Critical review of the recent progress and challenges of polyanion Na₃V₂(PO₄)₃ cathode materials in rechargeable sodium-ion batteries

With the increasing demand for sustainable energy sources, sodium-ion batteries (SIBs) have emerged as a rational substitute for large energy storage grid applications in contrast to current lithium-ion batteries (LIBs) owing to the low cost of sodium precursors. Hence, sodium-ion batteries (SIBs) have attracted interest as a future next-generation energy storage system (ESS). However, to date, the commercialization of SIBs has not been realized because of the drawbacks of the present electrode materials, particularly cathodes. Specifically, the electrochemical performance of SIBs is significantly influenced by the inherent properties of their cathode materials. In this regard, layered oxides and polyanion compounds have attracted significant attention among the reported cathode materials for SIBs. However, the poor specific discharge capacity and low-capacity retention of layered oxide materials restrict their practical applications. Among the reported polyanion cathode materials, rhombohedral Na3V2(PO4)(3) (NVP) with open three-dimensional (3D) channels, good structural stability, reasonably high capacity, and high voltage platform (3.4 V) has been proven to be a potential cathode material for SIBs. Thus, from a future application perspective, this review highlights the intrinsic challenges and corresponding strategies for the extensively researched NVP cathode material. Comprehensive insights into the progress in the synthesis of NVP using methods such as sol-gel, solid-state, hydrothermal, electrospinning, and spray drying are presented together with their challenges. The summarized synthesis approaches and strategies may be helpful to researchers for the future directions of SIBs.