Carbothermal synthesis of LiVPO4F and its structural change in a broad potential range observed by in-situ X-ray diffraction

In this work, a novel lithium storage material LiVPO4F is synthesized and reported for advanced lithium-ion batteries. By using the carbothermal reduction method, LiVPO4F is prepared with VPO4 as the intermediate precursor. The as-prepared LiVPO4F particles reveal an average particle size of 400 nm and are surrounded by conductive carbon black particles with size of 30–50 nm. Over-discharge tests show that LiVPO4F has good reversibility with the discharge/charge capacities of 556.0/391.4 mAh g−1 in the potential range of 0.0–4.7 V. In-situ and ex-situ observations prove that the structural evolution of VPO4F during an over-discharge process to 0.0 V is associated with the phase transformation of VPO4F→LiVPO4F→Li2VPO4F→Li3VPO4F. The corresponding recharge process is a quasi-reversible reaction, which is related to the delithiation process of Li3VPO4F→Li2VPO4F→LiVPO4F→LixVPO4F→VPO4F. All these results indicate that LiVPO4F has good over-discharge resistant ability as cathode material for lithium-ion batteries.