Thermodynamic stability and cathode performance of LiMn2-xMgxO4 as cathode active material for the lithium secondary battery

To improve the cycle performance of the 4 V class lithium manganese oxide positive electrode material for the lithium secondary battery, we have been investigated the partial substitution of an another metal for Mn. In this study, the quaternary spinel, LiMn2-xMgxO4, in which a part of the Mn is replaced by Mg is prepared. The Mn valence was determined by chemical analysis. The heats of dissolution of the samples were measured by the solution calorimetry method. The standard enthalpy of formation, Delta tH(0), and the change in the enthalpy of the reaction, Delta H, were calculated from the heat of dissolution. The Delta tH(0) and dfi decreased and the Mn valence increased with increasing Mg content. The effect of the electrode characteristics on these properties of the positive electrode active materials was investigated in the 4 V range. The discharge capacity decreased with increasing Mg content. On the other hand, the cycle performance was improved by increasing the Mg content. We investigated the relation between the cathode performance and the thermodynamic stability of the quaternary spinel, LiMn2-xMgxO4 (x = 0-0.2).