Interfacial Engineering and Coupling of MXene/Reduced Graphene Oxide/C₃N₄ Aerogel with Optimized d-Band Center as a Free-Standing Sulfur Carrier for High-Performance Li-S Batteries

To overcome the shuttle effect and improve the energy density of Li-S batteries, developing free-standing sulfur carriers with high capture and catalytic effect towards polysulfides is an effective strategy. Herein, a MXene/reduced graphene oxide/C3N4 aerogel (MG/C3N4) with three-dimensional architecture prepared through low-temperature hydrothermal approach followed by thermal treatment is used as sulfur carrier for free-standing cathode of Li-S batteries. In the MG/C3N4, MXene and rGO construct a highly conductive framework, and the MXene nanosheets offer chemical capture and catalytic activity towards lithium polysulfides, in favor of good cycling stability. The introduction of g-C3N4 further enhances the reactivity of C-Ti-N at the hetero-interface by engineering the electronic state of Ti atoms, leading to the optimized metal d-band for expediting the multistep conversion of sulfur electrochemistry. Therefore, the free-standing sulfur cathode with MG/C3N4 carrier achieves excellent performance with a capacity of 1315.6 mAh g(-1) at 0.2 C and a capacity retention of 97.5% after 100 cycles as well as superior rate capability with 1167.4 mAh g(-1) at 2 C. Even at a high sulfur loading of 4.92 mg cm(-2), the cathode remains 940.3 mAh g(-1) (4.62 mAh cm(-2)) after 200 cycles, indicating its promising potential for achieving high-performance Li-S batteries.