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

• Published in: Advanced materials (Weinheim) 2021-12, Vol.33 (51), p.e2105067-n/a
• Main Authors: Li, Hongtai, Chen, Chi, Yan, Yingying, Yan, Tianran, Cheng, Chen, Sun, Dan, Zhang, Liang
• Format: Article
• Language: English
• Subjects: built‐in electric field; Catalysis; Catalysts; Cathodes; Cobalt oxides; Conversion; Decay rate; Electric fields; Electrical junctions; Heterostructures; Lithium sulfur batteries; Li–S batteries; P-n junctions; Phase transitions; polysulfide conversion; Polysulfides; Reaction kinetics; Redox reactions; stepwise catalysis; Sulfur; Synergistic effect; Titanium dioxide
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202105067

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 S8(solid) → Li2S4(liquid) → Li2S(solid). Co3O4 sheets physiochemically immobilize the pristine sulfur and ensure the rapid reduction of S8 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. Novel hierarchical and defect‐rich Co3O4/TiO2 p–n junctions with built‐in electric field are designed as the host materials of sulfur electrodes for Li–S batteries. The elaborate p–n junctions not only induce the directional migration of lithium polysulfides to suppress the dissolution of sulfur intermediates into the electrolyte but also implement the spatially sequential catalysis to ensure the superior utilization of sulfur.