Structure–Activity Relationship between Quantitative Regulation of Perovskite Quantum Dot Band Gaps and Adsorption–Catalytic Performance in Lithium–Sulfur Batteries

The commercialization of lithium–sulfur batteries is limited by the shuttle effect of lithium polysulfides (LiPSs) and sluggish conversion kinetics. Perovskite quantum dots (PQDs) with their precisely tunable band gap (E_g) can provide a novel pathway for regulating the performance of catalytic systems in lithium–sulfur batteries. In this study, the band gap width of CsPbCl_3–xBr_x quantum dots is adjusted by controlling the doping amount of Br^–, and the PTI-CsPbCl_3–xBr_x composite is constructed by combining them with polyaniline-modified TiO₂ (PTI). Electrochemical tests and density of states calculations confirm that the material achieves optimal adsorption–catalytic performance for LiPSs when E_g is regulated to 1.47 eV. At this point, the interfacial built-in electric field strength of the composite can reach 1.72 V, and the reaction activation energy decreases to 0.087 eV with a lower d-band center (2.10 eV) and a narrower d-p energy gap (3.29 eV). These characteristics collectively promote the conversion kinetics between active sites and LiPSs, as well as the deposition/decomposition process of Li₂S. In addition, the PTI-CsPbCl₂Br₁/S composite cathode based on this optimized band gap system exhibits an average capacity decay rate of only 0.077% per cycle at 0.5 C under harsh operating conditions of lean electrolyte (5 μL·mg^–1) and high sulfur loading (6 mg·cm^–2).