Sulfate-Based Polyanionic Compounds for Li-Ion Batteries: Synthesis, Crystal Chemistry, and Electrochemistry Aspects

Electrochemical storage has become an integral part of our mobile society and great hopes are being placed in Li-ion batteries to meet future demands dictated by the upcoming electric vehicle (EV) and grid application markets. Batteries with greater autonomy and comprising materials having minimal environmental footprint need to be developed. This calls for both innovative chemistry and new concepts. Currently battery researchers are turning their attention to the design of polyanionic electrodes made up of abundant elements. Here we review recent studies which have led to the synthesis of new sulfate-based polyanionic compounds such as AMSO4 X (A = Li, Na, K; M = Fe, Mn, Ni, Co; X = F, OH) and Li2 M(SO4)2 (M = Fe, Co, Mn). We highlight their rich crystal chemistry, comment on structural–electrochemical relationships, and report on the feasibility of using the Fe-based compounds as positive electrodes in secondary Li-ion batteries. Additionally, we present premises for an electrochemical–magnetism correlation and offer an outlook on the future of polyanionic compounds.