Facile synthesis of carbon nanofiber confined FeS2/Fe2O3 heterostructures as superior anode materials for sodium-ion batteries

Abstract

Sodium-ion batteries are recognized as an alternative energy storage device for lithium-ion batteries. However, the sluggish electrochemical kinetics and huge volume changes hinder their further application. In this work, FeS₂/Fe₂O₃ heterostructures confined by carbon fibers (FeS₂/Fe₂O₃@N-CNFs) are fabricated by the electrospinning method and a post-heat treatment with commercial Fe₂O₃ particles and polyacrylonitrile (PAN) as precursors. FeS₂/Fe₂O₃ heterostructures can be easily obtained by a time-dependent sulfuration treatment. The FeS₂/Fe₂O₃@N-CNF composite with an optimized nano-structure and composition exhibits enhanced electrochemical performance compared to the original composite (Fe₂O₃ confined by carbon fibers, Fe₂O₃/N-CNFs). Specifically, a specific capacity of 246.2 mA h g⁻¹ is gained at current densities of 3.2 A g⁻¹, which is much higher than that of the Fe₂O₃/N-CNF electrode (152.6 mA h g⁻¹). In addition, a discharge capacity of 287.3 mA h g⁻¹ can be maintained after 600 cycles at 1 A g⁻¹, corresponding to a capacity retention of 82.8%. The density functional theory (DFT) calculations and kinetics analysis reveal that the heterostructures in the composite are not only beneficial for electronic conductivity, but are also favorable for the sodium adsorption ability. This work paves a practicable way to construct anode materials with excellent sodium storage performances and prolonged cyclic life.