Rheological behavior of concentrated slurry and wet granules for lithium ion battery electrodes

Dynamic rheological behaviors of concentrated slurry and wet granules made of graphite, carboxymethyl cellulose, and water have been investigated, because there are few studies on wet granules despite the importance of controlling them. The internal structure and the rheological behaviors of the wet granules were compared with those of the concentrated slurry through the X-ray computed tomography (CT) observation and large amplitude oscillatory shear (LAOS) measurement. At small strain (1%), the concentrated slurry showed larger storage modulus G′ than loss modulus G″, that is, tanδ (=G″/G′) less than 1.0. In contrast, the wet granules indicated larger G″ than G′, that is, tanδ more than 1.0. This rheological behavior of wet granules seems to be attributed to the voids that was suggested to exist in the granular layer. On the other hand, at large strain (100%), the tanδ values of the wet granules were extremely higher than those of the slurry. It appears that this behavior of wet granules is due to the collapse of the granular layer indicated by the high second-harmonic intensities observed in the LAOS measurement. These results elucidated the change of rheological behavior from slurry to wet granules with increasing solid content.