▎ 摘　　要

In recent years, graphene-based composite films have been greatly developed in the field of electromagnetic shielding interference (EMI). However, it is still a huge challenge to prepare graphene-based composite films with excellent mechanical properties, conductivity and electromagnetic shielding properties. In this work, we adopted a facile and effective method by annealing the alkali-treated polyacrylonitrile (aPAN) nanofibers reinforced graphene oxide (GO) composite films at 2000 degrees C to obtain graphene-carbon nanofibers composite films (GCFs). Microscopically, carbon nanofibers (CNFs) were intercalated into the graphene sheets, and microgasbags structure was formed during the heat treatment process. The special structure makes GCFs have superior tensile strength (10.4 MPa) at 5% strain. After repeated folding over 1000 times, the films still demonstrate excellent structural integrity and flexibility performance. Interestingly, the graphene-based composite films with 10 wt% aPAN nanofibers exhibit an extremely low density of about 0.678 g/cm(3) and excellent electrical conductivity of 1.72 x 10(5) S/m. Further, an outstanding electromagnetic shielding effectiveness (SE) of 55-57 dB was achieved, and the corresponding value of the specific SE/thickness can reach 67,601-70,059 dB.cm(2)/g, which is the highest among reported graphene-based shielding materials. The significant electromagnetic shielding performance is due to the synergistic enhancement effect brought by the excellent conductivity of carbon nanofibers and graphene, the formed effective conductive network and the microgasbags structure. Electromagnetism simulation further clarified that the underlying mechanism should be mainly attributed to the conduction loss and multiple reflections caused by the special structure of GCFs. This work will provide new solutions for low density, high flexibility and excellent electromagnetic shielding properties materials in the next generation of foldable and wearable electronics. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.