Fabrication of thin silica layer-coated magnetite clusters (nFe3O4/silica) as anode materials for improved Li-ion batteries

Thin silica layer-coated magnetite clusters (nFe3O4/silica) were prepared as active anode materials for Li-ion batteries. First, citrate-capped magnetites (C-Fe3O4) were synthesized by the co-precipitation method. Then, 3-aminopropyl trimethoxysilane (APTMS)-linked magnetite clusters (A-nFe3O4) were formed via electrostatic interactions between carboxylate groups of C-Fe3O4 and amine groups of APTMS, and the resulting A-nFe3O4 were heat-treated under N2 flow for 2 h. The calcined A-nFe3O4 at 500 °C exhibited the X-ray diffraction (XRD) patterns mostly attributed to fcc crystalline phases of Fe3O4, whereas the calcined C-Fe3O4 at 500 °C exhibited the XRD patterns attributed to the mixture of fcc crystalline phases of Fe3O4 and hexagonal crystalline phases of α-Fe2O3. The calcined A-nFe3O4 (i.e., nFe3O4/silica) exhibited the improved retention capacity by more than ca. 50% after 50 cycles as compared to the pristine iron oxides. The improved retention capacity of nFe3O4/silica was attributed to the enhanced chemical stability and large surface area of the thin silica layer-coated iron oxide clusters.