Fundamentals

Fundamentals

Linking Solvation Equilibrium Thermodynamics to Electrolyte Transport Kinetics for Lithium Batteries Lai et al. systematically studied the structural evolution of ion–solvent and ion–ion local coordination in both carbonate- and ether-based Li+ electrolytes, and combined in-situ FTIR and Raman spectroscopies to investigate the temperature-responsive solvation equilibrium. Li+ solvation can either be found in a solvent-separated ion pair SSIP or a contact ion pair CIP configuration, with both coexisting in a thermodynamic equilibrium that varies with temperature and composition. Compared to ether-based electrolytes, carbonate-based electrolytes showed a preference for CIP association. The solvation equilibrium thermodynamics were linked to transport kinetics, with the dimethyl ether DME) electrolyte exhibiting the highest conductivity and Li+ diffusivity due to its higher solvent-separated ion pair SSIP) concentration and lower average coordination number. Moreover, the contact ion pair association reaction was found to closely link to the Li+ transference number across different temperatures, with ethers exhibiting higher Li+ transference numbers.

Thermodynamic solvation equilibrium properties offer new descriptors for quantifying dynamic solvation structure, and were shown to closely link to the Li+ transference number of electrolytes through the changes in their Gibbs free energy.

Source: Lai, Jianwei, et al. American Chemical Society 2025

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