The characterisation of electrode slurries for lithium-ion batteries (LIBs) is crucial for ensuring stable manufacturing processes and consistent electrode quality. Producing high quality electrode slurries becomes particularly relevant when recycled active materials are used which is likely to impact the properties of the slurry. Rheology is currently used in slurry manufacturing primarily as a quality control tool. The objective of this work is to establish an accessible and unified characterisation methodology for slurries based on a single, coherent measurement concept that is useful for both pristine and recycled materials.
Initially, a model slurry system was developed to systematically investigate the influence of individual components and their composition on the resulting rheological properties. As typical defects associated with recycled materials include agglomerates of the active material, binder degradation and inactive binders, a series of aqueous cathode slurries was prepared with varied LFP particle sizes. The influence of binder properties, e.g. polymer chain length on the elastic behaviour of the dispersions was examined by changing the molecular weight of the sodium carboxymethylcellulose.
Overall, this work demonstrates how the ratio between particle size and the binder chain length is the main distributor to the viscosity of the slurry. This is contributed to network formation in the dispersion. The observed linear regression of this structural formation shows that the binding mechanism is not only governed by adsorption but also mechanical interactions. This lays the foundation for tuning the viscosity of slurries containing recycled materials optimizing the electrode manufacturing process and the electrode quality.