Mixed polyanion cathode materials: Toward stable and high-energy sodium-ion batteries

Sodium-ion batteries (SIBs) are considered as one of the most fascinating alternatives to lithium-ion batteries for grid-scale energy storage applications because of the low cost and wide abundance of sodium resources. Among various cathode materials, mixed polyanion compounds come into the spotlight as promising electrode materials due to their superior electrochemical properties, such as high working voltage, long cycling stability, and facile reaction kinetics. In this review, we summarize the recent development in the exploration of different mixed polyanion cathode materials for SIBs. We provide a comprehensive understanding of the structure-composition-performance relationship of mixed polyanion cathode materials together with the discussion of their sodium storage mechanisms. It is anticipated that further innovative works on the material design of advanced cathode materials for batteries can be inspired.