Two-dimensional borophene and borides as promising topological electrodes for ion batteries

Based on first-principles calculations, we propose two borophene (B1 and B2) and two borides (NiB and SiB) as promising electrode materials for lithium-ion and sodium-ion batteries. All four materials have excellent metallic properties with favorable electrical conductivity. Among them, the two-dimensional B1, B2 and NiB monolayers have unique topological properties with the presence of a nodal loop near the Fermi energy level. These four materials can stably adsorb lithium and sodium ions and there is sufficient charge exchange between them. All two-dimensional monolayers have good wettability with commonly used battery electrolytes. They all have low diffusion barriers and suitable open-circuit voltages. In particular, the NiB monolayer has a diffusion barrier as low as 34 meV for Li and 28 meV for Na, which is lower than many two-dimensional materials. In addition, they have a high storage capacity, much higher than conventional graphite electrodes. These properties indicate that monolayers B1, B2, NiB and SiB are promising anode materials for metal ion batteries.