Insights into Solvation Transition Driven by Concentration Crossover in Ether-Based Electrolytes

Understanding how solvation structures evolve across multiple length scales is critical for designing electrolytes that can unlock the full potential of lithium-metal batteries. Localized high-concentration electrolytes commonly employ concentrated LiFSI–ether solutions prior to dilution with weakly coordinating cosolvents, yet the intrinsic solvation behavior of these parent systems remains poorly understood. Here, we combine the synchrotron small-angle X-ray scattering/wide-angle X-ray scattering with Raman and nuclear magnetic resonance spectroscopies, as well as molecular dynamics simulations, to elucidate the solvation structures of LiFSI:DME electrolytes across macroscopic to atomistic length scales. Unlike in aqueous imide-based electrolytes, we observe a left shift of the primary structure-factor peak at high concentrations, evidencing a change in Li + solvation. Spectroscopic analyses reveal a crossover from solvent-dominated Li + coordination to anion-rich environments, characterized by rapid formation of contact ion pairs and aggregates around the salt-to-solvent molar ratio 1:3. Furthermore, we relate this shift in the electrolyte structure to lithium-ion transport properties. Together, these results establish a unified multiscale picture of solvation collapse in concentrated ether-based electrolytes, offering guidance for the rational design of next-generation lithium battery electrolytes.