Oxygen-Deficient Titanium Dioxide Nanosheets as More Effective Polysulfide Reservoirs for Lithium-Sulfur Batteries.

In this work, oxygen-deficient anatase TiO2 nanosheets (A-TiO2-x NSs) are proposed as a substrate to improve the electrochemical properties of sulfur electrodes for lithium-sulfur (Li-S) batteries. The A-TiO2-x NSs are prepared by partly reducing pristine TiO2 nanosheets (A-TiO2 NSs) in NaBH4 solution. With some oxygen vacancies on the surface of the TiO2 nanosheets, A-TiO2-x NSs not only promote electronic transfer, but also act as more effective polysulfide reservoirs to minimize the dissolution of lithium polysulfides (LiPSs) than the A-TiO2 NSs control. Hence, upon utilization as modifiers for cathodes of Li-S batteries, the A-TiO2-x NSs-modified sulfur (A-TiO2-x NSs-S) cathode exhibits a higher reversible specific capacity and greater cycling performance and rate capability than the A-TiO2 NSs-modified one (A-TiO2 NSs-S). For example, A-TiO2-x NSs-S delivers an initial specific capacity of 1277.1 mAh g-1 at 0.1 C and maintains a stable Coulombic efficiency of approximately 99.2 % after the first five cycles; these values are higher than those of 997.3 mAh g-1 and around 96.7 %, respectively, for A-TiO2 NSs-S. The enhanced electrochemical properties of the A-TiO2-x NSs-S cathode can be ascribed mainly to the more effective adsorption of dissolvable and diffused LiPSs by the oxygen vacancies. Therefore, utilization of the structure of oxygen vacancies in Li-S batteries demonstrates great prospects for practical application.