A long-life aqueous Zn battery enabled by simultaneous suppressing cathode dissolution and Zn dendrites via a novel water-in-deep eutectic solvent

Aqueous Zn metal batteries (ZMBs) are promising to provide high energy density and inherent safety at a low cost, which is a candidate for large-scale energy storage. However, the cycle life of ZMBs is challenged by the cathode dissolution and irreversible plating/stripping of Zn metal anode (ZMA). Herein, we report a novel deep eutectic solvent electrolyte, 30 m ZnCl2 + 15 m C5H14ClNO (choline chloride, ChCl), where ChCl restrains wa-ter's activity in both the bulk electrolyte and the Zn2+ solvation sheaths by coordinating with Zn2+. The presence of ChCl mitigates the cathode dissolution problem and eliminates the zinc dendrites of ZMBs. With this elec-trolyte, the vanadium oxide cathode, V2O5.0.41H2O, maintains a capacity of-305 mAh g-1 over 100 cycles at a harsh current density of 50 mA g-1 and-180 mAh g-1 over 1500 cycles at 500 mA g-1; the ZMA can be cycled up to 1600 h at a harsh current density of 0.2 mA cm-2, 950 h higher than 30 m ZnCl2, without dendrite for-mation. This study highlights the function of ChCl as a co-salt for ZnCl2 to facilitate high performance of ZMBs.

Automated summary

In this study, a novel deep eutectic solvent electrolyte containing choline chloride (ChCl) and ZnCl2 was developed to improve the cycle life of aqueous Zn metal batteries (ZMBs). ChCl coordinates with Zn2+ to reduce water activity and mitigate cathode dissolution and zinc dendrite formation. With this electrolyte, the vanadium oxide cathode maintains a high capacity over 100 cycles at a harsh current density, and the Zn metal anode can be cycled for a longer time without dendrite formation. The results highlight the importance of ChCl as a co-solvent for ZnCl2 in facilitating high performance of ZMBs.