Combining Accurate O₂ and Li₂O₂ Assays to Separate Discharge and Charge Stability Limitations in Nonaqueous Li–O₂ Batteries

Li–air batteries have generated enormous interest as potential high specific energy alternatives to existing energy storage devices. However, Li–air batteries suffer from poor rechargeability caused by the instability of organic electrolytes and carbon cathodes. To understand and address this poor rechargeability, it is essential to elucidate the efficiency in which O₂ is converted to Li₂O₂ (the desired discharge product) during discharge and the efficiency in which Li₂O₂ is oxidized back to O₂ during charge. In this Letter, we combine many quantitative techniques, including a newly developed peroxide titration, to assign and quantify decomposition pathways occurring in cells employing a variety of solvents and cathodes. We find that Li₂O₂-induced electrolyte solvent and salt instabilities account for nearly all efficiency losses upon discharge, whereas both cathode and electrolyte instabilities are observed upon charge at high potentials