Controllable synthesis of carbon-coated Fe₃O₄ nanorings with high Li/Na storage performance

Fe₃O₄ with high capacity and low cost has been a promising anode for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, the intrinsic issues from the severe volume change of Fe₃O₄ during cycling and its inferior electronic conductivity result in poor capacity retention. Herein, carbon-coated Fe₃O₄ nanorings (R-Fe₃O₄@C) were fabricated by a facile method. The hollow nanorings with a small size below 80 nm are designed to mitigate the severe volume expansion of Fe₃O₄ upon cycles, whereas the amorphous carbon layer with a thickness of 12 nm is created to induce the fast electronic transfer. Benefiting from the unique carbon-coated nanostructure, R-Fe₃O₄@C exhibits superior electrochemical behaviors in both LIBs and SIBs. As an anode of LIBs, it delivers a high capacity of 1003.4 mAh g⁻¹ at 0.5 A g⁻¹ over 100 cycles, and of 421.2 mAh g⁻¹ at 5 A g⁻¹ over 800 cycles. Being an anode for SIBs, it shows a considerable capacity of 365.1 mAh g⁻¹ at 0.1 A g⁻¹ after 200 cycles, and of 160.3 mAh g⁻¹ at 2 A g⁻¹ after 300 cycles. Our work achieves the remarkable electrochemical properties of R-Fe₃O₄@C via the facile fabrication in which relatively low-cost ingredients are used.