When fabricating battery electrodes, their properties are strongly determined by the adjusted drying parameters. This does not only affect their microstructure in terms of adhesion, but also influences cell performance. The reason is found to be the binder transported to the surface during drying. Herein, it is shown that when thicker electrodes are processed, new challenges arise. On the one hand, loss of adhesion associated with certain drying conditions becomes a more serious problem; on the other hand, cracking occurs at a certain drying rate and with increasing electrode thickness.

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.

A reduction of the inactive components can increase the energy density and reduce production cost of Li‐ion batteries. But an effective reduction of the binder amount also negatively affects the adhesion of the electrode. Herein, slot‐die coating of a primer layer for Li‐ion anodes is investigated. It is shown that the use of a primer layer with only 0.3 g m−2 can increase the adhesive force by the factor of 5 as well as the cell performance for anodes with low binder content. The process limits for a stable, defect‐free primer coating are investigated at coating speeds of up to 550 m min−1. The limits coincide both for a setup without vacuum box and with vacuum box with theory‐based equations. By using a vacuum box, the minimum wet film thickness can be reduced by half.

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.

External surface engineering of metal–organic framework nanoparticles (MOF NPs) is emerging as an important design strategy, leading to optimized chemical and colloidal stability. To date, most of the MOF surface modifications have been performed either by physical adsorption or chemical association of small molecules or (preformed) polymers. However, most of the currently employed approaches cannot precisely control the polymer density, and dynamic modifications at the surfaces on demand have been a challenging task. Here, we introduce a general approach based on covalent modification employing alkoxyamines as a versatile tool to modify the outer surface of MOF nanoparticles (NPs). The alkoxyamines serve as initiators to grow polymers from the MOF surface via nitroxide-mediated polymerization (NMP) and allow dynamic attachment of small molecules via a nitroxide exchange reaction (NER). The successful surface modification and successive surface polymerization are confirmed via time-of-flight secondary ion mass spectrometry (ToF-SIMS), size exclusion chromatography (SEC), and nuclear magnetic resonance (NMR) spectroscopy. The functionalized MOF NPs exhibit high suspension stability and good dispersibility while retaining their chemical integrity and crystalline structure. In addition, electron paramagnetic resonance spectroscopy (EPR) studies prove the dynamic exchange of two different nitroxide species via NER and further allow us to quantify the surface modification with high sensitivity. Our results demonstrate that alkoxyamines serve as a versatile tool to dynamically modify the surface of MOF NPs with high precision, allowing us to tailor their properties for a wide range of potential applications, such as drug delivery or mixed matrix membranes.