Rechargeability of Li-air cathodes pre-filled with discharge products using an ether-based electrolyte solution: Implications for cycle-life of Li-air cells

The instability of currently used electrolyte solutions and of the carbon support during charge-discharge in non-aqueous lithium-oxygen cells can lead to discharge products other than the desired Li₂O₂, such as Li₂CO₃, which is believed to reduce cycle-life. Similarly, discharge in an O₂ atmosphere which contains H₂O and CO₂ impurities would lead to LiOH and Li₂CO₃ discharge products. In this work we therefore investigate the rechargeability of model cathodes pre-filled with four possible Li-air cell discharge products, namely Li₂O₂, Li₂CO₃, LiOH, and Li₂O. Using Online Electrochemical Mass Spectrometry (OEMS), we determined the charge voltages and the gases evolved upon charge of pre-filled electrodes, thus determining the reversibility of the formation/electrooxidation reactions. We show that Li₂O₂ is the only reversible discharge product in ether-based electrolyte solutions, and that the formation of Li₂CO₃, LiOH, or Li₂O is either irreversible and/or reacts with the electrolyte solution or the carbon during its oxidation.