Abstract

At ambient conditions, the quaternary sulfides LiCuFeS 2 and KCuFeS 2 present totally different crystal structures: while LiCuFeS 2 crystallizes in a trigonal CaAl 2Si 2-type structure, a tetragonal ThCr 2Si 2-like structure is found for KCuFeS 2. In this work, we present a computational study describing first the changes in the structural preference of the ACuFe 2 phases as a function of the alkali ion and second, the structural stability of the CuFeS 2 phases obtained by electrochemical removal of the alkali cations from the two ACuFeS 2 compounds. A high copper mobility is found to be responsible for the observed metastability of the layered trigonal CuFeS 2 phase obtained by delithiation of LiCuFeS 2. In contrast, the tetragonal CuFeS 2 structure obtained removing potassium from KCuFeS 2 is predicted to be stable, both from the kinetic and thermodynamic points of view. The possibility of stabilizing mixed Li xCu 1-xFeS 2 phases with a ThCr 2Si 2-type structure and the mobility of lithium in these is also explored. © 2011 American Chemical Society.