Suitable lithium polysulfides diffusion and adsorption on CNTs@TiO2-bronze nanosheets surface for high-performance lithium-sulfur batteries

The shuttle effect of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) has been hampered their commercialization. Metal oxides as separator modifications can suppress the shuttle effect. Since there is no direct electron transport between metal oxides and LiPSs, absorbed LiPSs should be diffused from the surface of metal oxides to the carbon matrix to go through redox reactions. If diffusivity of LiPSs from metal oxides surface to carbon substrate is poor, it would hinder the redox reactions of LiPSs. Nevertheless, researchers tend to focus on the adsorption and overlook the diffusion of LiPSs. Herein, same morphology and different crystal phase of TiO2 nanosheets grown on carbon nanotubes (CNTs@TiO2-bronze and CNTs@TiO2-anatase) have been designed via a simple approach. Compared with CNTs and CNTs@TiO2-anatase composites, the battery with CNTs@TiO2-bronze modified separator delivers higher specific capacities and stronger cycling stability, especially at high current rates (∼ 472 mAh·g−1 at 2.0 C after 1,000 cycles). Adsorption tests, density functional theory calculations and electrochemical performance evaluations indicate that suitable diffusion and adsorption for LiPSs on the CNTs@TiO2-B surface can effectively capture LiPSs and promote the redox reaction, leading to the superior cycling performances.