DFT studies on electrochemical properties of halide ions doped GDY-28 nanoflake for Na-ion battery applications

Efficiency of pristine and halogens doped graphdiyne analogue (GDY-28) is theoretically investigated for application as anode material in sodium ion batteries (NIBs). In this scenario, density functional theory (DFT) calculations are implemented to study electrochemical properties of Na/X@GDY-28 and Na⁺/X@GDY-28 (X = F⁻, Cl⁻ and Br⁻) complexes in the presence of carbon tetracholride solvent. Na and Na⁺ prefer to adsorb in the middle of GDY-28 nanoflake. The adsorption energy (E_ad) of Na⁺ is stronger as compared to Na for both pristine and halides doped GDY-28, E_ad of Na ⁺ on GDY-28 in Na⁺@GDY-28 is −661.90 kcal mol⁻¹. However, the calculated Gibbs free energy and cell voltage of pristine GDY-28 nanoflake are −3.82 kcal mol⁻¹ and 0.17, respectively. Adopting a strategy of doping halides on GDY-28 nanoflake considerably increased the Gibbs free energy, which resulted in the enhancement of cell voltage. The cell voltage of these systems is increased from 0.17 V (for pristine GDY-28) to 0.20 V–0.52 V (for X⁻@GDY-28 (X⁻ = F⁻, Cl⁻ and Br⁻)). A monotonic increase in cell voltage is noticed with increase in electronegativity of halide ion. The reason is strong binding of Na⁺ with more electronegative halide ion doped GDY-28 nanoflake. The highest ΔG (−12.00 kcal mol⁻¹) and cell voltage (0.52 V) is reported for Na/F@GDY-28 complex in the presence of carbon tetracholride.