Numerical simulations on non-reactive multiphase flow during the transition from vent activation to venting with vent cap fragments in 18650 lithium-ion batteries

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Mandatory safety devices, prevalent in lithium-ion batteries (LIBs), enable current interrupt device (CID)-and vent-activated power-off protection by sensing the electrochemical gas production boost triggered by thermal runaway (TR). For an in-depth understanding of the early warning of safety devices, the thermodynamic and multiphase flow behaviour of gases-vent particles interaction under the non-combustion venting phase is numerically investigated. From the gas phase simulation results, the flow field structure of the counter-rotating vortex pairs (CVPs) bounded by vent cap fragments enhances the heat transfer between ambient air and the venting gas, and the local venting gas temperature can reach a drop of >100 K. The transient three-dimensional spatial evolution characteristics of vent particles interacting with vent cap fragments at the early stage of the venting process after 18650 thermal runaway-induced vent-activation is originally demonstrated, including gas temperature and velocity as well as particle size and temperature. The spatial distributions of polydisperse particle size and temperature under the process of non-combustion venting are used to characterize the ejected particles' behaviour, which reveals the particle trajectories in particle-laden streams and their heat-transfer characteristics. The results show that ejected particles with relatively high temperatures and large sizes are mainly clustered within the cell diameters, and possible thermal runaway propagation inside the module can be triggered by the smaller-size particles of higher temperature sprayed in the periphery when the blocking effect of the vent cap fragment is weakened.