Background
A new version of UL 1642 was released. An alternative to heavy impact tests is added for pouch cells. The specific requirements are: For pouch cell with capacity that are greater than 300 mAh, if pass the heavy impact test were not passed, they can be subjected to Section 14A round rod extrusion test.
Pouch cell has no hard case, which often leads to cell rupture, tap fracture, debris flying out and other serious damage caused by failure in heavy impact test, and makes it impossible to detect the internal short circuit caused by the design defect or process defect. With round rod crush test, possible defects in the cell can be detected without damaging the cell structure. The revision was made with this situation in consideration.
Testing flow
Experimental analysis
a) Uneven thickness distribution (uneven thickness between the pole tab and the surrounding active substance leads to uneven stress distribution)
b) Welding marks in the tab area (stress distribution at the weld point and non-weld point)
Summary
The new round rod extrusion test is different from the original extrusion test of UL 1642. The original extrusion test is to use flat extrusion, and apply a constant 13kN force without holding time. It’s applicable to all types of cell. This test examines the mechanical strength of the cell as a whole (including the case) and its ability to withstand mechanical stress; while the round rod extrusion only test a part of cell, the smaller area of the indenter will make the internal stress concentrated, easy to lead to internal short circuit. Especially, the extrusion position is selected in the weak area of the pole tab welding, which can better investigate the safety performance of the cell.
At present, this round rod method is also used in the extrusion test of pouch cell in GB 31241. MCM has rich testing experience in this operation.
Article Source: https://www.un383mcm.com/news/issue-of-ul-1642-new-revised-version-heavy-impact-replacement-test-for-pouch-cell/
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