Kinetic study of ozone-sensitized low- and high-temperature oxidation of dimethyl carbonate

Abstract

The low- and high-temperature oxidation of dimethyl carbonate (DMC), a key electrolyte component in lithium-ion batteries (LIBs), was carried out with ozone (O₃) addition by using an atmospheric pressure Jet Stirred Reactor (JSR) from 400 to 1200 K. Kinetic analysis of DMC oxidation was conducted using the coupled Plug Flow Reactor-Perfectly Stirred Reactor (PFR-PSR) module. Without O₃ addition, the oxidation of DMC initiated at 950 K with no low-temperature reactivity. However, the low-temperature chemistry of DMC was observed from 450 K with O₃ addition, and O₃ significantly enhanced the low-temperature reactivity of DMC. Two kinetic models with incorporating the O₃ sub-model were employed and predicted the experimental data reasonably well, even though slightly overpredicted DMC oxidation above 550 K under the fuel-lean condition. Furthermore, a temperature-independent coefficient (TIC) behavior of DMC with O₃ addition was observed between 600 and 950 K both in experiments and simulations, which was associated with the pyrolysis of DMC radicals to CH₂O and CO₂, and then to CO, while the low-temperature oxidation pathway through 1^st and 2^nd O₂ addition and CO oxidation to CO₂ was negligible. The fast pyrolysis reaction rates of O₃ and DMC radicals, such as CH₃OC(=O)OCH₂ and CH₃OC(=O), explain the TIC behavior in the pathway and sensitivity analyses. This work used O₃ to mimic the oxidizing environment in LIBs by providing active atomic oxygen, and implied that the early degradation of LIBs could be attributed to the low-temperature oxidation of DMC with reactive oxygen species. It provides kinetic evidence for a higher level of CO₂ and a lower level of CO in the initial stage of the thermal runaway in LIBs.