Origin of the Capacity of Spinel LiMn_(2-y)Li_yO_(4+-delta) (0 <= y <= 0.15) in the 5 V Region

摘要

Unlike the LiMn_2O_4 spinel, the lithium-substituted LiMn_(2-y)Li_yO_(4+-delta) (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_yO_(4+-delta) 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+).