Morphological investigations on the solid electrolyte Li3.6Ge0.6V0.4O4 and use in a solid state lithium battery

The development of a solid state thin film lithium battery system needs a detailed investigation of the electrolyte as well as the electrodes. The realisation of a total solid state battery includes the assumption, that the interfacial contact between the electrodes and the electrolyte is as good as possible. The interfacial resistance should be low for an easily intercalation or deintercalation of lithium at the electrodes and the ionic conductivity of the electrolyte should be high. A further critical aspect of the solid state battery is the porosity of the electrodes and the electrolyte. A homogeneous surface coverage and a high density are useful for a high contact concentration between the grains of electrolyte itself and between the electrolyte and the electrodes. As a possible electrolyte we have investigated the system Li₄GeO₄/Li₃VO₄, which we prepared in the stoichiometry Li_3.6 Ge_0.6 V_0.4 O₄. This lithium conducting system shows a high lithium conductivity of about 4 x 10⁻⁵ S/cm at room temperature and higher values at elevated temperatures. The conductivity is the result of interstitial Li cations in the solid state solution. The deposition of the inorganic thin film was done by a spray pyrolysis technique on different substrates. A variety of different substrates were investigated as a function of adhesion and modified surface conditions. The aim is to find a correlation between the substrate and the morphology of the thin film. The temperature of the deposition was varied between 400 and 600 °C. The temperature dependent cristallinity was also studied. Furthermore the change of the unit cell volume and its constants a, b and c has been investigated as a function of temperature by high temperature diffractometry. The thermal expansion coefficient of the electrolyte could be calculated, to examine stresses with various substrates. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995