Thermodynamic Investigation and Cathode Performance of Li-Mn-O Spinel System as Cathode Active Material for Lithium Secondary Battery.

Abstract

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, ΔfH0, the enthalpy change of reaction, ΔH, and the enthalpy change per mole of atoms for the formation reaction, ΔHR, were calculated from the heat of dissolution. |ΔHR| decreased in order of Li4Mn5O12>Li2Mn4O9>LiMn2O4, a larger |ΔHR| 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 |ΔHR|. A more thermodynamically stable sample makes a stable crystal structure and leads to a good cycle performance.