Polyanionic Cathode Materials for Practical Na-Ion Batteries toward High Energy Density and Long Cycle Life

[Image: see text] Na-ion batteries (NIBs) as a supplement to Li-ion batteries deliver huge application potential in the field of grid-scale energy storage. At present, it is a particularly imperative to advance commercialization of the NIBs after ten years of intensive research. Among the exploited cathodes for NIBs, polyanionic compounds have great commercial prospects due to their favorable ion diffusion channels, high safety, and superior structure stability determined by their unique structure framework; however, there is still a long way to go before large-scale industrialization can be realized. This outlook summarizes the recent progress of polyanion-type cathodes for NIBs and includes V-based, Fe-based, and Mn-based polyanionic compounds toward high energy density and long cycle lifespan. The remaining challenges and guidelines/suggestions for the design of the practically available polyanionic cathode materials with desirable energy density and cycling performance are presented. We hope that this outlook can provide some insights into the development of polyanionic cathodes for practical NIBs toward commercialization.