Robust Polyurethane Binders Intensified by Hydrogen Bonding, a Dynamic S–S Bond, and Metal-Ion Coordination for Silicon Anodes

Silicon (Si) anodes undergo severe volume expansion during charging and discharging, resulting in degradation of their electrochemical performance. Polymer binders are one of the most cost-effective ways to suppress the volume expansion of Si particles. In this paper, polyurethane (BFPU) containing conductive cycloalkane, a dynamic S–S bond, and multiple hydrogen bonds is synthesized. After that, polymeric cross-linked network binders with multiple functional bond groups are obtained by cross-linking BFPU and polydopamine (PDA) with metal ions like Zn2+, Fe3+, and Al3+ (PDA-M-BFPU; M = Zn, Fe, Al). The introduction of metal ions, hydrogen bonding, and a dynamic S–S bond network significantly improves the Li+ diffusion rate and mechanical strength, which effectively inhibits the volume expansion of the Si anode. With the addition of metal ions, the initial Coulombic efficiency (ICE) of half-cells increases from 76.5% to over 80%, especially for Si/PDA-Al-BFPU, which reaches 84.5%. Also, the capacity retention rate of Si/PDA-Al-BFPU is 76.8% after 200 cycles at 0.3 C. In addition, the full cell of NCM811//Si/PDA-Al-BFPU shows good cycle stability and rate performance. The robust BFPU binder intensified by hydrogen bonding, a dynamic S–S bond, and metal-ion coordination already exhibits great potential for application in Si anodes.