Journal
ENERGY STORAGE MATERIALS
Volume 45, Issue -, Pages 696-703Publisher
ELSEVIER
DOI: 10.1016/j.ensm.2021.12.016
Keywords
SAXS; WAXS; MD; WIEs
Funding
- Joint Center for Energy Storage Research
- Energy Innovation Hub
- U.S. Department of Energy , Office of Science, Basic Energy Sciences [AC02- 06CH11357]
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In this study, the solvation structures of a series of imide-based lithium salt aqueous solutions were investigated using SAXS/WAXS and MD simulation techniques. Two competing structures were found, and the anion network played a crucial role in obtaining a stable and enlarged electrochemical window.
Water-in-salt electrolyte (WISE) series have been studied for lithium-ion batteries and supercapacitor applications, but so far, most of the focus has been on the LiTFSI salt-based systems. Herein, we used small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) and molecular dynamics (MD) simulation to investigate the solvation structure of a series of lithium salts with four different symmetric anions: (bis(fluoro sulfonyl)imide (FSI), bis(trifluoromethane sulfonyl)imide (TFSI), bis(pentafluoroethane sulfonyl) imide (BETI) and bis(nonafluorobutane sulfonyl)imide (BNTI)), which have similar parent structures but different lengths of the fluorocarbon chains. Two competing structures were found in the four lithium salts aqueous solutions: anion solvated structure and anion network. The anion network plays a crucial role in obtaining a stable and enlarged electrochemical window. The d spacing of the anion solvated structure follows a linear correlation with the number of carbons in the fluorocarbon chains and an exponential correlation with the concentrations. We also observed that the transition from one structure to another is predominantly controlled by the salt volume fraction for all imide-based aqueous solutions. This work provides a systematic study of the atomistic scale structures of a series of imide-based lithium salt aqueous solutions that could extend the knowledge of WIS electrolytes.
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