Modeling of the Lithium Calendering Process for Direct Contact Prelithiation of Lithium-Ion Batteries

The automotive industry's rapid advancement and complex demands concerning energy storage capacities and service life require lithium-ion batteries with improved energy density and cycle life. There are several ways to improve these two performance indicators for battery cells, such as using innovative, high-capacity electrode materials or novel and improved processes within battery production. One approach is prelithiation, a method to compensate for the initial capacity losses occurring either during the cell formation or during battery operation through the addition of lithium during cell production. In the case of direct contact prelithiation, thin lithium foils with a thickness below 10 µm are necessary to ensure the safe and accurate execution of the prelithiation process. However, the commercial availability of free-standing lithium foils is limited to minimum thicknesses of down to only 20 µm. For this reason, the present work examines in detail the calendering process of lithium. As part of a comprehensive parameter study, the influences of lithium foil geometries, line load, and roller temperature on the deformation behavior of lithium during calendering are investigated. A suitable process model is developed to understand the processing and thickness reduction of lithium and the calendering of lithium foils for direct contact prelithiation. For this purpose, a model based on empirical and semi-analytical approaches using fundamental physical interactions during calendering and material properties is developed and is parameterized based on experimental investigations on a laboratory scale. The combination of empirical and analytical modeling allows predictions about lithium processing and their validity ranges. The modeling intends to enable upscaling of the process and a transferability of direct contact prelithiation to the production of lithium-ion batteries on an industrial scale. Finally, the developed model contributes to understanding metallic lithium processing and its use for direct contact prelithiation in a roll-to-roll process and enables transferability of direct contact prelithiation to the production of lithium-ion batteries.