Bismuth-Based Heterojunctions with a Built-In Electric Field Boosting High-Efficiency Polysulfide Conversion in Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) stand out as promising next-generation energy storage devices due to their ultrahigh theoretical capacity and energy density, while their practical utilization is largely restricted by the polysulfide shuttle effect and sluggish redox kinetics. In this work, Bi2O3/Bi2S3 heterojunctions with morphologies of nanoflowers and needle-like rods were successfully synthesized via a facile one-step hydrothermal method. In the Bi2O3/Bi2S3 heterojunction system, Bi2O3 exerts adsorption and catalytic reduction toward long-chain polysulfides, while Bi2S3 improves electrical conductivity and dominates polysulfide oxidation. Electrochemical tests and in situ UV–vis spectroscopy measurements confirm that LSBs with the heterojunction-modified separator show a low capacity decay rate of just 0.067% per cycle after 800 cycles at 2 C. Even at high sulfur loadings of 5.5 and 7.3 mg cm–2, the Bi2O3/Bi2S3 derived LSB cell delivers areal capacities of 7.0 and 6.3 mAh cm–2, respectively. The batteries also maintain excellent cycling stability at extreme temperatures of 0 and 60 °C. This work provides a new strategy for the application of bismuth-based heterojunctions for performance advancement of lithium–sulfur batteries.