Dual-Fe-Atom Doped Graphene D²-Fe₂C₁₂: An Ultrahigh Theoretical Capacity Anode for Li/Na/K-Ion Batteries

Driven by lithium resource constraints and cost volatility, there is a critical need for high-performance, universal anodes for non-lithium systems such as Na and K, while maintaining rapid ion transport and structural stability. Addressing the limited intrinsic interaction between graphene and alkali-metal ions─and the resulting capacity limitations─this study proposes and systematically evaluates, based on density functional theory (DFT), a design strategy for dual Fe-atom-doped graphene, D²-Fe₂C₁₂. Introducing dual Fe atoms breaks local symmetry, reconstructs the electronic states near the Fermi level, and creates a high density of strong anchoring sites, thereby synergistically enhancing adsorption thermodynamics and surface diffusion kinetics. Calculations show that the theoretical specific capacity for Na reaches 2513.25 mAh/g, and those for Li and K are 1675.50 and 837.75 mAh/g, respectively, markedly outperforming conventional carbon-based anodes. Structural analysis further indicates that the lattice variation induced by ion adsorption is less than 5%, corroborating structural stability under multi-ion storage. Meanwhile, favorable electronic conductivity and low migration barriers (Li/Na/K all <0.5 eV) jointly ensure excellent rate performance and fast charge-discharge capability. In summary, D²-Fe₂C₁₂ achieves a balanced optimization of high capacity, low strain, and superior kinetics, demonstrating strong potential as a universal anode for Li/Na/K systems and providing a reusable theoretical foundation for the atomistic, rational design of dual-Fe-doped two-dimensional carbon materials.