Unraveling the exceptional kinetics of Zn||organic batteries in hydrated deep eutectic solution

Abstract

Intuitively, the solvation structure featuring stronger interacted sheath in deep eutectic solution (DES) electrolyte would result in sluggish interfacial charge transfer and intense polarization, which obstructs its practical application in emerging Zn based batteries. Unexpectedly, here we discover a Zn||organic battery with exceptional kinetics properties enabled by a hydrated DES electrolyte, which can render higher discharge capacity, smaller voltage polarization, and faster kinetics of charge transfer in comparison with conventional aqueous 3 M ZnCl₂ electrolyte, though its viscosity is two orders of magnitude higher than the latter. The improved kinetics of charge transfer and ion diffusion is demonstrated to originate from the local electron structure regulation of cathode in hydrated DES electrolyte. Furthermore, the DES electrolyte has also been shown to restrict parasitic reaction associated with active water by preferential urea-molecular adsorption on Zn surface and stronger water trapping in solvation structure, giving rise to long-term stable dendrite-free Zn plating/stripping. This work provides a new rationale for understanding electrochemical behaviors of organic cathodes in DES electrolyte, which is conducive to the development of high-performance Zn||organic batteries.