Manganese-based polyanionic cathodes for sodium-ion batteries

Owing to abundant resources and low cost, sodium-ion batteries (SIBs) are sweeping the world at a rapid pace. The cathode is the key to determining the energy density of the battery, and polyanionic compounds have become a representative class of cathode materials due to their stable three-dimensional framework structure, high operating voltage, and good safety. Vanadium-based and iron-based polyanionic compounds are highly regarded in academic communities, but environmental hazards or low energy densities have once overshadowed them in the practical arena. In contrast, manganese (Mn)-based polyanion is one of the potential candidates in terms of cost, voltage, and environmental friendliness, besides, many noteworthy advances have been recorded in recent years. This review summarizes the current research progress of Mn-based polyanions and discusses the challenges they face while looking forward to the future development of such materials and ideas to solve the key problems. It is expected to have a positive effect, that is, to attract more practitioners to focus on the practical way out of such materials.