Effect of Electrode Curvature on Cell Behavior in Cylindrical Lithium-Ion Batteries

Abstract

Lithium-ion batteries come in various form factors, with cylindrical lithium-ion batteries featuring electrodes wound in a jellyroll shape. This winding process introduces curvature to the electrodes, resulting in varying curvatures depending on the radius of the jellyroll. In this study, we investigated the influence of electrode curvature within cylindrical lithium-ion batteries on battery performance. We fabricated single-coated electrode pouch cells using an NCM622 cathode and graphite-silicon composite anode. We developed devices to simulate various curvatures based on the radius of the jellyroll and applied these devices to the pouch cells to analyze the effect of curvature on the cell’s charging and discharging behavior. The results revealed that changes in electrode curvature, depending on the radius of the jellyroll, alter the area available for reaction at the anode. As a result, the potential of the anode changed, leading to a corresponding change in the potential of the cathode at the same full cell's cut-off charging voltage. Additionally, we observed differences in cathode/anode utilization depending on whether they were on the inner or outer coated surface, even with the same curvature. Particularly, we found an increased risk of lithium deposition when the curvature is large with the anode on the outer coated surface. Furthermore, these effects influence changes in silicon utilization in the anode, affecting the thickness expansion and degradation differences in the anode. Consequently, the non-uniformity of cell reactions due to electrode curvature increases. Therefore, we propose methods for designing cylindrical lithium-ion batteries to minimize such non-uniformity in reactions. Our research emphasizes the importance of curvature within cylindrical lithium-ion batteries and its impact on battery performance by elucidating the mechanism of battery performance changes due to electrode curvature. These findings are expected to contribute to the design and development of cylindrical lithium-ion batteries.