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Issue 27, 2013
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Mechanistic study of the electrochemical extraction of K+ from KFeSO4F

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Abstract

KFeSO4F was recently reported as a cathode candidate for the removal and insertion of Li+, Na+ and K+. Here the mechanism for the electrochemical extraction of K+ from KFeSO4F is unveiled using density functional calculations. Consistent with experimental observations, first-principles calculations predict a thermodynamically favourable phase transition when the potassium content in KxFeSO4F is below 50% (x ≤0.5). The mechanism that drives this phase transition is carefully investigated. It is shown that the extraction of K+ can be expressed as a sequential removal of K+ and selective oxidation of Fe2+ ions. Before the composition reaches K0.5FeSO4F the selective oxidation only produces neighbouring Fe2+–Fe3+ pairs. The crystal structure is stable in this stage. Further removal of K+ after the composition reaches K0.5FeSO4F generates Fe3+–Fe3+ pairs. It triggers the phase transition in order to minimize the strong electrostatic repulsion between highly charged Fe3+ ions. The voltage profile for the removal of K+ from KFeSO4F is also affected by this special mechanism. These results not only provide a mechanistic explanation of the experimental observations, but also suggest the cation repulsion is a key factor that affects the structural stability and the voltage profile of the cathode material.

Graphical abstract: Mechanistic study of the electrochemical extraction of K+ from KFeSO4F

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Article information


Submitted
01 Mar 2013
Accepted
30 Apr 2013
First published
30 Apr 2013

J. Mater. Chem. A, 2013,1, 8000-8006
Article type
Paper

Mechanistic study of the electrochemical extraction of K+ from KFeSO4F

C. Ling and F. Mizuno, J. Mater. Chem. A, 2013, 1, 8000
DOI: 10.1039/C3TA10884H

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