High‐Energy Interlayer‐Expanded Copper Sulfide Cathode Material in Non‐Corrosive Electrolyte for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMB) have been regarded as an alternative to lithium-based batteries because of their abundant elemental resource, high theoretical volumetric capacity, and multi-electron redox reaction without the dendrite formation of magnesium metal anode. However, their development is impeded by their poor electrode/electrolyte compatibility and the strong Coulombic effect of the multivalent Mg²⁺ ions in cathode materials. Herein, copper sulfide material is developed as a high-energy cathode for RMBs with a non-corrosive Mg-ion electrolyte. Given the benefit of its optimized interlayer structure, good compatibility with the electrolyte, and enhanced surface area, the as-prepared copper sulfide cathode exhibits unprecedented electrochemical Mg-ion storage properties, with the highest specific capacity of 477 mAh g^-1 and gravimetric energy density of 415 Wh kg^-1 at 50 mA g^-1 , among the reported cathode materials of metal oxides, metal chalcogenides, and polyanion-type compounds for RMBs. Notably, an impressive long-term cycling performance with a stable capacity of 111 mAh g^-1 at 1 C (560 mA g^-1 ) is achieved over 1000 cycles. The results of the present study offer an avenue for designing high-performance cathode materials for RMBs and other multivalent batteries.