Design of Localized High-Concentration Electrolytes from the Perspective of Physicochemical Properties.

The physicochemical properties of electrolytes profoundly impact the energy density, rate performance, and manufacturability of rechargeable lithium batteries. Localized high-concentration electrolytes (LHCEs), a novel electrolyte class, have attracted considerable interest, yet the impact of diluents on their physicochemical properties remains unclear, as most reports involve only a few samples. Here we prepared 345 electrolyte samples using 21 diluents and systematically investigated the effect of diluent type and content on the miscibility, density, viscosity, and ion conductivity of LHCEs. We found that the physicochemical properties of LHCEs are mainly affected by the diluents' density and viscosity, regardless of type. Notably, the ionic conductivity exhibits two typical variance trends, "volcano" and "descending," both correlating strongly with diluents' viscosity rather than dielectric constant, a parameter commonly employed in electrolyte design. This anomaly can be explained by the "plum pudding" solvation model, providing essential insights for developing lightweight, highly fluid, and conductive LHCEs.