Abstract
The electrochemical Li+–Na+ alkaline cation substitution of a lithium nickel manganese oxide (LiNi0.5Mn1.5O4, LNMO), which is characterized via structural analysis, has previously been reported. However, detail characterizations of the chemical and electronic features are lacking. In this study, we characterized that by using analytical transmission electron microscopy. Energy dispersive X-ray spectroscopy (EDS) revealed uniform Na-insertion into a single particle. Electron energy-loss spectroscopy (EELS) analysis exhibited complete Li-extraction. Energy loss near edge structure (ELNES) of Mn and Ni L-edges indicated that only Ni contributes to the redox reaction as Ni2+ ⇔ Ni4+ during the Li+–Na + substitution. The elemental composition ratio analysis using both EDS and EELS indicated Na0.6Ni0.5Mn1.5O3.8 as a formula of the Na-substituted material. Oxygen desorption was provoked during the Na-insertion process, and oxygen defect formation was found to be essential for the Li+–Na+ substitution mechanism of the LNMO material.
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