Sulfur-TiO2 Yolk-Shell Nanoarchitecture for Long-Cycle Lithium-Sulfur Batteries

Sulfur is an attractive cathode material with a high specific capacity of 1,673 mAh g^-1, but its rapid capacity decay due to polysulfide dissolution presents a significant technical challenge. Although much effort has been devoted to encapsulating sulfur particles with conducting materials to limit polysulfide dissolution, relatively little emphasis has been placed on dealing with the large volumetric expansion of the sulfur core during lithiation (~80%), which will lead to cracking and fracture of the protective shell. Here, we demonstrate the design of a sulfur–TiO₂ yolk–shell nanoarchitecture with internal void space for stable and prolonged cycling over 1,000 charge/discharge cycles in lithium–sulfur batteries. Compared to bare sulfur and sulfur–TiO₂ core–shell nanoparticles, the yolk–shell nanostructures were found to exhibit the highest capacity retention due to the presence of sufficient empty space to accommodate the volume expansion of sulfur, resulting in a structurally-intact TiO₂ shell to minimize polysulfide dissolution. Using the yolk–shell nanoarchitecture, an initial specific capacity of 1,030 mAh g^-1 at 0.5C and Coulombic efficiency of 98.4% over 1,000 cycles was achieved. Most importantly, the capacity decay after 1,000 cycles was found to be as small as 0.033% per cycle, which represents the one of the best performance for long-cycle lithium–sulfur batteries so far.