Charting Water-in-Natural-Salt (WiNS) Electrolytes. Part I: Effect of Anion’s Alkyl Tail Length
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Abstract
Water-in-natural-salt electrolytes offer a fluorine-free route to safe, high-voltage aqueous energy storage. We study a homologous series of potassium carboxylates at 20 m to show how anion amphiphilicity governs structure, transport, and stability. Small-angle X-ray scattering reveals a pre-peak shifting to lower q from formate to butyrate, consistent with a longer modulation length and a distorted-L3 morphology. Molecular dynamics confirms the pre-peak arises from concentration–concentration fluctuations that co-localize water and K⁺, with anticorrelated anions. Water is predominantly interfacial; cluster analysis shows decreasing average size from formate to acetate, correlating with a wider electrochemical window. Conductivity decreases and Vogel temperatures increase along the series, linking transport to medium-range segregation. A mid-q shoulder emerges in SAXS for longer tails, marking local charge alternation. Tail length thus controls modulation length, water clustering, and the trade-off between stability and mobility, offering a design rule for fluorine-free aqueous electrolytes.
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Abstract
Water-in-natural-salt electrolytes offer a fluorine-free route to safe, high-voltage aqueous energy storage. We study a homologous series of potassium carboxylates at 20 m to show how anion amphiphilicity governs structure, transport, and stability. Small-angle X-ray scattering reveals a pre-peak shifting to lower q from formate to butyrate, consistent with a longer modulation length and a distorted-L3 morphology. Molecular dynamics confirms the pre-peak arises from concentration–concentration fluctuations that co-localize water and K⁺, with anticorrelated anions. Water is predominantly interfacial; cluster analysis shows decreasing average size from formate to acetate, correlating with a wider electrochemical window. Conductivity decreases and Vogel temperatures increase along the series, linking transport to medium-range segregation. A mid-q shoulder emerges in SAXS for longer tails, marking local charge alternation. Tail length thus controls modulation length, water clustering, and the trade-off between stability and mobility, offering a design rule for fluorine-free aqueous electrolytes.
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ENERGY & ENVIRONMENTAL MATERIALS
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Alessandra Del Giudice, Laura Hildebrandt, Jin Han, et al.
Charting Water-in-Natural-Salt (WiNS) Electrolytes. Part I: Effect of Anion’s Alkyl Tail Length. Authorea. 06 November 2025.
DOI: https://doi.org/10.22541/au.176244853.32233693/v1
DOI: https://doi.org/10.22541/au.176244853.32233693/v1
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