Ti‐Doped and Fluoride‐Encapsulated Borospherene (B40) Nanocages for Calcium‐Ion Battery Anodes: First Principles Insights

Abstract

The development of efficient anode materials is essential for calcium‐ion batteries (CaIBs). Using density functional theory (DFT‐D3) calculations with Grimme's D3 dispersion correction, we investigated pristine borospherene (B 40 ), heteroatom‐doped (B 39 N, B 39 Si, B 39 Ti), and halide‐encapsulated nanocages (F – B 40 , Cl – B 40 , Br – B 40 , and F – B 39 X). Calcium and Ca 2+ interactions were analyzed via binding energy, charge transfer, and conductivity. Ti‐doping enhanced Ca storage with favorable adsorption (−2.15 eV), high voltage (4.45 V), and strong reactivity. Fluoride encapsulation further strengthened Ca binding, reaching −3.626 eV in Ca/F – B 39 Ti. Molecular dynamics (MD) simulations confirmed structural stability, and theoretical capacities of 441.2–477.9 mAh g −1 compare well with reported CaIB anodes. Significant bandgap reductions (e.g., 57.88% in Ca/F – B 39 N, 51.99% in Ca/F – B 39 Ti) indicate improved conductivity. Spin‐polarized PDOS for Ca/B 39 Ti and Ca/F – B 39 Ti revealed asymmetric spin states, suggesting net magnetism. Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) analyses highlighted electrostatic and partial covalent interactions. Notably, Ca adsorption on fluoride‐encapsulated B 39 X produced the highest hyperpolarizability ( β 0 ), indicating potential for optoelectronic use. Open‐circuit voltages of Ca 6 /B 40 , Ca 6 /Br – B40, and Ca 6 /F – B 39 Ti (0.1–1 V) confirm stability at high Ca content. Overall, borospherene nanocages, particularly fluoride‐encapsulated and Ti‐doped systems, emerge as promising CaIB anodes and multifunctional materials for energy and photonic devices.