Influence of the Molecular Weight of Poly-Acrylic Acid Binder on Performance of Si-Alloy/Graphite Composite Anodes for Lithium-Ion Batteries.

In this study Si-alloy/graphite composite electrodes are manufactured using water-soluble poly-acrylic acid (PAA) binder of different molecular weights (250, 450 and 1250 kg mol). The study aims to assess the behavior of the different binders across all the steps needed for electrodes preparation and on their influence on the electrodes electrochemical behavior. At first, rheological properties of the water-based slurries containing Si-alloy, graphite, conductive carbon and PAA are studied. After coating, the adhesion strength and electronic conductivity of the manufactured electrodes are evaluated and compared. Finally, the electrochemical behavior of the composite anodes is evaluated. The electrodes show high gravimetric as well as high areal capacity (∼750 mAh/g; ∼3 mAh/cm). The influence of the binder on the first cycle irreversible loss is considered as well as its effectiveness in minimizing the electrode volume variation upon lithiation/de-lithiation. It is finally demonstrated that the use of 8 wt.% of PAA-250k in the electrode formulation leads to the best performance in terms of high rate performance and long term stability.