Excessive moisture adsorbed in electrodes and separators of a Li‐ion battery hampers its performance and is, therefore, removed to a certain amount in a post‐drying process. An insufficient understanding of the process results thereby in high process costs. Cost reductions can only be achieved efficiently with an improved process understanding by modeling this post‐drying process. As process modeling requires knowledge of sorption equilibria of water in the components of the battery, the sorption equilibria of water in different anodes are determined by means of a magnetic suspension balance and compared with different experimental setups. The measured data of the adsorption isotherms are described mathematically and give an impression of the amount of moisture, which is going to adjust at an equilibrium starting from a dry anode. Moreover, the materials of the anode are evaluated for their moisture sorption behavior. It is shown that mass‐weighted sorption equilibria of water in the materials yield a good approximation of equivalent equilibria in the anode. In the investigated anodes, the binder and rheology additive carboxymethyl cellulose (CMC) accounts for the most water uptake.

Herein, an experimental setup comprised of a stationary convection dryer (Comb Nozzle Dryer) supplemented by a measurement for gravimetric drying curves is introduced. The drying process of anodes for lithium‐ion batteries is experimentally investigated and compared to modeling results, showing very good agreement for the investigated films. Heat transfer coefficients of the issued impinging nozzles are characterized and measured quantitatively and are used for the drying simulation of the gravimetric drying experiments. In situ temperature changes in the films are measured and presented using an infrared camera setup.

The drying of electrodes is a crucial and often limiting process step in the manufacturing chain of lithium-ion batteries. [1] While the coating step can be carried out at high coating speeds, as shown by Diehm et al., the application of high drying rates still challenges the throughput in electrode production. [2] High energy demand on the one hand and drying condition-dependent electrode properties on the other demand the necessity of an optimally conducted drying process. [3,4] The negative influence on the product properties thereby primarily occurs at high drying rates. [5] The application of high drying rates can lead to a migration of additives like binder and carbon black to the surface of the electrode layer, resulting in low adhesion between active material and current collector foil. [6][7][8][9][10] Furthermore, the electrochemical performance deteriorates compared with gently dried electrodes due to the accumulation of insulating binder and carbon black at the surface, resulting in an increased electrical resistance. [6,11] Binder migration is attributed to the capillary pressure-driven induction of concentration differences during the emptying of the porous electrode structure, leading to an inhomogeneous distribution of components over the electrode height. [5] Nevertheless, it has been shown that these effects can be compensated for by selecting suitable process parameters. Isothermal drying tests indicate that a high film temperature and a low heat transfer coefficient can have a positive effect on adhesion, therefore indicating a more homogeneous distribution of electrode components. [9] The authors reasoned that binder diffusion processes could take place to compensate for concentration differences caused by capillary pore emptying to some extent. Due to the proportionality of diffusion coefficient and temperature, as well as the antiproportionality of viscosity and temperature, higher electrode temperatures increase binder mobility and therefore adhesion. [6,9,11] In addition, the authors illustrate the influences and limitations regarding electrode temperature and drying rate in the convective drying process, which are determined by air temperature, convective heat transfer coefficient, and humidity. Based on an enthalpy balance for double-sided heat input, a maximum electrode temperature of about 50 °C is determined during the evaporation process, while the air temperature was set to 150 °C, the dew point to 15 °C, and the convective heat transfer coefficient to 80 W m À2 K À1 , resulting in a drying rate of 6.15 g m À2 s À1 . [9] These limitations in terms of electrode film temperature are due to the enthalpy transferred with the evaporation flow, which cools the electrode layer below the temperature of the supplied air.

In this manuscript, a method to reduce superelevations of lateral edges in cross-web direction during slot die coating of shear-thinning slurries for Li-ion battery electrodes (LIB) was developed. Therefore, the impact of the inner slot die geometry on the edge elevations was investigated. These elevations of the coating could be almost eliminated by optimizing the flow profile at the outlet of the slot die by modification of the internal geometry. This adaption is an essential step in optimizing the coating quality of slot die coating for battery electrodes to significantly reduce coating edges and, hence, the resulting production reject during the coating step of the industrial roll-to-roll process. It was also shown that lateral edges of the coating can be influenced explicitly by process parameters such as volume flow and gap between slot die and substrate. This correlation has already been shown for other shear-thinning material systems in previous works, which is now confirmed for this material system. At the beginning, the influence of different internal geometries on the formation of the edge elevations was shown. Finally, for the shear-thinning electrode slurry used in this work, optimal dimensions of the previously determined inner geometry for the slot die outlet were found. The optimization was performed for a state-of-the-art electrode area capacity (approximately 2.2 mAh cm−2). The results enable a significant reduction of defects and reject in the coating step of large-scale production of LIB electrodes in the future, adding to a more sustainable battery production.

In this work, a detailed study of the drying of battery electrodes of different thicknesses is presented. A mathematical model to calculate the solvent loading and film temperature over the drying time is experimentally validated. The model is based on a first study presenting a simulation model to predict the drying course when linear drying kinetics prevail and no resistance exists for solvent transport within the film. To shed some light on the drying behavior of electrode films with different thicknesses, the start of capillary pore emptying is observed using a digital microscope. In the experiments, an onset of capillary transport even before the end of film shrinkage is observed for the electrode films with thicknesses above state‐of‐the‐art‐thickness. A clusterwise drying behavior becomes more distinct for thicker electrodes, with large areas of dry and wet capillaries next to each other, compared to a more homogenous drying of the thin electrodes. Based on these findings, the linear model is extended to consider transport limitations within the porous electrode film in the form of a moving drying front. The experiments show an increasing deviation from the linear model with increasing electrode thickness and the extended simulation, which considers transport resistances within the film, shows good agreement.