Abstract
Using scanning transmission electron microscopy-electron energy-loss spectroscopy (STEM-EELS), we have investigated the charge-discharge mechanism in the first cycle and the origin of its high charge-discharge capacity for Li1.2Mn0.4Fe0.4O2(0.5Li2MnO3·0.5LiFeO2) positive electrode material of lithium ion batteries. Results revealed that local valence states of Mn ions, behaviors of extraction and insertion of Li ions, and the contribution of oxide ions into charge compensation in the entire region of the Li1.2Mn0.4Fe0.4O2 particles composed of Mn-rich and Fe-rich nanodimains during the first charge. The high charge-discharge capacity can be attributed to extraction and insertion of the partial oxide ions. The origin of the irreversible capacity can be related to the irreversible loss of oxygen during the charge.
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