Total Overlap Population Analysis for Cyclic Capacity of Metal-Substituted-Spinel Lithium Manganate LiMn₂O₄ for Positive Electrode Material of Rechargeable Lithium-Ion Battery

The capacity fading with charge-discharge cycles, which is a problem in the practical use of spinel lithium manganate (LiMn₂O₄) for the positive electrode material of rechargeable lithium-ion battery, is analyzed using extended Hückel band calculations. The strength of the Mn-O bond is characterized by total overlap population (TOP) analyses. The manganese atom in spinel lithium manganate is substituted with other elements and the TOP of the Mn-O bond is calculated and analyzed. The TOP of the Mn-O bond in substituted spinel lithium manganate is compared with experimental data for the capacity performance in charge-discharge cycles. When the ionic radius of the substituted atom is close to that of manganese, the larger the TOP is, the larger is the suppression of capacity fading of the charge-discharge cycles. In such a case, TOP is a good index for measuring the capacity fading with charge-discharge cycles for substituted lithium manganate. However, when the ionic radius of the substituted atom of a typical element is larger than that of manganese, in spite of the magnitude of the TOP, the capacity performance in the charge-discharge cycles is poor. The combination of TOP and ionic radius is applicable to the search and examination for the best composition in the lithium manganate whose durability is determined by the strength of the Mn-O bond. Lithium manganate materials substituted by alkali metal elements show very high value of TOP with respect to the Mn-O bond.