Analyzing Bending Stresses on Lithium-Ion Battery Cathodes induced by the Assembly Process

The industrialized winding of electrode–separator composites (ESCs; “jelly rolls”) applies bending stress to the winding mandrel. This affects the mechanical integrity of the substrate's coating and adhesion and may reduce the cycle stability and the battery life. Even though this motivates strong interest in the minimization of bending stress during production, there is no testing method available yet to characterize the composite such that process parameters can be derived. This article introduces a test method and apparatus for the effect of bending stress of electrodes. In this test method, electrodes are pulled over defined radii while the coating adhesion is observed continuously. This resembles the variation of the mandrel diameter and gives detailed insight into the limits of the allowed production parameter window. In a case study, a cathode material with Li(LiMnAl)2O4 (LMO) as active material is selected as an example to show the effectiveness of the method. Critical Jelly Roll! The term “jelly roll” refers to the wrapped electrode–separator‐composite (ESC). If winding radii tolerances are exceeded in the electrode's manufacture, bending stresses occur and negatively impact the electrode layer's mechanical integrity and thereby the lithium‐ion battery's functionality. In this study, the respective coherency is analyzed.