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 lithium manganese spinels, LiMn2O4, Li2Mn4O9, Li4Mn5O12, as cathode active materials for lithium secondary battery, has been investigated. The heat of dissolution of these samples was measured by the solution calorimetry method. The standard enthalpy of formation, Delta H-f(0), the enthalpy change of reaction, DeltaH, and the enthalpy change per mole of atoms for the formation reaction, DeltaH(R), were calculated from the heat of dissolution. \ DeltaH(R)\ decreased in order of Li1Mn5O12 > Li2Mn4O9 > LiMn2O4, a larger \ DeltaH(R)\ meaning a thermodynamically more stable sample. In addition, lattice energies of these samples were calculated for a unit-cell. The trend order for lattice energies was the same as that for \ DeltaH(R)\. A more thermodynamically stable sample makes a stable crystal structure and leads to a good cycle performance.