Solvent Effects on Li⁺ Insertion Kinetics at LiMn₂O₄ in LiN(SO₂CF₃)₂ Electrolytes with H₂O, THF, and n-Dibutyl Ether

抄録

In lithium-ion batteries, the desolvation of Li⁺ is widely regarded as the activation barrier for interfacial charge-transfer reactions; however, the governing factors remain unclear. This study investigated the effect of solvent properties on charge-transfer kinetics for a Li_1.05Mn_1.95O₄ thin-film electrode using lithium bis(trifluoromethanesulfonyl)amide-based electrolytes with H₂O, tetrahydrofuran, and n-dibutyl ether. Electrochemical impedance spectroscopy revealed that the concentrated aqueous electrolyte exhibited a significantly lower charge-transfer resistance (R_ct) than the monoether-based systems, contrary to expectations based on viscosity. Analysis of Li⁺ activity indicated that the high activity in the concentrated aqueous system contributed to the reduced R_ct; however, comparisons using 1 mol dm⁻³ (1 M) electrolytes showed that neither viscosity nor Li⁺ activity alone could explain the observed trends. These results suggest that dynamic solvent properties play a critical role, and that the rapid molecular reorientation of water facilitates faster solvation and desolvation of Li⁺ at the interface.