Patent ID: 8907133

Claim:
An electrochemical double layer capacitor (EDLC) comprising: a positive electrode; a negative electrode; a separator between the positive electrode and the negative electrode; and an electrolyte composition in contact with the positive electrode, the negative electrode, and the separator, wherein the electrolyte composition comprises: one or more phosphonium ionic liquids, or one or more phosphonium salts dissolved in a solvent, the one or more phosphonium ionic liquids or phosphonium salts comprising one or more cations of the formula: P(CH 3 CH 2 CH 2 ) y (CH 3 CH 2 ) x (CH 3 ) 4-x-y (where x,y= 0 to 4 ; x+y≦ 4) and one or more anions of the formula: (CF 3 ) x BF 4-x (where x= 0 to 4) (CF 3 (CF 2 ) n ) x PF 6-x (where n= 0 to 2 ; x= 0 to 4) (—OCO(CH 2 ) n COO—)(CF 3 ) x BF 2-x (where n= 0 to 2 ; x= 0 to 2) (—OCO(CH 2 ) n COO—) 2 B (where n= 0 to 2) (—OSOCH 2 SOO—)(CF 3 ) x BF 2-x (where x= 0 to 2) (—OCOCOO—) x (CF 3 ) y PF 6-2x-y ( x= 1 to 3 ; y= 0 to 4; 2 x+y≦ 6).