Electrocatalytic activity of lithium polysulfides adsorbed into porous TiO coated MWCNTs hybrid structure for lithium-sulfur batteries.

Lithium-sulfur batteries have attracted great attention because of their high energy density, environmental friendliness, natural abundance and intrinsically low cost of sulfur. However, their commercial applications are greatly hindered by rapid capacity decay due to poor conductivity of electrode, fast dissolution of the intermediate polysulfides into the electrolyte, and the volume expansion of sulfur. Herein, we report a novel composite MWCNTs@TiO-S nanostructure by grafting TiO onto the surface of MWCNTs, followed by incorporating sulfur into the composite. The inner MWCNTs improved the mechanical strength and conductivity of the electrode and the outer TiO provided the adsorption sites to immobilize polysulfides due to bonding interaction between TiO and polysulfides. The MWCNTs@TiO-S composite with a mass ratio of 50% (MWCNTs in MWCNTs@TiO) exhibited the highest electrochemistry performance among all compositing ratios of MWCNTs/TiO. The performance improvement might be attributed to the downward shift of the apparent Fermi level to a more positive potential and electron rich space region at the interface of MWCNTs-TiO that facilitates the reduction of lithium polysulfide at a higher potential. Such a novel hybrid structure can be applicable for electrode design in other energy storage applications.