Structural, Electronic, and Li-ion Adsorption Properties of PolyPyGY Explored by First-Principles and Machine Learning Simulations: A New Multi-Ringed 2D Carbon Allotrope

Two-dimensional (2D) carbon materials have been intensively investigated because of their distinctive structural framework and electronic behaviors as alternatives in energy conversion and storage applications. This study proposes a novel 2D carbon allotrope, Polymerized Pyracyclene Graphyne (PolyPyGY), characterized by a multi-ringed structure with 4-, 5-, 6-, 8-, and 16-membered rings comprising a porous structure. Using first-principles calculations and machine-learning techniques, we explore its structural, electronic, mechanical, optical, and lithium-ion storing properties. The vibrational properties assessed through the density functional perturbation theory framework confirm its structural stability. Moreover, ab initio molecular dynamics simulations at 1000 K demonstrate its thermal resilience, with no bond breaking or reconfiguration observed. The electronic band structure reveals a metallic nature, and the material exhibits anisotropic elastic properties, with Young's modulus varying between 421 and 664 GPa, suggesting good mechanical stability. Furthermore, lithium diffusion studies indicate low energy barriers (0.05-0.9 eV) and a high diffusion coefficient ( $>$ 6 $\times$ 10$^{-6}$ cm$^{2}$/s), along with a stable open circuit voltage of 1.2 V. These results highlight PolyPyGY's potential as a highly effective and durable anode material for lithium-ion batteries, featuring rapid Li-ion diffusion, stable intercalation, and consistent performance during charge and discharge cycles.