“…Compared to TMO-based electrodes, TMS-based electrodes possess their own beneficial properties including their relatively small volume change, superior reversibility, and higher electrical conductivity because of proportionally-weaker M–S ionic bonds relative to their M–O counterparts, which enables enhanced rechargeable battery performance [7]. Among the TMS-based anode materials, cuprous sulfide (Cu x S) has been intensively investigated as a strong candidate electrode material for LIBs [8,9,10,11,12,13,14,15,16,17] and SIBs [3,7,18,19], owing to its unique properties of high theoretical capacity (~560 mAh/g for CuS and 337 mAh/g for Cu 2 S), low cost, the environmental harmlessness of sulfur, and good electrical conductivity (10 −3 S/cm) [7,20]. Although the Cu x S-based electrodes have been extensively studied, they have posed some major issues including [3,7,18,19]: (1) irreversible conversion reaction between Cu x S and the Li + /Na + ion, which induces a large volume variation of the Cu x S-based electrodes during prolonged cycling, bringing about corruption of structural integrity and capacity decay; (2) dissolution of sodium sulfide (Na x S) into electrolytes during cycling, causing the loss of active materials.…”