Goethite nanorods as anode electrode materials for rechargeable Li-ion batteries

Although various transition metal oxides have been reported to act as low potential Li insertion hosts, the oxyhydroxides have remained unexplored to date. We show here that the hydroxide ions present in transition metal oxyhydroxides do not interfere with the lithium uptake and extraction, permitting very good reversibility of the reduction/oxidation reactions. Goethite (α-FeOOH) nanocrystals can uptake and extract large amount of Li via the conversion reaction mechanism, providing a reversible capacity of 500 mA h g−1 at an average potential of 0.85 V vs. Li/Li+. The mechanism was examined using a combination of X-ray diffraction, electron microscopy, and the corresponding selected area electron diffractions (SAEDs). The α-FeOOH is reduced into nanoparticles of metallic Fe0 embedded in an amorphous matrix of Li2O and LiOH in the first discharge; the subsequent cyclings are redox reactions between metallic Fe0 and Fe2O3 clusters.