Synthesis and Characterization of New LiNi[sub 1−y]Mg[sub y]O[sub 2] Positive Electrode Materials for Lithium-Ion Batteries

New layered oxides were synthesized by a coprecipitation method followed by a high‐temperature thermal treatment. Rietveld refinements of their X‐ray diffraction patterns showed that they exhibit a quasi‐two‐dimensional structure, isostructural to , for small substitution amounts ( y ≤ 0.10). For larger amounts ( y = 0.15, 0.20), the Li/(Ni + Mg) ratio is significantly lower than unity. In all cases, the extra ions located in the inter‐slab space for lithium deficiency compensation are preferentially ions. A magnetic study confirmed the cationic distributions which result from the size difference between and ions. An electrochemical study showed reversible behavior for all materials. A high capacity was found for phases ( y ≤ 0.02), which decreased when y increased. The presence of cations in the inter‐slab space, which cannot be oxidized and have a size close to , prevents the local collapses of the structure which occurs for the system; therefore good cycling stability is observed. © 2000 The Electrochemical Society. All rights reserved.