Structural and Electrochemical Characterization of Composite Layered-Spinel Electrodes Containing Ni and Mn for Li-Ion Batteries

The structural features of a series of intergrown "layered-spinel" composite materials with initial formulation , previously shown to have attractive properties as positive electrodes in lithium batteries, were studied. The existence of a layered and a spinel component in samples with was confirmed by both X-ray diffraction and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The unit-cell volume of the layered component was shown to decrease as a function of , while the unit-cell parameter of the cubic spinel phase did not vary significantly. The MAS NMR spectra confirmed that the cation distribution in these layered-spinel composite structures is extremely complex; analysis of the data, particularly for intermediate values of , suggested that , , , and ions are present, rather than just and as implied by the ideal formula . The structural changes induced by the electrochemical removal and reinsertion of lithium in the composite electrode for were followed by MAS NMR and related to the different signatures in the composition-voltage profiles. The activity of both the layered and the spinel component within a 5–2 V voltage window was confirmed.