A review of metal sulfide cathode materials for non-aqueous multivalent ion (Mg2+, Ca2+, Al3+) batteries

With the rising cost and safety concerns associated with lithium-ion batteries (LIBs), multivalent metal-ion batteries (MMIBs) have been considered as promising candidates for energy storage applications, due to their abundant reserves, high theoretical volume capacity, and low cost. However, the development of MMIBs is seriously hampered by the lack of suitable cathode materials that can reversibly accommodate the insertion/ extraction of multivalent metal ions. Metal sulfides (MSs) are promising cathode materials for MMIBs owing to the relatively weak electrostatic interaction between their soft lattice anions and highly polarized multivalent metal ions. Unfortunately, the conventional MSs suffer from low diffusion kinetics, poor material efficiency, and large volume expansion, resulting in unsatisfying electrochemical performance. In this review, we first review the challenges faced by MSs in non-aqueous MMIBs and summarize the effective strategies commonly used to improve electrochemical performance. Additionally, the recent progress regarding MSs cathodes in MMIBs is also summarized. Finally, the challenges of MS cathodes used in MMIBs are discussed and the potential future di-rection is also highlighted. This review is expected to provide guidance for the development of high-performance cathode materials based on MSs for MMIBs.