Bi-Cation Electrolyte for a 1.7 V Aqueous Zn Ion Battery

Rechargeable aqueous zinc-ion batteries (ZIBs) are receiving increased attention because of their high safety and low cost. However, their practical application is plagued by their low energy density as a result of low output voltage and a narrow voltage window of aqueous electrolytes. Here, we explored a ZIB with a wider potential window using bication (1 M Al(CF₃SO₃)₃/1 M Zn(CF₃SO₃)₂) as the electrolyte and α-MnO₂ as the cathode, obtaining a discharge voltage of 1.7 V, ∼0.3 V higher than the value reported earlier. The resultant cell delivers a record high energy density of 448 W h kg^-1 (based on MnO₂ mass) and retains 100% capacity over 1000 cycles. The ion-storage mechanism and the role of Al³⁺ in enlarging the output voltage were elucidated. This research indicates the important role of using bications in improving the electrochemical performance of aqueous ZIBs, opening a new way to increase the energy density of aqueous energy storage devices.