In this paper, we report on 1-pyrene sulfonic acid sodium salt (1-PSA) modified graphene nanosheets (imGNS) prepared by a novel one-pot in situ supercritical fluid exfoliation and modification reaction. The 1-PSA molecules on the surface of the graphene layers acted as electron withdrawing groups resulting in an electron transfer from the GNS surface to the 1-PSA molecules. This was confirmed by a red shift of 1572∼1576 cm-1, in the graphitic 'G' band of the Raman spectra. This novel approach led to an increase in the yield of mono to double layer graphene sheets (about 60%). The charge-discharge measurement shows improved Li-ion charge-discharge properties of the imGNS with an increase in the concentration of 1-PSA molecules in comparison with starting graphite materials. This report provides a new direction for graphene exfoliation and surface modification for technological applications.