Reinvestigation of the OP4-(Li/Na)CoO2- layered system and first evidence of the (Li/Na/NaCoO2 phase with OPP9 oxygen stacking
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en
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Ce document a été publié dans
Inorganic Chemistry. 2011, vol. 50, n° 6, p. 2420-2430
American Chemical Society
Résumé en anglais
The composition and synthesis conditions of the (Li/Na)CoO<sub>2</sub> phase with an ordered 1:1 Li/Na stacking alternating with CoO<sub>2</sub> slabs were determined from a careful study of the P2-Na<sub>0.7</sub>CoO<su ...Lire la suite >
The composition and synthesis conditions of the (Li/Na)CoO<sub>2</sub> phase with an ordered 1:1 Li/Na stacking alternating with CoO<sub>2</sub> slabs were determined from a careful study of the P2-Na<sub>0.7</sub>CoO<sub>2</sub>−O3-LiCoO<sub>2</sub> system. An in situ X-ray diffraction (XRD) thermal study emphasizes the metastable character of this phase that can be stabilized only by very fast quenching. Its composition, (Li<sub>0.42</sub>Na<sub>0.37</sub>)CoO<sub>2</sub>, is significantly different from the ideally expected one, (Li<sub>0.50</sub>Na<sub>0.35</sub>)CoO<sub>2</sub>, and its structure, confirmed by Rietveld refinement of the XRD pattern, presents an ideal alternate ordering of lithium, cobalt, and sodium layers within OP4-type oxygen packing. The presence of vacancies in both alkali-ion layers was confirmed by electrochemical intercalation of lithium and sodium. For the first time, a new type of layered oxide exhibiting OPP9-type oxygen packing was evidenced. Between the CoO<sub>2</sub> slabs, alkali ions are intercalated in the following order: Li<sub>octa</sub>−Na<sub>prism</sub>−Na<sub>prism</sub>. This material crystallizes in the <i>R</i><i>m</i> space group with <i>a</i><sub>hex</sub> = 2.828 Å and <i>c</i><sub>hex</sub> = 46.85 Å cell parameters.< Réduire
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