Dynamic structural evolution and controllable redox potential for abnormal high-voltage sodium layered oxide cathodes

Developing high-voltage cathode materials for sodium-ion batteries (SIBs) is both challenging and extremely urgent. Here, we report an abnormal high-voltage Na2/3Ni1/3Sn2/3O2 cathode material with a P2-structure stoichiometric composition and an O3-type layered phase. Using a classic P2-type layered oxide cathode Na2/3Ni1/3Mn2/3O2 as a model system, we demonstrate the accurate manipulation of orbital hybridization between transition metal and oxygen atoms to regulate the redox potential through engineering the chemical composition and corresponding electronic structure. Meanwhile, an in-depth systematic investigation of dynamic structural evolution during the formation process and highly reversible O3–P3 phase transition as well as charge compensation mechanism throughout Na+ intercalation/deintercalation process is clearly demonstrated through various in situ techniques. Overall, this study not only reveals intrinsic chemical and structural properties, adjustable electrochemical behavior, and dynamic evolution process, but also explores an orbital-level understanding of controllable redox potential for high-voltage SIBs.