Accessing the O Vacancy with Anionic Redox Chemistry Toward Superior Electrochemical Performance in O3 type Na‐Ion Oxide Cathode

Abstract Anionic redox chemistry is now viewed as the effective paradigm of improving the capacity of layered oxide materials in Sodium‐ion battery. In this study, O3‐type layered oxide NaLi 0.18 Co 0.23 Ru 0.59 O 2 (NLCR) with O redox ability is successfully synthesized via a facile solid‐state synthesis method. By manipulating the calcinate atmosphere with air and argon (sort by NLCR‐Air NLCR‐Ar respectively), a large amount of O vacancy is introduced in the NLCR‐Air cathode. NLCR‐Air with sufficient O vacancy exhibited superior rate performance which showed 87.7% capacity retention after 1000 cycles at 20 C. Both NLCR‐Air and NLCR‐Ar showed activation of O redox properties which is supported by the soft X‐ray absorption spectroscopy (sXAS). Nevertheless, the in‐situ X‐ray diffraction and sXAS studies disclosed the O vacancy can promote the reversible phase transition and effectively suppress the irreversible O redox upon cycling. These are further supported by theoretical study which suggested a fast kinetic of Na diffusion and less electron agglomeration around the O atom for NLCR‐Air with O vacancy.The research proposed a modification strategy with extraordinary reversible O redox property within O3‐type layered cathode and offered a novel insight into understanding the anionic redox mechanism thus provide guidance of material design advanced energy storage systems.