Rational Design of TiO-TiO₂ Heterostructure/Polypyrrole as a Multifunctional Sulfur Host for Advanced Lithium-Sulfur Batteries

Despite outstanding theoretical energy density (2600 Wh kg^-1) and low cost of lithium-sulfur (Li-S) batteries, their practical application is seriously hindered by inferior cycle performance and low Coulombic efficiency due to the "shuttle effect" of lithium polysulfides (LiPSs). Herein, we proposed a strategy that combines TiO-TiO₂ heterostructure materials (H-TiO _x, x = 1, 2) and conductive polypyrrole (PPy) to form a multifunctional sulfur host. Initially, the TiO-TiO₂ heterostructure can enhance the redox reaction kinetics of sulfur species and improve the conductivity of sulfur cathode together with the PPy coating layer. Moreover, the defect-abundant H-TiO _x matrices can trap LiPSs by the formation of Ti-S bond via the Lewis acid-base interaction. Furthermore, the PPy coating can physically hinder the diffusion of LiPSs, as well as chemically adsorb LiPSs by the polar-polar mechanism. Benefiting from the synergistic effect of H-TiO _x and PPy layer, the novel cathode delivered high specific capacities at different current rates (1130, 990, 932, 862, and 726 mAh g^-1 at 0.1, 0.2, 0.3, 0.5, and 1C, respectively) and an ultralow capacity decay of 0.0406% per cycle after 1000 cycles at 1C. This work can not only indicate effectiveness of employing H-TiO _x materials to realize the LiPSs immobilization but also shed light on the feasibility of combining different materials to achieve the multifunctional sulfur hosts for advanced Li-S batteries.