Constructing electron transport channels in FeSe₂ microspheres by a facile strategy for superior long-life and ultrafast sodium-ion storage

The electrochemical battery performance is largely determined by electron transport occurring in the electrode materials. The microsphere-structured transition metal selenides (TMSes) with high tap density are prospective anode materials for commercial sodium ion batteries (SIBs), however, they suffer from sluggish electron transport, leading to poor rate and inadequate cycle stability. Herein, a carbon nanotubes (CNTs) intercalation strategy is firstly proposed to enhance the electron transport kinetics in FeSe₂ microspheres via a facile method. In the obtained CNTs@FeSe₂-C composite, the FeSe₂ microspheres composed of FeSe₂ nanoparticles feature high tap density and short Na⁺ diffusion distances, while the CNTs networks enable pathways for fast electron transfer in the FeSe₂ microspheres. In consequence, the CNTs@FeSe₂-C delivers high volumetric/gravimetric capacity (885.4 mAh cm⁻³, 530.2 mAh g⁻¹), an ultra-long lifespan (234.5 mAh g⁻¹ after 10,000 loops at 10 A g⁻¹), and a superior rate performance (57.8% capacity retention at the current density increase of 150 times). Ex-situ XRD, XPS, Raman, TEM and quantitative kinetics analyses are further conducted to reveal the energy storage mechanism underlying the enhanced electrochemical properties of CNTs@FeSe₂-C. This work demonstrates that the proposed strategy could optimize metal selenides as commercial-value anodes for SIBs.