Challenges in the Scale-Up Process of Si/C Anode Coatings with Different Si Solid Contents

摘要

In order to make electromobility commercially affordable for society, a number of challenges still need to be overcome. In addition to the lowest possible manufacturing costs, performance, sustainability and the CO2 balance of the product life cycle play a decisive role. At the chair of production engineering of e-mobility components (PEM) of the RWTH Aachen University, we develop innovative ideas and concrete solutions along the entire value chain, which are evaluated through the construction of prototypes at first and implemented in industry relevant applications afterwards. Starting at the lowest level of battery production, cell chemistry is one important aspect for improving battery performance. The low specific capacity of commercially available graphite anodes is one limiting factor in the development of Li-ion batteries. To increase the performance, substances with enhanced properties can be incorporated into the anode material. Silicon is one of the potential additives, which has a specific capacity that is more than an order of magnitude greater than that of graphitic carbon. However, due to the high volume change of silicon particles during charging and discharging, the development of a cycle-stable Si/C-coating is the focus of many research projects. In addition, the mixing and coating process of Si/C slurries poses some challenges due to the preferred formation of Si agglomerates. The goal of this work is to develop a mixing and coating procedure to get homogeneous Si/C coatings with different silicon content on copper foil. With regard to industrial production, the scale-up from laboratory scale to a pilot plant of the mixing and coating process is evaluated. In order to ensure a transfer of the developed mixing and coating process to the currently used industrial manufacturing processes, comparable slurry formulations are used with respect to the solid content as well as the selection of binder and carbon black. Pouch cells and coin cells with standard lithium iron phosphate cathodes were then built up. Influences of the Si content on the charging and discharging process were analysed. On a laboratory scale, slurries could be produced in a mixing process for less than one hour, resulting in homogeneous Si/C coatings with Si solid content between 5 - 50%. No agglomeration formation is observed on light microscopic images with a magnification factor of 132. In addition, the coatings exhibit good adhesion to the copper foil, which is within the same size range as the adhesion of the pure graphite coating. The scale- up procedure showed a big difference in the mixing process compared to the laboratory scale, which has to be further optimized by adjusting the mixing and addition times. This work is funded by the German Federal Ministry of Education and Research (BMBF).