Cu7S4 superionic with liquid-like mobility of copper ions for high-performance room-temperature rechargeable magnesium batteries

Rechargeable magnesium batteries (RMBs) are promising energy storage systems due to their high volumetric capacity, good safety, and abundant resources. However, it is still a great challenge to develop high-performance cathode materials for RMBs owing to the strong Coulombic interaction between the highly polarized Mg2+ and lattice anions of hosts. Herein, Cu7S4 superionic nanoparticles are prepared by in situ reduction method and used as a durable cathode material for RMBs. The small size of Cu7S4 is beneficial for the full contact between active materials and electrolytes and meanwhile greatly shortens Mg2+ diffusion length, leading to rapid kinetics of Mg2+ participation in electrochemical reaction. Moreover, the high mobility of copper ion in Cu7S4 superionic can enhance the capacitive contribution, improving the rate and long-term performance. Benefiting from these advantages, at room temperature, Cu7S4 superionic cathode delivers high reversible capacity of ∼211.8 mAh/g at 100 mA/g, high rate capability with the capacity up to 134 mAh/g at 500 mA/g, and a long cycling lifespan with initial capacity retention of 71.6% after 500 cycles at 500 mA/g. This work offers an avenue for developing high-performance cathode materials for RMBs.