Unveiling the Complex Effects of H₂O on Discharge–Recharge Behaviors of Aprotic Lithium–O₂ Batteries

The addition of H₂O, even trace amount, in aprotic Li-O₂ batteries has a remarkable impact on achieving high capacity by triggering solution mechanism, and even reducing charge overpotential. However, the critical role of H₂O in promoting solution mechanism still lacks persuasive spectroscopic evidence, moreover, the origin of low polarization remains incompletely understood. Herein, by in situ spectroscopic identification of reaction intermediates, we directly verify that H₂O additive is able to alter oxygen reduction reaction (ORR) pathway subjected to solution-mediated growth mechanism of Li₂O₂. In addition, ingress of H₂O also induces to form partial LiOH, resulting in reduced charging polarization due to its higher conductivity; however, LiOH could not contribute to O₂ evolution upon recharge. These original results unveil the complex effects of H₂O on cycling the aprotic Li-O₂ batteries, which are instructive for the mechanism study of aprotic Li-O₂ batteries with protic additives or soluble catalysts.