Cell-nucleus structured electrolyte for low-temperature aqueous zinc batteries

Abstract

Rechargeable aqueous zinc (Zn) batteries hold great promise for large-scale energy storage, but their implementation is plagued by poor Zn reversibility and unsatisfactory low-temperature performance. Herein, we design a cell-nucleus structured electrolyte by introducing low-polarity 1,2-dimethoxyethane (DME) into dilute 1 M zinc trifluoromethanesulfonate (Zn(OTf)2) aqueous solution, which features an OTf−-rich Zn2+-primary solvation sheath (PSS, inner nucleus) and the DME-modulated Zn2+-outer solvation sheath (outer layer). We find that DME additives with a low dosage do not participate in the Zn2+-PSS but reinforce the Zn-OTf− coordination, which guarantees good reaction kinetics under ultralow temperatures. Moreover, DME breaks the original H-bonding network of H2O, depressing the freezing point of electrolyte to −52.4 °C. Such a cell-nucleus-solvation structure suppresses the H2O-induced side reactions and forms an anion-derived solid electrolyte interphase on Zn and can be readily extended to 1,2-diethoxyethane. The as-designed electrolyte enables the Zn electrode deep cycling stability over 3500 h with a high depth-of-discharge of 51.3% and endows the Zn||V2O5 full battery with stable cycling over 1000 cycles at −40 °C. This work would inspire the solvation structure design for low-temperature aqueous batteries.