Eutectic Electrolytes Composed of Li Salt and Sulfones

Sulfone-based highly concentrated electrolytes are promising electrolytes for high-voltage Li-ion batteries (LIBs), owing to the high thermal and oxidative stabilities of sulfones. In addition, highly concentrated Li salt/sulfone electrolytes exhibit unique Li + ion hopping/exchange conduction mechanism and high Li + ion transference number (>0.6). 1,2 However, the application of these electrolytes at low temperatures is limited due to the precipitation of a stable crystalline solvate. In this study, the applicability of ternary mixtures of Li salt, sulfolane (SL), and dimethyl sulfone (DMS) as LIB electrolytes was assessed. Due to the increased entropy of mixing, the crystallization of the solvates was suppressed in the ternary electrolytes, resulting in a wide temperature range of liquid sate of the electrolytes. 3 In the ternary electrolytes, the network structures of Li + –sulfone–Li + and Li + –anion–Li + were formed, and Li + ion dynamically exchanges sulfones and anions and diffuses more rapidly than these ligands, resulting in a relatively high Li + transference number. Highly reversible charge–discharge behaviors of the LiCoO 2 and graphite electrodes were attained using the ternary electrolyte. Despite the lower ionic conductivity of the sulfone-based electrolyte, the rate capability of the Li/LiCoO 2 cell with the ternary electrolyte was comparable to that in a conventional carbonate-based electrolytes. Acknowledgements This study was partially supported by the JSPS KAKENHI (Grant No. JP19H05813 and JP22H00340). References K. Dokko et. al., J. Phys. Chem. B 2018, 122, 10736. Y. Ugata et. al., J. Phys. Chem. B 2021, 125, 6600. Y. Ugata et. al., J. Phys. Chem. C 2022, 126, 10024.