Bifunctional electrolyte regulation towards low-temperature and high-stability Zn-ion hybrid capacitor

Aqueous Zinc-based energy storage devices are considered as one of the potential candidates in future power technologies . Nevertheless, poor low temperature performance and uncontrollable Zn dendrite growth lead to the limited energy storage capability. Herein, an anti-hydrolysis, cold-resistant, economical, safe, and environmentally friendly electrolyte is developed by utilizing water, ethylene glycol (EG), and ZnCl 2 with high ionic conductivity (7.9 mS cm −1 in glass fiber membrane at −20 °C). The spectra data and DFT calculations show the competitive coordination of EG and Cl - to induce a unique solvation configuration of Zn 2+ , conducive to effectively inhibiting the hydrolysis of Zn 2+ , suppressing the dendrite growth, and broadening the working voltage range and temperature range of ZnCl 2 electrolyte. The isotope tracing data confirm that Cl - could effectively destroy the ZnO passivation film, promoting the formation of Zn nuclei and improving its reaction activity. Compared to the corresponding ZnSO 4 electrolyte, the Cu/Zn half-cell with the ZnCl 2 electrolyte exhibits a stable cycle life of more than 1600 h at −20 °C, even at the current density of 5 mA cm −2 . The assembled Zn-ion hybrid capacitor possesses an average capacity of 42.68 mA h g −1 under −20 °C at a current density of 5 A g −1 , 3.5 times than that of the modified ZnSO 4 electrolyte. Our work proposes a new approach for optimizing aqueous electrolytes to meet low temperature energy storage applications .