Toward the High‐Voltage Stability of Layered Oxide Cathodes for Sodium‐Ion Batteries: Challenges, Progress, and Perspectives

Sodium‐ion batteries (SIBs) have garnered significant attention as ideal candidates for large‐scale energy storage due to their notable advantages in terms of resource availability and cost‐effectiveness. However, there remains a substantial energy density gap between SIBs and commercially available lithium‐ion batteries (LIBs), posing challenges to meeting the requirements of practical applications. The fabrication of high‐energy cathodes has emerged as an efficient approach to enhancing the energy density of SIBs, which commonly requires cathodes operating in high‐voltage regions. Layered oxide cathodes (LOCs), with low cost, facile synthesis, and high theoretical specific capacity, have emerged as one of the most promising candidates for commercial applications. However, LOCs encounter significant challenges when operated in high‐voltage regions such as irreversible phase transitions, migration and dissolution of metal cations, loss of reactive oxygen, and the occurrence of serious interfacial parasitic reactions. These issues ultimately result in severe degradation in battery performance. This review aims to shed light on the key challenges and failure mechanisms encountered by LOCs when operated in high‐voltage regions. Additionally, the corresponding strategies for improving the high‐voltage stability of LOCs are comprehensively summarized. By providing fundamental insights and valuable perspectives, this review aims to contribute to the advancement of high‐energy SIBs. Layered oxide cathodes (LOCs) encounter significant challenges when operated in high‐voltage regions (> 4.0 V versus Na+/Na) in sodium‐ion batteries. In this review, the prominent challenges and the recent efforts made to improve the high‐voltage stability of LOCs are highlighted. Moreover, the future directions and prospects of LOCs are outlined for enabling high‐energy sodium‐ion batteries.