Gas Immersion Enabled Atmospheric-Pressure Near-Ambient Phase-Change Refrigeration Cycle for Active Safety Protection of LFP Battery Thermal Runaway: A Single-Cell Proof of Concept

Abstract

Gas venting during thermal runaway of lithium iron phosphate cells can lead to flaming combustion of combustible vent gases, creating severe fire hazards. This study originally proposes the conceptual framework of an active safety protection strategy under a non-flammable refrigerant gas atmosphere, and validates its feasibility through a combination of experiments, simulations, and thermodynamic analysis. The evaporator of a vapor‑compression refrigeration cycle is conceptually integrated with a sealed battery enclosure. By screening working fluids, determines a non‑flammable refrigerant with a saturation temperature slightly below ambient temperature at atmospheric pressure, achieving a coupled function of active cooling, atmospheric inerting, and safe gas discharge. Under normal operation, the refrigerant evaporates in a cold plate to absorb heat for thermal management, while maintaining a non‑flammable atmosphere in the enclosure. During thermal runaway, the refrigerant gas suppresses combustion reactions and entrains the vent gas into a gas-liquid separator, where flammable components are separated and discharged safely. Explosion‑limit tests show that increasing the volumetric fraction of trans-1-Chloro-3,3,3-trifluoropropene(R1233zd(E)) in hydrogen mixtures markedly narrows the flammability range, with no combustion observed when the fraction exceeds 95%. Single-cell thermal runaway experiments on a 28 Ah lithium iron phosphate cell show that no visible flaming combustion of the vented gases was observed under the tested refrigerant atmosphere. Numerical simulations of gas-liquid separation indicate that the two-phase flow field inside the separator is uniformly distributed, enabling continuous and efficient separation of the gases generated during thermal runaway. Thermodynamic calculations show that, at an evaporation temperature of 20 oC and a condensation temperature of 60 oC, this refrigerant exhibits the best cycle performance among all candidate working fluids, achieving a coefficient of performance of 4.85. Overall, the results demonstrate the feasibility of suppressing secondary vent-gas combustion in a single-cell lithium iron phosphate configuration.