Computation of Thermodynamic Oxidation Potentials of Organic Solvents Using Density Functional Theory

Abstract

Ethers and organic carbonates are commonly used as solvents in lithium battery electrolyte. It is important to determine the oxidation potentials of these organic solvents due to the high cathode potential (∼5 V) in many of these batteries. There are significant variations in the reported oxidation potentials for electrolytes containing these solvents. The factors contributing to the variation include the type of salt used in the electrolyte, composition of the electrode, and a somewhat arbitrary determination of the oxidation potential from the anodic cutoff current. We report here the application of density functional theory (DFT) to calculate solvent oxidation potentials assuming oxidation occurs via one-electron transfer to form the radical cation. No specific ion-ion, ion-solvent, or ion-electrode interactions are included. These values are then compared to the experimental observations. Eleven solvent molecules are studied: 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, diethylcarbonate, dimethylcarbonate, ethylmethylcarbonate, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and catechol carbonate. Optimized geometries of the radical cations correlate well with the fragmentation patterns observed in mass spectrometry. The oxidation potentials of saturated carbonates are calculated to be approximately 1 V higher than the organic ethers, which is consistent with reported literature values. Quantitative comparison with experiment will require more careful measurements to eliminate other oxidation reactions and a standardized procedure for determining the oxidation potential. © 2001 The Electrochemical Society. All rights reserved.

Carbon Coating Stability on High-Voltage Cathode Materials in H2O-Free and H2O-Containing Electrolyte

“…• C is ≈6/1, 22 consistent with the above conclusions by Zhang et al 34 Interestingly, Figure 5b and Table II show that in the presence of 4000 ppm H 2 O much less 12 CO is evolved than 12 CO 2 , which might suggest that the presence of water favors one of the two depicted CO 2 formation pathways. Again, an unambiguous determination is only possible from our previous experiments with 13 C-labeled EC, where the CO 2 /CO ratio from the anodic oxidation of EC with 4000 ppm H 2 O at 25…”

“…At the same time, Zhang et al 34 presented ab-initio calculations, which proposed a thermodynamically favorable pathway for CO 2 evolution upon the anodic oxidation of EC. In a later, more detailed ab-initio computational study, Xing et al 32 evaluated several feasible pathways for CO 2 and CO evolu- 34 do not report on a pathway leading to CO formation, Xing et al 32 propose another, compared to CO 2 formation (i.e., path 1) energetically less favorable pathway, which can lead to CO release via the formation of formaldehyde and +• O=CH 2 (see path 3 in Scheme 1). 32 Unfortunately, since the 12 CO 2 / 12 CO ratio in our experiments is determined by the anodic oxidation of both EC and conductive carbon (Super C65), the data in Table II and in Figure 4 does not allow to quantify the CO 2 /CO ratio exclusively due to the anodic oxidation of EC.…”

Computational understanding of Li-ion batteries

“…Zhang et al 122 proposed an indirect method to compute the electrolyte redox potentials based on thermodynamic cycles. A schematic of an essentially identical approach is shown in Figure 5a.…”

Anodic Polymerization of Vinyl Ethylene Carbonate in Li-Ion Battery Electrolyte

“…Although there are numerous compounds in the patent literature that are claimed to have such properties, only a few have been studied and discussed in publications. Examples are ethylene sulfite [4], and the unsaturated carbonates vinylene carbonate (VC) [5][6][7][8][9][10] and vinyl ethylene carbonate (VEC) [11][12]. The electrochemical reduction of both VC and VEC has been studied in some detail, including quantum chemical calculations of the energetics that identified the most probable reaction pathway [13][14].…”

“…However, these studies have focused on the reduction chemistry of VC and VEC without discussing the anodic stability of the additive. The chemical stability of VC is a concern [5], and the stabilizers typically added to VC have oxidation potentials in the 3.5 -4.0 V region. Hu et al [11] proposed that VEC was more stable than VC and demonstrated that it functioned successfully as a film forming additive in PC based electrolyte.…”