Herstellung und Charakterisierung von Festelektrolyten als Modellsysteme für Batterie- und Kondensatoranwendungen: Lokale elektrochemische Prozesse und in-situ Elektrodenbildung

In the first part of this thesis, potential-dependent capacitances of the interface between silver-ion conducting glasses and ion-blocking Pt electrodes were measured by means of impedance spectroscopy. A detailed study of the electrode polarisation behaviour at individual electrodes offers perspectives for improved modifications of double layer capacitors. An asymmetric electrode configuration with highly dissimilar electrode areas on both faces of the sample enabled the determination of the capacitance at the small area electrode. The potential-dependent anode capacitance shows a weak maximum and drops significantly at higher potentials. The cathode capacitance exhibits a more pronounced maximum at higher critical bias voltages. Using a numerical procedure, it could be demonstrated that the pronounced cathode maximum is responsible for the maximum in the total capacitance observed in measurements with symmetrical electrode configuration. The experimental anode and cathode capacitances show significant deviations from the theoretical predictions by Shklovskii and coworkers. In the second part of this thesis, local electrochemical processes at the interface were investigated at different silver ion conducting glasses and at a lithium ion conducting glass ceramic (LIC-GC) using an electrical conductive AFM-tip. When a critical cathodic voltage was exceeded, a current response due to metal particle formation could be detected at the tip. The dendritic structure of the deposited silver particles caused difficulties in the exact determination of the lateral particle area. In contrast to the silver particles, the lithium particles exhibited a compact structure. An in-situ method for studying the particle growth mechanism by simultaneously monitoring the reduction current and the geometric parameters of the growing particle was developed. In addition, a quantitative study of the time dependence of the particle growth was performed. It could be shown that the current, height and lateral radius were square-root-functions of the time. The lateral radius was 2-3 times larger than the height indicating that the vertical particle growth was hindered, possibly due to slow lithium diffusion in the metallic particle. Using different electrochemical methods of analysis, it was checked whether the metallic particle can act as in-situ electrode for measuring the local ionic conductivity of a solid state ion conductor. Using the spreading resistance formula, the local admittance was scaled with the lateral radius of the deposited metal particle. For silver ion conducting glasses, the local and macroscopic conductivities were in good agreement for cathodic voltages even below -1 V implying that the silver particles work perfectly as in-situ electrodes. In contrast, lithium particles deposited on a LIC-GC exhibited a local conductivity which was about two orders of magnitude lower than the macroscopic conductivity. This is most likely due to the fact that the LIC-GC is not stable against metallic lithium, so that a resistive layer is formed at the interface of the LIC-GC surface and the metallic lithium particle. The lithium particles deposited on the LIC-GC surface are therefore not suitable as local electrodes. In order to deposit silver band electrodes, the silver glass surface was modified with tracks with sharp edges using a laser ablation technique. Metallic silver was then deposited with a negatively charged AFM tip from one point along the border of the tracks, and thereby band-like silver structures were obtained. When negative voltage pulses of -0.5 to -1 V with duration of 0.5 to 1 s were applied to the tip, silver bands with lateral extensions of about 50 μm and an with average height of about 1 μm were obtained. The deposited silver bands offer perspectives not only for the application as nano- or microelectrodes.