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

摘要

The relation between cathode performance and thermodynamic stability of lithium manganese spinels, LiMn_2O_4, Li_2Mn_4O_9, Li_4Mn_5O_(12), 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#_fH~0, the enthalpy change of reaction, #DELTA#H, and the enthalpy change per mole of atoms for the formation reaction, #DELTA#H_R, were calculated from the heat of dissolution. |#DELTA#H_R| decreased in order of Li_4Mn_5O_(12) > Li_2Mn_4O_9 > LiMn_2O_4, a larger |#DELTA#H_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 |#DELTA#H_R|. A more thermodynamically stable sample makes a stable crystal structure and leads to a good cycle performance.