity of coke.
- the CTE is less than 4.0 ⁇ 10 ⁇ 6 / ° C.
- the graphite has high crystallinity, so that the discharge capacity increases, but the particle shape tends to be plate-like.
- the CTE is larger than 5.0 ⁇ 10 ⁇ 6 / ° C., the aspect ratio is decreased, but the graphite crystal is not developed and the discharge capacity is decreased.
- the CTE of the graphite material is measured in the same manner as the CTE of the carbon raw material.
- the graphite material preferably has an (002) plane distance d002 of 0.3354 nm or more and 0.3450 nm or less, more preferably 0.3362 nm or more and 0.3370 nm or less, as determined by X-ray diffraction.
- the d002 of the graphite material is measured by the same method as described above.
- the graphite material preferably has an aspect ratio (major axis length / minor axis length) of 6 or less, particularly 1 or more and 5 or less.
- the aspect ratio can be obtained from an optical microscope image.
- the measurement may be performed by image analysis using an FPIA 3000 manufactured by Sysmex.
- the graphite material preferably has a specific surface area (BET method) of 7 m 2 / g or less, particularly 1.5 m 2 / g or more and 6.0 m 2 / g or less.
- BET method specific surface area
- graphite material is obtained by graphitizing by directly energizing the powder, it is moderately oxidized although its surface oxidation is suppressed compared to the graphite material obtained by the conventional graphitization method. It is in the state. Thereby, the surface is stabilized and a side reaction with the electrolytic solution is suppressed.
- the degree of oxidation in the peak intensity of O 1s obtained by HAX-PES measurement using hard X-rays of 7940 eV, the amount of oxygen a (mass%) between the particle surface and the depth direction up to 40 nm is It is preferable that 0.010 ⁇ a ⁇ 0.04, and more preferably 0.010 ⁇ a ⁇ 0.03.
- the graphite material has a loose bulk density (0 times tapping) of 0.7 g / cm 3 or more and a hardened bulk density (tap density) of 0.9 g / cm 3 or more and 1.30 g / It is preferable that it is cm 3 or less.
- the loose bulk density is 0.7 g / cm 3 or more, it is possible to further increase the electrode density before pressing when applied to the electrode. From this value, it can be predicted whether or not a sufficient electrode density can be obtained with a single roll press.
- the compacted bulk density (tap density) is within the above range, the electrode density reached during pressing can be sufficiently increased. These are measured by the same method as described above.
- the graphite material preferably has an average particle size (D50) of 5 ⁇ m or more and 30 ⁇ m or less in a volume-based particle size distribution measured by a laser diffraction method.
- D50 average particle size
- the iron content of the graphite material is preferably 0 to 30 ppm by mass. When the iron content is within this range, it is possible to prevent a minute short circuit in the case of a battery, and it is possible to improve safety and improve battery product yield. If the iron content is high, there is a high possibility that a micro short circuit will occur in the case of a battery, which may cause a reduction in safety and a decrease in battery product yield.
- the iron content (residual iron amount) is decomposed by weighing 50 to 100 mg of sample, adding sulfuric acid and heating, and after allowing to cool, adding nitric acid to thermally decompose, repeating this until the solution becomes transparent,
- the obtained liquid is made up to a volume of 50 ml, and further measured by performing ICP mass spectrometry after 10-fold dilution.
- Slurry for a lithium ion battery electrode includes the graphite material and a binder.
- the slurry is obtained by kneading a graphite material and a binder.
- known apparatuses such as a ribbon mixer, a screw kneader, a Spartan rewinder, a ladyge mixer, a planetary mixer, and a universal mixer can be used.
- the electrode paste can be formed into a sheet shape, a pellet shape, or the like.
- binder examples include known polymers such as fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene, and rubbers such as SBR (styrene butadiene rubber).
- the amount of the binder used is preferably 0.5 to 20 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the graphite material.
- the slurry may contain conductive carbon such as carbon black such as acetylene black and ketjen black, carbon nanofiber such as vapor grown carbon fiber, carbon nanotube, and graphite fine powder as a conductive aid.
- the blending amount of the conductive assistant is not particularly limited, but is preferably 0.5 to 30 parts by mass with respect to 100 parts by mass of the graphite material.
- a solvent can be used when kneading.
- the solvent include known solvents suitable for each binder, such as toluene and N-methylpyrrolidone for fluorine-based polymers; water for SBR; dimethylformamide, isopropanol and the like.
- water water for SBR
- a binder using water as a solvent it is preferable to use a thickener together. The amount of the solvent is adjusted so that the viscosity is easy to apply to the current collector.
- Lithium ion battery electrode The lithium ion battery electrode is formed by molding the slurry.
- the electrode can be obtained, for example, by applying the slurry onto a current collector, drying, and pressure forming.
- the current collector include foils such as aluminum, nickel, copper, and stainless steel, and meshes.
- the coating thickness of the slurry is usually 20 to 150 ⁇ m. If the coating thickness becomes too large, the electrode may not be accommodated in a standardized battery container.
- the method for applying the slurry is not particularly limited, and examples thereof include a method in which the slurry is applied with a doctor blade or a bar coater and then molded with a roll press or the like.
- the pressure molding method include molding methods such as roll pressing and press pressing.
- the pressure during pressure molding is preferably about 1 to 3 t / cm 2 .
- the battery capacity per volume usually increases. However, if the electrode density is increased too much, the cycle characteristics tend to generally decrease.
- the electrode density of the electrode obtained using the slurry is 1.2 to 1.9 g / cm 3 .
- Lithium ion secondary battery has a structure in which a positive electrode and a negative electrode are immersed in an electrolytic solution or an electrolyte. Said electrode is used for the negative electrode of a lithium ion secondary battery.
- a lithium-containing transition metal oxide is usually used as the positive electrode active material, preferably at least selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W.
- An oxide mainly containing one kind of transition metal element and lithium wherein a compound having a molar ratio of lithium to the transition metal element of 0.3 to 2.2 is used, more preferably V, Cr, Mn,
- An oxide mainly containing at least one transition metal element selected from Fe, Co, and Ni and lithium and having a molar ratio of lithium to transition metal of 0.3 to 2.2 is used.
- Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like may be contained in a range of less than 30 mole percent with respect to the transition metal present mainly.
- the value of x is a value before the start of charging / discharging, and increases / decreases by charging / discharging.
- the average particle size of the positive electrode active material is not particularly limited, but is preferably 0.1 to 50 ⁇ m.
- the volume of particles of 0.5 to 30 ⁇ m is preferably 95% or more. More preferably, the volume occupied by a particle group having a particle size of 3 ⁇ m or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 ⁇ m or more and 25 ⁇ m or less is 18% or less of the total volume.
- the specific surface area is not particularly limited, but is preferably 0.01 ⁇ 50m 2 / g by BET method, particularly preferably 0.2m 2 / g ⁇ 1m 2 / g.
- the pH of the supernatant when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water is preferably 7 or more and 12 or less.
- a separator may be provided between the positive electrode and the negative electrode.
- the separator include non-woven fabrics, cloths, microporous films, or a combination thereof, mainly composed of polyolefins such as polyethylene and polypropylene.
- electrolyte and electrolyte constituting the lithium secondary battery known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used.
- organic electrolyte is preferable from the viewpoint of electrical conductivity.
- Solvents for the organic electrolyte include diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, ethylene glycol phenyl ether Ethers such as formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide, N, N -Diethylacetamide, N, N-dimethylpropionamide, hexamethylphospho Amides such as Luamide; sulfur-containing compounds such as dimethyl sulfoxide and sulfolane; dialkyl ketones such as methyl ethyl ketone and
- Cyclic ethers of: carbonates such as ethylene carbonate and propylene carbonate; ⁇ -butyrolactone; N-methylpyrrolidone; acetonitrile, nitromethane and the like are preferable.
- esters such as ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, vinylene carbonate, ⁇ -butyrolactone, ethers such as dioxolane, diethyl ether, diethoxyethane, dimethyl sulfoxide, acetonitrile, tetrahydrofuran, etc.
- Particularly preferred are carbonate-based non-aqueous solvents such as ethylene carbonate and propylene carbonate. These solvents can be used alone or in admixture of two or more.
- Lithium salts are used as solutes (electrolytes) for these solvents.
- Commonly known lithium salts include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCl, LiCF 3 SO 3 , LiCF 3 CO 2 , LiN (CF 3 SO 2 ) 2 and the like. is there.
- polymer solid electrolyte examples include a polyethylene oxide derivative and a polymer containing the derivative, a polypropylene oxide derivative and a polymer containing the derivative, a phosphate ester polymer, a polycarbonate derivative and a polymer containing the derivative. There are no restrictions on the selection of members other than those described above necessary for the battery configuration.
- Particle size (D50 and D90) Laser Scattering / Diffraction Method Using CILAS as a particle size distribution measuring device, volume-based average particle diameter (D50) and particle diameter (D90) were determined.
- the compression ratio is (hardened bulk density ⁇ relaxed bulk density) ⁇ 100 / relaxed bulk density (%).
- the loose bulk density is obtained by dropping 100 g of a sample from a height of 20 cm onto a measuring cylinder and applying volume and mass without applying vibration.
- the solid bulk density (tap density) is a density obtained by measuring the volume and mass of 100 g of powder tapped 400 times using a cantachrome auto tap. These are measurement methods based on ASTM B527 and JIS K5101-12-2, and the drop height of the auto tap in the tap density measurement was 5 mm.
- the aspect ratio of the particles was measured by image analysis using a FPIA 3000 manufactured by Sysmex.
- the number of measurement points was 3000 points or more, preferably 30000 points or more, more preferably 50000 points or more, and the calculated average value was used.
- Residual oxygen amount Using a permanent device at SPring-8 (beam line BL46XU), HAX-PES measurement with an incident energy of 7940 eV is performed to quantify the oxygen amount on the surface of the graphite material.
- the measurement conditions are such that, in the narrow spectrum of C 1s , the energy range of photoelectron Kinetic Energy is 7638-7658 eV, and in the narrow spectrum of O 1s , the energy range of photoelectron Kinetic Energy is 7396-7416 eV.
- the amount of oxygen on the surface of the graphite material is quantified according to the following method. ⁇ Energy calibration of photoelectron spectrum A plate-like Au sample is measured as a standard sample.
- Negative electrode KF polymer L1320 (N-methylpyrrolidone (NMP) solution product containing 12% by weight of polyvinylidene fluoride (PVDF)) and Temcal carbon black as graphite material, and the composition after coating and drying is graphite.
- PVDF carbon black was added so as to have a mass ratio of 92: 5: 3, and kneaded with a planetary mixer to obtain a main agent stock solution.
- Positive electrode manufactured by Nippon Kagaku Kogyo Co., Ltd., lithium cobaltate (D50: approx. 10 ⁇ m), KF polymer L9320 manufactured by Kureha Chemical Co., Ltd.
- NMP N-methylpyrrolidone (NMP) solution product containing 12% by weight of polyvinylidene fluoride (PVDF)) Carbon black manufactured by Showa Denko Co., Ltd. and VGCF-H manufactured by Showa Denko Co., Ltd. were added so that the composition after coating and drying was lithium cobaltate: PVDF: carbon black: VGCF-H in a mass ratio of 92: 5: 1: 2. It knead
- NMP N-methylpyrrolidone
- PVDF polyvinylidene fluoride
- Negative electrode NMP was added to the above-mentioned negative electrode main agent stock solution to adjust the viscosity, and then applied on a high purity copper foil to a thickness of about 100 ⁇ m using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 16 mm ⁇ . The punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 ⁇ 10 2 to 3 ⁇ 10 2 N / mm 2 (1 ⁇ 10 3 to 3 ⁇ 10 3 kg / cm 2 ) with respect to the electrode. Was pressed as follows. Then, it dried at 120 degreeC and 12 hours with the vacuum dryer, and was set as the negative electrode for evaluation.
- Positive electrode NMP was added to the above-mentioned positive electrode main agent stock solution to adjust the viscosity, and then applied to a thickness of about 100 ⁇ m on a high purity Al foil using a doctor blade. This was vacuum-dried at 120 ° C. for 1 hour and punched out to 16 mm ⁇ . The punched electrode is sandwiched between super steel press plates, and the press pressure is about 1 ⁇ 10 2 to 3 ⁇ 10 2 N / mm 2 (1 ⁇ 10 3 to 3 ⁇ 10 3 kg / cm 2 ) with respect to the electrode. Was pressed as follows. Then, it dried at 120 degreeC and 12 hours with the vacuum dryer, and was set as the positive electrode for evaluation.
- Bipolar cell battery evaluation: A bipolar cell was produced using the positive electrode and the negative electrode produced in (b) above as follows. The following operation was performed in a dry argon atmosphere with a dew point of -80 ° C or lower. In a cell with a screw-in lid made of polypropylene (inner diameter of about 18 mm), the carbon negative electrode with copper foil and the Co positive electrode with Al foil prepared in (b) above are sandwiched by a separator (polypropylene microporous film (Cell Guard 2500)). Laminated. An electrolytic solution was added thereto to obtain a test cell. The negative electrode capacity / positive electrode capacity was 1.15 when the single electrode evaluation capacity of each material was defined as the basic capacity.
- Electrolytic solution LiPF 6 was dissolved in an amount of 1 mol / liter as an electrolyte in a mixed solution of 8 parts by mass of EC (ethylene carbonate) and 12 parts by mass of DEC (diethyl carbonate).
- Bipolar bipolar cell A constant current low voltage charge / discharge test was conducted at a current density of 1.0 to 5.0 mA / cm 2 . Charging was performed by CC (constant current) at 1.0 mA / cm 2 up to 4.2 V. Next, it switched to CV (constant volt
- Example 1 Petroleum-based raw coke (non-needle coke) having a heating loss of 12.5% by mass according to TG measurement at 300 ° C. to 1200 ° C. was treated at 1200 ° C. while flowing nitrogen gas through a roller hearth kiln made by Nippon Choshi. Next, after pulverizing with a Hosokawa Micron bantam mill, airflow classification was carried out with a Nisshin Engineering turbo classifier to obtain a carbon material 1 having a D50 of 20.0 ⁇ m. When this carbon material 1 was compressed to a density of 1.4 g / cm 3 , the compacted powder resistance was 0.25 ⁇ cm, and the angle of repose was 36 °.
- a furnace having a length of 500 mm, a width of 1000 mm, and a depth of 200 mm was made of ceramic bricks, and electrode plates of 450 ⁇ 180 mm and a thickness of 20 mm were installed on both inner end faces.
- the furnace was filled with the carbon material 1 and covered with a nitrogen gas inlet and an exhaust port.
- a carbon material 1 was graphitized by installing a transformer and heating by flowing current between the electrode plates for about 5 hours while flowing nitrogen gas. The maximum temperature was 3200 ° C.
- Various physical properties of the obtained graphite material (carbon material 2) and battery evaluation results are shown in Table 1 together with the physical properties of the organic carbon raw material and carbon material 1.
- FIG. 1 shows an SEM photograph.
- Comparative Example 1 Petroleum-based raw coke (non-acicular coke) having a heating loss of 12.5% by mass according to TG measurement at 300 ° C. to 1200 ° C. was pulverized with a Hosokawa Micron bantam mill. Air classification was performed with a turbo classifier manufactured by Nisshin Engineering, and an organic carbon raw material having a D50 of 20.0 ⁇ m was obtained. Next, this pulverized organic carbon raw material was treated at 1000 ° C. while flowing nitrogen gas through a roller hearth kiln made by Nippon Choshi, and a carbon material 1 was obtained.
- the carbon material 1 When the carbon material 1 was compressed to a density of 1.4 g / cm 3 , the compacted powder resistance was 0.35 ⁇ cm and the angle of repose was 34 °.
- the carbon material 1 is graphitized in the same manner as in Example 1, and various physical properties and battery evaluation results of the obtained graphite material (carbon material 2) are summarized in Table 1 together with the organic carbon raw material and the physical properties of the carbon material 1. It was. Compared to Example 1, the capacity was lower, and the capacity at a particularly high discharge current tended to decrease. The cycle life was also inferior.
- Example 2 A mixture of petroleum-based raw coke similar to Example 1 (non-acicular coke) and petroleum-based raw needle coke having a heating loss of 11.5% by mass according to TG measurement at 300 ° C. to 1200 ° C. in a ratio of 1: 1.
- a carbon material 1 having a D50 of 19.0 ⁇ m was obtained in the same manner as in Example 1 except that it was used as an organic carbon raw material.
- the carbon material 1 was compressed to a density of 1.4 g / cm 3 , the compacted powder resistance was 0.20 ⁇ cm, and the angle of repose was 42 °.
- the carbon material 1 is graphitized in the same manner as in Example 1, and various physical properties and battery evaluation results of the obtained graphite material (carbon material 2) are summarized in Table 1 together with the organic carbon raw material and the physical properties of the carbon material 1. It was. Compared to Example 1, d002 was small and the capacity was high, but the initial efficiency was slightly low.
- Example 3 A graphite material (carbon material 2) was obtained in the same manner as in Example 1 except that 1000 ppm by mass of B 4 C was added during graphitization. Various physical properties of the obtained graphite material (carbon material 2) and battery evaluation results are shown in Table 1 together with the physical properties of the organic carbon raw material and carbon material 1. Compared to Example 1, the addition of the graphitization cocatalyst resulted in a small d002 and a high capacity, but the initial efficiency was slightly lower.
- Comparative Example 2 Carbon material 1 obtained by the same method as in Example 1 was filled in a graphite crucible with a lid and graphitized at 3000 ° C. in an Atchison furnace. Various physical properties of the obtained graphite material (carbon material 2) and battery evaluation results are shown in Table 1 together with the physical properties of the organic carbon raw material and carbon material 1. Compared to Example 1, the physical properties were almost the same, but the initial efficiency was slightly low because the amount of oxygen was slightly low. The cycle life was also inferior. There was a lot of iron.
- Comparative Example 3 Petroleum raw coke similar to Example 1 (non-needle coke) was treated at 600 ° C. while flowing nitrogen gas through a roller hearth kiln made by Nippon Choshi. Next, after pulverizing with a Hosokawa Micron bantam mill, airflow classification was carried out with a Nisshin Engineering turbo classifier to obtain a carbon material 1 having a D50 of 20.0 ⁇ m. When the carbon material 1 was compressed to a density of 1.4 g / cm 3 , the compacted powder resistance was 0.50 ⁇ cm, and the angle of repose was 38 °.
- the carbon material 1 is graphitized in the same manner as in Example 1, and various physical properties and battery evaluation results of the obtained graphite material (carbon material 2) are summarized in Table 1 together with the organic carbon raw material and the physical properties of the carbon material 1. It was. Compared to Example 1, the specific surface area is high, the d002 is large, and the capacity is low. Therefore, it can be understood that graphitization is not sufficiently performed.
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Abstract
Description
負極活物質に使用される黒鉛としては、天然黒鉛と人造黒鉛とがある。
(1)炭素原料粉体を黒鉛製ルツボに充填してアチソン炉で黒鉛化する(特許第3838618号公報(米国特許第6783747号明細書);特許文献4)。
(2)炭素原料粉体をピッチやポリマーなどのバインダーを用いて一定の形に成形し、アチソン炉で黒鉛化し、その後、成形体を解砕する(特許文献3)。
(3)炭素原料粉体を黒鉛材の容器に入れて、熱源としてのヒーターにより加熱して黒鉛化する。
(4)炭素原料粉体またはその成形体をヒーターによって加熱した空間の中を移動させる。
しかし、前記の(1)~(4)で示した従来のリチウムイオン電池用負極のための人造黒鉛の黒鉛化方法には、以下のような問題が存在する。
(a)黒鉛材料からなるルツボ等の容器の消耗、るつぼからの不純物の混入。
(b)アチソン炉の詰め粉コークスからのコンタミによる汚染。
(c)アチソン方式の場合は、詰め粉コークスなど製品以外の材料をあわせて熱処理するので生産性が落ちる。
(d)成形体の場合は、黒鉛化後の解砕時の不純物の混入、粉体表面の劣化。
(e)ヒーターを用いる場合は、ヒーター部材が消耗する上に、3000℃以上の高温にすることは難しいこと。
(f)ヒーターを用いる場合は、不活性ガスの使用によるコストアップ。
従って、本発明の課題は、不純物の混入が少なく、安定性に優れた高品質のリチウムイオン二次電池用負極のための黒鉛材料を生産性よく低コストで製造できる方法を提供することにある。
[1]リチウムイオン電池用電極材料の製造方法であって、炭素材料に直接電流を流すことにより発熱させて黒鉛化する工程を含み、黒鉛化前の炭素材料1が密度1.4g/cm3に圧縮したときの圧密粉体抵抗値が0.3Ωcm以下で、安息角が20°以上50°以下、レーザー回折法により測定した体積基準の粒子径分布におけるD90が120μm以下であり、黒鉛化後の炭素材料2がX線回折法による(002)面の平均面間隔d002が0.3354nm以上0.3450nm以下であり、前記炭素材料1が有機系炭素原料を800℃以上1500℃以下で熱処理したあとに粉砕されたものであるリチウムイオン電池用電極材料の製造方法。
[2](前記黒鉛化後の炭素材料2を密度1.4g/cm3に圧縮したときの圧密粉体抵抗)/(前記黒鉛化前の炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗)≦0.5である前記1に記載のリチウムイオン電池用電極材料の製造方法。
[3]前記黒鉛化前の炭素材料1のレーザー回折法により測定した体積基準の粒子径分布におけるD50が30μm以下である前記1または2に記載のリチウムイオン電池用電極材料の製造方法。
[4]前記黒鉛化前の炭素材料1の安息角が30°以上50°以下、緩め嵩密度と固め嵩密度から算出される圧縮率((固め嵩密度-緩め嵩密度)×100/緩め嵩密度)が20%以上50%以下である前記1乃至3のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
[5]前記有機系炭素材料が、不活性雰囲気下で300℃から1200℃まで加熱した際、この温度領域における加熱減量分が5質量%以上20質量%以下である前記1乃至4のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
[6]前記有機系炭素原料中の硫黄分が2質量%以下である前記1乃至5のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
[7]前記有機系炭素原料が、石油ピッチ、石炭ピッチ、石炭コークス、石油コークスおよびこれらの混合物から選ばれる1種以上である前記1乃至6のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
[8]前記黒鉛化前の炭素材料1が、ホウ素系化合物および/または珪素系化合物が10~100000質量ppmを含む前記1乃至7のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
[9]黒鉛化の工程において、セラミックスレンガ製であって、上方が開口した直方体状の炉体を用いる前記1に記載のリチウムイオン電池用電極材料の製造方法。
[10]前記炉体が、開口部方向から見て長手方向の長さが短手方向の長さの2倍以上である前記9に記載のリチウムイオン電池用電極材料の製造方法。
[11]前記炉体の長手方向の両端面内側に通電用の電極を配置させる前記9または10に記載のリチウムイオン電池用電極材料の製造方法。
[12]空気と接する面に酸素をバリヤする層を設ける前記9乃至11のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
1.リチウムイオン電池用電極材料のための黒鉛材料の製造方法
(1)黒鉛化前の炭素材料1の物性、製法
本発明では炭素材料1(炭素粉体)を黒鉛化して黒鉛材料を製造する。
炭素材料の原料としては、特に制限はないが、不活性雰囲気下で300℃から1200℃まで加熱した際、この温度領域における加熱減量分が5質量%以上20質量%以下である有機系炭素原料が好ましく使用できる。加熱減量分が5質量%未満になると黒鉛化後の粒子形状が板状になりやすい。また、粉砕面(エッジ部分)が露出しやすく比表面積が大きくなるため、負極として用いた場合に電解液との副反応が多くなる。逆に20質量%を超えると黒鉛化後の粒子同士の結着が多くなり、収率に影響する。有機系炭素原料の加熱減量分が上記範囲にあることによって、得られる黒鉛材料の表面が安定化し、負極として用いた場合に電解液との副反応が減少する。この理由は300~1200℃の加熱で揮発する成分のために、露出したエッジ部分の結晶が、炭化後黒鉛化することにより再構成し安定化され、また粒子表面もなめらかになることによると考えられる。
硫黄の量は試料数十mgを専用容器に秤量し、高周波加熱(助燃剤としてW1.5g、及びSn0.2g)により分解した後、鉄鋼用炭素標準試料を用い、炭素硫黄同時測定装置(堀場製作所製EMIA―920V)により測定する。
黒鉛化前の炭素材料1は、黒鉛化時に直接炭素材料に電流を流すため、抵抗は低いほうがよい。具体的には、密度1.4g/cm3に圧縮したときの圧密粉体抵抗値を0.4Ωcm以下とする。粉体の抵抗を下げる方法としては、800℃~1500℃で予備的な低温の熱処理を行ない、炭化度を上げる。好ましい熱処理温度は、用いる有機系炭素原料の種類や次工程の黒鉛化条件によって異なるが、900~1300℃である。生産性の観点からは、熱処理の温度はできるだけ下げたいが、低すぎると抵抗が十分に下がらない。
粉砕する方法に特に制限はないが、例えば、公知のジェットミル、ハンマーミル、ローラーミル、ピンミル、振動ミル等を用いて粉砕する。
D50(平均粒度)は30μm以下になるように分級することが好ましく、さらに好ましくは4μm以上25μm以下になるように分級する。平均粒度が大きいと、電解液との安定性が増す、塗工しやすいなどのメリットを有するが、逆に、高電流特性は悪い方向に進み、電極密度が上がりにくくなる。逆に小さいと充放電時に副反応が起きやすくなる。
粉体の粒度はレーザー散乱・回折式 粒度分布測定装置(CILAS)にて測定することができる。
安息角はタップデンサーを用いて測定することができる。具体的には、セイシン企業製KYT-4000を用い、50gの測定用サンプルを装置上部の専用投入口より自由落下させて、付属のテーブル上に三角錐型に堆積させ、次いで前記テーブルと三角錐の立ち上がり角度を分度器により測定し、それを安息角とすることができる。
緩め嵩密度は、高さ20cmから試料100gをメスシリンダーに落下させ、振動を加えずに体積と質量を測定して得られる密度である。また、固め嵩密度(タップ密度)は、カンタクローム製オートタップを使用して400回タッピングした100gの粉の体積と質量を測定して得られる密度である。
これらはASTM B527およびJIS K5101-12-2に準拠した測定方法であるが、タップ密度測定におけるオートタップの落下高さは5mmとした。
黒鉛化は、上記の炭素材料1に直接電流を流して発熱させることにより行う。
炭素材料に直接電流を流す方法としては、例えば、セラミックスレンガ製であって、上方が開口した直方体状の炉体を用いて行うことができる。この炉体は、開口部方向から見て長手方向の長さを短手方向の長さの2倍程度あるいはそれ以上とし、前記の長手方向の両端面内側に通電用の電極を配置させる。この炉に炭素材料を入れ、通電による発熱によって黒鉛化する。
このような炉体構造を採用することにより、炭素材料に熱が均一に加わるため、黒鉛化の際に凝集が生じないとの利点を有する。また、温度分布が均一で、不純物揮発のトラップ部分がないという理由から不純物の少ない黒鉛材料が得られる。
黒鉛化処理温度の下限は、通常2000℃、好ましくは2500℃、さらに好ましくは2900℃、もっとも好ましくは3000℃である。黒鉛化処理温度の上限は特に限定されないが、高い放電容量が得られやすいという観点から、好ましくは3200℃である。
前記炭素材料を黒鉛化してなる黒鉛材料(黒鉛化後の炭素材料)は、ラマン分光スペクトルで測定される1360cm-1の付近にあるピーク強度(ID)と1580cm-1の付近にあるピーク強度(IG)との強度比ID/IG(R値)が0.01以上0.2以下であることが好ましい。R値が0.2より大きいと表面に活性の高いエッジ部分が多く露出して充放電時に副反応が多く発生しやすくなる。一方0.01未満ではリチウムの出入りの障壁が高くなり、入出力特性が低下しやすくなる。レーザーラマンR値は、日本分光製NRS3100を用いて、励起波長532nm、入射スリット幅200μm、露光時間15秒、積算2回、回折格子600本/mmの条件で測定する。
酸化の度合いとしては、7940eVの硬X線を用いたHAX-PES測定により得られるO1sのピーク強度において、粒子の表面から深さ方向に対し40nmまでの間の酸素量a(質量%)が0.010≦a≦0.04であることが好ましく、0.010≦a≦0.03がさらに好ましい。酸素量aが多すぎると黒鉛材料中に存在する黒鉛結晶の導電性低下が顕著となり、抵抗成分が高まる結果、充放電反応を阻害して容量の低下や大電流特性の低下に繋がる場合がある。
これらは前記と同様の方法により測定する。
鉄含量(残鉄量)は、試料50~100mgを秤量して硫酸を加えて加熱することにより分解し、放冷後に硝酸を加えて加熱分解を行い、これを溶液が透明になるまで繰り返し、得られた液体を50mlに定容し、さらに10倍に希釈後ICP質量分析を行うことにより測定する。
スラリーは、前記黒鉛材料とバインダーとを含む。
スラリーは、黒鉛材料とバインダーとを混練することによって得られる。混錬には、リボンミキサー、スクリュー型ニーダー、スパルタンリューザー、レディゲミキサー、プラネタリーミキサー、万能ミキサー等の公知の装置が使用できる。電極用ペーストは、シート状、ペレット状等の形状に成形することができる。
バインダーとしては、ポリフッ化ビニリデンやポリテトラフルオロエチレン等のフッ素系ポリマー、SBR(スチレンブタジエンラバー)等のゴム系など公知のものが挙げられる。バインダーの使用量は黒鉛材料100質量部に対して0.5~20質量部が好ましく、1~20質量部がさらに好ましい。
スラリーは、導電助剤としてアセチレンブラックやケッチェンブラックなどのカーボンブラック、気相法炭素繊維などのカーボンナノファイバー、カーボンナノチューブ、黒鉛微粉などの導電性カーボンを含んでいてもよい。前記導電助剤の配合量は特に限定されないが、黒鉛材料100質量部に対して0.5~30質量部が好ましい。
混練する際に溶媒を用いることができる。溶媒としては、各々のバインダーに適した公知のもの、例えばフッ素系ポリマーならトルエン、N-メチルピロリドン等;SBRなら水等;その他にジメチルホルムアミド、イソプロパノール等が挙げられる。溶媒として水を使用するバインダーの場合は、増粘剤を併用することが好ましい。溶媒の量は集電体に塗布しやすいような粘度となるように調整される。
リチウムイオン電池用電極は前記スラリーを成形してなる。電極は、例えば前記スラリーを集電体上に塗布し、乾燥し、加圧成形することによって得られる。
集電体としては、例えばアルミニウム、ニッケル、銅、ステンレス等の箔、メッシュなどが挙げられる。スラリーの塗布厚は、通常20~150μmである。塗布厚が大きくなりすぎると、規格化された電池容器に電極を収容できなくなることがある。スラリーの塗布方法は特に制限されず、例えばドクターブレードやバーコーターなどで塗布後、ロールプレス等で成形する方法等が挙げられる。
加圧成形法としては、ロール加圧、プレス加圧等の成形法を挙げることができる。加圧成形するときの圧力は1~3t/cm2程度が好ましい。電極の電極密度が高くなるほど体積あたりの電池容量が通常大きくなるが、電極密度を高くしすぎるとサイクル特性が通常低下する傾向にある。前記スラリーを用いると電極密度を高くしてもサイクル特性の低下が小さいので、高い電極密度の電極を得ることができる。前記スラリーを用いて得られる電極の電極密度は、1.2~1.9g/cm3である。
リチウムイオン二次電池は、正極と負極とが電解液または電解質の中に浸漬された構造を有する。上記の電極はリチウムイオン二次電池の負極に使用される。
リチウムイオン二次電池の正極には、正極活物質として、通常、リチウム含有遷移金属酸化物が用いられ、好ましくはTi、V、Cr、Mn、Fe、Co、Ni、Mo及びWから選ばれる少なくとも1種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属元素のモル比が0.3乃至2.2の化合物が用いられ、より好ましくはV、Cr、Mn、Fe、Co及びNiから選ばれる少なくとも1種の遷移金属元素とリチウムとを主として含有する酸化物であって、リチウムと遷移金属のモル比が0.3乃至2.2の化合物が用いられる。なお、主として存在する遷移金属に対し30モルパーセント未満の範囲でAl、Ga、In、Ge、Sn、Pb、Sb、Bi、Si、P、Bなどを含有していても良い。上記の正極活物質の中で、一般式LixMO2(MはCo、Ni、Fe、Mnの少なくとも1種、x=0~1.2。)、またはLiyN2O4(Nは少なくともMnを含む。y=0~2。)で表されるスピネル構造を有する材料の少なくとも1種を用いることが好ましい。
なお、上記以外の電池構成上必要な部材の選択についてはなんら制約を受けるものではない。
実施例及び比較例において、d002等は、「発明を実施するための形態」に詳述した方法により測定する。また、その他の物性の測定方法は以下の通りである。
示差熱-熱重量同時測定装置(セイコーインスツルメント社製TGDTAw6300)を用い、測定サンプル約15mgを正確に測りとり、プラチナ製パンにのせて装置にセットし、アルゴンガスを200ml/分で流し、昇温速度10℃/分で昇温して、300℃~1200℃の範囲における質量変化を測定した。リファレンスとして和光純薬製αアルミナを1500℃で3時間あらかじめ処理し、揮発分を除去したものを用いた。
試料500gを振動ミルで28メッシュ以下に粉砕した。この試料を篩い分けて、28~60メッシュ60g、60~200メッシュ32g、200メッシュ以下8gの割合で混合し、全量を100gにした。この配合試料100gをステンレス容器に入れ、バインダーピッチ25gを加え、125℃のオイルバスで20分間加熱し均一に混合した。混合物を冷却し、振動ミルで粉砕し、全量を28メッシュ以下にした。該試料30gを125℃の加圧成形機に入れ、ゲージ圧450kg/cm2で5分間加圧し、成形した。成形品を磁性ルツボに入れ、焼成炉で室温から1000℃まで5時間で昇温し、1000℃で1時間保持して冷却した。この焼成品を精密切断機で4.3×4.3×20.0mmに切断し、テストピースを得た。本テストピースをTMA(熱機械分析装置)で30~100℃の熱膨張測定を行い、CTEを算出した。TMAとしては、セイコー電子製TMA/SS350を用いた。
レーザー散乱・回折式 粒度分布測定装置としてCILASを用いて、体積基準の平均粒子径(D50)および粒子径(D90)を求めた。
電流電圧端子が側面に設置された樹脂製容器に試料10gを充填し、縦方向に下に向かって荷重をかけ、試料を圧縮しながら100mAの電流を流して試料に流れる電流の抵抗値を測定した。試料の密度が1.4g/cm3となった時点で読み取った抵抗を圧密粉体抵抗とした。
圧縮率は(固め嵩密度-緩め嵩密度)×100/緩め嵩密度(%)であり、緩め嵩密度は、高さ20cmから試料100gをメスシリンダーに落下させ、振動を加えずに体積と質量を測定して得られる密度であり、固め嵩密度(タップ密度)は、カンタクローム製オートタップを使用して400回タッピングした100gの粉の体積と質量を測定して得られる密度である。
これらはASTM B527およびJIS K5101-12-2に準拠した測定方法であるが、タップ密度測定におけるオートタップの落下高さは5mmとした。
試料数十mgを専用容器に精秤し、高周波加熱(助燃剤としてW1.5gおよびSn0.2g)により分解した後、鉄鋼用炭素標準試料を用い、炭素硫黄同時測定装置(堀場製作所製EMIA-920V)により測定した。
タップデンサー(セイシン企業製KYT-4000)を用い、50gの測定用サンプルを装置上部の専用投入口より自由落下させて、付属のテーブル上に三角錐型に堆積させ、次いで前記テーブルと三角錐の立ち上がり角度を分度器により測定し、それを安息角とした。
比表面積測定装置NOVA-1200(ユアサアイオニクス(株)製)を用いて、一般的な比表面積の測定方法であるBET法により測定した。
粒子のアスペクト比は、シスメックス製のFPIA3000を用い、画像解析で測定した。測定点数は3000点以上、好ましくは30000点以上、さらに好ましくは50000点以上測定し、算出した平均値を使用した。
日本分光製NRS3100を用いて、励起波長532nm、入射スリット幅200μm、露光時間15秒、積算2回、回折格子600本/mmの条件でラマン分光スペクトルを測定し、1360cm-1の付近にあるピーク強度(ID)と1580cm-1の付近にあるピーク強度(IG)との強度比ID/IGをR値とした。
SPring-8(ビームラインBL46XU)に常設の装置を用いて、入射エネルギー7940eVのHAX-PES測定を行い、黒鉛材表面の酸素量を定量する。
測定条件は、C1sのナロースペクトルでは光電子のKinetic Energyが7638~7658eVのエネルギー範囲を測定し、O1sのナロースペクトルでは光電子のKinetic Energyが7396~7416eVのエネルギー範囲を測定する。
黒鉛材料表面の酸素量は以下の方法に従って定量する。
・光電子スペクトルのエネルギー校正
標準試料として板状のAu試料の測定を行う。Au4fのナロースペクトルとしてKinetic Energyが7648~7859eVのエネルギー範囲を測定し、測定で得られたAu4f7/2のピーク位置とAu4f7/2の理論ピーク位置との差を計算することでBL46XUの常設装置の仕事関数φ値を算出した。算出したφ値を元に、黒鉛材のナロースペクトルのエネルギー校正を行う。
・光電子スペクトル強度の規格化
黒鉛材のO1sナロースペクトル強度を任意のC1sナロースペクトル強度と測定で得られたC1sナロースペクトル強度をもとに規格化する。ノーマライズ強度x(O1s)は下記式1から算出する。
[式1]
ノーマライズ強度x(O1s)=測定強度(O1s)×任意の強度(C1s)/測定強度(C1s)
・黒鉛材表面の酸素量の定量
上記に基づき、実施例及び比較例の黒鉛材のノーマライズ強度(O1s)から、黒鉛材料の表面酸素量を下記式2より定量する。ここで、式2における任意の強度(C1s)は式1で用いた値である。
[式2]
黒鉛材料表面酸化量a(mol%)=(ノーマライズ強度x(O1s)/c任意の強度(C1s))×測定積算回数d(C1s)/測定積算回数e(O1s)
本測定は、非常に高輝度の放射光を用いることで、黒鉛材料表面から40nm程度の深度までの情報を積算している。そのため、黒鉛材料表面の汚染の影響をほとんど受けずに、精度の高い測定結果が得られる。
黒鉛材料は主成分の炭素の占める割合が圧倒的に高いため、炭素のC1sナロースペクトル強度から規格化した上記方法による酸素量の算出は妥当である。
試料50~100mgを秤量して硫酸を加えて加熱することにより分解し、放冷後に硝酸を加えて加熱分解を行い、溶液が透明になるまで繰り返した。この操作によって得た液体を50mlに定容し、さらに10倍に希釈後ICP質量分析により残鉄量を測定した。
(a)スラリー作製:
負極:黒鉛材料に呉羽化学社製KFポリマーL1320(ポリビニリデンフルオライド(PVDF)を12質量%含有したN-メチルピロリドン(NMP)溶液品)とテイムカル製カーボンブラックを、塗布乾燥後の組成が黒鉛:PVDF:カーボンブラックが、質量比で92:5:3になるように加え、プラネタリーミキサーにて混練し、主剤原液とした。
正極:日本化学工業製にコバルト酸リチウム(D50:約10μm)に呉羽化学社製KFポリマーL9320(ポリビニリデンフルオライド(PVDF)を12質量%含有したN-メチルピロリドン(NMP)溶液品)とテイムカル製カーボンブラック、昭和電工社製VGCF-Hを、塗布乾燥後の組成がコバルト酸リチウム:PVDF:カーボンブラック:VGCF-Hが、質量比で92:5:1:2になるように加え、プラネタリーミキサーにて混練し、主剤原液とした。
負極:上記の負極主剤原液にNMPを加え、粘度を調整した後、高純度銅箔上でドクターブレードを用いて約100μm厚に塗布した。これを120℃で1時間真空乾燥し、16mmφに打ち抜いた。打ち抜いた電極を超鋼製プレス板で挟み、プレス圧が電極に対して約1×102~3×102N/mm2(1×103~3×103kg/cm2)となるようにプレスした。その後、真空乾燥器で120℃、12時間乾燥して、評価用負極とした。
正極:上記の正極主剤原液にNMPを加え、粘度を調整した後、高純度Al箔上でドクターブレードを用いて約100μm厚に塗布した。これを120℃で1時間真空乾燥し、16mmφに打ち抜いた。打ち抜いた電極を超鋼製プレス板で挟み、プレス圧が電極に対して約1×102~3×102N/mm2(1×103~3×103kg/cm2)となるようにプレスした。その後、真空乾燥器で120℃、12時間乾燥して、評価用正極とした。
単極セル(単極評価):下記のようにして3極セルを作製した。なお以下の操作は露点-80℃以下の乾燥アルゴン雰囲気下で実施した。
ポリプロピレン製のねじ込み式フタ付きのセル(内径約18mm)内において、上記(b)で作製した銅箔付き炭素電極と金属リチウム箔をセパレーター(ポリプロピレン製マイクロポーラスフィルム(セルガード2500))で挟み込んで積層した。さらにリファレンス用の金属リチウムを同様に積層した。これに電解液を加えて試験用セルとした。
両極セル(電池評価):下記のようにして上記(b)で作製した正極と負極を用いて2極セルを作製した。なお以下の操作は露点-80℃以下の乾燥アルゴン雰囲気下で実施した。
ポリプロピレン製のねじ込み式フタ付きのセル(内径約18mm)内において、上記(b)で作製した銅箔付き炭素負極とAl箔つきCo正極をセパレーター(ポリプロピレン製マイクロポーラスフィルム(セルガード2500))で挟み込んで積層した。これに電解液を加えて試験用セルとした。各材料の単極評価の容量を基本容量とした場合の、負極容量/正極容量は1.15とした。
EC(エチレンカーボネート)8質量部及びDEC(ジエチルカーボネート)12質量部の混合液に、電解質としてLiPF6を1モル/リットル溶解した。
単極評価:3極式単極セル 電流密度1.0mA/cm2で定電流低電圧充放電試験を行った。
充電(炭素へのリチウムの挿入)はレストポテンシャルから0.002Vまで1.0mA/cm2でCC(コンスタントカレント:定電流)充電を行った。次に0.002VでCV(コンスタントボルト:定電圧)充電に切り替え、電流値が25.4μAに低下した時点で停止させた。
放電(炭素からの放出)は1.0mA/cm2でCC放電を行い、電圧1.5Vでカットオフした。
電池評価:2極式両極セル
電流密度1.0~5.0mA/cm2で定電流低電圧充放電試験を行った。
充電は、4.2Vまで1.0mA/cm2でCC(コンスタントカレント:定電流)充電を行った。次に4.2VでCV(コンスタントボルト:定電圧)充電に切り替え、電流値が25.4μAに低下した時点で停止させた。
放電は、各電流値1.0~5.0mA/cm2でCC放電を行い、電圧2.7Vでカットオフした。
300℃~1200℃のTG測定による加熱減量分が12.5質量%の石油系生コークス(非針状コークス)を日本碍子製ローラーハースキルンで窒素ガスを流しながら、1200℃で処理した。ついで、ホソカワミクロン製バンタムミルで粉砕したあと、日清エンジニアリング製ターボクラシファイアーで気流分級し、D50が20.0μmの炭素材料1を得た。この炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗は0.25Ωcm、安息角は36°であった。
セラミックレンガで縦500mm、横1000mm、深さ200mmの炉を作り、内側の両端面に450×180mm、厚み20mmの電極板を設置した。その炉の中に、上記炭素材料1を詰め込み、窒素ガス投入口と排気口が設けられた蓋をした。トランスを設置し、窒素ガスを流しながら、電極板間に約5時間電流を流すことで加熱し、炭素材料1を黒鉛化した。最高温度は3200℃であった。
得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。また、図1にSEM写真を示す。
d002および放電容量から、炉内の広範囲に渡って黒鉛結晶化が進んでいることがわかる。すなわち、本黒鉛化方法では、黒鉛ルツボ容器を用いるものであって製品とならない詰め粉が炉内に存在する従来法と同様以上に、3000℃以上に短時間で熱処理され全粉体が効率的に黒鉛化されていることが確認された。また、放電容量、初期効率ともに良好な電池を得ることができた。
300℃~1200℃のTG測定による加熱減量分が12.5質量%の石油系生コークス(非針状コークス)をホソカワミクロン製バンタムミルで粉砕した。日清エンジニアリング製ターボクラシファイアーで気流分級し、D50が20.0μmの有機系炭素原料を得た。ついで、この粉砕された有機系炭素原料を、日本碍子製ローラーハースキルンで
窒素ガスを流しながら、1000℃で処理し、炭素材料1を得た。この炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗は0.35Ωcm、安息角は34°であった。
この炭素材料1を実施例1と同様の方法で黒鉛化し、得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。
実施例1に比較して、容量が低めで、特に高い放電電流での容量が下がる傾向にあった。またサイクル寿命も劣った。
実施例1と同様の石油系生コークス(非針状コークス)と300℃~1200℃のTG測定による加熱減量分が11.5質量%の石油系生ニードルコークスを1:1で混合したものを有機系炭素原料として用いた以外は、実施例1と同様の方法で、D50が19.0μmの炭素材料1を得た。この炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗は0.20Ωcm、安息角は42°であった。
この炭素材料1を実施例1と同様の方法で黒鉛化し、得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。実施例1に比較し、d002が小さく、高容量であるが、初期効率がやや低かった。
黒鉛化時にB4Cを1000質量ppm加えた以外は、実施例1と同様に操作をし、黒鉛材料(炭素材料2)を得た。得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。実施例1に比較し、黒鉛化助触媒を添加したことによりd002が小さく高容量であるが、初期効率がやや低かった。
実施例1と同様の方法で得られた炭素材料1を蓋つき黒鉛ルツボに充填し、アチソン炉にて3000℃で黒鉛化処理した。得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。
実施例1と比較して、ほぼ同等の物性であるが、酸素量がやや低いためか、初期効率がやや低かった。またサイクル寿命も劣った。鉄残量も多かった。
実施例1と同様の石油系生コークス(非針状コークス)を日本碍子製ローラーハースキルンで窒素ガスを流しながら、600℃で処理した。ついで、ホソカワミクロン製バンタムミルで粉砕したあと、日清エンジニアリング製ターボクラシファイアーで気流分級し、D50が20.0μmの炭素材料1を得た。この炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗は0.50Ωcm、安息角は38°であった。
この炭素材料1を実施例1と同様の方法で黒鉛化し、得られた黒鉛材料(炭素材料2)の各種物性および電池評価結果を、有機系炭素原料および炭素材料1の物性と共に表1にまとめた。実施例1に比較し、比表面積が高く、d002が大きく、容量が低いことから、黒鉛化が十分に行われてないことが理解できる。
Claims (12)
- リチウムイオン電池用電極材料の製造方法であって、炭素材料に直接電流を流すことにより発熱させて黒鉛化する工程を含み、黒鉛化前の炭素材料1が密度1.4g/cm3に圧縮したときの圧密粉体抵抗値が0.3Ωcm以下で、安息角が20°以上50°以下、レーザー回折法により測定した体積基準の粒子径分布におけるD90が120μm以下であり、黒鉛化後の炭素材料2がX線回折法による(002)面の平均面間隔d002が0.3354nm以上0.3450nm以下であり、前記炭素材料1が有機系炭素原料を800℃以上1500℃以下で熱処理したあとに粉砕されたものであるリチウムイオン電池用電極材料の製造方法。
- (前記黒鉛化後の炭素材料2を密度1.4g/cm3に圧縮したときの圧密粉体抵抗)/(前記黒鉛化前の炭素材料1を密度1.4g/cm3に圧縮したときの圧密粉体抵抗)≦0.5である請求項1に記載のリチウムイオン電池用電極材料の製造方法。
- 前記黒鉛化前の炭素材料1のレーザー回折法により測定した体積基準の粒子径分布におけるD50が30μm以下である請求項1または2に記載のリチウムイオン電池用電極材料の製造方法。
- 前記黒鉛化前の炭素材料1の安息角が30°以上50°以下、緩め嵩密度と固め嵩密度から算出される圧縮率((固め嵩密度-緩め嵩密度)/緩め嵩密度)が20%以上50%以下である請求項1乃至3のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
- 前記有機系炭素材料が、不活性雰囲気下で300℃から1200℃まで加熱した際、この温度領域における加熱減量分が5質量%以上20質量%以下である請求項1乃至4のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
- 前記有機系炭素原料中の硫黄分が2質量%以下である請求項1乃至5のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
- 前記有機系炭素原料が、石油ピッチ、石炭ピッチ、石炭コークス、石油コークスおよびこれらの混合物から選ばれる1種以上である請求項1乃至6のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
- 前記黒鉛化前の炭素材料1が、ホウ素系化合物および/または珪素系化合物が10~100000質量ppmを含む請求項1乃至7のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
- 黒鉛化の工程において、セラミックスレンガ製であって、上方が開口した直方体状の炉体を用いる請求項1に記載のリチウムイオン電池用電極材料の製造方法。
- 前記炉体が、開口部方向から見て長手方向の長さが短手方向の長さの2倍以上である請求項9に記載のリチウムイオン電池用電極材料の製造方法。
- 前記炉体の長手方向の両端面内側に通電用の電極を配置させる請求項9または10に記載のリチウムイオン電池用電極材料の製造方法。
- 空気と接する面に酸素をバリヤする層を設ける請求項9乃至11のいずれか1項に記載のリチウムイオン電池用電極材料の製造方法。
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US20140255292A1 (en) | 2014-09-11 |
KR20140010180A (ko) | 2014-01-23 |
CN103650221A (zh) | 2014-03-19 |
TW201336783A (zh) | 2013-09-16 |
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