Net‐C18: A Predicted Two‐Dimensional Planar Carbon Allotrope and Potential for an Anode in Lithium‐Ion Battery

Net‐C18, a predicted two‐dimensional (2D) graphene‐like carbon allotrope, is investigated via first‐principles calculations. Its space group is Pmmm . There are 18 carbon atoms per cell. Net‐C18 has five‐, six‐, and eight‐membered rings. Net‐C18 may be formed by adding even pairs of carbon atoms on the top of hexagons to reconstruct new five‐ and eight‐membered rings, extending the strategy of Haeckelite. Compared to that of graphene (−9.28 eV atom −1 ), the total energy of net‐C18 (−9.15 eV atom −1 ) is only 0.13 eV atom −1 higher, revealing that net‐C18 is energetically metastable. The calculations of phonon and ab initio molecular dynamics (AIMD) demonstrate dynamical and thermal stability of net‐C18. The independent elastic constants of net‐C18 meet the criterial for the mechanical stability of 2D structure. Its in‐plane stiffness along x or y axis is comparably large. The AIMD results reveal that net‐C18 has good thermal stability at 1500 K. The band structure also demonstrates that it is metallic. Furthermore, the diffusion of Li atoms on net‐C18 has a low energy barrier (0.32 eV), and net‐C18 has a low open‐circuit voltage (0.024 V) and a high theoretical specific capacity (403 mAh g −1 ). Thus, net‐C18 may provide high‐temperature resistant, flexible electrode in electronics and a promising metallic anode in lithium‐ion battery. The proposed formation of net‐C18 may open a new pattern defect for the designs of new carbon allotropes.