Vertically rooting carbon nanotubes on cobalt-loaded hollow Titanium Dioxide spheres as conductive multifunctional sulfur hosts for superior lithium-sulfur performance

Abstract

The rechargeable lithium-sulfur (Li–S) batteries have been regarded as the most promising alternatives for Li-ion batteries. However, the poor conductivity, the large volume expansion of sulfur, and the “shuttle effect” of polysulfides lead to the rapid capacity decay of sulfur cathodes, which impedes the practical application of Li–S batteries. Herein, a novel three-dimensional (3D) hierarchical structured high-efficiency sulfur host (Co-CNTs@TiO2), which was assembled by hollow TiO2 spheres and vertically rooted carbon nanotubes (CNTs) network framework, was developed by simple chemical vapor deposition (CVD) method. The 3D CNTs network promoted long-range conductivity and efficiently exposed the Co active sites. Remarkably, the Co particles acted as adsorptive and catalytic sites, which were effective for chemical fixation and conversion of polysulfides. Meanwhile, the hollow and porous structures of Co-CNTs@TiO2 microspheres were conducive to the buffering of volume change during the cycling process, and could physically encapsulate polysulfides. Consequently, the S/Co-CNTs@TiO2 cathode can deliver a high initial specific capacity of 1134.9 mAh g−1 at 0.2C, remarkable long-term cycling stability over 500 cycles with a low capacity fading rate of 0.072% per cycle at 1.0C, as well as excellent performance under high sulfur loading up to 5.9 mg cm−2.