Characteristics of electric double layer capacitors with an ionic liquid electrolyte containing Li ion

The performance of electric double layer capacitor, (EDLC) with an ionic liquid, 1-ethy-3-methylimidazolium tetrafluoroborate (EMIBF4) electrolyte containing LiBF4, has been investigated and compared with that of EDLC containing EMIBF4 without LiBF4 as well as containing a conventional organic electrolyte, triethylmethylammonium tetrafluoroborate/propylene carbonate (TEMABF(4)/PC). EDLC with EMIBF4 + LiBF4 showed an excellent electrochemical stability; the electrolyte was not decomposed even at a cell voltage of ca. 3.6 V. Calculated energy density in EDLC with EMIBF4 + LiBF4 was highest among EDLCs with the cited electrolytes. The addition of LiBF4 to EMIBF4 also improved double layer capacitance especially at a positive electrode.