Fe3O4/Fe2N heterostructured hollow microspheres as functional electrocatalysts for high stability lithium-sulfur batteries

Abstract

Lithium-sulfur batteries (LSBs) are considered as a promising candidate for next-generation energy storage devices due to the high theoretical capacity, giant energy density, affordability, and environmental friendliness. However, the notorious shuttle effect and poor redox kinetics of lithium polysulfide (LiPS) tremendously hinder their commercial application. Herein, we have developed a Fe₃O₄/Fe₂N heterostructure by growing Fe₂N in situ on the surface of Fe₃O₄ hollow microspheres as a cathode electrocatalyst. This heterostructure effectively integrates the immobilization of sulfur species and reinforced redox transformation kinetics, enhancing the high-rate capability and reversible cycling lifetime. The Fe₃O₄ hollow microspheres enhance chemisorption sites and inhibit the shuttle of polysulfide. Meanwhile, incorporating Fe₂N significantly accelerates the kinetics and thermodynamics of multistep polysulfide redox reactions. These advantages are confirmed through operando characterizations and electrochemical tests, demonstrating enhanced adsorption interactions and accelerated LiPS redox reactions. Also, this configuration provides excellent conductivity and enables high charge transfer efficiency. Leveraging these merits, a coin cell assembled with Fe₃O₄/Fe₂N heterostructure shows a decent initial capacity of 1128.37 mAh g⁻¹ at 0.2 C, while the reversible capacity over 100 cycles attained 900.34 mAh g⁻¹. Furthermore, the average specific capacity fade is as low as 0.0391 % per cycle after 1000 cycles at 1 C.