Cation Solvation in Co-Solvent Doped Water-in-Salt Electrolytes

Water-in-salt electrolytes (WiSEs) are an exciting class of highly concentrated electrolyte. They have recently come to the forefront of battery research owing to their desirable properties: they can be safer, less expensive, and more environmentally friendly than traditional electrolytes currently used in state-of-the-art batteries. However, some hurdles remain before they become commonplace: namely, parasitic hydrogen evolution still limits their useable lifespan. One notable and highly scaleable way of mitigating this is to use an appropriate co-solvent. However, the mechanism of co-solvent action is still disputed. The aim of the experiment is to investigate the impact of the promising co-solvent candidate methyl urea on local and bulk structure in the archetypal WiSE formed of 20 molal lithium bistriflimide (NTf2) in water. We recently studied 20 molal lithium NTf2 in pure water only (manuscript in preparation) and we will draw comparison between these two cases. These results will have significant implications for the mechanism of co-solvation within WiSEs and will be key to the design of future batteries.

盐包水电解质（Water-in-salt electrolytes, WiSEs）是一类极具应用前景的高浓度电解质体系。近年来，因其相较于现有顶尖商用电池所使用的传统电解质更安全、成本更低廉且环境友好性更优，该体系已成为电池研究领域的前沿热点。然而，该体系实现规模化普及仍存在若干技术瓶颈：其中寄生析氢反应仍是制约其可用服役寿命的关键问题。一种可有效缓解该问题且适配工业化大规模生产的可行方案，是引入合适的共溶剂，但目前学界对于共溶剂的作用机制仍存在争议。本实验旨在探究极具潜力的共溶剂候选物——甲基尿素，对以20质量摩尔浓度双三氟甲磺酰亚胺锂（lithium bistriflimide, NTf₂）水溶液为原型的盐包水电解质的局域结构与整体体相结构的影响。本团队此前仅针对纯水中的20质量摩尔浓度双三氟甲磺酰亚胺锂体系开展过相关研究（稿件筹备中），本次实验将与前述研究结果进行对照分析。本研究结果将对阐明盐包水电解质体系内的共溶剂化作用机制具有重要理论价值，同时可为下一代高性能电池的设计开发提供关键支撑。