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 Na3V1.47(Fe,Al,Ga,Mg,Mn)0.5Mo0.01Nb0.02(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 (V3+/4+/5+ and Mn2+/3+/4+) and obtaining a reversible 2.18-electron reaction. Consequently, the high-entropy cathode of Na3V1.47(Fe,Al,Ga,Mg,Mn)0.5Mo0.01Nb0.02(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. Show more