Electric double layer capacitor and process for its production

Abstract

An electric double layer capacitor includes, contained in a casing, an electrolyte and positive and negative electrodes each containing carbon black, to form an electric double layer at the interface with the electrolyte, and a separator interposed between the positive electrode and the negative electrode. At least one electrode of the positive electrode and the negative electrode has protruded portions or bent portions formed continuously in the height direction against the bottom face of the casing. Further, a space due to the height of the protruded portions or the bent portions is formed between the at least one electrode and the separator.

1 . A process for producing an electric double layer capacitor, comprising steps of: 
 forming a positive electrode and a negative electrode each containing carbon black to form an electric double layer at the interface with an electrolyte;    forming protruded portions or bent portions on at least one of the positive electrode and the negative electrode;    interposing a separator between the positive electrode and the negative electrode to form an element;    containing the element in a casing;    impregnating the element with the electrolyte; and    at least one charging operation, wherein a space due to a height of the protruded portions or the bent portions is formed between said at least one electrode and the separator,    wherein a plurality of the positive electrode and the negative electrode are alternately stacked with the separator between them, or the positive electrode and the negative electrode each having a long strip shape, are wound with the separator between them, and contained in the casing having a bottomed rectangular or cylindrical shape.    
   
   
       2 . The process according to  claim 1 , wherein the protruded portions or the bent portions on the positive electrode and the negative electrode are formed continuously in a height direction against the bottom face of the casing.  
   
   
       3 . The process according to  claim 1 , wherein the protruded portions or the bent portions include at least one electrode deformed on one side or both sides, and the protruded portions or the bent portions are formed in a plurality at every predetermined distance in a direction perpendicular to the height direction.  
   
   
       4 . The process according to  claim 1 , wherein the electrode includes a metal current collector and an electrode sheet, and the electrode sheet contains from 5 to 30 mass % of carbon black.  
   
   
       5 . The process according to  claim 1 , wherein the separator has a thickness of from 10 to 60 μm, a porosity of from 40 to 85% and a maximum pore size of at most 1 μm as measured by the test method prescribed in JIS K3832.  
   
   
       6 . The process according to  claim 1 , wherein the electrolyte includes a non-aqueous electrolyte containing a quaternary onium salt as a solute.  
   
   
       7 . The process according to  claim 1 , wherein forming the protruded portions or the bent portions is carried out on both the positive electrode and the negative electrode.  
   
   
       8 . The process according to  claim 1 , wherein the electrode is formed by bonding with an adhesive layer an electrode sheet containing a carbonaceous material as the main component and having a thickness of from 80 to 400 μm on at least one side of a metal current collector.  
   
   
       9 . The process according to  claim 8 , wherein the protruded portions or the bent portions are formed so that a sum of a thickness of the electrode and a height of the protruded portions or the bent portions becomes to be from 1.01 to 1.20 times the thickness of the electrode, said thickness of the electrode includes a sum of a thicknesses of the metal current collector, the electrode sheet and the adhesive layer.  
   
   
       10 . The process according to  claim 3 , wherein the protruded portions and the bent portions are formed at a distance of at most 20 mm in a direction perpendicular to a height direction of the casing.  
   
   
       11 . The process according to  claim 8 , wherein the electrode is formed by bonding an electrode sheet to each side of a metal current collector with an adhesive layer.  
   
   
       12 . The process according to  claim 1 , wherein the impregnating the electrolyte and the at least one charging operation causes a thickness of the electrode to expand from 1.1 to 1.6 times.  
   
   
       13 . The process according to  claim 8 , wherein the impregnating the electrolyte and the at least one charging operation causes a thickness of the electrode to expand from 1.1 to 1.6 times.  
   
   
       14 . The process according to  claim 2 , wherein forming the protruded portions or the bent portions is carried out on both the positive electrode and the negative electrode.  
   
   
       15 . The process according to  claim 2 , wherein the protruded portions or the bent portions are formed so that a sum of a thickness of the electrode and a height of the protruded portions or the bent portions becomes to be from 1.01 to 1.20 times the thickness of the electrode, said thickness of the electrode includes a sum of thicknesses of the metal current collector, the electrode sheet and the adhesive layer.  
   
   
       16 . The process according to  claim 2 , wherein the protruded portions and the bent portions are formed at a distance of at most 20 mm in a direction perpendicular to a height direction of the casing.