Abstract:
The purpose of the present invention is to provide a capacitor having a novel structure in which electric energy is stored by means of charge transfer between a polarizable electrode and a metallic compound, as well as an electric double layer formed at an interface between the polarizable electrode and an electrolytic solution. The capacitor of the present invention has: a positive electrode collector; a positive electrode active material layer containing carbon material, polylactide, and V 3+  compound; a separator; a negative electrode active material layer containing carbon material, polylactide, and V 4+  compound; a negative electrode collector; and an electrolytic solution that is impregnated into the positive active material layer, the separator, and the negative active material layer.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a capacitor. More specifically, the present invention relates to the capacitor comprising a positive electrode active material layer containing a V 3+  compound, and a negative electrode active material layer containing a V 4+  compound. 
       BACKGROUND ART 
       [0002]    An Electric double layer capacitor accumulates electric energy in an electric double layer formed at an interface between a polarizing electrode and an electrolyte solution. In comparison with a lithium ion secondary battery, a nickel metal hydride secondary battery or the like, the electric double layer capacitor has characteristics of superior input-output properties, life-time properties, and safety properties, since no chemical reaction is involved at the time of charging and discharging. Such electric double layer capacitor is capable of miniaturization and charging of a high capacity, and widely used for the purpose of backing up microcomputers, memories, timers or the like, and the purpose of assisting various types of power sources. In addition, making full use of their characteristics, electric double layer capacitors having more capacity have been developed in recent years. 
         [0003]    The electric double layer capacitor suffers from the problem that it has more power density but less energy density in comparison with the secondary battery which generates electricity by chemical reaction. A redox-capacitive capacitor or a pseudo-capacitance capacitors based on charge transfer at interfaces of electrodes, a hybrid capacitor which is a combination of the above two type capacitors, ionic liquid capacitor in which ionic liquid is used as the electrolyte, and the like have been developed, in order to increase the energy density of the electric double layer capacitors. For example, PTL1 discloses an electric double layer capacitor having a negative electrode sheet onto the surface of which lithium is flame spray coated (see PTL1). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL1: Japanese Patent Laid-open No. 2010-080858. 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    The purpose of the present invention is to provide a capacitor of a novel structure, which stores electric energy by not only an electric double layer formed at an interface between an polarizable electrode and an electrolytic solution, but also charge transfer between the polarizable electrode and metallic compound. 
       Solution to Problem 
       [0006]    The capacitor of the present invention comprises: a positive electrode collector; a positive electrode active material layer comprising carbon material, polylactic acid and V 3+  compound selected from the group consisting of V 2 O 3 , VF 3 , VCl 3 , V(acac) 3 , and VSO 4 OH; a separator; a negative electrode active material layer comprising carbon material, polylactic acid and V 4+  compound selected from the group consisting of VOSO 4 , VF 4 , VCl 4 , VO(acac) 2 , and V(SO 4 ) 2 ; a negative electrode collector; and an electrolytic solution which is impregnated into the positive electrode active material layer, the separator, and the negative electrode active material layer. 
         [0007]    The capacitor of the other embodiment of the present invention comprises a plurality of a first electrode laminates, one or more of a second electrode laminates, a plurality of separators, and an electrolytic solution, wherein: the first electrode laminate comprises a first collector and a first active material layer comprising carbon material, polylactic acid and one of V +  or V 4+  compound; the second electrode laminate comprises a second collector and a second active material layer comprising carbon material, polylactic acid and the other of V 3+  or V 4+  compound; each of the separators is disposed between the first and second electrode laminates; and the electrolytic solution is impregnated into the first active material layer, the second active material layer, and the separator. Here, the first active material layer may comprise the V 3+  compound, the first electrode laminate is a positive electrode collector, the second active material layer may comprise the V 4+  compound, and the second electrode laminate is a negative electrode collector. Alternative, the first active material layer may comprise the V 4+  compound, the first electrode laminate is a negative electrode collector, the second active material layer may comprise the V 3+  compound, and the second electrode laminate is a positive electrode collector. Further, the plurality of the first electrode laminates may be electrically connected to each other, and the one or more of the second electrode laminates may be electrically connected to each other. Further, the carbon material in the first and second active material layer may comprise a mixture of activated carbon and carbon nanotubes or fullerene. The V 3+  compound may be selected from the group consisting of V 2 O 3 , VF 3 , VCl 3 , V(acac) 3 , and VSO 4 OH. The V 4+  compound may be selected from the group consisting of VOSO 4 , VF 4 , VCl 4 , VO(acac) 2 , and V(SO 4 ) 2 . 
       Advantageous Effects of Invention 
       [0008]    The capacitor of the present invention has advantages of capability of rapid charging and low-cost production. Further, the capacitor of the present invention does not cause any problem even in an overcharged state, since generation of ignitable component or toxic gas, which is a problem in lithium-based secondary batteries, never occurs in the capacitor of the present invention. Further, no problem occurs in reuse of the capacitor of the present invention, even if the capacitor is over-discharged, differently from the lithium-based secondary batteries. In addition, the capacitor of the present invention can be stably supplied, since the capacitor of the present invention is made from inexpensive material and free from rare-metals or the like. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a schematic cross-sectional view of an example of the capacitor of the present invention; 
           [0010]      FIG. 2A  is a schematic cross-sectional view of the capacitor of an example of the other embodiment of the present invention; 
           [0011]      FIG. 2B  is a schematic cross-sectional view of an example of a top single-sided positive electrode laminate; 
           [0012]      FIG. 2C  is a schematic cross-sectional view of an example of a double-sided positive electrode laminate; 
           [0013]      FIG. 2D  is a schematic cross-sectional view of an example of a bottom single-sided negative electrode laminate; and 
           [0014]      FIG. 2E  is a schematic cross-sectional view of an example of a double-sided negative electrode laminate. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0015]    As shown in  FIG. 1 , the capacitor of the present invention comprises a positive electrode collector  110 , a positive electrode active material layer  120 , a separator  130 , a negative electrode active material layer  140 , a negative electrode collector  150 , and an electrolytic solution that is impregnated into the first active material layer  120 , the separator  130 , and the second active material layer  140 . 
         [0016]    The negative electrode collector  150  in the present invention is made from metal, preferably copper. The negative electrode collector  150  is preferably made with a copper foil having a thickness of 40 to 50 μm, in order to facilitate shaping of the capacitor 
         [0017]    The positive electrode collector  110  in the present invention is made from metal, preferably aluminum. Similarly to the negative electrode collector  150 , the positive electrode collector  110  is preferably made with an aluminum foil having a thickness of 40 to 50 μm, in order to facilitate shaping of the capacitor. Further, it is preferable to roughen a surface of the positive electrode collector  110 , the surface being in contact with the positive electrode active material layer  120 . The roughness of the surface of the positive electrode collector  110  provide anchoring effect of fixing nanocarbon in the positive electrode active material layer  120 , which can be dissociated from the positive electrode collector  110  during the step of shaping the capacitor. In the present invention, it is preferable to subject the surface of the positive electrode collector  110  to a roughening treatment referred to as “A20” processing, to increase the actual surface area to 20 times of the apparent surface area. 
         [0018]    The separator  130  of the present invention is a structural element which prevents from a short circuit of the capacitor by maintaining the positive electrode active material layer  120  and the negative electrode active material layer  140  in a non-contact state, and facilitates transfer of ions in the electrolytic solution between the positive electrode active material layer  120  and the negative electrode active material layer  140 . The separator  130  may be an insulating paper made from wood pulp, glass fiber, polyolefin-based fiber, fluorine-based fiber, polyimide-based fiber, aramid fiber, or the like. Alternatively, an insulating paper made from polylactide fiber can be used as the separator  130 . More preferably, the separator  130  may be an insulating paper made from glass fiber or polylactide fiber. The separator  130  may have a thickness of 8 to 100 μm and a porosity of 30 to 95%, in order to achieve the above-described functions. 
         [0019]    The positive electrode active material layer  120  of the present invention is a porous layer which comprises carbon material, polylactide, and V 3+  compound, and is capable of being impregnated with the electrolytic solution. 
         [0020]    The carbon material of the present invention is a mixture of nanocarbons having a size of the order of nanometers, and carbonous or graphite material having a size of the order of micrometers. The nanocarbons include commercially available carbon nanotubes and fullerenes. Desirably, the carbonous or graphite material is material having an average particle size of 2 to 6 μm and comprising pores of a size of the order of nanometers. Preferable carbonous or graphite material includes activated carbon. 
         [0021]    The polylactide in the positive electrode active material layer functions as a binder for binding the nanocarbons and the carbonous or graphite material. Further, the polylactide also functions as a binder for binding the carbon material bound by the polylactide as described above and the positive electrode collector. In the present invention, the polylactide has a number average molecular weight of 30,000 to 100,000. 
         [0022]    The V 3+  compound in the positive electrode active material layer  120  is a salt of trivalent vanadium. In the present invention, the V 3+  compound is selected from the group consisting of V 2 O 3 , VF 3 , VCl 3 , V(acac) 3  (wherein “acac” represents acetylacetonate) and VSO 4 OH. The V 3+  compound contributes to achieving a function of storing electric charge to increase capacitance of the capacitor, by the mechanism that the center metal V 3+  releases one electron to form V 4+  during charging, and such formed V 4+  accepts one electron to form V 3+  during discharging. 
         [0023]    The positive electrode active material layer  120  comprises 20 to 65 parts by weight of the polylactide and 1 to 3 parts by weight of the V 3+  compound, per 100 parts by weight of the carbon material. On the other hand, the carbon material comprises 1 to 50% by weight of the nanocarbons and 50 to 99% by weight of the carbonous or graphite material, based on the total weight of the carbon material. Preferably, the carbon material comprises 1 to 5% by weight of the nanocarbons and 95 to 99% by weight of the carbonous or graphite material, based on the total weight of the carbon material. 
         [0024]    The positive electrode composition is formed by adding the carbon material into the polylactide which is softened or melted by heating in the absence of solvent and kneading them, and then adding the V 3+  compound and kneading them. It is preferable to carry out the kneading step under reduced pressure, in order to prevent from trapping bubbles in the composition. Subsequently, the positive electrode active material layer can be formed by applying the positive electrode composition onto one or both surfaces of the positive electrode collector  110 . Any means known in the art such as gravure coating, doctor blade coating, roll coating can be used in the application of the composition onto the positive electrode collector  110 . The positive electrode active material layer  120  of the present invention preferably has a thickness of 100 to 200 μm. Alternatively, self-supporting positive electrode active material layer  120  can be formed by applying the positive electrode composition onto a temporary substrate followed by peeling the resultant coated film from the temporary substrate. 
         [0025]    The negative electrode active material layer  140  of the present invention is a porous layer which comprises carbon material, polylactide, and V 4+  compound, and is capable of being impregnated with the electrolytic solution. The carbon material and polylactide useful in the negative electrode active material layer  140  are the same as those in the positive electrode active material layer. 
         [0026]    The V 4+  compound in the negative electrode active material layer  140  is a salt of tetravalent vanadium. In the present invention, the V 4+  compound is selected from the group consisting of V 2 O 4 , VOSO 4 , VF 4 , VCl 4 , VO(acac) 2 , and V(SO 4 ) 2 . The V 4+  compound contributes to achieving a function of storing electric charge to increase capacitance of the capacitor, by the mechanism that the center metal V 4+  accepts one electron to form V 3+  during charging, and such formed V 3+  releases one electron to form V 4+  during discharging. 
         [0027]    The negative electrode active material layer  140  comprises 20 to 65 parts by weight of the polylactide and 1 to 3 parts by weight of the V 3+  compound, per 100 parts by weight of the carbon material. On the other hand, the ratio between the nanocarbons and the carbonous or graphite material in the carbon material is similar to that in the positive electrode active material layer  120 . 
         [0028]    The negative electrode active material layer  140  can be formed by the similar procedure to that for the positive electrode active material layer  120 . The negative electrode active material layer of the present invention has a thickness of 100 to 200 μm. 
         [0029]    The electrolytic solution is an organic solution comprising an electrolyte and organic solvent. The electrolyte comprise a cationic component such as quaternary ammonium salt, imidazolium salt or pyridinium salt, and an anionic component such as BF 4   − , PF 6   − , CF 3 SO 3   − , or (CF 3 SO 2 )N − . The electrolyte of the present invention is preferably a BF 4   −  salt of quaternary ammonium, more preferably (C 2 H 5 ) 3 (CH 3 )NBF 4 . The electrolyte of the present invention is present in a range of 1 to 1.5 mole percent in the electrolytic solution. The organic solvent used in the electrolytic solution of the present invention includes polar aprotic solvent such as propylene carbonate, sulfolane, ethylene carbonate, γ-butyrolactone, N,N-dimethylformamide, or dimethylsulfoxide. Mixtures of the above-described solvent can be used as the organic solvent of the present invention. Preferably, the organic solvent is a mixture of propylene carbonate and sulfolane. 
         [0030]    The capacitor of the other embodiment of the present invention comprises a plurality of a first electrode laminates, one or more of second electrode laminates, a plurality of separators, and an electrolytic solution, wherein: the first electrode laminate comprises a first collector and a first active material layer comprising carbon material, polylactic acid and one of V 3+  or V 4+  compound; the second electrode laminate comprises a second collector and a second active material layer comprising carbon material, polylactic acid and the other of V 3+  or V 4+  compound; each of the separators is disposed between the first and second electrode laminates; and the electrolytic solution is impregnated into the first active material layer, the second active material layer, and the separator. A constitutional example, where the first electrode laminate is a positive electrode collector and the second electrode laminate is a negative electrode collector, is shown in  FIGS. 2A to 2E . In the constitution shown in  FIGS. 2A to 2E , separator  130 , double-sided negative electrode laminate  220  in which negative electrode active material layers  140  are provided on the both surfaces of negative electrode collector  150 , and separator  130  are disposed between top single-sided positive electrode laminate  210 T and bottom single-sided positive electrode laminate  210 B, wherein both of the top single-sided positive electrode laminate  210 T and bottom single-sided positive electrode laminate  210 B comprise a positive electrode active material layer  120  provided on one surface of positive electrode collector  110 , and wherein the electrolytic solutions is impregnated into the positive electrode active material layer  120 , the negative electrode active material layer  140 , and the separator  130 . In this constitution, more of internal capacitors can be formed by further laminating additional structure  240  consisting of double-sided positive electrode laminate  210 M in which positive electrode active material layers  120  are provided on the both surfaces of positive electrode collector  110 , separator  130 , the double-sided negative electrode laminate  220  and separator  130 . If necessary, a plurality of additional structures  240  can be laminated. 
         [0031]      FIG. 2A  shows a constitution in which a plurality of internal capacitors are connected in series. However, laminated capacitor, in which a plurality of internal capacitors are parallelly connected can be formed, by electrically connecting the top single-sided positive electrode laminate  210 T, the one or more double-sided positive electrode laminate  210 M, and the bottom single-sided positive electrode laminate  210 B to each other, and electrically connecting the one or more double-sided negative electrode laminate  220  to each other. Further,  FIG. 2A  shows an example in which the positive electrode laminate is disposed at the top and bottom of the capacitor. However, alternative constitution, where the negative electrode laminate is disposed at the top and bottom of the capacitor, is also adoptable. 
         [0032]    The first step of production of the capacitor of the present invention is: to laminate a positive electrode laminate in which the positive electrode active material layers  120  are provided on the both surfaces of the positive electrode collector  120 , separator  130 , a negative electrode laminate in which the positive electrode active material layers  140  are provided on the both surfaces of the negative electrode collector  140 , and separator  130  in this order; to apply a pressure to the resultant laminate for integrating these layers; and to wind it up into a rolled shape. Then, the intermediate of the rolled shape is compression molded into a desired shape, an approximately rectangular parallelepiped shape for example. Subsequently, the electrolytic solution is impregnated into the positive electrode active material layer, the negative electrode active material layer, and the separator in the intermediate. The capacitor of the present invention can be obtained by carrying out further processing such as attaching terminals for external connection and wrapping with an insulative seal material. The insulative seal material may include any material known in the art, as long as it can prevent leakage of the electrolytic solution and electrical connection between inside and outside of the capacitor. 
         [0033]    A method for producing the capacitor of the other embodiment of the present invention comprises: laminating respective constituting layers (the separator  130 , the double-sided negative electrode laminate  220 , and the separator  130  between the top single-sided positive electrode laminate  210 T and the bottom single-sided positive electrode laminate  210 B); and impregnating the electrolytic solution into the positive electrode active material layers  120 , the negative electrode active material layers  140 , and the separators  130 . In this method, a desired number of the additional structures  240  may further laminated in the first step. 
         [0034]    The above description explains the case where the positive electrode active material layer  120  and negative electrode active material layer  140  are formed on the positive electrode collector  110  and negative electrode collector  150 , respectively. Alternatively, the positive electrode active material layer  120  and negative electrode active material layer  140 , which are self-supporting, can be used to form the capacitor of the present invention. In this case, the capacitor of the present invention can be formed by similar method to that described above, except that the positive electrode active material layer  120 , the positive electrode collector  110 , the positive electrode active material layer  120 , the separator  130 , the negative electrode active material layer  140 , the negative electrode collector  150 , the negative electrode active material layer  140 , and the separator  130  are laminated in this order. 
         [0035]    Further, the capacitor obtained as above can be subjected to processing such as cutting, cutting off, folding, perforating, molding. 
       EXAMPLES 
     Example 1 
       [0036]    Polylactide (3.572 g) having a number average molecular weight of 32,000 was heated to 200° C. under reduced pressure to melt. To the molten polylactide was added carbon nanotube (0.64 g) and activated carbon (5 g) having an average particle diameter of 1 μm and kneaded. Then, VSO 4 OH (0.188 g) was added and kneaded to obtain a positive electrode composition. The positive electrode composition was coated onto the both surfaces of an aluminum foil having a thickness of 40 μm which had been subjected to “A20” treatment by roll coating, to form a positive electrode laminate wherein the positive electrode active material layers having a thickness of 150 μm were formed on the both surfaces of the aluminum foil (a positive electrode collector). 
         [0037]    Polylactide (3.572 g) having a number average molecular weight of 32,000 was heated to 200° C. under reduced pressure to melt. To the molten polylactide was added carbon nanotube (0.64 g) and activated carbon (4 g) having an average particle diameter of 1 μm and kneaded. Then, V(SO 4 ) 2  (0.188 g) was added and kneaded to obtain a negative electrode composition. The negative electrode composition was coated onto the both surfaces of a copper foil having a thickness of 40 μm by roll coating, to form a negative electrode laminate wherein the negative electrode active material layers having a thickness of 150 μm were formed on the both surfaces of the copper foil (a negative electrode collector). 
         [0038]    Triethylmethylammonium tetrafluoroborate was dissolved in a mixture of sulfolane and propylene carbonate in a ratio of 1:2.8 to form an electrolytic solution. The concentration of triethylmethylammonium tetrafluoroborate was 1.5 mole percent. 
         [0039]    The positive electrode laminate, a separator (pulp separator manufactured by Nippon Kodoshi Corporation), the negative electrode laminate, and a separator are laminated in this order and passed through a pair of press rolls to integrate these constituting layers, and then wound into a rolled shape. Then, the intermediate of the rolled shape was placed in a mold and pressed into an approximately rectangular parallelepiped shape. Subsequently, the electrolytic solution was impregnated into the positive electrode active material layers, the negative electrode active material layers, and the separators in the intermediate. After that, attachment of the terminals for external connection and wrapping with an insulative seal material was carried out to obtain a capacitor. 
         [0040]    The resultant capacitor had a mass of 22.9 g, an equivalent series resistance (ESR) of 400 mΩ, a residual voltage of 10 mV, and a capacitance of 640 F. Further, a current of 3.7 V and 1 A can be taken out of the resultant capacitor. 
       Example 2 
       [0041]    Polylactide (3.572 g) having a number average molecular weight of 32,000 was heated to 200° C. under reduced pressure to melt. To the molten polylactide was added carbon nanotube (0.64 g) and activated carbon (5 g) having an average particle diameter of 1 μm and kneaded. Then, VSO 4 OH (0.188 g) was added and kneaded to obtain a positive electrode composition. A positive electrode collector  110  was formed from an aluminum foil having a thickness of 30 μm which had been subjected to “A20” treatment. The positive electrode collector  110  was constituted of an electrode part having a long side of a length of 5.9 cm and a short side of a length of 3.9 cm, and a tab for external connection disposed on the short side of the electrode part and having a dimension of 1.5 cm by 0.5 cm. The positive electrode composition was coated onto a single surface of the electrode part of the positive electrode collector  110  by roll coating, to form top and bottom single-sided positive electrode laminates  210 T and  210 B on which a positive electrode active material layer  120  having a thickness of 80 μm was formed. Further, the positive electrode composition was coated onto both surfaces of the electrode part of the positive electrode collector  110  by roll coating, to form a double-sided positive electrode laminates  210 M, on each surface of which a positive electrode active material layer  120  having a thickness of 80 μm was formed. 
         [0042]    Polylactide (3.572 g) having a number average molecular weight of 32,000 was heated to 200° C. under reduced pressure to melt. To the molten polylactide was added carbon nanotube (0.64 g) and activated carbon (4 g) having an average particle diameter of 1 μm and kneaded. Then, V(SO 4 ) 2  (0.188 g) was added and kneaded to obtain a negative electrode composition. 
         [0043]    A negative electrode collector is formed from a copper foil having a thickness of 30 μm. Similarly to the positive electrode collector  110 , the negative electrode collector  150  was constituted of an electrode part having a long side of a length of 5.9 cm and a short side of a length of 3.9 cm, and a tab for external connection disposed on the short side of the electrode part and having a dimension of 1.5 cm by 0.5 cm. The negative electrode composition was coated onto both surfaces of the electrode part of the negative electrode collector  150  by roll coating, to form a double-sided negative electrode laminates  220 , on each surface of which a negative electrode active material layer  140  having a thickness of 60 μm was formed. 
         [0044]    Triethylmethylammonium tetrafluoroborate was dissolved in a mixture of sulfolane and propylene carbonate in a ratio of 1:2.8 to form an electrolytic solution. The concentration of triethylmethylammonium tetrafluoroborate was 2.5 mole percent. 
         [0045]    Separator  130  (pulp separator manufactured by Nippon Kodoshi Corporation, having a long side of a length of 6 cm, a short side of a length of 4 cm, and a thickness of 20 μm), the double-sided negative electrode laminate  220 , the separator  130 , and the double-sided positive electrode laminate  210 M were laminated in this order, onto the positive electrode active material layer  120  of the bottom single-sided positive electrode laminate  210 B. This lamination was repeated for sixteen times. Further, onto the double-sided positive electrode laminate at the top of the laminate, the separator  130 , the double-sided negative electrode laminate  220 , the separator  130 , and the top single-sided positive electrode laminate  210 T were laminated. Here, the positive electrode active material layer  120  of the top single-sided positive electrode laminate  210 T was in contact with the separator  130 . In the above lamination, the tabs for external connection of the positive electrode laminates ( 210 B,  210 M and  210 T) were disposed on a single straight line extending to the laminating direction, and the tabs for external connection of the negative electrode laminates ( 220 ) were disposed on the other straight line extending to the laminating direction, such that the tabs for external connection of the positive electrode laminates ( 210 B,  210 M and  210 T) kept form overlapping with the tabs for external connection of the negative electrode laminates ( 220 ), in view of the laminating direction. The resultant laminate had eighteen positive electrode laminates ( 210 B,  210 M, and  210 T) and seventeen negative electrode laminates ( 220 ). The resultant laminate had a structure wherein the adjacent positive electrode laminate ( 210 B,  210 M, or  210 T) and negative electrode laminate ( 220 ) was separated by the separator. 
         [0046]    Subsequently, the resultant laminate was passed through a pair of press rolls to integrate the constituting layers. Then, the electrolytic solution was impregnated into the separators, the positive electrode active material layers  120 , and the negative electrode active material layers  140 . After that, the tabs for external connection of all of the positive electrode laminates ( 210 B,  210 M and  210 T) were connected to externally connecting positive electrode terminal, and the tabs for external connection of all of the negative electrode laminates ( 220 ) were connected to externally connecting negative electrode terminal, such that internal capacitors, which were constituted of a pair of the positive electrode laminate ( 210 B,  210 M and  210 T) and the negative electrode laminate ( 220 ), were connected parallelly. Subsequently, the laminate was wrapped with an insulative seal material to obtain a capacitor having an approximately rectangular parallelepiped shape having a long side of a length of 6.2 cm, a short side of a length of 4.0 cm, and a height of 7.0 mm (except for connecting terminals). The resultant capacitor had a mass of 42.0 g, an equivalent series resistance (ESR) of 25 mΩ, and a service capacity of 2000 mAh. Further, a current of 3.7 V and 2 A can be taken out of the resultant capacitor. 
         [0047]    A durability test for charging and discharging of the resultant capacitor was carried out in accordance with the following procedure. A single cycle of charging and discharging consists of charging at a constant current of 2 A for 1 minutes (1 C), an idle period for 10 seconds, and discharging at a constant current of 2 A for 1 minutes (1 C). Charging and discharging was carried out with a charging and discharging cycle checker manufactured by DENSHI HYOGEN COMPANY, which was made for this test, and with intervals between the cycles of 10 seconds. At every hundred cycles of charging and discharging, the capacitor was fully charged with LiPo8 expert charger (manufactured by ABC Hobby Co., Ltd.) under the conditions of a constant voltage of 4.1 V and a constant current of 2 A. Subsequently, the service capacity was measured when carrying out discharging at a constant current of 2 A (discharge cut-off voltage of 3.3 V) with LiPo8 expert charger. Table 1 shows the relationship between the number of cycles of charging and discharging and the service capacity. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 The number of charging and 
                 Service capacity 
               
               
                   
                 discharging 
                 (mAh) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 2000 
               
               
                   
                 100 
                 1856 
               
               
                   
                 200 
                 1875 
               
               
                   
                 300 
                 1850 
               
               
                   
                 400 
                 1839 
               
               
                   
                 500 
                 1866 
               
               
                   
                 600 
                 1895 
               
               
                   
                 700 
                 1807 
               
               
                   
                 800 
                 1840 
               
               
                   
                 900 
                 1874 
               
               
                   
                 1000 
                 1872 
               
               
                   
                 1100 
                 1820 
               
               
                   
                 1200 
                 1853 
               
               
                   
                 1300 
                 1852 
               
               
                   
                 1400 
                 1754 
               
               
                   
                 1500 
                 1801 
               
               
                   
                 1600 
                 1814 
               
               
                   
                 1700 
                 1859 
               
               
                   
                 1800 
                 1826 
               
               
                   
                   
               
             
          
         
       
     
         [0048]    From the above results, it can be seen that the capacitor of the present invention has a service capacity of about 92% of the initial service capacity, even after repeated 1800 cycles of charging and discharging. It is seen that the capacitor of the present invention has a high durability for charging and discharging. Further, the above results obtained even though this test was carried out under severe conditions of a low temperature of 10-17° C. Taking the characteristics of this capacitor into account, it is expected that better result would be obtained under the conditions of higher temperature. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               110  Positive electrode collector 
               120  Positive electrode active material layer 
               130  Separator 
               140  Negative electrode active material layer 
               110  Negative electrode collector 
               210 T Top single-sided positive electrode laminate 
               210 B Bottom single-sided positive electrode laminate 
               210 M Double-sided positive electrode laminate 
               220  Double-sided negative electrode laminate 
               240  Additional structure