Fe3O4 Nanoparticles Confined in Mesocellular Carbon Foam for High Performance Anode Materials for Lithium-Ion Batteries

Fe3O4 nanocrystals confined in mesocellular carbon foam (MSU-F-C) are synthesized by a "host-guest " approach and tested as an anode material for lithium-ion batteries (LIBs). Briefly, an iron oxide precursor, Fe(NO3)(3)center dot 9H(2)O, is impregnated in MSU-F-C having uniform cellular pores similar to 30 nm in diameter, followed by heat-treatment at 400 degrees C for 4 h under Ar. Magnetite Fe3O4 nanocrystals with sizes between 13-27 nm are then successfully fabricated inside the pores of the MSU-F-C, as confirmed by transmission electron microscopy (TEM), dark-field scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen sorption isotherms. The presence of the carbon most likely allows for reduction of some of the Fe3+ ions to Fe2+ ions via a carbothermoreduction process. A Fe3O4/MSU-F-C nanocomposite with 45 wt% Fe3O4 exhibited a first charge capacity of 1007 mA h g(-1) (Li+ extraction) at 0.1 Ag-1 (similar to 0.1 C rate) with 111% capacity retention at the 150(th) cycle, and retained 37% capacity at 7 Ag-1 (similar to 7 C rate). Because the three dimensionally interconnected open pores are larger than the average nanosized Fe3O4 particles, the large volume expansion of Fe3O4 upon Li-insertion is easily accommodated inside the pores, resulting in excellent electrochemical performance as a LIB anode. Furthermore, when an ultrathin Al2O3 layer (< 4 angstrom) was deposited on the composite anode using atomic layer deposition (ALD), the durability, rate capability and undesirable side reactions are significantly improved.