Abstract
High temperature gases released through the safety vent of a lithium-ion cell during a thermal runaway event contain flammable components that, if ignited, can increase the risk of thermal runaway propagation to other cells in a multi-cell pack configuration. Computational fluid dynamics (CFD) simulations of flow through detailed geometric models of four vent-activated commercial 18650 lithium-ion cell caps were conducted using two turbulence modeling approaches: Reynolds-averaged Navier-Stokes (RANS) and scale-resolving simulations (SRS). The RANS method was compared with independent experiments of discharge coefficient through the cap across a range of pressure ratios and then used to investigate the ensemble-averaged flow field for the four caps. At high pressure ratios, choked flow occurs either at the current collector plate when flow through the current collector plate is more restrictive or the positive terminal vent holes when flow through the current collector plate is less restrictive. Turbulent mixing occurred within the vent cap assembly, in the jets emerging from the vent holes, and in recirculating zones directly above the vent cap assembly. The global maximum turbulent viscosity ratio (μT/μ) of the MTI, LG MJ1, K2, and LG M36 caps at pressure ratio ofP1/P2= 7 were 4,575, 3,360, 3,855, and 2,993, respectively. SRS and RANS simulations showed that both velocity magnitude and fluctuating velocity magnitude were lower for vent holes which are obstructed by the burst disk. SRS showed high levels of fluctuating velocity in the jets, up to 48.5% of the global maximum velocity. The present CFD models and the resulting insights provide the groundwork for future studies to investigate how jet structure and turbulence levels influence combustion and heat transfer in propagating thermal runaway scenarios.
Highlights
Lithium-ion batteries (LIB) are a prevailing energy storage device widely used in mobile applications like portable electronic devices, electrical vehicles and aircraft because of their high energy and power density (Feng et al, 2018; Wang et al, 2019)
A mesh sensitivity analysis was conducted for the benchmarking case, using the same global element sizing and inflation layer settings as those used for the LIB cap simulations
Results of the benchmarking cases agreed with literature data and, the Computational fluid dynamics (CFD) solution procedure was considered suitable for the LIB cap simulations
Summary
Lithium-ion batteries (LIB) are a prevailing energy storage device widely used in mobile applications like portable electronic devices, electrical vehicles and aircraft because of their high energy and power density (Feng et al, 2018; Wang et al, 2019). Safety remains a challenge for LIBs, especially with increasing power and energy density at the module- and system-level. The high level of heat and gas generation rates during thermal runaway cause the temperature and pressure inside the cell increase, nearly instantaneously. The vented flammable gas may ignite, causing fire and increasing risk of thermal runaway propagation within a multi-cell module or system (Wang et al, 2012). Developing methods, either numerical or experimental, to investigate the flow field during venting can help provide new insights into the combustion and heat transfer during propagating failures
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