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

To improve the cycle performance of the 4 V class lithium manganese oxide p ositive electrode material for the lithium secondary battery, we have been investigated the partial substitution of an another metal for Mn. In this s tudy, the quaternary spinel, LiMn2-xMgxO4, in which a part of the Mn is rep laced by Mg is prepared. The Mn valence was determined by chemical analysis . The heats of dissolution of the samples were measured by the solution cal orimetry method. The standard enthalpy of formation, Delta tH(0), and the c hange in the enthalpy of the reaction, Delta H, were calculated from the he at of dissolution. The Delta tH(0) and dfi decreased and the Mn valence inc reased with increasing Mg content. The effect of the electrode characterist ics on these properties of the positive electrode active materials was inve stigated in the 4 V range. The discharge capacity decreased with increasing Mg content. On the other hand, the cycle performance was improved by incre asing the Mg content. We investigated the relation between the cathode perf ormance and the thermodynamic stability of the quaternary spinel, LiMn2-xMg xO4 (x = 0-0.2).