Exploration of High and Low Molecular Weight Polyacrylic Acids and Sodium Polyacrylates as Potential Binder System for Use in Silicon Graphite Anodes

The commercialization of silicon anodes requires polymer binders that are both mechanically robust and electrochemically stable in order to ensure that they can accommodate the volume expansion experienced during cycling. In this study, we examine the use of both low and high molecular weight (MW) polyacrylic acids (PAAs), and sodium polyacrylates (Na-PAAs), at different degrees of partial neutralization, as a possible binder candidate for use in silicon graphite anodes. High MW PAAs were found to have stable capacity retentions of 672 mAh g^-1 for over 100 cycles, whereas with the low MW PAAs the capacity was found to already have declined to 373 mAh g^-1 after the first 30 cycles. Furthermore, the partial neutralization of Na-PAA binder system was found to provide superior cycling performances, as compared to non-neutralized or fully neutralized PAA systems. The high MW and partially neutralized PAAs were also found to provide the electrode coatings with higher cohesion strengths, which allow for the electrodes' microstructure to be more effectively maintained over several cycles. Overall, these findings suggest that partially neutralized and higher MW PAAs are the more suitable polymer binder candidates for use within silicon-graphite anodes.