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 xLi[Mn(1.5)Ni(0.5)]O(4)center dot(1-x)(Li(2)MnO(3)center dot Li[Mn(0.5)Ni(0.5)]O(2)), 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 0 < x < 1 was confirmed by both X-ray diffraction and (6)Li 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 x, while the unit-cell parameter of the cubic spinel phase did not vary significantly. The (6)Li 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 x, suggested that Mn(4+), Mn(3+), Ni(3+), and Ni(2+) ions are present, rather than just Mn(4+) and Ni(2+) as implied by the ideal formula xLi[Mn(1.5)Ni(0.5)]O(4)center dot(1-x)(Li(2)MnO(3)center dot Li[Mn(0.5)Ni(0.5)]O(2)). The structural changes induced by the electrochemical removal and reinsertion of lithium in the composite electrode for x=0.5 were followed by (6)Li 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.