Quantifying simulated venting flow from 18650 format lithium ion batteries with optical techniques*

Thermal abuse and overcharge can lead to decomposition reactions within lithium ion batteries which lead to self-sustaining thermal runaway. Gas generation within these events causes significant increases in pressure; vent mechanisms are therefore integral to commercial battery designs to avoid case rupture. The venting flows present significant safety concerns due to the flammable and potentially toxic vented gases and liquid electrolyte. Tests are performed here on vents from common 18650 size cells to characterize the venting process. A test fixture was designed to pressurize the vents to failure.  High-speed schlieren and particle image velocimetry techniques are implemented here to quantify the transient velocity field immediately after vent opening. Experiments are performed to identify how variations in the vent burst disk opening affects the extent and direction of gas flows. Further analysis related early venting flow to the measured burst pressure.