Process- Structure Property Correlations in Continuous Processing of High-Power Anode Electrode Pastes for Application in Lithium Ion Batteries

Abstract

For efficient production of lithium ion batteries, the growing demands on the production process, particularly a reduction of processing costs which consist of process time, material and energy consumption, must be met. In this regard, the mixing process is of particular importance. Its quality significantly determines the properties of the produced electrode paste and consequently the quality of the subsequent process steps (coating, drying) and finally of the electrochemical performance, including longevity and fast-charging capability, of the fabricated electrodes and batteries [1,2]. Process parameters and equipment setup for the mixing process need to be optimized such that the electrode compounds including active material(s), binder(s) and conductive additive(s) are efficiently deagglomerated, homogenized and dispersed while the generation of particle agglomerates due to insufficient deagglomeration and particle fractures due to excessive energy input is prevented. The state-of-the-art process for electrode paste production is a batch-type process which offers high flexibility particularly beneficial in the field of academic research where novel materials are commonly only available in limited scales. With respect to upscaling and production on industrial scales, though, innovative continuous mixing processes represent a promising alternative since they allow for continuous production of electrode pastes with consistently high quality [3].Therefore, in this study an innovative continuous mixing process using a twin-screw extruder is investigated for graphite-based aqueous anode formulations for high-power applications.For systematic adaption of relevant properties of the electrode paste (e.g., viscosity and particle size distribution) in the extrusion process the kneading concentration is one of the key machine parameters. Varying the kneading concentration for different active materials, a clear correlation to the change in viscosity can be observed up to a certain reversal point where the opposite behavior and a change of the rheological behavior is identified. The underlying mechanism for the observed behavior and its impact on the material and battery cell level is revealed by elaborating further analysis (particle size analysis, scanning electron microscopy, X-ray diffraction, electrochemical cycling). Beyond that, it is also presented how process and product properties correlate and how monitoring the machine parameters can indicate the observed change of the characteristics of the electrode paste.Literature[1] Haarmann, Matthias, Wolfgang Haselrieder, and Arno Kwade. "Extrusion‐Based Processing of Cathodes: Influence of Solid Content on Suspension and Electrode Properties." Energy Technology 8.2 (2020): 1801169.[2] Bockholt, Henrike, et al. "The interaction of consecutive process steps in the manufacturing of lithium-ion battery electrodes with regard to structural and electrochemical properties." Journal of Power Sources 325 (2016): 140-151.[3] Haarmann, Matthias, Desiree Grießl, and Arno Kwade. "Continuous Processing of Cathode Slurry by Extrusion for Lithium‐Ion Batteries." Energy Technology (2021): 2100250.