FeS2 nanosheets encapsulated in 3D porous carbon spheres for excellent Na storage in sodium-ion batteries

Abstract

FeS₂ nanosheets encapsulated in 3D porous carbon spheres (FeS₂@C-2 h) were fabricated by a series of treatments using Fe₂O₃ hollow nanospheres as starting materials. We first fabricated Fe₂O₃@PPy by a facile process in solution. Then, Fe₂O₃@PPy was converted to Fe₃O₄@C by annealing treatment under an Ar atmosphere. Fe₃O₄@C composites were etched in HCl and they formed Fe₃O₄ nanoparticles dispersed in porous carbon hollow spheres. Finally, the FeS₂ nanosheets encapsulated in porous carbon hollow spheres were obtained by a sulfidation treatment. Thus, the FeS₂-carbon structure is believed to be beneficial for improving the sodium storage performance of the products. Our experimental results show that FeS₂@C-2 h exhibit a significantly improved electrochemical performance compared with pure FeS₂ without carbon coating and etching when used as anode materials for sodium-ion batteries. At a current density of 500 mA g⁻¹, the FeS₂@C-2 h anode delivered a high capacity of 514.9 mA h g⁻¹ after 100 cycles. The capacity of 420.1 mA h g⁻¹, 410.5 mA h g⁻¹ and 396.6 mA h g⁻¹ can be achieved at high current densities of 1000, 2000 and 3000 mA g⁻¹ after 200 cycles, respectively. The capacity is still as high as 272.4 mA h g⁻¹ after 500 cycles at a higher current density of 5000 mA g⁻¹. The excellent electrochemical performance suggests that the FeS₂@C-2 h nanomaterials hold potential to serve as electrode materials for sodium-ion batteries.