Hierarchical Mesoporous Iron Fluoride and Reduced Graphene Oxide Nanocomposite as Cathode Materials for High-performance Sodium-ion Batteries.

Sodium-ion batteries have been considered as one of ideal power sources for energy storage system. However, the choice of cathode material with good cycling stability and high capacity is limited. Herein, an nanocomposite of hierarchical mesoporous iron fluoride and reduced graphene oxide is prepared by an in situ approach. The as-prepared nanocomposite exhibits remarkably high discharge specific capacity of 227.5 mAh/g at 0.1 C. Specifically, the discharge specific capacity of the sample still remains 87.5 mAh/g at a high rate of 15C after 100th cycle. The electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements show that the addition of reduced graphene oxide can effectively reduce the charge transfer resistance and enhance the Na+ diffusion rate in the FeF3•0.33H2O nanoparticles. The structural changes of FeF3•0.33H2O is further investigated by ex-situ XRD, XPS and ex-situ high resolution transmission electron microscopy.