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-TiOx, 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-TiOx 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-TiOx 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-TiOx 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.