Structural modifications induced by the second discharge process in the Ni(OH)2/NiOOH redox system |
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Authors: | S Deabate F Fourgeot F Henn |
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Institution: | (1) Laboratoire de Physicochimie de la Matière Condensée, UMR 5617, Université Montpellier II, Montpellier, France;(2) R.B.C., 89-95 Boulevard Alsace Lorraine, 93110 Rosny sous Bois, France |
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Abstract: | Electrochemical behavior and related structural modifications of the nickel hydroxide/oxyhydroxide electrode are investigated
as a function of the reduction state achieved on discharge. Reduction proceeds at two successive potential steps, with recovering
of the initial structural properties only after the second discharge process. Active material cycled in the positive potential
range (vs. Hg/HgO), including only the first discharge step, is non-stoichiometric and characterized by high lattice defect
content. Whatever the oxidation state, the presence of Ni3+ defects and protonic delocalization are observed. The 2nd discharge process restores O-H covalent bonds and a better defined
Ni(II) state, similar to the precursor nickel hydroxide chemically obtained. Electrochemical cycling in the positive potential
range is characterized by the retention of the same nanocrystallite dimension and a high fragmented morphology, while the
2nd discharge induces crystallite agglomeration.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. |
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