Improved and scalable method for the preparation of Sn-doped hexagonal tungsten bronze-type iron fluoride materials as cathode for sodium-ion batteries

Abstract

With its potential high energy density and high safety, FeF3 materials are viewed as very promising candidate cathode materials for the next generation of lightweight in SIBs (sodium-ion batteries). However, so far, the fabrication procedures for FeF3 materials commonly entail high-energy ball milling, solvothermal synthesis, utilization of costly ionic liquids, and even handling highly hazardous gases, rendering the preparation process intricate and impeding the successful incorporation of heteroatom doping into FeF3 materials. Herein, an improved and scalable aqueous solution approach is developed and implemented to obtain FeF3·0.33H2O (hexagonal tungsten bronze-type) materials. Currently, in the field of improving the cycling performance of FeF3 materials through metal doping, research focus has been primarily on transition metal doping, with limited investigation into non-transition metal doping. In non-transition metals, due to the similar electronegativity of Sn and Fe, and the low cost of Sn, the electrochemical characteristics of Sn-doped FeF3·0.33H2O were investigated in this work. Meanwhile, the utilization of DFT reveals that Sn-doped increases the atomic cloud density at neighboring Fe sites and expands the unit cell, consequently enhancing the conductivity and ion diffusion rate of the material. The synthesis method is simple and practical, providing a reliable experimental approach for promoting the commercialization of FeF3·0.33H2O.