Electrochemical Performance Of V₂O₃-LiF And V₂O₃-Li₃PO₄ Composite Cathode Materials

The metal oxide-lithium fluoride composite cathode materials for lithium ion battery based on surface conversion reaction mechanism are favored by many scholars because of their unfixed crystal structures and high specific capacity.In this paper,V₂O₃-LiF/ketjin black（KB）and V₂O₃-Li₃PO₄/KB composites were prepared by spray drying and heat treatment.The effects of sintering temperature,sintering time,KB content and the molar ratio of V₂O₃and lithium salt on the structure,morphology and electrochemical properties of the materials were discussed.The ex situ X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）were used to study the electrochemical reaction mechanism of the materials at different stages of discharge and charge.The optimum conditions for preparing V₂O₃-LiF/KB composites were as follows:sintering temperature 400℃,sintering time 3 h,KB content 5%,V₂O₃/LiF molar ratio 1:2.Under the optimized conditions,the initial discharge specific capacity of V₂O₃-LiF/KB composites was 210.1 m Ah/g.After 50 cycles,the specific capacity decreased to 87.1m Ah/g,and the capacity retention rate was 38.9%.After lithium oxalate borate（Li BOB）was added into the electrolyte as additive,the discharge capacity retention rate aftre 30cycle was 100.8%,indicating that the addition of Li BOB can significantly improve the cycle performance of the material.The results of cyclic voltammetry and XPS analysis showed that the surface-controlled reaction was dominant in the electrochemical reaction of V₂O₃-LiF/KB,and the reversible conversion of V（Ⅲ）（?）V（Ⅳ）（?）V（Ⅵ）was realized.The optimum conditions for preparing V₂O₃-Li₃PO₄/KB composites were as follows:sintering temperature 500℃,sintering time 4 h,the content of KB 15%,V₂O₃/Li₃PO₄molar ratio is 1:1.Under the optimized preparation conditions,initial discharge specific capacity of V₂O₃-Li₃PO₄/KB composites was 191.3 m Ah/g.After 50 cycles,the specific capacity decreased to 149.4 m Ah/g,and the capacity retention rate was 78.1%.The results of cyclic voltammetry,XPS and XRD analysis showed that the surface-controlled reaction was dominant in the V₂O₃-Li₃PO₄/KB electrochemical reaction,and the reversible conversion of V（Ⅲ）（?）V（Ⅳ）（?）V（Ⅵ）was realized.In summary,the above works demonstrated the feasibility of V₂O₃-LiF/KB and V₂O₃-Li₃PO₄/KB composites as new cathode materials,which provides new ideas and strategies for the preparation of new cathode materials based on surface conversion reaction.