O3-NaNi0.4Fe0.2Mn0.4O2 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, NaNi0.2Fe0.2Mn0.2Cu0.1Ti0.2Li0.1O1.95F0.05 (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.
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