Ionic liquid-solvent mixture of propylene carbonate and 1,2-dimethoxyethane as electrolyte for electric double-layer capacitor

Ionic liquid EMIBF4 (EMI) was combined with propylene carbonate (PC) and/or 1,2-dimethoxyethane (DME) for electric double-layer capacitors (EDLCs). The effects of these support solvents on physicochemical properties of the electrolyte and capacitance performances of the capacitor were investigated. Compared to pure EMI, the existence of support solvent of PC or PC-DME provides better power characteristic mainly profited from improved ion conductivity, but sacrifices the stable potential window to some extent. The capacitor employing activated carbon and the electrolyte EMI-PC-DME yields an active mass normalized energy density of 38.5 Wh kg−1 at ~ 900 W kg−1 for the cut-off voltage of 3 V. It is a significant performance improvement compared to EMI and EMI-PC system at identical operation condition. This research guides an attractive direction to construct advanced 3 V based EDLC with excellent overall properties.