Amorphous Metal Oxide Nanosheets Featuring Reversible Structure Transformations as Sodium-Ion Battery Anodes

The size and shape control of amorphous nanomaterials has long been a bottleneck restricting their further development. Here, we present a general approach to synthesize more than twenty kinds of amorphous metal oxide nanosheets. The amorphous state of the nanosheets is determined using aberration-corrected high-resolution transmission electron microscopy and X-ray diffraction. By using extended X-ray absorption fine structure analysis, we demonstrate that amorphous nanosheets have a larger interatomic distance and a looser packing characteristic compared with crystalline counterparts. The as-prepared amorphous FeOx nanosheets are used as sodium-ion batteries anode materials, exhibiting notable performance with a specific capacity of 263.4 mAh g−1 at 100 mA g−1 and long-term cyclic stability. Significantly, a reversible amorphous-crystalline-amorphous structure transformation phenomenon during the cycling test is observed at the atomic scale.