Unveiling single-layer Hittorf's violet phosphorus as a novel sodium host anode to advance Na-ion battery technology

While sodium-ion batteries (SIBs) are widely regarded as the most viable successor to lithium-ion batteries, thanks to sodium's abundant supply and low cost, their progress is still hampered by the lack of efficient anode materials. Here, we explore a newly exfoliated two-dimensional phase of Hittorf's violet phosphorus (2D VP) as a potential sodium host anode using density functional theory and ab initio molecular dynamics simulations. The results confirm that 2D VP is energetically, kinetically, and thermally stable. The material behaves as a direct semiconductor with a band gap of 1.72 eV, which disappears upon multiple Na adsorption. Moreover, 2D VP exhibits strong Na adsorption (−2.17 eV) and rapid diffusion (0.13 eV), effectively suppressing Na dendrite formation and demonstrating compatibility with common electrolytes. Notably, 2D VP offers an average potential of 0.62 V and a high theoretical capacity of 618.06 mAh/g, outperforming several known phosphorus allotropes. We anticipate that these computationally screened results will not only broaden the landscape of phosphorus-based anodes but also stimulate experimental efforts toward synthesizing and evaluating 2D VP for practical sodium-ion energy storage solutions.