Unravelling Cation–Anion Redox Mechanisms in CrSe2 Cathodes for Potassium-Ion Batteries via In-Operando X-ray Absorption Spectroscopy at the

This project aims to resolve the redox mechanisms responsible for the exceptional electrochemical performance of CrSe2 in potassium-ion batteries (PIBs). While most layered PIB cathodes show only partial capacity, CrSe2 uniquely delivers near-theoretical values with long-term stability. Our previous in-operando synchrotron PXRD at ID15A revealed a three-stage intercalation mechanism combining phase-transition and solid-solution processes, with intermediate phases not reported before and impossible to isolate ex situ. The key question remains whether the high capacity is governed solely by Cr cationic redox or also involves hidden Se anion redox activity. Using in-operando XAS at BM23, we will probe both the Cr and Se K-edges, directly correlating electronic and structural evolution. The results will clarify the origin of capacity in CrSe₂ and provide guidance for the rational design of next-generation PIB cathodes.