Effect of Polymeric Binders on Dispersion of Active Particles in Aqueous LiFePO$_{4}$-Based Cathode Slurries as well as on Mechanical and Electrical Properties of Corresponding Dry Layers

We investigated the effect of carboxymethyl cellulose (CMC) and the particulate fluorine/acrylate hybrid polymer (FAHP) on the flow behavior of LiFePO$_{4}$-based cathode slurries as well as on electrical and mechanical properties of the corresponding dry layers. CMC dissolves in water and partly adsorbs on the active particles. Thus, it has a strong impact on particle dispersion and a critical CMC concentration distinguished by a minimum in yield stress and high shear viscosity is found, indicating an optimum state of particle dispersion. In contrast, the nanoparticulate FAHP binder has no effect on slurry rheology. The electrical conductivity of the dry layer exhibits a maximum at a CMC concentration corresponding to the minimum in slurry viscosity but monotonically decreases with increasing FAHP concentration. Adhesion to the current collector is provided by FAHP, and the line load in peel tests strongly increases with FAHP concentration, whereas CMC does not contribute to adhesion. The electrical conductivity and adhesion values obtained here excel reported values for similar aqueous LiFePO$_{4}$-based cathode layers using alternative polymeric binders. ... mehrBoth CMC and FAHP contribute to the cohesive strength of the layers; the contribution of CMC, however, is stronger than that of FAHP despite its lower intrinsic mechanical strength. We attribute this to ist impact on the cathode microstructure since high CMC concentrations result in a strong alignment of LiFePO$_{4}$ particles, which yields superior cohesive strength.