The Development of Vanadyl Phosphate Cathode Materials for Energy Storage Systems: A Review.

Various cathode materials have been proposed for high-performance rechargeable batteries. Vanadyl phosphate is an important member of the polyanion cathode family. VOPO has seven known crystal polymorphs with tunneled or layered frameworks, which allow facile cation (de)intercalations. Two-electron transfer per formula unit can be realized by using V /V and V /V redox couples. The electrochemical performance is closely related to the structures of VOPO and the types of inserted cations. This Review outlines the crystal structures of VOPO polymorphs and their lithiated phases. The research progress of vanadyl phosphate cathode materials for different energy storage systems, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, multivalent batteries, and supercapacitors, as well as the related mechanism investigations are summarized. It is hoped that this Review will help with future directions of using vanadyl phosphate materials for energy storage.