Ultrathin titanium carbide-modified separator for high-performance lithium-sulfur batteries

Despite a high theoretical capacity, the practical application of lithium-sulfur batteries has been primarily limited by the migration of long-chained polysulfide species during the charge/discharge processes. One effective approach to address the issues is to design a functional separator or interlayer. Here, we prepared a modified separator with an ultrathin layer of titanium carbide (TiC) using radio-frequency sputtering on a commercial Celgard polypropylene membrane. The 240-nm TiC coating layer can enhance the interfacial properties of Celgard separators in porosity, wettability, roughness, etc. Hence, via experimental and theoretical investigation, we discovered that TiC can efficiently adsorb polysulfides and boost charge transfer via strong covalent C-S bonds. Using a TiC-modified separator can impede the shuttle effect and improve the kinetics of sulfur conversion reactions. Thus, the Li-S batteries with TiC separator deliver excellent electrochemical performances with a good rate capability (717 mAh g- 1 at 7.0C) and an ultra-low decay rate of 0.058 % per cycle over 800 cycles at a C-rate of 2.0C. Furthermore, a high areal capacity of 4.3 mAh cm- 2 was achieved with a high mass-loading of sulfur cathode up to 7.0 mg cm- 2 .