Electric double-layer capacitor and method for making the same

In an electric double-layer capacitor consisting of

• (a) an open-top casing having at least one side and a bottom;
• (b) a porous layered electrode assembly disposed in said casing, said electrode assembly consisting of two layers of porous electrically-conductive electrode material having between them, in abutting relationship, a separator consisting of a layer of ion permeable material,
• said electrode material consisting of a porous polymeric matrix containing electrically-conductive particles;
• (c) a casing cover, said casing cover electrically-insulated from and sealed to said casing by a dielectric sealant material interposed between said cover and said casing;
• wherein one said electrode material layer is electrically-connected to said casing, and the other said electrode material layer is electrically-connected to said casing cover, and wherein said electrode assembly is impregnated with an electrolyte;
• the improvement wherein each of said porous electrically-conductive electrode material layers comprises a polytetrafluoroethylene composition at least containing acicular electrically-conductive particles, said acicular particles having a size and concentration in the polytetrafluoroethylene composition which is sufficient to provide directional orientation of said acicular particles by extrusion means, said acicular particles oriented in a direction approximately normal to the planar direction of said electrode material layer.