Enhancement of Functionalized 1T-NbS ₂ Monolayer Properties for the Superior Anode of Na-Ion Batteries

One of the most important factors influencing the performance of Na-ion batteries (NIBs) is the anode’s quality. Currently, NIB anodes have numerous disadvantages, including low capacity, rapid volume change, temperature variable conductivity and poor thermal/chemical stability. In this work, the electronic and transport properties of undoped, doped and defective 1T-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> monolayers were investigated using density functional theory calculations. The maximum quantum capacitance of 1T-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with S-vacancy (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub>-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) changes from 20.49 to 16.92 μF/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> across temperature ranges of 200 K to 1000 K, indicating its suitability as anode with temperature-stable capacity. The 1T-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> monolayers exhibit high electrical conductivity with less than 6% fluctuation across a temperature range of 200 K to 1000 K, indicating thermally stable conductance. The 1T-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layered structure has substantially larger interlayer spacing of 0.615 nm than the size of Na ion (0.095 nm), as well as a relatively tiny variation (0.05 eV for V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub>-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) in cohesive energies between sodiated and de-sodiated phases, making it a good choice for anodes. For V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub>-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>, the seebeck coefficient ranges from -5 to -40 μV/K, which is often obtained by the most commonly used Na-metal anode, demonstrating its appropriateness as anode. According to our findings, 1T-NbS<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is a great option for thermally stable NIB electrode applications.