Structural complexity of layered-spinel composite electrodes for Li-ion batteries

The complexity of layered-spinel yLi(2)MnO(3)center dot(1-y)Li+xMn2-xO4 (Li:Mn = 1.2:1; 0 <= x <= 0.33; y >= 0.45) composites synthesized at different temperatures has been investigated by a combination of x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), and nuclear magnetic resonance (NMR). While the layered component does not change substantially between samples, an evolution of the spinet component from a high to a low lithium excess phase has been traced with temperature by comparing with data for pure Li1+xMn2-xO4. The changes that occur to the structure of the spinel component and to the average oxidation state of the manganese ions within the composite structure as lithium is electrochemically removed in a battery have been monitored using these techniques, in some cases in situ. Our Li-6 NMR results constitute the first direct observation of lithium removal from Li2MnO3 and the formation of LiMnO2 upon lithium reinsertion.