High-entropy Na4Fe2.65(NiCrMgCoMn)0.027(PO4)2P2O7 cathode for high-rate sodium-ion batteries

Na4Fe3(PO4)(2)P2O7 (NFPP) cathodes have received significant attention due to the promising theoretical capacity, high average working voltage, and low volume change, but usually suffer from poor rate performance and cycling stability due to their inferior electronic conductivity. Herein, we report a new high-entropy Na4Fe2.65(NiCrMgCoMn)(0.027)(PO4)(2)P2O7 (NFPPHE) as outstanding cathode materials for sodium-ion batteries, by which Fe-defects are generated and electronic & ionic transport kinetics are enhanced. The as assembled NFPPHE//Na half-cell demonstrates an excellent rate performance of 57 mAh/g at 100C and a high-capacity retention of 80 % after 4000 cycles at 20C. In addition, the full cell assembled with hard carbon anode displays an energy density of 165 Wh/kg with 76 % capacity retention after 300 cycles at 0.5C. These results demonstrate the feasibility of Fe-defect strategy to enhance the electrochemical performance of cathode material for sodium-ion batteries.