Origin of the Capacity of Spinel LiMn[sub 2−y]Li[sub y]O[sub 4±δ] (0≤y≤0.15) in the 5 V Region

Unlike the LiMn 2 O 4 spinel, the lithium-substituted LiMn 2 − y Li y O 4 ± δ ( 0.05 ⩽ y ⩽ 0.15 ) spinel oxides exhibit capacity in the 5 V region. The 5 V capacity increases with increasing amount of excess lithium y . In contrast to a recent literature report, the data demonstrate that excess oxygen is not needed to impart the 5 V capacity. With the samples having a significant amount of excess lithium y > 0.1 , the 4 V capacity increases with cycling while the 5 V capacity decreases. The 5 V capacities of the LiMn 2 − y Li y O 4 ± δ spinels are explained on the basis of an electrochemical oxidation of Mn 4 + or O 2 − , which subsequently results in a self-discharge reaction involving the evolution of oxygen from the lattice and a reduction of Mn 4 + to Mn 3 + .