Discharge and Flame Chemistry in Lithium-Ion Battery Vent Gases : Investigations using Breakdown Experiments with Laser-Based Diagnostics

Abstract: Due to the environmental impact of fossil fuels, there has been a growing interest in lithium-ion batteries for electric vehicles. However, safety concerns have arisen regarding potential fire hazards associated with the vent gases of these batteries. This work aims to investigate the role of electrical discharge as a proposed ignition source of battery vent gases. A set of research questions for the study of this newly discovered issue is formulated, and two gas mixtures are selected for this particular work. The chemical compositions of the mixtures represent vent gases from lithium nickel cobalt aluminium oxide (NCA) batteries and lithium iron phosphate (LFP) batteries. An experimental setup is implemented to study the breakdown voltage of these gas mixtures, using gas flow between two electrodes. The impact of gas temperature, flow velocity, chemical composition and electrode separation distance is studied, as current and voltage across the electrodes are recorded. Furthermore, an arrangement for planar laser-induced fluorescence measurements (PLIF) of hydroxyl (OH) radicals is added to the setup, with the purpose of evaluating the flame behaviour following ignition by the discharge. Chemical kinetics simulations are also performed, the trends of which are discussed in relation to the OH PLIF results. The breakdown voltage of both gas mixtures is found to increase with increasing electrode separation. No firm conclusion can be drawn regarding the effect of temperature, flow velocity or chemical composition, which is attributed to the sensitivity of the setup. The discussion of the results is limited by the lack of literature on breakdown in non-uniform electric fields, which is the case in the present setup. If made more robust, the setup however shows promise to reveal the breakdown characteristics of gas media. The trends of the chemical kinetics simulations can be related to the OH PLIF results. Combined, the simulations and the OH PLIF measurements show that the combustion of gas mixtures at a high fuel-to-air ratio is driven by H radicals. This implies that fire can sustain inside a battery pack despite the absence of oxygen, which is highly relevant for the development of safer electrical vehicle batteries.