Electrochemical activity of 3d transition metal ions in polyanionic compounds for sodium‐ion batteries

Abstract Sodium‐ion batteries are expected to replace lithium‐ion batteries in large‐scale energy storage systems due to their low cost, wide availability, and high abundance. Polyanionic materials are considered to be the most promising cathode materials for sodium‐ion batteries because of their cycling stability and structural stability. However, limited by its poor electronic conductivity, the electrochemical performance needs to be further improved. This paper reviews the characterization and development of 3d transition metal ions polyanionic compounds, along with the summarized effect of structure and particle size on the performance and improvement of electrochemical properties. Meanwhile, crystal structure modulation, transition metal ion choice, and transition metal ion doping can improve the electrochemical performance and energy density of polyanionic compounds. Finally, this review points out the challenges of polyanionic compounds and puts forward some particular standpoints, contributing to the promising development of polyanionic compounds in the large‐scale energy storage market.