Spinel manganese oxide: A high capacity positive electrode material for the sodium ion battery

The ex-situ synchrotron X-ray diffraction (SR-XRD) and transmission electron microscopy (TEM) analyses revealed that the spinel domain of Li2−xMnO3 retains its crystallographic structure during the Na insertion and extraction, although the crystal significantly loses its periodicity when Na is inserted. A numerical simulation of the SR-XRD profile suggests that the Na-inserted Li2−xMnO3 has the periodicity of only one to two unit cells while retaining the spinel structure. XAS revealed that the reversible capacity is found to be dominated by the redox between Mn(III) and Mn(IV) and the Mn-Mn distance significantly loses its correlation upon Na-insertion, which is consistent with the broad SR-XRD profile.