Achieving Fast and Stable Sodium Storage in Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) via Entropy Engineering

Abstract Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) (NFPP) has been considered a promising cathode material for sodium‐ion batteries (SIBs) owing to its environmental friendliness and economic viability. However, its electrochemical performance is constrained by connatural low electronic conductivity and inadequate sodium ion diffusion. Herein, a high‐entropy substitution strategy is employed in NFPP to address these limitations. Ex situ X‐ray diffraction analysis reveals a single‐phase electrochemical reaction during the sodiation/desodiation processes and the increased configurational entropy in HE‐NFPP endows an enhanced structure, which results in a minimal volume variation of only 1.83%. Kinetic analysis and density functional theory calculation further confirm that the orbital hybrid synergy of high‐entropy transition metals offers a favorable electronic structure, which efficaciously boosts the charge transfer kinetics and optimizes the sodium ion diffusion channel. Based on this versatile strategy, the as‐prepared high‐entropy Na 4 Fe 2.5 Mn 0.1 Mg 0.1 Co 0.1 Ni 0.1 Cu 0.1 (PO 4 ) 2 (P 2 O 7 ) (HE‐NFPP) cathode can deliver a prominent rate performance of 55 mAh g −1 at 10 A g −1 and an ultra‐long cycling lifespan of over 18 000 cycles at 5 A g −1 . When paired with a hard carbon (HC) anode, HE‐NFPP//HC full cell exhibits a favorable cycling durability of 1000 cycles. This high‐entropy engineering offers a feasible route to improve the electrochemical performance of NFPP and provides a blueprint for exploring high‐performance SIBs.