From interlayer to lightweight capping layer: Rational design of mesoporous TiO2 threaded with CNTs for advanced Li–S batteries

Abstract

Lithium-sulfur (Li-S) battery with high theoretical energy density has been considered a promising candidate of the next-generation energy storage systems. Its commercialization, however, is mainly hindered by the fast capacity decay induced by the polysulfide shuttle behavior between two electrodes. Herein, we report a scalable production of mesoporous TiO2-carbon nanotubes (MTO-CNTs) in which each mesoporous oval-shaped TiO2 particle is threaded with a CNT in the axis direction. As its one dimensional structure with a self-weaving feature, two different approaches enlisting the use of MTO-CNTs as an interlayer between cathode and separator or a capping layer coated directly onto the sulfur cathode, both aiming to suppress the polysulfide shuttle. The threaded structure provides excellent interfacial contact between TiO2 and CNTs allowing CNTs to provide fast and continuous electron pathway toward the TiO2-polysulfide polar adsorption interface, thus dynamically accelerating the redox conversion of the trapped polysulfides. As a result of the synergetic effect, the cell with an ultra-lightweight MTO-CNTs capping layer (merely 0.06 mg cm−2) exhibits a long-term cyclability with a low capacity decay of 0.07% per cycle within 500 cycles at 0.5 C.