A kinetic descriptor of solvent polarization for rational electrolyte design in lithium–metal batteries

Abstract

The construction of solvation structures is crucial for the rational design of electrolytes. However, previous efforts to regulate solvation structures have mainly focused on the static coordination environment around Li⁺, such as the anion coordination number or ligand identity, while the reconstruction and relaxation processes of solvation structures driven by polarization during Li⁺ migration remain largely unexplored, mainly due to the difficulty of direct observation. In this work, we capture the dynamic evolution of the total dipole moment of the system and propose an integral dielectric relaxation time descriptor (τ_i) to quantify the polarization response rate of coordinating solvents. This method simultaneously predicts bulk ion transport and interfacial characteristics of the electrolyte and reflects the combined effects of solvent size, viscosity, and intermolecular interactions. Based on this framework, we apply the τ_i descriptor to a deep eutectic electrolyte system, screen 95 additives, and design an optimized formulation that significantly enhances electrochemical performance, enabling an ultrahigh limiting current density of 6 mA cm⁻² and stable cycling of high-voltage cathodes from −15 to 50 °C. These results establish τ_i as a kinetically grounded descriptor for the efficient screening and rational design of electrolytes for next-generation lithium–metal batteries.