Abstract:
A separator sheet for manufacturing an electric double layer capacitor, and a method for manufacturing the electric double layer capacitor using the same, are provided. According to an embodiment, the separator sheet for manufacturing the electric double layer capacitor comprises: a plurality of separators; and a resin film holding the plurality of separators, wherein the separators are disposed in the resin film at a predetermined interval.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electric double layer capacitor, particularly to a separator sheet used for manufacturing the electric double layer capacitor, and a method for manufacturing the same. 
   2. Description of the Related Art 
   The electric capacity of a conventional capacitor is generally determined by the dielectric constant of the dielectric material interposed between two oppositely disposed electrodes. 
   However, an electrical double layer capacitor has a different feature from conventional capacitors using dielectric material in that positive charge and negative charge are distributed with a considerably short distance around the interface between two different layers of a solid and a liquid. 
   The layer formed around the interface is referred to as Electric Double Layer, and the capacitor using it is classified as electric double layer capacitor. 
   For the solid of the electric double layer capacitor, it is preferable to use a material having large specific surface area so that more electric double layers are formed to obtain large capacity. Accordingly, activated carbon or activated fiber whose surface area is more than 1000 m 2 /g, and diluted sulphuric acid, can be employed for the solid and the liquid, respectively, to result in a considerably higher capacity of F (Farad) level of capacitor than conventional capacitor. 
   The electric double layer capacitor has intermediate characteristics between an electrolytic capacitor and a secondary battery, and is an energy storage device that has high efficiency, excellent durability, and fast charge/discharge ability. Thus, the electric double layer capacitor may be used in combination with a conventional secondary battery, or be a substitutable energy storage device for it. 
   In addition, the electric double layer capacitor can input/output energy within a short time, and thus may be used for rectifier circuit, noise attenuation, and pulse generation for power supply unit. Moreover, the capacitor&#39;s capacitance is highly increased, compared with other electric chemical condenser, and so the electric double layer capacitor has high output of pulse power capacity and high energy storage capacity. Thus, the electric double layer capacitor may be applicable for a compact electrochemical energy storage device and load leveling of high output of pulse power and peak power. 
   Further, the electric double layer capacitor has been more important environmentally and economically among other energy storage devices in that it uses environmentally friendly materials, and has long life span and high charge/discharge efficiency. This electric double layer is expected to be used for a main power supply source and an auxiliary power supply source of high output of pulse power for highly value added equipments in various technical fields such as military defense, aerospace, medical equipment, HEV, etc. 
     FIG. 1A  is a cross-sectional view of a conventional electric double layer capacitor, illustrating a schematic structure of the electric double layer capacitor, and  FIG. 1B  is a schematic view of the basic cell illustrated in  FIG. 1A . 
   Referring to  FIG. 1A , an electric double layer capacitor  1  comprises at least one basic cell  10 . Here, the multilayer cell  20  manufactured by stacking 5 basic cells  10  in series is illustrated. An electrode plate  21  with its lead terminal is attached to outer surface of the basic cells  10  disposed in the outermost positions, and an outer package  22  is covering the electrode plate  21 . The packaging is performed under pressure reduced condition. 
   The lead terminal attached to the electrode plate  21  is made by doing solder plating on the surface of copper plate, and made up of a flat electrode plate body  24  and a band-shaped lead terminal  25  extended from the electrode plate body  24 , wherein the electrode plate body  24  is bonded to the outer surface of the outermost basic cells  10  of the multilayer cell  20 . 
   Referring to  FIG. 1B , the basic cell  10  comprises a porous separator  11  in the form of a sheet; a pair of current collector films  12  oppositely disposed relatively to the separator  11 ; a pair of polarized electrodes  13  disposed between the separator  1  and the current collect films  12 ; and a frame form of gasket  14  which is laterally contiguous to the separator  11  and the polarized electrodes  13  and interposed between the pair of current collector films  12 . The basic cell  10  is sealed with an electrolytic solution therein. 
   The steps for manufacturing the basic cell  10  are described with reference to  FIG. 2  below. 
     FIG. 2  is a view illustrating some of the steps for manufacturing an electric double layer capacitor. 
   As shown in  FIG. 2(   a ), a current collector film  12  is prepared, and cut to be a certain size as shown in  FIG. 2(   b ). The current collector film  12  is a conductive film made up of an insulation resin and a conductive material. 
   Next, as shown in  FIG. 2(   c ), a frame form of gasket  14  is installed on the surface of the current collector film  12 . As the gasket  14  is positioned at the edge of the current collector film  12 , a portion of the current collector film  12  is exposed inside the gasket  14 . 
   Next, as shown in  FIG. 2(   d ), a polarized electrode  13  is formed on the surface of the exposed current collector film  12 , and as shown in  FIG. 2(   e ), a separator  11  is disposed to cover inside of the gasket. 
   Next, as shown in  FIG. 2(   f ), two intermediate structures formed from  FIG. 2(   a ) to  FIG. 2(   d ) are oppositely disposed with having the separator  11  in between. 
   Finally, the structure shown in  FIG. 2(   f ) is thermo-compressed for the gaskets  14  to be thermally fusion-bonded to each other, to complete the basic cell shown in  FIG. 2(   g ). 
   However, in case that basic cell array including a plurality of basic cells is produced from one current collector film, there is a difficult problem that a plurality of separators should be aligned precisely on each corresponding gasket. Therefore, there has been a need to develop a method to dispose the separators easily and precisely on their respective gaskets. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a separator sheet, and a method for manufacturing an electric double layer capacitor which can easily and precisely dispose a plurality of separators at their respective position. 
   The separator sheet according to a preferable embodiment of the present invention comprises a plurality of separators; and a resin film holding the plurality of separators, wherein the separators are disposed in the resin film at a predetermined interval. 
   The method for manufacturing an electric double layer capacitor according to a preferable embodiment of the present invention comprises: (a) forming a plurality of polarized electrodes on a current collector film; (b) installing a gasket element around each polarized electrode; (c) installing the above described separator sheet on the gasket element; (d) oppositely disposing two intermediate structures prepared by the process including the steps (a) and (b) with interposing a separator sheet between the two structures; and (e) thermally fusion-bonding the gasket elements with the resin film of the separator sheet to unite two intermediate structures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the detailed description in conjunction with the following drawings. 
       FIG. 1A  is a cross-sectional view of an electric double layer capacitor, illustrating a schematic structure of the electric double layer capacitor; 
       FIG. 1B  is a schematic view of the basic cell illustrated in  FIG. 1A ; 
       FIG. 2  is a view illustrating some of the steps for manufacturing an electric double layer capacitor; 
       FIG. 3A  is a plane view of the separator sheet according to a preferable embodiment of the present invention; 
       FIG. 3B  is a cross-sectional view of the separator sheet of  FIG. 3A  as taken along the line I—I; and 
       FIG. 4  is a view illustrating some of the steps illustrating the electric double layer capacitor according to a preferable embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will be more clearly understood from the detailed description in conjunction with the following drawings. 
     FIG. 3A  is a plane view of the separator sheet according to a preferable embodiment of the present invention; and  FIG. 3B  is a cross-sectional view of the separator sheet of  FIG. 3A  as taken along the line I—I. 
   Referring to  FIG. 3A , the separator sheet  31  comprises a resin film  31   b  and a plurality of separators  31   a  that are disposed at a predetermined distance therein. 
   Advantageously, a porous film having ion permeability and non electroconductivity may be used as separator  31   a , but not limited thereto. Such porous film is a form of sheet, for example, polypropylene, polyethylene, glass fiber, etc. 
   Referring to  FIG. 3B , the separator sheet  31  is configured for each separator  31   a  to be held by the resin film  31   b  therein. 
   Advantageously, the resin film  31   b  of the separator sheet  31  may be made up of a material that can be fused with the gasket which will be described below, at the step of thermocompression, to block leakage of the electrolyte through the separator  31   a  after the thermocompression. A preferable material for the resin film  31   b  may be ABS, Isobutylene-Isoprene rubber, polyolefin-based resin, etc. 
   Advantageously, the separator  31   a  has same thickness as the resin film  31   b.    
   Hereinafter, the method for manufacturing the electric double layer capacitor according to a preferable embodiment of the present invention will be described with reference to the accompanying drawings. 
     FIG. 4  is a view illustrating some of the steps illustrating the electric double layer capacitor according to a preferable embodiment of the present invention. 
   As shown in  FIG. 4(   a ), a plurality of polarized electrodes  32  are formed on a current collect film  33 . The polarized electrodes  32  may be formed by the steps comprising, for example, installing a mask (not shown) on the current collect film  33 ; forming a pattern by spraying a slurry prepared by blending a material constituting the polarized electrodes, for example, conductive particles, with a binder and a solvent, through openings formed in the mask; drying the pattern by heat flow; and thermocompressing the structure formed by the above steps, but not necessarily limited thereto, and various modification will be available to those skilled in the art. 
   The binder, a component of the polarized electrode  32 , serves to improve cohesion of the conductive particles and adhesion between the polarized electrode  32  and the current collect film  33 , and to reduce density of electrode (g/cm 2 ), and the contact resistance between components of the electrode  32  and the current collect film  33 . 
   Carboxymethyl cellulose, polyvinyl alcohol, polyvinyl fluoride, polyvinyl pyrrolidone, methylcellulose, etc. may be used as the binder. 
   As conductive material, one or more from the group consisting of granular acetylene black, Super P Black, carbon black, activated carbon, hard carbon, soft carbon, graphite, metal powder (Al, Pt, Ni, Cu, Au, stainless steel, or an alloy including at least one metal aforementioned), or a powder produced by coating carbon black, activated carbon, hard carbon, soft carbon, or graphite may be used alone or in combination, but not limited thereto. 
   Preferably, the current collect film  33  is a conductive film made of stylene-ethylene-butylene-stylene copolymer resin, but not limited thereto. 
   After forming the polarized electrode  32  on the current collect film  33 , as shown in  FIG. 4(   b ), an electrolytic solution is impregnated into the polarized electrode  32  in vacuum. The electrolytic solution may be an aqueous electrolytic solution produced by dissolving sulfuric acid, potassium hydroxide, etc in water, or an organic electrolytic solution produced by dissolving quaternary ammonium as electrolyte in an organic solvent, for example, propylene carbonate. In this embodiment, the electrolytic solution is impregnated prior to installing a later described gasket  34 , but may be impregnated after installing the gasket  34 . 
   Next, as shown in  FIG. 4(   c ), a gasket  34  in the form of frame, which is suitable for receiving the polarized electrode  32 , is installed. The gasket  34  may be made up of, for example, ABS, Isobutylene-Isoprene rubber, or polyolefin-based resin, preferably, colorless and transparent polyolefin-based resin. 
   Next, as shown in  FIG. 4(   d ), the above described separator sheet according to the present invention is disposed. Here, it is preferable that the resin film  31   b  disposed between the adjacent separators  31   a  is aligned along the upper surface of the gasket  34 . 
   Next, as shown in  FIG. 4(   e ), the two structures produced by the steps of  FIG. 4(   a ) through  FIG. 4(   c ) are oppositely disposed with having the separator sheet  31  in between, and are subjected to thermocompression in a longitudinal direction to thermally fusion-bond the oppositely disposed two gaskets  34  and the resin film  31   b  of the separator sheet  31 , thereby producing the structural device as shown in  FIG. 4(   f ). The thermally fusion-bonded area of the gaskets  34  and the resin film  31   b  of the separator sheet  31  can prevent leakage of the electrolytic solution through the separator  31 . 
   Finally, the structure of  FIG. 4(   f ) is cut along the dotted line between the adjacent separators to produce a plurality of basic cells  30 . 
   Although not shown in the figure, the pluralities of basic cells  30  produced through the above steps are stacked in sequence, and then external electrodes are attached to the surface of the current collect films  31  of the basic cells  30  disposed in the outermost positions, and then packaged with an outer package to produce the present electric double layer capacitor. 
   The preferred embodiments of the present invention have been described for illustrative purposes, and those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims. 
   The present invention has an advantage that a plurality of separators may be disposed precisely to their respective positions in a single step in the process of manufacturing a plurality of basic cells to simplify the process and reduce the processing time.