Achieving Fast and Stable Sodium Storage in Na4 Fe3 (PO4 )2 (P2 O7 ) via Entropy Engineering.

Abstract

Na4 Fe3 (PO4 )2 (P2 O7 ) (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 Na4 Fe2.5 Mn0.1 Mg0.1 Co0.1 Ni0.1 Cu0.1 (PO4 )2 (P2 O7 ) (HE-NFPP) cathode can deliver a prominent rate performance of 55mAhg-1 at 10Ag-1 and an ultra-long cycling lifespan of over 18000cycles at 5Ag-1 . When paired with a hard carbon (HC) anode, HE-NFPP//HC full cell exhibits a favorable cycling durability of 1000cycles. This high-entropy engineering offers a feasible route to improve the electrochemical performance of NFPP and provides a blueprint for exploring high-performance SIBs.