Impact of slurry preparation method on the rheological behaviour of dense anode slurries for lithium-ion batteries

Understanding and controlling the rheology of electrode slurries for lithium-ion batteries is critical both for improving their manufacturing efficiency and for achieving desirable battery performance. Here, we show drastic “slurry-preparation-dependent” rheology in an anode slurry for lithium-ion batteries, focusing on the behaviour of carboxymethyl cellulose (CMC), which is the most popular dispersant for graphite particles in anode slurries. Slurry preparation with dry-state mixing, where water is added to a dry mixture of graphite and CMC powder, results in much higher viscosity, yield stress, and elastic modulus than those achieved with conventional wet-state mixing, where graphite is added to a CMC solution. Cryogenic scanning electron microscopy reveals strange CMC “clumps” formed among the graphite particles in the slurry prepared with dry-state mixing. We attribute the increases in viscosity, yield stress, and elastic modulus for the slurries prepared with dry-state mixing to these clumps of CMC, which can enhance the adhesion between graphite particles and thereby constrain their motion. We also show that pre-shearing irreversibly decreases viscosity, yield stress, and elastic modulus, suggesting that the clumps of CMC are irreparably broken down by applied shear. The influence of the slurry preparation method on the rheological properties of anode slurries has not received attention in previous studies. Hence, we believe that our results might provide new strategies for controlling the rheology of the anode slurry in the manufacturing process for lithium-ion batteries.