Comparison of a discontinuous and continuous slurry manufacturing process for silicon-containing anodes in lithium-ion batteries

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Intensive efforts have been made to improve the energy density of lithium-ion batteries. Particularly, it has been proven to be advantageous to use active materials containing silicon due to their high capacity. For this reason, the processing of active materials containing silicon is becoming increasingly popular. Additionally, the production of battery slurries in a continuous process like the extrusion process offers several advantages over a discontinuous production like in a high-intensive mixing device. In this respect the mean residence time, the high throughput and the constant product quality are only a few things that can be mentioned. In order to establish a comparison between the two processing variants, the Specific Energy Input (Em) is introduced. This parameter is generally defined by the stress energy and the number of stress events. An increased Em leads to a reduction of the particle size of the carbon black particles in the slurry, which significantly influences the suspension and electrode properties. In order to generate a particularly high energy input, a kneading phase with increased solid contents was introduced in the high-intensive mixing device. In the high-intensity mixer, an increase of the specific energy input was observed by increasing the mixing tool speed and the kneading time. The energy input, which was achieved with the extrusion process, was able to reach the same level of energy as in the high-intensity mixing device. A clear connection between energy input and particle size can be seen. Higher energy inputs lead to smaller particles of the carbon black. The small particles also lead to an increased adhesion strength with a constant coating density. So there was no change of the coating thickness. Finally, the produced electrodes were assembled into full cells (anode: 8 mAh/cm2; cathode: 6 mAh/cm2) and cyclized. The previously improved suspension and electrode properties also lead to increased capacities. It was shown that the production of battery slurries with an extrusion process, despite significantly reduced residence times, is able to reach similar energy inputs as in the high-intensive mixing device and so similar particle sizes as well.

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