Experimental and Numerical Study on the Pyrolysis Pathways of C7H4F12O in a Simulated Battery Immersion System

Lithium-ion batteries have become crucial energy carriers in multiple core fields owing to their excellent comprehensive performance. Nevertheless, as battery energy and power densities continue to rise and operating conditions grow increasingly complex, thermal safety issues have become increasingly prominent. Immersion liquid cooling technology has attracted widespread attention in academic and engineering fields for its outstanding heat transfer and temperature uniformity performance. As a core component of this technology, the selection of liquid coolants is of vital importance. Various coolants investigated in existing studies generally suffer from limitations to varying degrees. Against this backdrop, intrinsically safe fluorocarbon C7H4F12O (3F-135) serves as an ideal liquid cooling medium for lithium-ion batteries, thanks to its high thermal stability, superior electrical insulation and environmental friendliness (zero ODP, extremely low GWP). However, its decomposition mechanism and reaction pathways under extreme thermal runaway conditions of batteries remain unclear. In this study, a tube furnace was adopted to simulate high-temperature environments induced by thermal runaway, and gas chromatography–mass spectrometry (GC-MS) was employed to analyze decomposition products and decomposition ratios of 3F-135. Subsequently, density functional theory (DFT) calculations were utilized to construct the pyrolysis reaction network of 3F-135. Ultimately, the dominant pyrolysis pathways in different temperature ranges were clarified, providing theoretical support for the application and selection of intrinsically safe liquid coolants.