Optimization of acetamide based deep eutectic solvents with dual cations for high performance and low temperature-tolerant aqueous zinc ion batteries via tuning the ratio of co-solvents

In this work, a novel acetamide-based deep eutectic solvent (DES) with Zn2+/ Li+ dual ions is designed and its physicochemical properties are tuned by adjusting the co-solvents (water and acetonitrile). Furthermore, the interplay between electrolyte components is investigated by spectroscopic analyses and molecular dynamics calculations. The addition of acetonitrile facilitates the formation of solid electrolyte interphase (SEI) with organic/inorganic components on the zinc anode. The presence of SEI coating enhances Coulombic efficiency and cycling stability by inhibiting the parasitic reactions and dendrite formation in the anode. The advantages of using dual cations in DES are demonstrated by assembling Zn ion batteries (ZIB) with the composite of δ-MnO2 and reduced graphene oxide as the cathode. The study of electrode kinetics in hybrid DES electrolytes suggests that Zn2+ and Li+ ions are responsible for battery-like and pseudocapacitive behavior of δ-MnO2 electrodes, respectively. With these merits, ZIB with the cutoff voltage of 2 V delivers a high cell capacity of 208 mAh g-1 at 0.1 Ag-1 and achieves 91% capacity retention after 1500 cycles at 2 Ag-1. More importantly, ZIB with hybrid DES is stably operated at the temperature of -20 °C, which is impossibly achieved by ZIB with conventional aqueous electrolytes.