Theoretical investigation of Janus Ti2BST (T = O, Se) monolayers as anode materials for Na/K-ion batteries†

The structures, stability, and electrochemical performances of Janus Ti₂BST (T = O, Se) monolayers as anode materials for Na/K-ion batteries (NIBs/KIBs) are investigated by first-principles calculations. The results demonstrate that Ti₂BST monolayers are mechanically, dynamically, and thermally stable. The electronic structures display good conductivity. Moreover, the low diffusion barriers of 0.107/0.039 eV (0.111/0.063 eV) for Na/K indicate that the Ti₂BSO (Ti₂BSSe) monolayer has excellent rate performance for NIBs/KIBs. Low average open circuit voltages (OCVs) (0.322–0.439 V) can produce a high voltage in NIBs/KIBs. Meanwhile, little structural changes during charge/discharge ensure great cycle stability. Especially, the Ti₂BSO monolayer has a high theoretical capacity of 691.64/537.75 mA h g⁻¹ for NIBs/KIBs. The outstanding performances demonstrate that the Ti₂BST monolayers are potential anode materials for NIBs/KIBs.