X-ray diffractometric study of in situ oxidation of Ni in Li/K and Li/Na carbonate eutectic

The formation of NiO, particularly the lithiation process, in molten carbonate at 923 K under oxidizing condition has been investigated by open circuit potential (OCP), AC impedance, and X-ray diffraction (XRD) measurements. Thin film electrodes of Ni were exposed to the Li/K and Li/Na carbonate eutectic and subjected to in situ oxidation. Quantification of lithium in the lithiated NiO with XRD revealed that the lithiation reaction continues even after the electrode potential reached the oxygen electrode potential. Lithium content, x in LixNi1-xO, of the sample immersed in molten carbonate reached 0.041 and 0.033 in Li/K and Li/Na melt, respectively after 200 h of immersion. Difference observed in OCP decay and electrode impedance at 1 kHz for Ni oxidation in the Li/K and Li/Na carbonate has been also interpreted based on XRD data. (C) 2002 Elsevier Science B.V. All rights reserved.