We report ultrafast charge transfer along the Li-ion pathway via a dielectric layer at the electrolyte−electrode interface. The rate capabilities of dielectric-modified cathodes were evaluated as a function of the combination of electrolyte solvents and dielectric layers having various dielectric constants, εr. The high-rate capability was enhanced when the loaded dielectric layer's εr was close to that of the electrolyte solvent. Density functional theory molecular dynamics calculations and atomic force microscope force measurements confirmed that the activation energies related to Li+ adsorption and desolvation were notably reduced when the loaded dielectric layer's εr approached that of the solvent. In this case, the solvated Li+ ion preferentially underwent desolvation on the solid surface. The discharge capacity at the ultrahigh rate of 50 C (1 C = 160 mA g−1) of the dielectric-modified thin films steadily increased with increasing length of the dielectrics−electrode−electrolyte triple-phase interface (TPI). Experimental and computational results reveal that, when the permittivity of the dielectrics and solvent are similar, solvated Li+ ions are preferentially involved in the physical adsorption and desolvation on the dielectric surface, followed by Li+ intercalation near the TPI.