Utilizing the Built‐in Electric Field of p–n Junctions to Spatially Propel the Stepwise Polysulfide Conversion in Lithium–Sulfur Batteries

Abstract

Integrating sulfur cathodes with effective catalysts to accelerate polysulfide conversion is a suitable way for overcoming the serious shuttling and sluggish conversion of polysulfides in lithium-sulfur batteries. However, because of the sharp differences in the redox reaction kinetics and complicated phase transformation of sulfur, a single-component catalyst cannot consistently accelerate the entire redox process. Herein, hierarchical and defect-rich Co₃ O₄ /TiO₂ p-n junctions (p-Co₃ O₄ /n-TiO₂ -HPs) are fabricated to implement the sequential catalysis of S_8(solid) → Li₂ S_4(liquid) → Li₂ S_(solid) . Co₃ O₄ sheets physiochemically immobilize the pristine sulfur and ensure the rapid reduction of S₈ to Li₂ S₄ , while TiO₂ dots realize the effective precipitation of Li₂ S, bridged by the directional migration of polysulfides from p-type Co₃ O₄ to n-type TiO₂ attributed to the interfacial built-in electric field. As a result, the sulfur cathode coupled with p-Co₃ O₄ /n-TiO₂ -HPs delivers long-term cycling stability with a low capacity decay of 0.07% per cycle after 500 cycles at 10 C. This study demonstrates the synergistic effect of the built-in electric field and heterostructures in spatially enhancing the stepwise conversion of polysulfides, which provides novel insights into the interfacial architecture for rationally regulating the polysulfide redox reactions.