Sodium-ion layered oxide cathode materials based on oxygen anion redox: Mechanism study, voltage hysteresis, and air stability improvement

With the growing demand for lithium-ion batteries (LIBs) in electric vehicles and large-scale energy storage, the scarcity and uneven distribution of lithium resources pose significant challenges. Sodium-ion batteries (SIBs) present a promising alternative due to their low cost and abundant sodium reserves. Among the various cathode materials, layered oxides have gained attention for their cost-effectiveness, simple synthesis, and high specific capacity. However, the limited contribution of cationic redox reactions to total capacity necessitates the exploration of anionic redox reactions (ARR), which can enhance capacity and overall electrochemical performance. Despite the potential benefits of ARR, challenges such as poor air stability, voltage decay, hysteresis, and cycle life hinder the commercialization of sodium-ion layered materials. This review systematically summarizes the mechanisms underlying ARR, voltage hysteresis, and air stability, while also proposing modification strategies to enhance performance. By examining energy band theory, bonding mechanisms, and vacancy defects, as well as the mechanisms of voltage hysteresis and air stability, this study aims to provide valuable insights and guidance for advancing the development of sodium-ion layered oxide cathodes.