Sodium in situ modulated phase transition to construct iron/vanadium bimetallic sulfide anodes for “fast-charging” sodium-ion batteries

Abstract

Fast-charging of iron sulfides, as an advanced anode for sodium-ion batteries, is severely restricted by the poor diffusion kinetics of sodium ions and rapid capacity fading. Utilizing the mechanism of in situ modulated phase transition of sodium species, herein, iron/vanadium bimetallic sulfides with various phase structures are synthesized to solve this challenge. The presence and content variation of sodium species could effectively adjust the electron density of the Fe atom, thereby implementing the modulation of bimetallic sulfides’ phase structure during the sulfidation process. The appropriate phase structure and promising capacitive behavior boost sodium ion transport and reduce capacity attenuation. Consequently, the iron/vanadium bimetallic sulfides exhibit superior sodium storage capacity (424.67 mAh g⁻¹ at 0.05 A g⁻¹), a high rate capability of 192.82 mAh g⁻¹ at 10 A g⁻¹, and fast sodium ion diffusion kinetics. Furthermore, the assembled full-batteries deliver a remarkable capacity retention of 43.4% after 1200 cycles at 1 A g⁻¹. This work, inspired by the use of sodium as an electron promoter for iron-based catalysts for CO₂ hydrogenation, promises a convergence of catalysis and the synthesis of bimetallic sulfides to achieve fast-charging of sulfides.