Regulation on Morphology and Electronic Structure Design of Vanadium-Based Sodium Phosphate Cathodes for High-Performance Sodium-Ion Batteries

Abstract

Sodium-ion batteries have emerged as promising candidates for next-generation large-scale energy storage systems due to the abundance of sodium resources, low solvation energy, and cost-effectiveness. Among the available cathode materials, vanadium-based sodium phosphate cathodes are particularly notable for their high operating voltage, excellent thermal stability, and superior cycling performance. However, these materials face significant challenges, including sluggish reaction kinetics, the toxicity of vanadium, and poor electronic conductivity. To overcome these limitations and enhance electrochemical performance, various strategies have been explored. These include morphology regulation via diverse synthesis routes and electronic structure optimization through metal doping, which effectively improve the diffusion of Na+ and electrons in vanadium-based phosphate cathodes. This review provides a comprehensive overview of the challenges associated with V-based polyanion cathodes and examines the role of morphology and electronic structure design in enhancing performance. Key vanadium-based phosphate frameworks, such as orthophosphates (Na3V2(PO4)3), pyrophosphates (NaVP2O7, Na2(VO)P2O7, Na7V3(P2O7)4), and mixed phosphates (Na7V4(P2O7)4PO4), are discussed in detail, highlighting recent advances and insights into their structure–property relationships. The design of cathode material morphology offers an effective approach to optimizing material structures, compositions, porosity, and ion/electron diffusion pathways. Simultaneously, electronic structure tuning through element doping allows for the regulation of band structures, electron distribution, diffusion barriers, and the intrinsic conductivity of phosphate compounds. Addressing the challenges associated with vanadium-based sodium phosphate cathode materials, this study proposes feasible solutions and outlines future research directions toward advancement of high-performance vanadium-based polyanion cathodes.