Boosting Multielectron Reaction Stability of Sodium Vanadium Phosphate by High-Entropy Substitution

Abstract

Na₃V₂(PO₄)₃ (NVP) based on the multielectron reactions between V²⁺ and V⁵⁺ has been considered a promising cathode for sodium-ion batteries (SIBs). However, it still suffers from unsatisfactory stability, caused by the poor reversibility of the V⁵⁺/V⁴⁺ redox couple and structure evolution. Herein, we propos a strategy that combines high-entropy substitution and electrolyte optimization to boost the reversible multielectron reactions of NVP. The high reversibility of the V⁵⁺/V⁴⁺ redox couple and crystalline structure evolution are disclosed by <i>in situ</i> X-ray absorption near-edge structure spectra and <i>in situ</i> X-ray diffraction. Meanwhile, the electrochemical reaction kinetics of high-entropy substitution NVP (HE-NVP) can be further improved in the diglyme-based electrolyte. These enable HE-NVP to deliver a superior electrochemical performance (capacity retention of 93.1% after 2000 cycles; a large reversible capacity of 120 mAh g^-1 even at 5.0 A g^-1). Besides, the long cycle life and high power density of the HE-NVP∥natural graphite full-cell configuration demonstrated the superiority of HE-NVP cathode in SIBs. This work highlights that the synergism of high-entropy substitution and electrolyte optimization is a powerful strategy to enhance the sodium-storage performance of polyanionic cathodes for SIBs.