▎ 摘　　要

Graphene films prepared through a self-assembly of graphene oxide and its derivatives have been recently explored for electromagnetic interference (EMI) shielding applications. However, this film preparation usually requires long-time high-temperature annealing, leading to a dramatic increase in energy and time-consumption and thus the total cost of mass production. Herein, a free-standing, highly flexible and conductive graphene film was fabricated via a simple and inexpensive method. The fabrication process starts with the chemical exfoliation of graphite in a novel binary-component system comprised of sodium peroxyborate and sulfuric acid, as a graphene suspension, which is then vacuum-filtered and mechanically pressed, not involving high-temperature post-treatment. The obtained graphene film shows excellent electrical conductivity of 1.53 x 10(6) S m(-1). More importantly, it also exhibits an ultrahigh EMI SE of 68 dB at a frequency of 8.2-12.4 GHz, which can block 99.99999% of incident radiation. To the best of our knowledge, this is the highest EMI SE performance reported so far in such thin thickness (about 3.2 mu m) of pure graphene materials. These outstanding properties make this ultrathin graphene film a promising alternative building block for electronic devices.