Deciphering the energy storage mechanism of CoS nanowire arrays for High-Energy aqueous copper-ion batteries.

Transition metal sulfide (TMs) offers ultra-high specific capacity through multi-electron transfer, showing promise for aqueous batteries. However, the poor cycling performance and the uncleared energy storage mechanism are restricted from further development. Herein, CoS nanowire arrays grown on carbon cloth (CoS/CC) are proposed as binder-free and self-supporting electrodes for aqueous copper-ion batteries. The energy storage mechanism is clarified by a series of ex-situ tests: a multi-electron electrode reaction through a three-step reaction of CoS → CuS → CuS → CuS. Electrochemical results suggest that the CoS/CC cathode exhibits excellent long cycle stability (capacity retention of 99.7 % after 1000 cycles at 10 A/g) along with high specific capacity (762.3 mAh g at 1 A/g). The carbon cloth with stable three-dimensional (3D) conductive structure can not only offer high-speed pathways to promote the transfer of electrons but also inhibit the volume change. Meanwhile, CoS nanowire arrays with high surface-to-volume ratios can improve wettability of electrolyte and promote redox reactions. Furthermore, an advanced Zn-CoS/CC hybrid ion aqueous battery reveals an energy density of 724 Wh kg and an output voltage of 1.24 V, providing a promising strategy for the establishment of transition metal sulfide cathode in high-energy aqueous batteries.