JP2008251831A - Aqueous hybrid capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous hybrid capacitor with which high output density can be obtained and whose assembly process is simple. <P>SOLUTION: In the aqueous hybrid capacitor, electrodes which are oppositely arranged through a separator 14 and electrolyte are stored in a basic cell. One electrode is the polarizing electrode 12 which is mainly composed of active carbon, and the other electrode is the electrode 15 which is mainly composed of a proton conductive compound. An electrolyte is an aqueous electrolyte. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a water-based hybrid capacitor used for electronic devices, electric vehicles, and the like, and more particularly to a water-based hybrid capacitor having high energy density and output density.

  In recent years, secondary batteries typified by nickel metal hydride and lithium ion have been used as electronic devices typified by mobile phones or power storage devices of electric vehicles. These secondary batteries have high energy density and are put into practical use in many portable devices and hybrid cars.

 However, with the development of mobile devices, the load current has been increasing due to the cordless communication devices such as high-performance CPUs and wireless LANs, and the enhancement of in-vehicle electrical equipment and devices. kg), a new power storage device has been demanded.

  As such a power storage device, an electric double layer capacitor has attracted attention. Electric double layer capacitors are broadly classified into aqueous and non-aqueous depending on the electrolyte used. For example, as shown in the cross-sectional view of FIG. 2, the coin-type water-based electric double layer capacitor has a basic structure called a basic cell 22 that has a power storage function and is laminated alone or in series, and is formed of a stainless steel can through an insulating packing 23. It is obtained by mechanically caulking the case 24 and the stainless steel cap 21. These power storage devices are excellent in instantaneous charge / discharge characteristics, have high output characteristics that can withstand charge and discharge of over tens of thousands of cycles without depending on the end-of-discharge voltage, and maintenance-free characteristics. Since there is no advantage, there is an advantage that the peripheral circuit can be simplified, but the water system has a low energy density.

  In recent years, as a power storage device for applications that require such high energy and high output characteristics, a power storage device called a hybrid capacitor that combines the power storage principle of a proton polymer battery or a lithium ion secondary battery and the power storage principle of an electric double layer capacitor. Is attracting attention. The proton polymer battery is an electrochemical storage battery using a proton conductive compound as an electrode active material. A proton polymer battery mainly uses an aqueous electrolyte containing protons. This storage battery has a higher energy density than an electric double layer capacitor, and, like an electric double layer capacitor, is a battery capable of charging and discharging over tens of thousands of cycles without depending on the final discharge voltage.

  On the other hand, a hybrid capacitor usually uses a polarizable electrode for the positive electrode and a non-polarizable electrode for the negative electrode. For example, a negative electrode that can occlude and desorb lithium ions is brought into contact with lithium metal in advance. It is a capacitor intended to increase the withstand voltage and increase the energy density by occluding and carrying lithium ions (hereinafter also referred to as doping) by a conventional method or an electrochemical method to lower the negative electrode potential (for example, Patent Document 1).

  However, although this type of hybrid capacitor can be expected to have higher energy compared to electric double layer capacitors and proton polymer batteries with low withstand voltage, it uses lithium ion doping in the non-aqueous electrolyte and charge / discharge process. Output characteristics are poor compared to electric double layer capacitors and proton polymer batteries. In addition, an overdischarge prevention circuit is required because there is a life deterioration due to overdischarge peculiar to the secondary battery. The life deterioration due to overdischarge is mitigated by optimizing the negative electrode active material and lowering the withstand voltage, but the output density is still low because a non-aqueous electrolyte is used (for example, Patent Document 2).

Japanese Patent Laid-Open No. 8-1007048 JP 2000-195555 A

  The conventional hybrid capacitor is based on the premise that the electrolyte is non-aqueous, and it is advantageous in terms of energy density because the withstand voltage can be increased compared to the aqueous electrolyte, but the conductivity of the electrolyte itself is low. It is disadvantageous in terms of power density. Further, since lithium ions to be doped into the negative electrode do not exist on the positive electrode side as in the lithium ion battery, it is necessary to dope lithium ions into the negative electrode by chemical and electrochemical methods before assembling the battery. Therefore, there is a problem that the process becomes complicated.

  That is, an object of the present invention is to provide a water-based hybrid capacitor having a high output density and a simple electrode doping process.

  The present invention has been made to solve the above problems, and the hybrid capacitor of the present invention is a hybrid capacitor in which an electrode and an electrolytic solution arranged opposite to each other via a separator are contained in a basic cell having high acid resistance, One electrode is a polarizable electrode mainly composed of activated carbon, the other is an electrode mainly composed of a proton conductive compound, and the electrolytic solution is an aqueous electrolytic solution.

  As the proton-conducting compound, a polymer that exhibits conductivity by forming a redox pair by doping can be used. For example, polyaniline, polythiophene, polypyrrole, polyacetylene, poly-p-phenylene, polyphenylene vinylene, polyperiphthalene , Π-conjugated polymers such as polyfuran, polyflurane, polythienylene, polypyridinediyl, polyisothianaphthene, polyquinoxaline, polypyridine, polypyrimidine, polyindole, indole trimer, polyaminoanthraquinone, polyimidazole and their derivatives, poly Polymers containing hydroxyl groups such as anthraquinone and polybenzoquinone (quinone oxygen is converted into hydroxyl groups by conjugation), proton transfer copolymerized from two or more monomers Such as the type of polymer, and the like.

  As the proton-conducting compound, a π-conjugated compound or π-conjugated polymer having a nitrogen atom, a quinone compound or a quinone polymer can be preferably used. Among these, indole trimer compounds and quinoxaline polymer compounds (polyphenylquinoxaline) described in JP-A No. 2004-342595 are particularly preferable.

  For example, indole trimer compounds have good cycle characteristics from 200 mV to 1200 mV (vs. Ag / AgCl) by CV test (cyclic voltammogram test) using Ag / AgCl as reference electrode and Pt as counter electrode in 40% sulfuric acid. . For example, polyphenylquinoxaline having a quinoxaline skeleton has good cycle characteristics from −150 mV to 500 mV (vs. Ag / AgCl) in a 40% sulfuric acid by a CV test using Ag / AgCl as a reference electrode and Pt as a counter electrode. Moreover, since there is almost no difference in oxidation / reduction capacity from the first cycle to the tenth cycle, it is suggested that these are sufficiently doped only by impregnation. This is probably because the proton doping in the aqueous electrolyte is more reactive than the lithium ion doping in the non-aqueous electrolyte.

  The aqueous electrolyte is an inorganic or organic acid, for example, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid or other inorganic acid, saturated carboxylic acid And organic acids such as aliphatic carboxylic acid, oxycarboxylic acid, p-toluenesulfonic acid and lauric acid. Of these, a sulfuric acid aqueous solution is particularly preferable.

  In the present invention, one electrode is a polarizable electrode and the other electrode is an electrode mainly composed of a proton-conducting compound, an aqueous electrolyte is used as an electrolyte, and the chemical is contained in a basic cell container having high acid resistance. It is possible to provide a water-based hybrid capacitor that does not require a chemical or electrochemical doping treatment and has excellent overdischarge characteristics and output characteristics.

  First, a basic cell manufacturing method according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a basic cell used in an aqueous hybrid capacitor according to an embodiment of the present invention. The aqueous hybrid capacitor of the present embodiment is the same as the coin-type aqueous electric double layer capacitor of FIG. 2 described above except for the basic cell structure.

  As shown in FIG. 1, the basic cell according to the present embodiment includes each electrode having acid resistance (polarizable electrode 12, electrode 15 mainly composed of proton conductive compound), current collector 11, separator 14 and gasket 13. Composed. As the current collector 11, butyl rubber or elastomer to which carbon is added to impart conductivity is used. On the other hand, the gasket 13 is used to prevent a short circuit between the current collectors 11 facing each other through the separator 14 and electrodes and to seal the aqueous electrolyte solution, and soft plastic such as butyl rubber or thermoplastic elastomer is used. Sealing adhesion is performed by vulcanization adhesion or heat fusion.

  The separator 14 is used for preventing a short circuit between opposing electrodes and for passing electrolyte ions, and is made of polypropylene, polytetrafluoroethylene, polyethylene, or the like.

Activated carbons that can be used for the polarizable electrode 12 include coconut palm-based and phenol resin-based activated carbons, and it is preferable to use phenol resin-based activated carbon to obtain a large-capacity electric double layer. As the activated carbon, one having an average particle size of 15 μm or less and a specific surface area of 1000 to 3000 m ² / g is preferably used. By using such activated carbon, the capacity can be increased and the internal resistance can be decreased. In addition, it is possible to further reduce the internal resistance by adding a conductive auxiliary material, but if the added amount of the conductive auxiliary material is too large, the capacity decreases, so 0 to 15 with respect to the total weight of the activated carbon and the conductive auxiliary material. It is preferable to set it as weight% (excluding 0 weight%). Examples of the conductive auxiliary material include ketjen black, acetylene black, VGCF (vapor grown carbon fiber), natural graphite, and artificial graphite. An aqueous electrolyte is added to activated carbon (or mixed powder obtained by adding a conductive auxiliary material to activated carbon) to make a slurry, which is imprinted in a gasket to form a polarizable electrode 12. If the amount of the aqueous electrolyte is too large, the amount of the activated carbon powder is reduced and the capacity is reduced. Therefore, the amount is preferably 250% by weight or less based on the activated carbon powder (or the mixed powder obtained by adding a conductive auxiliary material to the activated carbon).

  When an aqueous electrolyte is used, the hydrogen generation potential and the oxygen generation potential vary depending on the proton concentration (hereinafter referred to as pH). For example, when pH = 1.0, the hydrogen generation potential is about −260 mV (vs. Ag / AgCl) and the oxygen generation potential is about 1000 mV (vs. Ag / AgCl). Therefore, as a material for the proton conductive compound electrode, for example, a material that undergoes a redox reaction at a relatively high potential (1000 mV (vs. Ag / AgCl)) with respect to proton doping, such as an indole trimer compound ( 370 mV (vs. Ag / AgCl) or more) is used as a positive electrode, for example, redox at a relatively low potential (formula oxidation / reduction potential 50 mV (vs. Ag / AgCl)) with respect to proton doping, such as polyphenylquinoxaline. When using the material which reacts (less than 370 mV (vs. Ag / AgCl)), it is more preferable to use as a negative electrode because the withstand voltage can be increased.

  A plurality of basic cells 22 obtained as described above are singly or stacked in series, and are stored in a case 24 and a cap 21 made of, for example, stainless steel via an insulating packing 23. At this time, a conductive paste may be applied in advance to the portion of the basic cell 22 that contacts the current collector 11, the case 24, and the cap 21. Examples of the conductive paste include a silver paste, a nickel paste, a gold paste, a vanadium paste, a carbon paste, and a graphite paste depending on the filler, but a silver paste having a low contact resistance is preferable.

  Hereinafter, specific examples of the present invention will be described.

Example 1
Gasket 13 (inner diameter (non-electron conductive butyl rubber sheet) formed on a current collector 11 (diameter: 9.0 mm, thickness: 0.1 mm) made of a conductive butyl rubber sheet in which carbon is dispersed in butyl rubber to provide conductivity. (Diameter) 4.5 mm, outer diameter (diameter) 9.0 mm, thickness 0.25 mm) are arranged concentrically, and are pressure-bonded using the adhesiveness of rubber to obtain a sheet having a current collector / gasket. (Hereinafter, electrode sheet).

  Next, a method for producing a negative electrode using polyphenylquinoxaline will be described. 25% by weight of Ketjen Black (trade name: Ketjen Black EC600JD) as a conductive auxiliary material is added to polyphenylquinoxaline, a proton-conducting compound, as a total weight of 100% by weight of polyphenylquinoxaline and ketjen black. A negative electrode sheet of 24 mm was obtained. The obtained sheet-like negative electrode was punched with a punching blade into a diameter of 4.3 mm and a thickness of 0.24 mm to obtain a thin disc-like negative electrode (electrode 15 mainly composed of a proton-conducting compound).

  A negative electrode was inserted into the electrode sheet, and a separator having a thickness of 0.055 mm punched out in advance with a diameter of 5.5 mm was concentrically arranged, pressure-bonded using the adhesiveness of rubber, and an electrolyte solution was injected. The electrolyte used 40% sulfuric acid. Moreover, the porous sheet (thickness 0.05mm) which consists of polytetrafluoroethylene was used for the separator.

Next, a method for producing the positive electrode (polarizable electrode 12) will be described. 140% by weight of 40% sulfuric acid was added to phenol-based activated carbon (specific surface area 1600 m ² / g, average particle size 5 μm) and kneaded to obtain an activated carbon electrode slurry. An activated carbon slurry is applied to the electrode sheet with PET in which PET (polyethylene terephthalate) is arranged concentrically with an inner diameter (diameter) of 4.5 mm, an outer diameter (diameter) of 10.0 mm, and a thickness of 0.1 mm on the electrode sheet gasket. Then, PET was peeled off to obtain an electrode sheet with activated carbon.

The above-mentioned electrode sheet with negative electrode and electrode sheet with activated carbon were bonded together in a vacuum, pressurized at 10 kgf / cm ² , and vulcanized and bonded at 120 ° C. for 2 hours to obtain a basic cell 22.

  The basic cell 22 was integrated into an exterior container composed of a stainless steel cap 21 and a stainless steel case 24 via a polypropylene insulating packing 23, and then caulked and sealed to obtain a coin-type aqueous hybrid capacitor.

(Example 2)
A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 1 except that the negative electrode sheet was impregnated in 40% sulfuric acid in an environment of 25 ° C., doped in advance, and used as a punched electrode after drying.

(Example 3)
Except for adding 240% by weight of aqueous electrolyte to mixed powder of 25% by weight of ketjen black (total weight of polyphenyl quinoxaline and ketjen black being 100% by weight) to polyphenylquinoxaline. A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 1.

Example 4
A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 1 except that indole trimer, which is a proton conductive compound, was used as the positive electrode and the activated carbon polarizable electrode was used as the negative electrode.

  A method for producing a positive electrode using an indole trimer will be described. The indole trimer is mixed with 20% by weight of vapor-grown carbon as a conductive auxiliary material in a powder blender, and 60% PTFE dispersion is added to the mixture so that the PTFE polytetrafluoroethylene particles become 10% by weight. After mixing in the machine, it was dried. 100% by weight was added to the obtained mixture and kneaded in a mortar. Thereafter, the kneaded product was rolled with a roll molding machine to obtain a positive electrode sheet. The obtained positive electrode sheet was punched into a positive electrode (diameter 4.3 mm, thickness 0.24 mm).

(Example 5)
A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 4 except that the positive electrode sheet was impregnated in 40% sulfuric acid in an environment of 25 ° C., doped in advance, and used as a punched electrode after drying.

(Example 6)
A positive electrode slurry was prepared by adding 160% by weight of an aqueous electrolyte to a mixed powder obtained by adding 20% by weight of vapor-grown carbon to indole trimer (with the total weight of indole trimer and vapor-grown carbon being 100% by weight). A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 1 except that.

(Example 7)
A coin-type aqueous hybrid capacitor was obtained in the same manner as in Example 1 except that the conductive paste was applied to the case and the cap in advance before integrating the basic cell with the exterior container.

(Example 8)
Same as Example 1, except that 15% by weight of VGCF was added to the activated carbon powder (the total weight of the activated carbon and VGCF was 100% by weight), and 200% by weight of the aqueous electrolyte was added to the resulting mixed powder to obtain an activated carbon electrode slurry. A coin-type water-based hybrid capacitor was obtained.

(Comparative Example 1)
A coin-type aqueous electric double layer capacitor was obtained in the same manner as in Example 1 except that the activated carbon electrode slurry was applied to the positive electrode side and the negative electrode side.

(Comparative Example 2)
Phenol-based activated carbon (specific surface area 1600 m ² / g, average particle size 5 μm) 80% by weight, ketjen black 10% by weight, polytetrafluoroethylene 10% by weight, kneaded and roll-rolled, It dried at 150 degreeC for 3 hours, and obtained the activated carbon sheet | seat (width 5cm, length 5cm, thickness 0.24mm). The obtained activated carbon sheet was punched out into a circle having a diameter of 4.3 mm, and adhered to a stainless steel case and a cap using a carbon paste. These were dried at 200 ° C. under reduced pressure for 5 hours, then transferred to a glove box in an argon atmosphere, impregnated with an organic electrolyte solution, placed facing each other through a separator, and caulked with polypropylene insulating packing. Then, a coin-type organic electric double layer capacitor was obtained. The organic electrolyte was a propylene carbonate solution containing tetraethylammonium tetrafluoroborate having a concentration of 0.8 mol / liter.

  Table 1 shows the results of measuring the internal resistance, withstand voltage, and capacitance of the obtained coin-type aqueous hybrid capacitor and coin-type electric double layer capacitor. The internal resistance was an impedance when an alternating current having an effective voltage of 10 mV and a frequency of 1 kHz was applied to the element.

(Comparative Example 3)
Phenol-based activated carbon (specific surface area 1600 m ² / g, average particle diameter 5 μm) 80% by weight, ketjen black 10% by weight, polytetrafluoroethylene 10% by weight, kneaded and roll-rolled, Drying was performed at 150 ° C. for 3 hours to obtain an activated carbon sheet (width 5 cm, length 5 cm, thickness 0.24 mm). The obtained activated carbon sheet was punched into a circle having a diameter of 4.3 mm to be a positive electrode (polarizable electrode), and was bonded to a stainless steel cap using a carbon paste. Next, N-methylpyrrolidone was added three times to a mixture of 90% by weight of natural graphite powder and 10% by weight of polyvinylidene fluoride to form a slurry, which was applied to a slenless case to obtain a negative electrode. These were dried under reduced pressure at 200 ° C. for 5 hours, then transferred into a glove box in an argon atmosphere, and a lithium metal foil having a diameter of 4.3 mm and a thickness of 0.01 mm was pressure-bonded onto the negative electrode, and 1.0 mol / liter A solution of ethylene carbonate and ethyl methyl carbonate (volume ratio 1: 1) containing LiBF ₄ was impregnated on both electrodes. Thereafter, they were placed opposite to each other with a separator interposed therebetween and caulked with a polypropylene insulating packing, and then left standing in a constant temperature bath at 65 ° C. for 20 hours to obtain a coin-type organic hybrid capacitor. The characteristic measurement results are shown in Table 1.

  As can be seen from Table 1, the water-based hybrid capacitors of Examples 1 to 8 produced according to the present invention have a higher withstand voltage and higher capacitance than the water-based electric double layer capacitor of Comparative Example 1, and thus have a high energy density. I understand. Moreover, since the internal resistance is remarkably reduced as compared with the organic electric double layer capacitor of Comparative Example 2 and the organic hybrid capacitor of Comparative Example 3, it can be seen that the output density is high. Further, from the results of Examples 1, 2, 4 and 5, the electrode doping is not performed by a chemical or electrochemical treatment process, but only by the process of impregnating the electrode with an electrolyte at room temperature. It can be seen that capacitance and internal resistance can be obtained.

Sectional drawing of the basic cell used for the water-system hybrid capacitor of this invention. Sectional drawing of a coin type water-system electric double layer capacitor.

Explanation of symbols

11 Current collector 12 Polarized electrode 13 Gasket 14 Separator 15 Electrode 21 mainly composed of proton-conducting compound Cap 22 Basic cell 23 Insulating packing 24 Case

Claims (5)

  An electrode and an electrolyte solution facing each other through a separator are accommodated in an acid-resistant material container, one electrode is a polarizable electrode mainly composed of activated carbon, and the other is an electrode mainly composed of a proton-conducting compound. An aqueous hybrid capacitor, wherein the liquid is an aqueous electrolyte.   In the proton-conducting compound, an electrode mainly composed of a material that undergoes a redox reaction at a formula oxidation / reduction potential of 370 mV (vs. Ag / AgCl) or higher in an aqueous electrolyte is used as a positive electrode, and a polarizable electrode mainly composed of activated carbon. The water-based hybrid capacitor according to claim 1, wherein the water-based hybrid capacitor is a negative electrode.   In the proton-conducting compound, an electrode mainly composed of a material that undergoes an oxidation-reduction reaction at a formula oxidation / reduction potential of less than 370 mV (vs. Ag / AgCl) in an aqueous electrolyte is used as a negative electrode, and a polarizable electrode mainly composed of activated carbon. The water-based hybrid capacitor according to claim 1, wherein the water-based hybrid capacitor is a positive electrode.   The water-based hybrid capacitor according to any one of claims 1 to 3, wherein the electrode mainly composed of the proton-conducting compound is previously impregnated in a water-based electrolyte and doped.   The polarizable electrode mainly composed of activated carbon is characterized in that a conductive auxiliary material is added in an amount of 15% by weight or less (excluding 0% by weight) based on the total weight of the mixed powder of activated carbon and conductive auxiliary material. The water-system hybrid capacitor of any one of Claims 1-4.

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