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

In this work, oxygen‐deficient anatase TiO2 nanosheets (A‐TiO2−xNSs) are proposed as a substrate to improve the electrochemical properties of sulfur electrodes for lithium‐sulfur (Li‐S) batteries. The A‐TiO2−xNSs are prepared by partly reducing pristine TiO2 nanosheets (A‐TiO2NSs) in NaBH4 solution. With some oxygen vacancies on the surface of the TiO2 nanosheets, A‐TiO2−xNSs not only promote electronic transfer, but also act as more effective polysulfide reservoirs to minimize the dissolution of lithium polysulfides (LiPSs) than the A‐TiO2NSs control. Hence, upon utilization as modifiers for cathodes of Li‐S batteries, the A‐TiO2−xNSs‐modified sulfur (A‐TiO2−xNSs‐S) cathode exhibits a higher reversible specific capacity and greater cycling performance and rate capability than the A‐TiO2NSs‐modified one (A‐TiO2NSs‐S). For example, A‐TiO2−xNSs‐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‐TiO2NSs‐S. The enhanced electrochemical properties of the A‐TiO2−xNSs‐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. Oxygen‐deficient cathode: A sulfur cathode modified with oxygen‐deficient anatase TiO2 nanosheets (A‐TiO2−xNSs‐S cathode) performs better in lithium‐sulfur batteries than the A‐TiO2NSs‐S cathode (see figure). Oxygen vacancies on the surface of the A‐TiO2−xNSs provide robustly interactional active sites for lithium polysulfides, which efficiently relieve the shuttle effect, so the A‐TiO2−xNSs‐S cathode shows superior electrochemical properties to the A‐TiO2NSs‐S cathode.