Hydrogenation of Oxides in Nonaqueous Battery Electrolytes and Beyond

The study of lithium-ion batteries (LIBs) has historically focused on the movement of lithium ions, which is coupled with electron transfer to reversibly store and release energy from metal oxides thousands of times. However, a recent discovery identified an additional coupled electron–ion transfer process occurring between oxide cathodes and nonaqueous electrolytes, particularly during the self-discharge process. Here, we discuss ongoing efforts to probe and understand how chemical processes (e.g., reactions and transport involving solvent-derived hydrogen) impact the self-discharge of LIBs and the evolution of heterogeneity and disorder in layered oxide cathodes. Beyond batteries using nonaqueous electrolytes, we further discuss the implications of solvent-mediated or other hydrogen-related pathways of significance to other electrochemical materials and devices. We envision future directions to understand and control how oxide hydrogenation impacts electrochemical behaviors so that research efforts can be better aligned toward mitigating the multiple sources of self-discharge and chemo-mechanics in electrochemical energy storage devices.