Solvent-in-Salt electrolyte (SISE) is a new class electrolyte with splendid performance emerging in recent years. Among them, water-in-salt electrolytes have been extensively studied both in battery performance and solvation structures. These studies have significant implications for the study of SISE. Nonetheless, water-based electrolytes are not sufficient to represent all Solvent-in-Salt electrolytes. Introducing new groups in the solvent may lead to entirely different properties. To further explore the cornerstone of SISE, methanol, the simplest saturated monohydric alcohol, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), known for being one of the lowest lattice energy salts, were chosen for this proposed research. Herein, we are here to utilize advanced characterization methods, namely Small-Angle X-ray Scattering/Wide-Angle X-ray Scattering (SAXS/WAXS) and Fourier-Transform Infrared Spectroscopy (FTIR). From SAXS/WAXS, TFSI- solvation structure can be observed in low concentrations (up to 3 mmol) and gradually became unobservable as the concentration increased. Meantime, the TFSI- networks were formed at very low concentrations. Unlike the Water-in-LiTFSI system, the TFSI- networks barely change regardless of the concentration. Distances among the TFSI- anions within the network became larger initially, then the distances among them got closer with higher concentration. In addition to the change of TFSI- anions, transformations in hydroxyl bonding can be characterized by FTIR. There is a notable blue shift of hydroxy peak frequency. A new peak formed at a higher wavenumber indicated the hydroxy-hydroxyl hydrogen bonds in methanol broken when the TFSI- anions were present and formed a new bond with TFSI- anions to contribute to the TFSI- network.

Deep understanding of methanol-in-slat electrolyte by SAXS/WAXS and FTIR

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