Polyanion Sodium Vanadium Phosphate for Next Generation of Sodium‐Ion Batteries—A Review

Abstract Polyanion‐type sodium (Na) vanadium phosphate in the form of Na 3 V 2 (PO 4 ) 3 has demonstrated reasonably high capacity, good rate capability, and excellent cyclability. Two of three Na ions per formula can be deintercalated at a potential 3.4 V versus Na + /Na with oxidation of V 3+/4+ . In the reversible process, two Na ions intercalate back resulting in a discharge capacity of 117.6 mAh g −1 . Further intercalation is possible but at a low potential of 1.4 V versus Na + /Na accompanied by vanadium reduction V 3+/2+ , leading to a capacity of 60 mAh g −1 . Due to its marvelous electrochemical performance, it has attracted a lot of attention since its discovery in the 1990s. To develop truly useable polyanion‐type vanadium phosphate, better understanding of its crystal configuration, sodium ions' transportation, and electronic structure is essential. Therefore, this review only focuses on the inside of crystal configuration and electronic structure of polyanion‐type vanadium phosphate, Na 3 V 2 (PO 4 ) 3 , since there are a few good reviews on various processing technologies.