Enhancing lithium-ion battery safety: Investigating the flame-retardant efficacy of bis(2,2,2-trifluoroethyl) carbonate during ethyl methyl carbonate combustion

Bis(2,2,2-trifluoroethyl) carbonate (BtFEC) is a candidate fire suppressant for lithium-ion batteries (LIBs). The high flammability of the electrolyte is the reason behind the frequent fire incidents reported with LIBs. These incidents are due to various factors, such as a default in the conception of the battery or operational abuse. The flame-retardant effectiveness of BtFEC was investigated by measuring its effect on the oxidation of ethyl methyl carbonate (EMC), a common LIB electrolyte component. Laminar flame speed (LFS) measurements for EMC-BtFEC in air mixtures were carried out at 403 K, 1 atm, for equivalence ratios (ϕ) between 0.8 and 1.4, and with 0.5 % vol. BtFEC. Additional measurements were made at ϕ = 1.1 with BtFEC addition ranging from 0.1 up to 1.4 % vol. To further understand the combustion chemistry of the EMC-BtFEC system, ignition delay times (time at the maximum peak production of the excited radical OH*) and CO time histories were measured in a shock tube with temperatures ranging from 1217 to 1732 K, at near-atmospheric pressure (1.24–1.42 atm), and for three equivalence ratios (ϕ = 0.5, 1.0, and 2.0). These new results constitute an experimental database that was used to evaluate the performance of a model assembled for both BtFEC and EMC using previous work from our group. The updated, detailed chemical kinetics mechanism presented in this study consists of 237 species and 1630 reactions. Sensitivity, rate-of-production, and reaction pathway analyses permitted the oxidation of the BtFEC-EMC system to be described. A flame sensitivity analysis exhibited the significant effect from the reactions H + CF₂O ⇆ HF + CFO and CF₃ + H ⇆ CF₂ + HF, which consume H radicals that are involved in the branching reaction H + O₂ ⇆ OH + O, ultimately reducing the LFS. This study shows that improvements in the base fluorine chemistry are still necessary to obtain better agreement with the experiments, especially at the speciation level.