Structure and Interface Stabilization Enabled High‐Performance O3‐Type Layered Sodium Cathode
Qiang Huang, Deliang Cheng, Bing Wu, Zhengbo Liu, Kun Zhang, Yue Zou, Longbin Li, Yiwang Chen
Abstract
Abstract O3‐NaNi 0.4 Fe 0.2 Mn 0.4 O 2 is a prominent cathode for sodium‐ion batteries, recognized for its high reversible capacity (>180 mAh g −1 ). However, it suffers from poor structural stability and interfacial stability due to complex phase transitions, large volume change, and transition metal (TM) ions dissolution/migration during charge/discharge processes, which results in severe performance degradation. Here, a high‐entropy oxyfluoride cathode with a high configurational entropy of 1.865 R, NaNi 0.2 Fe 0.2 Mn 0.2 Cu 0.1 Ti 0.2 Li 0.1 O 1.95 F 0.05 (NFMCTLF) is designed. The synergy of high‐entropy design and fluorine doping strengthens TM–O bonds and prevents interlayer sliding, thereby enhancing reversible O3‐P3‐OP2 phase transitions and reducing volume change. Moreover, such a high‐entropy oxyfluoride cathode also provides a thin, uniform cathode electrolyte interface layer and elevates the Ni/Fe/Mn ions migration energy barrier, which significantly suppresses interfacial side reactions and inhibits TM ions dissolution/migration. Thus, the NFMCTLF cathode exhibits a specific capacity of 182.4 mAh g −1 with minimal volume change (<1%) in a broad voltage range of 2.0–4.2 V, achieving a capacity retention of 91.45% after 200 cycles at 0.5C and 80.43% after 1000 cycles at 5C. The full battery also exhibits excellent performance with 80.14% capacity retention after 1350 cycles at 5C. This work highlights the great potential in developing high‐performance cathodes with high‐entropy oxyfluoride.