Doping Engineering of Sodium Vanadium Fluorophosphates Cathodes for Sodium-Ion Batteries

Abstract Sodium-ion batteries offer a promising alternative to lithium-ion batteries due to the abundance and low cost of sodium resources. Na 3 V 2 (PO 4 ) 2 F 3− y O y (NVPFO y ) stands out as a cathode material with high average operating potential (~ 3.9 V vs Na + /Na), fast Na⁺ transport, and strong structural stability (minimal volumetric strain of ~ 2%). This review addresses the structural characteristics and charge storage mechanisms of NVPFO y , focusing on charge compensation and Na⁺/vacancy ordering. It also discusses recent advances in lattice regulation and doping strategies to enhance electrochemical properties. Finally, we highlight challenges and future directions for practical applications, emphasizing the correlation between crystal structure and performance.