Development of a Polarizable Force Field for Molecular Dynamics Simulations of Lithium-Ion Battery Electrolytes: Sulfone-Based Solvents and Lithium Salts

A many-body polarizable force field (PFF) was developed for molecular dynamics (MD) simulations of sulfone-based solvents and lithium salts. Development of the polarizable force field included parameterization of atomic polarizabilities, electrostatic interactions, and van der Waals interactions of electrolyte components. 1λ6-thiolane-1,1-dione or sulfolane (SLF) compound was selected as one of the most appropriate solvents for high-voltage battery electrolytes. Atomic polarizabilities for the sulfolane solvent and lithium salts were obtained by means of a combination of quantum mechanics (QM) and molecular mechanics (MM) approaches using the isotropic atomic dipole polarizable (IADP) model. High-quality atomic polarizabilities were refined for 10 atomic types. Intermolecular interactions of Li+ ions with SLF were parameterized to reproduce the binding energies at the MP2/aug-cc-pvDZ level of theory in the gas phase. Intermolecular interactions of Li+ ions with polyatomic anions, such as nitrate [NO3]-, tetrafluoroborate [BF4]-, perchlorate [ClO4]-, hexafluorophosphate [PF6]-, bis(fluorosulfonyl)imide [FSI]-, and bis(trifluoromethylsulfonyl)imide [TFSI]-, were parameterized employing a similar methodology. A series of molecular dynamics simulations was performed for sulfolane-based electrolytes at several different lithium salt concentrations. Thermodynamic, structural, and transport properties were evaluated to validate the force field parameters against available simulation and experimental data. Transport properties of sulfolane were significantly improved as compared with those obtained from MD simulations using a nonpolarizable force field (NFF). A newly developed polarizable potential was shown to reproduce Li+ ion dynamics as a function of salt concentration. Faster diffusion of Li+ ions, among other electrolyte components, was obtained for high salt concentration electrolytes.