Comparison of Current Interrupt Device and Vent Design for 18650 Format Lithium-ion Battery Caps

The current interrupt device (CID) and vent mechanism in the cap of 18650 lithium-ion cells decrease thermal runaway risks by electrically isolating the cell upon internal pressure increase and relieving internal pressure before case rupture, respectively. Geometry analysis, CID- and vent-activation pressure measurement, and finite element analysis mechanical simulation of the vent mechanism were performed for MTI and LG MJ1 18650 caps. The MTI cap used a spot-weld and the LG MJ1 cap used a notch-groove connection for the CID. The vent-activation mechanism was a notch-grooved disk for both caps. The CID-activation pressures were 1.058 ± 0.053 and 1.293 ± 0.119 MPa at ambient temperature and 0.920 ± 0.076 and 1.066 ± 0.068 MPa at 100°C for the MTI and LG MJ1 caps, respectively. The vent-activation pressures were 2.308 ± 0.196 and 2.202 ± 0.083 MPa at ambient temperature and 1.919 ± 0.132 and 1.866 ± 0.084 MPa at 100°C for the MTI and LG MJ1 caps, respectively. Mechanical simulations predicted vent-activation pressures in agreement with experiments and showed decrease maximum stress sensitivity to applied pressure near the vent-activation pressure, consistent with observed sample-to-sample vent-activation pressure variation. Mechanical simulation also predicted vent-activation pressures of 0.448 and 0.400 MPa for the MTI and LG MJ1 caps, respectively, at 300°C.