A Low-Cost and Green Zinc-Iron Battery Achieved by Ethaline Deep Eutectic Solvent

Deep eutectic solvents (DESs) were considered as a potential electrolyte because of their low price, harmless to environment and wider electrochemical window potential compared to water. In this work, Fe(III)/Fe(II) and Zn(II)/Zn redox couples were used as the positive and negative active materials, respectively, in a DES system using choline chloride and ethylene glycol in a molar ratio of 1 : 2 (ethaline). The possible working mechanism of the battery was studied by cyclic voltammetry, spectroscopic and simulation methods. The effects of different temperatures, concentrations of zinc ions in the anolyte and current densities on battery performance were evaluated. The results showed that the designed zinc-iron battery should preferably be operated at a current density of 0.5 mA cm^-2 and the temperature of 313~323 K, which will improve the energy efficiency and maintain a high coulombic efficiency. The variation of cycle performance test presents a different pattern from the usual batteries, which is due to the effect of RO^- group. At 313 K and 0.5 mA cm^-2, the coulombic efficiency increases from 14.1 % to 100.2 % after 46 cycles, and then remains at about 100 % during the rest 54 cycles, which demonstrates a good cycle stability of DES-based zinc-iron battery.