TiO2–TiN Decorated Carbon Nanoplates Derived from NH2-MIL-125 with Efficient Polysulfide Catalytic Conversion for Long-Life Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries reveal unequaled theoretical capacity and higher energy density compared to commercial Li-ion batteries. Still, the commercialized application process of Li–S battery is impeded by low utilization of sulfur and capacity fading from the "shuttle effect" and sluggish lithium polysulfides (LiPSs) redox conversion kinetics, especially for the battery with high areal sulfur loading and lean electrolyte. Herein, nitrogen-doped carbon nanoplates embedded with ultrafine TiO2–TiN heterojunctions (TiON@CNPs) are prepared by copyrolysis of NH2-MIL-125 nanoplates with melamine, serving as the multifunctional interlayer for LiPSs blocking, efficient conversion and fast Li2S nucleation. In this design, the LiPSs could be physically blocked by the N-doped carbon nanoplates and ultrafine TiO2–TiN heterostructures via chemical interaction and then subsequently converted to Li2S with enhanced kinetics and electrochemical efficiency and nucleation on the surface of ultrafine TiO2–TiN heterostructures. Meanwhile, the porous nanoplate structure of the carbon skeleton could also shorten the Li+ diffusion path and afford more electrochemical active sites for Li2S/S uniform deposition. As a consequence, the cell with TiON@CNPs modified separator achieves a high capacity retention of 83.2% (1147 mAh·g–1 at 0.2 C) after 300 cycles, a preferred rate performance of 908 mAh·g–1at 4.0 C, and a low capacity decaying of 0.026% per cycle at 1 C over 1200 cycles. Remarkably, the cathode with sulfur loading of 4.5 mg·cm–2 achieves a reversible capacity of 4.28 mAh·cm–2 after 200 cycles, demonstrating a potential for future application in Li–S batteries.