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Descripción
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| We describe the synthesis, crystal structure and lithium deinsertion?insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R%3m) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn3+ and low spin configuration for Ru4+ where the itinerant electrons occupy a p*-band. The onset of a net maximum in the w vs. T plot at 9.5 K and the negative value of the Weiss constant (y) of ?31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g?1 (2.3 Li per f.u.) and 144 mA h g?1 (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge? charge cycling points to partial reversibility (ca. 160 mA h g?1 and 45 mA h g?1 for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn3+ and Ru4+ are partially oxidized to Mn4+ and Ru5+ in the sloping region at low voltage, while in the long plateau, O2? is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O2? ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O2? (plateau) while Fe seems to retain its 3+ state. | |
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Internacional
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JCR del ISI
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Título de la revista
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Physical Chemistry Chemical Physics |
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ISSN
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1463-9076 |
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Factor de impacto JCR
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4,198 |
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Información de impacto
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Datos JCR del año 2013 |
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Volumen
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17 |
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DOI
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Número de revista
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Desde la página
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3749 |
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Hasta la página
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3760 |
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Mes
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SIN MES |
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