Minimizing Experimental Effort: A Two-Equation Model for Wide-Range Ionic Conductivity in Lithium-Ion Battery Electrolytes

For concentrated lithium-ion battery electrolytes, ion association and ion crowding cause the ionic conductivity σ to deviate from the classical Walden rule, and existing empirical equations require dense grid-based measurement campaigns to capture these deviations. We derive a density-corrected Walden (DCW) equation that introduces the solution density ρ as a second transport descriptor alongside the dynamic viscosity η; the model contains two free parameters and is calibratable by linear regression. A complementary mass-action model, based on the classical ion-association equilibrium, separates ion pairing from ionic mobility and yields a physically interpretable dissociation profile. Both models are validated on LiPF$_6$ in EC:DMC:EMC spanning 0.25 mol L$^{−1}$ to 3.00 mol L$^{−1}$ and −20 to 45 °C. Using only three calibration concentrations, the DCW model reconstructs the full σ(c, T) surface with a root-mean-square error of 0.27 mS cm$^{−1}$, approaching the accuracy of established benchmark Eqs. that require 5 to 10 calibration concentrations. Cross-validation on LiFSI in three pure solvents confirms transferability to other salt–solvent systems. ... mehrThe deterministic σ–η–ρ link additionally enables real-time quality control of conductivity measurements.