Understanding reversibility of lithium–oxygen batteries based on LiOH formation and decomposition

Lithium–oxygen batteries based on four-electron conversion to LiOH have demonstrated great potential for next-generation high-energy batteries. However, the understanding of LiOH-based cathode chemistry remains incomplete. Here, we use systematic characterization techniques to study LiOH chemistry, revealing that “high-performance” LiOH chemistry is achieved at the expense of electrolyte degradation and is irreversible in commonly used liquid organic electrolytes. LiOH forms via four-electron reduction of O2 during discharge, whereas LiOH decomposes via one-electron oxidation during charge. This one-electron oxidation of LiOH generates surface-reactive hydroxyl species that aggressively degrade organic electrolytes. The reaction mechanisms are further supported by computational studies. Our findings suggest that the key to enable reversible LiOH chemistry is bypassing surface-reactive hydroxyl formation or using stable solid-state electrolytes, which can be explored by future research. Our findings also shed lights on the reversibility of four-electron cathode chemistries in other metal–air batteries.