Synthesis and characterization of TiO2-coated magnetite clusters (nFe3O4@TiO2) as anode materials for Li-ion batteries

TiO2-coated magnetite clusters (nFe3O4@TiO2) were facilely prepared through the sol–gel reaction between Ti alkoxides (TEOT) and magnetite clusters (nFe3O4) with terminated alkoxy groups. The composite particles represented a core–shell nanostructure (nFe3O4@TiO2) consisting of a Fe3O4 cluster core and a TiO2 capsule layer. The capsule layer of nFe3O4@TiO2 was increased with increasing amounts of TEOT (150, 300, 500 μl) in sol–gel reaction. The Fe3O4@TiO2 (150 μl of TEOT) with a thin TiO2 layer (ca. 10 nm) exhibited two kinds of cathodic (0.79 V and 1.61 V) and anodic (1.78 and 2.1 V) peaks attributed to the reduction and oxidation process by Fe3O4 core and TiO2 layer, respectively. The thin nFe3O4@TiO2 (150 μl of TEOT) exhibited the enhanced capacity retention by ca. 40% probably due to the buffering effect of TiO2 capsule layer. However, the thick nFe3O4@TiO2 (300–500 μl of TEOT) exhibited a rapid capacity fading due to the disintegrated core–shell nanostructure, i.e., unfavorable hetero-junction between TiO2 matrix and magnetite clusters.