Computation of thermodynamic oxidation potentials of organic solvents using density functional theory

Ethers and organic carbonates are commonly used as solvents in lithium batt ery electrolyte. It is important to determine the oxidation potentials of t hese organic solvents due to the high cathode potential (similar to5 V) in many of these batteries. There are significant variations in the reported o xidation potentials for electrolytes containing these solvents. The factors contributing to the variation include the type of salt used in the electro lyte, composition of the electrode, and a somewhat arbitrary determination of the oxidation potential from the anodic cutoff current. We report here t he application of density functional theory (DFT) to calculate solvent oxid ation potentials assuming oxidation occurs via one-electron transfer to for m the radical cation. No specific ion-ion, ion-solvent, or ion-electrode in teractions are included. These values are then compared to the experimental observations. Eleven solvent molecules are studied: 1,2-dimethoxyethane, t etrahydrofuran, 1,3-dioxolane, diethylcarbonate, dimethylcarbonate, ethylme thylcarbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and catechol carbonate. Optimized geometries of the ra dical cations correlate well with the fragmentation patterns observed in ma ss spectrometry. The oxidation potentials of saturated carbonates are calcu lated to be approximately 1 V higher than the organic ethers, which is cons istent with reported literature values. Quantitative comparison with experi ment will require more careful measurements to eliminate other oxidation re actions and a standardized procedure for determining the oxidation potentia l. (C) 2001 The Electrochemical Society. [DOI: 10.1149/1.1362546] All right s reserved.