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

Abstract

Unlike the LiMn 2 O 4 spinel, the lithium-substituted LiMn 2 - y Li y - δ (0.05 ≤ y ≤ 0.15) sinel oxides exhibit capacity in the 5 V region. The 5 V capacity increases with increasing amount of excess lithium y. In contrastto 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 4 - .