JP2007317812A - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor which betters an adhesion between a collector and a terminal plate to materialize a low ESR, and has an excellent durability during using at a high temperature. <P>SOLUTION: A pair of electrodes which are disposed opposite to each other through a separator, a pair of collectors which are disposed outside of the pair of electrodes, and a plurality of unit cells 5 are laminated which have a frame-shaped gasket which seals circumferences of the separator and electrode together with the collectors. The collectors on upper and lower ends are connected to a terminal plate 7 for taking out a terminal via a conductive adhesive 6 containing a low repulsive elastic rubber based binder. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor, and in particular, a porous body is used for an electrode, a porous insulator is used for a separator, and the electrode and the separator are laminated in a flat shape without being wound, and an electric double layer capacitor using an electrolytic solution About.

  In recent years, in portable electronic devices such as mobile phones, low current and low voltage have been achieved. However, depending on the function, a very large current may be required instantaneously. As a result of voltage fluctuations (IR drop, etc.) in the power source, the electronic circuit may not operate normally or the life of the battery may be shortened.

  For example, in a communication card or the like, if the operating voltage falls below the lower limit value, the communication state cannot be secured and a communication error occurs. For this reason, only when instantaneously a large current is required, power is supplied from an electric double layer capacitor capable of rapid charging and discharging of a large current to level the entire power. Furthermore, with the miniaturization and thinning of electronic devices, electric double layer capacitors are also required to be small and thin.

  However, as the size and thickness are reduced, conversely, ESR (equivalent series resistance) increases, and it has become difficult to supply a large current as an original function. The ESR is composed of, for example, a specific resistance such as an electrode, a terminal and a lead wire, and a contact resistance, which constitute a capacitor as an element.

  FIG. 3 is an exploded perspective view for explaining a cell of an electric double layer capacitor according to the prior art, and FIG. 4 is a diagram for explaining the prior art, a schematic configuration diagram and assembly of the electric double layer capacitor. It is a disassembled perspective view which shows a method. FIG. 5 is a cross-sectional view for explaining a conventional electric double layer capacitor.

  As shown in FIG. 3 to FIG. 5, in the electric double layer capacitor cell 5, a pair of plate-like electrodes 1 are disposed on both sides of the separator 2, and a current collector 3 is disposed on the opposite side of the separator 2 of the electrode 1. It has a frame-like gasket 4 which is disposed and is interposed in the current collector 3 around the electrode 1 and the separator 2, and is sealed in a state in which an electrolytic solution is contained therein. Since the electrode 1 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 those activated carbon molded with a binder such as polytetrafluoroethylene ( For example, Patent Document 1) or solid activated carbon obtained by binding activated carbon to polyacene and carbon (for example, Patent Document 2 and Patent Document 3) is used. 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, quaternary ammonium salts are mainly dissolved in propylene carbonate as electrolytes. Things are used. For the separator 2, a porous film having an electronic insulating property and a high ion permeability such as a nonwoven fabric such as glass fiber and polypropylene fiber and a polyolefin-based porous film is used. For the current collector 3, 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 4 has a role of maintaining the shape of the cell, preventing leakage of the electrolyte, and preventing a short circuit due to contact between the upper and lower current collectors 3. As shown in FIG. 4, the electric double layer capacitor 9 is provided with terminal plates 7 for taking out terminals above and below the cell 5, and usually sealed with an exterior film 8 made of a laminate film from the outside of the terminal plate 7. Yes.

  The withstand voltage of the 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 about 2.0 to 3.0 V depending on the electrolyte to be configured in the case of an organic solvent system. In an electric double layer capacitor, cells are stacked in series according to the required withstand voltage.

  The characteristics required for the electric double layer capacitor include low ESR because it can be used even at high currents, and improvement in durability at high temperature use. In the conventional electric double layer capacitor, the contact resistance between the current collector and the terminal plate is large, and thus the ESR may be increased. In addition, when the contact resistance between the current collector and the terminal plate is large, the durability during high temperature use is reduced. As a method for improving the contact resistance between the current collector and the terminal plate, there is a description (for example, Patent Document 4) in which a silver paste is applied as a conductive adhesive between the current collector and the terminal plate.

JP-A-6-196364 Japanese Patent No. 2778425 Japanese Examined Patent Publication No. 7-70448 JP 2001-250742 A

  Even the technique of Patent Document 4 described above is not sufficient for reducing the contact resistance between the current collector and the terminal plate and high-temperature durability.

  The present invention was made to solve such problems, and the technical problem was to improve the contact resistance between the current collector and the terminal plate, to reduce ESR, and to improve the durability during high temperature use. It is to provide an electric double layer capacitor.

  In order to solve the above-mentioned problems, the present invention improves the adhesion between the current collector and the terminal plate by adding a low-rebound elastic rubber binder to the conductive adhesive applied between the current collector and the terminal plate. It has been found to improve.

  The electric double layer capacitor of the present invention includes a pair of electrodes disposed opposite to each other via a separator, a pair of current collectors disposed outside the pair of electrodes, and the current collector together with the separator and the electrodes A plurality of unit cells each having a frame-like gasket that seals the periphery are stacked, and the current collector on the upper and lower end surfaces and the terminal plate for taking out the terminal contain a low-rebound resilience rubber-based binder. It is characterized by being connected through a conductive adhesive.

  In the electric double layer capacitor of the present invention, it is preferable that the content of the low-elasticity rubber binder in the conductive adhesive is 3 to 18% by weight.

  The electric double layer capacitor of the present invention improves the adhesion between the current collector and the terminal plate by incorporating a low-elasticity rubber-based binder into the conductive adhesive applied between the current collector and the terminal plate. Therefore, ESR can be reduced, and furthermore, the adhesion between the current collector and the terminal board during high temperature use can be maintained, so that the increase in ESR due to temperature change is small and high temperature durability is improved. be able to.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the electric double layer capacitor of the present invention, and FIG. 2 is a cross-sectional view showing a cell as a unit of the electric double layer capacitor of the present invention.

  As shown in FIG. 1, the electric double layer capacitor according to the present invention includes a plurality of cells 5 that are units composed of electrodes, separators, current collectors, and gaskets, which are stacked in accordance with a predetermined voltage. In order to take out, what comprised the terminal board 7 arrange | positioned on the electrical power collector of an upper-lower-end surface through the conductive adhesive 6 is sealed with the exterior film 8, and is comprised. Here, the conductive adhesive 6 is made of a conductive material such as silver, copper, or carbon, and a low-rebound resilience rubber-based binder, such as fluorine rubber, acrylic rubber, or butyl rubber. The terminal plate 7 is a metal plate having a thickness of 0.05 to 1 mm, and the exterior film 8 is made of a laminate film obtained by bonding a metal foil and a polyolefin film, polyolefin, polyester, polyvinyl chloride, neoprene, or the like. A heat-shrinkable tube or the like is used.

  A cell 5 serving as a unit used in the electric double layer capacitor of the present invention is formed of an electrode 1, a separator 2, a current collector 3 and a gasket 4 as shown in FIG. The electrode 1 is made of activated carbon typified by an insulator pattern, carbon for ensuring conductivity, and a binder. The separator 2 is a porous film. For example, a polytetrafluoroethylene film or a polyolefin film is used. The outer dimension of the separator 2 is not less than the outer dimension of the electrode 1 and not more than the outer dimension of the current collector 3. The current collector 3 is made of metal foil or conductive rubber or resin. The gasket 4 is for securing insulation in the cell, and a thermoplastic resin typified by polyethylene, polypropylene, ethylene-methacrylic acid copolymer, or a rubber or resin that can be bonded to the thermoplastic resin is used. Here, the gasket is disposed on the outer periphery of the electrode 1, the separator 2, and the current collector 3.

  Next, the structure of the cell will be described using an example of dimensions. The electrode 1 is an activated carbon / carbon composite material and is processed into a rectangle having dimensions of 12 × 24 × 0.05 mm. The separator 2 is made of polytetrafluoroethylene-based fiber, and is processed into a rectangle with dimensions of 14 × 26 × 0.025 mm. The current collector 3 is made of a conductive olefin copolymer, and is processed into a rectangle having a size of 16 × 28 × 0.05 mm.

  The gasket 4a on the outer periphery of the electrode is made of ethylene-methacrylic acid copolymer resin. The outer dimensions are 18x30mm, the inner dimension is 12x24, and the thickness is 0.05mm. Each is processed into a frame shape. The gasket 4b on the outer periphery of the separator has an outer dimension of 18 × 30 mm, an inner dimension of 14 × 26, and a thickness of 0.025 mm, and is processed into a frame shape. The gasket 4c on the outer peripheral portion of the current collector has two outer dimensions of 18 × 30 mm, an inner dimension of 16 × 28 mm, and a thickness of 0.050 mm. Each cell is processed into a frame shape. The resin used for each of the gaskets 4a, 4b, and 4c can be a resin having significantly different physical properties depending on the structure. Here, a resin having a softening point of 61 ° C. and a melting point of 88 ° C. was used.

  The dimension of the cell 5 as a unit produced is a rectangular parallelepiped of 18 × 30 × 0.225 mm. Six cells 5 serving as a unit were laminated, and the terminal plate 7 was connected to the current collector 3 on the upper and lower end faces through a conductive adhesive 6 mainly composed of silver containing a low-elasticity rubber-based binder. The terminal plate 7 is made of a copper plate having a thickness of 0.1 mm, and a lead tab portion having a width of 3 mm is formed on a 17 × 29 mm rectangular portion that contacts the cell. Furthermore, the exterior film 8 is arrange | positioned from the outer side, the exterior film sealing body is formed by heat-sealing the part which the exterior films overlapped, and an electrical double layer capacitor is produced. Here, a laminate film having a thickness of 0.11 mm was used as the exterior film 8.

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

As shown in FIG. 2, two sheets were prepared by bonding the current collector 3 and the gaskets 4a and 4c by thermocompression bonding. A slurry formed with a ratio of 75: 10: 10: 5 of a composition ratio of 75: 10: 10: 5 of powdered coconut shell activated carbon having an average particle diameter of 15 μm, non-spherical carbon having an average particle diameter of 15 μm, fibrous carbon having a fiber diameter of 10 to 20 μm, and a binder, This was applied onto a current collector inside the gasket and dried to form an electrode 1. In this way, two current collectors 3 to which the electrode 1 was applied were produced, and then a gasket 4b was bonded to one of them by thermocompression bonding. Next, a 40 wt% aqueous sulfuric acid solution was added onto the electrode 1. A portion other than 12 × 24 mm in contact with the electrode 1 in the separator 2 was subjected to pressure pretreatment at 25 ° C., 5 kg / cm ² for 1 second. After this separator 2 was placed on one of the sheets added with sulfuric acid, the two sheets were bonded so that the current collector was on the outside, and the gasket was melted and bonded by thermocompression bonding.

  As shown in FIG. 1, six cells 5 as a unit produced by this method were stacked to prepare a stacked cell. From both sides of the prepared laminated cell, a copper terminal board 7 having a thickness of 0.1 mm and a conductive adhesive 6 made of a silver paste containing 3% by weight of a fluororubber binder with a thickness of 0.01 mm is laminated. In this state, the exterior film 8 was further arranged from the outside, and the overlapping portion of the exterior films was heat-sealed under reduced pressure to form the terminal film 7 and the exterior film sealing body of the laminated cell. Here, a laminate film having a thickness of 0.11 mm was used as the exterior film 8. Ten electric double layer capacitors 9 were produced by the above method.

  In Example 1, the fluororubber binder content of the conductive adhesive 6 was 10% by weight. Otherwise, ten electric double layer capacitors were produced in the same manner as in Example 1.

  In Example 1, the fluororubber binder content of the conductive adhesive 6 was 18% by weight. Otherwise, ten electric double layer capacitors were produced in the same manner as in Example 1.

  About the electric double layer capacitor produced by the above method, the ESR was measured immediately after producing the sample and after cooling to room temperature by applying a load of 1,000 hours at 70 ° C., 5.4 V (0.9 V per cell). The results shown in Table 1 were obtained. In addition, a numerical value is an average value of 10 produced samples. Here, ESR and capacitance were determined by applying an alternating voltage of 1 kHz and 10 mVrms and measuring the current and phase difference. Further, as Reference Example 1, an electric double layer capacitor using a conductive adhesive made of a silver paste containing 20% by weight of the same kind of fluororubber binder as in Example 1, and as a comparative example 1, a high resilience rubber binder. An electric double layer capacitor using a conductive adhesive comprising a silver paste containing 10% by weight of a urethane binder, and, as Comparative Example 2, a silver paste containing 10% by weight of a polyamide binder as a resin binder Ten electric double layer capacitors using a conductive adhesive consisting of the following were prepared, and immediately after the sample was prepared and after being loaded at 70 ° C., 5.4 V, 1,000 hours and cooled to room temperature, ESR was measured.

  As a result, as shown in Table 1, when the initial ESR is compared, it can be seen that Examples 1, 2, and 3 are all about 10% lower than the comparative example. Here, the initial ESR of Reference Example 1 using a low-rebound resilience rubber-based binder of the same type as in Examples 1, 2, and 3 is higher than that in Examples 1, 2, and 3 in that the amount of binder added If the amount is too much, the silver ratio on the surface and inside of the silver paste decreases, indicating that the effect of reducing the contact resistance between the current collector and the terminal plate is reduced. To reduce ESR, the binder addition rate is 18% by weight. It turns out that the following is effective. In addition, the initial ESR of Comparative Example 1 using a high resilience rubber-based binder is higher than that of Example 2 because of the high resilience of the binder present on the silver paste surface, It is considered that contact with the silver component is inhibited.

  Next, when ESR after 1,000 hours was compared at 70 ° C., 5.4 V, Examples 1, 2, and 3 had a change rate of 10% or less with respect to ESR immediately after sample preparation. Comparative Example 1 had a change rate of 10% or more, and Comparative Example 2 had a change rate of 400% or more. This is because Examples 1, 2, and 3 using a rubber binder, Reference Example, and Comparative Example 1 are slightly deformed even when current collectors, gaskets, terminal boards, laminates, and the like due to voltage application and high temperature storage are slightly deformed. The silver paste also follows and deforms due to the elasticity of the binder, so that the ESR is hardly lowered. However, in Comparative Example 2 using a resin-based binder that does not have elasticity, the current collector or gasket is When the terminal board, laminate, etc. were deformed, the silver paste itself could not follow the deformation, and the adhesion between the current collector and the terminal board was weakened during the long-term test, and the ESR was lowered due to peeling.

  In Examples 1, 2, and 3, since Example 2 showed the best results for both the initial ESR and the ESR after the high temperature test, the binder content should be around 10% by weight. It can be said that a greater effect can be obtained.

  The embodiment of the present invention has been described in detail with reference to the drawings. Needless to say, the specific configuration is not limited to this embodiment, and the design of the present invention is not limited to the scope of the present invention. Any changes or the like are included in the present invention.

Sectional drawing of the electric double layer capacitor of this invention. Sectional drawing of the cell used as the unit of the electric double layer capacitor of this invention. The disassembled perspective view for demonstrating the cell of the electric double layer capacitor of a prior art. The disassembled perspective view which shows schematic structure of the electrical double layer capacitor of a prior art. Sectional drawing which shows the structure of the electrical double layer capacitor of a prior art typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode 2 Separator 3 Current collector 4,4a, 4b, 4c Gasket 5 Cell 6 Conductive adhesive 7 Terminal board 8 Exterior film 9 Electric double layer capacitor

Claims (3)

  A pair of electrodes opposed to each other via a separator, a pair of current collectors arranged outside the pair of electrodes, and a frame-like shape that seals the separator and the electrodes together with the current collector A plurality of unit cells having gaskets are stacked, and the current collectors on the upper and lower end surfaces and the terminal plate for taking out the terminals are connected via a conductive adhesive containing a low-elasticity rubber binder. An electric double layer capacitor characterized by that.   2. The electric double layer capacitor according to claim 1, wherein the content of the low rebound elastic rubber binder in the conductive adhesive is 3 to 18% by weight.   The electric double layer capacitor according to claim 1 or 2, wherein the low-rebound resilience rubber is at least one selected from fluorine rubber, acrylic rubber, and butyl rubber.

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