Background: Due to the difference in the numbers of graphene layers, graphene can be
classified as Single-Layer Graphene (SLG), Bi-Layer Graphene (BLG), and few-layer graphene. The
band gap of SLG is zero, which greatly limits its application to electronic devices.
Objective: Bi-layer graphene (BLG), graphene with two layers, not only possesses most of the advantages
of single-layer graphene, but also has some special properties. The opened band gap makes
BLG one of the promising materials in the field of electronic devices.
Strategy: The interesting electronic properties of BLG have drawn extensive attention; however, it is
still challenging to realize its commercial applications currently due to the limitation in large-scale
production and development of advanced applied technologies. Therefore, a timely and deep discussion
of BLG is quite necessary.
Review: In this review, the recent progress of BLG is introduced in detail, including the structure,
properties and preparation. Then, its potential applications are discussed, involving in ultrafast lithium
ion conductors, superconductors, ultrahard carbon films and field-effect transistors, revealing its
tremendous prospects. Finally, a summary is given to guide the further study of BLG.