Temperature Effects on the Microstructural, Dynamic, and Dielectric Properties of the {CholiniumBF₄–γ-Butyrolactone} Ionic Liquid Solution: A Combined Molecular Dynamics and DFT Study

Choline-based ionic liquids have attracted considerable interest as electrolyte components for energy-storage devices because of their low volatility, thermal stability, and potentially biodegradable character. However, their relatively high viscosity can limit ionic mobility and transport. Herein, the temperature-dependent structural, transport, and dielectric properties of a 1 mol L⁻¹ ChBF₄–γ-butyrolactone (GBL) electrolyte were investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Independent MD simulations were performed from 298.15 to 373.15 K using GROMACS and the OPLS-AA force field, while DFT calculations were conducted with ORCA at the B3LYP-D3 level using def2-TZVPP and 6-311++G(d,p) basis sets with the CPCM solvation model. Radial distribution functions reveal pronounced Ch⁺–GBL interactions and a progressive reduction in contact ion pairs with increasing temperature. The Ch⁺–BF₄⁻ coordination number decreases, whereas Ch⁺–GBL coordination slightly increases. DFT calculations indicate that the [Ch⁺(GBL)₂] configuration exhibits the highest thermodynamic stability among the investigated clusters. Increasing temperature enhances the self-diffusion coefficients of all species, with GBL remaining the most mobile component, while reducing viscosity and increasing ionic conductivity. Conversely, the dielectric constant decreases with temperature. These results provide molecular-level insight into the temperature-dependent behavior of {ChBF₄–GBL} electrolytes and their potential relevance to electrochemical energy-storage applications.