Ionometallurgical Step‐Electrodeposition of Zinc and Lead and its Application in a Cycling‐Stable High‐Voltage Zinc‐Graphite Battery

Abstract Ionometallurgy is a new development aiming at the sustainable low‐temperature conversion of naturally occurring metal ores and minerals to their metals or valuable chemicals in ionic liquids (ILs) or deep eutectic solvents. The IL betainium bis((trifluoromethyl)sulfonyl)imide, [Hbet][NTf₂], is especially suited for this process due to its redox‐stability and specific‐functionalization. The potentiostatic electrodeposition of zinc and lead starting directly from ZnO and PbO, which dissolve in [Hbet][NTf₂] in high concentrations is reported. The initial reduction potentials of zinc(II) and lead(II) are about −1.5 and −1.0 V, respectively. The ionic conductivity of the solution of ZnO in [Hbet][NTf₂] is measured and the effect of various temperatures and potentials on the morphology of the deposited material is explored. The IL proves to be stable under the chosen conditions. From IL‐solutions, where ZnO, PbO, and MgO have been dissolved, metallic Zn and Pb are deposited under potentiostatic control either consecutively by step‐electrodeposition or together in a co‐electrodeposition. Using the method, Zn is also deposited on 3D copper foam and assembles into high‐voltage zinc‐graphite battery. It exhibits a working‐voltage up to 2.7 V, an output midpoint discharge‐voltage of up to 2.16 V, up to 98.6% capacity‐retention after 150 cycles, and good rate performance.