JP2006278618A - Electric double-layer capacitor and gas discharge valve thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor which can acquire superior durability thereof with the inclusion of a vessel, while the maximum characteristic of a carbon material is attained, even when the principal material of polarizing electrodes uses the carbon material having a larger expansion coefficient resulting from charging, such as a non-porous carbon. <P>SOLUTION: The vessel 21 is formed of a soft resin film in the laminated structure including an intermediate layer of metal foil, and a liquid storing unit 35 which can store a certain amount of electrolytic liquid, corresponding to the increase in the amount of impregnation resulting from expansion of a laminate 22 is set in the periphery of the laminate 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor and a gas vent valve suitable for an electric double layer capacitor.

  2. Description of the Related Art In recent years, attention has been focused on application technologies of electric double layer capacitors that are excellent in high-speed charge / discharge, charge / discharge depth, and charge / discharge cycle characteristics as various power storage elements. The electric double layer capacitor includes a laminate composed of a positive electrode body, a negative electrode body, and a separator interposed therebetween, a container for sealing the laminate together with an electrolyte solution, and a pair of electrodes disposed outside the container. And a pair of terminals are connected to a bundling portion of the positive and negative electrodes having the same polarity.

  In the positive electrode body and the negative electrode body, a polarizable electrode is formed using a carbonaceous material as a main raw material, and a current collector is attached to the carbon electrode. Electric charges are accumulated on the carbon electrode, and electricity is supplied and taken out through a pair of terminals (connected to the bundling portions of the current collector with the same polarity). As a carbonaceous material for forming a polarizable electrode, porous activated carbon is often used (Patent Document 1, Patent Document 2). Moreover, nonporous carbon is known as a carbonaceous material replacing activated carbon (Non-patent Document 1).

Non-porous carbon is obtained by dry distillation and alkali activation of graphitized charcoal, and has a specific surface area of 100 m ² / g or less, which is so small that it can be regarded as almost only the external specific surface area, and the interlayer distance of the carbon structure is small. It is 0.36-0.37 nm graphite-like carbon. For an electric double layer capacitor using a polarizable electrode formed of such non-porous carbon as a main raw material, capacitance is generated for the first time by charging. Before charging, even though non-porous carbon does not have pores that can take in various electrolyte ions, solvents, N ₂ gas, etc., the capacitance is generated by charging because of the solvent between the layers of the carbon structure. It is presumed that this is due to intercalation of electrolyte ions accompanied by (solvent co-intercalation).
JP 2002-299168 A JP2003-124078 “High Energy Density Electric Double Layer Capacitor” (Applied Physics Vol. 37, No. 8 (2004))

  In the case of Patent Document 1 and Patent Document 2, the container for sealing the laminate together with the electrolyte solution is formed from a resin film having a laminated structure including an intermediate layer of metal foil, and the laminate is accommodated together with the electrolyte solution by heat welding. Sealing is applied.

  In the electric double layer capacitor, when a gaseous decomposition product is generated due to charge and discharge, the internal pressure of the container is increased, which may impair the sealing performance of the container. For this reason, in order to maintain the internal pressure of the container at a predetermined level while preventing the intrusion of outside air, it is conceivable to assemble a gas vent valve in the sealed part of the container. However, when the main material of the polarizable electrode is a carbonaceous material having a large expansion coefficient associated with charging, such as non-porous carbon, peeling of the sealed portion (thermal welding portion) of the container is likely to occur due to the expansion of the laminate. Become. Further, when the laminate contracts with discharge, the amount of the electrolyte solution impregnated in the laminate decreases, so that the electrolyte solution overflows outside the laminate inside the container and easily enters the vent valve. There is also a possibility of damaging the good function of the.

  In order to cope with such a problem, the present invention maximizes the characteristics of the carbonaceous material even when the main material of the polarizable electrode is a carbonaceous material having a large expansion coefficient associated with charging, such as non-porous carbon. An object of the present invention is to provide an electric double layer capacitor capable of ensuring good durability including a container while drawing out to the limit.

  The first invention includes a step of forming a polarizable electrode using a carbonaceous material as a main raw material and attaching a current collector to the carbon electrode to form a positive electrode body and a negative electrode body, and a positive electrode body, a negative electrode body, and a separator. A step of composing a flat laminate, a step of bonding a pair of terminals to the bundling portions of the same polarity as the lead portions of the positive electrode body and the negative electrode body, and a state in which a part of the pair of terminals protrudes from the container The step of impregnating the injected electrolyte solution containing the laminated body, the step of applying a voltage between the pair of terminals in order to activate the electric field of the carbon electrode, and sealing the opening of the container from which a part of the pair of terminals protrudes In the electric double layer capacitor manufactured through the process, the container is formed from a flexible resin film having a laminated structure including an intermediate layer of metal foil, and an electrolyte solution corresponding to an increase in the amount of impregnation accompanying expansion of the laminated body Accommodating quantity Characterized in that setting the capacity of the liquid retaining portion to the periphery of the laminate.

  The second invention is characterized in that in the electric double layer capacitor according to the first invention, a material having a good liquid retention property such as a tube or a separator is accommodated in the liquid retention part.

  According to a third invention, in the electric double layer capacitor according to the second invention, the tube is made of a fluororesin.

  According to a fourth aspect of the invention, in the electric double layer capacitor according to the first aspect of the invention, a gas vent valve is assembled by heat welding to a sealed portion of a container from which a part of a pair of terminals protrudes.

  According to a fifth aspect of the present invention, in the gas vent valve used in the electric double layer capacitor according to the fourth aspect of the present invention, at least a part of the valve body is formed of a heat-weldable resin, and the ribs on which the heat-weldable resin swells It has the shape of a convex part.

  In the first invention, the increase in the amount of the electrolyte solution impregnated in the laminate due to the expansion of the laminate due to charging is compensated by the electrolyte solution in the liquid retaining portion. When the laminate shrinks with the discharge, the amount of electrolyte solution impregnated in the laminate decreases, and the amount of electrolyte solution outside the laminate increases inside the container. The For this reason, the change in the amount of impregnation according to the expansion of the laminate is absorbed by the liquid retaining part, and the electric double layer capacitor including the container has good durability without overloading the sealed part (thermal welding part) of the container. Sex can be secured.

  In the second invention, even if a compressive force is applied to the liquid retaining part due to a pressure difference between the inside and outside of the container, the liquid retaining part is prevented from being crushed by the tube, and the volume required for the inner diameter of the tube as the liquid retaining part. Can be secured. In addition, in order to secure the volume, a material having good liquid retention properties such as a separator may be used instead of the tube.

  In the third invention, the properties (mechanical strength, chemical resistance, electrical insulation, etc.) necessary for the tube are ensured by the fluororesin.

  In the fourth aspect of the invention, even when a gaseous decomposition product is generated along with charging / discharging, the internal pressure of the container can be maintained at a predetermined level while preventing the entry of outside air by the gas vent valve. Further, the electrolyte solution holding part can prevent the electrolyte solution from overflowing to the outside of the laminate during discharge and entering the gas vent valve (overflow). As a result, it is possible to ensure good durability of the electric double layer capacitor including the sealed portion of the container and the gas vent valve.

  In the fifth aspect of the invention, the amount of resin forming the heat-welded portion is increased by the rib-like convex portion, so that the sealing portion of the container (the assembly portion of the gas vent valve) can be sufficiently reinforced. In order to increase the mechanical strength of the container, even when the thickness of the metal foil of the resin film is relatively increased, the rib-like convex portion can secure the amount of resin in the heat-welded portion and give the necessary welding strength. It is.

  1 and 2, an example of the electric double layer capacitor 1 will be described. Reference numeral 22 denotes a flat plate-type laminated body constituting the capacitor body, 21 denotes a container for sealing the laminated body 22 together with the electrolytic solution, and 24 denotes a pair of terminals protruding outside the container 21. Each terminal 24 is formed from a high-purity aluminum plate. Reference numeral 35 denotes a degassing valve for removing a gaseous decomposition product generated inside the container 21 to the outside of the container 21, and is assembled between a pair of terminals 24 at the upper part of the container 21.

  The flat plate-type laminate 22 is composed of a positive electrode body, a negative electrode body, and a separator interposed therebetween. The positive electrode body and the negative electrode body are composed of a polarizable electrode and a current collector. The polarizable electrode is formed using non-porous carbon (carbonaceous material) as a main raw material. The current collector is formed from a high-purity aluminum foil and is attached to a polarizable electrode (carbon electrode). The separator is made of 100 μm glass fiber in a compressed state, and is set to a thickness equal to or greater than that of the polarizable electrode in order to provide a retainer function for the electrolyte solution. The current collectors of the polarizable electrodes are bundled with the same polarity, and the terminals 24 corresponding to the polarities are joined to the respective binding portions.

  The container 21 is composed of two container members (a bottom side member and a lid side member) formed by drawing from a resin film (laminated film) having a laminated structure including an intermediate layer of metal foil. The accommodating part of the laminated body 22 is formed between the bottom-side member and the lid-side member by the facing recesses 21a. A side surface rising from the bottom surface of the recess 21a to the mating surface 21b is formed in a stepped shape having two bent portions 21c and 21d, and a liquid retaining portion 36 is provided around the storage portion. The liquid retaining portion 36 is set to a volume that can accommodate the amount of the electrolyte solution corresponding to the increase in the amount of impregnation accompanying the expansion of the laminate due to charging.

  The laminated body 22 is housed inside the bottom side member, and the lid side member is placed thereon. At the peripheral edge of the container 21, three sides are thermally welded except one side from which a part of the pair of terminals 24 is drawn. The container 21 can be opened at one side from which a part of the pair of terminals 24 protrudes, and when the electrolyte solution is injected into the inside through the opening and the impregnation treatment and the electric field activation are finished, the excess electrolyte in the container 21 is removed. It is extracted and the remaining openable side is heat welded.

  In order to ensure electrical insulation between the pair of terminals 24 and the metal foil (interlayer of the resin film) of the container 21, a plate-like heat-welding resin is attached to these terminals. On one openable side of the container 21, the plate-like heat-welding resin is solidified so as to wrap around the pair of terminals 24 while being melted with the inner surface of the container 21 (surface layer of the resin film). These terminals 24 are prevented from coming into contact with the intermediate layer (metal foil) of the resin film.

  3 to 6, reference numeral 40 denotes a valve body of the gas vent valve 35, which includes a heat welding portion 41 with the container 21, an insertion portion 42 inside the container 21, and a protruding portion 43 outside the container 21. , And a gas vent passage 44 extending therethrough is formed. An outlet side of the gas vent passage 44 is formed in the valve chamber 45, and a large-diameter space volume 46 in which a gaseous decomposition product is accumulated is set on the inlet side of the gas vent passage 44. A relay portion 47 is formed between the valve chamber 45 and the space volume 46, and a boundary (step surface) between the valve chamber 45 and the relay portion 47 is set in the valve seat 48. A valve body (not shown) and a spring (not shown) for setting the valve opening pressure are accommodated in the valve chamber 45 to prevent the electrolyte solution from being taken out together with the gaseous decomposition products. A gas permeable membrane (not shown) is interposed in the relay unit 47.

  The valve body 40 is integrally formed from a heat-weldable resin, and the outer periphery of the heat-welded portion 41 is formed in a wing shape in order to ensure a large heat-welded surface with the container 21. Since the main material of the polarizable electrode is non-porous carbon and has a large expansion coefficient at the time of charging, in order to reinforce the sealing part (thermal welding part) of the container 21, a heat welding resin is provided on the outer surface of the thermal welding part 41. A plurality of convex portions 49 that rise in a rib shape are provided.

  The gas vent valve 35 is formed on the periphery of the container 21 together with the plate-like heat-welding resin attached to the pair of terminals 24 by the heat-sealing sealing process on the remaining side after the three sides are heat-welded. It is assembled to the upper part of the container 21 via the heat welding part 41.

  According to such a configuration, even if a gaseous decomposition product is generated due to charging / discharging, the internal pressure of the container 21 is maintained below the valve opening pressure by the gas vent valve 35 while preventing intrusion of outside air. Yeah. The increase in the amount of the electrolyte solution impregnated in the multilayer body 22 due to the expansion of the multilayer body 22 due to charging is compensated by the electrolyte solution in the liquid retaining portion 36. When the laminate 22 contracts with the discharge, the electrolyte solution outside the laminate 22 is increased inside the container 21 as the amount of electrolyte solution impregnated in the laminate 22 is reduced. Housed in part 36. For this reason, the change of the impregnation amount according to the expansion of the laminated body 22 is absorbed by the liquid retaining part 36, and the sealing part (thermal welding part) of the container 21 is not forced, and the electric double layer capacitor including the container 21 Good durability can be secured.

  In the gas vent valve 35, the amount of resin in the heat-welded portion 41 is increased by the rib-like convex portion 49, so that the welding strength with the container 21 and the sealing performance of the container 21 can be sufficiently improved. In order to increase the mechanical strength of the container 21 corresponding to the expansion rate of the laminate 22, even when the thickness of the metal foil of the resin film is relatively large, the resin of the heat welded portion 41 is formed by the rib-like convex portions 49. The amount can be secured and the necessary welding strength can be provided. In addition, the electrolyte solution holding part 36 can prevent the electrolyte solution from overflowing to the outside of the laminate during discharge and entering the gas vent valve 35 (overflow). When the electrolyte solution enters the gas vent valve 35, the electrolyte solution may be stuck in the gas vent passage 44, which may hinder a normal gas vent function (valve opening / closing operation).

  FIG. 7 illustrates an apparatus for processing electric field activation or the like in the manufacturing process of the electric double layer capacitor. The tank 11 is installed inside the glove box together with the processing means of each process. The inside of the glove box is managed (maintained) in an inert atmosphere having a low pressure dew point at normal pressure (for example, a dew point temperature of −90 ° C.).

  In FIG. 7, 21 is a container stored in the tank 11, and one side from which a part of the pair of terminals 24 protrudes is configured to be openable. The tank 11 includes an opening 12 for piping connected to a vacuum pump, a passage 13 that opens the inside of the tank 11 to a glove box, and a valve 13a that opens and closes the passage 13. When the valve 13a and the lid 14 are closed, the inside of the tank 11 is maintained in a highly sealed state. Reference numeral 15 denotes a connector connected to the charging / discharging device. In the tank 11, a pair of terminals 34 protruding from the opening of the container 21 are separably connected via a wire (cord) opening extending from the connector 15. Is done.

  Reference numeral 25 denotes a jig that holds the container 21 in a predetermined state, and is provided with plates 28 and 29 that are screwed onto the plate 26 so that the fastening bolts 27 can be advanced and retracted, and are slidably supported on the fastening bolts 17. When a spring 30 is interposed between the plates 28 and 29 and the tightening bolt 27 is screwed from the initial position, the spring 30 is compressed and the pressing force acting on the container 21 between the plates 29 and 26 is increased. Yes. Although not shown, the tank 11 includes equipment for injecting the electrolyte solution into the container 21 and equipment for extracting the excess electrolyte solution in the container 21.

  The electric double layer capacitor includes (1) a step of forming a polarizable electrode using a carbonaceous material as a main raw material and attaching a current collector to the carbon electrode to create a positive electrode body and a negative electrode body, and (2) a positive electrode body and A step of composing a flat laminate 22 from a negative electrode body and a separator; (3) a step of bonding a pair of terminals 24 to the bundling portions of the same polarity as lead portions of the positive electrode body and the negative electrode body; ) A step of placing the laminate 22 in a state where a part of the pair of terminals protrudes from the container 21 and impregnating the injected electrolyte solution; and (5) a voltage between the pair of terminals 24 to activate the electric field of the carbon electrode. And (6) sealing the opening of the container from which a part of the pair of terminals protrudes.

In the step (1), the non-porous carbon is a graphite-like carbon having a specific surface area of 100 m ² / g or less and a carbon structure interlayer distance of 0.36 to 0.37 nm, and is easily graphitized coke or pitch (precursor). Body) is subjected to dry distillation at 300 to 400 ° C., and then the raw coal is mixed with caustic (eg, KOH) and heated to 650 to 850 ° C. in an inert atmosphere (alkali activation). When carbonization is not performed, porous activated carbon is generated.

  Non-porous carbon is processed into a sheet-like shape after being subjected to treatment such as washing and pulverization by a usual method, and then a conductive material (for example, carbon black) and a binder (for example, polytetrafluoroethylene) are added and kneaded. A positive electrode body and a negative electrode body are formed by forming a polarizable electrode and attaching a current collector to the carbon electrode.

In the step (2), a plate-type laminate 22 is composed of a positive electrode body, a negative electrode body, and a separator interposed therebetween. The positive electrode body and negative electrode body before composition are put in a vacuum drying furnace and heated to a temperature of 200 ° C. or higher in a reduced pressure state with a vacuum degree of 10 ⁻⁵ Pa or lower. A turbo molecular pump is used to ensure an extremely reduced pressure state. After this treatment (vacuum drying) is completed, the low dew point (for example, dew point temperature is −90 ° C.) is inert so that the positive electrode body and the negative electrode body are returned to normal pressure before being transported from the vacuum drying furnace to the glove box. Fill with gas. The glass fiber separator is also put in a vacuum drying furnace together with the positive electrode body and the negative electrode body, and heated to a temperature of 200 ° C. or higher in a reduced pressure state with a vacuum degree of 10 ⁻⁵ Pa or lower.

  In the step (3), the current collectors of the laminate 22 are bundled with the same polarity, and the terminals 24 corresponding to the polarities are welded to the bundling portions.

  In the step (4), the laminated body 22 is housed inside the bottom side member of the container 21, and the lid side member is placed thereon. At the peripheral edge of the container 21, three sides are thermally welded except one side from which a part of the pair of terminals 24 is drawn. The container 21 can be opened at one side from which a part of the pair of terminals 24 protrudes, and is stored in the tank 11 of FIG. The inside of the sealed tank 11 is depressurized to 10 Pa or less, and when a predetermined time elapses while maintaining a depressurized state of 10 Pa or less, the tank is filled with an inert gas having a low dew point (for example, a dew point temperature of −90 ° C.). 11 is returned to normal pressure, and the electrolyte solution is injected into the container 21 while maintaining the normal pressure state. After the injection, the process of maintaining the inside of the tank 11 in a reduced pressure state of 10 Pa or less and the process of maintaining the normal pressure state by filling with an inert gas having a low dew point are alternately repeated. As a result, the electrolyte solution can sufficiently penetrate the carbon electrode (polarizable electrode) and the separator, and the impregnation time is also shortened.

In the step (5), primary electric field activation and secondary electric field activation are processed. The primary electric field activation is a charge / discharge cycle performed while maintaining the inside of the sealed tank 11 in a reduced pressure state of 10 Pa or less, and by constant current charging with a current density less than a predetermined value (for example, 1 mA / cm ² ), When the voltage is gradually increased over a long period of time and reaches a predetermined maximum voltage that can be applied (for example, 3 V to 5 V), the voltage is kept at 0 V by constant current discharge after a predetermined time while maintaining the voltage. To lower. In the secondary electric field activation, the inside of the sealed tank 11 is maintained in a charging cycle performed while maintaining an inert atmosphere with a low pressure dew point (for example, a dew point temperature of −90 ° C.) and a reduced pressure state of 10 Pa or less. Charging and discharging cycles carried out while being carried out alternately at a predetermined number of times (for example, 2 to 15 times), and in each charging and discharging cycle, constant current charging with a current density of a predetermined value (for example, 1 mA / cm ² ) or more. By increasing the voltage in a short time and reaching a predetermined maximum voltage that can be applied (for example, 3 V to 5 V), the voltage is kept to 0 V by constant current discharge after a predetermined time while maintaining the voltage. Reduce.

  In the final charge / discharge cycle, which is performed while maintaining the inside of the sealed tank 11 of the secondary electric field activation in an inert atmosphere with a low dew point at normal pressure, a predetermined maximum voltage that can be applied is maintained for a certain period of time. In the state where the lid 14 of the tank 11 is opened, the tightening bolt 27 of the jig 25 is screwed by a predetermined amount from the initial position, thereby increasing the spring force of the spring 30 (the pressing force to the container 21), and the container The excess electrolyte solution in 21 is collected. Thereafter, the fastening bolt 27 of the jig 25 is loosened to the initial position, and the voltage is reduced to 0 V by constant current discharge.

  In the step (6), the gas vent valve 35 is assembled between the pair of terminals 24 by thermally welding the remaining side of the container 21. The degassing valve 35 is assembled to the upper part of the container 21 through the heat welding portion 41 of the valve body 40 together with the plate-like heat welding resin attached to the pair of terminals 24 by a sealing process of heat welding.

  In such a manufacturing process, the inside of the tank 11 is converted into an inert atmosphere at normal pressure and a reduced pressure state of 10 Pa or less. Therefore, in the step (5), when the container 21 is compressed by the conversion to a reduced pressure state of 10 Pa or less and the liquid retaining part 36 is also crushed, the inside of the container 21 is caused by the contraction of the laminate 22 accompanying the discharge. In this case, the electrolyte solution on the outside of the laminate 22 increases, and the container 21 may overflow. FIGS. 8 to 10 illustrate countermeasures, and a fluororesin tube 50 is accommodated in the liquid retaining portion 36 of the container 21. Specifically, in the step (4), a U-shaped tube 50 surrounding the three sides of the laminate 22 is placed in the bottom member of the container 21. And the cover side member is covered, and the three sides excluding the one side from which a part of the pair of terminals 24 is drawn are heat-welded.

  Therefore, in the step (5), even if a compressive force acts on the liquid retaining part 36 due to the pressure difference between the inside and outside of the container 21, the liquid retaining part 36 is prevented from being crushed by the tube 50, and the inner diameter of the tube 50 is reduced. As a liquid retaining part 36, a necessary volume can be secured. The tube 50 is formed with a plurality of holes (electrolyte solution inlet / outlet ports). In addition, the electric double layer capacitor (product) has a built-in tube 50, and the protective function of the multilayer body 22 can be obtained by the tube 50. 8-10, the same code | symbol is attached | subjected to the site | part which has the same function as FIG. In addition, instead of the tube 50, a material having good liquid retention properties such as a separator may be accommodated in the liquid retention portion 36.

1 is a partial configuration diagram of an electric double layer capacitor according to an embodiment of the present invention. It is CC sectional drawing similarly. It is a front view of a valve body similarly. It is a top view of a valve body similarly. It is AA sectional drawing of a valve body similarly. It is a right view of a valve body similarly. It is explanatory drawing of a manufacturing process similarly. It is explanatory drawing of the electric double layer capacitor which concerns on another embodiment. Similarly it is DD sectional drawing. It is the enlarged view of the B section similarly.

Explanation of symbols

21 Container 22 Laminated body 24 Terminal 35 Liquid retaining part 35 Gas vent valve 40 Valve body 41 Heat welding part of valve body 49 Rib-shaped convex part 50 Tube

Claims (5)

  A step of forming a polarizable electrode using a carbonaceous material as a main material and attaching a current collector to the carbon electrode to create a positive electrode body and a negative electrode body, and a flat laminate from a positive electrode body, a negative electrode body, and a separator The composition step, the step of bonding a pair of terminals to the bundling portion of the same polarity as the lead portion of the positive electrode body and the negative electrode body, and placing the laminated body in a state in which a part of the pair of terminals protrudes into the container Manufactured through a step of impregnating the electrolyte solution, a step of applying a voltage between the pair of terminals to activate the electric field of the carbon electrode, and a step of sealing the opening of the container from which a part of the pair of terminals protrudes. In the electric double layer capacitor, the container is formed of a flexible resin film having a laminated structure including an intermediate layer of metal foil, and can hold an electrolyte solution amount corresponding to an increase in the amount of impregnation accompanying expansion of the laminate. Liquid part Electric double layer capacitor, characterized in that set in the neighborhood of the lamina.   2. The electric double layer capacitor according to claim 1, wherein a material having good liquid retention properties such as a tube or a separator is accommodated in the liquid retention portion.   3. The electric double layer capacitor according to claim 2, wherein the tube is made of a fluororesin.   2. The electric double layer capacitor according to claim 1, wherein a gas vent valve is assembled by heat welding to a sealed portion of a container from which a part of a pair of terminals protrudes.   In the degassing valve used for the electric double layer capacitor according to claim 4, at least a part of the valve body is formed of a heat-welding resin, and a rib-like convex portion is formed on the resin surface. A gas vent valve characterized by that.

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