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

Abstract

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 crosslinking BFPU and polydopamine (PDA) with metal ions like Zn 2+ , Fe 3+ , and Al 3+ (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.

Assembling a dense grid structure with green polyhydroxyurethane and a high-capacity Si-based anode for lithium ion batteries

“…On the other hand, ex situ infiltration of the bifunctional polyurethane (BFPU) that contains self-healable disulfide and ion conductive polyethylene glycol (PEG) into the Si-PAA electrode leads to stable cycle retention of Si anodes by energy-dissipative capability. 23,24 However, without direct chemical crosslinking, these options rely solely on the weak hydrogen bonds regardless of the number of interaction sites which are insufficient for accommodating the large internal stress of Si anodes. To fully exploit PU as a crosslinked binder, it is crucial to appropriately modify the functional groups.…”