Defect detection in lithium ion cells by magnetic field imaging and current reconstruction

The detection of production failures in commercial lithium ion cell productions is important to decrease scrap rates and save energy by early recognition. However, there is still a lack of fast and inexpensive methods to test for cell defects, which affect the cell's current distribution and therefore the cell's aging.This work presents an improved setup for magnetic field imaging (MFI) and current reconstruction of lithium ion cells that can be used to detect and locate production failures. The method bases on a previous paper using anisotropic magnetic resistance (AMR) sensors to scan the magnetic field in a two-dimensional plane above the cell. Experimental cells with various defects were produced, simulated and measured. The defects include missing welds, cuts and cracks in the active material and current collector as well as blocking elements between the layers of the cell. Our results show that many, although not all, types of defects can be observed using the proposed setup.