•Sub-micron sized particles for TEM analysis synthesized by sol-gel method.•MgO-LiCoO2 exhibited a much more homogeneous distribution of Li after the cycling tests.•A coherent orientation relationship was observed at the MgO//LiCoO2 interface.The surfaces of LiCoO2 particles were modified to improve the charge-discharge cycling properties of Li-ion batteries containing LiCoO2 cathodes. The sol-gel technique was used to modify the surface of LiCoO2 particles with magnesium oxide. Capacity retention during cycling of the magnesium oxide-coated LiCoO2 cathode was superior to that of a cathode comprising pristine LiCoO2. Moreover, results obtained from TEM measurements indicate that the Li concentration was relatively homogeneous in the magnesium oxide-coated LiCoO2 particles after cycling tests. The crystallographic planes of the coating were found to be coherently oriented with those of the substrate, MgO(111)[1−10]//LiCoO2(003)[100]. Therefore, we believe that a thin cover of Mg on the surface of LiCoO2 stabilizes the surface, contributing to the homogeneity of charge and discharge reactions.

•The scanning REELS technique using the SEM apparatus has been applied to Li K-edge spectra.•The present SEM-REELS technique can provide the distinct fine structure.•For Li4Ti5O12 and Li7Ti5O12 electrode samples, the Li distribution has been successfully visualized by the REELS spectrum-imaging scheme.Analyses of Li has been performed by reflection electron energy-loss spectroscopy (REELS) technique, using a scanning electron microscopy (SEM) apparatus, where Li signals can be detected with high spatial resolution without severe requirements for sample shapes. For Li4Ti5O12 and Li7Ti5O12 samples as electrode materials of Li-ion batteries, the Li distribution was successfully revealed by the spectrum-imaging scheme. The fine structure of REELS spectra was able to be applied to the chemical analysis of Li-containing compounds.