Correlated Calorimetric and Potentiometric Titration Elucidates Quantitative Lithium Cation Coordination Thermodynamics

Understanding the thermodynamics of interactions within the coordination environment of Li⁺ ions is critical for rational electrolyte design. Drawing a physical analogy to ligand-receptor binding in biological systems, in this work, we introduce a combined isothermal titration calorimetry (ITC) and potentiometric titration (PT) framework to quantitatively determine the Gibbs free energy (Δ<i>G</i>), enthalpy (Δ<i>H</i>), and entropy (Δ<i>S</i>) associated with solvent displacement─an exemplar coordination sphere reaction that powerfully reports on the underlying energetics─in nonaqueous Li-based electrolytes. The physical understanding behind the solvent displacement scheme is first validated with Raman spectroscopy, such that the heat measured during ITC is confirmed to arise predominantly from differential changes in coordinated solvent as the bulk electrolyte composition is systematically modified. A statistical binding model is then developed to interpret the thermodynamic data and parametrize single-site displacement enthalpy and equilibrium constants in a set of exemplar dual-solvent electrolytes. The framework is tested across systems with both dissimilar (DMSO:acetonitrile or DMSO:PC) and structurally similar (EC:PC) solvents, revealing how subtle differences in solvent-cation interaction enthalpy and entropy govern coordination preferences. These results provide new experimental insight into the driving forces behind microscopic coordination sphere changes and offer a powerful approach to guide electrolyte formulation.