Influence of molecular weight and concentration of carboxymethyl cellulose on rheological properties of concentrated anode slurries for lithium-ion batteries

The detailed behavior of carboxymethyl cellulose (CMC) as a dispersant in model anode slurries for lithium-ion batteries was investigated. Slurries with different graphite and CMC concentrations using three types of CMCs having different molecular weights were prepared, and changes in viscosity in the low shear rate range together with shear thickening in the high shear rate range were assessed. At a constant CMC concentration, the viscosities at low shear rates decreased as the graphite concentration was increased. Shear thickening was also more evident at low CMC concentrations and when using CMCs with lower molecular weights as well as at high graphite concentrations. These results suggest that, within the CMC concentration range investigated in the present work, the majority of the CMC was adsorbed on the graphite particles and this adsorbed CMC affected the rheological properties of the slurry. Increases in graphite concentration decreased the amount of adsorbed CMC per graphite particle, which in turn lowered the viscosity in the low shear rate range and enhanced shear thickening in the high shear rate range. The adsorbed CMC affected the slurry viscosity via electrostatic and steric interactions at low shear rates and acted as a buffer to inhibit shear thickening at high shear rates, primarily as a result of steric effects.