Lithium Storage Properties of a Bioinspired 2-Line Ferrihydrite: A Silicon-Doped, Nanometric, and Amorphous Iron Oxyhydroxide

Inspired by a nanometric iron-based oxide material of bacterial origin, silicon (Si)-doped iron oxyhydroxide nanoparticles or 2-line ferrihydrites (2Fhs) were prepared and their lithium (Li) storage properties were investigated. The structures of the Si-doped 2Fhs strongly depended on the Si molar ratio [x = Si/(Fe + Si)] whose long-range atomic ordering gradually vanished as the Si molar ratio increased, with a structural change from nanocrystalline to amorphous at x = 0.30. The most striking properties were observed for the sample with x = 0.30. Over the voltage range of 1.5-4.0 V at a current rate of 500 mA/g, this material exhibited a relatively high reversible capacity of ∼100 mAh/g, which was four times greater than that of the Si-free 2Fh and indicated a good rate capability and cyclability. The large capacity and good rate and cycle performances are presumably because of the amorphous structure and the strong and stabilizing covalent Si-O bonds, respectively. The minor amount of Si⁴⁺ in the structure of the iron oxyhydroxides is considered to improve the electrochemical properties. Use of more appropriate doping elements and fabrication of more appropriate nanostructures could drastically improve the Li storage properties of the developed bioinspired material.