Sodium In-situ Modulated Phase Transition Toward Iron/Vanadium Bimetallic Sulfides Anode 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 proper phase structure and promising capacitive behavior boost sodium ion transport and impair the capacity attenuation. Consequently, the iron/vanadium bimetallic sulfides present superior sodium storage capacity (424.67 mAh/g at 0.05 A/g), high-rate capability of 192.82 mAh/g at 10 A/g, and fast sodium ion diffusion kinetics. Furthermore, the assembled full-batteries deliver a cheering capacity retention of 43.4 % after 1, 200 cycles at 1 A/g. This work, inspired by employing 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 the fast-charging of sulfides.