Entropy‐Enhanced Multi‐Doping Strategy to Promote the Electrochemical Performance of Na4Fe3(PO4)2P2O7

Abstract Sodium‐ion batteries (SIBs) have been regarded as promising candidates for large‐scale energy storage system, and their electrochemical performance is determined by the cathode materials. Recently, the polyanion‐type cathode Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) demonstrates decent performance, while there exists promotion space with respect to its cycle stability and rate capability. Herein, an entropy‐enhanced Na 4 Fe 2.95 (NiCoMnMgZn) 0.01 (PO 4 ) 2 P 2 O 7 (HE‐NFPP) cathode is proposed with improved rate performance (67.1 mAh g −1 at 50 C) and cycle performance (retention of 92.0% after 1000 cycles at 1 C). The enhancement of configuration entropy improves the structural stability of NFPP thermodynamically. In‐situ XRD illustrates the sodium storage mechanism of HE‐NFPP as an imperfect solid solution reaction driven by Fe 2+ /Fe 3+ redox with a low volume change of 4.0% (90.9% of NFPP). Through doping, the structure distortion and abrupt rearrangement are inhibited. Additionally, HE‐NFPP and hard carbon (HC) are utilized to fabricate pouch cell that demonstrates an average working voltage of 3.0 V and a maximum energy density of 165 Wh kg −1 (based on the total mass of active materials). These results highlight the potential for enhancing the high‐rate and long‐cycle performance of NFPP as a promising cathode for SIBs through an entropy‐enhanced multi‐doping strategy.