Rheology of Battery Slurry in the Production Process – The Importance of Mixing Routes
Electrodes represent a key component to fulfilling the demands for improved electrochemical battery performance. Along with formulation, slurry mixing is known to have great potential for reducing processing time and energy consumption, as well as improving mechanical and electrochemical electrode properties. This report compares two multi-step slurry mixing processes and demonstrates how stepwise rheological characterization with a Modular Compact Rheometer (MCR) aids in the optimization of formulation, process design, and storage behavior.
Batteries and fuel cells play a pivotal role for mobile and stationary energy supply to leverage emerging fields like electromobility, portable devices and industrial energy storage. Various types of batteries utilize a bouquet of different raw materials; however,the assembly of components generally includes electrodes (anode and cathode), seperators, electrolytes and housing (e.g. Heimes et al. 2018). In short, the typical battery production process starts with mixing raw materials to form a slurry (with different composition of anode and cathode) that is coated onto a metal substrate, forming the electrode. Stacking, welding and packaging of electrodes and the separator is followed by electrolyte filling and final sealing.
The main solid components of battery slurries typically include active material (80 to 97 %w/w), binders (1 to 10 %w/w) and conductive agents (0.5 to 10 %w/w), in addition to optional additives (e.g. Lanceros-Méndez & Costa 2018). The solids are mixed and dispersed with a solvent, which typically constitutes 30 to 60 %w/w of the final slurry. Process requirements for the slurry are sufficient homogenization, sedimentation stability at low shear rates and low viscosity at high shear rates. The latter is required for the subsequent coating process. In addition, appropriate leveling and desired wet layer thickness after the coating process are controlled by the timedependent visco-elastic properties (e.g. Mezger2020). For water-based slurries, the rheological properties usually need to be adjusted by dispersing aids and thickeners to match coating equipment requirements (Li et al. 2011).
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