A facile liquid phase exfoliation method to prepare graphene sheets with different sizes expandable graphite

•This study presented a novel method for the production of high-quality graphene sheets through the exfoliation of Li-intercalated EG with sonication.•The quality of the graphene sheets produced from different sizes EG was compared for the first time and the formation mechanism was discussed.•The graphene sheets obtained from the small size EG have less layers than the large size EG. In this work, graphene sheets suspension were synthesized directly from expandable graphite (EG) via an intercalation and exfoliation pathway using n-butyl lithium as the intercalating agent, water and N,N-dimethylformamide (DMF) as the exfoliating agent. The quality of the graphene sheets produced from different sizes EG was compared and the formation mechanism was discussed. The formation of the graphene sheets and its formation mechanism were confirmed by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy measurement, inductively coupled plasma atomic emission spectrometry (ICP-AES) and thermogravimetric analysis (TGA). The graphene sheets obtained from the small size EG have less layers than the large size EG.