Self-standing Na-storage anode of Fe₂O₃ nanodots encapsulated in porous N-doped carbon nanofibers with ultra-high cyclic stability

Ultrasmall γ-Fe₂O₃ nanodots (~ 3.4 nm) were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers (labeled as Fe₂O₃@C) at a considerable loading (~ 51 wt.%) via an electrospinning technique. Moreover, the size and content of Fe₂O₃ could be controlled by adjusting the synthesis conditions. The obtained Fe₂O₃@C that functioned as a self-standing membrane was used directly as a binder- and current collector-free anode for sodium-ion batteries, displaying fascinating electrochemical performance in terms of the exceptional rate capability (529 mA·h·g^-1 at 100 mA·g^-1 compared with 215 mA·h·g^-1 at 10, 000 mA·g^-1) and unprecedented cyclic stability (98.3% capacity retention over 1, 000 cycles). Furthermore, the Na-ion full cell constructed with the Fe₂O₃@C anode and a P2-Na_2/3Ni_1/3Mn_2/3O₂ cathode also exhibited notable durability with 97.2% capacity retention after 300 cycles. This outstanding performance is attributed to the distinctive three-dimensional network structure of the very-fine Fe₂O₃ nanoparticles uniformly embedded in the interconnected porous N-doped carbon nanofibers that effectively facilitated electronic/ionic transport and prevented active materials pulverization/aggregation caused by volume change upon prolonged cycling. The simple and scalable preparation route, as well as the excellent electrochemical performance, endows the Fe₂O₃@C nanofibers with great prospects as high-rate and long-life Na-storage anode materials.