Enhancing Voltage Output in Polyanion‐Type Cathode Materials for Sodium Ion Batteries

Abstract Sodium‐ion batteries (SIBs) are promising in several aspects due to their many advantages over lithium‐ion batteries. Among SIB's several outstanding attributes, its low cost, resource abundance, and potential safety make it suitable for large‐scale energy storage systems (ESS). Among the potential cathode materials, poly‐anionic cathode materials could be a better choice for their stability and safety in comparison to layered transition metal oxides and Prussian blue analogues (PBA). However, on the other hand, the conductivity as well as the available capacity of the polyanion compounds are still poor, which limits their applications; moreover, some polyanion cathode operate at low voltage, which reduces the energy density and raises the cost of the battery system. We here try to summarize the recent progress of polyanion compounds as cathode materials for SIB. These compounds are categorized based on the metal redox couple, including V‐, Cr‐, Mn‐, Fe‐, Co‐, and Ni‐polyanion compounds. Our attention is specifically drawn to properties such as reversible redox voltage, capacity, cycling stability, and sodium storage mechanisms. We also discuss the challenges and potential development strategies for the future.