Theoretical Investigations on Oxidative Stability of Solvents and Oxidative Decomposition Mechanism of Ethylene Carbonate for Lithium Ion Battery Use

Abstract

The electrochemical oxidative stability of solvent molecules used for lithium ion battery, ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the forms of simple molecule and coordination with anion PF(6)(-), is compared by using density functional theory at the level of B3LYP/6-311++G (d, p) in gas phase. EC is found to be the most stable against oxidation in its simple molecule. However, due to its highest dielectric constant among all the solvent molecules, EC coordinates with PF(6)(-) most strongly and reaches cathode most easily, resulting in its preferential oxidation on cathode. Detailed oxidative decomposition mechanism of EC is investigated using the same level. Radical cation EC(*+) is generated after one electron oxidation reaction of EC and there are five possible pathways for the decomposition of EC(*+) forming CO(2), CO, and various radical cations. The formation of CO is more difficult than CO(2) during the initial decomposition of EC(*+) due to the high activation energy. The radical cations are reduced and terminated by gaining one electron from anode or solvent molecules, forming aldehyde and oligomers of alkyl carbonates including 2-methyl-1,3-dioxolane, 1,3,6-trioxocan-2-one, 1,4,6,9-tetraoxaspiro[4.4]nonane, and 1,4,6,8,11-pentaoxaspiro[4.6]undecan-7-one. The calculation in this paper gives a detailed explanation on the experimental findings that have been reported in literatures and clarifies the mechanism on the oxidative decomposition of EC.

Survey of Gas Expansion in Li-Ion NMC Pouch Cells

“…It is possible that the CO 2 is mainly caused by the oxidation of EC. [11][12][13] The bottom panels show that carbonyl sulfide is produced in the cells containing PES charged to 4.7 V. This is consistent with oxidation of PES at the positive electrode, creating the fragment carbonyl sulfide, which is similar to CO 2 from the oxidation of EC. The bottom left panel also shows that methyl formate might be produced during this second gas step.…”

“…It has been argued, both experimentally and through computational work, that EC can be oxidized to produce mainly carbon dioxide (CO 2 ) and carbon monoxide (CO) in much smaller quantities. [11][12][13] Gas consumption has, to the authors' knowledge, however not been the subject of much scholarship, but, as will be shown, occurs and is important. There nonetheless have been suggestions that gases could polymerize on the surface of electrodes, e.g.…”

Effect of Lithium Bis(oxalato)borate Additive on Electrochemical Performance of Li1.17Ni0.17Mn0.5Co0.17O2Cathodes for Lithium-Ion Batteries

“…• C. For instance, the EC solvent may undergo the oxidative decomposition resulting in radical cation (EC •+ ), 24 as depicted in Fig. 9.…”

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

“…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.…”