Anionic Effects on\nLi-Ion Transport and Electrochemical\nProperties of High-Concentration Li Salt/Sulfone Electrolytes

High-concentration electrolytes (HCEs) comprising Li\nsalts and\nsulfones are regarded as promising materials for boosting the thermal\nstability, energy density, and rate capability of Li batteries. In\nthis study, to obtain a deeper understanding of the correlation between\nelectrolyte composition and physicochemical properties, the anionic\neffects in binary mixtures of various Li salts and 3-methylsulfolane\n(MSL) were systematically studied. The ionic conductivity of the Li\nsalt/MSL mixtures increased as the Lewis basicity of the anions becomes\nweaker. In HCEs with a molar ratio of Li salt/MSL = 1/4, the fraction\nof free MSL decreased as the Lewis basicity of the anions weakened,\nleading to a higher activity of Li<sup>+</sup>. The Li ion transference\nnumber in the HCEs decreased with weakening of the Lewis basicity\nof the anion. Electrochemical impedance measurements revealed that\nthe charge-transfer kinetics of the LiCoO<sub>2</sub> and Li metal\nelectrodes in the HCEs were enhanced using weaker Lewis basic anions.\nOur findings reveal that the utilization of Li salts with weak Lewis\nbasic anions is essential for enhancing the power density of lithium\nbatteries with HCEs. This work provides insights into the functions\nof anions in sulfone-based HCEs and the correlation between the HCE\ncomposition and battery performance, which may be helpful for the\ndesign of electrolytes of advanced lithium batteries.