15-Crown-5 ether as efficient electrolyte additive for performance enhancement of aqueous Zn-ion batteries

Aqueous rechargeable Zn-ion batteries (ZIBs) have been regarded as a complement to LIBs due to their merits in terms of high safety, low cost, environmentally benignity, and long cycle life. However, the Zn metal anode suffers from corrosion and parasitic reactions in the aqueous electrolyte, which lead to growth of byproduct flakes and hydrogen gas evolution in the Zn platting/stripping process. Here, an organic additive, 15-crown-5 ether (15-CE-5), is added into the aqueous ZnSO4 electrolyte to improve the Zn anode performance by altering the Zn2+ solvation sheath. Other CE molecules such as 12-CE-4 and 18-CE-6 are also tested, while their efficacies are inferior compared to that of 15-CE-5. The optimal concentration of 15-CE-5 in the ZnSO4 electrolyte is found to be 2 wt%, which enables the best performance of Zn anode in either Zn||Zn symmetric cells or MnO2||Zn full cells. Using this modified electrolyte, the Zn||Zn symmetric cell exhibits a cycle life of 770 h when tested at 2 mA cm−2 and a set capacity of 2 mAh cm−2, and the MnO2||Zn full cell shows enhanced and stable capacity over 1000 cycles. The experimental results are elucidated by theoretical studies including molecule dynamics simulations and density functional theory calculations.