Localized anion-rich solvation structure in low-concentration electrolytes enabled by non-coordinating chaotrope for deep-cycling zinc metal batteries

Abstract

Extending the lifespan of aqueous zinc (Zn) batteries (AZBs) under deep-cycling conditions is critical for their practical applications, but it remains a great challenge because of the irreversible issues of Zn anodes involving H2 evolution, Zn dendrite growth, and Zn corrosion. Herein, we report a localized high-concentration electrolyte (LHCE) by introducing a non-Zn2+-coordinating chaotropic additive (tetramethylurea, TM-Urea) in a non-concentrated aqueous electrolyte (2 M Zn(CF3SO3)2), which enables deep-cycling AZBs. Mechanistic studies reveal that the TM-Urea addition promotes a localized anion-rich Zn2+-solvation structure, which induces in situ formation of an anion-derived solid-electrolyte interphase (SEI) to stabilize Zn electrode. Moreover, the TM-Urea features preferred adsorption on Zn, disrupts the water’s original H-bond network, and creates an H2O-poor electrical double-layer, which homogenizes Zn electrodeposition and suppresses water-induced parasitic reactions. Consequently, the optimized electrolyte (0.3 TM-Urea) enables the Zn anode to achieve long-term cycling life over 3500 h (10 mA cm−2 and 10 mAh cm−2) and deep-cycling stability under 25 mAh cm−2 with 85.5% Zn utilization rate. In addition, the Zn||V2O5·nH2O full batteries with the 0.3 TM-Urea electrolyte exhibits 76.8% capacity retention over 4000 cycles at 2 A g−1 and stable operation under 5.1 mAh cm−2, showing great promise for practical applications.