Reactions in the Rechargeable Lithium-O2 Battery with Alkyl Carbonate Electrolytes

The nonaqueous rechargeable lithium-O-2 battery containing an alkyl carbonate electrolyte discharges by formation of C3H6(OCO2Li)(2), Li2CO3, HCO2Li, CH3CO2Li, CO2, and H2O at the cathode, due to electrolyte decomposition. Charging involves oxidation of C3H6(OCO2Li)(2), Li2CO3, HCO2Li, CH3CO2Li accompanied by CO2 and H2O evolution. Mechanisms are proposed for the reactions on discharge and charge. The different pathways for discharge and charge are consistent with the widely observed voltage gap in Li-O-2 cells. Oxidation of C3H6(OCO2Li)(2) involves terminal carbonate groups leaving behind the OC3H6O moiety that reacts to form a thick gel on the Li anode. Li2CO3, HCO2Li, CH3CO2Li, and C3H6(OCO2Li)(2) accumulate in the cathode on cycling correlating with capacity fading and cell failure. The latter is compounded by continuous consumption of the electrolyte on each discharge.