Experimental and DFT investigations on multifunctional Ti₃C₂T_x MXenes/PDAAQ free standing interlayer for enhancing the cycle life and high-rate performance of Na–S batteries

Sodium–sulfur (Na–S) batteries have attracted considerable attention owing to their remarkable theoretical specific capacity and elevated energy density. However, the practical application of Na–S batteries is impeded by swift capacity degradation and the insulating characteristics of the sulfur cathode. In this study, PDAAQ was produced through the chemical oxidation of DAAQ, utilizing APS as the initiating agent and HClO₄ as the acidic environment. This process is facilitated by the creation of poly(1,5-diaminoanthraquinone) through interfacial polymerization, followed by the integration of MXene through vacuum-assisted filtration and electrostatic self-assembly. The addition of PDAAQ significantly improved electrical conductivity and reduced the diffusion distance for Na⁺ ions, thereby enhancing material efficiency and reaction kinetics. Furthermore, this method effectively inhibited the re-stacking of MXene layers. As a result, the cell equipped with an MXene/PDAAQ interlayer, a sodium metal anode, and a S/Carbon black (CB) composite cathode exhibited a discharge capacity of 602.9 mAh g⁻¹ after 800 cycles, demonstrating an impressive Coulombic efficiency of 96.7 %. These results highlight the promise of MXene/PDAAQ as a sophisticated MXene-based separator for the improvement of high-capacity Na–S batteries. Our DFT calculations reveal that the MXene/PDAAQ layer facilitates the dissociation of sodium polysulfides into adsorbed sulfur and mobile sodium ions, thereby elucidating the experimental observations.