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Abstract 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. 

Vibrational strong coupling (VSC) can steer chemical reactivity and energy transfer by hybridizing molecular vibrations with cavity photons. However, it remains unclear how coupling a macroscopic ensemble of molecules to an infrared (IR) cavity alters local molecular dynamics, particularly in the absence of external IR pumping. Herein, a collective and remote energy transfer pathway from molecular electronic to vibrational transitions is identified under VSC conditions using the Pauli–Fierz light-matter Hamiltonian. Following sudden electronic transitions, real IR photons are produced due to rapid change of permanent dipoles, akin to the dynamical Casimir effect; vibrational polaritons then coherently funnel the photonic excitation to molecular vibrations before any dissipation occurs. Analytical solutions and numerical simulations reveal that the rate of this electronic-to-vibrational energy transfer depends quadratically on the number of molecules and is resonantly enhanced by VSC. During this “supervibronic” transition process, the vibrational energy gain per molecule can remain meaningful in the macroscopic limit, suggesting experimentally accessible signatures using conventional VSC devices.