Can Borophite Outperform Graphite as an Anode Material for Sodium-Ion Batteries? A First-Principles Perspective

Sodium-ion batteries (SIBs) are regarded as a potential alternative to lithium-ion batteries (LIBs). Although sodium shares chemical similarities with lithium, the conventional graphite anode used in LIBs cannot effectively intercalate sodium ions, posing a long-standing challenge for SIB development. Motivated by boron’s unique electron-deficient properties, we theoretically propose borophite, a bulk-layered boron allotrope composed of van der Waals-stacked δ₅ borophene, as a potential high-performance anode material for SIBs. Unlike the s-p orbital hybridization in Na-intercalated graphite, the hybridization between Na-3p and B-2p orbitals enhances the Na binding strength in borophite. Borophite enables efficient Na intercalation via two stable configurations, NaB_6n and NaB_8n (n = 1, 2, 3, 4). The fully sodiated NaB₆ phase achieves a high theoretical specific capacity of 406 mAh g^–1. Additionally, borophite exhibits fast ion mobility, with a low in-plane diffusion barrier of 0.27 eV, which facilitates rapid charge/discharge rates. These findings demonstrate that borophite is a promising anode candidate for next-generation SIBs.