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Phase separation of intercalation electrodes

Phase separation of intercalation electrodes Lithium ion cells are widely used for portable equipment because of their high energy density. These cells employ lithium intercalation materials as their anode and cathode active materials. Lithium intercalation materials sometimes show phase separation as a function of the amount of inserted Li, and the cell voltage becomes a constant at the two-phase region. The thermodynamic criterion of the phase separation of binary mixtures is already known using Gibbs free energy. The criterion of the phase separation was applied to that of lithium intercalation materials. First, the phase separation of spinel LiMn2O4 and LiNiO2 was studied, with the assumption that the cathode materials do not deform during Li insertion and extraction, are completely ionic, and only the Coulomb potential is effective in terms of changing the internal energy. Our calculated phase separation was in agreement with the experiments at 0<x<0.5 for LixMn2O4 and 0<x<0.25 for LixNiO2. Our calculated voltage of LixMn2O4 was very high compared with the experimental value, because of a very low value of the Coulomb potential at the lithium tetrahedral site in LixMn2O4. Therefore, it seems that LiMn2O4 is not a perfect ionic crystal. Next, the phase separation of graphite was studied, considering a work (wa) to expand the layer when Li is inserted. When wa is small, it is expected that the phase separation is the co-existence of the Li-poor phase and the Li-rich phase. However, if wa is large, it is expected that the two-phases are a phase without Li and a phase filled with Li completely. From these considerations, graphite seems to have a large wa. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ionics Springer Journals

Phase separation of intercalation electrodes

Yamaki, J.; Egashira, M.; Okada, S.
Ionics , Volume 8 (2) – Mar 22, 2006
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References (12)

Publisher
Springer Journals
Copyright
Copyright © 2002 by IfI - Institute for Ionics
Subject
Chemistry; Biomedicine general; Analytical Chemistry; Physical Chemistry; Electrochemistry; Optical and Electronic Materials
ISSN
0947-7047
eISSN
1862-0760
DOI
10.1007/BF02377753
Publisher site
See Article on Publisher Site

Abstract

Lithium ion cells are widely used for portable equipment because of their high energy density. These cells employ lithium intercalation materials as their anode and cathode active materials. Lithium intercalation materials sometimes show phase separation as a function of the amount of inserted Li, and the cell voltage becomes a constant at the two-phase region. The thermodynamic criterion of the phase separation of binary mixtures is already known using Gibbs free energy. The criterion of the phase separation was applied to that of lithium intercalation materials. First, the phase separation of spinel LiMn2O4 and LiNiO2 was studied, with the assumption that the cathode materials do not deform during Li insertion and extraction, are completely ionic, and only the Coulomb potential is effective in terms of changing the internal energy. Our calculated phase separation was in agreement with the experiments at 0<x<0.5 for LixMn2O4 and 0<x<0.25 for LixNiO2. Our calculated voltage of LixMn2O4 was very high compared with the experimental value, because of a very low value of the Coulomb potential at the lithium tetrahedral site in LixMn2O4. Therefore, it seems that LiMn2O4 is not a perfect ionic crystal. Next, the phase separation of graphite was studied, considering a work (wa) to expand the layer when Li is inserted. When wa is small, it is expected that the phase separation is the co-existence of the Li-poor phase and the Li-rich phase. However, if wa is large, it is expected that the two-phases are a phase without Li and a phase filled with Li completely. From these considerations, graphite seems to have a large wa.

Journal

Ionics – Springer Journals

Published: Mar 22, 2006

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