PHP-graphene nanoribbon-assembled porous metallic carbon for sodium-ion battery anode with high specific capacity

In recent years, a number of three-dimensional (3D) porous metallic carbon allotropes have been proposed to be used as anode materials for metal-ion batteries by assembling graphene or penta-graphene nanoribbons. Here, based on density functional theory and tight-binding model, we design a new 3D porous metallic carbon monolith (termed Hex-C568) consisting of PHP-graphene nanoribbons which contain pentagonal, hexagonal and octagonal rings. It is thermally, dynamically and mechanically stable. We find that its metallicity is attributed to the delocalized electrons in the p-orbitals of the sp2 hybridized carbon atoms, and Hex-C568 is a promising anode material for Na-ion batteries with high performance. Its reversible gravimetric and volumetric capacities are 787.53 mAhg−1 and 718.10 mAhcm−3, respectively, with low diffusion energy barrier (0.04–0.30 eV), low average open-circuit voltage (0.26 V), and small volume change during the charging/discharging process (3.71%). These electrochemical properties are superior to those of most recently reported anode materials, suggesting that PHP-graphene nanoribbon is a promising building unit for the design of novel carbon anode materials going beyond graphene and penta-graphene.