RIXS of oxygen in oxide-based battery cathodes

Modern energy applications like electric vehicles and green grid rely largely on batteries that could offer high-energy and high-kinetics energy storage solutions. However, improvements of battery energy density has been bottlenecked by the battery cathodes, which are mostly trantion-metal (TM) oxide based. The challenge is also fundamental because the intrsic states of highly oxidized oxides remain unclear and its controls and detections are under active debates.

This presentation will first quickly survey some of the key findings of the highly oxidized states in oxide based battery cathodes studied by resonant soft X-ray inelastic scattering (RIXS), then we show recent studies on various oxide cathodes that reveal the intrinsic TM and O states upon charging to high voltages. In general, in many high-energy battery cathodes, conventionally defined oxide states fail in such highly oxidized states, new groundstates are triggered, which lead to strongly coupled TM-O unit that becomes responsible for the redox (reduction and oxidation) process during battery charge and discharge. We conclude that reliable experimental characterizations of the intrinsic states in such highly oxidized oxides are yet to be improved, and coupling spectroscopic results with theoretical calculations is critical to understand the redox mechanism in high-energy batteries.