Synthesis of bimetallic sulfide FeCoS₄@carbon nanotube graphene hybrid as a high-performance anode material for sodium-ion batteries

As an anode for sodium-ion battery, we prepare the bimetallic sulfide FeCoS₄@carbon nanotube graphene hybrid (FCS@CNTGH) via a simple two-step synthetic route. The carbon nanotube graphene hybrid (CNTGH) is generated by in situ solid-state growth with the nanosized FCS embedded into it. With such a spatial distribution, nanosized FeCoS₄ (FCS) active material particles wrapped within the supporting CNTGH matrix prevent the growth of large Na₂S and Fe/Co clusters, alleviate volume changes, and result in both superb rate performance and long cycle life. The reversible capacity of FCS@CNTGH is 745 mAh g⁻¹ at 0.5 A g⁻¹ during the initial cycle and exceeds 660 mAh g⁻¹ even at 5.0 A g⁻¹. A long-term cycle life test of FCS@CNTGH shows its capacity after 1000 cycles at 2.0 A g⁻¹ is 680 mAh g⁻¹. The feasibility of using the FCS@CNTGH anode for SIBs was further evaluated in a full cell vs. Na₃V₂(PO₄)₃/C (NVP/C) cathode. The capacity retention of the FCS@CNTGH || NVP/C full cell exceeded 80% after 4000 cycles. The high-rate capability and superior cycle life even in the full cell configuration demonstrate that FCS@CNTGH is an appropriate anode material for SIBs.