Copper Activation Enabling Reversible Aqueous Cu-ZnS Battery Chemistry

The aqueous metal-sulfide batteries (AMSBs) have attracted research interest due to their high capacity, environmentally friendly qualities, and the accessibility of raw materials. However, the design strategies for metal-sulfide cathode have rarely been reported. Here, the copper-activated sphalerite in which Zn²⁺ is substituted by Cu²⁺ through ion exchange has been introduced for the first time as cathode for aqueous Cu/ZnS batteries. After sphalerite transformed to CuS, a two-step conversion of CuS→Cu₇ S₄ →Cu₂ S storage mechanism has been proposed. At 0.7 A g^-1 current density, the capacity can reach 532.4 mAh g^-1 after 100 cycles. When cycled once at a current density of 35 mA g^-1 , the initial reversible capacity can reach 461 mAh g^-1 under 1 A g^-1 . Furthermore, the assembled Zn//ZnS hybrid ion cell delivers an energy of up to 460 Wh kg^-1 , which is better than for many AMSBs.