Coupling of Oxygen Vacancies and Heterostructure on Fe3O4 via an Anion Doping Strategy to Boost Catalytic Activity for Lithium-Sulfur Batteries

The sluggish reaction kinetics and severe shutting behaviors of sulfur cathodes are the major roadblocks to realizing the practical application of lithium−sulfur (Li−S) batteries and need to be solved through designing/constructing rational sulfur hosts. Herein, an effective alternative material of Fe₃O_4−x/FeP in-situ embedded in N-doped carbon-tube (Fe₃O_4−x/FeP/NCT) is proposed. In this fabricated heterostructure, NCT skeleton works as a sulfur host provides physical barrier for lithium polysulfides (LiPSs), while Fe₃O_4−x/FeP heterostructure with abundant oxygen vacancies provides double active centers to simultaneously accelerate e⁻/Li⁺ diffusion/transport kinetics and catalysis for LiPSs. Through the respective advantages, Fe₃O_4−x/FeP/NCT exhibits synergy enhancement effect for restraining sulfur dissolution and enhancing its conversion kinetics. Furthermore, the promoted ion diffusion kinetics, enhanced electrical conductivity, and increased active sites of Fe₃O_4−x/FeP/NCT are enabled by oxygen vacancies as well as the heterogeneous interfacial contact, which is clearly confirmed by experimental and first-principles calculations. By virtue of these superiorities, the constructed cathode shows excellent long-term cycling stability and a high-rate capability up to 10 C. Specially, a high areal capacity of 7.2 mAh cm⁻² is also achieved, holding great promise for utilization in advanced Li−S batteries in the future.