Room-Temperature Intercalation and ∼1000-Fold Chemical Expansion for Scalable Preparation of High-Quality Graphene

Low-cost, scalable preparation of high-quality graphene has been a critical challenge that hampers its large-scale application. We here propose a novel, scalable liquidphase exfoliation method in which the intercalation, expansion, and exfoliation of graphite are achieved all under ambient conditions, not involving any heating or high-temperature treatment. We demonstrate that such room-temperature liquid-phase intercalation and expansion allow graphite flakes to expand up to 1000 times. Significantly different from thermally expanded graphite, the resulting chemically expanded graphite (CEG) exhibits a uniform, open, porous structure with a specific surface area (847 m(2)/g) comparable to the theoretical value of three-layer graphene. The CEG obtained is able to be exfoliated under mild conditions to give high-quality graphene with a yield of 70% relative to the starting graphite. The exfoliated graphene sheets have very few defects, with an atomic ratio of carbon to oxygen (C/O ratio) of 28. The as-prepared graphene exhibits an electrical conductivity of 1.17 X 10(5) S/m and the corresponding transparent films also reveal superior optical and electrical performance.