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Toward unlocking the $Mn^{3+}/Mn^{2+}$ redox pair in alluaudite-type $Na_{2+2z}Mn_{2-z}(SO_{4})_{3-x}(SeO_{4})_{x}$ cathodes for sodium-ion batteries

Journal Contribution - Journal Article

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.
Journal: Journal of solid state chemistry
ISSN: 0022-4596
Volume: 277
Pages: 804 - 810
Publication year:2019
Keywords:A1 Journal article
BOF-keylabel:yes
BOF-publication weight:1
CSS-citation score:1
Authors:International
Authors from:Government
Accessibility:Open