Thermodynamic investigation and cathode performance of Li-Mn-O spinel system as cathode active material for lithium secondary battery

The relation between cathode performance and thermodynamic stability of lit hium manganese spinels, LiMn2O4, Li2Mn4O9, Li4Mn5O12, as cathode active mat erials for lithium secondary battery, has been investigated. The heat of di ssolution of these samples was measured by the solution calorimetry method. The standard enthalpy of formation, Delta H-f(0), the enthalpy change of r eaction, DeltaH, and the enthalpy change per mole of atoms for the formatio n reaction, DeltaH(R), were calculated from the heat of dissolution. \ Delt aH(R)\ decreased in order of Li1Mn5O12 > Li2Mn4O9 > LiMn2O4, a larger \ Del taH(R)\ meaning a thermodynamically more stable sample. In addition, lattic e energies of these samples were calculated for a unit-cell. The trend orde r for lattice energies was the same as that for \ DeltaH(R)\. A more thermo dynamically stable sample makes a stable crystal structure and leads to a g ood cycle performance.