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

Ultrasmall gamma-Fe2O3 nanodots (similar to 3.4 nm) were homogeneously encapsulated in interlinked porous N-doped carbon nanofibers (labeled as Fe2O3@C) at a considerable loading (similar to 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-Na2/3Ni1/3Mn2/3O2 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.