Design of Three-Dimensional Metallic Biphenylene Networks for Na-Ion Battery Anodes with a Record High Capacity

Na-ion batteries (NIBs) capture intensive research interest in large-scale energy storage applications because of sodium's abundant resources and low cost. However, the low capacity, poor conductivity, and short cycle life of the commonly used anodes are the main challenges in developing advanced NIBs. Here, stimulated by the recent successful synthesis of biphenylene [Science 2021, 372, 852], we show that these problems can be curbed by assembling armchair biphenylene nanoribbons of different widths into three-dimensional architectures, which lead to homogeneously distributed nanopores with robust structural and mechanical stability. Through density functional theory and molecular dynamics calculations combined with the tight-binding model, we find that the assembled 3D biphenylene structures are metallic and thermally stable up to 2500 K, where the metallicity is further identified to originate from the p_z-orbitals (π-bonds) of the sp² carbon atoms. Especially, the optimal assembled structures HexC28 (HexC46) deliver a gravimetric capacity of 956 (1165) mA h g^-1 and a volumetric capacity of 1109 (874) mA h mL^-1, which are much higher than those of graphite and hard carbon anodes. Moreover, they also show a suitable average potential, negligible volume change, and low diffusion energy barrier. These findings demonstrate that assembling biphenylene nanoribbons is a promising strategy for designing next-generation NIB anodes.