The Impact of Aluminum and Iron Substitution on the Structure and Electrochemistry of Li(Ni[sub 0.4]Co[sub 0.2−y]M[sub y]Mn[sub 0.4])O[sub 2] Materials

and compounds were prepared to investigate the effect of replacement of all or part of the cobalt on the structural and electrochemical properties. The impact of substitution on the structure has been examined by both X-ray and neutron diffraction experiments. The incorporation of aluminum has minimal effect on the antisite defect concentration, but leads to structural changes that affect electrochemical performance. The most important effect is an opening of the lithium slab dimension upon substitution, which results in improved rate performance compared to the parent compound. In contrast, the lithium slab dimension is not affected by iron substitution and no rate enhancement effect is observed. The cycling stability of aluminum containing materials is superior to both the parent material and iron-substituted materials.