encapsulation of iron oxide nanoparticles into nitrogen-doped carbon nanotubes as anodic electrode materials of lithium ion batteries.

Fe-based oxides are considered as promising anode materials for lithium-ion batteries (LIBs) due to their high theoretical capacities, low cost, natural abundance and environmental friendliness. However, their severe volume expansion upon cycling and poor conductivity limit their cycling stability and rate capability. To address this issue, a hybrid of FeO nanoparticles encapsulated at the endpoints of nitrogen-doped CNTs (FeO@NCNTs) is designed and prepared using a metal-catalyzed graphitization-nitridization driven tip-growth process and subsequent oxidation in air. When evaluated as an anode material for LIBs, this FeO@NCNT hybrid exhibits a high capacity of 1145 mA h g at 100 mA g, excellent rate capability of 907 mA h g at 5.0 A g and remarkable cycling stability of 856 mA h g after 800 cycles at 1 A g, which are much superior to those of the FeO/carbon black (CB) control material. The outstanding electrochemical performance benefits from the unique nanoarchitecture of FeO@NCNTs, which provides a porous conductive matrix for effective electron-ion transport, and provides space confining carbon nanocaps as well as stress buffer nanocavities for robust structural stability during the lithiation/delithiation process. The results may pave the way for the rational structural design of high-performance metal oxide-based anode materials for next-generation LIBs.