Triggering Zn2+ Unsaturated Hydration Structure via Hydrated Salt Electrolyte for High Voltage and Cycling Stable Rechargeable Aqueous Zn Battery

Ocean-like free water in conventional aqueous electrolytes limits operating voltage and induces parasitic reactions in rechargeable Zn metal batteries (AZMBs). Herein, a hydrated salt electrolyte (HSE), which suppresses the presence of free water and triggers an unsaturated hydration structure (Zn(H2O)(n)(2+), n < 6), is proposed to circumvent the parasitic reactions occurring on the zinc anode and cathode and elevate the decomposition voltage (to approximate to 2.55 V vs Zn2+/Zn). In a full cell with a transition metal oxide cathode, the parasitic reactions of dissolution and diffusion of discharge products are inhibited, and high discharge capacity retention above 80% at 500 mA g(-1) and super-stable Coulombic efficiency (average value approximate to 99.97%) are delivered. Moreover, when applied in a high-voltage AZMB with zinc hexacyanoferrate cathode, the full cell yields an average output voltage above 1.8 V together with a 132.3 Wh kg(-1) energy density at 10 mA g(-1) and 1.78 V output voltage combining high energy density and power density (88.5 Wh kg(-1)/106.2 W kg(-1)). The exceptional electrochemical performance of HSE indicates rosy prospects for the prevention of parasitic reactions in AZMBs, a key step on the road to further commercialization of AZMBs.