Self-Templated Formation of Hollow Yolk-Like Spheres Iron Fluoride as Cathode Material for High-Performance Li-Ion Batteries

Iron fluoride is one of the representatives of multi-electron cathode materials for Li-ion batteries, which has attracted extensive attention. However, its poor rate performance and volume adaptability during charge-discharge cycles hinder its practical application. To solve these defects, hollow yolk-like spheres iron fluoride with micro-nano architectures has been synthesized by a new self-templated solvothermal method. Fe-glycerate precursor with hollow yolk-like spheres was first prepared and subsequent performing ion exchange with NH4F as fluorine source to form iron fluoride. The formation mechanism of the hollow yolk-like spheres Fe-glycerate is attributed to "Kirkendall effect". The hollow yolk-like spheres iron fluoride delivers a superior rate performance of 163 mAh g−1 at high current density of 712 mA g−1, with a low capacity fading rate of 0.58% per cycle for 40 cycles. Moreover, it displays a high discharge capacity of 306 mAh g−1 at 71.2 mA g−1. The superior electrochemical performance is attributed to the large specific surface area, short electrons and ions migration distance and hollow structure for electrolyte penetration deriving from the unique micro-nano hierarchical hollow yolk-like spheres structure. This work provides a new and general method for controllable synthesis of hollow structure materials for high rate performance Li-ion batteries.