Structural Analysis Using Synchrotron XRD and XAFS for Cobalt Oxyhydroxides Heat-Treated under Sodium Hydroxide Solution for Nickel Hydroxide Electrode

The structural analysis for the cobalt oxyhydroxide has been done by using high-energy synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis. The relationship between the structure and the electrical conductivity for cobalt oxyhydroxide was investigated. The structural refinement for cobalt oxyhydroxide heat-treated in the temperature range of 80-160 degrees C has been done successfully on the basis of two phase models (L and S phase) with large and small c lattice constants. With increasing treatment temperature, the phase abundance for the L phases was increased, whereas the one for the S phases was decreased. By heat-treatment above 100 degrees C, the cobalt ions for the cobalt oxyhydroxide were oxidized to the higher oxidation state over 3. The electrical resistivity was extremely decreased by treatment temperatures above 100 degrees C. The increase in the electrical conductivity for the cobalt oxyhydroxide could be explained by the increase in cobalt oxidation state. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3079421] All rights reserved.