ARTICLES Molecular Dynamics Simulation of Li + BF 4 - in Ethylene Carbonate, Propylene Carbonate, and Dimethyl Carbonate Solvents Jean-Christophe Soetens, † Claude Millot,* and Bernard Maigret Laboratoire de Chimie The ´ orique, URA CNRS no. 510, BouleVard des Aiguillettes, BP 239, 54506 VandoeuVre le ` s Nancy Cedex, France ReceiVed: July 28, 1997; In Final Form: NoVember 24, 1997 Molecular dynamics simulations of Li + BF 4 - in liquid ethylene carbonate, propylene carbonate, and dimethyl carbonate at low concentration are reported. Structural, thermodynamical, and dynamical properties have been obtained at 323 and 348 K in ethylene carbonate, 298 and 323 K in propylene carbonate, and 298 K in dimethyl carbonate. The diffusion coefficient of the lithium cation is found to be very similar in the three solvents ((0.3-0.6) × 10 -9 m 2 s -1 in this temperature range). This behavior is linked to the structure of the first solvation shell, which contains four strongly bound solvent molecules in a tetrahedral arrangement in all three cases. No exchange of solvent molecules between the first and the second solvation shells of the lithium ion have been observed during the 100-ps simulations. In the three carbonates, the fluoroborate ion is bound to 19 or 20 solvent molecules in the first solvation shell, the coordination shell being much less structured than in the case of the lithium ion, and the diffusion coefficient exhibits a more significant solvent and temperature dependence. I. Introduction Solutions of lithium salts in liquid propylene carbonate (PC), ethylene carbonate (EC), and dimethyl carbonate (DMC) or their mixtures have considerable industrial interest due to their use as electrolytes in rechargeable lithium batteries. 1 Such solvents and their mixtures have proved to be among the most efficient in terms of battery cyclability, 2 and the analysis of the electrolyte physical properties is a necessary step in the understanding of the differences between the electrolytes. Molecular dynamics simulations are often used to characterize the behavior of electrolyte solutions. Many works concern aqueous solutions 3-7 or aqueous solutions near an electrode. 8 In rechargeable lithium batteries, either liquid or polymer electrolytes are used industrially. In this field, molecular dynamics simulations have so far concerned polymer electrolytes such as poly(ethylene oxide)-like systems. 9-13 In this work, we focus our attention on the structural and dynamical properties of dilute solutions of lithium fluoroborate (LiBF 4 ) in liquid EC, PC, and DMC. For that purpose we have undertaken molecular dynamics (MD) simulations of one Li + - BF 4 - ion pair in liquid EC, PC, and DMC at different temperatures. The details of the simulations are given in section II. In section III, we present and discuss our results concerning the structure of the first solvation shell around the ions, the solvation energies, and the ionic diffusion. II. Simulation Details Intermolecular interactions are described by atom-atom Lennard-Jones 12-6 (LJ) and Coulomb interactions. The optimized parameters for liquid-phase simulation (OPLS) LJ * Corresponding author. † Present address: Laboratoire de Physico-Chimie Mole ´culaire (LPCM), Universite ´ de Bordeaux I, 351 Cours de la Libe ´ration, 33405 Talence Cedex, France. © Copyright 1998 by the American Chemical Society VOLUME 102, NUMBER 7, FEBRUARY 12, 1998 S1089-5639(97)02457-2 CCC: $15.00 © 1998 American Chemical Society Published on Web 01/27/1998