Graphene oxide-wrapped cobalt-doped oxygen-deficient titanium dioxide hollow spheres clusters as efficient sulfur immobilizers for lithium-sulfur batteries

Abstract

The design of efficient sulfur host material is of great importance to address the undesirable polysulfide shuttling effect in the lithium-sulfur battery. Herein, we designed and constructed a sulfur immobilizer with multi-level sulfur storage space, which consists of the cluster of Co@TiO2 hollow spheres tightly wrapped by graphene oxide (labeled as Co@TiO2/GO). This structure provided a multi-level sulfur storage space, that is, the sulfur was encapsulated in the cavity of the Co@TiO2 hollow spheres, between Co@TiO2 spheres and GO sheets and in the interlaminar pores of GO. This enabled the inner and outer surfaces of the Co@TiO2 hollow spheres to better participate in the conversion reaction of lithium polysulfides (LPS). Moreover, the incorporated Co nanoparticles and abundance of oxygen vacancies effectively captured LPS and boosted their redox reaction kinetics. Therefore, this multi-level sulfur storage space is very beneficial to the storage and blockade of polysulfides and the improvement of the energy storage performance of the lithium-sulfur battery. Due to these beneficial structural features, the initial discharge capacity of Co@TiO2/GO/S cathode reached 807 mAh g−1 at 1C with a slow decay rate of 0.053% per cycle for 500 cycles, and high rate performance with a capacity of 552 mAh g−1 at 5C.