Insights into Na ion adsorption and diffusion in biphenylene as an anode material for sodium-ion batteries: A first-principles study

Anode materials are essential for the advancement of sodium-ion batteries (NIBs). This study comprehensively evaluates the biphenylene network (BP) as a promising anode material using first-principles calculations. Density functional theory (DFT) results reveal that sodium (Na) ions stably adsorb on BP surfaces, with adsorption energies ranging from −1.29 eV to −2.92 eV, due to effective charge transfer and hybridization between Na () and carbon () orbitals. The diffusion barriers for Na ion migration are 0.31 eV for the monolayer and 0.76 eV for the bilayer, with optimal paths involving the C8-ring and passing through C6- or C4-rings. Notably, edge sites were found to provide strong Na adsorption on monolayer BP nanoribbon, with low diffusion barriers (0.36 eV), revealing the critical role of edge configurations in enhancing the BP performance as an anode material. The theoretical capacity of Na on the BP monolayer is 908.52 mAh·g⁻¹, surpassing many other two-dimensional materials, and the average open circuit voltage (OCV) is 0.64 V. Overall, BP offers high Na storage capacity, low diffusion barriers, and suitable OCV, positioning it as a strong candidate for high-performance NIB anodes.