Abstract
AbstractIn order to reduce the residual moisture in lithium‐ion batteries, electrodes and separators need to be post‐dried prior to cell assembly. On an industrial scale, this is often conducted batch‐wise in vacuum ovens for larger electrode and separator coils. Especially for electrodes, the corresponding post‐drying parameters have to be carefully chosen to sufficiently reduce the moisture without damaging the sensitive microstructure. This requires a fundamental understanding of structural limitations as well as heat transfer and water mass transport in coils. The aim of this study is to establish a general understanding of the vacuum post‐drying process of coils. Moreover, the targeted design of efficient, well‐adjusted and application‐oriented vacuum post‐drying procedures for electrode coils on the basis of modelling is employed, while keeping the post‐drying intensity as low as possible, in order to maintain the sensitive microstructure and to save time and costs. In this way, a comparatively short and moderate 2‐phase vacuum post‐drying procedure is successfully designed and practically applied. The results show that the designed procedure is able to significantly reduce the residual moisture of anode and cathode coils, even with greater electrode lengths and coating widths, without deteriorating the sensitive microstructure of the electrodes.
Highlights
In the long and complex process chain of lithium-ion batteries (LIBs), the post-drying step constitutes an important, improvable step with regard to its significant influence on the safety and cycling stability of the cells as well as its high energy costs
The crucial factor for post-drying whole electrode coils is to enable diffusion through the half of the coating width to a sufficient scale, so the major challenge lies within the long diffusion paths compared to post-drying of sheets with freely accessible surfaces
Diffusion can be accelerated by high temperatures, low vacuum and a high concentration gradient, so low dew points in the vacuum oven
Summary
In the long and complex process chain of lithium-ion batteries (LIBs), the post-drying step constitutes an important, improvable step with regard to its significant influence on the safety and cycling stability of the cells as well as its high energy costs. Post-drying usually takes place directly before cell assembly or cell closure, depending on the chosen cell format and process route. It aims at reducing the residual moisture in the cell components below a critical level to ensure a long battery cell life and high safety. Post-drying is most commonly conducted either in continuous roll-to-roll processes, where the electrodes or separators are often heated by infrared emitters, or batch-wise by post-drying whole coils in vacuum ovens.[1,2,3,4,5]. Batch-wise post-drying of coils in a vacuum oven is investigated.
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