Synthesis, Electrochemistry, and Structural Studies of Lithium Intercalation of a Nanocrystalline Li2MnO3-like Compound

Abstract

A nanocrystalline lithium-rich manganese (IV) oxide, synthesized by a low-temperature sol−gel route, is reported as a surprising lithium intercalation host. The composition of the material is very close to Li2MnO3. X-ray diffraction (XRD), electron diffraction, and high-resolution transmission electron microscopy analyses establish that the material possesses a nanocrystalline structure, similar to that of the rock salt monoclinic Li2MnO3, with a crystallite size of about 5 nm. X-ray absorption spectroscopy (XAS) analysis at the Mn K edge indicates that the Mn is in the 4+ oxidation state and in a local atomic/electronic environment similar to that in the rock salt monoclinic Li2MnO3. Unlike the microcrystalline Li2MnO3, which is known to be electrochemically inactive for lithium intercalation or deintercalation, this nanocrystalline counterpart surprisingly yields a reversible intercalation capacity of 0.71−0.87 Li per formula or 163−200 (mA h)/g and a specific energy density of 400−450 (mW h)/g, at diff...