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Title: Charge compensation and oxidation in Na {sub x} CoO{sub 2-} {sub {delta}} and Li {sub x} CoO{sub 2-} {sub {delta}} studied by XANES

Abstract

A comparative study on the oxidation and charge compensation in the A{sub x} CoO{sub 2-} {sub {delta}} systems, A=Na (x=0.75, 0.47, 0.36, 0.12) and Li (x=1, 0.49, 0.05), using X-ray absorption spectroscopy at O 1s and Co 2p edges is reported. Both the O 1s and Co 2p XANES results show that upon removal of alkali metal from A{sub x} CoO{sub 2-} {sub {delta}} the valence of cobalt increases more in Li {sub x} CoO{sub 2-} {sub {delta}} than in Na {sub x} CoO{sub 2-} {sub {delta}} . In addition, the data of O 1s XANES indicate that charge compensation by oxygen is more pronounced in Na {sub x} CoO{sub 2-} {sub {delta}} than in Li {sub x} CoO{sub 2-} {sub {delta}} . - Graphical abstract: The valence of cobalt increases more upon removal of alkali metal from Li {sub x} CoO{sub 2} than from Na {sub x} CoO{sub 2}.

Authors:
 [1];  [2];  [2];  [2];  [3];  [3];  [4];  [2];  [3];  [5]
  1. Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan), E-mail: markus.valkeapaa@tkk.fi
  2. Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan)
  3. Department of Chemistry and Center for Nano Storage Research, National Taiwan University, Taipei 10617, Taiwan (China)
  4. National Synchrotron Radiation Research Center (NSRRC), Hsinchu 30076, Taiwan (China)
  5. (Finland)
Publication Date:
OSTI Identifier:
21015816
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 5; Other Information: DOI: 10.1016/j.jssc.2007.03.001; PII: S0022-4596(07)00093-X; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION SPECTROSCOPY; COBALT; COBALT OXIDES; LITHIUM OXIDES; OXIDATION; SODIUM OXIDES; VALENCE; X-RAY SPECTROSCOPY

Citation Formats

Valkeapaeae, M., Katsumata, Y., Asako, I., Motohashi, T., Chan, T.S., Liu, R.S., Chen, J.M., Yamauchi, H., Karppinen, M., and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FIN-02015 Espoo. Charge compensation and oxidation in Na {sub x} CoO{sub 2-} {sub {delta}} and Li {sub x} CoO{sub 2-} {sub {delta}} studied by XANES. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.03.001.
Valkeapaeae, M., Katsumata, Y., Asako, I., Motohashi, T., Chan, T.S., Liu, R.S., Chen, J.M., Yamauchi, H., Karppinen, M., & Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FIN-02015 Espoo. Charge compensation and oxidation in Na {sub x} CoO{sub 2-} {sub {delta}} and Li {sub x} CoO{sub 2-} {sub {delta}} studied by XANES. United States. doi:10.1016/j.jssc.2007.03.001.
Valkeapaeae, M., Katsumata, Y., Asako, I., Motohashi, T., Chan, T.S., Liu, R.S., Chen, J.M., Yamauchi, H., Karppinen, M., and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FIN-02015 Espoo. Tue . "Charge compensation and oxidation in Na {sub x} CoO{sub 2-} {sub {delta}} and Li {sub x} CoO{sub 2-} {sub {delta}} studied by XANES". United States. doi:10.1016/j.jssc.2007.03.001.
@article{osti_21015816,
title = {Charge compensation and oxidation in Na {sub x} CoO{sub 2-} {sub {delta}} and Li {sub x} CoO{sub 2-} {sub {delta}} studied by XANES},
author = {Valkeapaeae, M. and Katsumata, Y. and Asako, I. and Motohashi, T. and Chan, T.S. and Liu, R.S. and Chen, J.M. and Yamauchi, H. and Karppinen, M. and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FIN-02015 Espoo},
abstractNote = {A comparative study on the oxidation and charge compensation in the A{sub x} CoO{sub 2-} {sub {delta}} systems, A=Na (x=0.75, 0.47, 0.36, 0.12) and Li (x=1, 0.49, 0.05), using X-ray absorption spectroscopy at O 1s and Co 2p edges is reported. Both the O 1s and Co 2p XANES results show that upon removal of alkali metal from A{sub x} CoO{sub 2-} {sub {delta}} the valence of cobalt increases more in Li {sub x} CoO{sub 2-} {sub {delta}} than in Na {sub x} CoO{sub 2-} {sub {delta}} . In addition, the data of O 1s XANES indicate that charge compensation by oxygen is more pronounced in Na {sub x} CoO{sub 2-} {sub {delta}} than in Li {sub x} CoO{sub 2-} {sub {delta}} . - Graphical abstract: The valence of cobalt increases more upon removal of alkali metal from Li {sub x} CoO{sub 2} than from Na {sub x} CoO{sub 2}.},
doi = {10.1016/j.jssc.2007.03.001},
journal = {Journal of Solid State Chemistry},
number = 5,
volume = 180,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • We report the synthesis and superconducting properties of a metastable form of the known superconductor Na{sub x}CoO{sub 2}{center_dot}yH{sub 2}O (x{approx_equal}1/3;y{approx_equal}4x). We obtained this metastable cobaltate superconductor due to the unique way it was synthesized. Instead of using the conventional bromine-acetonitrile mixture for the Na{sup +}-deintercalation reaction, we use an aqueous bromine solution. Using this method, we oxidize the sample to a point that the sodium cobaltate becomes unstable, leading to formation of other products if not controlled. This compound has the same structure as the reported superconductor, yet it exhibits a systematic variation of the superconducting transition temperature (T{sub c})more » as a function of time. Immediately after synthesis, this compound is not a superconductor, even though it contains appropriate amounts of Na{sup +} and H{sub 2}O. The samples become superconducting with low T{sub c} values after {approx}90 h. T{sub c} continually increases until it reaches a maximum value (4.5 K) after about 260 h. Then T{sub c} drops drastically, becoming nonsuperconducting approximately 100 h later. Corresponding time-dependent neutron powder diffraction data shows that the changes in superconductivity exhibited by the metastable cobaltate correspond to slow formation of oxygen vacancies in the CoO{sub 2} layers. In effect, the formation of these defects continually reduces the cobalt oxidation state causing the sample to evolve through its superconducting life cycle. Thus, the dome-shaped superconducting phase diagram is mapped as a function of cobalt oxidation state using a single sample. The width of this dome based on the formal oxidation state of cobalt is very narrow--approximately 0.1 valence units wide. Interestingly, the maximum T{sub c} in Na{sub x}CoO{sub 2}{center_dot}yH{sub 2}O occurs when the cobalt oxidation state is near +3.5. Thus, we speculate that the maximum T{sub c} occurs near the charge ordered insulating state that correlates with the average cobalt oxidation state of +3.5.« less
  • Cells using polyethylene oxide as a sodium ion conducting electrolyte, P2 phase Na[sub x]CoO[sub 2] as the positive electrode and either sodium or sodium/lead alloy as the negative electrode were assembled, discharged, and cycled. Na[sub x]CoO[sub 2] intercalates sodium over a range of x = 0.3--0.9, giving theoretical energy densities of 1,600 Wh/liter (for sodium) or 1,470 Wh/liter (for sodium/lead alloy). Cells could be discharged at rates up to 2.5 mA/cm[sup 2] corresponding to 25% depth of discharge and typically were discharged and charged at 0.5 mA/cm[sup 2] (100% depth of discharge) or approximately 1--2 C rate. Over one hundredmore » cycles to 60% utilization or more, and two hundred shallower cycles at this rate have been obtained in this laboratory. Experimental evidence suggests that the cathode is the limiting factor in determining cycle life and not the Na/PEO interface as previously thought. Estimates of practical energy and power densities based on the cell performance and the following configuration are presented: 30--45 w/o electroactive material in the positive electrode, a twofold excess of sodium, 10 [mu]m separators, and 5 [mu]m current collectors composed of metal coated plastic. On the basis of these calculations, practical power densities of 335 W/liter for continuous discharge at 0.5 mA/cm[sup 2] and up to 2.7 kW/liter for short periods of time should be attainable. This level of performance approaches or exceeds that seen for some lithium/polymer systems under consideration for electric vehicle applications, but with a lower anticipated cost.« less
  • The Raman spectra of the parent compound Na{sub x}CoO{sub 2} (x = 0.75) and the superconducting oxyhydrates Na{sub x}CoO{sub 2} {center_dot} yH{sub 2}O with different superconducting temperatures (T{sub c}) have been measured. Five Raman active phonons around 195 cm{sup -1} (E{sub 1g}), 482 cm{sup -1}, 522 cm{sup -1}, 616 cm{sup -1} (3E{sub 2g}), and 663 cm{sup -1} (A{sub 1g}) appear in all spectra. These spectra change systematically along with the intercalation of H{sub 2}O and superconducting properties. In particular, the Raman active phonons (A{sub 1g} and E{sub 1g}) involving the oxygen motions within the Co-O layers show up monotonous decreasemore » in frequency along with superconducting temperature T{sub c}. The fundamental properties and alternations of other active Raman phonons in the superconducting materials have also been discussed.« less
  • We have performed thermal expansion and compressibility measurements on the recently discovered superconducting material Na{sub x}CoO{sub 2}{center_dot}4xD{sub 2}O (x{approx_equal}1/3) using neutron powder diffraction over the temperature range 10-295 K and the pressure range 0-0.6 GPa. Pressure measurements were done in a helium-gas pressure cell. Both the thermal expansion and compressibility are very anisotropic, with the largest effects along the c axis, as would be expected for a layered material with weak hydrogen bonding nominally along the c axis. Near room temperature, the anisotropies of the thermal expansion and compressibility of the hexagonal crystal structure are nearly the same [({delta}c/c)/({delta}a/a){approx_equal}3-4], withmore » a 100 deg. C change in temperature being roughly equivalent to 0.2 GPa pressure. It might be then inferred that changes in atom position parameters are also the same, but this is not the case. While the effects of temperature on the atom positions are essentially what one might expect, the effects of pressure are surprising. With increasing pressure, the thickness of the CoO{sub 2} layer increases, due to the combined effects of an increasing Co-O bond length and changes in the O-Co-O angles of the CoO{sub 6} octahedra. We conclude that this unusual effect results from pressure-induced strengthening of the hydrogen bonding between the Na{sub x}(D{sub 2}O){sub 4x} layers and the CoO{sub 2} layers. The strengthening of these hydrogen bonds requires that charge be moved from elsewhere in the structure; hence, there is a pressure-induced charge redistribution that weakens (lengthens) the Co-O bonds and changes the electronic structure of the superconducting CoO{sub 2} layers.« less
  • The magnetic, thermoelectric, and structural properties of Li{sub x}Na{sub y}CoO{sub 2}, prepared by intercalation and deintercalation chemistry from the thermodynamically stable phase Li{sub 0.41}Na{sub 0.31}CoO{sub 2}, which has an alternating Li/Na sequence along the c-axis, are reported. For the high Li-Na content phases Li{sub 0.41}Na{sub 0.31}CoO{sub 2} and Li{sub 0.40}Na{sub 0.43}CoO{sub 2}, a sudden increase in susceptibility is seen below 50 K, whereas for Li{sub 0.21}Na{sub 0.14}CoO{sub 2} an antiferromagnetic-like transition is seen at 10 K, in spite of a change from dominantly antiferromagnetic to dominantly ferromagnetic interactions with decreasing alkali content. The Curie constant decreases linearly with decreasing alkalimore » content, at the same time the temperature-independent contribution to the susceptibility increases, indicating that as the Co becomes more oxidized the electronic states become more delocalized. Consistent with this observation, the low alkali containing phases have metallic-like resistivities. The 300 K thermopowers fall between 30 {mu}V/K (x+y=0.31) and 150 {mu}V/K (x+y=0.83). - Graphical abstract: The ordered layered arrangement of Li{sup +} and Na{sup +} ions between CoO{sub 2} sheets.« less