Lithium deintercalation behavior in Li-rich vanadium phosphate as a potential cathode for Li-ion batteries

Abstract

Layered Li-rich vanadium phosphate, Li₉V₃(P₂O₇)₃(PO₄)₂, is a novel and potential cathode material for lithium-ion batteries. It possesses both facile ion mobility due to its two-dimensional pathways, and high theoretical capacity (173.5 mAh g⁻¹) because of its ability to extract six lithium ions (per formula) from the trigonal framework accompanied with the double-electron reaction of vanadium. In this study, we first correlate the structural characters with the electrochemical process by using a combined experimental and computational method. The electrochemical recrystallization of Li₉V₃(P₂O₇)₃(PO₄)₂ is accomplished along with a metastable superstructure phase in different but related space group. Nevertheless, the structure as well as oxidation state can be easily recovered on reduction-oxidation, and the volume change is minimal. Furthermore, the electrochemical voltage-composition profile is predicted and understood as emerging from site energetics and redox couples via first-principles calculations.