Investigating the Rheological Properties of Silicon/Carbon (Si/C) Composite Supraparticles Used in Lithium-Ion Battery Anodes
Authors: Özcan Fatih , Watermann Jonas , Amin Adil , Loewenich Moritz , Wiggers Hartmut , Segets Doris 
Published: February 2024

Silicon-based active materials emerged as a very promising replacement for graphite in lithium-ion battery (LIB) anodes [1]. The unfavorable issue of particle pulverization due to inherent volume changes during lithiation / delithiation, which is still a problem hindering the full-scale implementation of silicon anodes in LIB, can be avoided by utilizing nanosized active materials. Our new approach of spray drying the nanometer-sized building blocks to micrometer-sized supraparticles enables additional improvement for Si-based anodes [2]. This approach, however, creates new hurdles for processing and quality control since a stable processing of the supraparticles to final electrodes is a key criterion for enhanced LIB performance.
Figure 1: Schematic representation of the deagglomeration/breakage behavior of Si/C supraparticles in a slurry as a factor of particle motion/shear [3].
In order to find indicators for supraparticle breakage early in the process chain of Si/C anode manufacturing, we conducted detailed rheological investigations on the slurry level. We parameterized structural kinetic models for slurries prepared with mixtures of supraparticles and nanosized building blocks particles to simulate supraparticle breakage (Fig. 1). With this approach, two indicators were found. First, the thixotropic response showed a strong dependence on the ratio between the spherical supraparticles and the nanosized building blocks. Second, the viscosity decreased with increasing percentage of the fractal-shaped nanosized particles. While further investigating this unexpected effect on viscosity, additional rheological characterizations of the components gave interesting insights into the overall rheological properties of hierarchically structured particle dispersions. The component carbon black and the nanosized/agglomerated active material were individually characterized in aqueous binder solutions to determine their individual contributions to the rheological properties of the full slurry. Here, the focus was laid on shear thinning and thixotropy and how the observed properties relate to the well-known rheology of hard spheres [4].
In conclusion, a deeper understanding of anode slurry rheology enables tailored formulations and process conditions. Moreover, our methodology is applicable to other energy-related materials that are a key part of formulation science and particle technology.

References

Xiao, L.; Sehlleier, Y. H.; Dobrowolny, S.; Orthner, H.; Mahlendorf, F.; Heinzel, A.; Schulz, C.; Wiggers, H., Si-CNT/rGO Nanoheterostructures as High-Performance Lithium-Ion-Battery Anodes, ChemElectroChem 2, 1983-1990 (2015).

Amin, A.; Loewenich, M.; Kilian, S. O.; Wassmer, T.; Bade, S.; Lyubina, J. et al, One-Step Non-Reactive Spray Drying Approach to Produce Silicon/Carbon Composite-Based Hierarchically Strucutured Supraparticles for Lithium-Ion Battery Anodes, J. Electrochem. Soc. 170,020523 (2023).

Watermann, J.; Amin, A.; Wiggers, H.; Segets, D.; Özcan, F., Connecting structure and rheology of silicon/carbon supraparticle-based lithium-ion battery anode slurries, In Powder Technology, manuscript submitted.

De Kruif, C.G.; van Lersel, E. M. F.;Vrij, A., Hard sphere colloidal dispersions: Viscosity as a function of shear rate and volume fraction, J. Chem. Phys. 83, 4717-4725 (1985).

Figure 1