Silk Fibroin-Induced Conformational Change for Robust Silicon Anodes

Conventional binders, commonly involving mechanical interlocking force and molecular interaction bonding, could not thoroughly address substantial volumetric expansion and subsequent rapid capacity degradation of silicon anodes during cycling, limiting large-scale commercial application of high-energy-density of Si-based anodes. Herein, we propose a new binding mechanism, i.e., conformational change induced by silk fibroin (SF) to address these issues. Triggered by polyacrylic acid (PAA), SF undergoes a conformational change from an amorphous phase to β-sheet-rich structure and constructs a hierarchically ordered framework PAA-SF, which provides excellent mechanical strength through the formation of densely packed structures. Additionally, the unique β-sheet-rich structure of the PAA-SF binder could facilitate lithium-ion diffusion via coordination bonds with lithium ions. Consequently, the PAA-SF binder effectively mitigates stress from the volume expansion, enhances the rate capability, and constructs a stable SEI layer, thereby extending the cycling stability of silicon anodes. The cells with this binder can sustain a high reversible capacity of 600 mAh g^-1 after 1100 cycles at 4.2 A g^-1. The concept of a conformational change-based binding mechanism opens a promising avenue for the commercialization of silicon and other silicon-carbon anodes.