Cathode of LiMg y Mn2 − y  O 4 and LiMg y Mn2 − y  O 4 − δ Spinel Phases for Lithium Secondary Batteries

To improve the cycle performance of as the cathode of 4 V class lithium secondary batteries, the cathode properties of the quaternary cubic spinel phases synthesized at 750°C were examined. Although the cycle performance of the was improved by the substitution of for in the octahedral sites, the first discharge capacity was reduced considerably compared with that of the parent . In order to compensate for the theoretical capacity reduction in , nonstoichiometric spinel oxides were prepared under controlled oxygen partial pressures at 750°C. The single‐phase region of δ in was 0 ≤ δ < 0.04, which was larger than that of parent (0 ≤ δ < 0.018) in our previous work. From density data, a metal excess model was proposed as the defect structure in the . The chemical diffusion coefficient of lithium ion for nonstoichiometric was smaller than that for the stoichiometric . This also supported the metal excess model, because excess metals in 16c sites prevented an easier diffusion of lithium in the 8a-16c-8a diffusion path. © 1999 The Electrochemical Society. All rights reserved.