The transmission electron micrographs of the pretreated Co(OH)_2-coated Ni(OH) showed that metallic Co nanoparticles were formed on the positive active material surface during the pretreatment as on the pretreated Co(OH)_2 electrode. The UV-Vis spectroscopy and ICPS also exhibited that the metallic Co nanoparticles effectively suppress the loss of Co(OH)_2 from the active material surface due to the suppress of its dissolution. From the comparison of the XRD patterns after charging for the pretreated and untreated positive electrodes, the state of charge or the valence of Ni ions for the former was not influenced by the depth of the active material layer in contrast to that for the latter. This may be ascribed to that mosaic CoOOH with higher conductivity is formed on the pretreated positive active material, and it forms a dense and high conductive network on the surface of the Co(OH)_2-coated Ni(OH)_2 positive active material, improving the electrochemical performance of the pretreated positive electrode.
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