Electrospun FeCo nanoparticles encapsulated in N-doped carbon nanofibers as self-supporting flexible anodes for lithium-ion batteries

Highlights: : • The flexible FeCo@NCNFs film was prepared by electrospinning method. • Ultrasmall FeCo nanoparticles (~ 10 nm) are uniformly encapsulated in the NCNFs. • The as-prepared FeCo@NCNFs film is directly used as a binder-free electrode. • The formation of three-dimensional conductive network can greatly promote Li⁺ insertion/extraction kinetics. • The electrode exhibits high capacity, good rate capability and cycling stability. -- Abstract: This work reports a flexible, self-supporting anode, as a novel electrode material to improve the energy density of lithium-ion batteries (LIBs). In this work, FeCo nanoparticles uniformly encapsulated in one-dimensional N-doped carbon nanofibers (denoted as FeCo@NCNFs) were synthesized by electrospinning and subsequent thermal treatment. The as-prepared FeCo@NCNFs films with high electrical conductivity and good flexibility can be directly used as LIBs anodes without the addition of any conductive agents and binders. The lithium storage performance of FeCo@NCNFs is far superior to that of pure NCNFs. The impact of the carbonization temperature on the structure and electrochemical properties of FeCo@NCNFs was also investigated. Results show that FeCo@NCNFs obtained at 600 °C exhibits the optimal electrochemical performance with a relatively high reversible capacity, i.e., 566.5 mAhg⁻¹ at 100 mAhg⁻¹ after 100 cycles. The enhanced electrochemical properties can be mainly attributed to the synergy between 3D conductive NCNFs network and small FeCo nanoparticles, which can effectively improve the utilization rate of active materials, facilitate the transport of the electrons and lithium ions, and promote the charge-transport kinetics. Moreover, the homogeneous dispersion of FeCo nanoparticles in the NCNFs can also greatly buffer the volume change and improve the structural stability of the electrodes during the charge-discharge cycling.