JP2005277346A - Electric double layer capacitor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor excellent in stability of long-term ESR and capacitance. <P>SOLUTION: As a material for a polarizable electrode 1 that makes up an electric double layer capacitor, the polarizable electrode 1 is composed of an electrically conductive ceramics having a structure of two or more layers with different pore sizes, and a separator 2 is made up of a non-conductive ceramics. The polarizable electrode 1 has a pore larger in size at a layer in contact with the separator. Further, the pore size of the separator 2 is smaller than that of the polarizable electrode layer 1b contacting the separator. The pore size of the polarizable electrode 1 is 1 to 20 nm, and the pore size of the separator 2 is 10 nm or smaller. The conductive ceramics making up the polarizable electrode 1, and the non-conductive ceramics making up the separator 2 are manufactured by a supramolecular template method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric double layer capacitor and a method for manufacturing the same, and more particularly to an electric double layer capacitor in which the material and structure of a polarizable electrode and a separator are optimized and a method for manufacturing the same.

  The electric double layer capacitor is a capacitor that accumulates electric charge in an electric double layer generated at the interface between the polarizable electrode and the electrolyte. The structure of the basic cell is shown in FIG. Since the polarizable electrode 10 needs to be stable and conductive with respect to the electrolytic solution and have a large surface area, powdered activated carbon and activated carbon fiber, and as shown in Patent Document 1, these activated carbons are made of polytetrafluorocarbon. As shown in Patent Document 2 and Patent Document 3, a solid activated carbon in which activated carbon is bonded to polyacene and carbon is used as formed by a binder such as fluoroethylene. Electrolyte solutions are broadly classified into aqueous solutions and organic solvents. As aqueous solutions, sulfuric acid and potassium hydroxide are mainly used, and as organic solvents, mainly quaternary ammonium salts are dissolved as an electrolyte in polypropylene carbonate. Things are used. For the separator 11, a porous film having a high ion permeability and an electronic insulating property such as a nonwoven fabric such as glass fiber or polypropylene fiber and a polyolefin-based porous film is used. As the current collector 12, rubber or elastomer imparted with conductivity by carbon powder or the like is used when an aqueous electrolyte is used, and a metal film is used when an organic solvent electrolyte is used. The gasket 13 has a role of maintaining the shape of the basic cell, preventing leakage of the electrolyte, and preventing a short circuit due to contact between the upper and lower current collectors 12. A terminal plate 14 is provided outside the current collector 12 for taking out the terminals. Further, normally, in order to reduce the internal resistance of the cell from the outside of the terminal board 14, it is fixed in a pressurized state.

  The breakdown voltage of the basic cell is determined by the electrolytic solution, and is about 0.6 to 1.0 V in the case of an aqueous solution system, and is about 2.0 to 3.0 V although it varies depending on the electrolyte to be configured in the case of an organic solvent system. In the electric double layer capacitor, basic cells are stacked in series according to a required withstand voltage in order to obtain a predetermined withstand voltage.

  Until now, electric double layer capacitors have been mainly used for relatively small current applications such as memory backup. On the other hand, in recent years, the importance of electric double layer capacitors that can supply a large current instantaneously has been recognized in order to extend the life of the battery that is the main power source and to prevent the instantaneous power supply from being interrupted. .

  One of the issues required for electric double layer capacitors is the improvement of durability when used at high temperatures. Activated carbon used for the polarizable electrode causes an electrochemical reaction between the surface functional group and the electrolytic solution, which is one of the factors that lower the durability of the electric double layer capacitor. In order to solve this factor, in patent document 4, the coating layer which consists of a silicon oxide or a metal oxide is formed in the surface of the activated carbon which comprises a polarizable electrode. In Patent Document 5, a porous conductive ceramic having a mesoporous structure is used for a polarizable electrode. In addition, as another measure for improving durability, Patent Document 6 uses a sintered ceramic fiber having ion permeability as a separator, thereby preventing the deterioration and deformation of the separator at high temperatures. .

JP-A-6-196364 Japanese Patent No. 2778425 Japanese Examined Patent Publication No. 7-70448 JP-A-9-63905 JP 2003-109873 A JP 2000-58388 A

  In the method of forming a coating layer made of silicon oxide or metal oxide on the surface of activated carbon constituting the polarizable electrode as in Patent Document 4, it is extremely difficult to form a coating layer on the entire activated carbon surface. The effect of improving the sexiness is insufficient. In Patent Document 5, since the porous conductive ceramic is an electrode material, the reaction between the activated carbon and the electrolyte does not occur, but a dry-up phenomenon in which the electrolyte solvent in the polarizable electrode evaporates to the outside is observed. Resistance). Even in a method using a sintered ceramic fiber having ion permeability as a separator as in Patent Document 6, since the polarizable electrode material itself is based on the same activated carbon as the conventional one, the reaction between the activated carbon and the electrolyte occurs. Therefore, it is still insufficient as an effect of improving durability. In order to improve durability, there is a demand for measures to prevent dry-up of the electrolyte solvent while using conductive ceramics as an electrode material as in Patent Document 5.

  That is, an object of the present invention is to provide an electric double layer capacitor that is excellent in stability of ESR and capacitance over a long period of time.

  According to the present invention, in the electric double layer capacitor comprising one or more cells containing a separator and a pair of porous polarizable electrodes facing each other through the separator inside the current collector and the gasket, The polarizable electrode is made of conductive ceramics having a structure of two or more layers having different pore diameters, and the separator is made of non-conductive ceramics, whereby an electric double layer capacitor is obtained.

  Further, according to the present invention, an electric double layer capacitor is obtained, wherein the polarizable electrode is composed of two layers, and the layer on the side in contact with the separator has a larger pore diameter.

  Further, according to the present invention, an electric double layer capacitor is obtained, wherein the pore diameter of the separator is smaller than the pore diameter of the polarizable electrode layer in contact with the separator.

  According to the invention, there is obtained an electric double layer capacitor characterized in that the pore diameter of the polarizable electrode is in the range of 1 to 20 nm.

  Further, according to the present invention, an electric double layer capacitor is obtained, wherein the pore diameter of the separator is in the range of 10 nm or less.

  Furthermore, according to the present invention, there is provided an electric double layer capacitor comprising at least one cell containing a separator and a pair of porous polarizable electrodes facing each other through the separator inside the current collector and the gasket. The manufacturing method includes a step of forming a polarizable electrode made of conductive ceramic on a current collector, and a step of forming a separator made of nonconductive ceramic on the polarizable electrode. A method for producing a multilayer capacitor is obtained.

  And according to this invention, the process of forming the said electroconductive ceramics and a nonelectroconductive ceramic includes the pore formation process by a supramolecular template method, The electric double layer capacitor manufacturing method characterized by the above-mentioned is obtained.

  As described above, the above-described solution means that the electrolyte solution in the pores can be easily impregnated and the electrolyte solution can be prevented from being dried up, so that durability during high temperature use can be improved.

  That is, according to the present invention, an increase in ESR and a decrease in capacitance during high temperature use can be suppressed, and an electric double layer capacitor excellent in reliability can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a cross-sectional view of a cell and a terminal plate portion of an electric double layer capacitor according to the present invention. As shown in FIG. 1, a laminated cell is formed by stacking a required number of unit cells formed of a polarizable electrode 1, a separator 2, a current collector 3 and a gasket 4, and a terminal plate 5 is arranged on both outer sides thereof. doing. A conductive layer 6 is formed at a portion where the terminal plate 5 and the current collector 3 are in contact with each other. Further, an exterior film 7 is disposed on the outer periphery of the terminal board 5.

  The polarizable electrode 1 is composed of a mixture of a porous conductive ceramic powder having a mesoporous structure and a binder powder. The polarizable electrode 1 further comprises two layers, a polarizable electrode 1a in contact with the current collector 3 and a polarizable electrode 1b in contact with the separator 2. The polarizable electrode 1b has a larger pore diameter than the polarizable electrode 1a. Here, the porous conductive ceramic powder in the polarizable electrode 1 is produced by a supramolecular template method. That is, it is produced by forming a pore structure based on a metal oxide and using a surfactant or a polymer material as a template. The difference in pore diameter between the polarizable electrode 1a and the polarizable electrode 1b is determined by the molecular weight of the surfactant or polymer material used for the template. In the polarizable electrode 1b having a large pore diameter, the surfactant or polymer used for the template is used. Set the molecular length of the material larger.

  The separator 2 is made of a mixture of porous ceramic powder and binder powder. The porous ceramic powder in the separator 2 is based on an insulating oxide typified by silica powder and can form a pore structure in the same manner as the polarizable electrode 1, but the pore diameters are adjacent. It is smaller than the pore diameter in the polarizable electrode 1b. The current collector 3 is made of metal foil, conductive rubber, or elastomer. The gasket 4 is a thing for ensuring the insulation in a cell, for example, butyl rubber and a thermoplastic resin are used. The terminal board 5 is a thing for taking out the electric charge inside a cell, and is a 0.05-1 mm-thick metal plate. The conductive layer 6 is for reducing the contact resistance between the terminal plate 5 and the cell, and is, for example, a layer of silver, carbon and resin. A typical example of the exterior film 7 is a laminate film.

  Next, the present invention will be specifically described with reference to some examples and comparative examples.

  First, the manufacturing process is shown in FIG. 2 using a schematic cross-sectional view. Twelve of the current collectors 3 on which the gasket 4 was bonded by thermocompression bonding were produced. The current collector 3 is made of a conductive olefin copolymer and has a size of 18 × 30 × 0.025 mm. The gasket 4 is made of an ethylene methacrylic acid copolymer resin, and has an outer size of 18 × 30 mm, an inner size of 12 × 24 mm, and a thickness of 0.050 mm, each processed into a frame shape.

Next, a sol was prepared using sodium stannate trihydrate as a starting material and a surfactant n-cetylpyridinium chloride as a template, an indium compound was added, and the resulting gel was dried at 40 ° C. for 24 hours. Was heat-treated at 600 ° C. for 5 hours to obtain fine powder of conductive mesoporous tin oxide. When the average pore diameter of the obtained powder was measured, it was 1.2 nm. The pore diameter was calculated by measuring the adsorption isotherm of N ₂ gas using a specific surface area measuring device “BELSORP28SA” manufactured by Nippon Bell Co., Ltd. A polytetrafluoroethylene-based binder was mixed with this powder, and ethanol was added as a solvent and kneaded. The paste thus obtained was applied onto the current collector 3 on which all 12 gaskets 4 were bonded, and dried to obtain a polarizable electrode 1a. The dimension of the polarizable electrode 1a is 12 × 24 × 0.020 mm.

  Subsequently, a fine powder of conductive mesoporous tin oxide was obtained in the same manner using sodium stannate trihydrate as a starting material and using P123 (Aldrich) instead of n-cetylpyridinium chloride. It was 7 nm when the average pore diameter of the obtained powder was measured. A paste composed of a polytetrafluoroethylene-based binder and ethanol as a solvent was prepared. This paste was applied on all 12 polarizable electrodes 1a and dried to obtain polarizable electrodes 1b. The dimension of the polarizable electrode 1b is 12 × 24 × 0.020 mm.

  Further, a sol was prepared using tetraethyl orthosilicate as a starting material and surfactant P123 (Aldrich) as a template, and then dried. The obtained gel was heat-treated at 500 ° C. for 5 hours to obtain a fine powder of mesoporous silicon oxide. It was. It was 5 nm when the average pore diameter of the obtained powder was measured. A paste composed of a polytetrafluoroethylene-based binder and ethanol as a solvent was prepared. This paste was applied onto 6 out of 12 polarizable electrodes 1b and dried to obtain a separator 2. The size of the separator is 12 × 24 × 0.020 mm.

  Thus, the current collector / gasket composite (first composite 8) coated only with polarizable electrodes 1a and 1b, and the composite coated with polarizable electrodes 1a and 1b and separator 2 (second composite). After preparing six bodies 9) each, 40 wt% sulfuric acid aqueous solution was added onto the polarizable electrode 1. The produced first composite 8 with added sulfuric acid and second composite 9 were superposed, and the internal gasket was melted and bonded by thermocompression bonding. After producing six single cells in this way, the single cells were overlapped to produce a six-cell laminate.

  A silver paste was applied to one side of a tin-plated copper terminal board 5 having a thickness of 0.1 mm and dried to form a conductive layer 6. From both sides of the prepared laminated cell, the terminal plate 5 is overlapped so that the conductive layer 6 and the laminated cell are in contact with each other, and an exterior film 7 is arranged from the outside, and the overlapping portions of the exterior films are heat-sealed under reduced pressure. By doing so, the terminal film and the exterior film sealing body of the lamination | stacking cell were formed. Here, a laminate film having a thickness of 0.08 mm was used as the exterior film 7. Ten electric double layer capacitors were produced by the above method.

  In Example 1, the conductive mesoporous tin oxide used for the polarizable electrode 1a was prepared by changing the average pore diameter to 1, 5, and 10 nm, and 10 electric double layer capacitors were respectively formed in the same manner as in Example 1. Produced. In addition, in order to change an average pore diameter, the kind of surfactant used for a casting_mold | template and the heat processing conditions of gel were changed as Table 1. FIG.

  In Example 1, the mesoporous silicon oxide used for the separator 2 was prepared by changing the average pore diameter to 7, 10, and 15 nm, and 10 electric double layer capacitors were produced in the same manner as in Example 1.

  In addition, in order to change an average pore diameter, the kind of surfactant used for a casting_mold | template and the heat processing conditions of gel were changed as Table 2.

  In Example 1, conductive mesoporous tin oxide used for the polarizable electrode 1b was prepared by changing the average pore diameter to 20 and 30 nm, and 10 electric double layer capacitors were produced in the same manner as in Example 1. .

  In addition, in order to change an average pore diameter, the kind of surfactant used for a casting_mold | template and the heat processing conditions of gel were changed as Table 3. FIG.

  (Comparative Example) FIG. 3 is a sectional view of an electric double layer capacitor used in the comparative example. The manufacturing method will be described below.

  In the comparative example, the polarizable electrode 1 was produced by the following method. A sol was prepared using sodium stannate trihydrate as a starting material and a surfactant n-cetylpyridinium chloride as a template, an indium compound was added, and the resulting gel was dried at 40 ° C for 24 hours. Was heat-treated for 5 hours to obtain fine powder of conductive mesoporous tin oxide. The average pore diameter of the obtained powder was 1.2 nm. A polytetrafluoroethylene-based binder was mixed with this powder, and ethanol was added as a solvent and kneaded. The paste thus obtained was applied onto the current collector 3 on which all 12 gaskets 4 were bonded, and dried to obtain the polarizable electrode 1. The dimension of the polarizable electrode 1 is 12 × 24 × 0.040 mm.

  The separator 2 was substituted by placing a sheet made of polytetrafluoroethylene fiber on the polarizable electrode 1. The dimensions of the separator 2 are 12 × 24 × 0.020 mm, and the average pore diameter is 20 nm.

  A sample was prepared in the same manner as in Example 1 except for the polarizable electrode 1 and the separator 2. Ten electric double layer capacitors were produced by the above method.

  As described above, electric double layer capacitors produced by the methods of Examples 1, 2, 3, 4 and Comparative Examples were obtained.

  For the electric double layer capacitors produced by the methods of Examples 1, 2, 3, 4 and Comparative Examples, the ESR and the capacitance were 70 ° C., 5.4 V (0.9 V per cell), Measurement was performed for each after a load of 000 hours and cooling to room temperature. Here, the ESR was determined by applying an alternating voltage of 1 kHz and 10 mVrms and measuring the current and the phase difference. The capacitance was determined by applying an alternating voltage of 1 Hz and 10 mVrms and measuring the current and phase difference.

  Table 4 shows the results of investigating the ESR and capacitance before and after voltage loading of the electric double layer capacitors produced by the methods of Example 1 and Comparative Example. In addition, ESR and an electrostatic capacitance are the average values of 10 produced samples.

  From Table 4, when the ESR and capacitance of Example 1 and the comparative example are compared, the ESR and capacitance immediately after sample preparation are almost unchanged, but the ESR and capacitance after voltage loading are the same as those of Example 1. Indicates a better value. This is because, in Example 1, the layer of the polarizable electrode 1b has a large pore diameter so that a large amount of the electrolyte can be retained, and because the separator 2 has a small pore diameter, the electrolyte is not absorbed on the separator side. The reason for this is that it is easy to be retained.

  From the above results, the polarizable electrode is composed of conductive ceramics having a structure of two or more layers having different pore diameters, the separator is composed of non-conductive ceramics, and the layer in contact with the separator has larger pores. Thus, it can be seen that durability during high temperature use can be improved.

  Table 5 shows the results of investigating the ESR and capacitance before and after voltage loading of the electric double layer capacitors produced by the methods of Examples 1 and 2. In addition, ESR and an electrostatic capacitance are the average values of 10 produced samples.

  From Table 5, when the ESR and capacitance of Examples 1 and 2 are compared, the ESR and capacitance after voltage loading tend to deteriorate in the sample with the average pore diameter of the polarizable electrode 1a of 10 nm. This is considered to be because when the average pore diameter of the polarizable electrode 1a is larger than 1b, the electrolytic solution is transmitted through the polarizable electrode 1a and the electrolytic solution is easily dried up from the current collector. From this, it can be seen that the polarizable electrode may be such that the layer on the side in contact with the separator has larger pores.

  Further, in the sample having the average pore diameter of the polarizable electrode 1a of 1 nm, the initial ESR is larger than that of the other samples. This is presumably because the movement of ions in the electrolyte becomes rate-limiting due to the decrease in pore diameter. This shows that the average pore diameter of the polarizable electrode should be 1 nm or more.

  Table 6 shows the results of investigating the ESR and capacitance before and after voltage loading of the electric double layer capacitors produced by the methods of Examples 1 and 3. In addition, ESR and an electrostatic capacitance are the average values of 10 produced samples.

  From Table 6, when comparing the ESR and capacitance of Examples 1 and 3, in the sample where the average pore diameter of the separator 2 exceeds the polarizable electrode 1b, the ESR and capacitance after voltage loading tend to deteriorate. This is considered to be because when the average pore diameter of the separator 2 is larger than the polarizable electrode 1b, the electrolytic solution is easily absorbed by the separator and the electrolytic solution in the polarizable electrode is easily lost. Therefore, the pore diameter of the separator is preferably smaller than the pore diameter of the polarizable electrode layer in contact with the separator.

  In addition, in the sample having an average pore diameter of 15 nm of the separator 2, the initial capacitance is greatly reduced. This is presumably because the leakage current increases as the average pore diameter of the separator 2 increases. From the above, it can be seen that the pore diameter of the separator should be 10 nm or less.

  Table 7 shows the results of investigating the ESR and capacitance before and after voltage loading of the electric double layer capacitors produced by the methods of Examples 1 and 4. In addition, ESR and an electrostatic capacitance are the average values of 10 produced samples.

  From Table 7, when the ESR and electrostatic capacity of Examples 1 and 4 are compared, the sample with the average pore diameter of the polarizable electrode 1b of 30 nm has a large initial ESR. This is presumably because the contact between the electrode materials is lost as the average pore diameter of the polarizable electrode 1b increases. From the above, it can be seen that the average pore diameter of the polarizable electrode may be 20 nm or less.

  As described above, by implementing the present invention, good results were obtained for ESR and capacitance before and after voltage loading of the electric double layer capacitor.

  The powder used for producing the polarizable electrode 1 is not limited to the substances described in the examples as long as it is another porous conductive ceramic powder material capable of realizing equivalent internal resistance and capacitance. Similarly, the surfactant and binder used for producing the polarizable electrode 1 are not limited to the substances described in the examples. The solvent used in the paste when forming the polarizable electrode 1 can be replaced by any solvent other than ethanol that does not cause dissolution and reaction of the substance used. The powder used in the separator 2 is not limited to the substances described in the examples as long as it is an insulating porous ceramic powder material. As the current collector 3, a conductive olefin copolymer is used, but the material is not limited to this as long as it is a material that can realize an equivalent internal resistance. As the gasket 4, an ethylene-methacrylic acid copolymer resin is used, but the material is not limited to this as long as the material contains a functional group having polarity in the molecule. The terminal board 5 is described as a tin-plated copper terminal board. However, the terminal board 5 is not limited to this as long as the material has equivalent resistance and ESR stability. The conductive layer 6 is made of a solid material obtained by drying a silver paste, but is not limited to this as long as an equivalent internal resistance can be realized. Although a laminate film having a thickness of 0.08 mm is used as the exterior film 7, it is not limited to this as long as equivalent internal resistance can be realized. Moreover, the polarizable electrode 1b may be comprised from the polarizable electrode of two or more layers, and the relationship of a mutual pore diameter should just be satisfy | filled with respect to the polarizable electrode 1a and a separator.

Sectional drawing of the electric double layer capacitor by this invention. Sectional drawing explaining the cell manufacturing process of the electric double layer capacitor by this invention. Sectional drawing of the electrical double layer capacitor by a comparative example. The typical section which shows the basic cell structure of an electric double layer capacitor.

Explanation of symbols

1, 1a, 1b, 10 Polarized electrode 2, 11 Separator 3, 12 Current collector 4, 13 Gasket 5, 14 Terminal plate 6 Conductive layer 7 Exterior film 8 First composite 9 Second composite

Claims (7)

  In the electric double layer capacitor comprising at least one cell that houses a separator and a pair of porous polarizable electrodes opposed via the separator inside the current collector and gasket, the polarizable electrode is thin. 2. An electric double layer capacitor comprising conductive ceramics having a structure of two or more layers having different hole diameters, wherein the separator is made of non-conductive ceramics.   2. The electric double layer capacitor according to claim 1, wherein the polarizable electrode is composed of two layers, and the layer on the side in contact with the separator has a larger pore diameter.   The electric double layer capacitor according to claim 1 or 2, wherein the pore diameter of the separator is smaller than the pore diameter of the polarizable electrode layer in contact with the separator.   The electric double layer capacitor according to any one of claims 1 to 3, wherein a pore diameter of the polarizable electrode is in a range of 1 to 20 nm.   The electric double layer capacitor according to any one of claims 1 to 4, wherein the separator has a pore diameter in a range of 10 nm or less.   In a method of manufacturing an electric double layer capacitor, comprising at least one cell that houses a separator and a pair of porous polarizable electrodes facing each other with the separator inside the current collector and gasket, A method for producing an electric double layer capacitor, comprising: a step of forming a polarizable electrode made of conductive ceramics; and a step of forming a separator made of nonconductive ceramics on the polarizable electrode.   7. The method of manufacturing an electric double layer capacitor according to claim 6, wherein the step of forming the conductive ceramic and the non-conductive ceramic includes a pore formation process by a supramolecular template method.

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