Unlocking Advanced Sodium Storage Performance: High-Entropy Modulates Crystallographic Sites with Reversible Multi-Electron Reaction

Abstract

Poor migration dynamics and low energy density are the main challenges of Na₃V₂(PO₄)₃ as a cathode material for sodium ion batteries. Herein, a nanoscale polyhedron high-entropy cathode of Na₃V_1.47(Fe,Al,Ga,Mg,Mn)_0.5Mo_0.01Nb_0.02(PO₄)₃ is designed to modify the crystal structure and enhance the electrons transfer. Distributed nanoparticles improve the electrolyte interface, promoting rapid migration of Na⁺, while the abundant specific surface area offers extra sites for Na⁺ storage. High entropy and multi-metal synergistic effects increase the number of occupied Na(1) and Na(2) sites, maintaining multiple redox couples (V^3+/4+/5+ and Mn^2+/3+/4+) and obtaining a reversible 2.18-electron reaction. Consequently, the high-entropy cathode of Na₃V_1.47(Fe,Al,Ga,Mg,Mn)_0.5Mo_0.01Nb_0.02(PO₄)₃ delivers excellent specific capacity of 130.2 mAh g⁻¹ at 0.5 C, achieving high energy density of 448.3 Wh kg⁻¹, and exhibiting the capacity retention of 95% after 500 cycles at 5 C and 86.5% after 1000 cycles at 15 C, respectively. In situ XRD, ex situ XAS and DFT calculations reveal the influence of structural evolution, valence changes, and high-entropy effects on chemical kinetics. This study provides a guideline for designing advanced polyanionic phosphate cathode materials for sodium ion batteries.