Locating Redox Couples in the Layered Sulfides with Application to Cu[Cr2]S4 > Publication | UNIST YK RESEARCH

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Publication

Locating Redox Couples in the Layered Sulfides with Application to Cu[Cr2]S4
Author
John B. Goodenough* and Youngsik Kim
Journal
Journal of the Solid-State Chemistry
Vol
182
Page
2904-2911
Year
2004-2009
Use of LiPF6 in EC:DEC as electrolyte has allowed electrochemical extraction of Li from LiV1−yMyS2 and LiTi1−yMyS2 (M=Cr or Fe). The data show access not only to the Ti(IV)/Ti(III) and V(IV)/V(III) redox couples, but also to the V(V)/V(IV) and Fe(III)/Fe(II) couples in these layered sulfides. However, the Cr(IV)/Cr(III) couple could not be accessed. The concept of redox-couple pinning is outlined and applied to the V(V)/V(IV) and Fe(III)/Fe(II) couples, which are pinned at the top of the S-3p bands. Holes associated with the “pinned” couples occupy orbitals of dominant S-3p character, but they have sufficient cation-3d character to prevent condensation of the holes into p–p antibonding states of disulfide bonds. Strong covalent bonding in the pinned couples creates itinerant-electron states in the partially occupied couples. Application to the metallic, ferromagnetic thiospinel Cu[Cr2]S4 favors location of the itinerant holes in states of a pinned Cu(II)/Cu(I) couple having primarily S-3p character.