Mechanical testing of battery electrodes by pull-off and peel tests: A comparative study

• Both tests, the peel test and the pull-off test, produce reproducible results • In both methods the electrodes fracture close to the current collector • The results of both tests are not comparable, as the fracture behavior differs significantly • The results show opposing trends for major process parameters like calendaring In battery cell production, electrodes are manufactured by coating current collectors with an active‐material slurry. Upon drying, this forms a porous composite of active material, conductive additives, and binder. The mechanical integrity of this coating is critical for electrode quality and subsequent processability. To assess these properties, pull-off tests and peel tests are commonly employed. While frequently categorized as “adhesion tests,” this label can be misleading; the fracture surfaces in these porous composites are rarely purely adhesive, yet a critical analysis of the specific fracture patterns is often neglected. This study evaluates and compares the qualitative fracture patterns and quantitative results of both methods. To assess the sensitivity of each test, electrode properties were systematically varied by altering electrode thickness, binder type, and applying different calendering parameters. Results indicate that pull-off tests yield significant scatter due to undefined, multiaxial stress distributions, leading to inhomogeneous fracture patterns. In contrast, peel tests demonstrate minimal scatter with well‐defined crack propagation in a single plane, allowing for the detection of slight deviations in mechanical properties. Notably, the two methods reveal diverging trends regarding the impact of electrode thickness and calendering. Consequently, data from these methods are strictly incommensurable due to their fundamental mechanical difference.