Chemical Vapor Deposition Techniques for Thin Films of Solid Electrolytes and Electrodes

Abstract

Chemical Vapor Deposition (CVD) is a promising technology for the fabrication of thin films for components of solid state electrochemical devices. Electrochemical Vapor Deposition (EVD) is a special CVD technique for the production of thin gas impervious films of the solid electrolyte, Yttria Stabilized Zirconia (YSZ) for Solid Oxide Fuel Cells (SOFC’s). The kinetics of the film growth of YSZ can be modeled considering the Wagner oxidation process and thermodynamic equilibrium at the gas-solid interphases. The calculated thermodynamic equilibrium can be used to predict the film growth rate. The results show that the EVD growth of YSZ is most likely governed by defect transport in the EVD layer, and a mass transfer limitation at the surface on the metal chloride side. Metal Organic Chemical Vapor Deposition (MOCVD) has been used for the fabrication of thin-film TiS2 cathodes for rechargeable batteries. The OCV of TiS2|1M LiClO4 in PC|Li batteries, and the chemical diffusion coefficient and thermodynamic enhancement factor have been determined as a function of lithium content in these films. Electrochemical measurements include GITT and Impedance Spectroscopy on the cell TiS2| 1M LiClO4 in PC|Li. The influence of the MOCVD conditions on the deposition rate and morphology has been investigated. The morphology of the films seems to be independent of temperature and pressure, in the temperature range from 250oC to 450oC and total pressures of 7.5 and 20 mbar, and preferred orientation of the TiS2 crystallites.