(Charles W. Tobias Young Investigator Award Address) Understanding Reactivity at Electrode-Electrolyte Interfaces in Li-O2 and Li-ion Batteries

Abstract

When expanding the limits of voltage stability, capacity retention, and rate capability in batteries, parasitic processes at electrode-electrolyte interfaces-- such as electrolyte degradation, oxide surface densification, and Li metal plating on graphite electrodes-- play a critical role in defining battery performance. Our laboratory’s objective is to combine quantitative analytical techniques with spectroscopy to understand, and ultimately suppress, these process’s role in observed system lifetime, capacity, and efficiency. This presentation will provide a perspective on our understanding of interfacial reactivity in two systems: the positive electrode in the nonaqueous metal-O2 batteries, and interfaces in Li-ion batteries operating at either high voltage or high rates. First, the impact of electrolyte composition on product formation mechanisms in metal-O2 batteries will be discussed, as will strategies to suppress reactive oxygen-induced degradation. Second, drawing a comparison to Li-O2 batteries, the influence of anionic oxygen redox in interfacial degradation processes will be discussed in emerging high-capacity cathode materials, such as cation disordered rocksalt oxide and oxyfluoride materials and Ni-rich NMC layered oxide materials. Finally, to highlight the versatility of gas evolution-based quantitative techniques developed to study oxygen activity in metal-O2 and Li-ion oxide cathodes, the accurate detection of Li plating onset during fast charging of graphite electrodes will be shown by monitoring hydrogen evolution upon exposure of nominally delithiated graphite electrodes to acid.