In various applications, Lithium-ion batteries can be exposed to crash events, where they have to withstand severe mechanical loads and deformations. In some cases, such events can remain undetected, for example, when power tool battery packs are dropped, where the plastic case may deform elastically but the cells within the cell undergo permanent plastic deformation, causing the battery storage system and the damaged cells to remain in use. As it is unclear if such damages may harm any the security functions of the cell, a study was conducted testing the functionality of the current interrupt device (CID) in overcharge tests.
Therefore, cylindrical 18650 cells (Samsung INR1865025 RM) were deformed in various depths at the positive pole using a cylindric impactor with 20 mm diameter and a Universal testing machine Test GmbH 112.50kN.H. Afterward, the damaged cells were overcharged within a self-constructed safety chamber. The overcharge tests were conducted with 1 C with a constant voltage phase after reaching 6 V using a Garmy Interface 5000 P. For temperature tracking, PT1000 sensors were attached to the cells. For each deformation depth, 4 cells were tested.
The results showed, that for the undamaged reference cells, the CID consistently interrupted the current path. Slightly damaged cells (1 mm deformation) showed delayed triggering of the CID. For deeper deformation depths (starting from 1.5 mm), thermal runaway could be observed for an increasing proportion of the tested cells depending on the deformation depth. These results indicate, that even slight deformation of the CID may harm the security functions of the cell, which is why proper shielding of the battery pack from such deformations is crucial to guarantee safety during operation.