High-Energy-Density Rechargeable Lithium-Nickel Chloride Aqueous Solution Batteries

High-energy-density rechargeable batteries with performance beyond that of lithium-ion batteries are required for next-generation electric vehicles. We propose a novel rechargeable battery with a lithium anode and a NiCl₂ aqueous cathode that is separated Li_1.4Al_0.4Ge_0.2Ti_1.4(PO₄)₃ as a water-stable lithium-ion-conducting solid electrolyte. The cell was discharged up to 93% of the theoretical cathode capacity at 0.5 mA cm^-2 and 25 °C. The calculated energy density, based on the weights of NiCl₂ and Li, and the average discharge voltage of 2.4 V at 0.5 mA cm^-2, was 852 Wh kg^-1, which is more than twice as high as that of conventional lithium-ion batteries. The cell was successfully cycled for 50 cycles without any degradation of the charge and discharge voltages at 0.5 mA cm^-2 and 25 °C for 5 h charge and 5 h discharge, where the utilization of NiCl₂ was 80%.