Acetate-based Electrolytes for Aqueous Zinc-ion Batteries: An Investigation of the Zinc Anode
Aqueous zinc (Zn) batteries are attractive for grid-scale storage because they combine low cost, intrinsic safety, and high Zn capacity, but their deployment is limited by water’s narrow electrochemical stability window, parasitic gas evolution, and poor Zn utilization in conventional alkaline electrolytes. This dissertation investigates acetate-based aqueous electrolytes—both highly concentrated “water-in-salt” (WiSE) formulations and pH-regulated dilute solutions—as a chemically tunable platform to expand electrochemical windows, suppress hydrogen/oxygen evolution, and approach practical Zn utilization under lean-electrolyte conditions. Using a combination of molecular dynamics simulations, pulsed-field-gradient NMR, and rotating-disk-electrode electrochemistry, I first show how increasing KOAc concentration from 5 m to 27 m transforms the solvation environment into an ion-coordinated network that dramatically slows HER/OER kinetics and yields working electrochemical windows exceeding 3 V vs Zn on inert collectors. Chronopotentiometric window measurements across Au, SS316L, CRS, Ni, and Ti establish that this apparent stability is fundamentally kinetic and interphase-controlled rather than a thermodynamic “water-activity” effect, debunking a common WiSE narrative. I then demonstrate that, despite its wide window, 27 m KOAc WiSE fails at practical current densities and areal capacities due to the formation of a dehydrated acetate-based solid–electrolyte interphase that blocks Zn electrostripping in compact cells. Motivated by this failure mode, I develop a pH-regulated 5 m KOAc electrolyte containing ~4 vol% acetic acid that suppresses ZnO/ZHA passivation, enabling reproducible single-discharge Zn utilizations of ~80% at 5 mA cm⁻² with metallic Zn redeposition on the counter electrode. Finally, I evaluate acetate electrolytes under commercially relevant lean-electrolyte conditions (~0.0066 mL mAh⁻¹), showing that performance becomes limited by Zn redistribution and morphology rather than gassing alone, and that foil vs mesh/powder architectures strongly influence overpotential and mass balance. Collectively, these results yield a mechanistic design map linking concentration, pH, collector choice, and morphology, and provide practical guidance for selecting between concentrated WiSE and dilute, pH-regulated acetate regimes in next-generation aqueous Zn batteries.
Batteries, zinc, acetate, water-in-salt, electrolyte, Other Chemical Engineering, Thermodynamics
City University of New York - City College
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