Ultrathin Double-Shell Nanotubes of Narrow Band-Gap Titanium Oxide@Carbon as Efficient Polysulfide Inhibitors towards Advanced Lithium-Sulfur Batteries

Low conductivity, shuttling phenomenon, and sluggish transformation of intermediate lithium polysulfides (LiPSs) constitute the primary obstacles for the practical application of lithium-sulfur (Li-S) batteries. Ultrathin double-shell nanotubes of titanium oxide with oxygen-vacancies@nitrogen-doped carbon (denoted as OVs-TiO2-x@NC) as sulfur host is designed. As demonstrated by experimental and computational results, ultrathin TiO2-x shell featuring a small aspect ratio can not only provide rapid charge transfer but also shorten the diffusion pathway of lithium-ion. Furthermore, the special double-shell nanostructure with large surface area can accommodate high amount sulfur species, furnish effective channels for the electrolyte penetration, supply adequate buffer space for alleviating the volume expansion of sulfur upon repeated cycling, and provide both physical and chemical adsorption function to efficiently capture LiPSs. The OVs-TiO2-x inner shell with small aspect ratio is compactly packed and tightly adhered to the carbon layer, which can effectively anchor LiPSs by strong chemical affinity and prevents their diffusion from the inner to the outside layer. More importantly, the introduction of oxygen-vacancies can enhance the conductivity of electrode, restrict the loss of LiPSs into electrolyte, strengthen electrocatalytic activity, and accelerate LiPSs conversion. Attributed to these superiorities, OVs-TiO2-x@NC/S electrode enables excellent electrochemical performance, including long cycle stability of 531 mAh g-1 for 3000 cycles at 5 C with decay rate of only 0.0123%, excellent rate capability of 675 mAh g-1 at 8 C and high areal capacity of 8.01 mAh cm-2 with sulfur mass loading of 9.5 mg cm-2 under low electrolyte/sulfur (E/S=5). This work furnishes a prospective on altering the electronic states of OVs-metal oxides toward high-energy-density Li-S batteries and promotes the progress of catalysis or energy storage systems.