Pentagonal B2N3-based 3D metallic boron nitride with high energy density.

Different from conventional insulating or semiconducting boron nitride,metallicBN has received increasing attention in recent years as its intrinsic metallicity grants it great potential for broad applications. In this study, by assembling the experimentally synthesized pentagonal B2N3units, we have proposed the first pentagon-based three-dimensional (3D) metallic boron nitride, labeled penta-B4N7.First-principles calculations together with molecular dynamics simulations and convex hull diagram show that penta-B4N7is not only thermally, dynamically and mechanically stable, but also three dimensionally metallic. A detailed analysis of its electronic structure reveals that the intrinsic metallicity comes from the delocalized electrons in the partially occupied antibonding N-Nπorbitals. Equally important, the energy density of penta-B4N7is found to be 4.07 kJ g-1, which is the highest among that of all the 3D boron nitrides reported so far.