Dynamic Proton-Coordination Equilibrium Enables Nonfreezing Ion Transport for Ultralow-Temperature Zinc Batteries.

Abstract

Hydrogel electrolytes (HEs) are promising for aqueous zinc batteries, yet suffer from freezing-induced loss of ionic transport and interfacial instability at subzero temperatures. Here we report a proton-mediated coordination equilibrium that enables nonfreezing Zn²⁺ transport in hydrogel electrolytes under ultralow-temperature conditions. By coupling phytic acid with zinc phytate, proton activity and Zn-O coordination are dynamically balanced, continuously reconstructing the local hydration environment to suppress hydrogen-bond ordering, stabilize bound water, and prevent water crystallization. Simultaneously, reversible coordination exchange sustains Zn²⁺ dissociation and migration through a hopping transport mechanism. At the Zn anode, proton-mediated interfacial evolution drives the formation of a ZnS/Zn₃(PO₄)₂-rich hybrid interphase that accelerates interfacial kinetics and suppresses degradation. Consequently, the optimized electrolyte achieves an ionic conductivity of 2.4 mS cm^{- 1} and an apparent Zn²⁺ transference number of 0.24 at -60°C, enabling Zn||Zn cells to cycle stably for over 3400 h and Zn||PANI full cells to retain 60.1% of their capacity after 4000 cycles at -60°C. These findings identify proton-mediated coordination equilibrium as a general mechanism for preserving ionic transport in frozen aqueous environments and provide a blueprint for low-temperature electrochemical energy storage.