X-ray absorption spectroscopic (XAS) and micro-Raman analyses have been performed to investigate the effect of delithiation/relithiation reaction on the electronic and crystal structures of layered LiMnO2. From the spectroscopic results presented here, it becomes clear that the local structure around manganese in LiMnO2 is changed from a layered α-NaFeO2-type structure to a spinel-like one upon Li deintercalation-intercalation reaction. Such results highlight the lattice instability of layered manganese oxide for the extraction of interlayer lithium, which is responsible for the remarkable capacity fading. On the basis of the present experimental findings, we have prepared the chromium-substituted LiMn1-xCrxO2 (0≤x≤0.15) oxides to improve the electrochemical performance of layered lithium manganate. As expected, the electrochemical measurements clarify that the Cr-substituted compounds possess better electrochemical properties than the pristine LiMnO2. According to the XAS and micro-Raman studies for these compounds, it is found that the trivalent chromium ions are fixed to the octahedral site of MnO2 layer before and after electrochemical charge-discharge process, and that the manganese ion can be stabilized through the shortening of (Mn-O) bond distances. In this regard, the improved electrochemical performance of LiMn1-xCrxO2 is surely attributed to the stabilization of layered lithium manganate lattice upon replacement of Mn with Cr.
Bibliographical noteFunding Information:
This work was supported in part by the Korean Ministry of Science and Technology through the 1999 National Research Laboratory (NRL) project. The authors are grateful to Prof. M. Nomura for his help in obtaining the XAS data in the Photon Factory as well as to Prof. M. Yoshimura and Prof. M. Kakihana for their help in obtaining the micro-Raman data. H.-S.P. is grateful to the Korean Ministry of Education for the Brain Korea 21 fellowship.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics