Interfacial Nanoscale Structuring in Water-in-Salt Electrolytes: Nanoheterogeneity and Potential-Dependent Layering

Le résumé fourni par la source

Water-in-salt electrolytes (WiSE) have emerged as promising alternatives to conventional electrolytes for next-generation energy storage, offering enhanced safety and electrochemical stability. Despite their growing significance, a detailed understanding of their interfacial nanoscale structuring remains limited. This study integrates insights from electrochemical measurements, atomic force microscopy (AFM), surface forces apparatus (SFA) and vibrational spectroscopy to explore the interfacial behavior, nanoheterogeneity, and the impact of multivalent cations in LiTFSI-based WiSE. The interfacial double-layer structure of LiTFSI WiSE exhibits potential-dependent layering behavior, as characterized through surface-enhanced infrared absorption spectroscopy (SEIRAS) and AFM. Our findings reveal that at positive potentials, the double layer is dominated by thick layers (~6.5 Å) associated with [Li(H 2 O) x ] + ([TFSI] − ) y ion pairs, whereas at negative potentials, thinner layers (~3.0 Å) correspond to [Li(H 2 O) x ] + alone. SEIRAS confirms these structural transitions, showing an enrichment of [TFSI] − at positive potentials and [Li(H 2 O) x ] + at negative potentials. Additionally, the introduction of multivalent cations (Zn 2+ , Mg 2+ , Ca 2+ , Al 3+ ) into LiTFSI WiSE significantly alters the electrical double layer. The nanoheterogeneity of LiTFSI WiSE is strongly influenced by both concentration and proximity to charged interfaces. Through surface forces measurements with SFA and AFM, we identify concentration-dependent structural transitions, revealing distinct nanodomains that grow in size with increasing salt concentration and are influenced by the proximity of the mica surface. These findings establish a framework for tailoring WiSE properties by modulating concentration-dependent nanoscale organization, offering critical insights for electrolyte design in energy storage applications.

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