MnFe2O4@C Nanofibers as High-Performance Anode for Sodium-Ion Batteries

MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g–1 at 10000 mA g–1 in comparison of 504 mA h g–1 at 100 mA g–1) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na+ + 8e– → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na+ + 8e–). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na+ + 8e– ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than...