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Effect of iron on delithiation in LixCo1-yFeyO2. Part 2: in-situ XANES and EXAFS upon electrochemical cycling

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Holzapfel,  M.
High Magnetic Field Laboratory, Former Departments, Max Planck Institute for Solid State Research, Max Planck Society;

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Citation

Holzapfel, M., Proux, O., Strobel, P., Darie, C., Borowski, M., & Morcrette, M. (2004). Effect of iron on delithiation in LixCo1-yFeyO2. Part 2: in-situ XANES and EXAFS upon electrochemical cycling. Journal of Materials Chemistry, 14(1), 102-110.


Cite as: https://hdl.handle.net/21.11116/0000-000E-FF31-C
Abstract
LixCo1-yFeyO2 solid solutions were examined in an in-situ
electrochemical X-ray absorption spectroscopy study using a plastic
battery configuration. XANES and EXAFS were applied to elucidate the
evolution of local symmetry and oxidation states of iron and cobalt
upon electrochemical cycling of three particular stoichiometries:
LixCo0.9Fe0.1O2, LixCo0.8Fe0.2O2 and LixCo0.6Fe0.4O2. While the cobalt
environment shows little variation, a distortion of the FeO6 octahedra
occurs quite rapidly for all three samples with a decrease in the next
neighbour numbers from six to four. This is ascribed to the Jahn-Teller
effect which affects Fe4+ (a d(4) system), that is formed upon
delithiation. No distortion is observed for cobalt. Along the
delithiation process a simultaneous increase in the edge energy occurs
for cobalt and iron in the case of y=0.1 and to a lesser extent for
iron than for cobalt for y=0.4. This means that the oxidation of Fe3+
occurs together with the oxidation of the cobalt matrix in the
cobalt-rich samples but becomes more difficult for iron-rich samples.
In the case of the cobalt-rich samples, the edge-energy for both
elements shifts back down at the end of charge, in spite of the
continuing oxidation of the cations. This effect is probably related to
the appearance of a new lithium-poor phase, that is not formed for
y=0.4, and confirms the in-situ X-ray diffraction results published in
the first part of this series.