The study of LiNi_0.5Mn_1.5O₄ 5-V cathodes for Li-ion batteries

In this work, we studied cycling and storage behavior at elevated temperatures of substituted spinel-nickel electrodes LiNi_xMn _2-xO₄ (x = 0.5) that can operate as cathodes in 5-V advanced lithium-ion batteries. A stable electrochemical performance and low capacity fading were found upon cycling and storage (charged state) of LiNi _0.5Mn_1.5O₄ electrodes in DMC-EC/LiPF ₆ solutions at elevated temperatures (60 °C). It was established that cycling/storage of these electrodes led to dissolution of manganese and nickel and reduction of Mn²⁺ and Ni²⁺ on the lithium counter electrode. These phenomena were studied by solution analysis (ICP) and surface chemistry and morphological measurements (ex situ X-ray photoelectron and Raman spectroscopies, and SEM) of the lithium and LiNi_0.5Mn _1.5O₄ electrodes. Since these electrodes perform well during prolonged cycling, it is clear that the above changes relate to surface phenomena and not changes in the bulk of the active mass.