Patent Publication Number: US-7708787-B2

Title: Electrode for electric chemical capacitor, manufacturing method and apparatus thereof

Description:
This application is a divisional and claims the benefit of priority under 35 U.S.C. §120 from U.S. application Ser. No. 11,016,842, filed Dec. 21, 2004, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application No. 2003-423969, filed Dec. 22, 2003 and Japanese Patent Application No. 2003-432272, filed Dec. 26, 2003. The entire contents of these applications are incorporated herein by reference. 

   TECHNICAL FIELD 
   The present invention relates to an electrode for an electrochemical capacitor and a method and an apparatus for the manufacture thereof, and more particularly to an electrode for an electrochemical capacitor having a high volume capacitance and a method and an apparatus for the manufacture thereof. 
   BACKGROUND ART 
   Since electrochemical capacitors including an electric double-layer capacitor can be easily made small in size and light in weight, they are expected as, for example, backup power sources for the power sources of portable equipment (small-sized electronic equipment) etc., and auxiliary power sources for an electric automobile and a hybrid vehicle, and various studies have been made for enhancing the performances of the electrochemical capacitors. Especially in a case where a large capacity is required as in the power source for the electric automobile, it has been desired to develop an electrochemical capacitor in which a capacitance per unit volume of electrodes (hereinbelow, termed “volume capacitance”) is high. 
   Each electrode for use in such an electrochemical capacitor has a laminated structure which includes a current collector and a polarizable electrode layer, and it can be fabricated by coating the front surface of the sheet-like current collector with a solution which is to become the material of the polarizable electrode layer, and which is subjected to drying (refer to Patent Document 1). Since, however, the density of the polarizable electrode layer to be formed is low merely by coating the front surface of the current collector with such a solution and then drying the solution, a sufficient volume capacitance cannot be attained. In order to attain a higher volume capacitance, therefore, the polarizable electrode layer needs to be compressed by roll press or the like after the formation thereof by the coating. 
   [Patent Document 1] JP-A-2000-106332 
   DISCLOSURE OF THE INVENTION 
   Problem that the Invention is to Solve 
   The inventors&#39; researches, however, have revealed that the compression of a polarizable electrode layer is insufficient merely by roll press employing a roller whose front surface is substantially smooth, so a volume capacitance (at least 17 F/cm 3 ) which is required of an electrochemical capacitor of high capacitance is difficult of achievement. 
   Accordingly, an object of the present invention is to provide a manufacturing method and a manufacturing apparatus for an electrode for an electrochemical capacitor having a higher volume capacitance. 
   Besides, another object of the invention is to provide a manufacturing method and a manufacturing apparatus for an electrode for an electrochemical capacitor having the volume capacitance of at least 17 F/cm 3 . 
   Means for Solving the Problem 
   A manufacturing method for an electrode for an electrochemical capacitor according to the present invention is characterized by comprising the first step of forming a polarizable electrode layer on a current collector; the second step of subjecting a front surface of the polarizable electrode layer formed on the current collector, to an embossment work; and the third step of flattening the front surface of the polarizable electrode layer as has undergone the embossment work. 
   Here, the expression “subjecting the front surface of the polarizable electrode layer to the embossment work” signifies that the polarizable electrode layer is compressed, thereby to form a rugged pattern in the front surface thereof. The rugged pattern to be formed may be either regular or random. Besides, the expression “flattening the front surface of the polarizable electrode layer as has undergone the embossment work” signifies that the height of the rugged pattern formed in the front surface of the polarizable electrode layer is decreased by compression. Accordingly, the embossment need not always be completely removed, but the height of the rugged pattern may decrease. In this case, as long as the height of the rugged pattern is decreased as a whole, a new embossment may well be formed. The “height of the rugged pattern” signifies the perpendicular distance between convex parts and concave parts. 
   In this manner, in the invention, the front surface of the polarizable electrode layer undergoes the embossment work, so that the polarizable electrode layer is effectively compressed, and it is consequently permitted to achieve a high volume capacitance of at least 17 F/cm 3 . Moreover, after the embossment work, the resulting embossment is flattened, so that porous grains contained in the polarizable electrode layer are prevented from falling off, and it is permitted to ensure a high reliability. 
   The first step should favorably be performed by coating the current collector with a coating liquid which contains porous grains having an electronic conductivity, a binder capable of binding up the porous grains, and a liquid capable of dissolving or dispersing the binder therein. According to this measure, it is permitted to easily form the polarizable electrode layer on the current collector. In this case, an electrically conductive assistant should favorably be further contained in the coating liquid. With the electrically conductive assistant, it is permitted to promote the migration of charges between the current collector and the polarizable electrode layer. 
   The second step should favorably be performed by roll press based on a roller whose front surface is provided with a rugged pattern. According to this measure, it is permitted to reliably subject the front surface of the polarizable electrode layer to the embossment work. In this case, the height of the rugged pattern should favorably be set at 20% through 70% inclusive, of the thickness of the polarizable electrode layer before performing the second step. The reason therefor is that, when the rugged pattern is excessively low, the polarizable electrode layer is not effectively compressed, whereas when the rugged pattern is excessively high, a damage to the current collector becomes heavy. 
   The third step should favorably be performed by roll press based on a roller whose front surface is substantially smooth. According to this measure, it is permitted to reliably flatten the embossment formed in the front surface of the polarizable electrode layer. 
   Besides, the third step may well be performed after the second step has been performed a plurality of times, or the third step may well be performed a plurality of times. According to this measure, the polarizable electrode layer is compressed still more, and the porous grains contained in the polarizable electrode layer are more reliably prevented from falling off. 
   A manufacturing apparatus for an electrode for an electrochemical capacitor according to the invention is a manufacturing apparatus for an electrode for an electrochemical capacitor, for manufacturing the electrode for the electrochemical capacitor by roll-pressing a laminated product in which, at least, a current collector and a polarizable electrode layer are stacked, characterized by comprising a first roll press section which subjects a front surface of the polarizable electrode layer to an embossment work; and a second roll press section which is disposed downstream of the first roll press section, and which flattens the front surface of the polarizable electrode layer as has undergone the embossment work. 
   With the manufacturing apparatus according to the invention, the polarizable electrode layer can be effectively compressed, and porous grains contained in the polarizable electrode layer can be prevented from falling off, so that a high reliability can be ensured. Besides, the apparatus is prevented from being polluted due to the porous grains which have fallen off. 
   The first roll press section should preferably include first and second rollers which roll-press the laminated product, and at least one of which is provided with a rugged pattern in its front surface, and the height of the rugged pattern should more preferably be 20% through 70% inclusive, of the thickness of the polarizable electrode layer before performing the roll press based on the first roll press section. Further, it is allowed that the rugged pattern is provided in an area which has substantially the same width as the width of the polarizable electrode layer, and that areas which are adjacent to the first-mentioned area are substantially flat. With such a roller, those parts of the current collector which are not covered with the polarizable electrode layer are subjected to no embossment work, so that a damage to the current collector can be relieved. 
   The second roll press section should favorably include third and fourth rollers which roll-press the laminated product, and the front surfaces of which are both substantially smooth. 
   Further, an electrode for an electrochemical capacitor according to the invention is characterized by comprising a sheet-like current collector, and a polarizable electrode layer which is provided on the current collector with a predetermined bare portion left, the polarizable electrode layer having undergone an embossment work, at least part of the bare portion of the current collector not having undergone any embossment work. 
   In this manner, in the invention, the front surface of the polarizable electrode layer has undergone the embossment work, so that the polarizable electrode layer is effectively compressed, and it is consequently permitted to achieve a high volume capacitance of at least 17 F/cm 3 . Moreover, at least part of the bare portion of the current collector has not undergone any embossment work, so that a damage to the current collector is relieved, whereby a high reliability can be ensured. In this case, it is favorable that substantially the whole surface of the bare portion of the current collector has not undergone any embossment work. 
   Porous grains having an electronic conductivity, and a binder capable of binding up the porous grains should preferably be contained in the polarizable electrode layer, and an electrically conductive assistant should more preferably be further contained. With the electrically conductive assistant, it is permitted to promote the migration of charges between the current collector and the polarizable electrode layer. 
   A manufacturing method for an electrode for an electrochemical capacitor according to the invention is characterized by comprising the first step of coating a current collector with a polarizable electrode layer so that a bare portion may be left at part of the current collector; and the second step of subjecting a front surface of the polarizable electrode layer formed on the current collector, to an embossment work, without subjecting at least part of the bare portion of the current collector, to the embossment work. 
   According to the invention, the electrode for the electrochemical capacitor having a high volume capacitance of at least 17 F/cm 3  can be manufactured owing to the effective compression of the polarizable electrode layer, while the reliability of a manufactured product is heightened by relieving a damage to the current collector. Also in this case, it is favorable that substantially the whole surface of the bare portion of the current collector is not undergone any embossment work. 
   At the first step, the current collector in a band shape as is conveyed in the lengthwise direction thereof should favorably be coated with the polarizable electrode layer of predetermined width so as to leave the bare portion at, at least, one end part of the current collector in the widthwise direction thereof. According to this measure, the polarizable electrode layer is continuously formed on the current collector, so that a high productivity can be attained. 
   The first step should favorably be performed by coating the current collector with a coating liquid which contains porous grains having an electronic conductivity, a binder capable of binding up the porous grains, and a liquid capable of dissolving or dispersing the binder therein. According to this measure, it is permitted to easily form the polarizable electrode layer on the current collector. In this case, an electrically conductive assistant should favorably be further contained in the coating liquid. With the electrically conductive assistant, it is permitted as stated above to promote the migration of charges between the current collector and the polarizable electrode layer. 
   The second step should favorably be performed by roll press based on a roller which is partially provided with a rugged pattern. Besides, at the second step, the front surface of the polarizable electrode layer formed on the current collector may well be subjected to an embossment work so as to leave part of the front surface. 
   A manufacturing apparatus for an electrode for an electrochemical capacitor according to the invention is a manufacturing apparatus for an electrode for an electrochemical capacitor, for manufacturing the electrode for the electrochemical capacitor by roll-pressing a laminated product in which, at least, a current collector and a polarizable electrode layer are stacked, characterized by comprising a roll press section which serves to subject a front surface of the polarizable electrode layer to an embossment work, and which includes a roller that is partially provided with a rugged pattern. 
   With the manufacturing apparatus for the electrode for the electrochemical capacitor according to the invention, the electrode for the electrochemical capacitor having a high volume capacitance of at least 17 F/cm 3  can be manufactured owing to the effective compression of the polarizable electrode layer, while the reliability of a manufactured product is heightened by relieving a damage to the current collector. Also in this case, it is favorable that the rugged pattern is provided in an area which has substantially the same width as the width of the polarizable electrode layer, and that areas which are adjacent to the first-mentioned area are substantially flat. 
   ADVANTAGES OF THE INVENTION 
   In this manner, according to the present invention, the front surface of a polarizable electrode layer has undergone an embossment work, so that the polarizable electrode layer is effectively compressed, and it is consequently permitted to achieve a high volume capacitance of at least 17 F/cm 3 . Moreover, after the embossment work, the resulting embossment is flattened, so that porous grains contained in the polarizable electrode layer are prevented from falling off, and it is permitted to ensure a high reliability. Thus, it is permitted to fabricate an electrochemical capacitor of high capacitance and high reliability. 
   Further, according to the present invention, the front surface of a polarizable electrode layer has undergone an embossment work, so that the polarizable electrode layer is effectively compressed, and it is consequently permitted to achieve a high volume capacitance of at least 17 F/cm 3 . Furthermore, at least part of the bare portion of the current collector has not undergone any embossment work, so that a damage to the current collector attributed to the embossment work is relieved, and during manufacture, winding round a roller for roll press can be relived to enhance a job efficiency. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view showing the structure of an electrode for an electrochemical capacitor as is fabricated by a manufacturing method according to a preferred embodiment of the present invention, wherein (a) is a schematic sectional view, and (b) is a schematic perspective view. 
       FIG. 2  is a flow chart for explaining the manufacturing method for the electrode for the electrochemical capacitor according to the preferred embodiment of the invention. 
       FIG. 3  is a model view for explaining a preparing method for a coating liquid (step S 1 ). 
       FIG. 4  is a schematic view showing the structure of a manufacturing apparatus for the electrode for the electrochemical capacitor according to a preferred embodiment of the invention. 
       FIG. 5  is a view showing an example in which a rugged pattern is provided over substantially the whole area of the front surface  131   a  of a first roller  131 . 
       FIG. 6  is a view showing an example in which a rugged pattern is provided in only an area  131   a   1  having substantially the same width as the width W 1  of a polarizable electrode layer  18 , in the front surface  131   a  of the first roller  131 . 
       FIG. 7  is a view exaggeratedly showing the rugged pattern which is provided in the front surface  131   a  of the first roller  131 , wherein (a) is a schematic sectional view, and (b) is a schematic plan view. 
       FIG. 8  is a view exaggeratedly showing that front surface of the polarizable electrode layer  18  which has been embossed by a first roll press section  130 , wherein (a) is a schematic sectional view, and (b) is a schematic plan view. 
       FIG. 9  is a view for explaining a process (step S 6 ) for cutting the electrode  10  for the electrochemical capacitor, out of a laminated product  20 , wherein (a) is a schematic plan view of the laminated product  20  which has been cut into a predetermined size, (b) is a schematic plan view of the laminated product  20  out of which the electrode  10  for the electrochemical capacitor has been cut, and (c) is a schematic plan view of the cut-out electrode  10  for the electrochemical capacitor. 
       FIG. 10  is a model view for explaining a method for fabricating the electrochemical capacitor from the electrodes  10  for the electrochemical capacitor. 
       FIG. 11  is a view showing an example in which a plurality of first roll press sections  130  are disposed. 
       FIG. 12  is a view showing an example in which the front surface  141   a  of a third roller  141  included in a second roll press section  140  is provided with a rugged pattern of small height. 
       FIG. 13  is a view showing an example in which a rugged pattern is provided also in the front surface  132   a  of a second roller  132  included in a first roll press section  130 . 
       FIG. 14  is a view showing an example in which the front surface  131 - 1   a  of a roller  131 - 1  included in an upper stream side roll press section  130 - 1 , and the front surface  132 - 2   a  of a roller  132 - 2  included in a lower stream side roll press section  130 - 2  are respectively provided with rugged patterns. 
       FIG. 15  is a flow chart for explaining a manufacturing method for an electrode for an electrochemical capacitor according to the second embodiment of the invention. 
       FIG. 16  is a schematic perspective view exaggeratedly showing a first roll press section  130  according to the second embodiment (and a second roll press section  140 ). 
       FIG. 17  is a view showing an example in which a rugged pattern is provided also in the area  141   a   1  of the front surface  141   a  of a third roller  141  included in the second roll press section  140  according to the second embodiment. 
       FIG. 18  is a view showing an example in which a rugged pattern is provided also in the area  132   a   1  of the front surface  132   a  of a second roller  132  included in the first roll press section  130  according to the second embodiment. 
       FIG. 19  is a view showing an example in which a rugged pattern is provided also in the area  142   a   1  of the front surface  142   a  of a fourth roller  142  included in the second roll press section  140  according to the second embodiment. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the ensuing description, the construction of an electrode for an electrochemical capacitor as is fabricated by a manufacturing method according to each of the embodiments will be first described, and the manufacturing method according to the embodiment will be thereafter described in detail. 
   First Embodiment 
     FIGS. 1(   a ) and ( b ) are a schematic sectional view and a schematic perspective view showing the structure of an electrode for an electrochemical capacitor as is fabricated by a manufacturing method according to the preferred embodiment of the present invention, respectively. 
   As shown in  FIG. 1 , the electrode  10  for the electrochemical capacitor according to the embodiment is constructed of a current collector  16  which has an electronic conductivity, and a polarizable electrode layer  18  which has an electronic conductivity and which is formed on the current collector  16 . 
   The material of the current collector  16  is not especially restricted as long as it is a good conductor of electricity capable of causing sufficient charges to migrate into the polarizable electrode layer  18 , and it is possible to employ a current collector material for use in a known electrode for an electrochemical capacitor, for example, aluminum (Al). The thickness of the current collector  16  is not especially restricted, either, but in order to make the electrochemical capacitor smaller in size, the current collector  16  should favorably be set at the smallest possible thickness as long as a satisfactory mechanical strength is ensured. Concretely, in the case where aluminum (Al) is employed as the material of the current collector  16 , the thickness thereof should preferably be set at 20 μm through 50 μm inclusive, and more preferably at 20 μm through 30 μm inclusive. When the thickness of the current collector  16  made of aluminum (Al) is set within the range, it is permitted to achieve reduction in the size of the electrochemical capacitor with the satisfactory mechanical strength ensured. 
   Besides, the current collector  16  includes a bare portion  12  which is not covered with the polarizable electrode layer  18 , and which is employed as a lead-out electrode. 
   The polarizable electrode layer  18  is the layer which is formed on the current collector  16 , and which contributes to the accumulation and release of charges. As its constituent materials, the polarizable electrode layer  18  contains at least, porous grains which have an electronic conductivity, and a binder which can bind up the porous grains. Although not especially restricted, the content of the porous grains in the polarizable electrode layer  18  should favorably be 84-92 mass-% based on the total quantity of the polarizable electrode layer  18 , and that of the binder should favorably be 6.5-16 mass-% based on the total quantity of the polarizable electrode layer  18 . In particular, the polarizable electrode layer  18  should favorably consist of 84-92 mass-% of porous grains, 6.5-16 mass-% of binder, and 0-1.5 mass-% of electrically conductive assistant having an electronic conductivity, on the basis of its total quantity. 
   The porous grains contained in the polarizable electrode layer  18  are not especially restricted as long as they have the electronic conductivity and contribute to the accumulation and release of charges. Mentioned as the material of the porous grains is, for example, granular or fibrous active carbon subjected to an activation process. Usable as such an active carbon is phenolic active carbon, coconut-husk active carbon, or the like. The mean grain diameter of the porous grains should favorably be 3-20 μm, and the BET specific surface area thereof as is calculated from a nitrogen adsorption isotherm by a BET isothermic adsorption formula should preferably be at least 1500 m 2 /g, more preferably 2000-2500 m 2 /g. With such porous grains, it is permitted to attain a high volume capacitance. 
   Besides, the binder contained in the polarizable electrode layer  18  is not especially restricted as long as it is capable of binding up the porous grains. Usable as the binder is any of, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), and fluorine rubber. Among them, the fluorine rubber is especially favorably used. The reason therefor is that, when the fluorine rubber is used, the porous grains can be sufficiently bound up even with a small content, whereby the coating film strength of the polarizable electrode layer  18  is enhanced, and the size of a double-layer interface can be enlarged to enhance the volume capacitance. 
   Mentioned as the fluorine rubber are, for example, vinylidene fluoride-hexafluoropropylene type fluorine rubber (VDF-HFP type fluorine rubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene type fluorine rubber (VDF-HFP-TFE type fluorine rubber), vinylidene fluoride-pentafluoropropylene type fluorine rubber (VDF-PFP type fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene type fluorine rubber (VDF-PFP-TFE type fluorine rubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene type fluorine rubber (VDF-PFMVE-TFE type fluorine rubber, and vinylidene fluoride-chlorotrifluoroethylene type fluorine rubber (VDF-CTFE type fluorine rubber). Herein, the fluorine rubbers in each of which at least two members selected from the group consisting of the substances VDF, HFP and TFE are copolymerized are preferable, and the VDF-HFP-TFE type fluorine rubber in which the three substances of the group are copolymerized is especially preferable because it has the tendency of more enhancing an adhering property and tolerances to chemicals. 
   Further, the electrically conductive assistant which is contained in the polarizable electrode layer  18  as may be needed is not especially restricted as long as it has the electronic conductivity capable of sufficiently carrying out the migration of charges between the current collector  16  and the polarizable electrode layer  18 . Carbon black, for example, is mentioned as the electrically conductive assistant. 
   Acetylene black, ketffen black, and furnace black, for example, are mentioned as the carbon black, and the acetylene black is favorably employed in the invention. The mean grain diameter of the carbon black should preferably be 25-50 nm, and the BET specific surface area thereof should preferably be at least 50 m 2 /g, more preferably 50-140 m 2 /g. 
   Besides, from the viewpoint of making the electrode  10  for the electrochemical capacitor small in size and light in weight, the thickness of the polarizable electrode layer  18  should preferably be 50-200 μm, more preferably 80-150 μm. By the way, in a case where the thickness of the polarizable electrode layer  18  is not uniform (in a case, for example, where an embossment remains on the surface thereof), the above thickness shall signify the maximum thickness. The electrochemical capacitor can be made small in size and light in weight by setting the thickness of the polarizable electrode layer  18  within the above range. 
   The thickness (maximum thickness) of the whole electrode  10  for the electrochemical capacitor as is constructed by stacking the current collector  16  and the polarizable electrode layer  18  should preferably be 70-250 μm, and it should more preferably be 100-180 μm. Owing to such a thickness, the electrochemical capacitor can be made small in size and light in weight. 
   The above is the construction of the electrode  100  for the electrochemical capacitor as is fabricated by the manufacturing method according to the preferred embodiment of the invention. Next, the manufacturing method according to the preferred embodiment of the invention will be described in detail. 
     FIG. 2  is a flow chart for explaining the manufacturing method for the electrode for the electrochemical capacitor according to the preferred embodiment of the invention. Now, the manufacturing method for the electrode for the electrochemical capacitor according to this embodiment will be described with reference to the flow chart. 
   First of all, a coating liquid to become the material of the polarizable electrode layer  18  is prepared (step S 1 ). The preparation of the coating liquid can be performed in the ensuing way. First, as shown in  FIG. 3 , the porous grains P 1  stated above, the binder P 2  stated above, a liquid S 1  to be stated below, and if necessary, the electrically conductive assistant P 3  stated above are thrown into a mixing device C 1  including an agitation unit SB 1 , and they are agitated therein. Thus, the coating liquid L 1  can be prepared. The preparation of the coating liquid should favorably include a kneading operation and/or a dilution mixing operation. Here, the “kneading” signifies to blend the constituent materials by agitating them in a state where the liquid has a comparatively high viscosity, while the “dilution mixing” signifies to mix the constituent materials together in a state where a solvent or the like is further added into the kneaded liquid so as to establish a comparatively low viscosity. The time periods of the operations and temperatures during the operations are not especially restricted, but from the viewpoint of establishing a uniform dispersion state, it is favorable to set the kneading time period on the order of 30 minutes-2 hours and the temperature during the kneading on the order of 40-80° C., and it is favorable to set the dilution-mixing time period on the order of 1-5 hours and the temperature during the dilution mixing on the order of 20-50° C. 
   The liquid S 1  shown in  FIG. 3  is not especially restricted as long as it is capable of dissolving or dispersing the binder P 2  therein. By way of example, a ketonic solvent such as methyl-ethyl-ketone (MEK) or methyl-isobutyl-ketone (MIBK) can be employed as the liquid S 1 . Besides, the compounding proportion of the liquid S 1  in the coating liquid L 1  should favorably be set at 200-400 mass-parts based on 100 mass-parts of the whole solid matter in the coating liquid L 1 . The content of the porous grains P 1  in the coating liquid L 1  should favorably be set so that the content of the porous grains P 1  after the formation of the polarizable electrode layer  18  may fall within the range specified before. 
   After the coating liquid L 1  has been prepared in this way, the surface of the current collector  16  is subsequently coated with the coating liquid L 1 , thereby to form a coating film (step S 2 ), and the liquid S 1  contained in the coating film is removed by drying (step S 3 ). Thus, a state is established where the polarizable electrode layer  18  not compressed yet has been formed on the current collector  16 . Any of various known coating methods can be used without any special restriction, as a method for coating the surface of the current collector  16  with the coating liquid L 1 . It is possible to adopt a method, for example, extrusion lamination, doctor blade coating, gravure coating, reverse coating, applicator coating, or screen printing. Besides, the drying of the coating film can be performed by heating for a predetermined time period. Concretely, the drying should favorably be performed under conditions of 70-130° C. and 0.1-10 minutes. 
   After the uncompressed polarizable electrode layer  18  has been formed on the current collector  16  in this way, the front surface of the polarizable electrode layer  18  is subsequently embossed (step S 4 ), and the embossed front surface of the polarizable electrode layer  18  is further flattened (step S 5 ). Here, the embossment work of the front surface of the polarizable electrode layer  18  is done for effectively compressing the polarizable electrode layer  18 , thereby to heighten a volume capacitance. On the other hand, the flattening of the embossed front surface of the polarizable electrode layer  18  is done for preventing the porous grains P 1  from falling off from the embossed front surface of the polarizable electrode layer  18 . More specifically, when the front surface is strongly embossed (in a case, for example, where the height of a rugged pattern to be stated later is large), the porous grains P 1  are liable to fall off, and hence, it is apprehended to degrade the reliability of a product or to pollute a manufacturing apparatus. 
   A method for embossing the front surface of the polarizable electrode layer  18  can be incarnated in such a way, for example, that a roller or the like transfer member whose front surface is provided with the rugged pattern is pressed against the front surface of the polarizable electrode layer  18 . In this case, the height of the rugged pattern provided in the front surface of the transfer member should preferably be set at 20%-70% inclusive, of the thickness of the polarizable electrode layer  18  before the embossment work, and it should more preferably be set at 30%-60% inclusive. The reason therefor is that, when the height of the rugged pattern is excessively small, the polarizable electrode layer  18  is not effectively compressed, whereas when the height of the rugged pattern is excessively large, a damage to be done to the current collector  16  becomes heavy. Incidentally, the “height of the rugged pattern” signifies the perpendicular distance between a convex part and a concave part. 
   Besides, a method for flattening the embossed front surface of the polarizable electrode layer  18  can be incarnated in such a way, for example, that a roller or the like flattening member whose surface is substantially smooth is pressed against the front surface of the polarizable electrode layer  18 . 
   Owing to the above operations, the polarizable electrode layer  18  which has been effectively compressed and which prevents the porous grains from falling off is formed on the current collector  16 . Accordingly, when the resulting structure is cut out into a size and a shape which are necessary (step S 6 ), the electrode  10  for the electrochemical capacitor is finished up. 
     FIG. 4  is a schematic view showing the structure of an apparatus which is capable of performing the above steps S 2 -S 5  (the manufacturing apparatus for the electrode for the electrochemical capacitor). 
   The manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4  includes a feed roll  101  round which a sheet-like current collector  16  is wound, a take-up roll  102  round which a laminated product  20  consisting of the current collector  16  and a polarizable electrode layer  18  is to be wound by rotating at a predetermined velocity, and a coating section  110 , a drying section  120 , a first roll press section  130  and a second roll press section  140  which are disposed between the feed roll  101  and the take-up roll  102  in the order mentioned. In this manner, the manufacturing apparatus  100  for the electrode for the electrochemical capacitor has the construction in which the coating section  110 , drying section  120 , first roll press section  130  and second roll press section  140  are successively arranged from the upper stream (feed roll  101 ) to the lower stream (take-up roll  102 ). 
   The coating section  110  is a portion for performing the process (step S 2 ) for coating the surface of the current collector  16  with a coating liquid L 1 . The coating section  110  includes a vessel  111  which reserves the coating liquid L 1  therein, a coating-liquid feed roll (gravure roll)  112  which feeds the current collector  16  with the coating liquid L 1  in the vessel  111 , and a backup roll  113  which rotates in interlocking with the coating-liquid feed roll  112 . As shown in  FIG. 4 , the current collector  16  fed from the feed roll  101  is conveyed in a state where it is held between the coating-liquid feed roll  112  and the backup roll  113  which are rotating, whereby a coating film L 2  serving as the material of the polarizable electrode layer  18  is formed on one surface of the current collector  16 . The current collector  16  formed with the coating film L 2  is moved toward the drying section  120  by a guide roll  103 . 
   The drying section  120  is a portion for performing the process (step S 3 ) for removing a liquid S 1  which is contained in the coating film L 2 . In the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4 , the drying section  120  is constituted by two dryers  121  and  122  which are arranged so as to hold the current collector  16  therebetween, and the liquid S 1  contained in the coating film L 2  is removed by heating based on the dryers  121  and  122 , until the coating film L 2  becomes the polarizable electrode layer  18 . Thus, a state is established where the polarizable electrode layer  18  has been formed on the surface of the current collector  16 . However, the density of the polarizable electrode layer  18  is low in this state, and a high volume capacitance cannot be attained in the state left intact. 
   The first roll press section  130  is a portion for performing the process (step S 4 ) for embossing the front surface of the polarizable electrode layer  18 . In the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4 , the first roll press section  130  includes a first roller  131  arranged on the side of the polarizable electrode layer  18 , and a second roller  132  arranged on the side of the current collector  16 , and the laminated product  20  is roll-pressed by the rollers  131  and  132 , thereby to compress the polarizable electrode layer  18  included in the laminated product  20 . Here, the front surface  131   a  of the first roller  131  is provided with a rugged pattern, whereby the rugged pattern is transferred onto the front surface of the polarizable electrode layer  18  having passed through the first roll press section  130 . That is, the front surface of the polarizable electrode layer  18  is embossed. On the other hand, the front surface  132   a  of the second roller  132  is substantially smooth. 
   In so far as the first roller  131  included in the first roll press section  130  is capable of embossing substantially the whole front surface of the polarizable electrode layer  18 , it may well be provided with the rugged pattern over substantially the whole area of the front surface  131   a  as shown in  FIG. 5 . Alternatively, as shown in  FIG. 6 , the first roller  131  may well be provided with the rugged pattern in only an area  131   a   1  which has substantially the same width as the width W 1  of the polarizable electrode layer  18 , the other areas  131   a   2  being substantially smooth. With the type of the first roller  131  as shown in  FIG. 5 , it is permitted to reliably emboss the whole front surface of the polarizable electrode layer  18  even in a case where the laminated product  20  has deviated relative to the first roller  131  in the axial direction thereof. On the other hand, with the type of the first roller  131  as shown in  FIG. 6 , those parts of the current collector  16  which are not covered with the polarizable electrode layer  18  are not embossed, and it is therefore permitted to relieve a damage which is to be done to the current collector  16 . 
     FIG. 7  is a view exaggeratedly showing the rugged pattern which is provided in the front surface  131   a  of the first roller  131 , wherein (a) is a schematic sectional view, and (b) is a schematic plan view. 
   As shown in  FIGS. 7(   a ) and ( b ), the front surface  131   a  of the first roller  131  is formed with concave parts  90   a  and convex parts  90   b , and the plurality of concave parts  90   a  each having a conical shape are provided regularly at equal intervals. Besides, the convex parts  90   b  are located among the concave parts  90   a . As already described, the perpendicular distance N 3  between the concave part  90   a  and the convex part  90   b , that is, the height of the rugged pattern should preferably be set at 20% through 70% inclusive, of the thickness of the polarizable electrode layer  18  before the embossment work, more preferably at 30% through 60% inclusive. Besides, in this example, the convex part  90   b  has a flat part  90   c , the width N 5  of which should favorably be set at 5-15 μm. In addition, the inclination α of the concave part  90   a  should preferably be set at 35°-75°, more preferably at 45°-65°. 
     FIG. 8  is a view exaggeratedly showing that front surface of the polarizable electrode layer  18  which has been embossed by the first roll press section  130 , wherein (a) is a schematic sectional view, and (b) is a schematic plan view. 
   As shown in  FIGS. 8(   a ) and ( b ), the rugged pattern provided in the front surface  131   a  of the first roller  131  is transferred onto the front surface of the polarizable electrode layer  18  having passed through the first roll press section  130 . More specifically, concave parts  91   a  are formed in areas corresponding to the convex parts  90   b  of the first roller  131 , and convex parts  91   b  are formed in areas corresponding to the concave parts  90   a  of the first roller  131 . Besides, areas corresponding to the flat parts  90   c  of the first roller  131  become flat parts  91   c . Thus, the polarizable electrode layer  18  is compressed most strongly especially at the flat parts  91   c , whereby the density of the polarizable electrode layer  18  is effectively heightened. 
   In this state, however, the density of the polarizable electrode layer  18  especially at the distal end parts of the convex parts  91   b  is not sufficient, and the porous grains P 1  are apprehended to fall off from the convex parts  91   b , on account of the shape of the distal end parts. Such problems are solved by the roll press based on the second roll press section  140  which is located downstream of the first roll press section  130 . 
   More specifically, the second roll press section  140  is a portion for performing the process (step S 5 ) for flattening the embossed front surface of the polarizable electrode layer  18 . In the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4 , the second roll press section  140  is constituted by a third roller  141  arranged on the side of the polarizable electrode layer  18 , and a fourth roller  142  arranged on the side of the current collector  16 . Both the front surfaces  141   a  and  142   a  of the third and fourth rollers  141  and  142  are substantially smooth, and the laminated product  20  is roll-pressed by such rollers  141  and  142 , whereby the embossment formed on the front surface of the polarizable electrode layer  18  is flattened. That is, the convex parts  91   b  of the polarizable electrode layer  18  are collapsed, whereby the density is further heightened, and the porous grains P 1  are prevented from falling off from the convex parts  91   b.    
   The laminated product  20  having completed such roll press is guided by a guide roll  104  so as to be wound round the take-up roll  102 . 
   In this manner, when the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4  is employed, it is permitted to continuously perform the steps S 2 -S 5  stated above. 
   Besides, the laminated product  20  wound round the take-up roll  102  is cut into a predetermined size as shown in  FIG. 9(   a ), and the laminated product  20  is punched in accordance with the scale of the electrochemical capacitor to-be-fabricated as shown in  FIG. 9(   b ). Then, the electrode  10  for the electrochemical capacitor is finished up as shown in  FIG. 9(   c ). On this occasion, that part of the current collector  16  which is not covered with the polarizable electrode layer  18  is simultaneously derived as shown in  FIG. 9(   c ), it can be utilized as the lead-out electrode  12 . 
   In the electrode  10  for the electrochemical capacitor as has been manufactured in the above way, the front surface of the polarizable electrode layer  18  has been embossed (step S 4 ) and has thereafter been flattened (step S 5 ), so that a high volume capacitance of at least 17 F/cm 3  can be achieved. Moreover, it is permitted to prevent the porous grains P 1  from falling off, and to ensure a high reliability. Also, the pollution of the apparatus attributed to the porous grains P 1  having fallen off is prevented. 
   Besides, as shown in  FIG. 10 , at least two fabricated electrodes  10  for the electrochemical capacitor are prepared, and a separator  40  is held between the two electrodes  10  for the electrochemical capacitor with the polarizable electrode layers  18  confronting each other. Thereafter, the resulting structure is accommodated in a case not shown, and the case is filled up with an electrolyte solution. Then, the electrochemical capacitor is finished up. 
   The separator  40  should favorably be formed from an insulating porous substance. Usable as the separator  40  is, for example, a laminated product which consists of films of polyethylene, polypropylene or polyolefin, an extended film which is made from a mixture consisting of the above resins, or a fibrous or unwoven fabric material which is made from at least one constituent material selected from the group consisting of cellulose, polyester and polypropylene. 
   Besides, usable as the electrolyte solution is an electrolyte solution (an electrolytic aqueous solution, or an electrolyte solution using an organic solvent) which is employed in a known electrochemical capacitor such as electric double-layer capacitor. However, in a case where the electrochemical capacitor is the electric double-layer capacitor, the electrolytic aqueous solution exhibits a low decomposition voltage electrochemically, and hence, the useful-life voltage of the capacitor is limited to be low, so that the electrolyte solution using the organic solvent (non-aqueous electrolyte solution) is favorable. Although the concrete sort of the electrolyte solution is not especially restricted, the electrolyte solution should favorably be selected in consideration of the solubility and the dissociation degree of a solute and the viscosity of a liquid, and an electrolyte solution of high electric conductivity and high potential window (high decomposition initiation voltage) is especially desirable. Used as a typical example is tetraethyl ammonium tetrafluoroborate or the like class-4 ammonium salt which is dissolved in the organic solvent such as propylene carbonate, diethylene carbonate or acetonitrile. By the way, in this case, a mixing water content needs to be severely managed. 
   Thus far, the preferred embodiment of the invention has been described in detail, but the invention is not restricted to the embodiment. 
   By way of example, although the embossment work for the front surface of the polarizable electrode layer  18  is performed only once in the embodiment, a plurality of times of embossment works may well be performed by disposing a plurality of first roll press sections  130  as shown in  FIG. 11 . In the example shown in  FIG. 11 , an upper stream side roll press section  130 - 1  and a lower stream side roll press section  130 - 2  are disposed, and the front surface  131 - 1   a  of a roller  131 - 1  included in the upper stream side roll press section  130 - 1 , and the front surface  131 - 2   a  of a roller  131 - 2  included in the lower stream side roll press section  130 - 2  are respectively provided with rugged patterns. In this case, the rugged pattern provided in the front surface  131 - 1   a  of the roller  131 - 1 , and the rugged pattern provided in the front surface  131 - 2   a  of the roller  131 - 2  need not be in an identical shape. By way of example, when the height of the rugged pattern is set larger in the roller  131 - 1  located on the upper stream side, than in the roller  131 - 2  located on the lower stream side, the polarizable electrode layer  18  is formed with a deep embossment by the upper stream side roll press section  130 - 1 , and further, the embossment is flattened and a new shallow embossment is formed by the lower stream side roll press section  130 - 2 . Besides, the shallow embossment formed by the lower stream side roll press section  130 - 2  is further flattened by a second roll press section  140 . 
   Conversely, the height of the rugged pattern may well be set larger in the roller  131 - 2  located on the lower stream side, than in the roller  131 - 1  located on the upper stream side. In this case, the polarizable electrode layer  18  is formed with a comparatively shallow embossment by the upper stream side roll press section  130 - 1 , and further, it is formed with a deep embossment by the lower stream side roll press section  130 - 2 . Also in this case, the deep embossment formed by the lower stream side roll press section  130 - 2  is flattened by the second roll press section  140 . 
   Alternatively, embossments of different shapes may well be formed in such a way that the heights of the rugged patterns are substantially equalized in the roller  131 - 1  located on the upper stream side and the roller  131 - 2  located on the lower stream side, while the pitches N 4  of the convex parts  90   b  or the inclinations α thereof (refer to  FIG. 7 ) are made different from each other. 
   Incidentally, although not shown, a plurality of second roll press sections  140  may well be disposed, thereby to perform a plurality of times of flattening operations for the embossments. 
   Further, as shown in  FIG. 12 , the front surface  141   a  of a third roller  141  which is included in a second roll press section  140  may well be provided with a rugged pattern of small height. According to this measure, a new shallow embossment is formed while a deep embossment formed by a first roll press section  130  is being flattened. In this case, however, for the purpose of satisfactorily preventing the porous grains P 1  from falling off from the front surface of the polarizable electrode layer  18 , the height of the rugged pattern which is provided in the front surface  141   a  of the third roller  141  should preferably be set at or below 15% of the thickness of the polarizable electrode layer  18  after the roll press by the first roll press section  130 , more preferably at or below 10%. 
   Further, in the embodiment, only one surface of the current collector  16  is formed with the polarizable electrode layer  18 , but both the surfaces of the current collector  16  can also be formed with polarizable electrode layers  18 . In this case, as shown in  FIG. 13 , also the front surface  132   a  of a second roller  132  included in a first roll press section  130  may be provided with a rugged pattern. According to this measure, the polarizable electrode layers  18  formed on both the surfaces of the current collector  16  can be simultaneously embossed. 
   However, when both the first roller  131  and the second roller  132  are provided with rugged patterns, the polarizable electrode layers  18  might fail to be sufficiently compressed in some ways of the superposition of the rugged patterns, or contrariwise, a damage to the current collector  16  might become heavy due to excessive compression. In order to avoid this drawback, it is favorable that, as shown in  FIG. 14 , a first roll press section  130  is divided into an upper stream side roll press section  130 - 1  and a lower stream side roll press section  130 - 2 , whereupon the front surface  131 - 1   a  of a roller  131 - 1  included in the upper stream side roll press section  130 - 1 , and the front surface  132 - 2   a  of a roller  132 - 2  included in the lower stream side roll press section  130 - 2  are respectively provided with rugged patterns. According to this measure, the front surfaces  132 - 1   a  and  131 - 2   a  of the other rollers  132 - 1  and  131 - 2  are substantially smooth, respectively, so that the above problem does not occur. 
   Besides, the manufacturing apparatus for the electrode for the electrochemical capacitor according to the invention need not always have the construction in which, as in the apparatus shown in  FIG. 4 , the coating section  110 , drying section  120 , first roll press section  130  and second roll press section  140  are arranged continuously and unitarily, but it may well be the aggregate of two or more apparatuses as long as the above order is ensured. By way of example, the sheet-like current collector  16  having passed through the drying section  120  may well be taken up once and be roll-pressed by another apparatus which includes the first roll press section  130  and the second roll press section  140 . Further, the first roll press section  130  and the second roll press section  140  may well be apparatuses which are separate from each other. 
   Incidentally, the electrode for the electrochemical capacitor as manufactured by the invention can be employed as an electrode for an electric double-layer capacitor, and it is also utilizable as an electrode for any of various electrochemical capacitors such as a pseudo-capacitance capacitor, a pseudo-capacitor and a Redox capacitor. 
   Second Embodiment 
   In an electrode  10  for an electrochemical capacitor according to this embodiment, a polarizable electrode layer  18  is embossed, whereby increase in the volume capacitance of the polarizable electrode layer  18  is attained. Although the details will be described later, the compression of the polarizable electrode layer  18  is insufficient, and the attainment of a volume capacitance of at least 17 F/cm 3  is difficult, merely by forming the polarizable electrode layer  18  and thereafter roll-pressing it with a roller whose front surface is substantially smooth. However, when the polarizable electrode layer  18  is roll-pressed using a roller whose front surface is provided with a rugged pattern, this polarizable electrode layer  18  is effectively compressed, whereby the volume capacitance of at least 17 F/cm 3  becomes attainable. 
   Meanwhile, in the electrode  10  for the electrochemical capacitor according to this embodiment, the bare portion  12  of a current collector  16  undergoes no embossment work over substantially the whole area thereof. The reasons therefor are that the current collector  16  itself need not be embossed, and that unfavorably the current collector  16  might be damaged when strongly embossed. In consideration of these points, only the polarizable electrode layer  18  is embossed in the electrode  10  for the electrochemical capacitor according to this embodiment. A method for embossing only the polarizable electrode layer  18  will be described later. 
     FIG. 15  is a flow chart for explaining the manufacturing method for the electrode for the electrochemical capacitor according to the preferred embodiment of the invention. Now, the manufacturing method for the electrode for the electrochemical capacitor according to this embodiment will be described with reference to the flow chart. 
   First of all, a coating liquid L 1  to become the material of the polarizable electrode layer  18  is prepared (step S 1 ), the surface of the current collector  16  is subsequently coated with the coating liquid L 1 , thereby to form a coating film (step S 2 ), and a liquid S 1  contained in the coating film is removed by drying (step S 3 ). Thus, a state is established where the polarizable electrode layer  18  not compressed yet has been formed on the current collector  16 . On this occasion, the polarizable electrode layer  18  is formed having a predetermined width, so that the bare portions  12  of the current collector  16  may be left behind at both the end parts of the current collector  16  in the widthwise direction thereof. Since these steps are the same as in the first embodiment, they shall be omitted from detailed description. 
   After the uncompressed polarizable electrode layer  18  has been formed on the current collector  16  in this way, the front surface of the polarizable electrode layer  18  is embossed (step S 4 ) by subjecting the bare portions  12  of the current collector  16  to substantially no embossment work. As stated above, the embossment work of the front surface of the polarizable electrode layer  18  is done for effectively compressing the polarizable electrode layer  18 , thereby to heighten a volume capacitance. In this case, after the front surface of the polarizable electrode layer  18  has been embossed, it should favorably be further flattened. When such flattening is done, it is permitted to effectively prevent porous grains P 1  from falling off from the embossed front surface of the polarizable electrode layer  18 . More specifically, when the front surface is strongly embossed (in a case, for example, where the height of a rugged pattern to be stated later is large), the porous grains P 1  are liable to fall off, and hence, it is apprehended to degrade the reliability of a product or to pollute a manufacturing apparatus. In this embodiment, however, it is not indispensable to perform the flattening of the embossment. 
   A method for embossing the front surface of the polarizable electrode layer  18  can be incarnated in such a way, for example, that a roller or the like transfer member whose front surface is provided with the rugged pattern is pressed against the front surface of the polarizable electrode layer  18 . In this case, the height of the rugged pattern provided in the front surface of the transfer member should preferably be set at 20%-70% inclusive, of the thickness of the polarizable electrode layer  18  before the embossment work, and it should more preferably be set at 30%-60% inclusive. The reason therefor is that, when the height of the rugged pattern is excessively small, the polarizable electrode layer  18  is not effectively compressed, whereas when the height of the rugged pattern is excessively large, a damage to be done to the current collector  16  becomes heavy. 
   According to the second embodiment, in the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4 , the front surface  131   a  of the first roller  131  is partially provided with the rugged pattern as stated below, whereby the rugged pattern is transferred onto the front surface of the polarizable electrode layer  18  having passed through the first roll press section  130 . That is, the front surface of the polarizable electrode layer  18  is embossed. On the other hand, the front surface  132   a  of the second roller  132  is substantially smooth. 
     FIG. 16  is a schematic perspective view exaggeratedly showing the first roll press section  130  (and second roll press section  140 ). 
   As shown in  FIG. 16 , the first roller  131  included in the first roll press section  130  is provided with the rugged pattern in only an area  131   a   1  which has substantially the same width as the width W 1  of the polarizable electrode layer  18 , the other areas  131   a   2  being substantially smooth. Thus, only the front surface of the polarizable electrode layer  18  can be embossed by subjecting the bare portions  12  of the current collector  16  to substantially no embossment work. It is consequently permitted to relieve a damage which is to be done to the current collector  16 , with the polarizable electrode layer  18  effectively compressed. Moreover, since the areas  131   a   2  corresponding to the bare portions  12  of the current collector  16  are substantially smooth, the possibility at which a laminated product  20  having passed through the first roll press section  130  will be wound round the first roller  131  becomes low to enhance a job efficiency. 
   In the same manner as in the first embodiment, as shown in  FIGS. 7(   a ) and ( b ), the concave parts  90   a  and the convex parts  90   b  are formed in the area  131   a   1  of the front surface  131   a  of the first roller  131 , and the plurality of concave parts  90   a  each having a conical shape are provided regularly at equal intervals. Detailed description shall be omitted here. 
   Also in the same manner as in the first embodiment, as shown in  FIGS. 8(   a ) and ( b ), the rugged pattern provided in the area  131   a   1  of the front surface  131   a  of the first roller  131  is transferred onto the front surface of the polarizable electrode layer  18  having passed through the first roll press section  130 . Since the areas  131   a   2  of the front surface  131   a  of the first roller  131  are substantially smooth as stated above, such an embossment is not formed in each of the bare portions  12  of the current collector  16 . However, those regions of the bare portions  12  of the current collector  16  which are near to the polarizable electrode layer  18  may well be somewhat embossed in relation to a machining precision. Accordingly, the expression “substantially the whole areas of the bare portions  12  of the current collector  16  are not embossed” shall cover the case where the slight regions of the bare portions extending along the polarizable electrode layer  18  are embossed in relation to the machining precision. 
   In this state, however, the density of the polarizable electrode layer  18  especially at the distal end parts of the convex parts  91   b  might not be sufficient. In this case, the porous grains P 1  are apprehended to fall off from the convex parts  91   b , on account of the shape of the distal end parts. Such problems are solved by roll press based on the second, roll press section  140  which is located downstream of the first roll press section  130 . 
   More specifically, the second roll press section  140  is a portion for flattening the embossed front surface of the polarizable electrode layer  18 . In the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4 , the second roll press section  140  is constituted by a third roller  141  arranged on the side of the polarizable electrode layer  18 , and a fourth roller  142  arranged on the side of the current collector  16 . Both the front surfaces  141   a  and  142   a  of the third and fourth rollers  141  and  142  are substantially smooth, and the laminated product  20  is roll-pressed by such rollers  141  and  142 , whereby the embossment formed on the front surface of the polarizable electrode layer  18  is flattened. That is, the convex parts  91   b  of the polarizable electrode layer  18  are collapsed, whereby the density is further heightened, and the porous grains P 1  are prevented from falling off from the convex parts  91   b . It is not indispensable, however, that the manufacturing apparatus according to this embodiment includes the second roll press section for flattening the embossment. 
   Incidentally, the pressure of the roll press for the embossment work and the flattening should favorably be set at 4900 N/cm (500 kgf/cm)−24500 N/cm (2500 kgf/cm). 
   The laminated product  20  having completed such roll press is guided by a guide roll  104  so as to be wound round a take-up roll  102 . 
   In this manner, when the manufacturing apparatus  100  for the electrode for the electrochemical capacitor as shown in  FIG. 4  is employed, it is permitted to continuously perform the steps S 2 -S 5  stated above. 
   Besides, the laminated product  20  wound round the take-up roll  102  is cut into a predetermined size as shown in  FIG. 9(   a ), and the laminated product  20  is punched in accordance with the scale of the electrochemical capacitor to-be-fabricated as shown in  FIG. 9(   b ). Then, the electrode  10  for the electrochemical capacitor is finished up as shown in  FIG. 9(   c ). On this occasion, that part of the current collector  16  which is not covered with the polarizable electrode layer  18 , namely, part of the bare portion  12  is simultaneously derived as shown in  FIG. 9(   c ), and it can be utilized as a lead-out electrode. 
   In the electrode  10  for the electrochemical capacitor as has been manufactured in the above way, the front surface of the polarizable electrode layer  18  has been embossed (step S 4 ), so that a high volume capacitance of at least 17 F/cm 3  can be achieved. Moreover, since the bare portions  12  of the current collector  16  are subjected to substantially no embossment work, it is permitted to relieve a damage to the current collector  16  and the winding of the laminated product round the first roller  131 . Besides, when the embossment formed on the front surface of the polarizable electrode layer  18  is flattened using the second roll press section  140 , it is permitted to prevent the porous grains P 1  from falling off, and to ensure a high reliability. Also, the pollution of the apparatus attributed to the porous grains P 1  having fallen off is prevented. 
   Besides, as shown in  FIG. 10 , at least two fabricated electrodes  10  for the electrochemical capacitor are prepared, and a separator  40  is held between the two electrodes  10  for the electrochemical capacitor with the polarizable electrode layers  18  confronting each other. Thereafter, the resulting structure is accommodated in a case not shown, and the case is filled up with an electrolyte solution. Then, the electrochemical capacitor is finished up. 
   Thus far, the preferred embodiment of the invention has been described in detail, but the invention is not restricted to the embodiment. 
   By way of example, although the embossment work for the front surface of the polarizable electrode layer  18  is performed only once in the embodiment, a plurality of times of embossment works for the front surface of the polarizable electrode layer  18  may well be performed in such a way that, as shown in  FIG. 17 , the third roller  141  included in the second roll press section  140  is also provided with a rugged pattern in an area  141   a   1  having substantially the same width as the width W 1  of the polarizable electrode layer  18 , the other areas  141   a   2  being made substantially smooth. In this case, the rugged pattern provided in the area  131   a   1  of the front surface  131  of the first roller  131 , and the rugged pattern provided in the area  141   a   1  of the front surface  141  of the third roller  141  need not be in an identical shape. By way of example, when the height of the rugged pattern is set larger in the first roller  131  located on the upper stream side, than in the third roller  141  located on the lower stream side, the polarizable electrode layer  18  is formed with a deep embossment by the first roll press section  130 , and further, the embossment is flattened and a new shallow embossment is formed by the second roll press section  140 . 
   Conversely, the height of the rugged pattern may well be set larger in the third roller  141  located on the lower stream side, than in the first roller  131  located on the upper stream side. In this case, the polarizable electrode layer  18  is formed with a comparatively shallow embossment by the first roll press section  130 , and further, it is formed with a deeper embossment by the second roll press section  140 . 
   Alternatively, embossments of different shapes may well be formed in such a way that the heights of the rugged patterns are substantially equalized in the first roller  131  and the third roller  141 , while the pitches N 4  of the convex parts  90   b  or the inclinations α thereof (refer to  FIG. 7 ) are made different from each other. 
   Even in the case where the embossment works for the polarizable electrode layer  18  are performed the plurality of times in this manner, the bare portions  12  of the current collector  16  are subjected to substantially no embossment work when the areas  131   a   2  and the areas  141   a   2  corresponding to the bare portions  12  of the current collector  16  are made substantially smooth as shown in  FIG. 17 . It is therefore permitted to relieve a damage to the current collector  16  and the winding of the laminated product round the first roller  131 . 
   Further, in the embodiment, only one surface of the current collector  16  is formed with the polarizable electrode layer  18 , but both the surfaces of the current collector  16  can also be formed with polarizable electrode layers  18 . In this case, as shown in  FIG. 18 , also the front surface  132   a  of a second roller  132  included in a first roll press section  130  may be provided with a rugged pattern. According to this measure, the polarizable electrode layers  18  formed on both the surfaces of the current collector  16  can be simultaneously embossed. Also in this case, it is permitted to relieve a damage to the current collector  16  and the winding of the laminated product round the second roller  132  when the rugged pattern is provided in the area  132   a   1  having substantially the same width as the width W 1  of the polarizable electrode layer  18 , the other areas  132   a   2  being made substantially smooth. 
   However, when both the first roller  131  and the second roller  132  are provided with the rugged patterns, the polarizable electrode layers  18  might fail to be sufficiently compressed in some ways of the superposition of the rugged patterns, or contrariwise, a damage to the current collector  16  might become heavy due to excessive compression. In order to avoid this drawback, it is recommendable that, as shown in  FIG. 19 , the front surface of a fourth roller  142  included in a second roll press section  140  is provided with a rugged pattern, while the front surface of a second roller  132  included in a first roll press section  130  is made substantially smooth. Also in this case, it is permitted to relieve a damage to the current collector  16  and the winding of the laminated product round the fourth roller  142  when the front surface of the fourth roller  142  is provided with the rugged pattern in the area  142   a   1  having substantially the same width as the width W 1  of each polarizable electrode layer  18 , the other areas  142   a   2  being made substantially smooth. According to this measure, the front surfaces  132   a  and  141   a  of the other rollers  132  and  141  are substantially smooth in both the first roll press section  130  and the second roll press section  140 , respectively, so that the above problem does not occur. 
   Besides, the manufacturing apparatus for the electrode for the electrochemical capacitor according to the invention need not always have the construction in which, as in the apparatus shown in  FIG. 4 , the coating section  110 , drying section  120 , first roll press section  130  and second roll press section  140  are arranged continuously and unitarily, but it may well be the aggregate of two or more apparatuses as long as the above order is ensured. By way of example, the sheet-like current collector  16  having passed through the drying section  120  may well be taken up once and be roll-pressed by another apparatus which includes the first roll press section  130  and the second roll press section  140 . Further, the first roll press section  130  and the second roll press section  140  may well be apparatuses which are separate from each other. As already described, however, it is not indispensable that the manufacturing apparatus according to the invention includes the second roll press section for flattening the embossment. 
   Further, in the embodiment, only the polarizable electrode layer  18  is subjected to the embossment work, and substantially the whole areas of the bare portions  12  of the current collector  16  are not subjected to the embossment work, but those regions of the bare portions  12  of the current collector  16  which are near to the polarizable electrode layer  18  may well be partially embossed as long as the above advantages of the invention are attainable. By way of example, the width of the area  131   a   1  of the first roller  131  may well be set somewhat broad, thereby to emboss the bare portions  12  in the vicinities of the polarizable electrode layer  18 . In this case, the current collector  16  might be damaged at the embossed parts, depending upon the height of a rugged pattern, but the whole front surface of the polarizable electrode layer  18  can be reliably embossed. 
   Further, in the embodiment, the embossment work (and the flattening) is performed for the polarizable electrode layer  18  by the roll press. However, this aspect is not restrictive, but the embossment work (and the flattening) may well be performed using a plate-shaped press device such as hot press. 
   Besides, it suffices to perform the embossment work of the polarizable electrode layer  18  in the region which is to be cut out as the electrode for the electrochemical capacitor, so that the other region need not be subjected to the embossment work. By way of example, in  FIG. 9 , the region except the portion cut out as the electrode  10  for the electrochemical capacitor need not undergo the embossment work. Accordingly, substantially smooth areas may well exist at regular intervals (each being larger than the size of the electrode to-be-cut-out) in the peripheral direction of the area  131   a   1  of the first roller  131  shown in  FIG. 14 . Moreover, a substantially smooth area may well exist at substantially the middle part of the first roller  131  in the widthwise direction thereof, depending upon the shape of the electrode to-be-cut-out for the electrochemical capacitor and the coating width of the polarizable electrode layer  18 . Further, the smooth areas may well be combined. 
   Besides, in the embodiment, the polarizable electrode layer  18  is formed by coating so that the bare portions  12  may be formed at both the end parts of the current collector  16  in the widthwise direction thereof. However, this aspect is not restrictive, but the polarizable electrode layers  18  and the bare portions  12  may well be alternately formed at regular intervals in the lengthwise direction of the current collector  16 . In this case, the bare portions  12  may well be formed in such a way that masking tape pieces are stuck on the current collector  16  at the regular intervals beforehand, whereupon the resulting structure is coated with the polarizable electrode layer  18 , which is then dried. Besides, after the embossment work has been performed with the masking tape pieces left stuck, the masking tape pieces are stripped off. Then, the current collector  16  is bared at the corresponding parts, and the bare portions  12  having undergone no embossment work can be obtained. 
   Incidentally, the electrode for the electrochemical capacitor according to the invention can be employed as an electrode for an electric double-layer capacitor, and it is also utilizable as an electrode for any of various electrochemical capacitors such as a pseudo-capacitance capacitor, a pseudo-capacitor and a Redox capacitor. 
   EXAMPLES 
   Examples of the present invention will now be described, but the invention shall not be restricted to the examples at all. 
   Example 1 
   Granular active carbon (produced by Kuraray Chemical Co., Ltd., trade name: “RP-20”) and acetylene black (produced by Denki Kagaku Kogyo Kabushiki Kaisha, trade name: “Denka Black”) were mixed for 15 minutes by using a planetary mixer. The resulting mixture and fluorine rubber (produced by Du Pont Kabushiki Kaisha, trade name: “Viton-GF”) were thrown into 150 mass-parts of MIBK, and these materials were kneaded for 45 minutes by using a planetary mixer. On this occasion, the compounding proportions of the active carbon, the acetylene black and the fluorine rubber were 90.0 mass-parts, 1.0 mass-part and 9.0 mass-parts, respectively. 150 mass-parts of MIBK were further added to the kneaded material obtained, and the resulting material was agitated for one hour. Thus, a coating liquid was prepared. 
   One surface of an aluminum foil (thickness: 20 μm) being a current collector was uniformly coated with the coating liquid by gravure coating, and the MIBK was removed in a drying oven at 100° C., thereby to obtain a laminated sheet. Thereafter, the laminated sheet was passed through the first roll press section  130  and the second roll press section  140  shown in  FIG. 5 , in the order mentioned, whereby a laminated sheet having a thickness of 150 μm was fabricated. 
   Here, the height (N 3 ) of a rugged pattern provided in the front surface  131   a  of the first roller  131  was 75 μm, the pitch (N 4 ) of concave parts  90   a  was 97 μm, and the width (N 5 ) of each flat part  90   c  was 10 μm. Besides, the inclination (α) of the concave part  90   a  was set at 60°. In addition, press pressures based on the first roll press section  130  and the second roll press section  140  were both set at a value of 9800 N/cm 2 ( 1000 kgf/cm 2 ). 
   Comparative Example 1 
   A laminated sheet was fabricated in the same way as in Example 1, except that a roll press section identical to the first roll press section  130  was employed instead of the second roll press section  140 . 
   Comparative Example 2 
   A laminated sheet was fabricated in the same way as in Example 1, except that a roll press section identical to the second roll press section  140  was employed instead of the first roll press section  130 . 
   Comparative Example 3 
   A laminated sheet was fabricated in the same way as in Example 1, except that the positions of the first roll press section  130  and the second roll press section  140  were reversed. 
   Comparative Example 4 
   A laminated sheet was fabricated in the same way as in Example 1, except that quite no roll press was performed. That is, a manufacturing process was ended at the point of time at which the coating liquid on the aluminum foil being the current collector was dried. 
   [Evaluation] 
   First, how much porous grains fell off was evaluated in such a way that the front surface of each of the laminated sheets on the side of a polarizable electrode layer, the laminated sheets having been fabricated by the methods of Example 1 and Comparative examples 1-4, was rubbed with fingers. 
   Further, each laminated sheet was punched into a size of 20 mm×40 mm, and the punched sample was subjected to vacuum drying at temperatures of 150° C.-175° C. for at least 12 hours, whereby a water content adsorbed in the porous layer was removed to fabricate an electrode for an electrochemical capacitor. Besides, the volume capacitance of the electrode for the electrochemical capacitor as was thus fabricated was measured in the following way: First, two samples of each fabricated electrode for the electrochemical capacitor were prepared for an anode and for a cathode. Subsequently, the anode and the cathode were confronted to each other, and a separator made of unwoven fabric of regenerated cellulose (21 mm×41 mm, thickness: 0.05 mm, produced by Nippon Kodoshi Corporation, trade name: “TF4050”) was arranged between the anode and the cathode, thereby to fabricate a lamination element in which the anode, the separator and the cathode were stacked in touched states (non-junction states) in the order mentioned. Besides, a measurement cell for the test evaluation was fabricated using the lamination element and an electrolyte solution (propylene carbonate solution of 1.2 mol/L of triethylmethyl ammonium borofluoride). 
   Subsequently, the fabricated measurement cell for the test evaluation was charged at a constant current of 2.5 mA by a charging-and-discharging test apparatus (“HJ-101SM6” produced by Hokuto Denko Corporation). A situation where a voltage rose as charges were accumulated in the electric double-layer capacitor was monitored, the constant-current charging was shifted to constant-voltage charging (relaxation charging) after the voltage reached 2.5 V, and the constant-voltage charging was ended when a current became 1/10 of the charging current. Besides, discharging was performed at the constant current of 2.5 mA, and a termination voltage was made zero V. After the test, charging was performed at a constant current of 5 mA, the constant-current charging was shifted to constant-voltage charging after a voltage reached 2.5 V, and the constant-voltage charging was ended when a current became 1/10 of the charging current. Besides, discharging was performed at the constant current of 5 mA, and a termination voltage was made zero V. With such constant-current/constant-voltage charging and discharging operations as one set, 10 sets of operations were repeatedly performed. Total discharge energy [W·s] was found as the temporal integral of discharge energy (discharge voltage×current (=5 mA)) from a discharge curve (discharge voltage−discharge time) thus obtained, a capacitance was found in conformity with the relation formula of capacitance [F]=2×total discharge energy [W·s]/(discharge initiation voltage [V]) 2 , and a value obtained by dividing the capacitance by the volume of both the electrodes (anode and cathode) was employed as a capacitance per unit volume (volume capacitance) [F/cm 3 ]. Incidentally, the measurement of the capacitance per unit volume was made under an environment of a temperature of 25° C. and a relative humidity of 60%. 
   The results of the evaluation are listed in Table 1. 
   
     
       
         
             
             
             
             
             
           
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
                 
               Falling- 
                 
             
             
                 
                 
                 
               off of 
             
             
                 
               First roll press 
               Second roll 
               Porous 
               Volume 
             
             
                 
               section 
               press section 
               grains 
               capacitance 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
          
             
               Ex. 1 
               Presence of 
               Absence of 
               ∘ 
               18 F/cm 3   
             
             
                 
               Rugged pattern 
               Rugged pattern 
             
             
               Comp. ex. 1 
               Presence of 
               Presence of 
               x 
               18 F/cm 3   
             
             
                 
               Rugged pattern 
               Rugged pattern 
             
             
               Comp. ex. 2 
               Absence of 
               Absence of 
               ∘ 
               16 F/cm 3   
             
             
                 
               Rugged pattern 
               Rugged pattern 
             
             
               Comp. ex. 3 
               Absence of 
               Presence of 
               x 
               18 F/cm 3   
             
             
                 
               Rugged pattern 
               Rugged pattern 
             
             
               Comp. ex. 4 
               — 
               — 
               Δ 
               13 F/cm 3   
             
             
                 
             
             
               ∘ Almost no falling-off, 
             
             
               Δ Some falling-off, and 
             
             
               x  Much falling-off. 
             
          
         
       
     
   
   As indicated in Table 1, the laminated sheet fabricated by the method of Example 1 underwent almost no falling-off of the porous grains, and it attained a very high volume capacitance of 18 F/cm 3 . 
   In contrast, the laminated sheets fabricated by the methods of Comparative examples 1 and 3, in each of which an embossments was not flattened, attained the high volume capacitance, but they underwent much falling-off of the porous grains. Besides, the laminated sheet fabricated by the method of Comparative example 2, in which no embossment work was performed, underwent almost no falling-off of the porous grains, but it did not attain a sufficient volume capacitance. Further, the laminated sheet fabricated by the method of Comparative example 4, in which no roll press was performed, exhibited a low volume capacitance and had the falling-off of the porous grains observed to some extent. 
   It has been verified from the above that the high volume capacitance is attained with the falling-off of the porous grains prevented, by performing the embossment work and thereafter flattening the embossment. 
   INDUSTRIAL APPLICABILITY 
   According to the present invention, it is permitted to provide a manufacturing method and a manufacturing apparatus for an electrode for an electrochemical capacitor having a high volume capacitance.