Synergy of Epoxy Chemical Tethers and Defect-Free Graphene in Enabling Stable Lithium Cycling of Silicon Nanoparticles

Abstract

We report a new approach for nanosilicon-graphene hybrids with uniquely stable solid electrolyte interphase. Expanded graphite is gently exfoliated creating "defect-free" graphene that is non-catalytic towards electrolyte decomposition, simultaneously introducing high mass loading (48 wt. %) Si nanoparticles. Silane surface treatment creates epoxy chemical tethers, mechanically binding nano-Si to CMC binder through epoxy ring-opening reaction while stabilizing the Si surface chemistry. Epoxy-tethered silicon pristine-graphene hybrid "E-Si-pG" exhibits state-of-the-art performance in full battery opposing commercial mass loading (12 mg cm^-2 ) LiCoO₂ (LCO) cathode. At 0.4 C, with areal capacity of 1.62 mAh cm^-2 and energy of 437 Wh kg^-1 , achieving 1.32 mAh cm^-2 , 340.4 Wh kg^-1 at 1 C. After 150 cycles, it retains 1.25 mAh cm^-2 , 306.5 Wh kg^-1 . Sputter-down XPS demonstrates survival of surface C-Si-O-Si groups in E-Si-pG after repeated cycling. The discovered synergy between support defects, chemical-mechanical stabilization of Si surfaces, and SEI-related failure may become key LIB anode design rule.

Keywords: Coulombic efficiency; graphene defects; silicon; solid electrolyte interphase (SEI); surface chemistry.