A combined spectroscopic and scattering workflow has shown how ionic liquids reorganize water and zinc ion solvation in aqueous electrolytes, offering a broader route to designing high-voltage zinc batteries.
In the study, researchers screened 25 combinations of five common zinc salts and five commercial ionic liquids, aiming to extend the water-in-salt strategy beyond the small set of salts soluble enough to suppress water activity. Sixteen combinations formed stable single-phase electrolytes at low water content, and the team selected one zinc triflimide electrolyte containing an imidazolium-based ionic liquid for detailed structural and electrochemical analysis.
“Ionic liquids are unique because they can function both as a salt and as a solvent,” explained Le Yu, co-first and corresponding author, in a recent press release. “This dual role allows us to create stable, homogeneous electrolytes even with zinc salts that are normally poorly soluble in water.”
Rather than relying on a single structural probe, the team used complementary spectroscopic and scattering methods to build a multiscale picture of the electrolyte. Infrared spectroscopy and proton nuclear magnetic resonance tracked changes in water’s hydrogen-bonding environment, while Raman spectroscopy and electrospray ionization mass spectrometry probed interactions between zinc ions (Zn²⁺) and bis(trifluoromethanesulfonyl)imide (TFSI⁻) anions. Synchrotron small-angle X-ray scattering then added information on longer-range molecular organization within the concentrated liquid.
Together, the measurements showed that reducing the water content gradually displaced water from the primary Zn²⁺ solvation sheath. In the optimized low-water electrolyte, TFSI⁻ anions instead dominated the zinc ion’s local environment, while water became more closely associated with the ionic liquid components. That anion-rich solvation structure differed from conventional dilute and water-in-salt electrolytes, where water remains more directly involved in metal-ion solvation.
In electrochemical tests, the optimized electrolyte reached a reported 3.8 V stability window and supported long-term zinc cycling, linking the observed solvation structure to improved battery performance.
The researchers suggest that ionic-liquid components also contribute to a stable interphase on zinc, helping block water while allowing zinc ion transport. “Our approach moves electrolyte research from a trial-and-error process toward rational design,” added co-corresponding author Chaoji Chen. “By understanding exactly how molecules arrange themselves at different scales, we can more reliably achieve desired electrochemical properties.”
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