Chemical Decomposition as a Likely Source of Ambient and Thermal Instabilities of Layered Sodium Cobaltate

• Published in: Chemistry of materials 2013-12, Vol.25 (23), p.4791-4797
• Main Authors: Vengust, Damjan, Jancar, Bostjan, Sestan, Andreja, Ponikvar Svet, Maja, Budic, Bojan, Suvorov, Danilo
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm403094b

With the application of an oxygen atmosphere, we synthesized a highly textured sodium cobaltate, Na0.75CoO2. At the same time, we identified its peculiarities that influence the measured parameters to a degree that poses serious questions about this material’s potential for use. We have systematically studied the influence of humidity on the ceramic pellets and identified the conditions under which the material completely deteriorates. By performing microstructural and thermal analyses, coupled with a determination of the evolved gases, we identified the chemical reactions that are involved in this process. In addition, we re-examined the performance of sodium cobaltate under the working conditions and found that the material behaves in a manner different from the expected manner. We have shown, in contrast to many other reports, that the oxygen vacancies do not play a very important role because the changes in the physical parameters can be attributed to the reduction of cobalt and consequently to the formation of CoO inclusions, which increases the amount of sodium in the sodium cobaltate lattice.