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 e V atom^(-1)),the total energy of net-C18(-9.15 e V atom^(-1))is only 0.13 e V 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 e V),and net-C18 has a low open-circuit voltage(0.024 V)and a high theoretical specific capacity(403 m Ah 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.