Free-standing Conductive Fe$_{3}$O$_{4}$/Graphene/CNT Film As Anodes for Lithium-Ion Batteries

Fe3O4 is known as a material for lithium-ion battery anodes due to its high theoretical specific capacity. But it has limitations, such as low conductivity and poor cyclic performance etc. To address these problems, free-standing Fe3O4/Graphene/Carbon nanotube(CNT) films were prepared via hydrothermal reaction methods. The synergistic effect of graphene and CNTs provide a flexible matrix for Fe3O4. A series of experiments were performed to determine important processing factors such as carbon ratio and annealing treatments, which influenced the overall LIB performances. Currently the best film had a sheet resistance of 23 ohm/sq and a BET surface area of 132 m2/g. In addition, the lightweight films were directly tested as lithium-ion battery anodes without using a current collector or a binder, eliminating unnecessary weight in the overall devices. This metal oxide loaded carbon film had both excellent conductivity and strong mechanical strengths. The discharge capacity was found to reach 880 mAh/g at 200 mA/g current density and 580 mA/g at 400 mA/g. The rate capability tests (from 200 mA/g up to 1200 mA/g) also indicated that the lab prepared Fe3O4 loaded films have much better performance as compared to the samples made by using commercial Fe3O4.