Facile synthesis of carbon nanofiber confined FeS ₂/Fe ₂O ₃ 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.

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, FeS ₂/Fe ₂O ₃ heterostructures confined by carbon fibers (FeS ₂/Fe ₂O ₃@N-CNFs) are fabricated by the electrospinning method and a post-heat treatment with commercial Fe ₂O ₃ particles and polyacrylonitrile (PAN) as precursors. FeS ₂/Fe ₂O ₃ heterostructures can be easily obtained by a time-dependent sulfuration treatment. The FeS ₂/Fe ₂O ₃@N-CNF composite with an optimized nano-structure and composition exhibits enhanced electrochemical performance compared to the original composite (Fe ₂O ₃ confined by carbon fibers, Fe ₂O ₃/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 Fe ₂O ₃/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.