The Preparation Of Fe₃O₄/C Composite Material And Its Application To Lithium-ion Battery Anode Material

Lithium-ion batteries(LIBs) have been extensively used in portable electronic devices and hybrid electric vehicles due to their high energy and power density, long lifetime, and environmental friendliness. Fe3O4 has become one of the most promising anode materials owing to its large specific capacity, low cost, non-pollution and high abundance in nature. However, Fe3O4 also suffers from large volume change during lithiation/delithiation process, which can lead to active particle cracking, electrode pulverization, and eventually result in poor reversibility and rapid capacity degradation. Therefore, it is important to take a solution to relieve the volume contraction/expansion and maintain the integrity of the electrode material. 1. We successfully synthesized ordered carbon microtubule arrays with carbon coated Fe3O4(Fe3O4@C/A-CMT)by high temperature alkali cooking, hydrothermal method and carbonization process. As comparison, ordered carbon microtubule arrays with carbon coated Fe3O4 without cooking and bare Fe3O4 particles were both prepared by identical procedures. Fe3O4 particles with a size of 10 nm uniformly embedded in the ordered microtube arrays. Fe3O4@C/A-CMT sample showed excellent electrochemical performance due to the synergistic effect of Fe3O4 and ordered carbon microtubule arrays. A reversible specific capacity of 856 mAh/g was obtained at a current density of 100 mA/g after 50 cycles. 2. Fe3O4/C, porous Fe3O4/C and porous graphene-doped Fe3O4/carbon(porous GN@Fe3O4/C) nanofibers were fabricated via electrospinning in situ synthesis and thermal treatment. Microstructure of samples was characterized by XRD, XPS,Raman spectra, FE-SEM, TEM and BET. The resulting porous GN@Fe3O4/C nanofibers showed unique dark/light banding and a hierarchical porous structure. Their specific Brunauer–Emmett–Teller(BET) surface area was 323.0 m2/g with a total pore volume of 0.337 cm3/g. 3. Fe3O4/C、porous Fe3O4/C and porous GN@ Fe3O4/C nanofibers as lithium-ion battery anode materials were assembled into half-cells, respectively. The electrochemical properties were tested by galvanostatic charge/discharge, cyclic voltammograms and electrochemical impedance spectroscopy. The first specific discharge capacity of porous GN@ Fe3O4/C composite was 1412 mAh/g at a current density of 100 mA/g. A reversible capacity of 872 mAh/gwas obtained after 100 cycles. Besides, porous GN@ Fe3O4/C electrode also showed excellent cycling stability and superior rate capability.