Stabilizing Reversible Oxygen Redox Chemistry in Layered Oxides for Sodium-Ion Batteries

Triggering oxygen-related activity is demonstrated as a promising strategy to effectively boost energy density of layered cathodes for sodium-ion batteries. However, irreversible lattice oxygen loss will induce detrimental structure distortion, resulting in voltage decay and cycle degradation. Herein, a layered structure P2-type Na0.66Li0.22Ru0.78O2 cathode is designed, delivering reversible oxygen-related and Ru-based redox chemistry simultaneously. Benefiting from the combination of strong Ru 4d-O 2p covalency and stable Li location within the transition metal layer, reversible anionic/cationic redox chemistry is achieved successfully, which is proved by systematic bulk/surface analysis by in/ex situ spectroscopy (operando Raman and hard X-ray absorption spectroscopy, etc.). Moreover, the robust structure and reversible phase transition evolution revealed by operando X-ray diffraction further establish a high degree reversible (de)intercalation processes (approximate to 150 mAh g(-1), reversible capacity) and long-term cycling (average capacity drop of 0.018%, 500 cycles).