Composite Binder with a Robust Rigid-Flexible Network for High Performance Silicon/Carbon Anodes in Lithium-Ion Batteries

Silicon/carbon (Si/C) composite anodes are highly promising for next-generation lithium-ion batteries, but their practical application is severely hindered by massive volume fluctuations during cycling and subsequent rapid electrode degradation and capacity decay. To address this issue, a synergistic “rigid-flexible” composite binder was fabricated by combining high-modulus polyacrylamide (PAM) with flexible waterborne polyurethane (WPU). In this architecture, the abundant amide groups in PAM and urethane groups in WPU create strong hydrogen bonds with the Si surface and between PAM and WPU segments, leading to the formation of a rigid-flexible network for robust interfacial adhesion. Meanwhile, the flexible segments in WPU act as “molecular springs”, dissipating internal stress and accommodating substantial strain. The resultant Si/C electrode with the composite binder A2U1 not only preserves electrode integrity but also facilitates rapid Li-ion transport (D Li+ ≈ 1.0 × 10 –7 cm 2 s –1 ). Consequently, the A2U1-based Si/C electrode exhibits excellent electrochemical stability, retaining a high reversible capacity of 1051.2 mAh g –1 after 200 cycles with 89.3% capacity retention. Notably, the electrode shows remarkable dimensional stability, with the thickness expansion suppressed to 21.5% after 50 cycles, in sharp contrast with electrodes using individual PAM (124.9%) or WPU (172.8%) binders. This work provides a facile yet effective binder design strategy for the practical implementation of high-performance Si/C or Si anodes.