▎ 摘　　要

Both graphene nanosheets and carbon nanotubes have exceptional electric and thermal conductivities, rendering them excellent candidates as second-phase fillers in composite materials to substantially enhance their effective conductivities. Their markedly different geometries, however, can have significant effect on the effective conductivities of composites, which we investigate using an effective medium approximation. It is demonstrated that graphene nanosheet is more effective in conductivity enhancement than carbon nantubes, and both fillers lead to substantially higher conductivity and much reduced percolation threshold in composites. The effects of conductivity anisotropy and interfacial resistance are also discussed.