Fe₃N/Fe₃O₄ hetero-nanocrystals embedded in porous carbon fibers for enhanced lithium storage

Energy storage devices have applications in large-scale portable and smart devices due to their high energy density and long lifespan, but the limited theoretical capacity of the graphite anode in lithium-ion batteries has slowed the development of portable electronic devices. Herein, we prepared porous fibers with heterogeneous Fe₃N/Fe₃O₄ nanocrystals wrapped by a carbon layer. A series of measurements, such as TEM images, Raman spectra, XRD pattern and XPS analysis, were used to unveil the formation of Fe₃N/Fe₃O4 nanocrystals. Due to the synergistic effect of the large specific surface area originating from the porous structure and the heterogeneous nanocrystals, the porous Fe₃N/Fe₃O₄@C fibers exhibit a good electron/ion transmission route and rich active sites. As anode materials for lithium-ion batteries (LIBs), porous Fe₃N/Fe₃O₄@C fibers delivered a reversible capacity of 964 mA h g^-1 after 200 cycles at 2 A g^-1 and long-term cycling stability (282 mA h g^-1 after 2000 cycles at 5 A g^-1). This work provides a method to regulate biphasic anode materials with desirable structures to enhance the reversibility of LIBs.