Effects of Electrode Curvature in Li-Ion Cells

Abstract

Bending of electrodes in certain cell designs (cylindrical cells or flat wound jellyrolls) leads to curved electrodes (curvature κ). For double side-coated electrodes, this curvature leads to convex and concave sides of the coating. In this work, we describe the effect of curved electrodes on the microstructure and aging. From a simple elastic model, we find that the porosities of the convex and concave sides of curved electrode coatings can deviate theoretically for first inner winding in a typical cylindrical cell in the order of ±2%, respectively. The elastic model is compared with light microscopy images and Post-Mortem analysis revealing additional plastic deformation for small electrode bending radii. Electrode resistance measurements of the electrode coating as a function of winding radius is added to the overall context. The study concludes with an evaluation and discussion on typical bending radii of electrodes in different cell types (pouch, PHEV1, and 21700) and states (fresh, aged, and abused).