CuS-based composite for high-performance magnesium storage with a clarified charge-discharge mechanism

Rechargeable magnesium batteries (rMBs) are regarded as an alternative to lithium -ion batteries but are hindered by low cycling stability and sluggish kinetics at present. Herein, we report a sandwichstructured CuS/hNCNC@rGO cathode for rMBs by immobilizing CuS nanoparticles on the hierarchical nitrogen -doped carbon nanocages (hNCNCs) followed by wrapping the reduced graphene oxide (rGO). The charge/discharge mechanism is established based on the unique mixed -valence CuS double -salt structure, i.e., Cu 2+ S 2 2- , Cu + 2 S 2- , which was neglected in the previous studies of CuS-based rMBs. The cathode achieves a high reversible specific capacity of 285 mAh g - 1 at 100 mA g - 1 , an outstanding rate capability of 158 mAh g - 1 at 1,000 mA g - 1 , and ultralong cycling stability at room temperature, superior to most reported cathode materials to date. This study provides a fundamental understanding on the Mg storage mechanism of CuS and suggests a promising strategy for constructing high-performance conversion -type cathodes for rMBs.