Atomic-scale insights into alkali metal (Li, Na, and K) ion anode performance of a low-energy graphyne polymorph

The development of high-capacity and fast-charging alkali-ion batteries requires the discovery of efficient and structurally robust anode materials. In this work, we theoretically investigate the electrochemical performance of a two-dimensional carbon allotrope, Cp-graphyne (CpG), as a potential anode material for alkali metal (Li-, Na- and K-) ion batteries using first-principles density functional theory calculations. Owing to its porous framework and extended π-conjugated carbon network, CpG exhibits excellent alkali-metal storage capability with a high theoretical specific capacity of 558.33 mAh g^-1. The calculated open-circuit voltages are 0.65 V for Li, 0.53 V for Na, and 1.51 V for K adsorption, indicating thermodynamically favorable operating voltage windows for rechargeable battery applications. Climbing-image nudged elastic band calculations reveal diffusion barriers of 0.71 eV, 0.60 eV, and 0.35 eV for Li, Na, and K ions, respectively, demonstrating favourable ion mobility across the CpG monolayer, especially for potassium. Charge-transfer analysis further confirms strong interaction between alkali-metal ions and the CpG surface, ensuring structural stability during ion storage. Ab initio molecular dynamics simulations additionally verify the thermal stability of metal-loaded configurations under ambient conditions. Overall, the present findings highlight CpG as a promising low-energy graphyne polymorph for next-generation alkali-ion batteries and provide valuable theoretical guidance for the rational design of high-performance carbon-based anode materials.