A chemical composition evolution for the shape-controlled synthesis and energy storage applicability of Fe3O4–C nanostructures

Temporarily stabilized iron oxychloride (FeOCl) nanospindles have been collected for the first time shortly after the forced hydrolysis of iron(III) chloride (FeCl3) in the reaction medium of glycerol and water (1 : 7, v/v) at 145 °C. In this paper, a novel chemical composition evolution of orthorhombic FeOCl to tetragonal akaganeite (β-FeOOH) and then to cubic magnetite (Fe3O4) has been successfully used for the shape-controlled synthesis of Fe3O4–C spindle-like nanocomposites. During this evolution process, the crystal structures of spindle-like intermediates have been investigated, along with the random doping of amorphous carbon into the final products. As a lithium ion battery anode, Fe3O4–C composite nanospindles can give a significantly high initial coulombic efficiency (80.6%), a reversible discharge capacity of 1029 mA h g−1 at 200 mA g−1 over 100 cycles, and the 100th retention value of 711.6 mA h g−1 at a high current rate of 1000 mA g−1. Therefore, a combination of the fine nanofabrication of Fe3O4 crystals with a spindle-like shape and the random doping of amorphous carbon may offer an effective approach to the development of transition metal oxide-based anode materials for high-energy lithium ion batteries.