Studies on spinel cobaltites, FeCo2O4 and MgCo2O4 as anodes for Li-ion batteries

The compounds, FeCo2O4 and MgCo2O4 are synthesized by the urea combustion and oxalate decomposition method, respectively. Powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) have been used to characterize the phases. Scanning electron microscopy (SEM) showed the distinct features in the morphology, submicron-size of FeCo2O4 and needle-shaped particles of MgCo2O4. Galvanostatic cycling was carried out in the voltage range 0.005-3.0 V vs. Li at a current of 60 mA g(-1) (similar to 0.08 C) up to 50 cycles. The observed first-cycle charge capacities are, FeCo2O4: 827 mA h g(-1) (corresponding to theoretical 7.3 mol of Li per mole of FeCo2O4) and MgCo2O4: 736 mA h g(-1) (5.7 Li). At the end of 50 cycles, FeCo2O4 retained similar to 90% of the first-charge capacity, and a coulombic efficiency of similar to 99% is noted between 20 and 50 cycles. MgCo2O4 showed extensive capacity-fading and retained only 0.9 mol of cyclable Li in the range 28-50 cycles. These results show that Fe is a better counter ion than Mg. The average charge and discharge voltages are similar to 2.0 V and similar to 1.2 V, respectively, for both the compounds. Cyclic voltammograms, up to 12 cycles on FeCo2O4 complement the galvanostatic cycling results. Impedance studies were carried out on FeCo2O4 at various voltages during the first cycle and after 10 cycles, and the data have been interpreted. (C) 2008 Elsevier B.V. All rights reserved.