JPWO2006098213A1 - Electrochemical element - Google Patents

Abstract

An electrochemical element having a bipolar conductive polymer and an electrolyte containing an ionic liquid, preferably the electrolyte is at least one selected from acetonitrile, propylene carbonate, ethylene carbonate, and γ-butyllactone 1 and an ionic liquid mixed in a volume ratio of 1: 3 to 10: 1. This provides a novel electrochemical device with improved repeated stability of the doping / dedoping reaction.

Description

  The present invention relates to an electrochemical device, and more particularly, to a redox capacitor using a doping and dedoping reaction of a bipolar conductive polymer.

  The electrochemical element is an element utilizing an electrochemical reaction, and includes elements used for energy storage such as a battery, a capacitor, and a fuel cell. It has been considered for a long time to use a conductive polymer doping / dedoping reaction in such an element. However, the doping and dedoping reactions of conductive polymers have a problem in that they are not repeatedly stable and do not occur during repeated reactions. Electrochemical devices based on these principles are a major problem in practical use. There is.

  An electric double layer capacitor is an electrochemical element for electrical storage that utilizes an electric double layer capacity generated at the interface between an electrode and an electrolyte when a voltage is applied. The mechanism of electricity storage by this electric double layer capacity has the characteristics that it can be charged / discharged faster than a secondary battery with an electrochemical reaction, and has excellent repeated life characteristics. However, the electric double layer capacitor has a drawback that its energy density is much smaller than that of the secondary battery. Since the electric double layer capacity is proportional to the surface area of the electrode, activated carbon having a large surface area is generally used as the electrode. However, even when such an activated carbon electrode having a large surface area is used, the energy density of the electric double layer capacitor remains at about 5 Wh / kg, and its capacity density is 1/10 or less as compared with the secondary battery.

In view of such a current situation, in order to drastically improve the capacitance density of the electric double layer capacitor, a capacitor using a pseudo capacitance by a conductive polymer has been proposed. Unlike the electric double layer capacity, the pseudo capacity is stored with an electron transfer process (Faraday process) at the electrode interface. Further, even in the process in which the pseudo capacity is developed, the electric double layer is formed at the interface, so that the electric double layer capacity and the pseudo capacity are developed in parallel, resulting in an increase in capacity. Such a pseudo capacity is manifested by a redox reaction of the conductive polymer, that is, a doping / dedoping reaction when the conductive polymer is used. The pseudocapacitance expressed by this redox reaction is theoretically estimated to be 10 ⁶ times the electric double layer capacitance. Therefore, a capacitor using the pseudocapacitance (referred to as a redox capacitor) uses only the electric double layer capacitance. Compared with a conventional electric double layer capacitor, the capacitor has a significantly higher capacity. As an example, for example, JP-A-6-104141 (Patent Document 1) discloses a capacitor formed of a conductive polymer film.

  As described above, a capacitor using a pseudo capacitance (redox capacitor) is an element capable of exhibiting breakthrough characteristics, but has not been put into practical use due to two major technical problems.

  First, there is a problem that the conductive polymer does not operate as an electrode because it is an insulator in an undoped state. Regarding this problem, there is a proposal relating to an electrode for a power storage element made of a carbon / conductive polymer composite having a structure in which the surface of a carbon material having a high specific surface area is coated with a conductive polymer (for example, Japanese Patent Laid-Open No. 2003-2003). No. 109875 (see Patent Document 2).

  The second problem is that the repeated stability of the conducting polymer doping / dedoping reaction is poor. The fact is that the second problem has not been fundamentally solved.

Apart from the technologies related to electrochemical devices as described above, molten salts that are liquid at room temperature have recently been developed and attracting attention. These are called ionic liquids, and are composed of a combination of a quaternary salt cation such as imidazolium or pyridium and an appropriate anion (Br ⁻ , AlCl ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ or the like). An ionic liquid has features such as non-volatility, non-flammability, chemical stability, and high ion conductivity, and is attracting attention as a reusable green solvent used for chemical reactions such as various syntheses and catalytic reactions. An ionic liquid has a large potential window, excellent voltage resistance, and a high ion concentration. In addition, since it is flame retardant and does not volatilize, there is no fear of evaporation and it is excellent in safety. For this reason, application of the ionic liquid as an electrolytic solution of an electric double layer capacitor has been studied.
JP-A-6-104141 JP 2003-109875 A Andy Rudge et al., Journal of Power Sources 47, 1994, 89-107

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a novel electrochemical device having improved repeated stability of doping and dedoping reactions.

  The electrochemical element of the present invention is characterized by having a bipolar conductive polymer and an electrolyte containing an ionic liquid. In the prior art, the reason why the doping reaction does not gradually occur during repeated doping and dedoping reactions in the electrolyte is that the dedope dopant diffuses into the electrolyte and is in the vicinity of the conductive polymer during doping. This is because there is no effective dopant. Therefore, we first examined the combination of a conductive polymer and an ionic liquid. If a component that can also be a dopant of a conductive polymer is selected as the anion component and / or cation component constituting the ionic liquid, the dopant should always be present in the vicinity of the conductive polymer. In such an ionic liquid, the anion and / or cation component constituting the ionic liquid is incorporated as a dopant of the conductive polymer while repeating the doping and dedoping reactions, and the anion constituting the ionic liquid. It is considered that the ionic liquid / conductive polymer composite is formed in which the component and / or cation component and part of the dopant of the conductive polymer are the same component. It is thought that it contributes to the development of excellent repeat stability of doping and dedoping reactions. Furthermore, the present inventors have found that a particularly high-performance electrochemical device can be realized by using bipolar polymers among conductive polymers, and have completed the present invention. That is, the present invention is as follows.

  The electrochemical element of the present invention is characterized by having a bipolar conductive polymer and an electrolyte containing an ionic liquid.

  Here, the electrolyte is preferably a mixture of an ionic liquid and an organic solvent, and at least one selected from acetonitrile, propylene carbonate, ethylene carbonate, and γ-butyl lactone and the ionic liquid is 1: More preferably, the mixture is mixed at a volume ratio of 3 to 10: 1.

  In the electrochemical device of the present invention, the bipolar conductive polymer preferably further contains an ionic liquid.

Ionic liquids used in the present invention, BF ₄ ^- anion, PF ₆ ^- is preferably an ionic liquid comprising an anion or sulfonate anion, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl - 3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tosylate, 1-butyl More preferably, it is at least one selected from -3-methylimidazolium tosylate.

  The bipolar conductive polymer used in the present invention has an electric conductivity of 1000 times or more in the doped state and in the undoped state, and the conductivity in the doped state is 0.01 S / cm or more. preferable.

  The bipolar conductive polymer used in the present invention is preferably a polythiophene derivative, such as poly-3- (4-fluorophenyl) thiophene, poly-3- (4-t-butylphenyl) thiophene, poly- Selected from 3- (4-trifluoromethylphenyl) thiophene, poly-3- (2,4-difluorophenyl) thiophene, poly-3- (2,3,4,5,6-pentafluorophenyl) thiophene More preferably, there is at least one.

  The electrochemical element of the present invention includes two electrodes facing each other and an electrolyte containing an ionic liquid sandwiched between the electrodes, and at least a surface of the electrode includes a bipolar conductive polymer. It is preferable that it exists so that it may contact | connect electrolyte.

  The electrochemical element of the present invention is preferably a redox capacitor used as a polar device.

  According to the present invention, there is provided a high-performance electrochemical device having improved repeated stability of doping and dedoping reactions by having a bipolar conductive polymer and an electrolyte containing an ionic liquid. Can do.

It is a figure which shows typically the structure of the redox capacitor 1 which is a preferable example of the electrochemical element of this invention. It is a figure which shows typically the voltage-current change at the time of charging / discharging of the type | system | group using the bipolar conductive polymer used for this invention. It is a figure which shows typically the cell used by the Example and comparative example of this invention. 3 is a graph showing cyclic voltammetry measured in Comparative Example 1.

Explanation of symbols

  1 Redox capacitor, 2, 3 electrodes, 4 separators, 5, 6 electrode elements, 7 gaskets.

The bipolar conductive polymer in the present invention is a conductive polymer that can be both P-doped and N-doped (anion / cation both-doped type conductive polymer). FIG. 2 schematically shows the state of charging and discharging in a system using a bipolar conductive polymer for two electrodes, with current on the vertical axis and voltage on the horizontal axis. The arrows in FIG. 2 represent the direction of change in voltage and current in the case of discharge. As shown in FIG. 2, in a system using a bipolar conductive polymer as an active material of each electrode, in the case of charging, one conductive polymer is P-doped (anion doped), The other conductive polymer is N-doped (cation doped). As a result, the voltage of the system after charging (voltage between the two electrodes) becomes V ₁ . In the case of discharging, contrary to the case of charging, one conductive polymer is dedoped with anions, the other conductive polymer is dedoped with cations, and a doping charge Q ₁ is released. Then, after the discharge is completed, both conductive polymers return to a state in which anions and cations are not doped. In the present invention, by using such a bipolar polymer among conductive polymers, it is possible to realize an electrochemical device having particularly high performance in characteristics such as discharge voltage, stored charge, and energy density.

  There are no particular limitations on the bipolar conductive polymer, and examples include various polythiophene derivatives.

  Preferred examples of polythiophene derivatives that are bipolar conductive polymers used in the present invention include poly-3- (4-fluorophenyl) thiophene, poly-3- (4-trifluoromethylphenyl) thiophene, poly- There may be mentioned at least one selected from 3- (2,4-difluorophenyl) thiophene and poly-3- (2,3,4,5,6-pentafluorophenyl) thiophene. Among these, a polythiophene derivative having 1 to 4 fluorine atoms per monomer unit is preferable because an N-doped polymer is moderately stabilized. That is, poly-3- (4-fluorophenyl) thiophene, poly-3- (4-t-butylphenyl) thiophene, poly-3- (4-trifluoromethylphenyl) thiophene, poly-3- (2,4 It is preferable to use at least one selected from -difluorophenyl) thiophene.

The bipolar conductive polymer used in the present invention is preferably one that can be doped / undoped with many dopants from the viewpoint of increasing the capacitance of the electrochemical device. For this purpose, it is preferable to use a conductive polymer whose electrical conductivity change due to doping / dedoping is 1000 times or more. For example, the polythiophene derivatives exemplified above can be used without any problem. In addition, the change of the electrical conductivity by the said dope and dedope can be known as follows, for example. That is, a conductive polymer film is formed on a conductive substrate such as SnO ₂ glass by an electropolymerization method, and the produced conductive substrate with the conductive polymer film is used as a reference electrode (for example, RE5 reference electrode manufactured by BAS Co., Ltd.). And a counter electrode (for example, a platinum plate) and an electrolytic solution containing ions as a dopant (for example, a 1 mol / L tetraethylammonium tetrafluoroborate propylene carbonate solution), and a conductive substrate with a conductive polymer film in the electrolytic solution. The conductive polymer film is sufficiently doped by maintaining the potential at which doping of the conductive polymer occurs for a certain period of time. Next, the conductive substrate with the conductive polymer film is taken out of the solution, and the conductive polymer film is peeled off from the conductive substrate, washed with methanol or the like, and dried. The electric conductivity of the obtained conductive polymer film in a doped state is measured by a general electric conductivity measuring method such as a four-terminal method. Next, electroconductive polymer film is electropolymerized in the same manner as above, and this is kept at a potential at which de-doping occurs in the electrolyte for a certain period of time, thereby producing a de-doped conductive polymer film. The electrical conductivity of the conductive polymer film in the state is measured. These two electrical conductivity measurements show the change in electrical conductivity between the doped state and the undoped state of the conductive polymer. When the conductive polymer is obtained as a powder sample by chemical polymerization or the like, the conductive polymer powder is pressed and hardened into a pellet, and this pellet-like conductive polymer is used as a dopant in the same manner as described above. Conductive polymer pellets in a doped state and a dedope state are prepared by maintaining a constant potential for a certain period of time in an electrolyte containing ions. If the electrical conductivity of these pellets is measured by a four-terminal method or the like, the change in the electrical conductivity of the conductive polymer in the doped state and the undoped state can be understood. For example, poly-polymerized by electropolymerization by maintaining SnO ₂ glass at +1.2 V for 120 seconds with respect to the RE5 reference electrode in a propylene carbonate solution containing 0.1 mol / L monomer and 1 mol / L tetraethylammonium tetrafluoroborate. 3- (4-Fluorophenyl) thiophene is sufficiently P-doped by maintaining the potential at +1.0 V for 600 seconds with respect to the RE5 reference electrode in a propylene carbonate solution of 1 mol / L tetraethylammonium tetrafluoroborate. It becomes a state. Moreover, if it keeps to -1.0V for 600 second with respect to RE5 reference pole, it will be in the state in which it was fully dedope, and if it was kept at -2.0V for 600 seconds, it will be in the state where sufficient N dope was carried out.

  In addition, the conductive polymer used in the present invention is preferably one having high electrical conductivity from the viewpoint of reducing the internal resistance of the capacitor. For this purpose, it is preferable to use a conductive polymer exhibiting a conductivity of 0.01 S / cm or more (more preferably 1.0 S / cm or more) in a doped state. For example, the polythiophene derivatives exemplified above have no problem. Can be used. In addition, the electrical conductivity in the said dope state can be measured using the method mentioned above, for example.

  The bipolar conductive polymer dopant preferably used in the present invention has the effect on the conductivity and thermal stability of the bipolar conductive polymer, the capacity, stability and speed of doping and dedoping. Selected in consideration. As a dopant preferably used for the bipolar conductive polymer of the present invention, p-toluenesulfonate ion, benzenesulfonate ion, anthraquinone-2-sulfonate ion, triisopropylnaphthalenesulfonate ion, polyvinylsulfonate ion, Examples include dodecylbenzene sulfonate ion, alkyl sulfonate ion, n-propyl phosphate ion, perchlorate ion, and tetrafluoroborate ion. The smaller the size of the dopant, the better the performance of doping / dedoping, and p-toluenesulfonic acid, benzenesulfonic acid or tetrafluoroborate ions are preferred.

  The bipolar conductive polymer in the present invention can be obtained by electropolymerization in the presence of an organic solvent because a thin and uniform conductive polymer film can be easily prepared and the film thickness can be controlled. It is preferable. In the electropolymerization, for example, a bipolar conductive polymer can be deposited on the anode by a method in which a monomer is dissolved in a solvent together with a supporting electrolyte and anodized to perform dehydrogenation polymerization. Generally, since the oxidation-reduction potential of a polymer is lower than that of a monomer, the oxidation of the polymer skeleton further proceeds in the polymerization process, and accordingly, an anion which is a supporting electrolyte is incorporated into the polymer as a dopant. In electropolymerization, such a mechanism has an advantage that a polymer having conductivity can be obtained without adding a dopant later. As will be described later, it is preferable to use a carbon electrode for electrolytic polymerization and to deposit a conductive polymer on the surface thereof, because such an electrode can be used as it is as a polarization electrode for a redox capacitor or the like.

  Examples of the supporting electrolyte in which the anionic component and / or the cationic component are incorporated into the polymer as a dopant include sodium alkylsulfonate, sodium p-toluenesulfonate, sodium dodecylbenzenesulfonate, sodium triisopropylnaphthalenesulfonate, sodium benzoate. Sodium dodecyl sulfate, n-propyl phosphate ester, isopropyl phosphate ester, n-butyl phosphate ester, n-hexyl phosphate ester, sodium polystyrene sulfonate, sodium polyvinyl sulfonate, tetra n-butyl ammonium perchlorate, tetrafluoro Examples thereof include tetraethylammonium borohydride and tetra-n-butylammonium tetrafluoride. Among these, sodium p-toluenesulfonate, tetraethylammonium boron tetrafluoride, tetra-n-butylammonium tetrafluoride, and the like, which have a common anionic component and anion component, are preferable.

  In addition, the bipolar conductive polymer in the present invention may be polymerized in an ionic liquid. Thereby, the bipolar electroconductive polymer (after-mentioned) containing an ionic liquid can be produced previously.

  The electrolyte used for the electrochemical device of the present invention is characterized by containing an ionic liquid. Here, the “ionic liquid” in the present specification refers to a liquid that is liquid only at room temperature despite being composed only of ions, and is composed of a combination of a cation such as imidazolium and an appropriate anion. . Since such an ionic liquid is flame retardant and non-volatile, the electrolyte contains an ionic liquid, which makes it more durable and safer than the case of using an electrolyte consisting of only an ordinary organic solvent. An excellent electrochemical device can be realized. Further, since the ionic liquid is a liquid composed only of ions and has a high ion concentration, an electrochemical element using an electrolyte containing the ionic liquid has an advantage of high doping / de-doping capacity and responsiveness. Furthermore, since the ionic liquid has a wide potential window (high withstand voltage), there is an advantage that an electrochemical element having a high withstand voltage can be produced by using an electrolyte containing the ionic liquid.

  Examples of the cation constituting the ionic liquid preferably used in the present invention include an imidazolium cation, a pyridinium cation, a pyrrolidinium cation, an ammonium cation, and a triazine derivative cation, but are not limited thereto. Absent. Of these, the imidazolium cation is preferably used from the viewpoint of ease of use.

Examples of the anion component constituting the ionic liquid include Br ⁻ , AlCl ₄ ⁻ , PF ₆ ⁻ , NO ₃ ⁻ , R _A NO ₃ ⁻ , NH ₂ CHR _A COO ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , SO ₄ ^2- etc. can be exemplified, but is not limited thereto. Here, R _A represents a substituent containing an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an ether group, an ester group, an acyl group, or the like, and may contain fluorine.

Furthermore, an anion containing carboxylato _{^{(-COO-), R B COO -}} , - OOCR B COOH, - OOCR B CCOO -, NH 2 CHR B COO - ( wherein, R _B is an aliphatic hydrocarbon group, Substituents including alicyclic hydrocarbon groups, aromatic hydrocarbon groups, ether groups, ester groups, acyl groups and the like, which may contain fluorine, are preferably used in the present invention.

R _C SO ₃ ⁻ , R _C OSO ₃ ⁻ (where R _C is an aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic, which is an anion including a sulfonate anion (—SO ₃ ⁻ )). Substituents containing a hydrocarbon group, an ether group, an ester group, an acyl group and the like are shown, and fluorine may be contained.), Benzenesulfonic acid, toluenesulfonic acid and the like are preferably used in the present invention.

Further, when BF ₄ ⁻ is used, an ionic liquid having a low viscosity can be obtained and can be preferably used in the present invention.

Ionic liquids according to the present invention, for reasons of excellent repetition stability of doping and dedoping, BF ₄ among the above ^- anionic, PF ₆ ^- is preferably an ionic liquid comprising an anion or sulfonate anion.

  Specific examples of the ionic liquid preferably used in the present invention include 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-ethyl-3-methylimidazole. Examples thereof include at least one selected from lithium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tosylate, and 1-butyl-3-methylimidazolium tosylate. Among them, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetratetraborate are preferred because of the large accumulated charge due to doping and dedoping and excellent repeatability of doping and dedoping. It is preferred to use fluoroborate as the ionic liquid.

  The ionic liquid is preferably contained in a ratio of 1: 3 to 1: 10000, preferably in a ratio of 1: 5 to 1: 100 with respect to the bipolar conductive polymer. More preferably. This is because if the ionic liquid is less than 1: 10000 relative to the bipolar conductive polymer, the proportion of the ionic liquid tends to be too small to contribute to the improvement of the doping / dedoping performance, and This is because when the ionic liquid exceeds 1: 3 with respect to the bipolar conductive polymer, there is a problem that the strength of the conductive polymer film becomes weak.

  The ionic liquid preferably used in the present invention can be synthesized by combining the above anions and cations using a known method. Specific examples of the synthesis method include an anion exchange method, an acid ester method, and a neutralization method.

  As long as the electrolyte used in the present invention contains an ionic liquid, it may be composed of only an ionic liquid or a mixture of an ionic liquid and an organic solvent. By using a mixture of liquid and organic solvent as the electrolyte, high ion concentration and low viscosity can be realized with a reasonable balance. By using this as an electrolyte, extremely high doping and dedoping capacity and response speed can be obtained. This is preferable.

  As an organic solvent used for the said mixture, the organic solvent conventionally used widely in this field | area, such as acetonitrile, propylene carbonate, ethylene carbonate, (gamma) -butyllactone, can be used without a restriction | limiting in particular. Among them, it is preferable to use acetonitrile because it is well mixed with various ionic liquids at an arbitrary ratio and the viscosity of the mixed liquid becomes low.

  When the electrolyte is a mixture of an ionic liquid and an organic solvent, the mixing ratio is not particularly limited. As described above, the organic solvent is selected from acetonitrile, propylene carbonate, ethylene carbonate, and γ-butyllactone. When at least one of the above is used, the organic solvent: ionic liquid is preferably 1: 3 to 10: 1 (volume ratio), more preferably 1: 3 to 3: 1. This is because when the volume ratio of the ionic liquid to the organic solvent is less than 1:10, the ion concentration tends to be thin, and the volume ratio of the ionic liquid to the organic solvent tends not to be advantageous. This is because when it exceeds 3: 1, the viscosity of the liquid mixture tends to be high and the electric conductivity tends to be low.

  In the electrochemical device of the present invention, the bipolar conductive polymer preferably further contains an ionic liquid. Here, the bipolar conductive polymer containing the ionic liquid may be prepared by later impregnating the conductive polymer with the ionic liquid, or the polymerization process of the conductive polymer. May be prepared by coexisting an ionic liquid. In addition, as an ionic liquid contained in a bipolar conductive polymer, what was mentioned above can be especially used without a restriction | limiting. The cation component or anion component constituting the ionic liquid may be a component that can be a dopant for a bipolar conductive polymer or a component that cannot be a dopant for a conductive polymer. Even if it is not a dopant for a conductive polymer, it can be contained in the conductive polymer (coexist with the conductive polymer). As described above, by using a bipolar conductive polymer further containing an ionic liquid, an electrochemical device having further improved charge storage and release capability can be realized.

  When the cation component or anion component constituting the ionic liquid is a component that can be a dopant of a bipolar conductive polymer, even if a dedoping reaction of the bipolar conductive polymer occurs, It is possible to realize a state in which an anionic component and / or a cationic component that can effectively serve as a dopant for the conductive polymer are always present in the vicinity of the conductive polymer. Therefore, the doping / de-doping reaction is carried out in an ionic liquid, and at that time, the anion component constituting the ionic liquid is set as a component that can be a dopant for a bipolar conductive polymer. This will have a significant effect on improving the repeated stability of the reaction.

In addition, after repeating the doping and dedoping reactions in the electrochemical device of the present invention, the bipolar conductive polymer dopant and a part of the anionic component and / or cationic component constituting the ionic liquid are common. An ionic liquid-conductive polymer complex as a component is formed. That is, at the start of the doping / de-doping reaction, the bipolar conductive polymer dopant and the anionic component and / or cation component constituting the ionic liquid are not necessarily the same, but are repeatedly doped / de-doped. At the time after the dope reaction has progressed, at least a part of the anionic component and / or cation component constituting the ionic liquid is taken in as a bipolar conductive polymer dopant, and the anionic component constituting the ionic liquid, At least a part of the cation component and the dopant of the conductive polymer have the same component. Of course, it is more preferable that the anion component and / or the cation component and the dopant are made the same component from the beginning using, for example, tetrafluoroborate ion (BF ₄ ⁻ ).

  Further, in the present invention, an electropolymerized film containing a bipolar conductive polymer electropolymerized in an organic solvent containing an ionic liquid, an electrode complex composed of an electrode, and an electrolyte containing an ionic liquid are combined. It may be an electrochemical element. In this case, the doping / de-doping reaction is carried out, and at that time, the anion component and / or the cation component constituting the ionic liquid is set as a component that can be a dopant of a bipolar conductive polymer. This will have a significant effect on improving the repeated stability of the dedoping reaction.

  The term “electrochemical element” as used in the present specification refers to all elements that repeatedly use the doping and dedoping reactions of conductive polymers, and includes capacitors such as redox capacitors, batteries, electrochromic elements, sensors, and the like. Especially, it is preferable that the electrochemical element of this invention is implement | achieved by the redox capacitor (type III redox capacitor).

  The electrochemical device of the present invention includes, for example, two electrodes facing each other and an electrolyte containing an ionic liquid sandwiched between the electrodes, and a bipolar conductive polymer is formed on at least the surface of the electrode. It is preferable to be realized by a structure that exists so as to be in contact with the electrolyte.

  FIG. 1 is a diagram schematically showing a configuration of a redox capacitor 1 which is a preferred example of the electrochemical device of the present invention. Here, the redox capacitor is a capacitor obtained by expanding the capacitance of the electric double layer capacitor by using a pseudo capacitance. The redox capacitor of the present invention uses all or part of oxidation / reduction of electrode material, charge / discharge in the electric double layer, and desorption of ions on the electrode surface for storage and release of electric energy. This is one type of electrochemical capacitor including a physical electrode system, a reversible redox solution system, an underpotential system, and the like. In general, an electrochemical capacitor having a capacity density of 120 Wh / kg at an active material level, an output density of about 20 kw / kg or more and capable of high-speed charge / discharge within a few seconds has been developed.

  The redox capacitor 1 of the example shown in FIG. 1 has, for example, two plate-like electrodes 2 and 3 arranged with a separator 4 interposed therebetween, and the electrode elements 5 and 6 are applied only to the electrodes 2 and 3, respectively. It has a contact structure. The laminated structure composed of the electrode 2, the separator 4, and the electrode 3 is fixed between the electrode elements 5 and 6 by the gasket 7 so that the electrode elements 5 and 6 do not contact each other.

  The material for forming the electrodes 2 and 3 is not particularly limited as long as it can be used for a redox capacitor. For example, an electrode formed only of a bipolar conductive polymer, a composite electrode of a carbon material and a bipolar conductive polymer, a composite electrode of a metal material and a bipolar conductive polymer, a metal material And a composite material electrode of carbon material and a bipolar conductive polymer can be used. Thus, in the present invention, it is preferable that the above-described bipolar conductive polymer is present on at least the surface of the electrode so as to be in contact with the electrolyte.

  A composite material electrode of a carbon material and a bipolar conductive polymer is, for example, bound to an organic solvent such as ethanol, methanol, or methylpyrrolidone, and the bipolar conductive polymer that is the electrode material and the carbon material. It can be produced by adding an agent to form a dispersion, applying this to the surface of the metal current collector, and then drying. As the binder, fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride are preferably used. It is preferable that the usage-amount with respect to the said electrode material of a binder is about 5 to 20 weight%. As the metal current collector, metals such as aluminum, nickel, stainless steel, titanium, and tantalum are preferably used. These metals may be plated with gold or platinum, or a metal film formed on a polymer film. But you can. The metal current collector is more preferably used in the form of a rolled foil, a punching foil, an etched foil, an expanded metal foil, or the like. When the polarizing electrode is not a current collector but in the form of a sheet, the conductive polymer / carbon composite material is mixed with the above binder, and further a lubricant is added to form a paste, which is then extruded. This can be rolled with a rolling roll to form an electrode sheet.

  Also, the carbon material can be mixed with the bipolar material by a method in which the carbon material is dispersed in a polymerization solution of the bipolar conductive polymer and chemical polymerization is performed to coat the surface of the carbon material with the bipolar conductive polymer. It is possible to produce a composite material electrode with a conductive polymer. An electrode is produced in the same manner as described above using the carbon material coated with the bipolar conductive polymer thus produced.

  A composite electrode of a carbon material and a bipolar conductive polymer can also be produced as follows. First, a carbon material and a binder are added to an organic solvent such as ethanol, methanol, or methylpyrrolidone to form a dispersion, which is applied to the surface of a metal current collector and then dried to produce a carbon electrode. Next, electrolytic polymerization is performed using this as an electrode to form a thin film of a conductive polymer on the surface of the carbon electrode, and the conductive polymer is thinly coated on the surface of the carbon material. The electrode produced by this method is a useful method for reducing impedance because the conductive polymer layer can be made extremely thin.

The carbon material used for the composite material electrode of the carbon material and the bipolar conductive polymer is not particularly limited as long as it is a carbon material used for electrode formation in this field, but activated carbon powder, And / or containing graphite powder. This is because the addition of activated carbon powder or graphite powder can reduce electrode resistance and increase surface area. Therefore, as carbon materials, carbon blacks such as acetylene black and furnace black having a large surface area, activated carbon particles having a relatively large pore diameter, carbon fibers having a relatively small particle diameter, graphite fibers, carbon nanotubes, and the like are particularly preferable. Can be mentioned. The carbon material preferably has a specific surface area (BET specific surface area obtained by analyzing data of nitrogen adsorption isotherm at liquid nitrogen temperature) of 20 m ² / g or more.

  The laminated structure of the electrode 2, the separator 4, and the electrode 3 shown in FIG. 1 is impregnated with an electrolyte containing the above-described ionic liquid (preferably a mixture of the ionic liquid and an organic solvent). As the separator 4, those conventionally used for capacitors can be used without any particular limitation, and a porous material is preferably used. Further, the electrode elements 5 and 6 and the gasket 7 can be used without any particular limitation as long as they are conventionally used for capacitors. As the gasket 7, an electrically insulating one is used.

  The method of charging / discharging the electrochemical device of the present invention is the same as that of a normal electric double layer capacitor, and can be performed by applying a voltage between a pair of electrodes or passing a current, and is particularly limited. It is not something. However, the lifetime of the electrochemical device of the present invention can be significantly increased by using one electrode only as a positive electrode and the other electrode only as a negative electrode. For this reason, since the electrochemical element of this invention is realizable as a redox capacitor used as a polar device which distinguishes and uses a positive electrode and a negative electrode, since a cycle life can be extended, it is preferable. In general, it is better to repeat doping and dedoping of either anion or cation in bipolar conductive polymer than repeating doping and dedoping of both anion and cation. It is because there is little deterioration of.

  Moreover, it is preferable from the viewpoint of extending the cycle life that the electrochemical element of the present invention is used in an appropriate voltage range without being overcharged. This is because, when the dopant is excessively doped, the bipolar conductive polymer is strongly oxidized or reduced, so that the bipolar conductive polymer itself deteriorates and the function as an electrode that repeats doping and dedoping decreases. Because it does.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Comparative Example 1>
A film of poly-3- (4-fluorophenyl) thiophene, which is a bipolar conductive polymer, was formed on SnO ₂ glass by electrolytic polymerization using the cell schematically shown in FIG. Note that the operation using the cell shown in FIG. 3 was performed in a glove box substituted with high-purity argon gas in order to eliminate the influence of moisture and oxygen in the atmosphere.

The electrolytic polymerization solution used was a propylene carbonate (PC) solution containing 0.1M 4-fluorophenylthiophene as a monomer and 1M boron tetrafluoride tetraethylammonium (tetraethylammonium tetrafluoroborate (TEA · BF ₄ )) as a supporting salt. The 1M propylene carbonate solution of TEA · BF ₄ used here was purchased from Sanwa Oil.

As a working electrode, a 3 × 3 cm SnO ₂ glass plate was used. As a counter electrode, a 3 × 4 cm platinum plate was used. In addition, the SnO ₂ glass plate which is a working electrode was prepared by applying SnO ₂ coating on one surface in advance, and the SnO ₂ coated side was arranged so as to face the counter electrode. In addition, as a reference electrode, RE-5 reference electrode (Ag / Ag ⁺ reference electrode manufactured by BAS), the solution in the reference electrode was 0.1 M tetrabutylammonium perchlorate (Bu ₄ N · ClO ₄ ), silver nitrate ( Acetonitrile solution containing 0.01M AgNO ₃ ) was used. The potential of this reference electrode is +490 mV (+0.49 V) compared to the standard hydrogen electrode (NHE).

As shown in FIG. 3, the electrolytic polymerization solution is accommodated in a container, and these are immersed in the electrolytic polymerization solution in a state where the working electrode is arranged with a 1 cm gap between the reference electrode and the counter electrode. It was. It should be noted that the working electrode was immersed in the electrolytic polymerization solution only in a region 1 cm from the end side (that is, the area immersed in the electrolytic polymerization solution of the working electrode was 3 × 1 cm). In this state, the potential of the working electrode was maintained at +1.2 V for 120 seconds with respect to the reference electrode, and a film of poly-3- (4-fluorophenyl) thiophene was formed on part of the SnO ₂ glass. At this point, the poly-3- (4-fluorophenyl) thiophene film is P-doped (in this case, doped with BF ₄ anion). Next, the potential of the SnO ₂ glass (working electrode) on which a poly-3- (4-fluorophenyl) thiophene film is partially formed is maintained at 0.0 V with respect to the RE-5 reference electrode for 240 seconds. The 3- (4-fluorophenyl) thiophene film was dedoped.

The poly-3- (4-fluorophenyl) thiophene dedope film formed as described above was washed lightly with propylene carbonate while being formed on the SnO ₂ glass (working electrode), and then TEA · BF ₄ was used as a supporting salt. Prepare a container containing 1M PC solution (manufactured by Sanwa Oil Chemical Co., Ltd.) and immerse the reference electrode, working electrode and counter electrode in this solution in the same manner as described above. ) And cyclic voltammetry (CV) measurement. In the CV measurement, a potential sweep was started from the natural potential of the poly-3- (4-fluorophenyl) thiophene dedope film toward the positive side. The obtained CV is shown in FIG. As shown in FIG. 4, the width of the potential sweep was -2.1 V to +0.8 V with respect to the RE-5 reference electrode, and the potential sweep (sweep) speed was 25 mV / s.

Here, in the CV shown in FIG. 4, the horizontal axis indicates the potential of the working electrode with the reference electrode potential set to 0 V, and the horizontal axis of 0 V in the graph is +490 mV (+0.49 V) of the standard hydrogen electrode. Equivalent to. Also, the upward peak on the right side of FIG. 4 (the peak of the current in the direction where the absolute value of the current increases in the + direction in the region of 0 V or more on the horizontal axis) corresponds to P doping (BF ₄ ⁻ doping). The downward peak (the peak of the current in the direction in which the absolute value of the current increases in the − direction in the region of 0 V or more on the horizontal axis) corresponds to P dedoping (BF ₄ ⁻ dedoping). Further, the downward peak on the left side in FIG. 4 (the peak of the current in the direction in which the absolute value of the current increases in the − direction in the region of −1.5 V or less on the horizontal axis) corresponds to N doping (tetraethylammonium cation doping). The upward peak on the left side (the peak of the current in the direction in which the absolute value of the current increases in the + direction in the region of 0 V or more on the horizontal axis) corresponds to N undoping (de-doping of tetraethylammonium cation).

  The capacities of P-doped / undoped and N-doped / dedope calculated by time integration of the current values in the graph shown in FIG. 4 were 0.025C and 0.021C, respectively.

<Example 1>
As described above, a poly-3- (4-fluorophenyl) thiophene film was formed on a part of SnO ₂ . Then, instead of using a PC solution containing 1M TEA · BF ₄ , a mixed solution in which 1-ethyl-3-methylimidazolium tetrafluoroborate, which is an ionic liquid, and acetonitrile was mixed at a volume ratio of 1: 1 was used. The CV measurement was performed in the same manner as in Comparative Example 1 described above, and the capacities of P-doped / dedope and N-doped / dedope were determined in the same manner, and were 0.029C and 0.024C, respectively. In Example 1, repeated stability (cycle characteristics) was improved as compared with Comparative Example 1 described above.

<Example 2>
As described above, a poly-3- (4-fluorophenyl) thiophene film was formed on a part of SnO ₂ . Thereafter, CV measurement was performed in the same manner as in Comparative Example 1 except that 1-ethyl-3-methylimidazolium tetrafluoroborate, which is an ionic liquid, was used instead of the PC solution containing 1M TEA · BF _4. The capacities of P-doped / de-doped and N-doped / dedope were determined in the same manner, and they were 0.003C and 0.002C, respectively. In Example 2, repeat stability (cycle characteristics) was improved as compared with Comparative Example 1 described above.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (11)

  An electrochemical device comprising a bipolar conductive polymer and an electrolyte containing an ionic liquid.   The electrochemical device according to claim 1, wherein the electrolyte is a mixture of an ionic liquid and an organic solvent.   The electrolyte is a mixture of at least one selected from acetonitrile, propylene carbonate, ethylene carbonate, and γ-butyllactone and an ionic liquid in a volume ratio of 1: 3 to 10: 1. The electrochemical device according to Item 2.   The electrochemical device according to claim 1, wherein the bipolar conductive polymer further contains an ionic liquid. Ionic liquids BF ₄ ^- anion, PF ₆ ^- is an ionic liquid comprising an anion or sulfonate anion, an electrochemical device according to claim 1.   The ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methyl The electrochemical device according to claim 5, which is at least one selected from imidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tosylate, and 1-butyl-3-methylimidazolium tosylate. .   2. The bipolar conductive polymer according to claim 1, wherein the electrical conductivity of the bipolar conductive polymer changes by 1000 times or more in a doped state and a dedope state, and the conductivity in the doped state is 0.01 S / cm or more. Electrochemical element.   The electrochemical element according to claim 1, wherein the bipolar conductive polymer is a polythiophene derivative.   Bipolar conductive polymers are poly-3- (4-fluorophenyl) thiophene, poly-3- (4-tert-butylphenyl) thiophene, poly-3- (4-trifluoromethylphenyl) thiophene, poly The method according to claim 8, which is at least one selected from -3- (2,4-difluorophenyl) thiophene and poly-3- (2,3,4,5,6-pentafluorophenyl) thiophene. The electrochemical element as described. Two opposing electrodes, and an electrolyte containing an ionic liquid sandwiched between the electrodes,
2. The electrochemical element according to claim 1, wherein a bipolar conductive polymer is present on at least the surface of the electrode so as to be in contact with the electrolyte.   The electrochemical element according to claim 10, which is a redox capacitor used as a polar device.

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