Binder is a crucial component of high-capacity silicon anodes. It allows the active material to cohere to itself and surrounding materials. In the past few years, there have been divergent conclusions on the cell performance of anodes using water-based PAA vs. LiOH-PAA binder [1-3]. While there is agreement that LiOH-PAA facilitates the coating process, cell performance between these two binders is not settled.

The difference in cell performance may be due to the pH value or the extra Li⁺ in the binder, both of which change when LiOH is added to PAA. In this work we examined these two factors separately to determine their effect on cell performance. Our hypothesis is that the extra Li⁺ could facilitate ion transfer and the low pH could affect current collector corrosion and silicon oxidation. NH₃(aq) is used to adjust the binder slurry pH and experimental results are compared between NH₃-PAA and LiOH-PAA electrodes otherwise made with the same pH value. Similarly, we compared performance of NH₃-PAA anodes with different pH values.

Multiple experiments were done to compare aspects of cell performance. Overall electrochemical performance was examined by cell cycling. Ionic conductivity was determined by an impedance test. Contact resistances to the current collector were measured with an apparatus developed in our lab. Silicon oxidation state was determined by XRD. Morphology of the anode can be compared by SEM.

In our cycling results silicon half cells with LiOH-PAA binder had a 10% higher capacity than those with PAA binder (Fig. 1), all other factors being constant. And the LiOH-PAA film had a lower impedance value which confirms the hypothesis that extra Li⁺ could facilitate ion transfer. The PAA anode had a lower contact resistance to the current collector than did the LiOH-PAA anode. This result agrees with Xiong’s work [3], which claims that the corrosion of current collector when using PAA slurry could form a more rigid coating surface and thus lead to the surface cracking and lower the capacity. Other parts of this work including cycling performance and XRD are still in progress and will be reported.

1. Hays, K.A., et al., Journal of Power Sources, 2018. 384: p. 136-144.
2. Hu, B., et al., Journal of Power Sources, 2019. 416: p. 125-131.
3. Xiong, J., et al., ACS Applied Materials & Interfaces, 2021. 13(24): p. 28304-28323.