Analytical transmission electron microscopy investigation of electrochemically Li+-Na+ substituted LiNi0.5Mn1.5O4 electrode

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+ & hArr; 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.

Automated summary

This study characterized the electrochemical Li+-Na+ alkaline cation substitution of LNMO material using analytical transmission electron microscopy. Sodium was uniformly inserted into single particles, while lithium was completely extracted. Only nickel contributed to the redox reaction, with manganese playing no role. The elemental composition ratio analysis confirmed Na0.6Ni0.5Mn1.5O3.8 as the formula for the substituted material. Oxygen desorption and defect formation were found to be important for the Li+-Na+ substitution mechanism.