Abstract
Solid state and solution phase decomposition of organometallic half sandwich and sandwich complexes of type [CpFeCODLi x DME] 1, [CpFeCODLi x TMEDA] 2 and [(Cp)(2)FeLi2 x 2TMEDA] 3 (Cp = cyclopentadienyl, COD = 1,5-cyclooctadiene, DME = dimethoxyethane, TMEDA = tetramethylethylenediamine) derived from ferrocene, yield different kinds of lithium ferrites under oxidative and inert conditions. Thermogravimetry (TG) and TG coupled mass spectrometry of these compounds indicate that the decomposition begins above 170 degrees C for 1, 185 degrees C for 2 and 190 degrees C for 3 with removal of all the organic ligands. In the absence of oxygen, compounds 1, 2 and 3 decompose to a mixture of Fe, Fe3C and Li2O/Li2CO3 at temperatures above 200 degrees C. Amorphous alpha-LiFeO2 is formed in the temperature range of 200-400 degrees C in the presence of oxygen. Crystal-line alpha-LiFeO2 is formed only above 400 degrees C using 1. Elemental analysis of the LiFeO2 obtained from 1 indicates a drastic decrease in the carbon and hydrogen content with the increase in the oxidation temperature. XRD reveals the presence of Li2CO3 as second phase formed for precursors 1, 2, and 3 under oxidative conditions. Solution phase decomposition of 2 and 3 in the absence of oxygen followed by annealing at 600 degrees C yields Li2Fe3O5, Li5FeO4 and Fe3C depending on the solvent to precursor ratio in contrast to the alpha-LiFeO2 phase formed under pure solid state decomposition conditions. However, all lithium ferrites (Li2Fe3O5, Li5FeO4) are converted to alpha-LiFeO2 when oxidized above 500 degrees C. The alpha-LiFeO2 products were further characterized by IR, XPS, and TEM. Electrochemical analysis of the alpha-LiFeO2 was performed, showing a moderate initial capacity of 13 mAh/g. (C) 2011 Elsevier B.V. All rights reserved.