The carbon-coated LiMn_0.8Fe_0.2PO₄ (LMFP) mesocrystals were designed to be favorable for kinetics of electron and lithium-ion conductivity due to its well-developed internal path composed of ~50-nm-sized nanocrystallites. The carbon-coated LMFP mesocrystals exhibited reasonable electrochemical cycle performance as well as superior rate capability, ensuring a proper model material to systematic study of reaction mechanism upon battery cycling. In order to investigate the reversibility of charge/discharge reaction on carbon-coated LMFP mesocrystals, we performed coherent x-ray diffraction microscopy to confirm the electronic-structure effects of each transition metal (Mn and Fe) and morphological changes. In addition, the electrochemical impedance spectroscopy at quasi-steady state has been analyzed as a supplementary tool. We believe that our systematic approaches as well as complementary analyses can provide clear experimental inspection on the origin of homogeneity/ inhomogeneity of charge/ discharge in LMFP electrodes via coherent x-ray diffraction microscopy and electrochemical impedance spectroscopy.