Tuning PAA-Based Binders Towards Optimized Performance for Silicon Anode in Lithium-Ion Batteries

Abstract

Poly(acrylic acid) (PAA) based binders have been widely used for silicon anodes in lithium-ion batteries to mitigate the issues caused by reversible volumetric expansion of silicon nanoparticles during lithiation/delithiation process. However, the performance of silicon anodes using PAA-based binders is still far from meeting the requirement of practical applications and the factors affecting the performance of these binders are not fully understood. Neutralization of PAA binders using LiOH is a common strategy for processing silicon anodes in lithium-ion batteries. In our previous studies, lithiated PAA solutions showed significant increased viscosity compared to straight PAA ones, which could benefit the large-scale lamination process and enable the fabrication of mechanically robust electrodes. However, lithiated PAA binders suffer more capacity loss in cycling tests due to the weakened adhesion and more severe side reaction of silicon particles that are mostly related to the increase of pH value of the binder solutions. In this work, non-lithium bases (e.g., NBu4OH, NH4OH, and Et3N) were used to neutralize and tune the viscosity of PAA solution. The resulting modified PAA binder solutions achieved desired viscosity with less increase of pH value. Notably, electrodes made with PAA-NH4 binder showed improved cell performance than electrodes made with PAA-Li binder. Despite the pH difference between PAA and PAA-Li binder solutions, the solvation behavior of the binders could also affect cycling performance. Therefore, a series of PAA solutions were prepared and investigated by small-angle X-ray scattering. The radius of gyration (Rg) of the binders were found to be significantly different depends on lithiation and the choice of solvent. Electrodes made with these binder solutions were evaluated in half cells to explore the relationship between solvation and performance of binders.