High Entropy Boosts the Low Temperature Na⁺-Storage Performance of Na₄Fe₃(PO₄)₂P₂O₇

Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) is considered a promising cathode material for sodium ion batteries (SIBs). However, the inferior electronic conductivity and inadequate Na⁺ ions diffusion kinetics of NFPP at low temperatures hinder its practical applications. In this study, high entropy Na₄Fe_2.95(MgCaAlCrMn)_0.01(PO₄)₂P₂O₇ (HE-NFPP) has been synthesized via a spray-drying and high temperature sintering technique. The incorporation of transition metal (TMs) ions into NFPP through HE strategy facilitates electron transportation by reducing the bandgap between the conduction and valence bands. Meanwhile, the 3D network Na⁺ ions diffusion channels formed in HE-NFPP can effectively improve the Na⁺ ions diffusion efficiency, resulting in enhanced electrode reaction kinetics at low temperatures. Moreover, it leads to a significantly mitigated volume expansion/contraction in HE-NFPP caused by Na⁺ ions extraction/insertion during (de)sodiation process. Consequently, the fabricated HE-NFPP exhibits an excellent rate and cyclic performance at low temperatures.