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Title
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Toward unlocking the redox pair in alluaudite-type cathodes for sodium-ion batteries
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Author
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Abstract
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| In polyanion cathodes, the inductive effect alters the potential of a M(n+1)+/Mn+ redox couple (M - transition metal) according to the electronegativity of the X cation in the polyanion groups (XO4m+). To manipulate the operating potential, we synthesized a series of mixed sulfate-selenate alluaudites, with structure formulas Na2+2zMn2-z(SO4)(3-x)(SeO4)(x) and Na2.81Ni1.60(SO4)(1.43)(SeO4)(1.57). Their crystal structure was determined from powder X-ray diffraction data, revealing that the Mn-based alluaudites form solid solutions with the same crystal structure for x = 0.75; 1.125 and 1.5. Na2.81Ni1.60(SO4)(1.43)(SeO4)(1.57) is isostructural to the Mn-based alluaudites. Although the Na2+2zMn2-z(SO4)(3-x)(SeO4)(x) compound with the highest selenium content demonstrates a reversible discharge capacity of 60 mAh g(-1), only a small part of this electrochemical activity can be ascribed to the Mn3+/Mn2+ redox couple. The redox potential of the Mn3+/Mn2+ pair in Na2+2zMn2-z(SO4)(3-)x(SeO4)(x) decreases with increasing values of x, in agreement with the lower electronegativity of Se compared to that of S. |
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Language
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English
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Source (journal)
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Journal of solid state chemistry. - London
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Publication
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London
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2019
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ISSN
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0022-4596
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DOI
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10.1016/J.JSSC.2019.07.032
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Volume/pages
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277
(2019)
, p. 804-810
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ISI
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000481726300103
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Full text (Publisher's DOI)
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Full text (open access)
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Full text (publisher's version - intranet only)
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