Experimental and Numerical Study on the Pyrolysis Pathways of C7H3F13O in Simulated Battery Immersion System

This study investigates the high-temperature pyrolysis pathways and product distribution of the battery immersion coolant HFE-7300 (C7H3F13O) within a simulated thermal runaway environment. Using a tube furnace system combined with GC-MS analysis across a temperature range of 300–800 °C (residence time of 3 s), the thermal stability and cracking evolution were evaluated. Experimentally, HFE-7300 exhibits low initial decomposition at 400 °C with a pyrolysis rate of 5.84%, which rapidly scales up to 48.72% at 500 °C, and reaches a near-complete degradation of 98.46% at 800 °C. Qualitative product characterization identified C2H4, C2F4, C3F6 C4F8, and C5H3F9O as the primary species evolved. To map the micro-scale degradation trajectories, a reaction network comprising 12 elementary pathways was constructed via density functional theory (DFT) calculations at the B3LYP/6-311+G(d,p) level. Using the TST method, we calculated the reaction rate constants for the main decomposition pathways. Analysis reveals that the C4–C5 bond scission pathway (R6) serves as the predominant initial decomposition channel, yielding C5H3F9O and CF2=CF2 as the definitive primary products. These findings provide baseline thermodynamic data and critical safety insights for the engineering design of immersion-cooled battery thermal management systems.