Synergistic effect of in-situ carbon-coated mixed phase iron oxides and 3d electrode architectures as anodes for high-performance sodium-ion batteries

Due to the high theoretical capacity, iron-oxide-based Fe2O3 2 O 3 (1007 mAh g- 1 ) and Fe3O4 3 O 4 (926 mAh g- 1 ) materials can be a promising conversion-type anode material for Sodium-ion batteries (SIBs). However, the low electronic conductivity (10-14-14 S cm-1 ) and 200% volume expansion of iron oxide lead to poor cycle life and capacity retention, limiting its commercial application. In this work, carbon-coated mixed-phase iron oxide C-Fe2O3- 2 O 3- Fe3O4 3 O 4 (C-IO) was synthesized by pyrolysis using ferrocene precursor. Subsequently, a 3D carbon fiber (CF) network was introduced to improve the electrochemical performance of the material by resolving the volume expansion and pulverization issues. Both the CF network and Fe3O4 3 O 4 provide an electron transport pathway. The conventional Cu-C-IO electrodes deliver a 2nd cycle capacity of 335 mAh g- 1 at 250 mA g- 1 and exhibit 61.5% capacity retention after 500 cycles. In contrast, the 3D-CF-based IO electrodes show 2nd cycle capacity of 607 mAh g- 1 at 50 mA g- 1 with 96.4% capacity retention after 35 cycles and 420 mAh g- 1 with-85.4% capacity retention after 500 cycles at 250 mA g- 1 (w.r.t. CF and C-IO active mass, CF contribute- 27% and C-IO- 73% capacity), making it a potential anode for SIBs.