Progress in multi-electron sodium vanadium phosphate cathode for emerging sodium-ion batteries

Sodium vanadium phosphate (NVP) has emerged as a promising cathode material for sodium-ion batteries (SIBs) due to its three-dimensional (3D) Sodium Super Ionic Conductor (NASICON) framework, which enables rapid sodium ion (Na⁺) diffusion, impressive thermal stability, and high theoretical energy density. However, the commercialization of NVP-based batteries faces challenges due to the large ionic radius of sodium (Na), which limits its electrical conductivity and structural stability. Advanced strategies have been developed to overcome these limitations, including integrating carbonaceous materials, targeted ion doping, nanosizing, and manipulating the shape and structure of NVP particles. Despite progress in Na⁺ migration pathways, synthesis, engineering, and electronic/ionic mobility improvements, an essential aspect of NVP is lacking, such as scalability, recycling, and electrolyte compatibility necessary for the commercial deployment of NVP-based SIBs. This review aims to fill this gap by comprehensively investigating these obstacles to delimit NVP-based SIBs. Moreover, a comparative analysis with lithium iron phosphate (LFP), a benchmark material in commercial lithium-ion batteries (LIBs), highlights NVP's potential advantages in cost, safety, and Na availability. However, challenges in energy density and scalability remain. By evaluating the relationships between these factors and electrochemical performance, this review provides a comprehensive understanding of NVP-based batteries and identifies opportunities for further improvement.