Exploring the charge compensation mechanisms in KVPO4F1-xOx positive electrodes for K-ion batteries using operando and ex situ XES.

We propose to use X-ray emission spectroscopy to investigate the charge compensation mechanisms in KV1-y(VO)y(PO4)F1-y positive electrode materials for K-ion batteries in operando and ex situ conditions. We expect to obtain unambiguous information on the evolution of V oxidation state and the impact of the vanadyl type “defects” (V=O) on the redox processes upon K+ extraction/intercalation. Finally, by comparing operando HERFD-XAS spectra with our previous XAS ones, we will provide a more accurate description of the electronic rearrangement of KV1-y(VO)y(PO4)F1-y positive electrodes upon cycling. This study will pave the way for future investigation on battery materials, where the average description of electronic structure is often insufficient to thoroughly understand the impact of the reaction mechanisms on the electrochemical properties, such as voltage fade, hysteresis, and life span.