The aim of this project is to study performance-limiting phenomena in complex metal oxides, present in a wide variety of rechargeable batteries, and to suggest practical means for improving their performance and lifetime in secondary consumer batteries. We prepare thin dense films from these oxides on electronically conductive substrates utilizing the pulsed laser deposition technique. This method is superior to other film-formation techniques, such as sputtering and vapor evaporation, based on both speed and simplicity. Films are characterized with x-ray diffraction, x-ray absorbance, XPS, optical and scanning electron microscopy and profilometry. In addition the groundwork has been laid for the characterization of films with Fourier Transform Infrared Spectroscopy (FTIR).
Transmission-mode FTIR spectra were obtained from LixMn2O4 cathodes, where x was varied electrochemically from “zero” to 2.4. The observed infrared absorption peaks can be assigned to the various Mn-O and Li-O environments within the spinel framework. The results correlate well with XRD and neutron diffraction analyses in the literature as well as with the phase behavior indicated by electrochemical measurements. The technique gives both qualitative and quantitative information and is shown to be an effective companion technique to x-ray diffraction. The mechanisms responsible for capacity fading during normal cycling of LiMn2O4 cells in both the 3 V and 4 V regions were determined by examination of spectra obtained from electrodes following 25 cycles at charge and discharge rates of C/6. In the 3 V region, electroactive material becomes electronically disconnected from the rest of the electrode possibly due to fracture of the oxide particles during the cubic-to-tetragonal phase transformation. In the 4 V region, the active electrode material is gradually converted to a lower-voltage defect spinel phase via dissolution of manganese in the electrolyte.
Electrochemical properties of the metal oxide films, such as electrocatalyst kinetics, film corrosion behavior and active species diffusivity, can be measured by employing standard techniques for geometries with well-defined electrode-electrolyte interfaces. The pulsed laser deposition technique has been used to prepare smooth dense films La0.6Ca0.4CoO3 , La0.6Ca0.4MnO3, La0.5Sr0.5FeO3, Bi2Ru2O7, LixMn2O4 and LixCoO2 on substrates of stainless steel, quartz and silicon. High-quality crystalline films of all of the oxides except Bi2Ru2O7 were obtained by deposition onto stainless steel at 600