Safety Componentry for Mitigating Catastrophic Failure in Lithium-Ion Cylindrical Cells

Abstract

The lithium-ion cylindrical cell is designed as a thin-walled pressure vessel, with various engineering controls to mitigate catastrophic failure. With an increase in pressure inside the cell, given suitable can wall thickness, the cell will fail through the header componentry. A tear down and inspection method has been developed to observe the header design and componentry of cells. A range of cylindrical cells were investigated - from 18650 to 46950 in size. This involved visual inspection, x-ray tomography, chemical analysis and microscopy. The presence of safety componentry, thickness and material type is discussed; factors which affect the propensity of the cell to fail at this location. Commonly observed was the Current Interrupt Device (CID) vent disc which is designed to mechanically deform in response to pressure increase within the cell. This in turn disconnects the cell circuitry and ruptures, initiating the venting process. Furthermore, cells typically contained a Positive Temperature Coefficient (PTC) device which protects the battery from external short circuits and electrical abuse conditions by limiting current flow when the cell reaches a particular temperature. This approach clearly outlines the safety componentry and their respective functions used within these cell sizes, allowing for a better understanding of battery safety. Additionally, we expect this work to disseminate new developments in larger format lithium-ion batteries as they are being sought for better system performance.