Spectroscopic Analysis of Electrolyte Solutions with Diverse Metal Ions for Aqueous Zinc-Ion Batteries

Abstract

The water-in-salt method, recognized for regulating metal ion solvation structure, garners attention in secondary batteries for its potential to broaden the electrolyte's operational range and reduce side reactions. However, the understanding of how anion size variations impact metal ion solvation structure remains limited. This study addresses the gap by employing mixed electrolytes with diverse anion sizes, investigating the effects of electrolyte concentration and anion size on the solvation structure of zinc cations crucial in electrochemical reactions. Various analytical techniques, including FT-IR, Raman, and NMR spectroscopy, are utilized. Mixed electrolytes are formulated by dissolving ZnCl2 and Zn (NO3)2 in water (1.0 mol kg‒1), with the addition of LiCl and LiNO3 (0.1 to 19.0 mol kg‒1). FT-IR and Raman analyses reveal weakened hydrogen bonds with increasing electrolyte concentration. Elevated concentration disrupts bonds between Li+ ions and water molecules, resulting in alterations in solvation structure. NMR and FT-IR spectra exhibit distinct behaviors, suggesting influences from molecular bonding structure and anion size, intricately linked to the specific salt used in electrolyte preparation.