The effect of web tension on calendering wrinkles and corrugations of coated foils

Abstract. Lithium-ion batteries have been widely used in energy storage for a range of applications from portable electronics, electric vehicles to power grids due to their high energy density, high power density and long cycle life. Calendering is a critical process in the manufacturing of lithium-ion batteries electrodes, which has a significant influence on volumetric energy density, long-term cycle stability, and electrochemical performance of lithium-ion batteries, etc. Wrinkles in the uncoated area and corrugations in the coated area of the electrode during the calendering process are serious problems in the industrial production of lithium-ion batteries, as shown in Fig. 1. Adjusting the web tensions has been a critical solution to mitigate these defects. However, large web tensions often lead to foil tearing, severe wrinkles, and high scrap rates, due to a lack of understanding of the wrinkling and corrugating behavior under different tension conditions. To cope with that, this stuedy aims to investigate the mechanism of wrinkling and the effect of web tension on the wrinkling of electrodes during calendering. Calendering experiments are carried out for lithium battery cathodes under different front and back tensions and the three-dimensional topographies of calendered electrodes are measured by a laser profiler. The corrugations of electrodes can be improved by the difference between the front and back tension, instead of the magnitude of the tension, and the tortuosity is reduced by 34.2% at a tension difference of 20 N, compared to that of 5 N. An increase of the tension difference leads to a linear increase of shear displacement δ, causing severe wrinkles in the uncoated area of electrodes. An analytical prediction model for the wrinkles during calendering is established based on shearing of the rectangular membrane and an electrode quality evaluation method for balancing wrinkles and corrugations is proposed. The determination of optimal web tension settings, with a tension difference of 17 N, is achieved to obtain the best quality calendered electrodes, which is in agreement with the experimental results. The method presented in this paper is helpful for the improvement of the production quality and efficiency of lithium battery electrodes.