Abstract

Two pressure-activated safety devices, a current interrupt device (CID) and a vent mechanism, are commonly built into the cap structure of cylindrical 18650 lithium-ion cells to isolate the cell electrically and relieve internal cell pressure prior to case rupture, respectively, in an abuse or thermal runaway event. The activation pressure for these two mechanisms, and how it varies with temperature, is an important parameter for the thermal runaway models incorporating electrolyte evaporation, gas generation and venting. This paper presents a method to extract the geometry of four commercial 18650 lithium-ion vent cap assemblies and measure the CID- and vent-activation pressures with a customized experimental setup. The experimental data were collected at ambient temperature and 100 °C. The CID-activation pressures of the MTI, LG MJ1, K2, and LG M36 caps were 1.058 ± 0.053, 1.293 ± 0.119, 0.997 ± 0.292 and 1.393 ± 0.113 MPa at ambient temperature and 0.920 ± 0.076, 1.066 ± 0.068, 0.834 ± 0.057 and 1.083 ± 0.077 MPa at 100°C, respectively. The vent-activation pressures of the MTI, LG MJ1, K2, and LG M36 caps were 2.308 ± 0.196, 2.202 ± 0.083, 2.190 ± 0.372 and 2.363 ± 0.199 MPa at ambient temperature and 1.919 ± 0.132, 1.866 ± 0.084, 1.781 ± 0.355 and 1.799 ± 0.284 MPa at 100°C, respectively. The experimental setup may be used in future studies to measure activation pressures of future cylindrical cells. The CAD model of the caps may be used to develop a finite element model (FEM) to simulate the CID- and vent-activation pressure and a computational fluid dynamics (CFD) model to design more reliable and effective CID and vent mechanisms.

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