WO2010089991A1 - リチウム二次電池用ファイバー電極及びその製造方法並びにファイバー電極を備えたリチウム二次電池 - Google Patents
リチウム二次電池用ファイバー電極及びその製造方法並びにファイバー電極を備えたリチウム二次電池 Download PDFInfo
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- WO2010089991A1 WO2010089991A1 PCT/JP2010/000600 JP2010000600W WO2010089991A1 WO 2010089991 A1 WO2010089991 A1 WO 2010089991A1 JP 2010000600 W JP2010000600 W JP 2010000600W WO 2010089991 A1 WO2010089991 A1 WO 2010089991A1
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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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
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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
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
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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
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/75—Wires, rods or strips
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to an improvement in a fiber electrode for a lithium secondary battery in which a battery active material is attached to the surface of a fibrous material having electron conductivity and a method for producing the same. Further, the fiber electrode is bundled or laminated as a woven fabric. It is related with the lithium secondary battery in which high output is possible by comprising.
- Such lithium secondary batteries are currently generally used as non-aqueous electrolytes in which lithium ions are dissolved in an organic solvent such as lithium cobaltate as a positive electrode, a carbon electrode as a negative electrode, and propylene carbonate as an electrolyte. Yes.
- LiCoO 2 lithium cobaltate
- Li 2 CO 3 lithium carbonate
- Co (OH) 2 cobalt hydroxide
- a method of firing at a high temperature is widely known.
- this method requires a high temperature of 700 to 900 ° C., and the manufacturing cost is high.
- the recoverable reserves of cobalt are extremely small at 8.4 million tons, an alternative material for LiCoO 2 has been demanded in consideration of the possibility that the price of cobalt will increase in the future.
- lithium manganese oxide is attracting attention from the viewpoint of being relatively cheaper than LiCoO 2 and from the environmental viewpoint, and spinel type lithium manganate (LiMn 2 O 4 ) and tetragonal type lithium manganate (LiMnO 2 ). Research and development has been actively conducted on lithium manganese oxides such as next-generation low-cost cathode materials.
- Non-patent Document a firing step at a temperature as high as 700 to 800 ° C. is required.
- the positive electrode active material can be mass-produced at low cost at a low temperature.
- Patent Document 2 discloses a step of obtaining a manganese hydroxide by reacting a manganese compound and an alkali, and a step of obtaining a manganese oxide by oxidizing the hydroxide in an aqueous medium or in a gas phase.
- a method for producing lithium manganate comprising a step of reacting the manganese oxide and a lithium compound in an aqueous medium to obtain a lithium manganate precursor, and a step of heating and firing the precursor is disclosed.
- the lithium manganate thus obtained has a cubic particle shape, has voids in the particles, and has an initial charge / discharge capacity when it is a lithium secondary battery incorporated as a positive electrode active material. It has been found that it is high and has excellent cycle characteristics due to repeated charge and discharge.
- Non-Patent Documents 1 and 2 and Patent Documents 1 and 2 are both obtained in a powder state, a positive electrode is produced. Furthermore, it was necessary to obtain a current collecting property by mixing a conductive material and a binder to prepare a positive electrode slurry, and applying and forming this to a current collector such as an aluminum foil using a doctor blade or the like.
- the surface area of the positive electrode is increased and the positive electrode mixture layer is formed.
- the direction to make it as thin as possible is preferable.
- Patent Document 3 there is a battery using a fiber electrode as a battery in which the surface area of the electrode is increased and the active material layer is thinned.
- the carbon electrode when a carbon electrode is used for the negative electrode of the lithium secondary battery, lithium ions are taken in between the carbon layers during charging, and thus the volume change of the electrode is apparently small in the charge / discharge reaction.
- the carbon electrode has a disadvantage that the usable current density is low, the capacity density is low as a theoretical value of 372 mAh / g, the manufacturing process is complicated, and the yield is low, resulting in an increase in manufacturing cost. .
- the one with the largest capacity density is metallic lithium
- the theoretical density of metallic lithium is as high as 3860 mAh / g
- the charge / discharge capacity is 10 times or more that of the carbon electrode.
- metallic lithium when metallic lithium is used as the negative electrode of a lithium secondary battery, lithium dendrite grows with repeated charge / discharge reactions, causing short-circuiting between electrodes, destruction of the separator, and the like. As a result, the charge / discharge cycle efficiency of the lithium secondary battery is abruptly lowered, and the safety of the battery is also lowered.
- Sn is attracting attention as a next-generation negative electrode material because it is low in price, has a relatively small environmental load, and has a theoretical capacity (energy density of 994 mAh / g) more than twice that of conventional carbon materials.
- the change in volume occurs up to 3 to 4 times due to the insertion and release of lithium that occurs during charging and discharging, so that the capacity drops to about 100 mAh / g after about 20 cycles, and the cycle life characteristics are extremely poor.
- Sn has catalytic ability, there is a problem that the electrolytic solution is decomposed.
- Patent Document 4 is for forming a Sn thin film on a copper plate as a current collector by electrolytic plating
- Patent Document 5 is for Sn, Zn, Sb, or them on a copper foil by electrolytic plating.
- a thin film is formed using the contained alloy as a raw material.
- Non-Patent Document 3 a thin film having an inclined structure in which Cu atoms and Sn atoms are mutually diffused at a Cu-Sn interface is obtained by heat-treating an Sn thin film formed on a Cu foil by an electrolytic plating method. It is described that it can. That is, when a thin film formed by plating Sn on a Cu foil is heat-treated near the melting point of Sn, interdiffusion of atoms occurs at the Cu—Sn interface, and finally Cu / Cu 3 Sn / Cu 6 Sn 5 / A Cu—Sn alloy having a crystal structure close to Sn or this composition is formed. The Cu 6 Sn 5 alloy formed at this time can occlude and desorb Li reversibly, has a small volume change compared to Sn, and has no catalytic ability. It is expected as a negative electrode material that can solve problems peculiar to thin films.
- Patent Documents 6 and 7 disclose that a current collector is formed by forming a Sn (or Sn alloy) plating film on a copper foil current collector and then performing heat treatment.
- An invention of a negative electrode is disclosed in which an intermetallic compound of copper and Sn is formed as an intermediate layer between a certain copper and a Sn (or Sn alloy) plating film.
- the capacity drops to about 300 mAh / g after about 50 cycles, and does not show a constant capacity.
- the heating temperature is higher than 190 ° C., there is a problem in that the interface between the current collector, the copper plate, and the layer containing Cu 3 Sn as a main component is peeled off and the cycle life is reduced.
- the surface area of a substance becomes very large by making it into a powder, which greatly contributes to the improvement of chemical reactivity.
- a battery active material is used as an electrode, it is very difficult to collect current by connecting a terminal to each powdery active material particle. Therefore, in general, the powder is mixed with a conductive additive or a binder to form a slurry, which is applied to a metal foil or impregnated into a porous metal, and then dried and press-molded to form an active material and a current collector. Collect electricity in close contact.
- the electrode produced in this way is a thick two-dimensional flat plate, cannot take advantage of the size of the surface area of the powder, and the diffusion of ions and electrons moving through the active material is rate limiting. High output is difficult. *
- a fiber electrode having a fibrous electron-conducting material as a current collector as a movement path for electrons, and having a thin battery active material layer on its surface a large surface area closer to that of powder can be obtained. An electrode can be produced.
- the electrode surface area is increased by replacing the foil electrode with a fiber electrode, so that the high output characteristics can be improved.
- lithium ions are extremely large compared to protons and have a slow diffusion rate in the electrolyte, it is not possible to expect a significant improvement in high output characteristics as in the case of nickel metal hydride batteries.
- an electrode-separator laminate with a thin separator layer formed on a fiber electrode is formed, and in addition to the electrode surface area, the separator surface area is increased to reduce the distance between the electrodes. It is possible to increase the output by shortening the moving distance.
- the present invention employs a fiber electrode having the above advantages as an electrode of a lithium ion secondary battery, and solves the problems described below. I will try.
- the present invention relates to a fiber positive electrode for a lithium secondary battery having a lithium-doped transition metal oxide suitable as a fiber positive electrode for a lithium secondary battery as a main active material, and a method for producing the same, and in particular, the activity of active material particles.
- Low-cost mass production of fiber positive electrodes for lithium secondary batteries using lithium-doped transition metal oxide as the main active material which suppresses area reduction, has excellent charge / discharge cycle characteristics, and can be charged / discharged at high current density
- the purpose is to provide.
- an object of the present invention is to improve a fiber negative electrode for a lithium secondary battery and a manufacturing method thereof. That is, as disclosed in the prior art documents, Sn is electrolytically plated on a Cu foil current collector, and heat treatment is performed, thereby forming a CuSn alloy phase in the vicinity of the interface between Cu and Sn, thereby achieving high adhesion. Sex is obtained. Therefore, even if the active material is pulverized due to the charge / discharge cycle, there is an advantage that the active material is less likely to fall off from the current collector foil and the charge / discharge cycle characteristics are improved.
- an object of the present invention is to provide a fiber negative electrode for a lithium secondary battery that has a high current density and energy density, is excellent in charge / discharge cycle characteristics, and is relatively easy to manufacture, and a method for manufacturing the same.
- an object of the present invention is to provide a lithium secondary battery obtained by forming a separator layer on the fiber positive electrode and / or fiber negative electrode, and combining these fiber positive electrode and fiber negative electrode.
- the present inventors have formed a transition metal oxide film in an annular shape on a carbon fiber current collector, and then used this as the presence of an oxidizing agent or a reducing agent.
- a transition metal oxide film in an annular shape on a carbon fiber current collector, and then used this as the presence of an oxidizing agent or a reducing agent.
- a fiber positive electrode for a lithium secondary battery using a lithium-doped transition metal oxide as a main active material by performing heat treatment in a sealed system at 100 to 250 ° C. in a solution containing lithium ions. It was a success.
- the present inventors as a negative electrode, coated a metal such as copper on a carbon fiber current collector, and then formed an Sn or Sn alloy plating film in an annular shape.
- a negative electrode obtained by laminating and heat-treating in a trace oxygen atmosphere it was found that the cycle life was greatly extended with a high capacity, and the invention of a fiber negative electrode for lithium secondary batteries was completed. is there.
- the current collector is a thin cylindrical conductive fiber
- an annular active material layer is formed on each fiber.
- the active material layer forms a closed ring
- volume change due to charging / discharging is suppressed, and even when the expansion and contraction are repeated, the active material layer is peeled off compared to the plate electrode. -Dropout is unlikely to occur.
- the fibers are pressure-bonded to each other, which is more effective in preventing the active material from falling off.
- the present invention provides the following fiber positive electrode for a lithium secondary battery and a production method thereof, a fiber negative electrode for a lithium secondary battery and a production method thereof, and a lithium secondary battery including the fiber positive electrode and the fiber negative electrode. is there. 1.
- the method for producing a fiber positive electrode for a lithium secondary battery is as follows: (A) forming a film made of a transition metal oxide or a transition metal hydroxide in an annular shape on a carbon fiber current collector; (B) A product in which a film made of a transition metal oxide or transition metal hydroxide is formed in an annular shape on the carbon fiber current collector, and in the presence of an oxidizing agent or a reducing agent in a sealed system, And a step of heat-treating at 100 to 250 ° C.
- step (a) is preferably a step of forming an annular transition metal oxide film or transition metal hydroxide film on the carbon fiber current collector by electrolytic deposition.
- step (a) a transition metal film is formed in an annular shape on a carbon fiber current collector by electroplating, followed by high-temperature oxidation treatment at 500 to 1000 ° C. in an oxidizing atmosphere. A step of forming an oxide film is preferable.
- the step (a) is a step of co-depositing the conductive auxiliary agent, in which the conductive auxiliary agent is dispersed in the electrolytic deposition bath and the precipitated film contains the conductive auxiliary agent.
- the step (a) is a step of co-depositing the conductive auxiliary agent, in which the conductive auxiliary agent is dispersed in the electroplating bath and the conductive film is contained in the deposited film.
- the heat treatment in the sealed system in the step (b) is a solvothermal treatment.
- an Al film is formed on the carbon fiber current collector. (8) The thickness of the Al film is preferably 0.1 to 1 ⁇ m.
- the carbon fiber current collector preferably has a diameter of 1 to 100 ⁇ m.
- the transition metal oxide has the formula (1): M a O b (In the formula (1), M is at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, and 1 ⁇ a ⁇ 3 and 1 ⁇ b ⁇ 5. Is)
- the lithium-doped transition metal oxide has the formula (2): Li d Me O c (In formula (2), 2 ⁇ c ⁇ 5, 0 ⁇ d ⁇ 2, 1 ⁇ e ⁇ 5, and M is the same as in formula (1)).
- the transition metal oxide is Mn 3 O 4
- the lithium-doped transition metal oxide has the formula (2-1): Li d1 Mn e1 O c1 (In formula (2-1), the valence of Mn is in the range of 3 to 4, 2 ⁇ c1 ⁇ 4, 0 ⁇ d1 ⁇ 2, 1 ⁇ e1 ⁇ 2). preferable.
- the transition metal oxide has the formula (1-2): (Mn 1-X A X ) 3 O 4 (In the formula (1-2), A is at least one element selected from the group consisting of Al, Ti, Cr, Fe, Co, Ni, Cu, Sr, Y, Zr, and rare earth elements; .05 ⁇ x ⁇ 0.25),
- the lithium-doped transition metal oxide has the formula (2-2): Li d2 (Mn 1-y A y ) e2 O c2 (In the formula (2-2), the valence of Mn is in the range of 3 to 4, 2 ⁇ c2 ⁇ 4, 0 ⁇ d2 ⁇ 2, 1 ⁇ e2 ⁇ 2, 0.05 ⁇ y ⁇ 0.
- the fiber positive electrode for a lithium secondary battery is preferably produced by any one of the production methods described above.
- the lithium-doped transition metal oxide which is a porous material formed into a flake shape, has a thickness of 5 to 600 nm, a width of 0.1 to 10 ⁇ m, and a length of 0.1 to 10 ⁇ m. It is preferable.
- the lithium secondary battery preferably includes the above-described fiber positive electrode for lithium secondary battery, an electrolyte, and a negative electrode. 2.
- LITHIUM SECONDARY BATTERY FOR LITHIUM SECONDARY BATTERY, LITHIUM SECONDARY BATTERY HAVING FIBER NEGATIVE ELECTRODE Fiber negative electrode for lithium secondary battery (C) a carbon fiber current collector; (D) an outer layer composed of a composite layer of Sn oxide and M X O y formed in an annular shape on the carbon fiber current collector, (E) It has the intermediate layer which has the lithium occlusion ability which consists of Sn alloy which exists in the interface of the said carbon fiber electrical power collector and the said outer side layer, It is characterized by the above-mentioned.
- M is at least one metal atom Fe, Mo, Co, Ni, Cr, Cu, In, selected from the group consisting of Sb, and Bi, x is 0 ⁇ x ⁇ 3, and the number y of oxygen atoms O is 0 ⁇ y ⁇ w, where w is the number of oxygen atoms O based on the stoichiometry in the chemical bond between the metal atom M and the oxygen atom O. is there.)
- the Sn alloy layer of the intermediate layer includes at least one metal component selected from the group consisting of Fe, Mo, Co, Ni, Cr, Cu, In, Sb, and Bi as an alloy component other than Sn.
- the Sn alloy plating layer is preferably included.
- the intermediate layer is a CuSn alloy layer, and the outer layer is a composite layer of Sn and Cu oxides.
- the intermediate layer is a Cu 3 Sn layer and the outer layer is a composite layer of SnO 2 and Cu 2 O.
- the total thickness of the intermediate layer and the outer layer is preferably 1 to 10 ⁇ m.
- the carbon fiber preferably has a single fiber diameter of 1 to 100 ⁇ m.
- the carbon fibers are preferably in a state where 100 to 5000 single fibers are bundled.
- the carbon fiber is preferably in a state in which 50 to 1000 single fibers are twisted.
- the intermediate layer and the outer layer have a conductive agent and / or a binder.
- the conductive agent is preferably carbon black.
- the binder is preferably polytetrafluoroethylene.
- the fiber negative electrode for lithium secondary battery after charging is (C) a carbon fiber current collector; (F) is formed in an annular shape on the carbon fiber current collector, Li 2 O matrix Fe during, Mo, Co, Ni, Cr , Cu, In, at least one selected from the group consisting of Sb, and Bi An outer layer comprising a layer in which seed metals and Li 4.4 Sn are dispersed; (G) It has the intermediate
- the fiber negative electrode for lithium secondary battery after discharge is (C) a carbon fiber current collector and (h) an annular shape formed on the carbon fiber current collector, and Fe, Mo, Co, Ni, Cr, Cu, In, Sb, and Bi in a Li 2 O matrix.
- An outer layer comprising a layer in which at least one metal selected from the group consisting of Sn and Sn or an Sn alloy is dispersed; (I) It is characterized by having an intermediate layer having a lithium occlusion ability present at the interface between the carbon fiber current collector and the outer layer.
- Method for producing fiber negative electrode for lithium secondary battery A method for producing a fiber negative electrode for a lithium secondary battery, On the carbon fiber current collector, at least one metal film selected from the group consisting of Fe, Mo, Co, Ni, Cr, Cu, In, Sb, and Bi, and Sn film, or Sn by electroplating. After the alloy film is formed, heat treatment is performed at 350 to 650 ° C. in a trace oxygen atmosphere. (33) It is preferable to disperse a conductive agent and / or a binder in the electroplating bath and to eutectify the conductive agent and / or the binder on the carbon fiber current collector.
- the negative electrode manufactured by the above-described method for manufacturing a fiber negative electrode for a lithium secondary battery is pre-doped with lithium.
- the lithium secondary battery includes the above-described fiber negative electrode for lithium secondary battery, an electrolyte, and a positive electrode.
- the lithium secondary battery includes the above-described fiber negative electrode for a lithium secondary battery, the above-described fiber positive electrode for a lithium secondary battery, and an electrolyte.
- Fiber positive electrode for lithium secondary battery and manufacturing method thereof The manufacturing method of the fiber positive electrode for lithium secondary battery of the present invention is as follows. (A) forming a film made of a transition metal oxide or a transition metal hydroxide in an annular shape on a carbon fiber current collector; (B) A product in which a film made of a transition metal oxide or transition metal hydroxide is formed in an annular shape on the carbon fiber current collector, and in the presence of an oxidizing agent or a reducing agent in a sealed system, And a step of heat-treating at 100 to 250 ° C. in a solution containing lithium ions to obtain a lithium-doped transition metal oxide film on the carbon fiber current collector.
- a film made of a transition metal oxide or a transition metal hydroxide is formed in an annular shape on the carbon fiber current collector.
- Carbon fiber current collector When the current collector is made of a thin cylindrical conductive fiber instead of a plate or foil, an annular active material layer is formed on each fiber in step (b). In this case, since the active material layer forms a closed ring, volume change due to charging and discharging is suppressed, and even when expansion and contraction are repeated, the active material layer is peeled off compared to the plate electrode. Dropping is unlikely to occur, and advantages such as improved charge / discharge cycle life and improved output characteristics are expected. Furthermore, by bundling the fibers, the fibers are pressure-bonded to each other, which is more effective in preventing the active material from falling off.
- the diameter of the carbon fiber current collector When the diameter of the carbon fiber current collector is small, its mechanical strength is insufficient, and there is a possibility that the fiber will be cut due to tightening when bundled with a crimping terminal or the weight of the attached active material. Extremely expensive. Further, since the diameter is small, the electrical conductivity is lowered, and it is difficult to deposit the active material uniformly. On the other hand, when the diameter of the carbon fiber current collector is large, the active material layer easily peels from the current collector, and the charge / discharge cycle life may be reduced. This is related to the curvature of the fiber side. For example, if the diameter of the single fiber is not so large, the curvature of the active material layer is increased in the circumferential direction, and distortion is unlikely to occur.
- the deposited active material layers are connected to each other to form a ring.
- the elasticity of the annular ring formed by connecting the active material layers comes to work, and even if the active material layer expands or contracts, it becomes difficult to peel off.
- the diameter of the single fiber is large, the curvature is small and the circumferential direction of the fiber approaches a flat plate, so that the shape of the coated active material layer is also close to a flat plate type, and distortion tends to occur, causing peeling or dropping. It becomes easy.
- the bulk of the electrode becomes large, and there is a problem in that the amount of active material filling per volume is reduced.
- the shape of the carbon fiber current collector used in the present invention is preferably a thin cylindrical conductive fiber having a diameter of 1 to 100 ⁇ m. A more preferable fiber diameter is 5 to 10 ⁇ m.
- the fiber to be used may be a single fiber, or a multifilament obtained by collecting a plurality of single fibers is also effective.
- the length and aspect ratio of the carbon fiber current collector are not particularly limited, but the length is preferably about 10 to 1000 mm, and the aspect ratio is preferably about 2000 to 200000.
- the electrode is formed by bundling 50 to 1000 twisted yarns of such fibers.
- C carbon
- a metal selected from Al (aluminum), Ti (titanium), Cr (chromium), Zr (zirconium), Hf (hafnium), Ta (tantalum) and W (tungsten), an alloy made of these, stainless steel, etc.
- C is preferable from the viewpoint of the best adhesion to the active material and cost performance.
- carbon fiber can be used as a current collector as it is, carbon is easily oxidized at a high voltage. Therefore, the problem can be solved by coating the carbon fiber current collector with Al. . At the same time, the electrical conductivity can be further improved by coating the carbon fiber current collector with Al. Therefore, it can be said that this is a desirable method for producing a current collector for applications requiring high output.
- a physical thin film forming method, an electrolytic plating method, or the like can be applied.
- the surface of the carbon fiber has fine irregularities, and considering the method that can uniformly coat Al on each carbon fiber group consisting of thousands, the electrolytic plating method should be adopted. Is preferred.
- Al electroplating is difficult to perform in an aqueous plating bath because Al has a high affinity for oxygen and the oxidation-reduction potential of Al is lower than that of hydrogen. Therefore, it is desirable to carry out in a non-aqueous solution (for example, organic solvent type, ionic liquid type) plating bath.
- a non-aqueous solution for example, organic solvent type, ionic liquid type
- an Al film can be uniformly formed even on a carbon fiber group having a complicated and intricate shape. it can.
- the surface of the carbon fiber has fine irregularities (the width of the groove constituting the concave portion is about 5 to 1000 nm, and the height of the groove is about 5 to 1000 nm). If the thickness of the Al film is too large, it is difficult to cover Al reflecting the unevenness. Moreover, when too small, carbon itself may contact an electrolyte solution and there exists a possibility that it may be oxidized, and it does not have sufficient electroconductivity. Therefore, the preferable thickness of the Al film is 0.1 ⁇ m to 1 ⁇ m.
- Examples of the non-aqueous plating bath for forming an Al coating on a carbon fiber current collector include aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl 3 -EMIC) room temperature molten salt, chloride Aluminum-1-butylpyridinium chloride (AlCl 3 -BPC) room temperature molten salt, aluminum chloride and general formula [(R 1 ) 3 N + R 2 ] X— (where R 1 is an alkyl group having 1 to 12 carbon atoms, R It is possible to use an existing plating bath such as a room temperature molten salt composed of a quaternary ammonium salt represented by 2 is an alkyl group having 1 to 12 carbon atoms, and X is a halogen atom.
- transition metal oxide or transition metal hydroxide is not particularly limited as long as it can form a film on the carbon fiber current collector.
- V 2 O 3 , V 2 O 5 , MnO, Mn 3 O 4 , Mn 2 O 3 , MnO 2 , MnO 3 , FeO, Fe 3 O 4 , Fe 2 O 3 , CoO, Co 2 O 3 , Co 3 O 4 , CoO 2 , NiO, Ni 3 O 4 , Ni 2 O 3 , NiO 2 and the like are preferable.
- V 2 O 3 , V 2 O 5 , MnO Mn 3 O 4 , Mn 2 O 3 , MnO 2 , MnO 3 , FeO, Fe 3 O 4 , Fe 2 O 3 , NiO, Ni 3 O 4 , Ni 2 O 3 , NiO 2, etc. are preferable, and the positive electrode voltage From the viewpoint, MnO, Mn 3 O 4 , Mn 2 O 3 , MnO 2 , MnO 3 , NiO, Ni 3 O 4 , Ni 2 O 3 , NiO 2 and the like are preferable.
- the method of forming a transition metal oxide or transition metal hydroxide film in an annular shape on a carbon fiber current collector is not particularly limited, but includes a slurry method, a physical thin film formation method, an aerosol. Examples include a deposition method, an electroplating method, and an electrolytic deposition method. Hereinafter, each forming method will be described.
- a slurry obtained by dispersing transition metal oxide particles or transition metal oxide particles and an organic substance in a solvent is applied onto a carbon fiber current collector, and the electrode is formed by vaporizing the solvent.
- This is the most popular manufacturing method.
- thickeners, binders and the like remain in the electrode, so that the conductivity is deteriorated, and it is very difficult to uniformly apply and form the very thin fibrous current collector used in the present invention. difficult.
- examples of the physical thin film forming method include vapor deposition and sputtering.
- a sputtering method when a sputtering method is used, a high-density transition metal oxide or transition metal hydroxide film can be formed.
- the transition metal oxide and the transition metal hydroxide have poor conductivity, and the efficiency is poor for laminating the transition metal oxide or the transition metal hydroxide on the carbon fiber current collector by the sputtering method.
- even if it is a vapor deposition method it takes time to vapor-deposit an oxide or hydroxide itself, and it is not suitable for mass production.
- the aerosol deposition method is a method in which a transition metal oxide powder or a transition metal hydroxide powder present in a positive pressure atmosphere is sprayed at once onto a carbon fiber current collector present in a negative pressure atmosphere to form a thin film.
- the positive pressure atmosphere means a state where the pressure is higher than the surroundings
- the negative pressure atmosphere means a state where the pressure is lower than the surroundings.
- transition metal oxides and transition metal hydroxides have little spreadability, and even when jetted onto a carbon fiber current collector at a high pressure, it is difficult to form a layer composed of a transition metal oxide or a transition metal hydroxide. In particular, when the transition metal oxide or transition metal hydroxide collides with the carbon fiber, the carbon fiber is broken.
- the electroplating method is a method of electrochemically forming a metal film on a carbon fiber current collector.
- the electroplating method it is not possible to laminate a transition metal oxide directly on the carbon fiber current collector. Therefore, after first plating the transition metal on the carbon fiber current collector, the transition metal is subjected to high-temperature oxidation such as heat treatment. It must be oxidized by treatment.
- the high temperature oxidation treatment at this time includes raising the temperature to 500 to 1000 ° C. in an oxidizing atmosphere.
- the conditions in the electroplating method are not particularly limited, and depend on the metal to be plated, but the current density is adjusted to 1 mA / cm 2 by adjusting the concentration of the transition metal salt to be plated in the range of 0.05 to 1 mol / liter.
- the transition metal is plated on the carbon fiber current collector by performing electroplating at ⁇ 0.1 A / cm 2 .
- the electrolytic deposition method means that a carbon fiber current collector that forms a film and an electrode that is a counter electrode are immersed in a solution containing the composition of the target film and energized.
- This is a method for forming a target film. If the composition ion of the target film is a cation, a metal oxide or hydroxide film is formed on the surface of the carbon fiber current collector by energizing the carbon fiber current collector as a cathode. Obtainable. It is also possible to perform anodic oxidation by energizing the carbon fiber current collector as an anode and to take in the composition ions in the bath to form a film on the surface of the carbon fiber current collector. When a hydroxide film is obtained instead of a metal oxide, the oxide film can be obtained by drying at 100 ° C. or higher in an air atmosphere.
- a transition metal oxide or a transition metal hydroxide can be directly formed on the carbon fiber current collector.
- the conditions in the electrolytic deposition method are not particularly limited, and depend on the metal to be deposited, but the concentration of the metal salt to be deposited is adjusted to be in the range of 0.05 to 1 mol / liter, and the current density is 1 mA / cm 2 to It may be performed at 0.1 A / cm 2 .
- the current collector is carbon fiber
- the current collector is carbon fiber
- an attempt is made to coat the carbon fiber current collector with the transition metal oxide or the fiber metal hydroxide by the aerosol deposition method. Attempting to do so destroys the current collector, making it very difficult to coat.
- the slurry method or the physical thin film forming method it is very difficult to uniformly coat the transition metal oxide or the transition metal hydroxide. Therefore, as a method for forming a film made of a transition oxide or a fiber metal hydroxide on a carbon fiber current collector, an electroplating method, an electrolytic deposition method, or the like is preferable.
- the transition metal oxide or transition metal on the surface of the carbon fiber current collector is sufficient as long as the carbon fiber current collector is in contact with the electroplating bath or the electrolytic deposition bath.
- a film made of hydroxide can be formed, adhesion is good, the smoothness of the film surface can be improved, and uniform lamination of a larger area is easy and inexpensive.
- the electrolytic deposition method is the most preferable method because a transition metal oxide or a transition metal hydroxide can be directly formed on the current collector.
- a conductive additive is added to the treatment bath (electroplating bath or electrolytic deposition bath).
- the treatment bath electroplating bath or electrolytic deposition bath.
- the conductive aid may be oxidized in the subsequent oxidation treatment, so when adopting the eutectoid method, the electroanalysis without the oxidation treatment step. It is preferable to adopt the extraction method and form a film made of a transition metal, a transition metal oxide or a transition metal hydroxide.
- the conductive support agent added to an electroplating bath or an electrolytic deposition bath should just be a material which has electroconductivity and exists stably also in a positive electrode potential. Specifically, carbon black, aluminum fine powder and the like are preferable.
- the amount of the conductive aid is preferably added so as to be about 1 to 20 wt% in the electroplating bath or electrolytic deposition bath. At this time, when a surfactant of about 1 wt% is added, the conductive additive is easily dispersed in the electrolytic deposition bath.
- the surfactant that can be used in this case is not particularly limited, and examples thereof include cationic, anionic, amphoteric, and nonionic surfactants.
- Suitable surfactants include Tamol SN (TAMOL (registered trademark) SN), Tamol (registered trademark) LG available from Rhom and Haas Company, Triton (commercially available from the company) TRITON (registered trademark) series, MARASPERSE (registered trademark) series commercially available from GAF, and IGEPAL (registered trademark) series, Terditol (TERGITL (registered trademark)) commercially available from the company Series, Strdex PK-90 (STRODEX (registered trademark) PK-90), Pluronic F-68 (PLURONIC (registered trademark) F-68) available from BASF, Maraspers Crow Perth TU commercially available (KARASPERSE TU (TM)), and the like.
- TAMOL registered trademark
- Tamol registered trademark
- LG available from Rhom and Haas Company
- Triton commercially available from the company
- TRITON registered trademark
- MARASPERSE registered trademark
- IGEPAL registered trademark
- the amount of the coating made of transition metal oxide or transition metal hydroxide on the carbon fiber current collector is preferably 1 to 30 mg / cm 2 .
- the average thickness of the film made of the transition metal oxide or transition metal hydroxide is not limited, but is usually about 0.5 ⁇ m to 30 ⁇ m, preferably about 1 ⁇ m to 10 ⁇ m.
- M is at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, and 1 ⁇ a ⁇ 3 and 1 ⁇ b ⁇ 5.
- M is at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co and Ni, and 1 ⁇ a ⁇ 3 and 1 ⁇ b ⁇ 5.
- the transition metal oxide formed in the lithium modified lithium, Equation (2): Li d M e O c (In formula (2), 2 ⁇ c ⁇ 5, 0 ⁇ d ⁇ 2, 1 ⁇ e ⁇ 5, and M is the same as in formula (1)) It becomes.
- M is preferably V, Mn, Fe, Co, Ni or the like from the viewpoint of positive electrode capacity, and more preferably Mn, Fe, or Ni from the viewpoint of cost.
- the final lithium-doped transition metal oxide is represented by the formula (2-1): Li d1 Mn e1 O c1 (In formula (2-1), the valence of Mn is in the range of 3 to 4, 2 ⁇ c1 ⁇ 4, 0 ⁇ d1 ⁇ 2, 1 ⁇ e1 ⁇ 2) Become.
- lithium secondary batteries using lithium and manganese oxides such as Li 1 + x Mn 2 O 4 and Li x Mn 2 O 4 as the positive electrode active material elute Mn when the temperature is raised. Is big.
- a material in which a part of manganese is substituted with Al, P, Ti, Cr, Fe, Co, Ni, Cu, Sr, Y, Zr, In, Sn, rare earth elements, or the like is preferable.
- Al, Cr, Co, Ni and the like are preferable, and from the viewpoint of cost, a material substituted with Al, Ni and the like is more preferable.
- transition metal oxide When coating the transition metal oxide on the carbon fiber current collector, two or more kinds of metal oxides such as nickel oxide and manganese oxide are formed on the carbon fiber current collector and then oxidized.
- nickel oxide and manganese oxide are coated on a carbon fiber current collector in a solution containing lithium ions in the presence of a reducing agent or a reducing agent, and a nickel-lithium manganate active material You can also get
- transition metal oxide fine particles dispersed in an electrolytic deposition bath are co-deposited on a carbon fiber current collector to form a transition metal oxide film composed of two or more metal oxides on the carbon fiber current collector. It may be obtained and heat-treated by the same method as above.
- the oxidizing agent only needs to have an oxidizing power, and examples thereof include air, oxygen, ozone, chlorine, bromine, chlorate, peroxodisulfate, hypochlorite, and hydrogen peroxide water. Hypochlorite is particularly preferable, and sodium hypochlorite is more preferable.
- the reducing agent only needs to have a reducing power, and examples thereof include hydrogen, formaldehyde, sodium ascorbate and the like, and sodium isoascorbate is preferable.
- the oxidizing agent or reducing agent may be a suitable gas. That is, a lithium-doped transition metal oxide film can also be obtained by a gas contact method in the presence of an oxidizing agent or a reducing agent. Gas contact can be performed by blowing gas into the lithium ion solution.
- the blowing gas at this time includes air, air diluted with an inert gas, oxidant gas (O 2 , O 3 , N 2 O, etc.) or reducing gas (H 2 , H 2 S, SO 2). , HCHO, etc.).
- oxygen in air plays the role of an oxidizing agent, it is preferable to carry out in inert gas.
- step (b) the amount of lithium ions and the amount of oxidizing agent or reducing agent vary depending on the oxidation form and amount of the transition metal oxide. That is, what is necessary is just to estimate the quantity of lithium ion, oxidation equivalent, or reduction equivalent required for a starting material to become a target object.
- the transition metal oxide Ma O b is defined as 1 equivalent
- the valence of the transition metal M in Formula (1) is ⁇
- the formula (2) When the valence of the transition metal M in ⁇ is ⁇ , an oxidizing agent having an oxidation equivalent of ⁇ - ⁇ or more may be used. However, when the value of ⁇ - ⁇ is a negative real number, a reducing agent having a reducing equivalent of ⁇ - ⁇ is used.
- NiO Ni valence is 2+
- LiNiO 2 LiNi valence is 3+
- V 2 O 5 When the starting material V 2 O 5 (V valence is 5+) is 1 equivalent, if it is 0.5 reducing equivalent or more, LiV 2 O 5 (V valence is 4.5+), 1 reducing equivalent or more. If it exists, Li 2 V 2 O 5 (V valence is 4+), and if it is 2 reduction equivalents or more, Li 4 V 2 O 5 (V valence is 3+).
- V 2 O 3 (V valence is 3+) is 1 equivalent, if it is one oxidation equivalent or more, Li 2 V 2 O 5 (V valence is 4+).
- the solution containing lithium ions used for the heat treatment is sufficient if the lithium ions are dissolved in the solution.
- a water-soluble lithium compound may be dissolved in water.
- lithium chloride aqueous solution, lithium nitrate aqueous solution, lithium hydroxide aqueous solution and the like can be suitably used.
- These water-soluble lithium compounds can be used singly or in combination of two or more, and any of anhydrides and hydrates may be used.
- Lithium-doped transition metal oxides can also be obtained.
- LiCoO 2 or the like having a layered structure releases 50% or more of lithium ions (Li 0.5 CoO 2 )
- the crystal structure is destroyed, the reversibility of insertion and extraction of lithium is reduced, and the charge / discharge cycle life is poor.
- the obtained discharge capacity had to be kept at about 150 mAh / g.
- the positive electrode material that can only be used up to about 50% of the theoretical capacity can be used up to nearly 80% of the theoretical capacity by partially replacing the Li site with Na or K.
- the Na source and the K source may be dissolved in the treatment field (solution containing lithium ions).
- a water-soluble sodium compound or potassium compound dissolved in water may be used.
- sodium chloride aqueous solution, sodium nitrate aqueous solution, sodium hydroxide aqueous solution and the like can be suitably used.
- These water-soluble sodium compounds and water-soluble potassium compounds can be used singly or in combination of two or more, and either an anhydride or a hydrate may be used.
- the amount of the water-soluble lithium compound used may be a lithium element molar ratio with respect to the number of moles of the transition metal in the target transition metal oxide. It is preferable to add 1 to 5 times the amount of lithium, and a more preferable range is 1 to 3 times the theoretical amount.
- the concentration of the water-soluble lithium compound is preferably in the range of 0.05 to 10 mol / liter, more preferably in the range of 1 to 6 mol / liter. When a sodium compound or potassium compound is used, the amount used is preferably about 5 to 20 mol% with respect to the concentration of lithium in the treatment field (solution containing lithium ions).
- the temperature at which a carbon fiber current collector formed with a transition metal oxide or transition metal hydroxide film in an annular shape is heat-treated in a solution containing lithium ions is 100 to 250 ° C., preferably 100 to 250 ° C. 200 ° C.
- the reaction proceeds even when the temperature of the heat treatment is less than 100 ° C, but is preferably 100 ° C or higher because the reaction rate is slow.
- the temperature exceeds 250 ° C. the apparatus becomes large and the cost performance deteriorates.
- the heat treatment is carried out by placing a transition metal oxide film or a transition metal hydroxide film formed on a carbon fiber current collector in a solution containing lithium ions in the presence of an oxidizing agent or a reducing agent. It is preferable to seal with a corrosion-resistant container and to carry out under saturated water vapor pressure or under pressure.
- the heat treatment is not particularly limited, and examples thereof include solvothermal treatment.
- solvothermal treatment is a chemical reaction (dissolution, precipitation, oxidation, reduction, ion exchange, crystallization, etc.) in a high-temperature, high-pressure liquid reaction field using a high-temperature, high-pressure sealed container such as an autoclave.
- the liquid used at this time is an organic solvent such as water, alcohol, acetone, ethylene glycol and combinations thereof, imidazole salt ionic liquid, pyridinium salt ionic liquid, or onium salt ionic liquid.
- An ionic liquid or the like is used.
- hydrothermal synthesis in particular, a substance such as choline chloride that is solid at room temperature but becomes liquid when the temperature is raised may be used as the reaction field.
- water used as a liquid
- this hydrothermal synthesis is preferable from the viewpoint of environment, ease of work, cost, and the like.
- Niobium, Inconel, and stainless steel are more preferable.
- the hydrothermal pressure may be 0.05 to 40 MPa. By making it within this range, lithium doping with respect to the transition metal is sufficient, and a large pressure / corrosion resistant container is not required, which is economically preferable. From such a viewpoint, the hydrothermal treatment pressure is more preferably within the range of 0.1 to 10 MPa.
- the heat treatment time varies depending on the heat treatment temperature, it may be 5 hours or longer if the temperature is in the range of 100 to 200 ° C, or 3 hours or longer if the temperature is in the range of 200 to 400 ° C. It should be noted that it is preferable to set an appropriate time so as not to drop the active material attached to the carbon fiber current collector. Specifically, the time is preferably in the range of 5 to 50 hours, and preferably in the range of 10 to 30 hours. It is.
- a fiber positive electrode in which a lithium-doped transition metal oxide film is formed on a carbon fiber current collector can be obtained.
- the fiber cathode can be used as a better cathode by drying under reduced pressure at about 80 to 150 ° C. to remove moisture.
- the fiber positive electrode of the present invention thus obtained has an active material layer formed directly on a carbon fiber current collector and has an annular shape. Therefore, there is no need for any step of converting the active material into an electrode, which was necessary in the conventional method. That is, a fiber positive electrode can be manufactured simultaneously with manufacture of an active material.
- the lithium-doped transition metal oxide has a flake shape formed in a direction perpendicular to the surface of the carbon fiber current collector, and has a thickness of 5 to 500 nm and a width of 0.005. It has the characteristics of 1 to 10 ⁇ m and a length of 0.1 to 10 ⁇ m.
- the flake shape refers to a flake shape having a small thickness with respect to the length.
- the formation in the vertical direction means that it is formed in the direction perpendicular to the surface of the carbon fiber current collector 1 as shown in FIG. 1, and 2 is a lithium-doped transition metal oxide. Showing things.
- the positive electrode active material material having a flake shape aggregates to form an aggregate, and the aggregate adheres in a direction perpendicular to the carbon fiber current collector.
- a porous positive electrode active material layer is formed. Therefore, the electrode surface area is extremely large, and the electrolyte solution has a structure that can easily penetrate, so that the stress due to the expansion and contraction of the active material volume can be relieved.
- the current collector is a thin cylindrical conductive fiber. Therefore, an annular active material layer is formed on the fiber and has a very large electrode surface area.
- the active material layer forms a closed ring, volume change due to charging / discharging is suppressed, and even when the expansion / contraction is repeated, the active material layer is more Peeling and falling off hardly occur. Furthermore, by bundling the fibers, the fibers are pressure-bonded to each other, which is more effective in preventing the active material from falling off. In other words, since it has a super three-dimensional structure, it can be a fiber positive electrode having a long life and excellent electrode characteristics.
- the negative electrode of the lithium secondary battery using the fiber positive electrode of the present invention is not particularly limited, and is carbon-based such as graphite; alloy-based such as Cu 3 Sn; oxide-based such as SnO and SiO; nitride-based such as LiN. A well-known thing can be used. Furthermore, the fiber negative electrode of the present invention may be used as a counter electrode. 2. Fiber negative electrode for lithium secondary battery and method for producing the same According to the lithium secondary battery using the fiber negative electrode for lithium secondary battery of the present invention, it has a high charge / discharge capacity due to the presence of Sn (tin).
- the fiber negative electrode for a lithium secondary battery of the present invention is obtained by electroplating a carbon fiber current collector with Fe (iron), Mo (molybdenum), Co (cobalt), Ni (nickel), Cr (chromium), After forming at least one metal film and Sn film or Sn alloy film selected from the group consisting of Cu (copper), In (indium), Sb (antimony), and Bi (bismuth), in a trace oxygen atmosphere It can be obtained by heat treatment at 350 to 650 ° C.
- the carbon fiber current collector used in the present invention is preferably a carbon fiber having a diameter of 1 to 100 ⁇ m.
- the plating layer peels off when the temperature exceeds 190 ° C.
- the diameter of the carbon fiber is more preferably 5 to 10 ⁇ m. The reason is the same as that of the fiber positive electrode described above.
- the diameter of the carbon fiber is as small as less than 1 ⁇ m, the mechanical strength and electrical conductivity are problematic, and it is difficult to produce an electrode.
- the diameter of the carbon fiber exceeds 100 ⁇ m, the active material layer is likely to be distorted due to a decrease in curvature, and peeling and dropping are likely to occur, and a decrease in the amount of active material filling per volume due to an increase in electrode bulk is also a problem become.
- the carbon fiber to be used may be a single fiber, or an aggregate of a plurality of single fibers is also effective.
- the binder when the metal M is plated on the carbon fiber, the binder may be eutectoidally plated.
- the diameter of the fiber cross section is increased, the binding force of the binder is weakened, and it becomes difficult to obtain the effect of adding the binder.
- the diameter of the carbon fiber is 100 ⁇ m or less, the binders are connected to each other within the alloy, and the elastic material layer has a strong elasticity. Even if the alloy expands or contracts, it is difficult to peel off. Become.
- the fiber circumference becomes relatively larger than the binder molecule, so that the cooperation between the binder molecules decreases. Therefore, it is difficult to obtain the effect of adding a binder.
- 100 to 5000 single fibers be one bundle, more preferably 1000 to 4000 single bundles.
- One electrode is formed by fixing one end of the fiber bundle with a crimp terminal or the like.
- the metal M coated on the surface of the carbon fiber by heat treatment After forming at least one selected metal (hereinafter also referred to as metal M) plating layer and Sn plating layer or Sn alloy plating layer, the metal M coated on the surface of the carbon fiber by heat treatment
- the plating layer and the Sn plating layer or the Sn alloy plating layer are alloyed.
- the alloyed film (plating layer) gradually begins to oxidize from the outer periphery and changes to a composite layer of Sn oxide and M x O y .
- the number x of metal atoms M is 0 ⁇ x ⁇ 3
- the number y of oxygen atoms O is the number of oxygen atoms O based on the stoichiometry in the chemical bond between the metal atom M and the oxygen atom O.
- w 0 ⁇ y ⁇ w.
- the metal atom M Cu and Ni are preferable.
- the fiber negative electrode for a lithium secondary battery of the present invention has a slightly lower charge / discharge capacity than metal lithium, but can suppress the generation of lithium dendrite during charge / discharge and improve battery safety.
- whiskers may be generated from the Sn film and the electrodes may be short-circuited, but as in the negative electrode of the lithium secondary battery of the present invention.
- the presence of an alloy of metal M and Sn can prevent whiskers from occurring.
- a conductive agent and / or a binder is dispersed in the plating bath and subjected to eutectoid plating, which is activated by a change in volume accompanying the charge / discharge reaction. It is also possible to prevent the substance from falling off the carbon fiber current collector and improve the electrical conductivity.
- the electroplating method is employed as a method for laminating the film on the surface of the carbon fiber current collector, the adhesion between the metal M film, Sn film, or Sn alloy film and the carbon fiber current collector is good, and a large area is laminated. Is easy and cheap.
- the conditions in the electroplating method are not particularly limited, but it is preferable to adjust the concentration of the metal salt to be deposited in the range of 0.1 to 2 mol / liter and perform electroplating at a low current.
- the Sn alloy can exhibit the effects of the present invention as long as it contains Sn as a main component.
- the alloy component other than Sn includes at least one metal M selected from the group consisting of Fe, Mo, Co, Ni, Cr, Cu, In, Sb, and Bi. And Ni are preferred.
- An electroplating method is suitable as a method for laminating the Sn alloy film on the surface of the carbon fiber current collector. According to this electroplating method, the adhesion of the Sn alloy film to the surface of the carbon fiber current collector is good, the smoothness of the Sn alloy film surface can be improved, and a larger area can be easily and inexpensively stacked.
- a negative electrode composed of SnO 2 , M x O y and SnM alloy can be obtained.
- the temperature during the heat treatment at this time is 350 to 650 ° C., preferably 400 to 500 ° C. If it is lower than 350 ° C., Sn oxide and M x O y may not be generated. On the other hand, if it exceeds 650 ° C., the carbon fiber is oxidized, which is not preferable.
- a trace oxygen atmosphere is an atmosphere having an oxygen concentration in the range of 0.05 to 5 vol%.
- a preferable oxygen concentration is in the range of 0.1 to 3 vol%.
- the oxygen concentration exceeds 5 vol%, all or most of the laminate is oxidized, the conductivity is lowered, the battery characteristics are deteriorated, and the effect of the present invention cannot be exhibited.
- the oxygen concentration is less than 0.05 vol%, the laminate is not easily oxidized, and the heat treatment time becomes considerably long, which is not economically preferable.
- the oxygen concentration is in the range of 0.05 to 5 vol%, the heat treatment time is 1 hour.
- atmospheric gas components other than oxygen include an inert gas such as Ar.
- a trace oxygen atmosphere can be achieved even in the range of 0.01 to 30 Pa, preferably 1 to 20 Pa, more preferably 1 to 10 Pa by reducing the pressure of the air, and similar effects can be achieved.
- the total thickness of the outer layer and the intermediate layer made of a composite layer of Sn oxide and M x O y formed in an annular shape on the carbon fiber current collector is preferably 1 to 10 ⁇ m.
- a binder or a conductive agent is dispersed in a plating bath, and a binder or a conductive agent is formed on the carbon fiber current collector by eutectoid plating.
- the conductivity and cycle life of the material layer can be further improved.
- PTFE polytetrafluoroethylene
- SBR styrene-butylene rubber
- PVA polyvinyl alcohol
- PE polyethylene
- styrene copolymer cellulose esters
- water repellent materials such as PTFE do not disperse uniformly, and therefore, when emulsified using a surfactant, they can be dispersed uniformly in the plating solution.
- surfactant saponins, phospholipids, peptides, tritons and the like are effective, and about 0.1 to 3 wt% may be added to the entire plating solution.
- the binder content with respect to the plating film is preferably 0.5 to 10 wt%, and more preferably 1 to 5 wt%. If there is too much binder, the resistance in the electrode of the negative electrode increases, leading to deterioration of the high rate discharge characteristics. If the amount of the binder is too small, the cycle characteristics are deteriorated.
- the conductive agent examples include metals, carbon black, and conductive polymers. Among these, carbon black is preferable, and specific examples include acetylene black (AB) and ketjen black (KB).
- the conductive agent is preferably contained in an amount of 0.1 to 10 wt%, more preferably 1 to 5 wt% with respect to the plating film. If the content is less than 0.1 wt%, the effect of combining the conductive agents cannot be achieved, leading to a decrease in high rate discharge characteristics and not suitable for high output applications. When the content exceeds 10 wt%, the plating film tends to drop off, and the capacity of the alloy negative electrode is reduced.
- the content is 1 to 10 wt%, a sufficient effect of improving the conductivity can be obtained, and the capacity reduction of the alloy negative electrode can be minimized.
- a water repellent conductive agent such as carbon black
- it may be dispersed with a stirrer or ultrasonic wave.
- a surfactant may be added to the plating solution.
- saponins, phospholipids, peptides, tritons and the like are also effective as the surfactant.
- it may be added simultaneously with the emulsified binder.
- Lithium secondary battery provided with fiber positive electrode and fiber negative electrode The lithium secondary battery obtained using the fiber positive electrode and / or fiber negative electrode of the present invention must contain lithium ions as an electrolyte salt thereof. Is preferably a lithium salt.
- the lithium salt is not particularly limited, and specific examples include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfonate, and the like. Among these, one or more types can be used. Since the lithium salt has high electronegativity and is easily ionized, it has excellent charge / discharge cycle characteristics and can improve the charge / discharge capacity of the secondary battery.
- Examples of the solvent for the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ⁇ -butyrolactone, and one or more of these can be used. Of these, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or ⁇ -butyrolactone alone is preferred. The mixing ratio of the mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted within the range of 10 to 90%.
- the separator may be any material that has good electronic insulation and good ion permeability, does not react with the electrolyte or electrode material, and exists stably in the battery operating voltage range.
- a conventional porous membrane having a large number of fine pores made of polypropylene or polyethylene (hereinafter referred to as a microporous membrane) can be used.
- the inner diameter of the hole is about 100 nm, and the film thickness is preferably 20 to 60 ⁇ m.
- Suitable separators include Celgard (registered trademark) series marketed by Celanese, E002 and E003 marketed by Sumitomo 3M, BX-100 marketed by Mitsubishi Kasei, and Nitto Denko. LBS-2015 and Hypore 4030U2 commercially available from Asahi Kasei.
- separator materials in addition to polypropylene and polyethylene, styrene-butylene-ethylene-styrene copolymer (SEBS), polytetrafluoroethylene (PTFE), styrene-butylene rubber (SBR), polyvinyl alcohol (PVA), styrene series General-purpose materials such as copolymers and cellulose esters are used.
- SEBS styrene-butylene-ethylene-styrene copolymer
- PTFE polytetrafluoroethylene
- SBR styrene-butylene rubber
- PVA polyvinyl alcohol
- styrene series such as copolymers and cellulose esters are used.
- a method of sandwiching a microporous membrane separator sheet between a fiber positive electrode or a fiber negative electrode and a counter electrode can be applied in the same manner as a flat plate electrode using a conventional foil-like current collector, and the electrolyte solution is sealed after injection. A battery is formed.
- a fiber positive electrode and / or fiber negative electrode is impregnated into a polymer solution such as polyethylene added with an oxide powder such as SiO 2 and dispersed, and the solvent is removed by drying treatment, followed by heating to 100 ° C.
- the separator can also be formed by a method in which the porous film is formed by immersing in a caustic aqueous solution so as to dissolve the oxide. Any oxide may be used as long as it is soluble in an aqueous caustic solution, and Al 2 O 3 or the like can be used in addition to SiO 2 .
- the particle size of the oxide is preferably 10 nm to 10 ⁇ m.
- the oxide particles are separated from each other by polyethylene molecules, and pores generated by alkali dissolution of the oxide are difficult to connect to each other, so that sufficient ion permeability cannot be obtained. If it is larger than 10 ⁇ m, the pores generated after dissolution of the alkali become large, so that the electrode surface is easily exposed, which is likely to cause a short circuit when a battery is constructed.
- the addition amount of the oxide is preferably 10 to 50 wt% with respect to the polymer, and more preferably 10 to 30 wt%. If it is less than 10 wt%, a sufficient porosity cannot be obtained.
- the porosity is sufficient, but the film strength is lowered, causing a short circuit during battery construction.
- the immersion time depends on the amount of oxide added, it is preferably about 10 minutes to 50 hours. If it is less than 10 minutes, dissolution of SiO 2 does not proceed and a porous film is difficult to be formed. On the other hand, if it exceeds 50 hours, the strength of the film will be lowered, the amount of moisture and alkali components accumulated in the fiber will increase, and it will take time for subsequent washing and drying.
- the added amount of SiO 2 or Al 2 O 3 is 10 to 50 wt%, the porosity will be in the range of 30 to 70%, and a separator film having good ion permeability and electronic insulation will be used as the fiber positive electrode and It can be formed on the fiber negative electrode.
- any of LiOH, NaOH, and KOH may be used, and a mixture of these may be used.
- concentration of the aqueous alkali solution used is not particularly limited, but 10 to 30 wt% is often used. When it is less than 10 wt%, it is necessary to immerse for a long time in order to dissolve the oxide. When it exceeds 30 wt%, an alkali component tends to remain after the alkali treatment, and it is necessary to repeat the water washing treatment many times.
- the electrode surface area is increased by replacing a conventional foil electrode with a fiber electrode, so that high output characteristics can be improved.
- lithium ions are extremely large compared to protons and have a low diffusion rate, it is not possible to expect a significant improvement in high output characteristics as in the case of nickel metal hydride batteries.
- both the positive electrode and the negative electrode are made into fibers like the present invention, and a thin separator layer is formed on the fiber surface by a method of impregnating the fiber with a polymer solution, and the fiber positive electrode and the fiber negative electrode are alternately laminated.
- the surface area of the separator is greatly increased and the distance between the electrodes is shortened compared to the case where the counter electrode is plate-like, so that lithium ions can move between the electrodes in a short time, resulting in a high current density.
- Significant improvement in charge / discharge characteristics can be expected.
- the fiber positive electrode and the fiber negative electrode exhibit better charge / discharge cycle life characteristics than the conventional flat electrode. Therefore, when a battery is configured by combining a fiber positive electrode or a fiber negative electrode with a flat electrode, the flat electrode is deteriorated before the fiber electrode, so that the battery capacity is reduced even if the fiber electrode performance is not deteriorated. become. By combining the fiber positive electrode and the fiber negative electrode, deterioration is unlikely to occur, and therefore a longer life of charge / discharge cycle characteristics can be expected.
- the fiber positive electrode and the fiber negative electrode have a larger capacity density per volume and weight than the conventional flat electrode. Therefore, even when a battery having the same size as that of the conventional battery is configured, it is possible to increase the capacity and reduce the weight.
- a flat electrode is used as a counter electrode, the volume and weight of the counter electrode are equivalent to those of the conventional one, and there is a limit to increasing the capacity and weight. For example, consider a battery in which the capacity ratio (N / P) of the negative electrode (N) and the positive electrode (P) is 2. By replacing the plate-like positive electrode with a fiber positive electrode, the volume density is considered to be improved up to about twice, so that the space occupied by the positive electrode is reduced to half of the original.
- Li is desorbed from the positive electrode, and a Li storage reaction occurs in the negative electrode.
- the inserted lithium is desorbed from the negative electrode at the time of discharge, but some of the lithium remains in the negative electrode without being partially desorbed. This is called the initial irreversible capacity.
- a test half-cell using metal Li as a counter electrode it has a large capacity of 3860 mAh / g. Therefore, even if irreversible capacity is generated, the battery capacity is not reduced thereby.
- the capacity of the Li-doped oxide positive electrode is 200 mAh / g
- the generation of irreversible capacity causes a decrease in the amount of Li re-occluded in the positive electrode during discharge, thereby causing a decrease in capacity of the entire battery.
- it is effective to pre-dope Li for the irreversible capacity in the negative electrode by previously forming a half-cell with the negative electrode and metal Li and performing charging. In this way, even if the entire battery is configured in combination with the positive electrode, no further irreversible capacity is generated, and thus an effect of hardly reducing the battery capacity can be obtained.
- the fiber cathode in which an active material layer is directly formed on a carbon fiber current collector can be manufactured, there is no need for a process of manufacturing an active material and converting it into an electrode as in the prior art. That is, the fiber cathode can be manufactured simultaneously with the manufacture of the active material.
- the fiber positive electrode obtained by the present invention basically does not require the addition of a conductive additive or a binder, the slurrying of the active material, the rolling step, and the like.
- the present invention mass production can be easily performed at low cost.
- the positive electrode active material of the present invention contains lithium element, it is not necessary to dope lithium in advance. That is, the manufacturing process and the safety of the battery can be improved.
- the lithium-doped transition metal oxide has a flake shape formed in a direction perpendicular to the surface of the carbon fiber current collector, so that a porous positive electrode active material layer is formed. It has a long life and excellent electrode characteristics.
- the carbon fiber current collector is a thin cylindrical conductive fiber
- an annular active material layer is formed on the fiber to form a closed ring. Therefore, even when the volume change due to charging / discharging is suppressed and the expansion and contraction are repeated, the active material layer is less likely to be peeled off and dropped compared to the plate electrode.
- the fibers are pressure-bonded to each other, which is more effective in preventing the active material from falling off, has a long life, and has excellent electrode characteristics.
- a lithium secondary battery using such a fiber positive electrode has a high current density and energy density, and has excellent charge / discharge cycle characteristics.
- the fiber negative electrode for lithium secondary batteries of the present invention has a long life and high charge / discharge capacity, and is easy to manufacture.
- a lithium secondary battery using such a negative electrode has a high current density and energy density, and has excellent charge / discharge cycle characteristics.
- the lithium secondary battery obtained by combining the fiber positive electrode and the fiber negative electrode of the present invention can greatly increase the separator surface area and shorten the distance between the electrodes, the internal resistance can be greatly reduced, The current density charge / discharge characteristics can be greatly improved. Furthermore, the life of the cycle characteristics can be extended and the capacity of the battery can be increased.
- FIG. 1 is a conceptual diagram showing a state in which a flaky lithium-doped transition metal oxide is formed in a direction perpendicular to the surface of a carbon fiber current collector in the fiber positive electrode of the present invention.
- FIG. 2 is a SEM photograph (scanning electron micrograph, 3000 times) of the fiber positive electrode of Production Example 1.
- FIG. 3 is a diagram showing X-ray diffraction patterns of Examples 2, 3-5, and Production Examples 1 and 2. 4 shows synchrotron X-ray diffraction patterns of Examples 3-1 to 3-4, and the right figure of FIG. 4 shows LiMn 2 O 4 of Examples 3-1 to 3-4. It is a figure which shows a production
- FIG. 1 is a conceptual diagram showing a state in which a flaky lithium-doped transition metal oxide is formed in a direction perpendicular to the surface of a carbon fiber current collector in the fiber positive electrode of the present invention.
- FIG. 2 is a SEM photograph (scanning electron micrograph
- FIG. 5 is a diagram showing synchrotron X-ray diffraction patterns of Examples 6 and 9.
- 6 is a diagram showing an X-ray diffraction pattern of Example 11.
- FIG. 7 is an SEM photograph (5,000 times) of the surface of the fiber positive electrode of Example 2.
- FIG. 8 is an SEM photograph (magnified 3000 times) of the surface of the fiber cathode of Example 3-5.
- FIG. 9 is an SEM photograph (5000 times) of the surface of the fiber positive electrode of Example 6.
- FIG. 10 is a diagram showing initial charge / discharge curves of Examples 2, 3-5, and 4 and Production Examples 1 and 2.
- FIG. 11 is a diagram illustrating an initial charge / discharge curve for each cycle of Example 6, in which a curve rising to the right indicates a charge curve and a curve decreasing to the right indicates a discharge curve.
- FIG. 12 is a diagram illustrating a discharge curve for each discharge rate in Example 6.
- FIG. 13 is a diagram showing an initial charge / discharge curve for each cycle of Example 9, in which a curve rising to the right indicates a charge curve and a curve decreasing to the right indicates a discharge curve.
- FIG. 14 is a diagram showing discharge curves for each discharge rate in Example 9.
- FIG. 15 is a diagram showing X-ray diffraction patterns of Example 12 and Comparative Examples 2 to 4.
- FIG. 16 is a graph showing the abundance ratio of each phase in Example 12 and Comparative Examples 2 to 4.
- FIG. 15 is a diagram showing X-ray diffraction patterns of Example 12 and Comparative Examples 2 to 4.
- FIG. 17 is a diagram schematically showing the cross-sectional structures of Example 12 and Comparative Examples 2-4.
- FIG. 18 is a diagram showing the charge / discharge cycle life test results of Example 12 and Comparative Example 4.
- FIG. 19 is a diagram illustrating a charge / discharge curve of Comparative Example 4, in which a curve rising to the right indicates a charge curve, and a curve decreasing to the right indicates a discharge curve.
- FIG. 20 is a diagram illustrating a charge / discharge curve of Example 12, a curve that rises to the right indicates a charge curve, and a curve that decreases to the right indicates a discharge curve.
- FIG. 21 is a diagram showing X-ray diffraction patterns of Example 14 and Comparative Examples 8 to 10.
- FIG. 22 is a graph showing the abundance ratio of each phase in Example 14 and Comparative Examples 8 to 10.
- FIG. 23 is a diagram schematically showing a cross-sectional structure of Example 14 and Comparative Examples 8 to 10.
- FIG. 24 is a diagram showing the charge / discharge cycle life test results of Example 14 and Comparative Examples 8 and 9.
- FIG. 25 is a diagram illustrating a charge / discharge curve of Comparative Example 9, in which a curve rising to the right indicates a charge curve, and a curve decreasing to the right indicates a discharge curve.
- FIG. 26 is a diagram showing a charge / discharge curve of Example 14, in which a curve rising to the right indicates a charge curve and a curve decreasing to the right indicates a discharge curve.
- FIG. 27 is a diagram schematically showing the cross-sectional structures of Example 12 and Example 14 after charging and discharging.
- FIG. 28 is a diagram showing X-ray diffraction patterns of Reference Examples 1, 3, 10 and Comparative Reference Examples 1, 5.
- FIG. 29 is a SEM photograph (6000 times) of the surface of the positive electrode of Reference Example 1 on the oxide film side.
- FIG. 30 is a SEM photograph (10,000 times) of the surface of the positive electrode of Reference Example 3 on the oxide film side.
- FIG. 31 is a diagram showing initial discharge curves of Reference Example 2, Reference Example 5, Reference Example 6, and Reference Example 13.
- FIG. 32 is a plan view showing a schematic configuration of the bipolar evaluation cell of Example 23.
- FIG. FIG. 33 is a plan view showing a schematic configuration of a bipolar evaluation cell of Example 24.
- Production Example 1 (Electrolytic Deposition Method) Mn 3 O 4 / Carbon Fiber First, Mn (NO 3 ) 2 aqueous solution (0.3 mol / liter) was used in the electrodeposition bath. , Carbon fiber (diameter 6 ⁇ m) was used for the working electrode, and platinum foil was used for the counter electrode. As electrolytic deposition conditions, electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 10 minutes.
- FIG. ⁇ Production Example 2 (Electrolytic Deposition Method) NiO / Carbon Fiber First, Ni (NO 3 ) 2 aqueous solution (0.3 mol / liter) is used for the electrodeposition bath, and carbon fiber (diameter 6 ⁇ m) is used for the working electrode. A platinum foil was used for the counter electrode.
- electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 30 minutes. Thereafter, the electrode was washed with water and dried at 130 ° C. for 24 hours or more in an air atmosphere to obtain an electrode in which carbon fiber was coated with NiO. In addition, it does not function as a positive electrode only by coating NiO.
- NiO / carbon fiber First, an aqueous solution of nickel sulfate (0.3 mol / liter) is used for the electroplating bath, carbon fiber (diameter 6 ⁇ m) is used for the working electrode, and the counter electrode is used. Platinum foil was used. As electroplating conditions, electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 30 minutes. Thereafter, the electrode was washed with water and oxidized at 650 ° C.
- Mn 3 O 4 + Al 2 O 3 / Carbon Fiber In order to coat Mn 3 O 4 and Al 2 O 3 by the electrolytic deposition method, Mn ( A mixture of a NO 3 ) 2 aqueous solution (0.3 mol / liter) and an Al (NO 3 ) 3 aqueous solution (0.03 mol / liter) was used. Carbon fiber (diameter 6 ⁇ m) was used for the working electrode, and platinum foil was used for the counter electrode. Electrodeposition was performed at a constant current density of 50 mA / cm 2 for 10 minutes.
- the electrode was washed with water and dried in an air atmosphere at 70 ° C. for 24 hours or more to obtain an electrode in which carbon fibers were coated with Mn 3 O 4 and Al 2 O 3 .
- carbon fibers were coated with Mn 3 O 4 and Al 2 O 3 .
- only coated with Mn 3 O 4 and Al 2 O 3 are not functions as a positive electrode.
- Electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 10 minutes. Thereafter, the electrode was washed with water and dried at 70 ° C. for 24 hours or more in an air atmosphere, and carbon fibers were coated with Mn 3 O 4 and Al 2 O 3 to obtain an electrode in which KB was eutectoid. Incidentally, only coated with Mn 3 O 4 and Al 2 O 3 are not functions as a positive electrode.
- Example 1 (Hydrothermal Synthesis Method) LiMnO 2 + Mn (OH) 2 / Carbon Fiber
- O gas 8 mg / liter
- hydrothermal synthesis was performed at 110 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain the fiber positive electrode of Example 1.
- Example 2 (Hydrothermal Synthesis Method) LiMnO 2 / Carbon Fiber
- One oxidation equivalent of sodium hypochlorite one equivalent of Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1
- the electrode of Production Example 1 was immersed in an aqueous lithium hydroxide solution to which sodium hypochlorite concentration: 0.01 mol / liter was added, and hydrothermal synthesis was performed at 130 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 2.
- Example 3 LiMn 2 O 4 / Carbon Fiber
- the oxidation equivalent was changed, and the LiMn 2 was deposited on the carbon fiber current collector.
- a fiber positive electrode having an O 4 film formed thereon was obtained.
- Example 3-1 >>: 1.5 Oxidation Equivalent
- One Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1 was taken as 1 equivalent, and 1.5 oxidation equivalent of sodium hypochlorite was added.
- the electrode of Production Example 1 was immersed in an aqueous lithium hydroxide solution (concentration of sodium hypochlorite: 0.02 mol / liter), and hydrothermal synthesis was performed at 110 ° C. for 20 hours.
- Example 3-2 2 Oxidation Equivalent Lithium hydroxide aqueous solution in which Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1 was taken as 1 equivalent and 2 oxidation equivalents of sodium hypochlorite were added
- the electrode of Production Example 1 was immersed in (concentration of sodium hypochlorite: 0.04 mol / liter), and hydrothermal synthesis was performed at 110 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 3-2.
- Example 3-3 2.5 Oxidation Equivalent
- One 2.5 equivalent of Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1 was added and 2.5 oxidation equivalent of sodium hypochlorite was added.
- the electrode of Production Example 1 was immersed in an aqueous lithium hydroxide solution (sodium hypochlorite: 0.06 mol / liter), and hydrothermal synthesis was performed at 110 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 3-3.
- sodium hypochlorite 0.06 mol / liter
- Example 3-4 3 Oxidation Equivalent Lithium hydroxide aqueous solution in which Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1 was used as 1 equivalent and 3 oxidation equivalents of sodium hypochlorite were added
- the electrode of Production Example 1 was immersed in (sodium hypochlorite: 0.08 mol / liter), and hydrothermal synthesis was performed at 110 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 3-4.
- Example 3-5 3.5 Oxidation Equivalent As a 1 equivalent of Mn 3 O 4 formed on the carbon fiber current collector in Production Example 1, 3.5 oxidation equivalent of sodium hypochlorite was added.
- the electrode of Production Example 1 was immersed in an aqueous lithium hydroxide solution (concentration of sodium hypochlorite: 0.1 mol / liter), and hydrothermal synthesis was performed at 125 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 3-5.
- Example 4 (Hydrothermal Synthesis Method) LiNiO 2 + Ni (OH) 2 / Carbon Fiber
- the electrode of Production Example 2 was immersed in a lithium hydroxide aqueous solution to which was added (hydrogen peroxide concentration: 0.005 mol / liter), and hydrothermal synthesis was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 4.
- Example 5 LiNiO 2 / Carbon Fiber Water containing 1 equivalent of NiO formed on the carbon fiber current collector in Production Example 2 and 2 parts of sodium hypochlorite equivalent to water
- the electrode of Production Example 2 was immersed in an aqueous lithium oxide solution (concentration of sodium hypochlorite: 0.04 mol / liter), and hydrothermal synthesis was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 5.
- Example 6 LiMn 1.9 Ni 0.1 O 4 / Carbon Fiber A total of 1 equivalent of Mn 3 O 4 and NiO formed on the carbon fiber current collector in Production Example 3
- the electrode of Production Example 3 was immersed in an aqueous lithium hydroxide solution (concentration of sodium hypochlorite: 0.02 mol / liter) to which an oxidizing equivalent amount of sodium hypochlorite was added, under the condition of 120 ° C. for 20 hours. Hydrothermal synthesis was performed. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 6.
- Example 7 (Hydrothermal Synthesis Method) LiNiO 2 + Ni (OH) 2 / Carbon Fiber
- a lithium hydroxide aqueous solution sodium hypochlorite concentration: 0.01 mol / liter
- hydrothermal synthesis was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 7.
- Example 8 (Hydrothermal synthesis method) LiMn 1.9 Ni 0.1 O 4 / Al-coated carbon fiber Mn 3 O 4 and NiO formed on the Al-coated carbon fiber current collector in Production Example 5 as a total of 1 equivalent Then, the electrode of Production Example 5 was immersed in an aqueous lithium hydroxide solution containing 1.5 oxidation equivalents of sodium hypochlorite (0.02 mol / liter) and hydrothermal synthesis was performed at 130 ° C. for 20 hours. went. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or longer to obtain a fiber positive electrode of Example 8.
- Example 9 (hydrothermal synthesis method) LiMn 1.9 Al 0.1 O 4 / carbon fiber Mn 3 O 4 and Al 2 O 3 formed on the carbon fiber current collector in Production Example 6 as a total of 1 equivalent,
- the electrode of Production Example 6 is immersed in an aqueous lithium hydroxide solution (0.02 mol / liter) containing 1.5 oxidizing equivalents of sodium hypochlorite, and hydrothermal synthesis is performed at 130 ° C. for 20 hours. It was. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 9.
- Example 10 (Hydrothermal Synthesis Method) LiMn 1.9 Al 0.1 O 4 + KB / Carbon Fiber A total of 1 equivalent of Mn 3 O 4 and Al 2 O 3 formed on the carbon fiber current collector in Production Example 7
- the electrode of Production Example 7 was immersed in a lithium hydroxide aqueous solution (0.02 mol / liter) to which 1.5 oxidation equivalent of sodium hypochlorite was added, and hydrothermal synthesis was performed at 130 ° C. for 20 hours. went. Thereafter, the electrode was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 10.
- Example 11 (Sorbothermal method) LiMnO 2 / carbon fiber An electrode in which Mn 3 O 4 was coated on the carbon fiber current collector obtained in Production Example 1 was subjected to choline chloride, urea and water in an air atmosphere. It was embedded in a mixed powder of lithium oxide and subjected to solvothermal treatment at 150 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain a fiber positive electrode of Example 11.
- the lithium source in Examples 1 to 11 and Comparative Example 1 is adjusted to be 2.5 or more (2 mol / liter or more) as a molar ratio of lithium element to the number of moles of transition metal.
- the carbon fiber used in the examples is a commercially available carbon fiber (manufactured by Toho Tenax Co., Ltd.) obtained by carbonizing polyacrylonitrile fiber at 1200 ° C., and the fiber diameter constituting the current collector is an average. This was 6 ⁇ m, and this was cut into 5 cm, and 3000 pieces were assembled to form a current collector.
- Test Example 1 >>: Observation of fiber cathode [X-ray diffraction] The X-ray diffraction patterns of Examples 2, 3-5, and 4 are shown in FIG. For reference, production examples 1 and 2 that were not subjected to heat treatment are also shown in FIG.
- Example 1 without heat treatment showed a diffraction peak of Mn 3 O 4 .
- Example 2 in which hydrothermal synthesis was performed in an aqueous lithium ion solution to which one equivalent of sodium hypochlorite was added, a diffraction peak clearly different from that in Production Example 1 was shown.
- a search by JCPDS revealed that it was a LiMnO 2 diffraction peak.
- Example 3-5 which was hydrothermally synthesized in an aqueous lithium ion solution to which 3.5 oxidizing equivalents of sodium hypochlorite were added, showed diffraction peaks different from those of Production Example 1 and Example 2. Similarly, when searching by JCPDS, it was found to be a diffraction peak of LiMn 2 O 4 . From the above, it was found that the active material can be selected from LiMnO 2 or LiMn 2 O 4 depending on the added oxidation equivalent.
- Example 2 without heat treatment showed a diffraction peak of NiO.
- Example 4 in which hydrothermal synthesis was performed in an aqueous lithium ion solution to which 1 oxidation equivalent of hydrogen peroxide was added showed a diffraction peak different from that in Production Example 2, and LiNiO 2 and Ni (OH) 2 It was found to be a diffraction peak.
- the diffraction peak of Ni (OH) 2 disappears in Example 5 where hydrothermal synthesis was performed in a lithium ion aqueous solution to which sodium hypochlorite equivalent to 2 oxidation equivalents was added, and the diffraction peak of LiNiO 2 only. I confirmed that there was.
- FIG. 7 shows an SEM (scanning electron microscope) photograph of the fiber positive electrode of Example 2.
- a porous substance is adhered to the carbon fiber current collector to form a layer.
- This layer is configured by forming active material particles having a flake shape in a direction perpendicular to the current collector.
- the flaky particles overlap each other, and new flaky particles are formed from the overlapping place as a starting point. Therefore, it is considered that a porous active material layer was formed by forming an aggregate in which flaky particles were aggregated.
- flaky particles having a thickness of about 100 nm, a width of about 1.5 ⁇ m, and a length of about 2 ⁇ m were aggregated to cover the electrode.
- the active material layer of Example 2 is mainly composed of lithium manganate. That is, the porous layer shown in FIG. 7 is LiMnO 2 .
- FIG. 8 shows an SEM photograph of the fiber positive electrode of Example 3-5.
- a porous substance is adhered to the carbon fiber current collector to form a layer.
- the active material layer of Example 3-5 is made of spinel type lithium manganate. Therefore, it can be said that the porous layer shown in FIG. 8 is LiMn 2 O 4 . Similarly to Example 2, it can be observed that these grow in a direction perpendicular to the surface of the current collector and have a flake-like shape.
- flaky particles overlap each other, and starting from the overlapped place, new flaky particles are formed from there, forming an aggregate in which the flaky particles are aggregated, and porous The active material layer is formed.
- flaky particles having a thickness of about 100 nm, a width of about 2 ⁇ m, and a length of about 2 ⁇ m aggregated to cover the entire electrode.
- FIG. 9 shows an SEM photograph of the fiber positive electrode of Example 6.
- the active material layer of Example 6 is made of LiMn 1.9 Ni 0.1 O 4 . Therefore, it can be said that the porous layer shown in FIG. 9 is LiMn 1.9 Ni 0.1 O 4 .
- the flaky particles overlap each other to form an aggregate in which the flaky particles are aggregated to form a porous active material layer.
- Test Example 2 Battery Test Each sample of Examples 1 to 11 was used as a test electrode, a metal lithium foil was used as a counter electrode, and ethylene carbonate (EC) and dimethyl carbonate (DMC) were used as an electrolyte solution in a volume ratio of 1:
- EC ethylene carbonate
- DMC dimethyl carbonate
- a bipolar evaluation cell was prepared using a solution prepared by dissolving LiPF 6 in the solvent mixed in 1 at a concentration of 1 mol / liter, and a charge / discharge test was performed. The test was controlled by a cut-off voltage, and was performed at a charge / discharge current corresponding to 0.2C.
- Examples 1 to 11 using the carbon fiber current collector are particularly excellent in battery performance at the 300th cycle as compared with Comparative Example 1 using the Al foil current collector. You can see that In addition, the comparative example 1 changes the electrical power collector in Example 2 into Al foil.
- Example 8 using a carbon fiber current collector coated with Al was found to exhibit better charge / discharge cycle life characteristics than Example 6 using a carbon fiber not coated with Al. Moreover, it turned out that Example 10 which codeposited carbon shows a favorable charge / discharge cycle life characteristic compared with Example 9 which did not codeposit.
- Example 6 using Li (Mn—Ni) 2 O 4 system as the positive electrode active material is shown in FIG. 11, and the high rate discharge curve is shown in FIG.
- FIG. 13 shows an initial charge / discharge curve of Example 9 using Li (Mn—Al) 2 O 4 system as the positive electrode active material
- FIG. 14 shows a high rate discharge curve.
- the sample in which the plated film of Cu and Sn was formed on the carbon fiber was subjected to heat treatment for 2 hours under the conditions described in Table 2 below to obtain each sample.
- Example 12 The sample thus obtained (Example 12, Comparative Examples 3 to 4) and the sample not subjected to heat treatment (Comparative Example 2) were subjected to qualitative analysis using powder X-ray diffraction (XRD).
- XRD powder X-ray diffraction
- FIG. 16 shows the abundance ratio of each phase of Example 12 and Comparative Examples 2 to 4.
- EDX energy dispersive X-ray analysis
- Example 13 treated at 400 ° C. in an atmosphere with an oxygen concentration of 5 vol% was the same as Example 12 except that the Cu 3 Sn layer was reduced, but Comparative Example 6 treated with an oxygen concentration of 10 vol% was Cu The 3 Sn layer disappeared and it was formed only with a composite of Cu 2 O and SnO 2 .
- Example 12 The results of the charge / discharge cycle life test of Comparative Example 4 and Example 12 are shown in FIG. 18, the charge / discharge curve of Comparative Example 4 is shown in FIG. 19, and the charge / discharge curve of Example 12 is shown in FIG. As shown in FIG. 19, when the number of cycles exceeded 70, Comparative Example 4 was near 250 mAh / g. As shown in FIG. 20, when the number of cycles exceeded 70, Example 12 was near 400 mAh / g. there were. As a result, as in Example 12, the capacity retention was better than that in the initial stage even after repeating the charge / discharge cycle by heat treatment at 400 ° C. in an atmosphere with an oxygen concentration of 1 vol%. The battery characteristics of Comparative Example 3 heat-treated at 200 ° C. were not noticeably different from Comparative Example 4, and were close to 230 mAh / g after 100 cycles.
- Samples (Examples 12 and 13) heat-treated at 400 ° C. in an oxygen concentration atmosphere of 1 to 5 vol% were successively formed with a Cu 3 Sn layer and a layer mainly composed of a composite of Cu 2 O and SnO 2. It turned out that it became the laminated structure and showed the especially outstanding battery characteristic.
- a sample (Comparative Example 6) treated at 400 ° C. in an atmosphere with an oxygen concentration of 10 vol% was composed only of a complex of Cu 2 O and SnO 2 and had poor conductivity.
- Example 14 and Comparative Examples 8 to 10 >> (CuSn alloy plating) A CuSn alloy plating film having a thickness of about 3 ⁇ m was formed on a carbon fiber (carbon fiber) having a single fiber diameter of 8 ⁇ m by electroplating.
- Example 14 A qualitative analysis was performed on the heat-treated sample (Example 14, Comparative Examples 8 to 9) and the non-heat-treated sample (Comparative Example 10) using powder X-ray diffraction (XRD).
- XRD powder X-ray diffraction
- FIG. 22 shows the abundance ratio of each phase in Example 14 and Comparative Examples 8 to 10.
- EDX energy dispersive X-ray analysis
- Comparative Example 10 where heat treatment was not performed, the CuSn alloy film was only formed, whereas in Comparative Example 8 where heat treatment was performed at 200 ° C. in a trace oxygen atmosphere, heat treatment was performed at 300 ° C.
- Comparative Example 9 had a structure in which a layer containing CuSn alloy and Sn as a main component was sequentially laminated on carbon fiber.
- Example 14 which was heat-treated at 400 ° C. in a trace oxygen atmosphere, had a structure in which a Cu 3 Sn layer and a layer made of a composite of Cu 2 O and SnO 2 were sequentially laminated on a carbon fiber. It was.
- FIG. 25 shows the charge / discharge curve of Comparative Example 9
- FIG. 26 shows the charge / discharge curve of Example 14.
- the discharge capacity deteriorated rapidly in several cycles. No. 14 shows excellent battery characteristics.
- the comparative example 10 which has not performed heat processing was made into the test pole, the result similar to the comparative example 8 was shown.
- the samples heat-treated at 300 ° C. or lower have a structure in which layers mainly composed of CuSn alloy layers are laminated, and the capacity at the time of 100 cycles is about 180 mAh / g. Few.
- the sample heat-treated at 400 ° C. has a structure in which a Cu 3 Sn layer and a layer mainly composed of a composite of Cu 2 O and SnO 2 are sequentially laminated. The capacity was 440 mAh / g, and it was found that excellent battery characteristics were exhibited.
- Electrode structure after charge / discharge (Examples 12 and 14)] When the battery of Example 12 and Example 14 after charging was disassembled and the electrode structure was examined, Cu, Li 4.4 Sn, and Li 2 O were newly observed.
- a carbon fiber current collector (2) a layer in which Cu and Li 4.4 Sn are dispersed in an annular Li 2 O matrix formed on the carbon fiber current collector, 3) It was a structure comprising an intermediate layer having a lithium releasing ability present at the interface between the carbon fiber current collector and a layer in which Cu and Li 4.4 Sn were dispersed in a Li 2 O matrix. This is probably because Cu 2 O and SnO 2 were reduced by lithium during occlusion (charging) of lithium.
- a carbon fiber current collector and (2) a layer in which Cu and Sn or an Sn alloy are dispersed in a Li 2 O matrix formed in an annular shape on the carbon fiber current collector, (3) The carbon fiber current collector and a Li 2 O matrix and a layer in which Cu and Sn or a Sn alloy are dispersed are present at the interface between the intermediate layer and the lithium storage capacity. .
- FIG. 27 schematically shows a cross-sectional structure of the electrodes of Example 12 and Example 14 after charging and discharging.
- Examples 15 to 22 >> (CuSn alloy eutectoid)
- a conductive agent and / or a binder was dispersed in a CuSn plating solution, and a CuSn alloy film containing a conductive agent and / or a binder having a thickness of about 3 ⁇ m was formed by electroplating on a carbon fiber having a single fiber diameter of 8 ⁇ m ( Eutectoid).
- the composition of the formed alloy film is as shown in Table 6 below.
- the sample in which the CuSn alloy film containing the conductive agent and / or the binder was formed was subjected to a heat treatment at 400 ° C. for 2 hours in an Ar atmosphere having an oxygen concentration of 0.5 vol% to obtain each sample.
- Example 7 As shown in Table 7, from the results of the charge / discharge cycle life test, the samples (Examples 15 to 18 and 20 to 22) on which the eutectoid of the conductive agent and / or the binder were conducted were obtained from Example 14 shown in Table 5. Further, the discharge capacity was further increased, and it was found that this was an excellent negative electrode.
- Example 15 The sample (Example 15) containing 2 wt% of KB (Ketjen Black) has improved charge / discharge cycle life characteristics as compared with Example 14 containing no conductive agent. This seems to be due to a decrease in the internal resistance of the electrode.
- the sample containing 2 wt% of PTFE (polytetrafluoroethylene) (Example 16) also improved the charge / discharge cycle life characteristics. This seems to have prevented the active material from falling off by containing the binder.
- the charge / discharge cycle life was further improved.
- Example 18 containing AB (acetylene black) instead of KB exhibited the same charge / discharge cycle life characteristics as Example 17.
- Example 19 when the PTFE was changed from 2 wt% to PTFE 10 wt%, the charge / discharge cycle life was improved as in Example 16, but the discharge capacity was reduced because of high internal resistance.
- Example 15 to 22 further improved the electrode capacity and the charge / discharge cycle life characteristics as compared with the samples that were not co-deposited (Example 14).
- Example 23 A polyethylene microporous membrane separator is sandwiched between the fiber positive electrode obtained in Example 9 and the fiber negative electrode obtained in Example 12, and ethylene carbonate (EC) and diethyl carbonate (DEC) are used as an electrolyte solution in a volume ratio.
- EC ethylene carbonate
- DEC diethyl carbonate
- FIG. 32 is a plan view showing a schematic configuration of the bipolar evaluation cell of Example 23, in which 3 is a cell outer wall, 4 is a fiber positive electrode, 5 is a fiber negative electrode, 6a is a microporous membrane separator, and 7 is an electrolytic solution. Show. Each fiber positive electrode 4 is connected to a positive electrode terminal (not shown), and each fiber negative electrode 5 is connected to a negative electrode terminal (not shown).
- Example 24 Each of the fiber positive electrode obtained in Example 9 and the fiber negative electrode obtained in Example 12 was impregnated with a polyethylene solution in which fine powder of SiO 2 (having a diameter of 30 nm or less) was dispersed and dried.
- the fiber positive electrode and the fiber negative electrode were immersed in a 30 wt% LiOH aqueous solution at 90 ° C. for 3 hours to form polyethylene porous membrane separators on the fiber positive electrode and the fiber negative electrode, respectively. Thereafter, the fiber negative electrode was predoped with irreversible capacity Li.
- the fiber positive electrode / separator laminate thus obtained and the fiber negative electrode / separator laminate were combined and ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 as the electrolyte.
- EC ethylene carbonate
- DEC diethyl carbonate
- Example 33 is a schematic configuration diagram of a bipolar evaluation cell of Example 24, 3 is a cell outer wall, 4 is a fiber positive electrode, 5 is a fiber negative electrode, 6b is a separator, and 7 is an electrolytic solution. Each fiber positive electrode 4 is connected to a positive electrode terminal (not shown), and each fiber negative electrode 5 is connected to a negative electrode terminal (not shown).
- Results of charge / discharge test (Examples 23 and 24)] As a result of conducting the charge / discharge test of Examples 23 and 24, the capacity and intermediate discharge voltage during high rate discharge are shown in Table 8 below. The test was controlled by a cut-off voltage, charging was performed at a current corresponding to 0.2 C, and discharging was performed at a current corresponding to 0.5 C to 300 C.
- the reaction in which Li was inserted into the Sn electrode was charged, and the reaction in which Li was released was discharged.
- Example 24 it was found that the high rate discharge characteristics were greatly improved by combining the fiber positive electrode and the fiber negative electrode. Compared with a half-cell test using metal Li as a counter electrode (for example, Example 6 of Test Example 2 shown in FIG. 12), the discharge amount at 0.5 C to 200 C is increased. In particular, in Example 24, ultra-rapid discharge characteristics such as 100 C to 300 C are further improved as compared with Example 23. In Example 23, it was possible to improve the discharge characteristics by increasing the contact area between the electrode and the electrolytic solution. However, in Example 24, the contact area between the electrolytic solution and the separator was obtained by forming the separator on the outer periphery of the electrode. Has also increased. Furthermore, it is considered that the high-rate discharge characteristics are improved because the internal resistance is reduced due to the decrease in the distance between the electrodes.
- the invention as a reference example provides the following positive electrode, a manufacturing method thereof, and a non-aqueous secondary battery.
- the method for producing a positive electrode for a lithium secondary battery is as follows: (X) forming a transition metal oxide film on the current collector; (Y) The current collector on which the transition metal oxide film was formed was hydrothermally treated at 100 to 400 ° C. in an aqueous solution containing lithium ions in the presence of an oxidizing agent or a reducing agent, and the current collector was lithium-doped. And a step of obtaining a transition metal oxide film.
- Step (X) is preferably a step of forming a transition metal oxide film on the current collector by electrolytic deposition.
- step (X) a paste in which a transition metal oxide powder and a thickener or binder are dispersed is applied and formed on a current collector, and then subjected to a high-temperature treatment at 500 to 1000 ° C. in an inert atmosphere to increase the viscosity.
- a step of removing or carbonizing the material or binder is preferable.
- step (X) a paste in which a transition metal powder and a thickening material or a binder are dispersed is applied and formed on a current collector, followed by high-temperature treatment at 500 to 1000 ° C. in an oxidizing atmosphere, and the thickening material or binder The step of removing or carbonizing is preferable.
- the step (X) is a step of forming a transition metal film on the current collector by a physical thin film forming method and then performing high-temperature oxidation treatment at 500 to 1000 ° C. in an oxidizing atmosphere.
- the step (X) is a step of forming a transition metal film on the current collector by an aerosol deposition method, followed by high-temperature oxidation treatment at 500 to 1000 ° C. in an oxidizing atmosphere.
- Step (X) is preferably a step in which a transition metal film is formed on the current collector by electroplating, followed by high-temperature oxidation treatment at 500 to 1000 ° C. in an oxidizing atmosphere.
- the current collector is a metal porous body.
- the transition metal oxide has the formula (3): M a O b (In Formula (3), M is at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, and Ni, and 1 ⁇ a ⁇ 3 and 1 ⁇ b ⁇ 5. Is)
- the lithium-doped transition metal oxide has the formula (4): Li d Me O c (In Formula (4), 2 ⁇ c ⁇ 5, 0 ⁇ d ⁇ 2, 1 ⁇ e ⁇ 5, and M is the same as Formula (3)).
- the transition metal oxide is Mn 3 O 4
- the lithium-doped transition metal oxide has the formula (4-1): Li d1 Mn e1 O c1 (In the formula (4-1), the valence of Mn is in the range of 3 to 4, 2 ⁇ c1 ⁇ 4, 0 ⁇ d1 ⁇ 2, 1 ⁇ e1 ⁇ 2.) It is preferable to be represented by
- the transition metal oxide has the formula (3-2): (Mn 1-x A x ) 3 O 4 (In the formula (3-2), A is at least one element selected from the group consisting of Al, Ti, Cr, Fe, Co, Ni, Cu, Sr, Y, Zr, In, Sn, and rare earth elements. And 0.05 ⁇ x ⁇ 0.25),
- the lithium-doped transition metal oxide has the formula (4-2): Li d2 (Mn 1-y A y ) e2 O c2 (In the formula (4-2), the valence of Mn is in the range of 3 to 4, 2 ⁇ c2 ⁇ 4, 0 ⁇ d2 ⁇ 2, 1 ⁇ e2 ⁇ 2, 0.05 ⁇ y ⁇ 0.
- A is preferably the same as in formula (3-2).
- the positive electrode is preferably produced by any one of the production methods described above.
- the positive electrode for a lithium secondary battery is preferably a porous material in which a lithium-doped transition metal oxide is formed in a flaky shape in a direction perpendicular to the current collector surface.
- the flaky lithium-doped transition metal oxide preferably has a thickness of 5 to 500 nm, a width of 0.1 to 10 ⁇ m, and a length of 0.1 to 10 ⁇ m.
- the lithium secondary battery preferably includes any one of the positive electrodes for lithium secondary batteries, an electrolyte, and a negative electrode.
- the method for producing the positive electrode of the invention as a reference example is as follows: (X) forming a transition metal oxide film on the current collector; (Y) The current collector on which the transition metal oxide film was formed was hydrothermally treated at 100 to 400 ° C. in an aqueous solution containing lithium ions in the presence of an oxidizing agent or a reducing agent, and the current collector was lithium-doped. And a step of obtaining a transition metal oxide film.
- step (X) a transition metal oxide film is formed on the current collector.
- the current collector may be a current collector having a two-dimensional structure such as a plate shape or a foil shape, but a current collector having a three-dimensional structure such as a mesh shape, a foam metal, or an expand is preferable.
- the current collector may be any metal selected from Al, Ti, Cr, Zr, Hf, Ta and W, an alloy made of these, stainless steel, etc., but from the viewpoint of cost performance, Al or stainless steel is preferable. .
- the transition metal oxide is not particularly limited as long as it can form a film on the current collector.
- TiO, Ti 2 O 3 , TiO 2 , V 2 O 3 , V 2 O 5 , CrO, Cr 2 O 3 , CrO 2 , MnO, Mn 3 O 4 , Mn 2 O 3 , MnO 2 , MnO 3 , FeO, Fe 3 O 4 , Fe 2 O 3 , CoO, Co 2 O 3 , Co 3 O 4 examples thereof include CoO 2 , NiO, Ni 3 O 4 , Ni 2 O 3 , NiO 2 , Cu 2 O, CuO, and ZnO.
- the method of forming the transition metal oxide film on the current collector is not particularly limited, but there are a slurry method, a physical thin film formation method, an aerosol deposition method, an electroplating method, an electrolytic deposition method, and the like. Can be mentioned. Hereinafter, each forming method will be described.
- the slurry method is a method in which, for example, a slurry obtained by dispersing transition metal oxide particles and organic substances in a solvent is applied onto a current collector, and the electrode is formed by vaporizing the solvent.
- the organic substance is not particularly limited as long as it has the ability to bind the current collector and the transition metal oxide particles, and dissolves in a solvent to cause thickening.
- Conventional thickeners, binders, etc. Preferably used.
- SBR styrene butadiene rubber
- SEBS styrene ethylene butylene styrene block copolymer
- CMC carboxymethyl cellulose
- PVdF polyvinylidene fluoride
- imide polyethylene
- PE polypropylene
- PE polypropylene
- PVA polytetrafluoroethylene
- citric acid sucrose
- sucrose sucrose
- a phenol resin phenol resin
- the addition amount of the organic substance is preferably within a range of 5 to 15% by mass with respect to the transition metal oxide serving as the active material. By setting the addition amount within this range, it is possible to suppress the transition metal oxide particles from dropping from the current collector during hydrothermal synthesis, to suppress an increase in electrode resistance, and to improve the electrode capacity.
- the solvent is not particularly limited as long as it can dissolve or disperse the above-mentioned organic substances (thickener, binder, etc.), and examples thereof include water, alcohol, acetone, N-methyl-2-pyrrolidone (NMP) and the like. Can be mentioned.
- the method for vaporizing the solvent is not particularly limited, and can be performed, for example, by heat treatment, reduced pressure treatment or the like.
- a conductive auxiliary agent may or may not be added.
- an active material layer having a large thickness is to be formed, there is an effect of preventing the conductivity from deteriorating. It is recommended to add about 2 to 10% by mass.
- the high temperature treatment temperature is preferably 500 to 1000 ° C. from the viewpoint that the thickener, binder and the like can be sufficiently removed or carbonized, the apparatus is not oversized, the cost performance is excellent, and the current collector is not deteriorated.
- the high temperature treatment time is preferably about 5 to 50 hours from the viewpoint of sufficiently removing or carbonizing the thickener, binder and the like and being excellent in cost performance.
- the vaporization of the solvent and the removal / carbonization of the thickener, binder, etc. may be performed simultaneously or separately.
- a solvent can be vaporized.
- a transition metal oxide film can be formed on a current collector by applying a slurry obtained by dispersing a transition metal and an organic substance in a solvent onto a current collector and subjecting the slurry to high-temperature oxidation treatment.
- the high temperature oxidation treatment includes, for example, raising the temperature to 500 to 1000 ° C. in an oxidizing atmosphere.
- the oxidizing atmosphere refers to an atmosphere in which air, oxygen, or the like exists, for example.
- examples of the physical thin film forming method include vapor deposition and sputtering.
- a sputtering method when used, a high-density transition metal oxide film can be formed.
- the transition metal oxide has poor conductivity, and is inefficient in stacking the transition metal oxide on the current collector by the sputtering method.
- the vapor deposition method it takes time to deposit the oxide itself, which is not suitable for mass production. Therefore, when adopting a physical thin film manufacturing method, a transition metal oxide film is formed by first laminating a transition metal and subjecting it to high-temperature oxidation treatment.
- the high-temperature oxidation treatment at this time can be the same as the high-temperature oxidation treatment in the slurry method, and specifically includes raising the temperature to 500 to 1000 ° C. in an oxidizing atmosphere.
- the aerosol deposition method is a method of forming a thin film by injecting a transition metal oxide powder existing in a positive pressure atmosphere to a current collector existing in a negative pressure atmosphere all at once.
- transition metal oxides have little spreadability, and even when sprayed to a current collector at high pressure, it is difficult to form a transition metal oxide layer. Therefore, a transition metal oxide film can be formed by first laminating a transition metal on a current collector and subjecting it to a high temperature oxidation treatment.
- the positive pressure atmosphere refers to a state where the pressure is higher than the surroundings, for example
- the negative pressure atmosphere refers to a state where the pressure is lower than the surroundings, for example.
- the pressure difference between the film formation chamber and the aerosol chamber may be 20 kPa or more.
- the high-temperature oxidation treatment at this time can be the same as the high-temperature oxidation treatment in the slurry method, and specifically includes raising the temperature to 500 to 1000 ° C. in an oxidizing atmosphere.
- the particle diameter of the transition metal employed in the aerosol deposition method at this time is such that the primary particle diameter is 50 nm to 500 nm, and the average particle diameter (average secondary particle diameter) of the secondary aggregate is 5 ⁇ m to 30 ⁇ m (and more 5 ⁇ m to 10 ⁇ m) is preferable.
- the average secondary particle diameter within this range, the particles can be hardly aggregated, and the adhesion to the current collector can be improved.
- a method for producing such a powder for example, it can be produced by a mechanical alloying method or the like.
- the electroplating method is a method of electrochemically forming a metal film on a current collector.
- the electroplating method it is not possible to stack transition metal oxides directly on the current collector. Therefore, after transition metal is first plated on the current collector, the transition metal must be oxidized by high-temperature oxidation treatment such as heat treatment. There is.
- the high-temperature oxidation treatment at this time can be the same as the high-temperature oxidation treatment in the slurry method, and specifically includes raising the temperature to 500 to 1000 ° C. in an oxidizing atmosphere.
- the conditions in the electroplating method are not particularly limited, and depending on the metal to be plated, the transition metal salt to be plated is adjusted to be in the range of 0.05 to 1 mol / liter, and the current density is 1 mA / cm 2 to 0.
- the current collector is plated with a transition metal by electroplating at 1 A / cm 2 .
- the electrolytic deposition method is a method in which a metal or a metal compound is deposited by causing an electrochemical reaction at the interface between the metal electrode and the electrolyte.
- the transition metal oxide can be directly formed on the current collector.
- the metal salt to be deposited is adjusted to be in the range of 0.05 to 1 mol / liter, and the current density is 1 mA / cm 2 to 0.00. It may be performed at 1 A / cm 2 .
- the current collector is a metal porous body (such as mesh, foam, or three-dimensional expand) as the current collector, among the film formation methods described above, the slurry method, physical thin film formation method and It is difficult to coat the current collector uniformly with the transition metal oxide by the aerosol deposition method. Therefore, an electroplating method, an electrolytic deposition method, or the like is preferable.
- the electroplating method, the electrolytic deposition method, etc. as long as the current collector is in contact with the plating bath or the electrolytic deposition bath, a transition metal oxide film can be formed on the current collector surface, and Adhesion is good, the smoothness of the coating surface can be improved, and uniform lamination of a larger area is easy and inexpensive.
- the electrolytic deposition method is the most preferable method because the transition metal oxide can be directly formed on the current collector.
- the stacking amount of the transition metal oxide layer is preferably 1 to 30 mg / cm 2 . By setting the stacking amount within this range, the capacity required for the battery can be obtained, and delamination between the transition metal layer and the current collector hardly occurs.
- the average thickness of the transition metal oxide layer is not limited, but is usually about 0.5 ⁇ m to 30 ⁇ m, preferably about 1 ⁇ m to 10 ⁇ m.
- step (Y) the current collector on which the transition metal oxide film is formed is hydrothermally treated at 100 to 400 ° C. in an aqueous solution containing lithium ions in the presence of an oxidizing agent or a reducing agent. A lithium-doped transition metal oxide film is obtained.
- the formula (3) M a O b (In Formula (3), M is at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, and Ni, and 1 ⁇ a ⁇ 3 and 1 ⁇ b ⁇ 5.
- the transition metal formed on the current collector is formed by hydrothermal treatment in an aqueous solution containing lithium ions in the presence of an oxidizing agent or a reducing agent.
- the oxide is lithium-modified and has the formula (4): Li d Me O c (In formula (4), 2 ⁇ c ⁇ 5, 0 ⁇ d ⁇ 2, 1 ⁇ e ⁇ 5, and M is the same as in formula (3)) It becomes.
- the final lithium-doped transition metal oxide is represented by the formula (4-1): Li d1 Mn e1 O c1 (In formula (4-1), the valence of Mn is in the range of 3 to 4, 2 ⁇ c1 ⁇ 4, 0 ⁇ d1 ⁇ 2, 1 ⁇ e1 ⁇ 2) Become.
- lithium secondary batteries using lithium and manganese oxides such as Li 1 + x Mn 2 O 4 and Li x Mn 2 O 4 as the positive electrode active material elute Mn when the temperature is raised. Is big.
- a material in which a part of manganese is substituted with Al, Ti, Cr, Fe, Co, Ni, Cu, Sr, Y, Zr, In, Sn, rare earth elements, etc. is preferable.
- a material substituted with Co, Ni, Al or the like is more preferable.
- a positive electrode using nickel-lithium manganate as an active material can also be obtained by hydrothermal treatment at
- the oxidizing agent only needs to have an oxidizing power, and examples thereof include oxygen, chlorine, bromine, chlorate, hypochlorite, hydrogen peroxide, and the like. Sodium hypochlorite, hydrogen peroxide Water is preferred.
- the reducing agent only needs to have a reducing power, and examples thereof include hydrogen, formaldehyde, sodium ascorbate and the like, and sodium isoascorbate is preferable.
- the oxidizing agent or reducing agent may be a suitable gas. That is, the presence of an oxidizing agent or a reducing agent can also be realized by a gas contact method. Gas contact can be performed by blowing gas into the lithium ion solution.
- the gas to be blown at this time includes air, air diluted with an inert gas, oxidant gas (O 2 , O 3 , N 2 O, etc.) or reducing gas (H 2 , H 2 S, SO 2). , HCHO, etc.).
- oxygen in air plays the role of an oxidizing agent, it is preferable to carry out in inert gas.
- step (Y) the amount of lithium ions and the amount of oxidizing agent or reducing agent vary depending on the oxidation form and amount of the transition metal oxide. That is, what is necessary is just to estimate the quantity of lithium ion, oxidation equivalent, or reduction equivalent required for a starting material to become a target object.
- the transition metal oxide M a O b when the transition metal oxide M a O b is 1 equivalent, it may be used to beta-alpha oxidation or more equivalents of the oxidizing agent. However, when the ⁇ - ⁇ value is a negative real number, an ⁇ - ⁇ reducing equivalent reducing agent is used.
- NiO Ni valence is 2+
- LiNiO 2 LiNi valence is 3+
- V 2 O 5 When the starting material V 2 O 5 (V valence is 5+) is 1 equivalent, if it is 0.5 reducing equivalent or more, LiV 2 O 5 (V valence is 4.5+), 1 reducing equivalent or more. If it exists, Li 2 V 2 O 5 (V valence is 4+), and if it is 2 reduction equivalents or more, Li 4 V 2 O 5 (V valence is 3+).
- V 2 O 3 (V valence is 3+) is 1 equivalent, if it is one oxidation equivalent or more, Li 2 V 2 O 5 (V valence is 4+).
- the aqueous solution containing lithium ions containing an oxidizing agent or a reducing agent when the aqueous solution containing lithium ions containing an oxidizing agent or a reducing agent is under alkaline conditions, the aqueous solution may be heated as it is, but under acidic conditions, particularly pH value (hydrogen
- the ion concentration index is small, for example, alkali hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide; ammonia compounds such as ammonia gas, aqueous ammonia; sodium carbonate, potassium carbonate, lithium carbonate, ammonium carbonate, etc. It is preferable to add an alkali carbonate compound or the like to raise the pH value and to heat.
- the aqueous solution containing lithium ions used for hydrothermal treatment may be obtained by dissolving a water-soluble lithium compound with water.
- a lithium chloride aqueous solution, a lithium nitrate aqueous solution, a lithium hydroxide aqueous solution, or the like is preferably used. it can.
- These water-soluble lithium compounds can be used singly or in combination of two or more, and any of anhydrides and hydrates may be used.
- the amount of the water-soluble lithium compound used may be a lithium element molar ratio with respect to the number of moles of transition metal in the transition metal oxide of interest, and it is sufficient to add more lithium than the theoretical amount to the target product. It is preferable to add 1 to 5 times the amount of lithium, and a more preferable range is 1 to 3 times the theoretical amount.
- the concentration of the water-soluble lithium compound is preferably in the range of 0.05 to 10 mol / liter, more preferably in the range of 1 to 6 mol / liter.
- the temperature of the hydrothermal treatment is 100 to 400 ° C, preferably 100 to 200 ° C.
- the reaction proceeds even when the temperature of the hydrothermal treatment is less than 100 ° C, but is preferably 100 ° C or higher because the reaction rate is slow.
- the temperature exceeds 400 ° C., the apparatus becomes large and the cost performance deteriorates.
- a current collector in which a transition metal oxide film is formed is placed in an aqueous solution containing lithium ions in the presence of an oxidizing agent or a reducing agent, sealed in a pressure / corrosion resistant container, and saturated water vapor pressure or It is preferable to carry out under pressure.
- Niobium, Inconel, and stainless steel are more preferable.
- the hydrothermal pressure may be 0.05 to 40 MPa. By making it within this range, lithium doping with respect to the transition metal is sufficient, and a large pressure / corrosion resistant container is not required, which is economically preferable. From such a viewpoint, the hydrothermal treatment pressure is more preferably within the range of 0.1 to 10 MPa.
- the hydrothermal treatment time varies depending on the hydrothermal treatment temperature, but it may be 5 hours or more if the temperature is in the range of 100 to 200 ° C, or 3 hours or more if the temperature is in the range of 200 to 400 ° C. . Note that it is preferable to set the time to an appropriate value so that the active material attached to the current collector does not fall off. Specifically, the time is preferably in the range of 5 to 50 hours, and preferably in the range of 10 to 30 hours. .
- a positive electrode in which a lithium-doped transition metal oxide film is formed on the current collector can be obtained. If the positive electrode is dried under reduced pressure at about 80 to 150 ° C. to remove moisture, it can be used as a better positive electrode.
- the positive electrode of the present invention thus obtained has an active material layer directly formed on a current collector. Therefore, there is no need for any step of converting the active material into an electrode, which was necessary in the conventional method. That is, the positive electrode can be manufactured simultaneously with the manufacture of the active material.
- the lithium-doped transition metal oxide of the present invention has a flake shape formed in a direction perpendicular to the surface of the current collector, and has a thickness of 5 to 500 nm and a width of 0.1 to 10 ⁇ m.
- the length is 0.1 to 10 ⁇ m.
- the flake shape refers to a flake shape having a small thickness with respect to the length.
- the positive electrode of the present invention is porous because the positive electrode active material material having a flake shape aggregates to form an aggregate, and the aggregate adheres in a direction perpendicular to the surface of the current collector. A positive electrode active material layer is formed. For this reason, the electrode surface area is extremely large, and the electrolyte solution has a structure that can easily penetrate, and it has a super-three-dimensional structure that can relieve stress due to expansion and contraction of the active material volume. It is an excellent positive electrode.
- the negative electrode of the lithium secondary battery obtained by using the positive electrode of the present invention is not particularly limited, carbon such as graphite; Cu 3 Sn Alloys based; SnO, oxide such as SiO; LiN nitride such as A well-known thing, such as a physical system, can be used.
- a lithium salt is suitable as the electrolyte salt.
- the lithium salt is not particularly limited, and specific examples include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium trifluoromethanesulfonate, and the like. Among these, one or two or more types can be used. Since the above lithium salt has high electronegativity and is easily ionized, it has excellent charge / discharge cycle characteristics and can improve the charge / discharge capacity of the secondary battery.
- Examples of the solvent for the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ⁇ -butyrolactone, and one or more of these can be used. Of these, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or ⁇ -butyrolactone alone is preferred. The mixing ratio of the mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted within the range of 10% to 90%.
- the lithium secondary battery having the above-described structure can function as a secondary battery having a high capacity and a good cycle life.
- a positive electrode in which an active material layer is directly formed on a current collector can be manufactured, a process of manufacturing an active material and converting it into an electrode as in the conventional method is not necessary. That is, the positive electrode can be manufactured simultaneously with the manufacture of the active material.
- the positive electrode obtained in the invention of the reference example basically does not require addition of a conductive additive or a binder, slurrying of an active material, rolling process, and the like.
- the positive electrode active material of the present invention contains lithium element, it is not necessary to dope lithium in advance. That is, the manufacturing process and the safety of the battery can be improved.
- the lithium-doped transition metal oxide has a flake shape formed in the vertical direction from the current collector, and thus a porous positive electrode active material layer is formed. It has a long life and excellent electrode characteristics.
- a lithium secondary battery using such a positive electrode has high current density and energy density, and has excellent charge / discharge cycle characteristics.
- ⁇ Reference Production Example 3> (Aerosol Method) Mn 3 O 4 / Aluminum Foil An Mn powder (average particle size 10 ⁇ m) was used as an aerosol deposition target, and a Mn thin film was formed on the aluminum foil. A high-temperature oxidation treatment was performed at 700 ° C. for 24 hours to obtain an electrode in which aluminum foil was coated with Mn 3 O 4 . Incidentally, only coated with Mn 3 O 4 are not functions as a positive electrode.
- a mixture of (0.25 mol / liter) and Ni (NO 3 ) 2 aqueous solution (0.01 mol / liter) was used.
- Aluminum foil was used for the working electrode, and platinum foil was used for the counter electrode.
- Electrodeposition was performed at a constant current density of 50 mA / cm 2 for 30 minutes. Thereafter, the electrode was washed with water and dried at 100 ° C. for 24 hours or more in an air atmosphere to obtain an electrode in which an aluminum foil was coated with Mn 3 O 4 and NiO. Incidentally, only coated with Mn 3 O 4 and NiO are not functions as a positive electrode.
- Reference Production Example 5 NiO / Aluminum Foil First, a Ni (NO 3 ) 2 aqueous solution (0.25 mol / liter) is used for the electrodeposition bath, an aluminum foil is used for the working electrode, and the counter electrode A platinum foil was used. As electrolytic deposition conditions, electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 30 minutes. Thereafter, the electrode was washed with water and dried at 120 ° C. for 24 hours or more in an air atmosphere to obtain an electrode in which an aluminum foil was coated with NiO. In addition, it does not function as a positive electrode only by coating NiO.
- ⁇ Reference production example 6> (Aerosol method) MnO 2 / aluminum foil Under the conditions that the average particle diameter of the MnO 2 powder is 100 ⁇ m, the average secondary particle diameter is 5 ⁇ m, and the pressure difference between the film formation chamber and the aerosol chamber is 40 kPa. An electrode obtained by coating MnO 2 on an aluminum foil was obtained. Incidentally, only coated with MnO 2 are not functions as a positive electrode.
- electrolytic deposition was performed at a constant current density of 50 mA / cm 2 for 30 minutes. Thereafter, the electrode was washed with water and oxidized at 650 ° C. for 24 hours or more in an oxygen atmosphere to obtain an electrode in which an aluminum foil was coated with NiO. In addition, it does not function as a positive electrode only by coating NiO.
- ⁇ Reference Example 2> (Electrolytic Deposition Method) LiMnO 2 + Mn (OH) 2 / Chrome-plated Foamed Nickel Same as Reference Example 1 except that the current collector was made of chrome-plated foamed nickel instead of aluminum foil In addition, a positive electrode of Reference Example 2 was produced.
- Reference Example 6 (Electrolytic Deposition Method) Li 2 Mn 2 O 4 / Chromium-plated Foamed Nickel
- the positive electrode active material is Li x Mn 2 O 4 and the active material is LiMn 2 O 4
- charging / discharging was performed in the range of 0 ⁇ x ⁇ 1 (theoretical capacity 148 mAh / g) in the 4V region.
- charge and discharge were performed in the range of 0 ⁇ x ⁇ 2 (theoretical capacity 285 mAh / g) in the 3V region so that the active material was Li 2 Mn 2 O 4, and the positive electrode of Reference Example 6 was manufactured. .
- Reference Example 7 (Slurry Method) LiMn 2 O 4 / Aluminum Foil
- the positive electrode of Reference Example 7 is the same as Reference Example 3 except that the electrode of Reference Production Example 2 is used instead of the electrode of Reference Production Example 1.
- Reference Example 8 (Aerosol Method) LiMn 2 O 4 / Aluminum Foil
- the positive electrode of Reference Example 8 is the same as Reference Example 3 except that the electrode of Reference Production Example 3 is used instead of the electrode of Reference Production Example 1.
- ⁇ Reference Example 9> (Electrolytic Deposition Method) LiMn 1.85 Ni 0.15 O 4 / Aluminum Foil A total of 1 equivalent of Mn 3 O 4 and NiO formed on the current collector in Reference Production Example 4 was equivalent to 2 oxidation equivalents.
- the electrode of Reference Production Example 4 was immersed in an aqueous lithium hydroxide solution (3 mol / liter) to which sodium hypochlorite was added, and hydrothermal treatment was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain a positive electrode of Reference Example 9.
- NiO formed on the current collector in Reference Production Example 5 was used to add one equivalent of hydrogen peroxide water.
- the electrode of Reference Production Example 5 was immersed in the added aqueous lithium hydroxide solution (3 mol / liter), and hydrothermal treatment was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain the positive electrode of Reference Example 10.
- Reference Example 11 (Electrolytic Deposition Method) LiNiO 2 / Aluminum Foil Hydroxylation with 1 equivalent of NiO formed on the current collector in Reference Production Example 5 and 2 equivalents of sodium hypochlorite added The electrode of Reference Production Example 5 was immersed in a lithium aqueous solution (3 mol / liter), and hydrothermal treatment was performed at 120 ° C. for 20 hours.
- Reference Example 12 (Electrolytic Deposition Method) LiNiO 2 / Aluminum Mesh A positive electrode of Reference Example 12 was produced in the same manner as Reference Example 11 except that the current collector was not an aluminum foil but an aluminum mesh.
- Reference Example 15 (Aerosol) LiMnO 2 / Aluminum Foil with Reducing Agent Similar to Reference Example 14 except that 4 reducing equivalents of sodium isoascorbate were added instead of 0.6 reducing equivalents of sodium isoascorbate A positive electrode of Reference Example 15 was obtained.
- the electrode of Reference Production Example 7 was immersed in the added aqueous lithium hydroxide solution (3 mol / liter), and hydrothermal treatment was performed at 120 ° C. for 20 hours. Thereafter, the electrode was washed with water and dried under reduced pressure at 100 ° C. for 24 hours or more to obtain the positive electrode of Reference Example 16.
- Reference Examples 1 to 16 are adjusted so that the molar ratio of lithium element to the number of moles of transition metal is 2.5 or more.
- Reference Test Example 1> Observation of positive electrode [X-ray diffraction] The X-ray diffraction patterns of Reference Examples 1, 3, and 10 are shown in FIG. In addition, the thing which did not perform the hydrothermal treatment in Reference Example 1 was shown as Comparative Reference Example 1, and the one which was not subjected to hydrothermal treatment in Reference Example 5 was shown as Comparative Reference Example 5 in the figure.
- Comparative Reference Example 1 in which no hydrothermal treatment was performed showed a diffraction peak of Mn 3 O 4 .
- a diffraction peak clearly different from that in Comparative Reference Example 1 was shown.
- a search by JCPDS revealed that the diffraction peaks were LiMnO 2 and Mn (OH) 2 .
- Reference Example 3 in which hydrothermal treatment was performed in a lithium ion aqueous solution to which 2.5 oxidation equivalents of sodium hypochlorite were added shows a diffraction peak different from Comparative Reference Example 1 and Reference Example 1.
- the active material can be selected from LiMnO 2 or LiMn 2 O 4 depending on the added oxidation equivalent.
- Comparative Reference Example 5 without hydrothermal treatment showed a NiO diffraction peak.
- Reference Example 10 in which hydrothermal treatment was performed in a lithium ion aqueous solution to which hydrogen peroxide solution of one oxidation equivalent was added, a diffraction peak different from that in Comparative Reference Example 5 was shown, and LiNiO 2 and Ni (OH) 2 It was found to be a diffraction peak.
- the diffraction peak of Ni (OH) 2 existing in Reference Example 10 disappears in Reference Example 11 in which hydrothermal treatment was performed in a lithium ion aqueous solution to which sodium dichlorite equivalent to 2 oxidation equivalents was added, It was confirmed that this was a diffraction peak of LiNiO 2 only.
- FIG. 29 shows an SEM photograph of the surface of the positive electrode of Reference Example 1 on the oxide film side.
- a porous substance is attached to the current collector to form a layer.
- This layer is configured by forming active material particles having a flake shape in a direction perpendicular to the surface of the current collector.
- the flaky particles overlap each other, and new flaky particles are formed from the overlapping place as a starting point. Therefore, it is considered that a porous active material layer was formed by forming an aggregate in which flaky particles were aggregated.
- the active material layer of Reference Example 1 contains lithium manganate as a main component. That is, the porous layer shown in FIG. 29 is LiMnO 2 .
- FIG. 30 shows an SEM photograph of Reference Example 3.
- a porous substance is attached to the current collector to form a layer.
- the active material layer of Reference Example 3 is made of spinel type lithium manganate. Therefore, it can be said that the porous layer shown in FIG. 30 is LiMn 2 O 4 .
- flaky particles overlap each other, and starting from the overlapping location, new flaky particles are formed from there, forming an aggregate in which the flaky particles are aggregated, and porous The active material layer is formed.
- flaky particles having a thickness of about 100 nm, a width of about 2 ⁇ m, and a length of about 2 ⁇ m aggregated to cover the entire electrode.
- EC ethylene carbonate
- DMC dimethyl carbonate
- a bipolar evaluation cell was prepared using a solution prepared by dissolving LiPF 6 at a concentration of 1 mol / liter in a solvent mixed at 1: and a charge / discharge test was performed. The test was controlled by a cut-off voltage, and the charge / discharge current corresponding to 0.3 C was performed.
- the lithium secondary battery including the fiber electrode for the lithium secondary battery according to the present invention described in detail above is used for portable use, mobile use, spare use, and the like. It is excellent as a power source that requires high capacity. Furthermore, it is possible to design a battery capable of rapid charging, for example, 300 C, which cannot be considered with a general-purpose secondary battery, and the industrial effect is extremely large, such as being able to be a high-capacitance capacitor.
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Abstract
Description
1.リチウム二次電池用ファイバー正極及びその製造方法並びにファイバー正極を備えたリチウム二次電池
[リチウム二次電池用ファイバー正極の製造方法 ]
(1) リチウム二次電池用ファイバー正極の製造方法は、
(a)炭素繊維集電体上に、遷移金属酸化物又は遷移金属水酸化物からなる皮膜を円環状に形成する工程と、
(b)上記の炭素繊維集電体上に遷移金属酸化物又は遷移金属水酸化物からなる皮膜が円環状に形成された物を、密閉された系内で酸化剤又は還元剤の存在下、リチウムイオンを含む溶液中で100~250℃で熱処理し、炭素繊維集電体上にリチウムドープした遷移金属酸化物の皮膜を得る工程とを備えることを特徴としている。
(2) 工程(a)が、電解析出法により、炭素繊維集電体上に遷移金属酸化物皮膜又は遷移金属水酸化物皮膜を円環状に形成する工程であることが好ましい。
(3) 工程(a)が、電気めっき法により、炭素繊維集電体上に遷移金属皮膜を円環状に形成し、その後酸化雰囲気下で500~1000℃で高温酸化処理することで,遷移金属酸化物皮膜を形成する工程であることが好ましい。
(4) 工程(a)が、導電助剤を共析させる方法で、電解析出浴に導電助剤を分散し、析出皮膜に導電助剤を含有させる工程であることが好ましい。
(5) 工程(a)が、導電助剤を共析させる方法で、電気めっき浴に導電助剤を分散し、析出皮膜に導電助剤を含有させる工程であることが好ましい。
(6) 工程(b)における密閉された系内での熱処理が、ソルボサーマル処理であることが好ましい。
(7) 炭素繊維集電体にAl皮膜が形成されていることが好ましい。
(8) 上記Al皮膜の厚さが0.1~1μmであることが好ましい。
(9) 炭素繊維集電体の直径が1~100μmであることが好ましい。
(10)遷移金属酸化物が、式(1):MaOb
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co及びNiよりなる群から選ばれる少なくとも1種の遷移金属であり、1≦a≦3、1≦b≦5である)で表され、
リチウムドープした遷移金属酸化物が、式(2):LidMeOc
(式(2)中、2≦c≦5、0<d≦2、1≦e≦5であり、Mは式(1)と同じである)で表されることが好ましい。
(11)遷移金属酸化物が、Mn3O4であり、
リチウムドープした遷移金属酸化物が、式(2-1):Lid1Mne1Oc1
(式(2-1)中、Mnの価数は3~4の範囲内であって、2≦c1≦4、0<d1≦2、1≦e1≦2である)で表されることが好ましい。
(12)遷移金属酸化物が、式(1-2):(Mn1-XAX)3O4
(式(1-2)中、Aは、Al、Ti、Cr、Fe、Co、Ni、Cu、Sr、Y、Zr、及び希土類元素よりなる群から選ばれる少なくとも1種の元素であり、0.05≦x≦0.25である)で表され、
リチウムドープした遷移金属酸化物が、式(2-2):Lid2(Mn1-yAy)e2Oc2
(式(2-2)中、Mnの価数は3~4の範囲内であって、2≦c2≦4、0<d2≦2、1≦e2≦2、0.05≦y≦0.25であり、Aは式(1-2)と同じである)で表されることが好ましい。
[リチウム二次電池用ファイバー正極]
(13)リチウム二次電池用ファイバー正極は、上記のいずれかに記載の製造方法により製造されることが好ましい。
(14)上記のいずれかに記載の製造方法により製造されるリチウム二次電池用ファイバー正極は、リチウムドープした遷移金属酸化物が、炭素繊維集電体の表面に対して垂直方向にフレーク状に形成されている多孔性物質であることが好ましい。
(15)上記のフレーク状に形成されている多孔性物質であるリチウムドープした遷移金属酸化物は、厚みが5~600nm、幅が0.1~10μm、長さが0.1~10μmであることが好ましい。
(16)上記のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法により製造される、炭素繊維集電体上に円環状に形成されるリチウムドープした遷移金属酸化物の皮膜上にセパレータ層を形成することによって、ファイバー正極とセパレータの積層体を得ることが好ましい。
[リチウム二次電池]
(17)リチウム二次電池は、上記のリチウム二次電池用ファイバー正極と電解質と負極とを備えることが好ましい。
2.リチウム二次電池用ファイバー負極及びその製造方法並びにファイバー負極を備えたリチウム二次電池
[リチウム二次電池用ファイバー負極]
(18)リチウム二次電池用ファイバー負極は、
(c)炭素繊維集電体と、
(d)上記炭素繊維集電体上に円環状に形成されたSn酸化物及びMXOyの複合層からなる外側層と、
(e)上記炭素繊維集電体と上記外側層との界面に存在する、Sn合金からなるリチウム吸蔵能を有する中間層とを有することを特徴としている。
((d)のMXOy中、Mは、Fe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属原子であり、xは0<x<3であり、酸素原子Oの数yは、金属原子Mと酸素原子Oとの化学結合における化学量論に基づく酸素原子Oの数をwとしたとき、0≦y≦wである。)
(19)上記中間層のSn合金層が、Sn以外の合金成分としてFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属成分を含むSn合金めっき層であることが好ましい。
(20)上記中間層がCuSn合金の層であって、外側層がSn及びCuの酸化物の複合層であることが好ましい。
(21)上記中間層がCu3Snの層であって、外側層がSnO2及びCu2Oの複合層であることが好ましい。
(22)上記中間層及び外側層の合計厚さが、1~10μmであることが好ましい。
(23)炭素繊維は、単繊維の直径が1~100μmであることが好ましい。
(24)炭素繊維は、単繊維100~5000本が束になった状態であることが好ましい。
(25)炭素繊維は、単繊維50~1000本が撚られた状態であることが好ましい。
(26)上記中間層及び外側層が、導電剤及び/又はバインダを有することが好ましい。
(27)上記導電剤がカーボンブラックであることが好ましい。
(28)上記バインダがポリテトラフルオロエチレンであることが好ましい。
(29)上記のいずれかに記載の外側層上にセパレータ層を形成することによって、ファイバー負極とセパレータの積層体を得ることが好ましい。
(30)充電後のリチウム二次電池用ファイバー負極は、
(c)炭素繊維集電体と、
(f)上記炭素繊維集電体上に円環状に形成され、Li2Oマトリックス中にFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属及びLi4.4Snが分散した層からなる外側層と、
(g)上記炭素繊維集電体と上記外側層との界面に存在する、リチウム放出能を有する中間層とを有することを特徴としている。
(31)放電後のリチウム二次電池用ファイバー負極は、
(c)炭素繊維集電体と
(h)上記炭素繊維集電体上に円環状に形成され、Li2Oマトリックス中にFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属及びSn、又はSn合金が分散した層からなる外側層と、
(i)上記炭素繊維集電体と上記外側層との界面に存在する、リチウム吸蔵能を有する中間層とを有することを特徴としている。
[リチウム二次電池用ファイバー負極の製造方法]
(32)リチウム二次電池用ファイバー負極の製造方法は、
炭素繊維集電体上に、電気めっき法によって、Fe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属皮膜並びにSn皮膜、又はSn合金皮膜を形成した後に、微量酸素雰囲気下、350~650℃で加熱処理を行うことを特徴としている。
(33)上記電気めっき浴に導電剤及び/又はバインダを分散させて、炭素繊維集電体上に、導電剤及び/又はバインダを共析めっきさせることが好ましい。
(34)上記リチウム二次電池用ファイバー負極の製造方法で製造された負極にリチウムをプリドープすることが好ましい。
[リチウム二次電池]
(35)リチウム二次電池は、上記のリチウム二次電池用ファイバー負極と電解質と正極とを備えることが好ましい。
(36)リチウム二次電池は、上記のリチウム二次電池用ファイバー負極と上記のリチウム二次電池用ファイバー正極と電解質を備えることが好ましい。
1.リチウム二次電池用ファイバー正極及びその製造方法
本発明のリチウム二次電池用ファイバー正極の製造方法は、
(a)炭素繊維集電体上に、遷移金属酸化物又は遷移金属水酸化物からなる皮膜を円環状に形成する工程と、
(b)上記の炭素繊維集電体上に遷移金属酸化物又は遷移金属水酸化物からなる皮膜が円環状に形成された物を、密閉された系内で酸化剤又は還元剤の存在下、リチウムイオンを含む溶液中で100~250℃で熱処理し、炭素繊維集電体上にリチウムドープした遷移金属酸化物の皮膜を得る工程とを備えることを特徴としている。
[工程(a)]
工程(a)では、炭素繊維集電体上に、遷移金属酸化物又は遷移金属水酸化物からなる皮膜を円環状に形成する。
[炭素繊維集電体]
集電体を板状、箔状等ではなく、細い円柱状の導電性繊維にすると、工程(b)において、各々の繊維上に円環状の活物質層が形成される。この場合、活物質層が閉じた円環を形成しているため、充放電に伴う体積変化が抑制され、膨張と収縮を繰り返した場合でも、板状電極と比べて、活物質層の剥離と脱落が起こりにくく、充放電サイクル寿命の向上と出力特性の向上等の利点が見込まれる。さらに、この繊維を束にすることにより、繊維同士が互いに圧着され、活物質の脱落防止にさらに効果的となる。
非水溶液系の電解めっき法によれば、めっき浴に炭素繊維集電体が接触さえしていれば、たとえ複雑で入り組んだ形状を持つ炭素繊維群にも、均一にAl皮膜を形成することができる。
[遷移金属酸化物又は遷移金属水酸化物]
遷移金属酸化物又は遷移金属水酸化物としては、上記炭素繊維集電体上に皮膜を形成できるものであれば特に制限されないが、例えば、TiO、Ti2O3、TiO2、V2O3、V2O5、CrO、Cr2O3、CrO2、MnO、Mn3O4、Mn2O3、MnO2、MnO3、FeO、Fe3O4、Fe2O3、CoO、Co2O3、Co3O4、CoO2、NiO、Ni3O4、Ni2O3、NiO2、Cu2O、CuO、ZnO等が挙げられ、これらの水和酸化物及び水酸化物等が使用できる。
[円環状皮膜の形成]
炭素繊維集電体上に、遷移金属酸化物又は遷移金属水酸化物からなる皮膜を円環状に形成する方法としては、特に制限されるわけではないが、スラリー法、物理的薄膜形成法、エアロゾルデポジション法、電気めっき法、電解析出法等が挙げられる。以下、それぞれの形成方法について説明する。
[工程(b)]
次に、工程(b)では、炭素繊維集電体上に遷移金属酸化物又は遷移金属水酸化物からなる皮膜が円環状に形成された物を、密閉された系内で酸化剤又は還元剤の存在下、リチウムイオンを含む溶液中で100~250℃で熱処理し、炭素繊維集電体上にリチウムドープした遷移金属酸化物の皮膜を得る。
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co及びNiよりなる群から選ばれる少なくとも1種の遷移金属であり、1≦a≦3、1≦b≦5である)で表される遷移金属酸化物皮膜を形成した後、これを酸化剤又は還元剤の存在下、リチウムイオンを含む溶液中で100~250℃で熱処理することで、炭素繊維集電体上に形成された遷移金属酸化物はリチウム変性し、
式(2):LidMeOc
(式(2)中、2≦c≦5、0<d≦2、1≦e≦5であり、Mは式(1)と同じである)で表されるリチウムドープされた遷移金属酸化物となる。
(式(2-1)中、Mnの価数は3~4の範囲内であって、2≦c1≦4、0<d1≦2、1≦e1≦2である)で表されるものとなる。
(式(1-2)中、Aは、Al、Ti、Cr、Fe、Co、Ni、Cu、Sr、Y、Zr及び希土類元素よりなる群から選ばれる少なくとも1種の元素であり、0.05≦x≦0.25である)で表される遷移金属酸化物皮膜を形成し、
その後リチウムドープすることで、式(2-2):Lid2(Mn1-yAy)e2Oc2
(式(2-2)中、Mnの価数は3~4の範囲内であって、2≦c2≦4、0<d2≦2、1≦e2≦2、0.05≦y≦0.25であり、Aは式(1-2)と同じである)で表されるリチウムドープされた遷移金属酸化物の皮膜を形成する。
[酸化剤と還元剤]
酸化剤は、酸化力を有していればよく、例えば、空気、酸素、オゾン、塩素、臭素、塩素酸塩、ペルオキソ二硫酸塩、次亜塩素酸塩、過酸化水素水等が挙げられ、特に次亜塩素酸塩が好ましく、さらに次亜塩素酸ナトリウムが好ましい。
[熱処理]
工程(b)の熱処理の際には、酸化剤又は還元剤およびリチウムイオンを含む溶液がアルカリ性条件下にある場合は、そのまま加熱してもよいが、酸性条件下、特にpH値(水素イオン濃度指数)が小さい場合は、例えば、水酸化ナトリウム、水酸化カリウム、水酸化リチウム等の水酸化アルカリ;アンモニアガス、アンモニア水等のアンモニア化合物;炭酸ナトリウム、炭酸カリウム、炭酸リチウム、炭酸アンモニウム等の炭酸アルカリ化合物等を添加してpH値を上昇させて加熱するとよい。
リコール及びこれらの組み合わせ等の有機溶媒、イミダゾール塩系イオン性液体、ピリジニウム塩系イオン性液体、又はオニウム塩系イオン性液体等のイオン性液体等が使用される。特に、塩化コリン等のように常温では固体だが、温度を上げると液体になる物質を反応場としてもよい。なお、液体として水を使用するものを、特に水熱合成と呼び、本発明では、環境面、作業の容易性、コスト等の点から、この水熱合成が好ましい。
2.リチウム二次電池用ファイバー負極及びその製造方法
本発明のリチウム二次電池用ファイバー負極を用いたリチウム二次電池によれば、Sn(スズ)の存在により、高い充放電容量を有する。
[炭素繊維集電体]
本発明に用いる炭素繊維集電体は、直径1~100μmの炭素繊維であるのが好ましい。特許文献3にも記載されているように、周知の箔状の集電体では、190℃を超えるとめっき層が剥離する。より好ましい炭素繊維の直径は、5~10μmである。理由は上記のファイバー正極と同様であり、炭素繊維の直径が1μm未満のように小さい場合には、その機械的強度や電気伝導性の低下が問題になり、電極作製が困難である。一方、炭素繊維の直径が100μmを超える場合、曲率低下によって活物質層に歪みが生じやすく、剥離や脱落が生じやすくなるほか、電極の嵩の増大による体積当たりの活物質充填量の低下も問題になる。また、ファイバー負極を作製する場合でも、用いる炭素繊維は単繊維でもよいし、複数の単繊維を集合させたものも有効である。
[Sn合金からなる中間層、Sn酸化物及びMXOyの複合層からなる外側層]
本発明のリチウム二次電池用ファイバー負極の製造方法において、炭素繊維集電体上に、電気めっき法によって、Fe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属(以下、金属Mともいう)めっき層並びにSnめっき層、又はSn合金めっき層を形成した後に、加熱処理することにより、炭素繊維の表面に被覆された該金属Mめっき層とSnめっき層、又はSn合金めっき層が合金化する。微量酸素雰囲気中でさらに温度を上げると、合金化した皮膜(めっき層)は外周から徐々に酸化が始まり、Sn酸化物及びMxOyの複合層に変化する。この際、金属原子Mの数xは0<x<3であり、また酸素原子Oの数yは、金属原子Mと酸素原子Oとの化学結合における化学量論に基づく酸素原子Oの数をwとしたとき、0≦y≦wである。金属原子Mとしては、Cu及びNiが好ましい。
[加熱処理]
金属M皮膜とSn皮膜、又はSn合金皮膜を形成した後、さらに300℃以下で加熱処理を施すと、Snと金属Mが合金化する。例えば、金属MがCuの場合、SnとCuが合金化し、Cu6Sn5及び/又はCu3Snが得られる。しかし、この際に得られる負極は合金化しただけで表面が酸化されていない。これに、微量酸素雰囲気中で300℃を超える温度で加熱処理を施すと、Sn、金属M、SnM合金が酸化する。例えば、金属MがCuの場合、Sn、Cu、Cu6Sn5及びCu3Snなどが酸化され、SnO2とCu2Oが生成する。
3.ファイバー正極およびファイバー負極を備えたリチウム二次電池
本発明のファイバー正極および/またはファイバー負極を用いて得られるリチウム二次電池は、電解質がリチウムイオンを含有する必要があることから、その電解質塩としては、リチウム塩が好適である。このリチウム塩としては、特に制限されないが、具体的には、ヘキサフルオロリン酸リチウム、過塩素酸リチウム、テトラフルオロホウ酸リチウム、トリフルオロメタンスルホン酸リチウム、トリフルオロメタンスルホン酸イミドリチウムなどが挙げられ、これらのうちから1種又は2種以上のものを用いることができる。上記リチウム塩は、電気陰性度が高くイオン化しやすいことから、充放電サイクル特性に優れ、二次電池の充放電容量を向上させることができる。
1.ファイバー正極に関する製造例、実施例および試験例
《製造例1》:(電解析出法)Mn3O4/炭素繊維
まず、電析浴にMn(NO3)2水溶液(0.3mol/liter)を用い、作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。電解析出条件としては、定電流密度50mA/cm2で10分間電解析出した。その後、電極を水洗いし、空気雰囲気下、100℃で24時間以上乾燥させ、炭素繊維にMn3O4を被覆した電極を得た。なお、Mn3O4を被覆しただけでは正極として機能はしない。製造例1の電極のSEM写真を図2に示す。
《製造例2》:(電解析出法)NiO/炭素繊維
まず、電析浴にNi(NO3)2水溶液(0.3mol/liter)を用い、作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。電解析出条件としては、定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、空気雰囲気下、130℃で24時間以上乾燥させ、炭素繊維にNiOを被覆した電極を得た。なお、NiOを被覆しただけでは正極として機能はしない。
《製造例3》:(電解析出法)Mn3O4+NiO/炭素繊維
電解析出法によって、Mn3O4及びNiOを被覆するため、電析浴にはMn(NO3)2水溶液(0.3mol/liter)及びNi(NO3)2水溶液(0.03mol/liter)の混合物を用いた。作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、空気雰囲気下、130℃で24時間以上乾燥させ、炭素繊維にMn3O4及びNiOを被覆した電極を得た。なお、Mn3O4及びNiOを被覆しただけでは正極として機能はしない。
《製造例4》:(電気めっき法)NiO/炭素繊維
まず、電気めっき浴に硫酸ニッケル水溶液(0.3mol/liter)を用い、作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。電気めっき条件としては、定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、酸素雰囲気下、650℃で24時間以上酸化処理し、炭素繊維にNiOを被覆した電極を得た。なお、NiOを被覆しただけでは正極として機能はしない。
《製造例5》:(電解析出法)Mn3O4+NiO/Al被覆炭素繊維
まず、1-エチル-3-メチルイミダゾリウムクロライドと塩化アルミニウムとを1mol:2molの割合で混合し、常温溶融塩を作製した。これを、Alめっき浴として用い、作用極へ炭素繊維(直径6μm)、対極へアルミニウム箔を用い、炭素繊維表面に約0.1μmのアルミニウムを被覆させた。めっき条件としては、定電流密度10mA/cm2で10分間めっきした。
《製造例6》:(電解析出法)Mn3O4+Al2O3/炭素繊維
電解析出法によって、Mn3O4及びAl2O3を被覆するため、電析浴にはMn(NO3)2水溶液(0.3mol/liter)及びAl(NO3)3水溶液(0.03mol/liter)の混合物を用いた。作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。定電流密度50mA/cm2で10分間電解析出した。その後、電極を水洗いし、空気雰囲気下、70℃で24時間以上乾燥させ、炭素繊維にMn3O4及びAl2O3を被覆した電極を得た。なお、Mn3O4及びAl2O3を被覆しただけでは正極として機能はしない。
《製造例7》:(電解析出法)Mn3O4+Al2O3+KB/炭素繊維
電解析出法によって、Mn3O4及びAl2O3を被覆するため、電析浴にはMn(NO3)2水溶液(0.3mol/liter)及びAl(NO3)3水溶液(0.03mol/liter)の混合物にケッチェンブラック(KB)を1wt%、トリトン(界面活性剤)を0.5wt%添加したものを用いた。作用極には炭素繊維(直径6μm)を用い、対極には白金箔を用いた。スターラーで電析浴をかき混ぜながら、定電流密度50mA/cm2で10分間電解析出した。その後、電極を水洗いし、空気雰囲気下、70℃で24時間以上乾燥させ、炭素繊維にMn3O4及びAl2O3を被覆し、KBが共析した電極を得た。なお、Mn3O4及びAl2O3を被覆しただけでは正極として機能はしない。
《参考製造例8》:(電解析出法)Mn3O4/Al箔(板状の集電体)
まず、電析浴にMn(NO3)2水溶液(0.3mol/liter)を用い、作用極には板状の集電体であるAl箔(厚み20μm)を用い、対極には白金箔を用いた。電解析出条件としては、定電流密度50mA/cm2で10分間電解析出した。その後、電極を水洗いし、空気雰囲気下、100℃で24時間以上乾燥させ、Al箔にMn3O4を被覆した電極を得た。なお、Mn3O4を被覆しただけでは正極として機能はしない。
《実施例1》:(水熱合成法)LiMnO2+Mn(OH)2/炭素繊維
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、0.5酸化当量の酸素ガス(8mg/liter)を加えた水酸化リチウム水溶液中に製造例1の電極を浸漬し、110℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、実施例1のファイバー正極を得た。
《実施例2》:(水熱合成法)LiMnO2/炭素繊維
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、1酸化当量の次亜塩素酸ナトリウム(次亜塩素酸ナトリウムの濃度:0.01mol/liter)を加えた水酸化リチウム水溶液中に製造例1の電極を浸漬し、130℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例2のファイバー正極を得た。
《実施例3》:(水熱合成法)LiMn2O4/炭素繊維
以下の実施例3-1~3-5のように、酸化当量を変化させ、炭素繊維集電体上に、LiMn2O4の皮膜を形成したファイバー正極を得た。
《実施例3-1》:1.5酸化当量
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、1.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウムの濃度:0.02mol/liter)中に製造例1の電極を浸漬し、110℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例3-1のファイバー正極を得た。
《実施例3-2》:2酸化当量
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、2酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウムの濃度:0.04mol/liter)中に製造例1の電極を浸漬し、110℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例3-2のファイバー正極を得た。
《実施例3-3》:2.5酸化当量
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、2.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウム:0.06mol/liter)中に製造例1の電極を浸漬し、110℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例3-3のファイバー正極を得た。
《実施例3-4》:3酸化当量
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、3酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウム:0.08mol/liter)中に製造例1の電極を浸漬し、110℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例3-4のファイバー正極を得た。
《実施例3-5》:3.5酸化当量
製造例1で炭素繊維集電体上に形成されたMn3O4を1当量として、3.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウムの濃度:0.1mol/liter)中に製造例1の電極を浸漬し、125℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例3-5のファイバー正極を得た。
《実施例4》:(水熱合成法)LiNiO2+Ni(OH)2/炭素繊維
製造例2で炭素繊維集電体上に形成されたNiOを1当量として、1酸化当量の過酸化水素水を加えた水酸化リチウム水溶液中(過酸化水素の濃度:0.005mol/liter)に製造例2の電極を浸漬し、120℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、実施例4のファイバー正極を得た。
《実施例5》:(水熱合成法)LiNiO2/炭素繊維
製造例2で炭素繊維集電体上に形成されたNiOを1当量として、2酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液中(次亜塩素酸ナトリウムの濃度:0.04mol/liter)に製造例2の電極を浸漬し、120℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、実施例5のファイバー正極を得た。
《実施例6》:(水熱合成法)LiMn1.9Ni0.1O4/炭素繊維
製造例3で炭素繊維集電体上に形成されたMn3O4及びNiOを合計1当量として、1.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウムの濃度:0.02mol/liter)中に製造例3の電極を浸漬し、120℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例6のファイバー正極を得た。
《実施例7》:(水熱合成法)LiNiO2+Ni(OH)2/炭素繊維
製造例4で炭素繊維集電体上に形成されたNiOを1当量として、1酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(次亜塩素酸ナトリウムの濃度:0.01mol/liter)中に製造例4の電極を浸漬し、120℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、実施例7のファイバー正極を得た。
《実施例8》:(水熱合成法)LiMn1.9Ni0.1O4/Al被覆炭素繊維
製造例5でAl被覆炭素繊維集電体上に形成されたMn3O4及びNiOを合計1当量として、1.5酸化当量の次亜塩素酸ナトリウム(0.02mol/liter)を加えた水酸化リチウム水溶液中に製造例5の電極を浸漬し、130℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例8のファイバー正極を得た。
《実施例9》:(水熱合成法)LiMn1.9Al0.1O4/炭素繊維
製造例6で炭素繊維集電体上に形成されたMn3O4及びAl2O3を合計1当量として、1.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液中(0.02mol/liter)に製造例6の電極を浸漬し、130℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例9のファイバー正極を得た。
《実施例10》:(水熱合成法)LiMn1.9Al0.1O4+KB/炭素繊維
製造例7で炭素繊維集電体上に形成されたMn3O4及びAl2O3を合計1当量として、1.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液中(0.02mol/liter)に製造例7の電極を浸漬し、130℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、実施例10のファイバー正極を得た。
《実施例11》:(ソルボサーマル法)LiMnO2/炭素繊維
製造例1で得られた炭素繊維集電体にMn3O4が被覆された電極を、空気雰囲気下、塩化コリン、尿素及び水酸化リチウムの混合粉末中に埋め、150℃で20時間の条件下で、ソルボサーマル処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、実施例11のファイバー正極を得た。
《比較例1》:(水熱合成法)LiMnO2/Al箔
参考製造例8でAl箔集電体上に形成されたMn3O4を1当量として、1酸化当量の次亜塩素酸ナトリウム(次亜塩素酸ナトリウムの濃度:0.01mol/liter)を加えた水酸化リチウム水溶液中に参考製造例8の電極を浸漬し、130℃で20時間の条件下で水熱合成を行った。その後、電極を水洗いし、110℃で24時間以上減圧乾燥を行い、比較例1の板状正極を得た。
《試験例1》:ファイバー正極の観察
[X線回折]
実施例2、3-5及び4のX線回折パターンを図3に示す。なお、参考として、熱処理を施していない製造例1及び2も同図に示した。
[走査電子顕微鏡]
図7に実施例2のファイバー正極のSEM(走査電子顕微鏡)写真を示す。図7から明らかなように、炭素繊維集電体に多孔質の物質が付着し、層を形成していることがわかる。この層は、フレーク形状を有する活物質粒子が集電体に対して垂直方向に形成して構成されている。また、このフレーク状粒子は互いに重なり合い、その重なった場所を起点として、そこからさらに新たなフレーク状の粒子が形成している。よって、フレーク状の粒子が凝集した集合体を形成することで、多孔質の活物質層が形成されたものと思われる。拡大して観察したところ、厚み約100nm、幅約1.5μm、長さ約2μmのフレーク状の粒子が、凝集して電極を被覆していたことが分かった。先のX線回折パターン測定の結果より明らかなように、実施例2の活物質層はマンガン酸リチウムを主成分としている。すなわち、図7に示した多孔質な層は、LiMnO2である。
《試験例2》:電池試験
実施例1~11の各サンプルを試験極とし、金属リチウム箔を対極として用い、電解液として、エチレンカーボネート(EC)とジメチルカーボネート(DMC)とを体積比1:1で混合した溶媒にLiPF6を1mol/literの濃度で溶解した溶液を用いて、2極式評価セルを作製し、充放電試験を行った。試験はカットオフ電圧で制御し、0.2Cに相当する充放電電流で行った。
2.ファイバー負極に関する実施例
《実施例12、13及び比較例2~7》(Cuめっき後にSnめっき)
単繊維の直径が8μmのカーボンファイバー(炭素繊維)上に、電気めっき法によって厚さ約1μmの銅めっき皮膜を形成し、その上に厚さ約2μmのSnめっき皮膜を形成した。
《実施例14及び比較例8~10》(CuSn合金めっき)
単繊維の直径が8μmのカーボンファイバー(炭素繊維)上に、電気めっき法によって厚さ約3μmのCuSn合金めっき皮膜を形成した。
[充放電後の電極構造(実施例12、14)]
充電後の実施例12と実施例14の電池を解体して電極構造を調べたところ、新たにCuとLi4.4SnとLi2Oが観測された。
《実施例15~22》(CuSn合金共析)
CuSnめっき液に導電剤及び/又はバインダを分散させ、単繊維の直径が8μmの炭素繊維上に、電気めっき法によって厚さ約3μmの導電剤及び/又はバインダを含むCuSn合金皮膜を形成した(共析)。形成した合金皮膜の組成は下記表6に記載の通りである。
した溶媒にLiPF6を1mol/literの濃度で溶解した溶液を用いて、2極式評価セルを作製し、充放電試験を行った。試験はカットオフ電圧で制御し、0.2Cに相当する充放電電流で行った。ここで、Sn極にLiが挿入される反応を充電、Liが放出される反応を放電とした。実施例15~22の充放電試験結果を、下記表7に示す。
3.ファイバー正極とファイバー負極を組み合わせて得られる二次電池に関する実施例
《実施例23》
実施例9で得られたファイバー正極と実施例12で得られたファイバー負極の間にポリエチレン製の微多孔膜セパレータを挟み、電解液として、エチレンカーボネート(EC)とジエチルカーボネート(DEC)を体積比1:1で混合した溶媒にLiPF6を1mol/literの濃度で溶解した溶液を用いて、2極式評価セルを作製し、充放電試験を行った。なお、ファイバー負極については、不可逆容量分のLiをプリドープしたものを用いた。図32は、実施例23の2極式評価セルの概略構成を示す平面図であり、3はセル外壁、4はファイバー正極、5はファイバー負極、6aは微多孔膜セパレータ、7は電解液を示す。各ファイバー正極4は正極端子(図示せず)に接続されており、各ファイバー負極5は負極端子(図示せず)に接続されている。
《実施例24》
実施例9で得られたファイバー正極と実施例12で得られたファイバー負極のそれぞれをSiO2の微粉末(直径30nm以下のもの)を分散させたポリエチレン溶解液に含浸し、乾燥させた。その後、ファイバー正極とファイバー負極を、90℃の30wt%LiOH水溶液に3時間浸漬し、ファイバー正極上とファイバー負極上に、それぞれポリエチレン多孔膜のセパレータを形成した。その後、ファイバー負極については、不可逆容量のLiをプリドープした。このようにして得られたファイバー正極とセパレータの積層体と、ファイバー負極とセパレータの積層体とを組み合わせ、電解液として、エチレンカーボネート(EC)とジエチルカーボネート(DEC)を体積比1:1で混合した溶媒にLiPF6を1mol/literの濃度で溶解した溶液を用いて、2極式評価セルを作製し、充放電試験を行った。図33は、実施例24の2極式評価セルの概略構成図であり、3はセル外壁、4はファイバー正極、5はファイバー負極、6bはセパレータ、7は電解液を示す。各ファイバー正極4は正極端子(図示せず)に接続されており、各ファイバー負極5は負極端子(図示せず)に接続されている。
[充放電試験結果(実施例23、24)]
実施例23と24の充放電試験を行って結果、高率放電時の容量と中間放電電圧を下記表8に示す。試験はカットオフ電圧で制御し、充電は0.2Cに相当する電流で行い、放電は0.5C~300Cに相当する電流で行った。ここで、Sn極にLiが挿入される反応を充電、Liが放出される反応を放電とした。
〈参考発明例〉
次に、参考発明例として、リチウム二次電池の正極として好適な、リチウムドープされた遷移金属酸化物を主活物質とする正極及びその製造方法を提供すること、特に、触媒粒子の活性面積の低下を抑え、長期耐久性に優れ、高い電流密度での充放電可能なリチウムドープされた遷移金属酸化物正極を安価に量産する方法を提供することについて、本発明者等は鋭意研究した結果、集電体へ遷移金属酸化物皮膜を形成した後、これを酸化剤又は還元剤の存在下、リチウムイオンを含む水溶液中で100~400℃で水熱処理を施すことで、リチウムドープされた遷移金属酸化物を主体活物質とするリチウム二次電池用正極を得ることに成功したので、以下に説明する。
(X)集電体上に遷移金属酸化物皮膜を形成する工程と、
(Y)遷移金属酸化物皮膜が形成された集電体を、酸化剤又は還元剤の存在下、リチウムイオンを含む水溶液中で100~400℃で水熱処理し、集電体上にリチウムドープした遷移金属酸化物の皮膜を得る工程とを備えることを特徴としている。
(式(3)中、Mは、Ti、V、Cr、Mn、Fe、Co及びNiよりなる群から選ばれる少なくとも1種の遷移金属であり、1≦a≦3、1≦b≦5である)で表され、
リチウムドープした遷移金属酸化物が、式(4):LidMeOc
(式(4)中、2≦c≦5、0<d≦2、1≦e≦5であり、Mは式(3)と同じである)で表されることが好ましい。
リチウムドープした遷移金属酸化物が、式(4-1):Lid1Mne1Oc1
(式(4-1)中、Mnの価数は3~4の範囲内であって、2≦c1≦4、0<d1≦2、1≦e1≦2である)
で表されることが好ましい。
(式(3-2)中、Aは、Al、Ti、Cr、Fe、Co、Ni、Cu、Sr、Y、Zr、In、Sn及び希土類元素よりなる群から選ばれる少なくとも1種の元素であり、0.05≦x≦0.25である)で表され、
リチウムドープした遷移金属酸化物が、式(4-2):Lid2(Mn1-yAy)e2Oc2
(式(4-2)中、Mnの価数は3~4の範囲内であって、2≦c2≦4、0<d2≦2、1≦e2≦2、0.05≦y≦0.25であり、Aは式(3-2)と同じである)で表されることが好ましい。
(X)集電体上に遷移金属酸化物皮膜を形成する工程と、
(Y)遷移金属酸化物皮膜が形成された集電体を、酸化剤又は還元剤の存在下、リチウムイオンを含む水溶液中で100~400℃で水熱処理し、集電体上にリチウムドープした遷移金属酸化物の皮膜を得る工程とを備えることを特徴としている。
(式(3)中、Mは、Ti、V、Cr、Mn、Fe、Co及びNiよりなる群から選ばれる少なくとも1種の遷移金属であり、1≦a≦3、1≦b≦5である)で表される遷移金属酸化物皮膜を形成した後、これを酸化剤又は還元剤の存在下、リチウムイオンを含む水溶液中で水熱処理することで、集電体上に形成された遷移金属酸化物はリチウム変性し、 式(4):LidMeOc
(式(4)中、2≦c≦5、0<d≦2、1≦e≦5であり、Mは式(3)と同じである)で表されるリチウムドープされた遷移金属酸化物となる。
(式(4-1)中、Mnの価数は3~4の範囲内であって、2≦c1≦4、0<d1≦2、1≦e1≦2である)で表されるものとなる。
(式(3-2)中、Aは、Al、Ti、Cr、Fe、Co、Ni、Cu、Sr、Y、Zr、In、Sn及び希土類元素よりなる群から選ばれる少なくとも1種の元素であり、0.05≦x≦0.25である)で表される遷移金属酸化物皮膜を形成し、
その後リチウムドープすることで、式(4-2):Lid2(Mn1-yAy)e2Oc2
(式(4-2)中、Mnの価数は3~4の範囲内であって、2≦c2≦4、0<d2≦2、1≦e2≦2、0.05≦y≦0.25であり、Aは式(3-2)と同じである)で表されるリチウムドープされた遷移金属酸化物の皮膜を形成する。
〈参考製造例1〉:(電解析出法)Mn3O4/アルミニウム箔
まず、電析浴にMn(NO3)2水溶液(0.25mol/liter)を用い、作用極にはアルミニウム箔を用い、対極には白金箔を用いた。電解析出条件としては、定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、空気雰囲気下、100℃で24時間以上乾燥させ、アルミニウム箔にMn3O4を被覆した電極を得た。なお、Mn3O4を被覆しただけでは正極として機能はしない。
〈参考製造例2〉:(スラリー法)Mn3O4/アルミニウム箔
Mn3O4粉末を90wt%、カルボキシメチルセルロース(CMC)を10wt%になるよう秤量し、これに水を加えて混合し、スラリーを作製した。作製したスラリーをアルミニウム箔上に塗布し、次いで、600℃で24時間、CMCを炭化処理し、アルミニウム箔にMn3O4を被覆した電極を得た。なお、Mn3O4を被覆しただけでは正極として機能はしない。
〈参考製造例3〉:(エアロゾル法)Mn3O4/アルミニウム箔
エアロゾルデポジションターゲットにMn粉末(平均粒子径10μm)を用い、アルミニウム箔上にMn薄膜を形成し、これを空気雰囲気下、700℃で24時間、高温酸化処理を施し、アルミニウム箔にMn3O4を被覆した電極を得た。なお、Mn3O4を被覆しただけでは正極として機能はしない。
〈参考製造例4〉:(電解析出法)Mn3O4+NiO/アルミニウム箔
電解析出法によって、Mn3O4及びNiOを被覆するため、電析浴にはMn(NO3)2水溶液(0.25mol/liter)及びNi(NO3)2水溶液(0.01mol/liter)の混合物を用いた。作用極にはアルミニウム箔を用い、対極には白金箔を用いた。定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、空気雰囲気下、100℃で24時間以上乾燥させ、アルミニウム箔にMn3O4及びNiOを被覆した電極を得た。なお、Mn3O4及びNiOを被覆しただけでは正極として機能はしない。
〈参考製造例5〉:(電解析出法)NiO/アルミニウム箔
まず、電析浴にNi(NO3)2水溶液(0.25mol/liter)を用い、作用極にはアルミニウム箔を用い、対極には白金箔を用いた。電解析出条件としては、定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、空気雰囲気下、120℃で24時間以上乾燥させ、アルミニウム箔にNiOを被覆した電極を得た。なお、NiOを被覆しただけでは正極として機能はしない。
〈参考製造例6〉:(エアロゾル法)MnO2/アルミニウム箔
MnO2粉末の平均粒子径が100μm、平均二次粒子径が5μm、成膜室とエアロゾル室との圧力差が40kPaの条件により、アルミニウム箔にMnO2を被覆した電極を得た。なお、MnO2を被覆しただけでは正極として機能はしない。
〈参考製造例7〉:(電気めっき法)NiO/アルミニウム箔
まず、電析浴に硫酸ニッケル水溶液(0.25mol/liter)を用い、作用極にはアルミニウム箔を用い、対極には白金箔を用いた。電気めっき条件としては、定電流密度50mA/cm2で30分間電解析出した。その後、電極を水洗いし、酸素雰囲気下、650℃で24時間以上酸化処理し、アルミニウム箔にNiOを被覆した電極を得た。なお、NiOを被覆しただけでは正極として機能はしない。
〈参考例1〉:(電解析出法)LiMnO2+Mn(OH)2/アルミニウム箔
参考製造例1で集電体上に形成されたMn3O4を1当量として、1酸化当量の過酸化水素水を加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例1の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例1の正極を得た。
〈参考例2〉:(電解析出法)LiMnO2+Mn(OH)2/クロムめっきした発泡ニッケル
集電体をアルミニウム箔ではなく、クロムめっきした発泡ニッケルを使用したこと以外は参考例1と同様に、参考例2の正極を製造した。
〈参考例3〉:(電解析出法)LiMn2O4/アルミニウム箔
参考製造例1で集電体上に形成されたMn3O4を1当量として、2.5酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例1の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例3の正極を得た。
〈参考例4〉:(電解析出法)LiMn2O4/アルミメッシュ
集電体をアルミニウム箔ではなく、アルミメッシュを使用したこと以外は参考例3と同様に、参考例4の正極を製造した。
〈参考例5〉:(電解析出法)LiMn2O4/クロムめっきした発泡ニッケル
集電体をアルミニウム箔ではなく、クロムめっきした発泡ニッケルを使用したこと以外は参考例3と同様に、参考例5の正極を製造した。
〈参考例6〉:(電解析出法)Li2Mn2O4/クロムめっきした発泡ニッケル
参考例5においては、正極活物質はLixMn2O4であり、活物質がLiMn2O4となるように4V領域である0<x≦1の範囲(理論容量148mAh/g)で充放電を行ったものである。参考例6においては活物質がLi2Mn2O4となるように3V領域である0<x≦2の範囲(理論容量285mAh/g)で充放電を行い、参考例6の正極を製造した。
〈参考例7〉:(スラリー法)LiMn2O4/アルミニウム箔
参考製造例1の電極ではなく、参考製造例2の電極を用いたこと以外は参考例3と同様に、参考例7の正極を製造した。
〈参考例8〉:(エアロゾル法)LiMn2O4/アルミニウム箔
参考製造例1の電極ではなく、参考製造例3の電極を用いたこと以外は参考例3と同様に、参考例8の正極を製造した。
〈参考例9〉:(電解析出法)LiMn1.85Ni0.15O4/アルミニウム箔
参考製造例4で集電体上に形成されたMn3O4及びNiOを合計1当量として、2酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例4の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例9の正極を得た。
〈参考例10〉:(電解析出法)LiNiO2+Ni(OH)2/アルミニウム箔
参考製造例5で集電体上に形成されたNiOを1当量として、1酸化当量の過酸化水素水を加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例5の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例10の正極を得た。
〈参考例11〉:(電解析出法)LiNiO2/アルミニウム箔
参考製造例5で集電体上に形成されたNiOを1当量として、2酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例5の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例11の正極を得た。
〈参考例12〉:(電解析出法)LiNiO2/アルミメッシュ
集電体をアルミニウム箔ではなく、アルミメッシュを使用したこと以外は参考例11と同様に、参考例12の正極を製造した。
〈参考例13〉:(電解析出法)LiNiO2/クロムめっき処理した発泡ニッケル
集電体をアルミニウム箔ではなく、クロムめっき処理した発泡ニッケルを使用したこと以外は参考例10と同様に、参考例13の正極を製造した。
〈参考例14〉:(エアロゾル法)還元剤によるLiMn4O2/アルミニウム箔
参考製造例6で集電体上に形成されたMnO2を1当量として、0.6還元当量のイソアスコルビン酸ナトリウムを加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例6の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例14の正極を得た。
〈参考例15〉:(エアロゾル)還元剤によるLiMnO2/アルミニウム箔
0.6還元当量のイソアスコルビン酸ナトリウムではなく、4還元当量のイソアスコルビン酸ナトリウムを加えたこと以外は参考例14と同様に、参考例15の正極を得た。
〈参考例16〉:(電気めっき法)LiNiO2+Ni(OH)2/アルミニウム箔
参考製造例7で集電体上に形成されたNiOを1当量として、1酸化当量の次亜塩素酸ナトリウムを加えた水酸化リチウム水溶液(3mol/liter)中に参考製造例7の電極を浸漬し、120℃で20時間の条件下で水熱処理を行った。その後、電極を水洗いし、100℃で24時間以上減圧乾燥を行い、参考例16の正極を得た。
〈参考試験例1〉:正極の観察
[X線回折]
参考例1、3及び10のX線回折パターンを図28に示す。なお、参考例1において水熱処理を施していないものを比較参考例1とし、参考例5において水熱処理を施していないものを比較参考例5として、同図に示した。
[走査電子顕微鏡(SEM)]
図29に参考例1の正極の酸化物皮膜側の表面のSEM写真を示す。図29から明らかなように、集電体に多孔質の物質が付着し、層を形成していることがわかる。この層は、フレーク形状を有する活物質粒子が集電体の表面に対して垂直方向に形成して構成されている。また、このフレーク状粒子は互いに重なり合い、その重なった場所を起点として、そこからさらに新たなフレーク状の粒子が形成している。よって、フレーク状の粒子が凝集した集合体を形成することで、多孔質の活物質層が形成されたものと思われる。拡大して観察したところ、厚み約100nm、幅約1.5μm、長さ約2μmのフレーク状の粒子が、凝集して電極を被覆していたことが分かった。先のX線回折パターン測定結果を示す図28より明らかなように、参考例1の活物質層はマンガン酸リチウムを主成分としている。すなわち、図29に示した多孔質の層は、LiMnO2である。
〈参考試験例2〉:電池試験
参考例1~16の各サンプルを試験極とし、金属リチウム箔を対極として用い、電解液として、エチレンカーボネート(EC)とジメチルカーボネート(DMC)とを体積比1:1で混合した溶媒にLiPF6を1mol/literの濃度で溶解した溶液を用いて、2極式評価セルを作製し、充放電試験を行った。試験はカットオフ電圧で制御し、0.3Cに相当する充放電電流で行った。
2 遷移金属酸化物
3 セル外壁
4 ファイバー正極
5 ファイバー負極
6a 微多孔膜セパレータ
6b セパレータ
7 電解液
Claims (36)
- (a)炭素繊維集電体上に、遷移金属酸化物又は遷移金属水酸化物からなる皮膜を円環状に形成する工程と、
(b)上記の炭素繊維集電体上に遷移金属酸化物又は遷移金属水酸化物からなる皮膜が円環状に形成された物を、密閉された系内で酸化剤又は還元剤の存在下、リチウムイオンを含む溶液中で100~250℃で熱処理し、炭素繊維集電体上にリチウムドープした遷移金属酸化物の皮膜を得る工程とを備えることを特徴とするリチウム二次電池用ファイバー正極の製造方法。 - 工程(a)が、電解析出法により、炭素繊維集電体上に遷移金属酸化物皮膜又は遷移金属水酸化物皮膜を円環状に形成する工程であることを特徴とする請求項1に記載のリチウム二次電池用ファイバー正極の製造方法。
- 工程(a)が、電気めっき法により、炭素繊維集電体上に遷移金属皮膜を円環状に形成し、その後酸化雰囲気下で500~1000℃で高温酸化処理することで、遷移金属酸化物皮膜を形成する工程であることを特徴とする請求項1に記載のリチウム二次電池用ファイバー正極の製造方法。
- 工程(a)が、導電助剤を共析させる方法で、電解析出浴に導電助剤を分散し、析出皮膜に導電助剤を含有させる工程であることを特徴とする請求項2に記載のリチウム二次電池用ファイバー正極の製造方法。
- 工程(a)が、導電助剤を共析させる方法で、電気めっき浴に導電助剤を分散し、析出皮膜に導電助剤を含有させる工程であることを特徴とする請求項3に記載のリチウム二次電池用ファイバー正極の製造方法。
- 工程(b)における密閉された系内での熱処理が、ソルボサーマル処理であることを特徴とする請求項1~5のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。
- 炭素繊維集電体にAl皮膜が形成されていることを特徴とする請求項1~6のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。
- Al皮膜の厚さが0.1~1μmであることを特徴とする請求項7に記載のリチウム二次電池用ファイバー正極の製造方法。
- 炭素繊維集電体の直径が1~100μmであることを特徴とする請求項1~8のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。
- 遷移金属酸化物が、式(1):MaOb
(式(1)中、Mは、Ti、V、Cr、Mn、Fe、Co及びNiよりなる群から選ばれる少なくとも1種の遷移金属であり、1≦a≦3、1≦b≦5である)で表され、
リチウムドープした遷移金属酸化物が、式(2):LidMeOc
(式(2)中、2≦c≦5、0<d≦2、1≦e≦5であり、Mは式(1)と同じである)で表されることを特徴とする請求項1~9のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。 - 遷移金属酸化物が、Mn3O4であり、
リチウムドープした遷移金属酸化物が、式(2-1):Lid1Mne1Oc1
(式(2-1)中、Mnの価数は3~4の範囲内であって、2≦c1≦4、0<d1≦2、1≦e1≦2である)で表されることを特徴とする請求項1~9のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。 - 遷移金属酸化物が、式(1-2):(Mn1-XAX)3O4
(式(1-2)中、Aは、Al、Ti、Cr、Fe、Co、Ni、Cu、Sr、Y、Zr、及び希土類元素よりなる群から選ばれる少なくとも1種の元素であり、0.05≦x≦0.25である)で表され、
リチウムドープした遷移金属酸化物が、式(2-2):Lid2(Mn1-yAy)e2Oc2
(式(2-2)中、Mnの価数は3~4の範囲内であって、2≦c2≦4、0<d2≦2、1≦e2≦2、0.05≦y≦0.25であり、Aは式(1-2)と同じである)で表されることを特徴とする請求項1~9のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法。 - 請求項1~12のいずれかに記載の製造方法により製造されることを特徴とするリチウム二次電池用ファイバー正極。
- リチウムドープした遷移金属酸化物が、炭素繊維集電体の表面に対して垂直方向にフレーク状に形成されている多孔性物質であることを特徴とする請求項13に記載のリチウム二次電池用ファイバー正極。
- フレーク状に形成されている多孔性物質であるリチウムドープした遷移金属酸化物は、厚みが5~600nm、幅が0.1~10μm、長さが0.1~10μmであることを特徴とする請求項14に記載のリチウム二次電池用ファイバー正極。
- 請求項1~12のいずれかに記載のリチウム二次電池用ファイバー正極の製造方法により製造される、炭素繊維集電体上に円環状に形成されるリチウムドープした遷移金属酸化物の皮膜上にセパレータ層を形成することによって得られることを特徴とするファイバー正極とセパレータの積層体。
- 請求項13~16のいずれかに記載のリチウム二次電池用ファイバー正極と、電解質と、負極とを備えることを特徴とするリチウム二次電池。
- (c)炭素繊維集電体と、
(d)上記炭素繊維集電体上に円環状に形成されたSn酸化物及びMXOyの複合層からなる外側層と、
(e)上記炭素繊維集電体と上記外側層との界面に存在する、Sn合金からなるリチウム吸蔵能を有する中間層とを有することを特徴とするリチウム二次電池用ファイバー負極。
((d)のMXOy中、Mは、Fe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属原子であり、xは0<x<3であり、酸素原子Oの数yは、金属原子Mと酸素原子Oとの化学結合における化学量論に基づく酸素原子Oの数をwとしたとき、0≦y≦wである。) - 中間層のSn合金層が、Sn以外の合金成分としてFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属成分を含むSn合金めっき層であることを特徴とする請求項18に記載のリチウム二次電池用ファイバー負極。
- 中間層がCuSn合金の層であって、外側層がSn及びCuの酸化物の複合層であることを特徴とする請求項18または19に記載のリチウム二次電池用ファイバー負極。
- 中間層がCu3Sn層であって、外側層がSnO2及びCu2Oの複合層であることを特徴とする請求項18または19に記載のリチウム二次電池用ファイバー負極。
- 中間層及び外側層の合計厚さが、1~10μmであることを特徴とする請求項18~21のいずれかに記載のリチウム二次電池用ファイバー負極。
- 炭素繊維は、単繊維の直径が1~100μmであることを特徴とする請求項18~22のいずれかに記載のリチウム二次電池用ファイバー負極。
- 炭素繊維は、単繊維100~5000本が束になった状態であることを特徴とする請求項18~23のいずれかに記載のリチウム二次電池用ファイバー負極。
- 炭素繊維は、単繊維50~1000本が撚られた状態であることを特徴とする請求項18~23のいずれかに記載のリチウム二次電池用ファイバー負極。
- 中間層及び外側層が、導電剤及び/又はバインダを有することを特徴とする請求項18~25のいずれかに記載のリチウム二次電池用ファイバー負極。
- 導電剤がカーボンブラックであることを特徴とする請求項26に記載のリチウム二次電池用ファイバー負極。
- バインダがポリテトラフルオロエチレンであることを特徴とする請求項26又は27に記載のリチウム二次電池用ファイバー負極。
- 請求項18~25のいずれかに記載の外側層上にセパレータ層を形成することによって得られることを特徴とするファイバー負極とセパレータの積層体。
- 充電後は、
(c)炭素繊維集電体と、
(f)上記炭素繊維集電体上に円環状に形成され、Li2Oマトリックス中にFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属及びLi4.4Snが分散した層からなる外側層と、
(g)上記炭素繊維集電体と上記外側層との界面に存在する、リチウム放出能を有する中間層とを有することを特徴とするリチウム二次電池用ファイバー負極。 - 放電後は、
(c)炭素繊維集電体と
(h)上記炭素繊維集電体上に円環状に形成され、Li2Oマトリックス中にFe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属及びSn、又はSn合金が分散した層からなる外側層と、
(i)上記炭素繊維集電体と上記外側層との界面に存在する、リチウム吸蔵能を有する中間層とを有することを特徴とするリチウム二次電池用ファイバー負極。 - 炭素繊維集電体上に、電気めっき法によって、Fe、Mo、Co、Ni、Cr、Cu、In、Sb、及びBiからなる群より選択される少なくとも1種の金属皮膜並びにSn皮膜、又はSn合金皮膜を形成した後に、微量酸素雰囲気下、350~650℃で加熱処理を行うことを特徴とするリチウム二次電池用ファイバー負極の製造方法。
- 電気めっき浴に導電剤及び/又はバインダを分散させて、炭素繊維集電体上に、導電剤及び/又はバインダを共析めっきさせることを特徴とする請求項30に記載のリチウム二次電池用ファイバー負極の製造方法。
- 請求項32又は33に記載のリチウム二次電池用ファイバー負極の製造方法で製造された負極にリチウムをプリドープして得られることを特徴とするリチウム二次電池用ファイバー負極。
- 請求項18~31および34のいずれかに記載のリチウム二次電池用ファイバー負極と、電解質と、正極とを備えることを特徴とするリチウム二次電池。
- 正極が請求項13~16のいずれかに記載のリチウム二次電池用ファイバー正極であることを特徴とする請求項35に記載のリチウム二次電池。
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Also Published As
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EP2395580B1 (en) | 2017-07-26 |
CN102292853A (zh) | 2011-12-21 |
TWI393287B (zh) | 2013-04-11 |
EP2395580A4 (en) | 2013-11-20 |
US9065139B2 (en) | 2015-06-23 |
US20120040246A1 (en) | 2012-02-16 |
KR20110111523A (ko) | 2011-10-11 |
EP2395580A1 (en) | 2011-12-14 |
TW201037882A (en) | 2010-10-16 |
CN102292853B (zh) | 2014-05-14 |
JP5283138B2 (ja) | 2013-09-04 |
KR101407859B1 (ko) | 2014-06-16 |
JPWO2010089991A1 (ja) | 2012-08-09 |
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