Characterizing and predicting 21700 NMC lithium-ion battery thermal runaway induced by nail penetration

Combined numerical and experimental studies are conducted to characterise 21700 cylindrical lithium-ion battery (LIB) thermal runaway (TR) induced by nail penetration. Both radial and axial penetrations are considered for 4.8 Ah 21700 NMC cell under 100% state of charge. Heat generation from the decomposition of the cell component materials are analysed. The maximum cell surface temperature rise and time to reach it in both types of penetration tests are compared. Snapshots from the video footages captured by three high definition and one high speed cameras shade light on the dynamic processes of spark ejection and flame evolution. A generic predictive tool is developed within the frame of the in-house version of open-source computational fluid dynamics code OpenFOAM for nail induced TR. The code treats the cell as a lumped block with anisotropic thermal conductivities and considers heat generation due to nail induced internal short circuit resistance, exothermic decomposition reactions and heat dissipation through convective and radiative heat transfer. Validation with the current measurements shows promising agreement. The predictions also provide insight on the magnitudes of heat generation due to internal short circuit resistance, decompositions of solid electrolyte interphase layer (SEI), anode, cathode and electrolyte. Parametric studies further quantify the effects of cell internal short circuit resistance, contact resistance between the nail and cell, convective heat transfer coefficient and cell surface emissivity on TR evolution

Numerical and experimental characterisation of high energy density 21700 lithium-ion battery fires

High energy density lithium-ion batteries (LIBs) are well suited for electrical vehicle applications to facilitate extended driving range. However, the associated fire hazards are of concern. Insight is required to aid the development of protective and mitigation measures. The present study is focused on 4.8 Ah 21700 cylindrical LiNixCoyMnzO (NMC) LIBs at 100% state of charge (SOC) with the aim to develop a viable predictive tool for simulating LIB fires, quantifying the heat release rate and temperature evolution during LIB thermal runaway (TR). To aid the model development and provide input parameters, thermal abuse tests were conducted in extended volume accelerating rate calorimetry (EV-ARC) and cone calorimetry. Some cells were instrumented with inserted temperature probe to facilitate in-situ measurements of both cell internal and surface temperatures. The mean peak values of the heat release rate, cell surface and internal temperatures were experimentally found to be 3.6 kW, 753 °C and 1080 °C, respectively. An analytical model has been developed to predict cell LIB internal pressure evolution following vent opening. The model uses the measured cell internal temperature and EV-ARC canister pressure as input data. Its predictions serve as boundary condition in the three-dimensional computational fluid dynamics (CFD) simulation of TR induced fire using opensource code OpenFOAM. The predicted transient heat release rate compare favourably with the measurements in the cone calorimetry tests. Predictions have also been conducted for an open cluster to assess the likelihood of TR propagation in the absence of cell side rupture. The present modelling approach can serve as a useful tool to assess the thermal and environment hazards of TR induced fires and aid design optimisation of mitigation measures in enclosed cell clusters/modules