Hollow spherical Na3.95Fe2.95V0.05(PO4)2P2O7 suppressing inactive Maricite-NaFePO4 with ultrahigh dynamics performance

Abstract

sodium ion batteries are considered as excellent energy storage battery materials with the characteristic of low cost and renewability. As a critical component of sodium-ion energy storage batteries, cathode materials have attracted great attention from scientists around the world. Recently, Na₄Fe₃(PO₄)₂P₂O₇ (NFPP) which offer a theoretical capacity of 129 mAh g⁻¹ has garnered widespread attention. However, the formation of inactive maricite NaFePO₄ (NFP) and low capacity Na₂FeP₂O₇ (Na₂FPO) during the synthesis process restricts the capacity utilization, while poor conductivity further limits its electrochemical performance. To address these issues, here, Na_3.95Fe_2.95V_0.05(PO₄)₂P₂O₇/C (V_0.05-NFPP/C) composite material was synthesized and assembled into cell for testing. A capacity of 114 mAh g⁻¹ was given at 0.1 C and rate performance also represent 90 mAh g⁻¹ at 10 C. Vanadium-ion improves the dynamic performance by inhibiting maricite NFP and participating in electrochemical reactions. Furthermore, sodium-ion storage mechanism of V_0.05-NFPP/C was revealed by ex-situ XRD patterns with the assistance of first-principles calculations, and the phase transformation mechanism during the sintering process was explored.