Abstract:
Zinc-ion batteries (ZIBs) are considered promising candidates for large-scale applications replacing lithium-ion batteries (LIBs). ZIBs having aqueous electrolytes have many advantages being low-cost, safe, and eco-friendly. However, a number of shortcomings hinder their application e.g. self-corrosion, hydrogen evolution, and Zn dendrite-formation. To mitigate these issues, nonaqueous electrolytes i.e. organic-based and room temperature ionic liquid electrolytes have been proposed. Nevertheless, nonaqueous electrolytes are yet to be elucidated. Herein, this work identifies nonaqueous electrolytes' state of the art and develops a new nonaqueous electrolyte system for ZIBs based on a manganese dioxide (MnO2) cathode. For this purpose, Zn chemistry in nonaqueous electrolytes is reviewed and described. In addition, gaps in this research area are highlighted. In brief, the review suggests that nonaqueous electrolytes can effectively suppress the above-mentioned issues allowing the use of high voltage host material and providing a reversible/stable Zn chemistry (~100% coulombic efficiency). Furthermore, this work demonstrates the use of deep eutectic electrolytes, namely chloride-urea (ChCl-urea) and organic electrolytes such as dimethyl sulfoxide (DMSO) in ZIBs based on MnO2 cathode for the first time. Battery testing results indicate that Zn/MnO2 cell having ChCl-urea revealed the highest discharge capacity of 170 mAh/g at 50 mA/g and a capacity fading rate of 0.7 % per cycle. Moreover, Zn/MnO2 and DMSO can cycle up to 1,000 cycles yielding capacity retention of 60 % (0.047 % per cycle) and the highest capacity of 159 mAh/g at 50 mA/g. In addition, both ChCl-urea and DMSO electrolytes are seen to be dendrite-free and gas-production-free. Overall, nonaqueous electrolytes as well as our proposed electrolytes indicate good promise for ZIBs and pave the way towards practical use in the future.
