Highly Concentration Aqueous Electrolytes for Zinc Metal Batteries

Abstract

Aqueous zinc batteries (AZB) emerged as a promising technology for renewable and low-cost storage devices.[1] Zinc (Zn) metal features high abundance, intrinsic safety, low cost (~USD $2 kg-1) and high theoretical capacity (820 mA h g-1).[2,3] However, AZBs do suffer from low Coulombic efficiency, dendrite growth and parasitic hydrogen evolution reaction (HER), which restrict their practical applications.[4] To combat this problem, highly concentrated electrolytes (HCEs) are employed to improve the cycling stability of AZBs.[5] In this work, we demonstrate that aqueous HCEs based on Zn and organic salts are a very effective way to address these issues. Aqueous eutectic electrolytes were obtained by simply optimizing the salt ratio, as evidenced by the low liquid-to-solid transition temperature. These unique HCEs feature a wider electrochemical stability window and an improved ionic conductivity. Additionally, the high-density of Zn cations near the electrode surface results in reversible and stable Zn electrodeposition - with relatively low overpotentials in comparison to other reported hybrid Zn electrolytes. Thus, this work presents an efficient, economically attractive and simple approach for the development of HCEs for practical applications of AZBs.