Interactions Between LiFePO4 and Binders in Water-Based Electrode Slurries
On the other hand, for considerations of environmental consistency and low cost, the technique of fabricating electrodes based on a water-based process by using water as the mixing solvent and water compatible polymer as the binder is gaining favor and has attracted significant interest. In this investigation, the interactions between the cathode active powder, LiFePO4, and the water soluble binder, SBR and CMC binder blend, in the water-based electrode slurries were discussed. The experimental results showed that the factor of the quality of the surface carbon coating on LiFePO4 dominated the interactions between LiFePO4 and the binder. When the surface carbon coating on the active powder was less completed and showing more exposure of the inner LiFePO4, the active powder gelled with the binder significantly and caused the as-prepared water-based electrode slurry to exhibit poorer dispersion property and higher elastic flow behavior. The poorer dispersion of slurry resulted in a less-uniform distribution of compositions in the dried electrode sheets and harmed the electrochemical performance. In addition, the initial mechanism for the gelation of LiFePO4 with the binder blend had also been proposed, which was highly probable due to the chemical chelation between the exposed iron from the inner LiFePO4 and the hydroxyl group of CMC.