Propylenidene: A two-dimensional carbon allotrope as a high-capacity anode for potassium-ion batteries

Two-dimensional (2D) carbon materials have garnered significant attention as potential anode materials for alkali metal-ion batteries (AIBs) due to their unique structural and electronic properties. In this work, we systematically investigate the feasibility of propylenidene, a novel metallic carbon allotrope monolayer, as an anode material for AIBs using first-principles density functional theory (DFT) calculations. Our results reveal that propylenidene exhibits excellent dynamic and thermal stability, as confirmed by phonon dispersion spectra and ab initio molecular dynamics simulations. Among the alkali metals investigated, only potassium demonstrates superior adsorption behavior, with a high theoretical storage capacity of 1115.8 mA h g −1 and a low average open-circuit voltage of 0.252 V. Furthermore, potassium diffusion on the monolayer surface exhibits a high diffusion coefficient of up to 1.4 × 10 −6 cm 2 /s at room temperature and an ultralow energy barrier of 0.24 eV, indicative of fast charging capability. In bilayer propylenidene, potassium diffusion on the outer surface remains highly favorable with a further reduced barrier of 0.21 eV. The fully potassium-loaded structure also shows relatively small lattice expansion and robust thermal stability at 300 K. These findings collectively underscore propylenidene as a highly promising anode candidate for high-performance potassium-ion batteries (PIBs).