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 surface is key to mitigate parasitic reactions and extending battery lifetimes. Herein we present a theoretical mechanistic study on the degradation of lithium peroxide degradation product in acetonitrile in the presence of water contaminant. In 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 the production of the parasitic product acetamide. We proposed Li2O2 with water reaction to serve as a prototype for conducting intensive and comprehensive computational analyses aimed at testing different solvents for their use in electrolyte solutions or in surface models for Li-O2 batteries straightforwardly.