Physicochemical characterization of CuFeO2 and lithium intercalation

CuFeO2 having delafossite structure was prepared by a solid-state reaction. From Rietveld analysis, the sample synthesized at 1000 degrees C by firing for 48 h under argon was close to ideal CuFeO2, with the refined lattice p arameters, a = 3.03333(6) Angstrom and c = 17.1582(4) A for the hexagonal u nit cell. The valence state of Fe and Cu were confirmed to be + 3 and 1 +,r espectively, from Fe-57 Mossbauer spectra and Cu K-edge XANES spectra, resp ectively. Lithium intercalation into the structure of delafossite was inves tigated by using CuFeO2, as cathode material in a Li battery, Li/CuFeO2. Wh en cycled between 1 and 3 V, a discharge capacity of 580 mAh/g was observed with intercalation of 3.25 mol of Li. The working voltage was 1 V. Only 75 % of capacity could be recovered on charge. When discharged to lower voltag e of 10 mV, a large discharge capacity of 1600 mAh/g was observed, with int ercalation of at least 6 mol of Li per formula unit of CuFeO2 without the c ontribution of acetylene black and it was not possible to charge as only th e cycling characteristics of acetylene black was observed due to the decomp osition of sample. An attempt has been made to understand the mechanism of lithium intercalation by subjecting the cathode samples to different studie s such as XANES spectroscopy, Fe-57 Mossbauer spectroscopy, thermal treatme nt, etc. (C) 2000 Elsevier Science B.V. All rights reserved.