(503j) Impact of Polymer Binder on Battery Slurry Rheology and Electrode Performance

Understanding the fundamental impact of processing parameters on composite battery electrode performance is critical for the scale-up and commercialization of new materials. Composite battery electrodes are composed of active and inactive materials, which include conductive additive and polymer binder. The active material provides a source or sink of ions, while conductive additive provides pathways for electrons, and the polymer binder improves mechanical stability and adhesion to the current collector. The inactive materials typically make up less than 5wt% of the final electrode, but their optimization is essential for good battery performance. Standard electrode processing mixes all the components with a solvent into a slurry. Previous research from our group has investigated the colloidal suspension behavior of battery slurries. We found that at critical solution volume fractions, the nano-sized carbon black forms a colloidal gel, independent of the presence of micron-sized non-Brownian active material particles. The colloidal gel is formed because the polymer binder creates a depletion force on colloidal particles that is proportional to concentration and molecular weight (Mw) of the polymer.

In this work, we investigate the impact of polymer molecular weight and chain scission during mixing on the colloidal behavior of battery slurries and the electrochemical performance of the final battery. For the final (dried) battery electrode, higher Mw of polymer is preferred in order to maximize electrode mechanical properties. Although this is an accepted convention, there has been almost no investigation into how the Mw impacts the slurry rheology and the electrode performance. We find that the Mw of the polymer can change the slurry’s behavior from a fluid to a gel and these different behaviors result in varying battery performance. Our results point to the critical importance of that the polymer binder Mw for rapid ion and electron transport and establish criteria for electrode manufacturing process design.