First-Principles Investigation of Phosphorus-Doped Graphitic Carbon Nitride as Anchoring Material for the...

The utilization of lithium-sulfur battery is hindered by various challenges, including the "shuttle effect", limited sulfur utilization, and the sluggish conversion kinetics of lithium polysulfides (LiPSs). In the present work, a theoretical design for the viability of graphitic carbon nitride (g-C₃N₄) and phosphorus-doping graphitic carbon nitride substrates (P-g-C₃N₄) as promising host materials in a Li-S battery was conducted utilizing first-principles calculations. The PDOS shows that when the P atom is introduced, the 2p of the N atom is affected by the 2p orbital of the P atom, which increases the energy band of phosphorus-doping substrates. The energy bands of P_C and P_i are 0.12 eV and 0.20 eV, respectively. When the lithium polysulfides are adsorbed on four substrates, the overall adsorption energy of P_C is 48-77% higher than that of graphitic carbon nitride, in which the charge transfer of long-chain lithium polysulfides increase by more than 1.5-fold. It is found that there are powerful Li-N bonds between lithium polysulfides and P-g-C₃N₄ substrates. Compared with the graphitic carbon nitride monolayer, the anchoring effect of the LiPSs@P-g-C₃N₄ substrate is enhanced, which is beneficial for inhibiting the shuttle of high-order lithium polysulfides. Furthermore, the catalytic performance of the P-g-C₃N₄ substrate is assessed in terms of the S₈ reduction pathway and the decomposition of Li₂S; the decomposition energy barrier of the P-g-C₃N₄ substrate decrease by 10% to 18%. The calculated results show that P-g-C₃N₄ can promote the reduction of S₈ molecules and Li-S bond cleavage within Li₂S, thus improving the utilization of sulfur-active substances and the ability of rapid reaction kinetics. Therefore, the P-g-C₃N₄ substrates are a promising high-performance lithium-sulfur battery anchoring material.