Water-Soluble Polyamide Acid Binder with Fast Li+ Transfer Kinetics for Silicon Suboxide Anodes in Lithium-Ion Batteries

Silicon suboxide (SiO_x) anodes have attracted considerable attention owing to their excellent cycling performance and rate capability compared to silicon (Si) anodes. However, SiO_x anodes suffer from high volume expansion similar to Si anodes, which has been a challenge in developing suitable commercial binders. In this study, a water-soluble polyamide acid (WS-PAA) binder with ionic bonds was synthesized. The amide bonds inherent in the WS-PAA binder form a stable hydrogen bond with the SiO_x anode and provide sufficient mechanical strength for the prepared electrodes. In addition, the ionic bonds introduced by triethylamine (TEA) induce water solubility and new Li⁺ transport channels to the binder, achieving enhanced electrochemical properties for the resulting SiO_x electrodes, such as cycling and rate capability. The SiO_x anode with the WS-PAA binder exhibited a high initial capacity of 1004.7 mAh·g^-1 at a current density of 0.8 A·g^-1 and a capacity retention of 84.9% after 200 cycles. Therefore, WS-PAA is a promising binder for SiO_x anodes compared with CMC and SA.