Electrochemical and structural properties of xLi2M‘O3·(1−x)LiMn0.5Ni0.5O2 electrodes (M‘ = Ti, Mn, Zr; 0 ≤ x ≤ 0.3) for lithium batteries are reported. Powder X-ray diffraction, lattice imaging by transmission electron microscopy, and nuclear magnetic resonance spectroscopy provide evidence that, for M‘ = Ti and Mn, the Li2M‘O3 component is structurally integrated into the LiMn0.5Ni0.5O2 component to yield “composite” structures with domains having short-range order, rather than true solid solutions in which the cations are uniformly distributed within discrete layers. Li2TiO3 and Li2ZrO3 components are electrochemically inactive, whereas electrochemical activity can be induced into the Li2MnO3 component above 4.3 V vs Li0. When cycled in lithium cells, xLi2MnO3·(1−x)LiMn0.5Ni0.5O2 electrodes with x = 0.3 provide capacities in excess of 300 mA·h/g over the range 4.6−1.45 V.

ions. Although a disordering temperature of approximately 1000 K is calculated, ordered fragments persist above the phase transition and these materials contain significant short-range order, even when quenched from high temperature.

We have investigated the local electronic and atomic structure of the LiMn0.5Ni0.5O2 electrode during the first charge and discharge process using in situ X-ray absorption spectroscopy (XAS) of the Mn and Ni K-edges. The Ni K-edge structure in the XANES spectrum shifts to higher energy during charge and shifts back reversibly during discharge in the higher voltage region of ∼4 V, whereas the Mn K-edge structure does not appear to exhibit a rigid edge shift. Further Li-ion intercalation during extended discharge in the 1-V plateau leads to the reduction of Mn4+ ions suggesting that the charge compensation in this region is achieved via the reduction of Mn4+ ions to Mn2+. Mn K-edge EXAFS results indicate that a small amount of Li is found in the Ni2+/Mn4+ layers. These Li ions in the transition metal layers are primarily present in the second coordination shell of Mn and not around Ni. Ni K-edge EXAFS fitting results suggest that the oxidation process upon Li deintercalation takes place in two steps:  Ni2+ to Ni3+ first, and then Ni3+ to Ni4+.