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

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 Co3O4/TiO2 p-n junctions (p-Co3O4/n-TiO2-HPs) are fabricated to implement the sequential catalysis of S-8(solid) -> Li2S4(liquid) -> Li2S(solid). Co3O4 sheets physiochemically immobilize the pristine sulfur and ensure the rapid reduction of S-8 to Li2S4, while TiO2 dots realize the effective precipitation of Li2S, bridged by the directional migration of polysulfides from p-type Co3O4 to n-type TiO2 attributed to the interfacial built-in electric field. As a result, the sulfur cathode coupled with p-Co3O4/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.