Effect of Antisolvent Additives in Aqueous Zinc Sulfate Electrolytes for Zinc Metal Anodes: The Case of Acetonitrile
Authors: Ilic Stefan , Counihan Michael , Lavan Sydney Nicole , Yang Yingjie , Jiang Yinke , Antonio Emma N. , Zhang Yong , Maginn Edward , Toney Michael F , Klie Robert F. , Connell Justin G. , Tepavcevic Sanja 
Published: December 2024

Aqueous zinc-ion batteries (ZIBs) employing zinc metal anodes are gaining traction as batteries for moderate to long duration energy storage at scale. While ZIBs with near-neutral pH electrolytes are attractive for safety reasons, corrosion of the zinc metal anode through reaction with water limits battery efficiency. Much research in the past few years has focused on additives that decrease hydrogen evolution, but the precise mechanisms by which this takes place are often understudied and remain unclear. In this work, we study the role of an acetonitrile antisolvent additive in improving the performance of aqueous ZnSO4 electrolytes using experimental and computational techniques. First, results of several electronic and vibrational techniques show that, contrary to previous reports, ACN never displaces water in the first solvation shell of the [Zn(H2O)6]2+ ion and only acts as an anti-solvent in the highly-charged, hydrophilic ZnSO4 solution. Instead, double-layer capacitance measurements and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) experiments indicate that, rather than modifying bulk solvation, acetonitrile modifies the interfacial chemistry, likely by adsorbing onto the electrode surface, resulting in modified Zn deposition and HER kinetics. The interfacial adsorption of acetonitrile then impacts the evolution of deposit morphology over subsequent cycles by modifying zinc nucleation and slowing the ZHS formation rate, as demonstrated using scanning electron microscopy (SEM) imaging and elemental analysis (energy-dispersive spectroscopy, EDS) of copper working electrodes extracted after half-cell cycling experiments. Collectively, this work demonstrates the effectiveness of solvent additive systems in battery performance and durability and provides a new framework for future efforts to optimize ion transport and performance in ZIBs.

Reference:
1. S.Ilic; M. J. Counihan; S. N. Lavan; Y. Yang; Y. Jiang; D. Dhakal; J. Mars; E. N. Antonio; L. Kitsu Iglesias; T. T. Fister; Y. Zhang; E. J. Maginn; M. F. Toney; R. F. Klie; J. G. Connell, S. Tepavcevic; Role of Antisolvent Additives in Aqueous Zinc Sulfate Electrolytes for Zinc Metal Anodes: The Case of Acetonitrile, ACS Energy Lett., 2024, 9(1), 201-208 DOI:10.1021/acsenergylett.3c02504
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