In this work, we studied cycling and storage behavior at elevated temperatures of substituted spinel–nickel electrodes LiNi x Mn2−x O4 (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 LiNi0.5Mn1.5O4 electrodes in DMC-EC/LiPF6 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 LiNi0.5Mn1.5O4 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.