EP1889270A1 - Method for producing electrode for electrochemical element and method for producing electrochemical element with the electrode - Google Patents

Method for producing electrode for electrochemical element and method for producing electrochemical element with the electrode

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Publication number
EP1889270A1
EP1889270A1 EP05751144A EP05751144A EP1889270A1 EP 1889270 A1 EP1889270 A1 EP 1889270A1 EP 05751144 A EP05751144 A EP 05751144A EP 05751144 A EP05751144 A EP 05751144A EP 1889270 A1 EP1889270 A1 EP 1889270A1
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European Patent Office
Prior art keywords
polymerization
electrode
producing
monomers
polymer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP05751144A
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German (de)
French (fr)
Other versions
EP1889270A4 (en
Inventor
Hidenori c/o NIPPON CHEMI-CON CORPORATION UCHI
Kenji c/o NIPPON CHEMI-CON CORPORATION TAMAMITSU
Shunzo c/o NIPPON CHEMI-CON CORPORATION SUEMATSU
Satoru c/o NIPPON CHEMI-CON CORPORATION TSUMEDA
Alexander M. Timonov
Sergey A Logvinov
Nikolay Shkolnik
Sam Kogan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Chemi Con Corp
Gen3 Partners Inc
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Nippon Chemi Con Corp
Gen3 Partners Inc
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Application filed by Nippon Chemi Con Corp, Gen3 Partners Inc filed Critical Nippon Chemi Con Corp
Publication of EP1889270A1 publication Critical patent/EP1889270A1/en
Publication of EP1889270A4 publication Critical patent/EP1889270A4/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/48—Conductive polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/24—Electrodes characterised by structural features of the materials making up or comprised in the electrodes, e.g. form, surface area or porosity; characterised by the structural features of powders or particles used therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/26—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features
    • H01G11/28—Electrodes characterised by their structure, e.g. multi-layered, porosity or surface features arranged or disposed on a current collector; Layers or phases between electrodes and current collectors, e.g. adhesives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
    • 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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0438—Processes of manufacture in general by electrochemical processing
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0438—Processes of manufacture in general by electrochemical processing
    • H01M4/0464—Electro organic synthesis
    • H01M4/0466—Electrochemical polymerisation
    • 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
    • H01M4/137—Electrodes based on electro-active polymers
    • 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
    • H01M4/1399—Processes of manufacture of electrodes based on electro-active polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • H01M4/602—Polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • H01M4/602—Polymers
    • H01M4/606—Polymers containing aromatic main chain polymers
    • 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
    • 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
    • Y02E60/13—Energy storage using capacitors
    • 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
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

  • the present invention relates to a method for producing an electrode for electrochemical element and a method for producing an electrochemical element with the electrode, and for more detail, relates to a method for producing an electrode for an electrochemical element and a method for producing an electrochemical element with the electrode in which energy density is improved and which is excellent in output characteristics.
  • an electric automobile and hybrid car have been expected instead of a gasoline-powered vehicle and diesel-powered vehicle which are engine-driven.
  • an electrochemical device having high energy density and high output density properties are used as a power source for driving a motor.
  • a secondary battery and a double electric layer capacitor are listed as this electrochemical device.
  • the secondary battery a lead battery, nickel/cadmium battery, nickel hydride battery, or proton battery and so on are listed. These secondary battery uses acidic or alkaline aqueous electrolyte solution which are high in ionic conductivity, thereby to have excellent output characteristics that large electric current is obtained when charging and discharging, however electrolysis voltage of water is 1.23V, therefore higher voltage may not be obtained. As a power source of the electric automobile, a high voltage of approximately 200V is required, therefore many batteries by just that much must be connected in series, resulting in disadvantage for downsizing and trimming weight of the power source.
  • a lithium ion secondary battery using organic electrolyte solution As a secondary battery of high voltage type, a lithium ion secondary battery using organic electrolyte solution is known.
  • This lithium ion secondary battery uses an organic solvent with high decomposition voltage as an electrolytic solvent, therefore when the lithium ion showing the lowest potential is an electric charge relating to charge/discharge reaction, potential of 3V or more is shown.
  • the lithium ion secondary battery brings a battery using carbon as a negative electrode occluding and releasing the lithium ion and lithium cobalt oxide (LiCoO 2 ) as a positive electrode into mainstream.
  • An electrolyte solution dissolving lithium salt such as hexafluorophosphate lithium (LiPF 6 ) into a solvent such as ethylene carbonate and propylene carbonate is used.
  • this lithium ion secondary battery is high in voltage and high in energy density to be excellent as a power source, however charge reaction is occlusion and release of the lithium ion of the electrode, therefore the secondary battery has a problem to be inferior in output characteristics, which is a disadvantage for the power source for the electric automobile requiring large instantaneous current.
  • there is an approach using derivative of polythiophene as a positive electrode for improving the charge/discharge property at a high voltage Japanese Laid-Open Patent Publication No.2003-297362.
  • An double electric layer capacitor uses a polarizable electrode such as activated carbon as positive and negative eletrodes, and uses a solution dissolving quaternary ammonium salt of boron tetrafluoride or phosphorus hexafuoride into an organic solvent such as propylene carbonate.
  • the double electric layer capacitor regards an double electric layer generating at the boundary surface between the surface of the electrode and the electrolyte solution as an electric capacitance, and there is no reaction involving ions such as a battery, thus the charge/discharge property is high and deterioration in capacity due to charge/discharge cycle is reduced.
  • an electrochemical capacitor using conductive polymer such as polyaniline, polypyrrole, polyacene, and polythiophene derivatives performs charge and discharge by p-doping or n-doping of anion or cation in non-aqueous electrolyte solution onto the conductive polymer.
  • the potential of this doping is low at a side of negative electrode and high at a side of positive electrode, therefore high voltage property is obtained (Japanese Laid-Open Patent Publication No.2000-315527).
  • an energy storage device such as a battery or super capacitor, that includes at least two electrodes, at least one of the electrodes includes an electrically conducting substrate having a layer of energy accumulating redox polymer complex compound of transition metal having at least two different degrees of oxidation, which polymer complex compound is formed of stacked transition metal complex monomers.
  • the stacked transition metal complex monomers have a planar structure with the deviation from the plane of no greater than 0.1 nm and a branched system of conjugated pi-bonds
  • the polymer complex compound of transition metal can be formed as a polymer metal complex with substituted tetra-dentate Schiff s base, and the layer thickness of redox polymer is within the range 1 nm-20 micrometer (International Patent Publication No.WO03/065536).
  • the above polymer complex compound may be used for both positive and negative electrodes since it's central metal could be reversibly oxidized-reduced.
  • the capacitor using these electrodes as the both electrodes allows to have a high operating voltage of 3V and a high energy density of 300Jg "1 , and a method for producing it by which this energy density is obtained is also described (International Patent Publication No. WO 04/030123). Summary of the Invention
  • an object of the present invention is to provide a method for producing an electrode for an electrochemical element and a method for producing an electrochemical element with the electrode having a high energy density and excellent output characteristics.
  • the present invention has had discussions on a method for producing electrode to solve the above problems. Consequently, the present invention provides a method for forming a thin and uniform electrode film more effectively through a method for producing an electrode for an electrochemical element, characterized by absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 300Om ⁇ "1 and having an average pore diameter in the range of 0.4 to lOOnm, performing electrolysis polymerization by applying pulse voltage using said conductive porous material as an electrode in electrolyte solution to stack said monomers for polymerization, and forming a conductive polymer layer on the surface of the conductive porous material.
  • the present invention makes it possible to produce an electrochemical element with the said electrode for the electrochemical element in the series of the steps through the electrolysis polymerization by applying pulse voltage from the external port of the electrochemical element after assembling the structure of the electrochemical element
  • the present invention enables more effectively thin and uniform coating of the surface of an electrode structure of a conductive porous material having a specific surface area of 100 to 300Om ⁇ "1 and having an average pore diameter in the range of 0.4 to lOOnm with polymer complex compound of transition metal, namely enables more effectively an increase of surface area compared to film thickness, consequently the electrode prepared by the present method increases ratio of doping and dedoping per unit volume against films of anion and cation, and achieves improvement of rate property and cycle property, resulting in an electrochemical device use electrode having high power properties.
  • the electrode prepared as described above is also possible to form the electrode film without blocking hole portions of porous material, therefore surface area is increased and energy density is improved. As a result, an electrochemical device use electrode which is excellent in output characteristics and high energy density can be obtained.
  • the double electric layer capacitor produced by the method of the present invention is formed as the electrode constituent of films in which polymer complex compound of transition metal is formed on the surface of the conductive porous material, such electrode can be used as a constituent element of the device such as the battery or capacitor as it is. Accordingly, it is possible to obtain in simplified and reduced steps the electrode for the electrochemical element including polymer complex compound of transition metal, which is excellent in output property and enhanced in energy density.
  • Fig 1. is a schematic view showing a stacked state of polymer metal complex (a - oxidized state, b - reduced state).
  • Fig 2. a) is a schematic view showing polymer metal complex in an oxidized state bonded on electrode surface by chemical adsorption
  • b) is a schematic view showing polymer metal complex in a reduced state bonded on the electrode surface by the chemical adsorption.
  • Fig 3. a) is a schematic view when polymer metal complex is in a neutral state, b) is a schematic view when polymer metal complex is in an oxidized state.
  • Fig. 4 is a cross sectional view of a double electric layer capacitor produced by a method of the present invention.
  • the process for adsorbing monomers for polymerization on the surface of the conductive porous material having a specific surface area in the range of 100 to 3000m 2 /g and having an average pore diameter in the range of 0.4 to 100 nm it is preferable to employ a process for adsorbing monomers for polymerization on the surface of the conductive porous material by removing solvent in the solution of monomers for polymerization after impregnating the conductive porous material with solution of monomers for polymerization.
  • the process is performed in such a way that the conductive porous material, for instance, activated carbon fabric woven in the form of cloth is impregnated with the solution of the monomers for polymerization, subsequently pulled up, and then a solvent in the solution of monomers for polymerization is removed by drying treatment, for instance. Removal of the solvent allows the monomers for polymerization to remain in the state of adhering so as not to easily desorb due to adsorptive power of the activated carbon.
  • the conductive porous material for instance, activated carbon fabric woven in the form of cloth
  • a solvent in the solution of monomers for polymerization is removed by drying treatment, for instance. Removal of the solvent allows the monomers for polymerization to remain in the state of adhering so as not to easily desorb due to adsorptive power of the activated carbon.
  • the conductive porous material used herein is preferable to be conductive porous material having a specific surface area in the range of 100 to 3000m 2 /g and having an average pore diameter in the range of 0.4 to 100 nm, specifically activated carbon, and particularly preferable to be activated carbon fabric woven in the form of cloth.
  • the conductive porous material may be molded in the form of disc, in which activated carbon powder, acetylene black, and polytetrafluorethylene as binder are blended respectively with 77: 20: 3 wt %.
  • the solution of the monomers for polymerization used herein is preferable to be a complex monomer solution of a transition metal having at least two different oxidation numbers
  • the conductive polymer formed by electrolysis polymerization is preferable to be an energy storage redox polymer layer including a polymer complex compound of a transition metal, which stores energy through the redox reaction.
  • electrolysis polymerization mode for instance, potential sweep polymerization method, constant potential polymerization method, constant current polymerization method, and potential step method as well as potential pulse method are listed.
  • potential pulse method may be used in the present invention.
  • the monomers of polymerization are adsorbed on the surface of the conductive porous material due to the effects of taking the monomers for polymerization in the pore as well as adsorbing power of substance which the conductive porous material holds.
  • polymerization reaction may develop remaining the state that the monomers of polymerization are thinly and uniformly adsorbed on the surface of the conductive porous material, thereby effecting conductive polymer.
  • Conditions of the electrolysis polymerization in the method for producing electrochemical elements according to the present invention are as follows.
  • the specific surface area of the electrode substrate preferably may be 200 to 3000m 2 g "1 , more preferably 1000 to 300QmV 1 .
  • the electrolysis polymerization on this substrate may be performed under the following condition of the electrolysis time, the downtime, the polymerization charge and the number of pulse.
  • the electrolysis time may be 0.1 to 60 second, preferably 0.5 to 10 second, more preferably 0.7 to 5 second.
  • the downtime may be 10 to 300 second, preferably 10 to 60 second, more preferably 20 to 30 second.
  • a pulse ratio which defines as a proportion of a pulse repetition time (the electrolysis time + the downtime) to the electrolysis time, is less than 1500, preferably less than 60, and less than 30.
  • down-state means that value of the electric potential becomes the value at which the polymerization of the monomer stops.
  • value of the electric potential may be -2 to +0.5 V, preferably -1 to +0.3 V, more preferably -0.5 to 0 V.
  • pulse voltage condition may be Ag/Ag+ of 0.5 to 1.0V, preferably AgZAg+ of 0.5 to 0.7V, more preferably AgZAg+ of 0.5 to 0.6V. If voltage is in this range, an enough amount of complex monomer oxide is formed through an electrochemical reaction, therefore the complex polymer compound of transition metal is formed efficiently, and further the formed complex polymer compound of transition metal is difficult to form over-oxide, consequently complex polymer compound of high-capacity density transition metal is formed.
  • polymerization is performed by immersing the above electrode into the electrolyte solution and applying pulse voltage, however not only such a double pole type but also triple pole type may be used, polymerization of which is performed by applying an constant potential to the reference electrode with using a working electrode and a counter electrode as well as the reference electrode or flowing oxidation current.
  • the number of cycle may be 100 to 10000 cycles, preferably 100 to 5000 cycles, more preferably 200 to 2000 cycles. If the number of cycle is in this range, an amount of production of the complex polymer compound of transition metal is enough, in addition, the complex polymer compound of transition metal is not produced excessively, therefore a thin film of the complex polymer compound of transition metal is maintained.
  • the electrolyte solution used for the electrolysis polymerization of the present invention is preferably non-aqueous type using organic solvent, and a salt which is soluble in organic solvent and which can ensure ions conductivity is preferably used in the supporting electrolyte solution, and both the kind and concentration are not limited.
  • an organic solvent preferably contains one or more substances selected from a group constituted of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, sulphorane, acetonitrile, and dimethoky ethane.
  • lithium salt having the lithium ion, quaternary ammonium salt or quaternary phosphonium salt having quaternary ammonium cation or quaternary phosphonium cation respectively may be listed.
  • LiPF 6 LiBF 4 , LiClO 4 , LiN(CF 3 SO 2 ) 2 , LiCF 3 SO 3 , LiC(SO 2 CF 3 ) 3 , LiAsF 6 and LiSbF 6 and so on are listed.
  • quaternary ammonium salt or quaternary phosphonium salt a salt comprising cation expressed by Rl R2 R3 R4N+ or Rl R2 R3 R4 P+ (where Rl, R2, R3, R4 are alkyl group with the number of carbon of 1 to 6), and anion consisting of PF6-, BF4-, C1O4-, N(CF3SO2)2-, C3SO3-, C(SO2CF3)3-, AsF6- or SbF6- is preferable. Specifically, PF6-, BF4-, C1O4- or N(CF3SO2)2- is used as anion.
  • the most preferable electrolyte solution utilized in the present electrolysis polymerization is propylene carbonate (PC) dissolving (C 2 Hs) 4 NBF 4 in the density unit of [mol/liter].
  • the conductive polymer layer formed by the present electrolysis polymerization is the layer of an energy storage redox polymer including a polymer complex compound of a transition metal, which stores energy through the redox reaction.
  • the polymer complex compound of transition metal may be the polymer metal complex of tetra-dentate Schiff's base, in particular, represented by the following graphical formula:
  • R is H or electron donating substituent
  • R' is H or halogen
  • n is an integer number of 2 to 200000.
  • transition metal Me Ni, Pd, Co, Cu, and Fe are listed.
  • R CH 3 O-, C 2 H 5 O-, HO-, and -CH 3 are listed.
  • a redox polymer complex compound of transition metal is configured as "unidirectional" or “stack" macromolecules.
  • Polymer metal complexes are bonded with the inter-electrode surface due to chemisorption.
  • Charge transfer in polymer metal complexes is effected due to "electron hopping" between metal centers with different states of charge. Charge transfer can be described mathematically with the aid of a diffusion model. Oxidation or reduction of polymer metal complexes, associated with the change in the states of charge of metal centers and with directed charge transfer over polymer chain, is accompanied, to maintain overall electrical neutrality of the system, by penetration into a polymer of charge-compensating counter-ions that are present in the electrolyte solution surrounding the polymer or by the egress of charge-compensating counter-ions from the polymer.
  • the existence of metal centers in different states of charge in a polymer metal complex is the reason for calling them "mixed-valence” complexes or "partially-oxidized” complexes.
  • the metal center in the exemplary polymer complex poly- may be in one of three states of charge: Ni 2+ -neutral state; Ni 3+ -oxidized state; Ni + -reduced state.
  • this polymer is in the neutral state ( Figure 3a)
  • Figure 3a When this polymer is in the neutral state ( Figure 3a), its monomer fragments are not charged and the charge of the metal center is compensated by the charge of the ligand environment.
  • the electrode of the present invention may use polymer metal complex in an oxidized state as a charged state of positive electrode and use a reduced state as a charged state of negative electrode. Therefore, the electrode of the present invention is allowed to be used for both positive and negative electrodes.
  • the present invention more effectively enables thin and uniform coating of the surface of an conductive porous material with polymer complex compound of transition metal, namely more effectively enables an increase of surface area compared to film thickness, consequently the electrode prepared by the present method increases ratio of doping and dedoping per unit volume against films of anion and cation, and achieves improvement of rate property and cycle property, resulting in an electrochemical device use electrode having high power properties.
  • a secondary battery may be prepared as following.
  • a non-aqueous electrolyte solution dissolving lithium salt as a solute is used as an electrolyte solution.
  • an electrode by a method of the present invention is used as a positive electrode, and an electrode occluding and releasing lithium such as lithium metal or carbon capable of occluding and releasing lithium is used as a negative electrode.
  • the secondary battery may also be produced by using the electrode of the present invention for the negative electrode, and using lithium metal oxide such as LiCoO 2 for the positive electrode. In any cases, output characteristics and energy density are improved.
  • acid aqueous solution having proton as an electrolyte solution is used.
  • an electrode of the present invention is used as a positive electrode and the negative electrode of the proton battery such as quinoxaline based polymer is used as a negative electrode.
  • the above proton battery is high in energy density.
  • a double electric layer capacitor may be prepared as following.
  • the above non-aqueous type may be used as an electrolyte solution.
  • this double electric layer capacitor improves in energy density.
  • an electrode having the double electric layer capacitor for a positive electrode and using the negative electrode of the present invention as a negative electrode, such as activated carbon for a negative electrode this double electric layer capacitor improves in energy density in the same way.
  • An electrochemical capacitor may be prepared as following.
  • an electrolyte solution a non-aqueous electrolyte solution dissolving lithium salt, quaternary ammonium salt or quaternary phosphonium salt as a solute is used.
  • a conductive polymer such as polythiophene having oxidation-reduction reaction responsiveness for a negative electrode
  • metal oxide such as the conductive polymer or ruthenium oxide as the positive electrode and using the negative electrode of the present invention as a negative electrode
  • energy density improves.
  • the polymer complex electrode by the method of the present invention may be used for both positive and negative electrodes, therefore the electrode of the present invention may be used for both electrodes, thereby that allows a electrochemical capacitor having high energy density to be obtained.
  • the double electric layer capacitor manufactured by the present invention is provided with a metallic casing 1 in the form of a flat vessel and cover 2, an activated carbon electrode 4, a separator 5 inserted between both activated carbon electrodes 4 and a top sealing gasket 6 for sealing surrounding area of the casing 1 and the cover 2.
  • the manufacturing process of such a double electric layer capacitor by the present invention is as follow.
  • the activated carbon fabric woven in the form of cloth is utilized as the activated carbon electrode 4.
  • the electrode 4 is impregnated with the solution of the monomers for polymerization, subsequently pulled up, and then a solvent in the solution of monomers for polymerization is removed by drying treatment, for instance. Removal of the solvent allows the monomers for polymerization to remain in the state of adhering so as not to easily desorb due to adsorptive power of the activated carbon.
  • the inside of the casing 1 is sealed by superimposing the separator 5 on the activated carbon electrode 4, fitting the cover 2 on the casing 1 and caulking the casing 1 around the top sealing gasket 6, after impregnating the activated carbon electrode 4 with electrolyte solution by pouring thereon.
  • the electrolysis polymerization of monomers for polymerization is performed by applying pulse voltage from the external electrode of the electrochemical element.
  • a conductive polymer is formed on the surface of the activated carbon electrode.
  • electric energy, which has been applied during the electrolysis polymerization is efficiently consumed for the polymerization reaction because the monomers for polymerization, which changes into a conductive polymer, remain in the state of adhering to the surface of the electrode. This enables to minimize the electric energy for forming the conductive polymer with a desired thickness, and also to reduce polymerization time.
  • the conditions regarding the conductive porous material, the solution of monomers for polymerization, the electrolysis polymerization, the electrolytic solution and the conductive polymer layer which are utilized in the manufacturing process of the electrochemical element according to the present invention are equivalent to those in the manufacturing process of the electrode for the electrochemical element described above.
  • the separator utilized in the manufacturing process of the electrochemical element according to the present invention it is preferable to employ a micro porous film or non woven fabric made of polyethylene or polypropylene in the range of 0.05 to 0.1 mm in thickness
  • a micro porous film or non woven fabric made of polyethylene or polypropylene in the range of 0.05 to 0.1 mm in thickness

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Abstract

To provide a method for producing an electrode for electrochemical element which is improved in energy density and is excellent in output characteristics. The present invention provides a method for producing an electrode for an electrochemical element, characterized by absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 3000m2g-1 and having an average pore diameter in the range of 0.4 to 100nm, performing electrolysis polymerization by applying pulse voltage using said conductive porous material as an electrode in electrolyte solution to stack said monomers for polymerization, and forming a conductive polymer layer on the surface of the conductive porous material : wherein a thin and uniform electrode film is formed, namely the electrode for electrochemical element which is excellent in output characteristics and improves energy density is manufactured according to the method. In addition, the present invention provides a method for producing an electrochemical element, characterized by forming a conductive polymer layer on the surface of the conductive porous material within an outer casing by a step of absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 3000m2g-1 and having an average pore diameter in the range of 0.4 to 100nm forming a electrochemical cell by using the conductive porous material wherein the monomers for polymerization are absorbed in the pores, putting said electrochemical cell and the electrolyte solution in an outer casing , and performing electrolysis polymerization of the monomers for polymerization in said electrolyte solution by applying pulse voltage from a external electrode of the outer casing to stack said monomer for polymerization : wherein it is possible to produce an electrochemical element with the said electrode for the electrochemical element in the series of the steps through the electrolysis polymerization, thereby reducing the number of steps required for producing the electrochemical element.

Description

DESCRIPTION
METHOD FOR PRODUCING ELECTRODE FOR ELECTROCHEMICALELEMENTAND METHOD FOR PRODUCING ELECTROCHEMICAL ELEMENT WITH THE ELECTRODE
Field of the Invention
The present invention relates to a method for producing an electrode for electrochemical element and a method for producing an electrochemical element with the electrode, and for more detail, relates to a method for producing an electrode for an electrochemical element and a method for producing an electrochemical element with the electrode in which energy density is improved and which is excellent in output characteristics.
Background of the Invention
In these years, an electric automobile and hybrid car have been expected instead of a gasoline-powered vehicle and diesel-powered vehicle which are engine-driven. In these electric automobile and hybrid car, an electrochemical device having high energy density and high output density properties are used as a power source for driving a motor. A secondary battery and a double electric layer capacitor are listed as this electrochemical device.
As the secondary battery, a lead battery, nickel/cadmium battery, nickel hydride battery, or proton battery and so on are listed. These secondary battery uses acidic or alkaline aqueous electrolyte solution which are high in ionic conductivity, thereby to have excellent output characteristics that large electric current is obtained when charging and discharging, however electrolysis voltage of water is 1.23V, therefore higher voltage may not be obtained. As a power source of the electric automobile, a high voltage of approximately 200V is required, therefore many batteries by just that much must be connected in series, resulting in disadvantage for downsizing and trimming weight of the power source.
As a secondary battery of high voltage type, a lithium ion secondary battery using organic electrolyte solution is known. This lithium ion secondary battery uses an organic solvent with high decomposition voltage as an electrolytic solvent, therefore when the lithium ion showing the lowest potential is an electric charge relating to charge/discharge reaction, potential of 3V or more is shown. The lithium ion secondary battery brings a battery using carbon as a negative electrode occluding and releasing the lithium ion and lithium cobalt oxide (LiCoO2) as a positive electrode into mainstream. An electrolyte solution dissolving lithium salt such as hexafluorophosphate lithium (LiPF6) into a solvent such as ethylene carbonate and propylene carbonate is used. However, this lithium ion secondary battery is high in voltage and high in energy density to be excellent as a power source, however charge reaction is occlusion and release of the lithium ion of the electrode, therefore the secondary battery has a problem to be inferior in output characteristics, which is a disadvantage for the power source for the electric automobile requiring large instantaneous current. Then, there is an approach using derivative of polythiophene as a positive electrode for improving the charge/discharge property at a high voltage (Japanese Laid-Open Patent Publication No.2003-297362).
An double electric layer capacitor uses a polarizable electrode such as activated carbon as positive and negative eletrodes, and uses a solution dissolving quaternary ammonium salt of boron tetrafluoride or phosphorus hexafuoride into an organic solvent such as propylene carbonate. Thus, the double electric layer capacitor regards an double electric layer generating at the boundary surface between the surface of the electrode and the electrolyte solution as an electric capacitance, and there is no reaction involving ions such as a battery, thus the charge/discharge property is high and deterioration in capacity due to charge/discharge cycle is reduced. However, energy density due to double layer capacity is low in the energy density compared to the battery, that is significantly insufficient as a power source of the electric automobile. At the same time, there is an approach using polypyrrole as a positive electrode for the purpose of large capacity (Japanese Laid-Open Patent Publication No.H6-104141). Then, an electrochemical capacitor using conductive polymer and metal oxide as an electrode material which is high in energy density and high in output characteristics has been developed. An electric charge storage mechanism of this electrochemical capacitor is adsorption and desorption of anion and cation in the electrolyte solution onto the electrode, and both energy density and output characteristics are excellent. Particularly, an electrochemical capacitor using conductive polymer such as polyaniline, polypyrrole, polyacene, and polythiophene derivatives performs charge and discharge by p-doping or n-doping of anion or cation in non-aqueous electrolyte solution onto the conductive polymer. The potential of this doping is low at a side of negative electrode and high at a side of positive electrode, therefore high voltage property is obtained (Japanese Laid-Open Patent Publication No.2000-315527).
However, the capacitor using the above conductive polymer was also desired to improved energy density and out put characteristics. In order to comply with the above desire, an energy storage device, such as a battery or super capacitor, is developed that includes at least two electrodes, at least one of the electrodes includes an electrically conducting substrate having a layer of energy accumulating redox polymer complex compound of transition metal having at least two different degrees of oxidation, which polymer complex compound is formed of stacked transition metal complex monomers. In the energy storage device, the stacked transition metal complex monomers have a planar structure with the deviation from the plane of no greater than 0.1 nm and a branched system of conjugated pi-bonds, the polymer complex compound of transition metal can be formed as a polymer metal complex with substituted tetra-dentate Schiff s base, and the layer thickness of redox polymer is within the range 1 nm-20 micrometer (International Patent Publication No.WO03/065536). Further, the above polymer complex compound may be used for both positive and negative electrodes since it's central metal could be reversibly oxidized-reduced. The capacitor using these electrodes as the both electrodes allows to have a high operating voltage of 3V and a high energy density of 300Jg"1, and a method for producing it by which this energy density is obtained is also described (International Patent Publication No. WO 04/030123). Summary of the Invention
Problems to Be Solved by the Invention
However, demand for downsizing for the use of power source of an electric automobile and so on is constant, therefore there is a strong demand for enhanced energy density and enhanced output characteristics. Then, an object of the present invention is to provide a method for producing an electrode for an electrochemical element and a method for producing an electrochemical element with the electrode having a high energy density and excellent output characteristics.
Means for Solving the Problems
The present invention has had discussions on a method for producing electrode to solve the above problems. Consequently, the present invention provides a method for forming a thin and uniform electrode film more effectively through a method for producing an electrode for an electrochemical element, characterized by absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 300Om^"1 and having an average pore diameter in the range of 0.4 to lOOnm, performing electrolysis polymerization by applying pulse voltage using said conductive porous material as an electrode in electrolyte solution to stack said monomers for polymerization, and forming a conductive polymer layer on the surface of the conductive porous material.
Further, through the method for producing an electrochemical element, characterized by forming a conductive polymer layer on the surface of the conductive porous material within an outer casing by a step of absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 3000m2g"1 and having an average pore diameter in the range of 0.4 to lOOnm, forming a electrochemical cell by using the conductive porous material wherein the monomers for polymerization are absorbed in the pores, putting said electrochemical cell and the electrolyte solution in an outer casing , and performing electrolysis polymerization of the monomers for polymerization in said electrolyte solution by applying pulse voltage from a external electrode of the outer casing to stack said monomer for polymerization, the present invention makes it possible to produce an electrochemical element with the said electrode for the electrochemical element in the series of the steps through the electrolysis polymerization by applying pulse voltage from the external port of the electrochemical element after assembling the structure of the electrochemical element, thereby reducing the number of steps required for producing the electrochemical element.
Effect of the Invention
The present invention enables more effectively thin and uniform coating of the surface of an electrode structure of a conductive porous material having a specific surface area of 100 to 300Om^"1 and having an average pore diameter in the range of 0.4 to lOOnm with polymer complex compound of transition metal, namely enables more effectively an increase of surface area compared to film thickness, consequently the electrode prepared by the present method increases ratio of doping and dedoping per unit volume against films of anion and cation, and achieves improvement of rate property and cycle property, resulting in an electrochemical device use electrode having high power properties. The electrode prepared as described above is also possible to form the electrode film without blocking hole portions of porous material, therefore surface area is increased and energy density is improved. As a result, an electrochemical device use electrode which is excellent in output characteristics and high energy density can be obtained.
Also, because the double electric layer capacitor produced by the method of the present invention is formed as the electrode constituent of films in which polymer complex compound of transition metal is formed on the surface of the conductive porous material, such electrode can be used as a constituent element of the device such as the battery or capacitor as it is. Accordingly, it is possible to obtain in simplified and reduced steps the electrode for the electrochemical element including polymer complex compound of transition metal, which is excellent in output property and enhanced in energy density.
Brief Description of the Drawings
Fig 1. is a schematic view showing a stacked state of polymer metal complex (a - oxidized state, b - reduced state).
Fig 2. a) is a schematic view showing polymer metal complex in an oxidized state bonded on electrode surface by chemical adsorption, b) is a schematic view showing polymer metal complex in a reduced state bonded on the electrode surface by the chemical adsorption.
Fig 3. a) is a schematic view when polymer metal complex is in a neutral state, b) is a schematic view when polymer metal complex is in an oxidized state.
Fig. 4 is a cross sectional view of a double electric layer capacitor produced by a method of the present invention.
Detailed Description of the Invention
First, the producing steps of the electrode for the electrochemical element according to the present invention will be explained.
As to the process for adsorbing monomers for polymerization on the surface of the conductive porous material having a specific surface area in the range of 100 to 3000m2/g and having an average pore diameter in the range of 0.4 to 100 nm, it is preferable to employ a process for adsorbing monomers for polymerization on the surface of the conductive porous material by removing solvent in the solution of monomers for polymerization after impregnating the conductive porous material with solution of monomers for polymerization. Specifically, the process is performed in such a way that the conductive porous material, for instance, activated carbon fabric woven in the form of cloth is impregnated with the solution of the monomers for polymerization, subsequently pulled up, and then a solvent in the solution of monomers for polymerization is removed by drying treatment, for instance. Removal of the solvent allows the monomers for polymerization to remain in the state of adhering so as not to easily desorb due to adsorptive power of the activated carbon.
The conductive porous material used herein is preferable to be conductive porous material having a specific surface area in the range of 100 to 3000m2/g and having an average pore diameter in the range of 0.4 to 100 nm, specifically activated carbon, and particularly preferable to be activated carbon fabric woven in the form of cloth. As for the rest, the conductive porous material may be molded in the form of disc, in which activated carbon powder, acetylene black, and polytetrafluorethylene as binder are blended respectively with 77: 20: 3 wt %.
In addition, the solution of the monomers for polymerization used herein is preferable to be a complex monomer solution of a transition metal having at least two different oxidation numbers, and the conductive polymer formed by electrolysis polymerization is preferable to be an energy storage redox polymer layer including a polymer complex compound of a transition metal, which stores energy through the redox reaction.
As to the process for performing electrolysis polymerization by applying pulse voltage using said conductive porous material on the surface of which monomers for polymerization are adsorbing as an electrode in electrolyte solution to stack said monomers for polymerization, and forming a conductive polymer layer on the surface of the conductive porous material, as electrolysis polymerization mode, for instance, potential sweep polymerization method, constant potential polymerization method, constant current polymerization method, and potential step method as well as potential pulse method are listed. However, the potential pulse method may be used in the present invention.
When electrolysis polymerization is performed under the condition of impregnating conductive porous material having very large specific surface area with the solution in which monomers for polymerization are dissolved or dispersed, partial polymerization reaction may develop on the conductive polymer stacked by the electrolysis polymerization to form irregularity on the polymer layer, thereby effecting uneven thickness. In addition, there is a constraint that a time interval for the electrolysis polymerization should be long in order to completely polymerize the monomers for polymerization in the solution. As long as an average pore diameter of the conductive porous material is in the range of 0.4nm to 100 nm, the monomers of polymerization are adsorbed on the surface of the conductive porous material due to the effects of taking the monomers for polymerization in the pore as well as adsorbing power of substance which the conductive porous material holds. In particular, it is possible to thinly and uniformly adsorb monomers for polymerization on the surface of the conductive porous material by removing solvent in the solution of monomers for polymerization after impregnating the conductive porous material with the solution of monomers for polymerization. When the electrolysis polymerization is performed in such condition, polymerization reaction may develop remaining the state that the monomers of polymerization are thinly and uniformly adsorbed on the surface of the conductive porous material, thereby effecting conductive polymer.
Conditions of the electrolysis polymerization in the method for producing electrochemical elements according to the present invention are as follows. In order to enhance the energy density of the polymer complex compound of transition metal, it is necessary to optimize a large variety of parameters relating to the electrolysis polymerization. In particular, it is desired to optimize the electrolysis time, the downtime and the polymerization charge. In addition, as a result of study about a improvement in the energy density of said electrode, not only these parameters but also a specific surface area of the electrode substrate influences on the enhancement of energy density. In the suitable characteristics, the specific surface area of the electrode substrate preferably may be 200 to 3000m2g"1, more preferably 1000 to 300QmV1. further more preferably 1500 to 250OmV1- Further, the electrolysis polymerization on this substrate may be performed under the following condition of the electrolysis time, the downtime, the polymerization charge and the number of pulse. Namely, the electrolysis time may be 0.1 to 60 second, preferably 0.5 to 10 second, more preferably 0.7 to 5 second. The downtime may be 10 to 300 second, preferably 10 to 60 second, more preferably 20 to 30 second. Accordingly, a pulse ratio, which defines as a proportion of a pulse repetition time (the electrolysis time + the downtime) to the electrolysis time, is less than 1500, preferably less than 60, and less than 30. When the electrolysis polymerization is performed to the electrode substrate having high-specific surface area characteristics within these ranges, the optimal conditions for the diffusion and the polymerization of the complex monomer oxidized during the electrolytic times into the holes of the substrate or the defects formed in the polymer could be obtained, thereby forming a thin polymer film and as the result the electrode having a high energy density could efficiently be produced. As to the downtime, down-state means that value of the electric potential becomes the value at which the polymerization of the monomer stops. Such value of the electric potential may be -2 to +0.5 V, preferably -1 to +0.3 V, more preferably -0.5 to 0 V.
In the present invention, pulse voltage condition may be Ag/Ag+ of 0.5 to 1.0V, preferably AgZAg+ of 0.5 to 0.7V, more preferably AgZAg+ of 0.5 to 0.6V. If voltage is in this range, an enough amount of complex monomer oxide is formed through an electrochemical reaction, therefore the complex polymer compound of transition metal is formed efficiently, and further the formed complex polymer compound of transition metal is difficult to form over-oxide, consequently complex polymer compound of high-capacity density transition metal is formed. In addition, in the electrolysis polymerization of the present invention, polymerization is performed by immersing the above electrode into the electrolyte solution and applying pulse voltage, however not only such a double pole type but also triple pole type may be used, polymerization of which is performed by applying an constant potential to the reference electrode with using a working electrode and a counter electrode as well as the reference electrode or flowing oxidation current.
In the electrolysis polymerization of the present invention, the number of cycle may be 100 to 10000 cycles, preferably 100 to 5000 cycles, more preferably 200 to 2000 cycles. If the number of cycle is in this range, an amount of production of the complex polymer compound of transition metal is enough, in addition, the complex polymer compound of transition metal is not produced excessively, therefore a thin film of the complex polymer compound of transition metal is maintained.
The electrolyte solution used for the electrolysis polymerization of the present invention is preferably non-aqueous type using organic solvent, and a salt which is soluble in organic solvent and which can ensure ions conductivity is preferably used in the supporting electrolyte solution, and both the kind and concentration are not limited.
Specifically, an organic solvent preferably contains one or more substances selected from a group constituted of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, sulphorane, acetonitrile, and dimethoky ethane. As a solute, lithium salt having the lithium ion, quaternary ammonium salt or quaternary phosphonium salt having quaternary ammonium cation or quaternary phosphonium cation respectively may be listed. As lithium salt, LiPF6, LiBF4, LiClO4, LiN(CF3SO2)2, LiCF3SO3, LiC(SO2CF3)3, LiAsF6 and LiSbF6 and so on are listed. Also as quaternary ammonium salt or quaternary phosphonium salt, a salt comprising cation expressed by Rl R2 R3 R4N+ or Rl R2 R3 R4 P+ (where Rl, R2, R3, R4 are alkyl group with the number of carbon of 1 to 6), and anion consisting of PF6-, BF4-, C1O4-, N(CF3SO2)2-, C3SO3-, C(SO2CF3)3-, AsF6- or SbF6- is preferable. Specifically, PF6-, BF4-, C1O4- or N(CF3SO2)2- is used as anion.
The most preferable electrolyte solution utilized in the present electrolysis polymerization is propylene carbonate (PC) dissolving (C2Hs)4NBF4 in the density unit of [mol/liter].
The conductive polymer layer formed by the present electrolysis polymerization is the layer of an energy storage redox polymer including a polymer complex compound of a transition metal, which stores energy through the redox reaction. The polymer complex compound of transition metal may be the polymer metal complex of tetra-dentate Schiff's base, in particular, represented by the following graphical formula:
where Y is
CH2 -CH2 / \
CHs CH3
I I
CH3- C - C-CH3 / \
or
H2C- • C H2 - -CH 2
where Me is transition metal,
R is H or electron donating substituent, R' is H or halogen, and n is an integer number of 2 to 200000.]
In particular, as preferable transition metal Me, Ni, Pd, Co, Cu, and Fe are listed. As preferable R, CH3O-, C2H5O-, HO-, and -CH3 are listed.
According to the principles of the present invention a redox polymer complex compound of transition metal is configured as "unidirectional" or "stack" macromolecules.
Representatives of the group of polymer metal suitable for the electrodes fall into the class of redox polymers, which provide novice anisotropic electronic redox conduction. For more detail on these polymer complexes, see Timonov A. M., Shagisultanova G. A., Popeko I. E. Polymeric Partially-Oxidized Complexes of Nickel,
Palladium and Platinum with Schiff Bases//Workshop on Platinum Chemistry.
Fundamental and Applied Aspects. Italy, Ferrara, 1991. P. 28. Formation of bonds between fragments can be considered, in the first approximation, as a donor-acceptor intermolecular interaction between a ligand of one molecule and the metal center of another molecule. Formation of the so- called "unidimensional" or "stack" macromolecules takes place as a result of said interaction. Such a mechanism of the formation of "stack" structures of a polymer currently is best achieved when using monomers of square-planar spatial structure. Schematically this structure can be presented as follows :
Superficially a set of such macromolecules looks to the unaided eye like a solid transparent film on an electrode surface. The color of this film may vary depending on the nature of metal and presence of substitutes in the ligand structure. But when magnified, the stack structures become evident, see Figure 1.
Polymer metal complexes are bonded with the inter-electrode surface due to chemisorption.
Charge transfer in polymer metal complexes is effected due to "electron hopping" between metal centers with different states of charge. Charge transfer can be described mathematically with the aid of a diffusion model. Oxidation or reduction of polymer metal complexes, associated with the change in the states of charge of metal centers and with directed charge transfer over polymer chain, is accompanied, to maintain overall electrical neutrality of the system, by penetration into a polymer of charge-compensating counter-ions that are present in the electrolyte solution surrounding the polymer or by the egress of charge-compensating counter-ions from the polymer.
The existence of metal centers in different states of charge in a polymer metal complex is the reason for calling them "mixed-valence" complexes or "partially-oxidized" complexes. The metal center in the exemplary polymer complex poly- [Ni (CH3O-Salen)] may be in one of three states of charge: Ni2+-neutral state; Ni3+-oxidized state; Ni+-reduced state. When this polymer is in the neutral state (Figure 3a), its monomer fragments are not charged and the charge of the metal center is compensated by the charge of the ligand environment. When this polymer is in the oxidized state (Figure 3b), its monomer fragments have a positive charge, and when it is in the reduced state, its monomer fragments have a negative charge. To neutralize spatial (volume) charge of a polymer when the latter is in the oxidized state, electrolyte anions are introduced into the polymer structure. When this polymer is in the reduced state, neutralization of the net charge results due to the introduction of cations (see Fig. 2). The electrode of the present invention may use polymer metal complex in an oxidized state as a charged state of positive electrode and use a reduced state as a charged state of negative electrode. Therefore, the electrode of the present invention is allowed to be used for both positive and negative electrodes.
The present invention more effectively enables thin and uniform coating of the surface of an conductive porous material with polymer complex compound of transition metal, namely more effectively enables an increase of surface area compared to film thickness, consequently the electrode prepared by the present method increases ratio of doping and dedoping per unit volume against films of anion and cation, and achieves improvement of rate property and cycle property, resulting in an electrochemical device use electrode having high power properties.
An electrochemical element provided with an electrode for the electrochemical element produced by the method of the present invention will be explained below. (Secondary battery)
A secondary battery may be prepared as following. In the case of lithium secondary battery, a non-aqueous electrolyte solution dissolving lithium salt as a solute is used as an electrolyte solution. And, an electrode by a method of the present invention is used as a positive electrode, and an electrode occluding and releasing lithium such as lithium metal or carbon capable of occluding and releasing lithium is used as a negative electrode. The secondary battery may also be produced by using the electrode of the present invention for the negative electrode, and using lithium metal oxide such as LiCoO2 for the positive electrode. In any cases, output characteristics and energy density are improved.
When forming a proton battery, acid aqueous solution having proton as an electrolyte solution is used. And an electrode of the present invention is used as a positive electrode and the negative electrode of the proton battery such as quinoxaline based polymer is used as a negative electrode. The above proton battery is high in energy density.
(Double electric layer capacitor)
A double electric layer capacitor may be prepared as following. The above non-aqueous type may be used as an electrolyte solution. When using the electrode by the method of the present invention for a positive electrode and using an electrode having double electric layer capacity such as activated carbon for a negative electrode, this double electric layer capacitor improves in energy density. Also when using an electrode having the double electric layer capacitor for a positive electrode and using the negative electrode of the present invention as a negative electrode, such as activated carbon for a negative electrode, this double electric layer capacitor improves in energy density in the same way.
(Electrochemical capacitor)
An electrochemical capacitor may be prepared as following. As an electrolyte solution, a non-aqueous electrolyte solution dissolving lithium salt, quaternary ammonium salt or quaternary phosphonium salt as a solute is used. When using the electrode by the method of the present invention for a positive electrode and using a conductive polymer such as polythiophene having oxidation-reduction reaction responsiveness for a negative electrode, or when using metal oxide such as the conductive polymer or ruthenium oxide as the positive electrode and using the negative electrode of the present invention as a negative electrode, energy density improves. Further, the polymer complex electrode by the method of the present invention may be used for both positive and negative electrodes, therefore the electrode of the present invention may be used for both electrodes, thereby that allows a electrochemical capacitor having high energy density to be obtained. (Example)
In the following, a manufacturing process of an electrochemical element provided with an electrode for the electrochemical element will be explained with regard to one example of the present invention.
As illustrated in Fig. 4, the double electric layer capacitor manufactured by the present invention is provided with a metallic casing 1 in the form of a flat vessel and cover 2, an activated carbon electrode 4, a separator 5 inserted between both activated carbon electrodes 4 and a top sealing gasket 6 for sealing surrounding area of the casing 1 and the cover 2. The manufacturing process of such a double electric layer capacitor by the present invention is as follow.
First, the activated carbon fabric woven in the form of cloth is utilized as the activated carbon electrode 4. The electrode 4 is impregnated with the solution of the monomers for polymerization, subsequently pulled up, and then a solvent in the solution of monomers for polymerization is removed by drying treatment, for instance. Removal of the solvent allows the monomers for polymerization to remain in the state of adhering so as not to easily desorb due to adsorptive power of the activated carbon. Then, the inside of the casing 1 is sealed by superimposing the separator 5 on the activated carbon electrode 4, fitting the cover 2 on the casing 1 and caulking the casing 1 around the top sealing gasket 6, after impregnating the activated carbon electrode 4 with electrolyte solution by pouring thereon. Next, the electrolysis polymerization of monomers for polymerization is performed by applying pulse voltage from the external electrode of the electrochemical element. By performing such electrolysis polymerization, a conductive polymer is formed on the surface of the activated carbon electrode. In the case, electric energy, which has been applied during the electrolysis polymerization, is efficiently consumed for the polymerization reaction because the monomers for polymerization, which changes into a conductive polymer, remain in the state of adhering to the surface of the electrode. This enables to minimize the electric energy for forming the conductive polymer with a desired thickness, and also to reduce polymerization time.
The conditions regarding the conductive porous material, the solution of monomers for polymerization, the electrolysis polymerization, the electrolytic solution and the conductive polymer layer which are utilized in the manufacturing process of the electrochemical element according to the present invention are equivalent to those in the manufacturing process of the electrode for the electrochemical element described above.
In addition, as to the separator utilized in the manufacturing process of the electrochemical element according to the present invention, it is preferable to employ a micro porous film or non woven fabric made of polyethylene or polypropylene in the range of 0.05 to 0.1 mm in thickness Thus, because the double electric layer capacitor produced by the method of the present invention is formed as the electrode constituent of films in which polymer complex compound of transition metal is formed on the surface of the conductive porous material, such electrode can be used as a constituent element of the device such as the battery or capacitor as it is. Accordingly, it is possible to obtain in simplified and reduced steps the electrode for the electrochemical element including polymer complex compound of transition metal, which is excellent in output property and enhanced in energy density.

Claims

1. A method for producing an electrode for an electrochemical element, characterized by absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 3000m g" and having an average pore diameter in the range of 0.4 to lOOnm, performing electrolysis polymerization by applying pulse voltage using said conductive porous material as an electrode in electrolyte solution to stack said monomers for polymerization, and forming a conductive polymer layer on the surface of the conductive porous material.
2. The method for producing the electrode according to claim 1, characterized in that the monomers for polymerization are absorbed on the surface of the conductive porous material by impregnating said conductive porous material with solution of the monomers for polymerization and subsequent removing solvent in the solution of the monomers for polymerization.
3. The method for producing the electrode according to claim 1 or 2, wherein the monomers for polymerization are in the form of complex monomer solution of a transition metal having at least two oxidation numbers, and wherein the conductive polymer formed by the electrolysis polymerization is an energy storage redox polymer layer including the polymer complex compound of the transition metal so as to store energy through redox reaction.
4. The method for producing the electrode according to claim 3, wherein polymer complex compound of said transition metal is a polymer metal complex of tetra-dentate Schiff 's base.
5. The method for producing the electrode according to claim 4, wherein the polymer metal complex of said tetra-dentate Schiff ' s base comprises the polymer complex compound represented by the following graphical formula:
wherein Y is
CH2 -CH2 / \
CH3 CH3
I I
CH3- C - C-CH3 / \
or
Me is transition metal, , R is H or electron donating substituent, R' is H or halogen, and, n is an integer number of 2 to 200000.
6. The method for producing the electrode according to claim 5, wherein said transition metal Me is selected from a group constituted of Ni, Pd, Co, Cu and Fe.
7. The method for producing the electrode according to claim 5, wherein said R is selected from a group constituted of CH3O-, C2H5O-, HO- and CH3-.
8. A method for producing an electrochemical element, characterized by forming a conductive polymer layer on the surface of the conductive porous material within an outer casing by a step of absorbing monomers for polymerization on a surface of a conductive porous material having a specific surface area of 100 to 300Om^"1 and having an average pore diameter in the range of 0.4 to lOOnm forming a electrochemical cell by using the conductive porous material wherein the monomers for polymerization are absorbed in the pores, putting said electrochemical cell and the electrolyte solution in an outer casing , and performing electrolysis polymerization of the monomers for polymerization in said electrolyte solution by applying pulse voltage from a external electrode of the outer casing to stack said monomer for polymerization.
9. The method for producing the electrochemical element according to claim 8, characterized in that the monomers for polymerization are absorbed on the surface of the conductive porous material by impregnating said conductive porous material with solution of the monomers for polymerization and subsequent removing solvent in the solution of the monomers for polymerization.
10. The method for producing the electrochemical element according to claim 8 or 9, wherein the monomers for polymerization are in the form of complex monomer solution of a transition metal having at least two oxidation numbers, and wherein the conductive polymer formed by the electrolysis polymerization is an energy storage redox polymer layer including the polymer complex compound of the transition metal so as to store energy through redox reaction.
11. The method for producing the electrochemical element according to claim 10, wherein the polymer complex compound of said transition metal is a polymer metal complex of tetra-dentate Schiff 's base.
12. The method for producing the electrochemical element according to claim 11, wherein the polymer metal complex of said tetra-dentate Schiff 's base comprises the polymer complex compound represented by the following graphical formula:
wherein Y is
CH2 -CH2 / \
CHs CH3
I I
CH3- C - C-CH3 / \ or
or
2
Me is transition metal,
R is H or electron donating substituent, R' is H or halogen, and, n is an integer number of 2 to 200000.
13. The method for producing the electrochemical element according to claim 12, wherein said transition metal Me is selected from a group constituted of Ni, Pd, Co, Cu and Fe.
14. The method for producing the electrochemical element according to claim 12, wherein said R is selected from a group constituted of CH3O-, C2H5O-, HO- and CH3-.
EP05751144A 2005-06-10 2005-06-10 Method for producing electrode for electrochemical element and method for producing electrochemical element with the electrode Withdrawn EP1889270A4 (en)

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