Mechanistic insights into Li2O2–solvent reactions: water-induced parasitic chemistry in Li–air batteries

Abstract

Despite being long considered inert, the common electrolyte solvent acetonitrile can actively participate in parasitic reactions that dictate Li–O₂ battery efficiency. Identifying how solvents interact with discharge products in solution or on the surface is key to mitigating parasitic reactions and extending battery lifetimes. Herein, we present a theoretical mechanistic study on the lithium peroxide degradation products in acetonitrile in the presence of water as a contaminant. Under these conditions, the oxidation of acetonitrile takes place in solution. According to the cluster model, the surface electronic effects are insufficient to initiate the acetonitrile oxidation reaction. Water as a contaminant in Li–O₂/ACN cells participates in LiOH formation that decomposes by reacting with intermediates to produce the original discharge product Li₂O₂, but at the expense of producing the parasitic product acetamide. We proposed a reaction of Li₂O₂ with water to serve as a prototype for conducting intensive and comprehensive computational analysis aimed at testing different solvents for their use in electrolyte solutions or in surface models for Li–O₂ batteries straightforwardly.