NaCuO₂ as Cathode Materials Studied Through Resonant Inelastic Soft X-Ray Spectroscopy (RIXS)

Anionic redox reactions have been proposed for a decade to provide higher capacity and higher power compared with conventional transition metal redox. However, the fundamental mechanism remains elusive and highly debated. Here, we are working on a model electrode system, NaCuO₂, to reveal the both cation and anion evolution upon the electrochemical cycling through high efficiency mapping of resonant inelastic X-ray scattering (mRIXS). Through the characterization of the oxygen state and copper state, we finally provide a comprehensive understanding of the electrochemical cycling mechanism of the NaCuO₂. We clarify that lattice oxygen redox dominates the reversible bulk redox, while the surface reactions with carbonation decomposition and Cu reaction also contribute the cycling capacity. This work suggests the important role of transition metals and their coupling and hybridization effect to oxygen for maintaining reversible oxygen redox activities.