Liquefied gas electrolytes for electrochemical energy storage devices.

Electrochemical capacitors and lithium-ion batteries have seen little change in their electrolyte chemistry since their commercialization, which has limited improvements in device performance. Combining superior physical and chemical properties and a high dielectric-fluidity factor, the use of electrolytes based on solvent systems that exclusively use components that are typically gaseous under standard conditions show a wide potential window of stability and excellent performance over an extended temperature range. Electrochemical capacitors using difluoromethane show outstanding performance from -78° to +65°C, with an increased operation voltage. The use of fluoromethane shows a high coulombic efficiency of ~97% for cycling lithium metal anodes, together with good cyclability of a 4-volt lithium cobalt oxide cathode and operation as low as -60°C, with excellent capacity retention.