First-Principles Insights into Li Storage and Ion Diffusion in B‑, P‑, and S‑Doped C₂N Anodes

Two-dimensional C₂N monolayers are promising anode materials for lithium-ion batteries due to their high nitrogen content, intrinsic porosity, and tunable electronic properties. In this work, first-principles density functional theory (DFT) is used to systematically investigate B-, P-, and S-doped C₂N monolayers at two dopant concentrations (2.78 and 5.56 at. %). Doping substantially modifies the electronic structure, closes the band gap, and enhances Li adsorption without compromising overall structural stability. B-doped C₂N exhibits the highest thermodynamic favorability for incorporation (E _f = 1.36 eV), while S-doping introduces lattice flexibility and facilitates fast Li diffusion with a low energy barrier of ∼0.36 eV, markedly lower than that of pristine C₂N. The average open-circuit voltage increases to 2.93 and 2.77 V for P- and B-doped systems, respectively, compared to pristine C₂N (∼2.18 V), while S-doped C₂N maintains a moderate voltage of 2.12 V with enhanced rate capability. High dopant concentrations further increase Li storage but introduce diffusion anisotropy, highlighting a trade-off between capacity and ion mobility. This study provides critical insights and design guidelines for developing high-capacity, fast-charging C₂N-based anodes.