Electrochemical properties of sulfur–carbon hollow nanospheres with varied polar titanium oxide layer location for lithium–sulfur batteries

Porous and graphitic carbon materials containing high amounts of sulfur are being actively studied for Li–S batteries on account of their diverse structural merits. However, the lithium polysulfides dissolution in the electrolyte during cycling is one of the obstacles in the practical application of Li–S batteries. Some strategies have been suggested to address this issue, including the physical confinement of nonporous structures or the use of polar materials. In addition, forming a polar coating layer over a sulfur-embedded carbon matrix is considered as a highly effective strategy. However, the arrangement of elemental sulfur, the porous carbon matrix, and polar materials in the composite cathode should be further optimized to minimize polysulfide dissolution during cycling. Here, ultrafine TiO_x nanodots are uniformly deposited over active sulfur embedded within hollow porous carbon nanospheres by a simple and rapid impregnation process. Depending on the infiltration order of the TiO_x precursor solution, different arrangements of ultrafine TiO_x nanodots are formed in the carbon shell. The polar TiO_x nanodots arranged in the outermost layer of HPCS-S efficiently block the diffusion of soluble polysulfides, which result in excellent cycle performance. The discharge capacity of the polar TiO_x layer-coated sulfur-embedded hollow carbon nanospheres for the 500th cycle at 1.0 C (1675 mA g⁻¹) is 630 mA h g⁻¹, and the specific capacity at 5.0 C is 513 mA h g⁻¹.