A Movable Fe2O3 Core in Connected Hierarchical Pores for Ultrafast Intercalation/Deintercalation in Sodium-Ion Batteries

Though great progresses have been made on improving the volume effect and electronic conductivity of anode materials in sodium-ion batteries (SIBs), the electrical performance at high current density for long cycling stability is still a huge challenge. To address this, a facile confined-impregnation/crystallization strategy is developed to construct a movable Fe2O3 core in nitrogen-doped hierarchical porous carbon nanospheres (MFe2O3@N-HCNs) for ultrafast intercalation/deintercalation of SIBs. The as-prepared MFe2O3@N-HCNs not only exhibit a connected and hierarchal porous structure with large surface specific area (similar to 367 m(2) g(-1)) but also possess a highly dispersed and moveable Fe2O3 core (similar to 5 nm) for the tolerance of volume expansion during the intercalation/deintercalation process of sodium ions. As SIBs anode materials, the MFe2O3@N-HCNs anode exhibits a capacity of 417 mAh g(-1) at 0.1 A g(-1) after 100 cycles and of 364 mAh g(-1) at 2 A g(-1) with 4500 cycles. Especially, a prominent discharge capacity of 102 mAh g(-1) is still obtained at 5 A g(-1) after 10000 cycles. Such remarkable performances should be attributed to the unique highly dispersed and moveable Fe2O3 core and conductive nitrogen-doped hierarchical porous carbon framework with large surface area. Consequently, this study develops a facile methodology to promote the energy storage and long cycling performance of hierarchically porous carbon@transition-metal oxide (TMO) composite anode materials for SIBs, especially at high current density.