Synergistic Enhancement of Strength and Ductility in Crosslinked Polymer Binders for High-Stability Silicon Anodes in Lithium-Ion Batteries

Abstract

Crosslinking of the polymer binder is a powerful approach to suppress volume changes of Si-anode in lithium-ion batteries. However, this curing system is predominantly effective for soft-type flexible polymeric backbones and not for hard-type rigid polymeric structures due to the excessive brittleness they induce. In this study, a highly efficient crosslinking system applicable to hard-type polyimide (PI) and polyamide imidazole (PAID) was developed via crosslinking-induced flexibilization of polymeric backbone. We newly found that the chemical reaction of PI and PAID with oxirane-functionalized polyhedral oligomeric silsesquioxane (POSS) induces crosslinking while surprisingly softening the polymer backbone, which is an effect that has not been previously reported. As a result, the crosslinking prevents excessive stiffening of the polymer backbone, which consequently enhances the ductility, strength, and toughness of the binder, thereby improving the overall mechanical stability of Si-based anodes during repeated charging/discharging cycles. In addition, the crosslinking generates additional hydroxyl groups within the polymer binders, which enhances their interfacial interactions with Si nanoparticles. This unique crosslinking system exhibited markedly higher reversible capacity and significantly improved cycle stability than the noncured binders over 200 cycles at a rate of 0.2 C. It shows strong potential for universal applicability across hard-type polymeric architectures.