A new 3D porous metallic carbon allotrope composed of 5–7 nanoribbons as an anode material for sodium-ion batteries

Motivated by the successful synthesis of three-dimensional (3D) graphene monoliths, tremendous effort has been devoted to the design of 3D porous metallic carbon allotropes with rich topology by assembling various nanoribbons for the anode materials of metal-ion batteries in recent years. Going beyond the allotropes reported so far we propose a new 3D carbon monolith, Hex-C57, by using 5–7 nanoribbons observed in the experiment as the building block. Hex-C57 is found to be dynamically, thermally, and mechanically stable, and electronically metallic. An analysis based on the tight-binding model reveals that the metallicity originates from the pz-orbitals of the sp2-hybridized carbon atoms, forming the conducting channels along the axial direction. With the advantages of intrinsic metallicity, mechanical ductility, and ordered pores, Hex-C57 is a highly promising anode material for sodium-ion batteries (SIBs). Calculations of the electrochemical properties show that Hex-C57 possesses a high reversible gravimetric capacity (334.69 mAhg−1) and volumetric capacity (314.61 mAhcm−3), a small volume change (1.45%), very low diffusion barriers (0.046–0.070 eV), and a low average open-circuit voltage (0.18 V). This work not only expands the 3D porous carbon family with different nanoribbons as the building blocks, but also demonstrates the functionality of unconventional 5–7 carbon rings-assembled materials.