Thin film batteries based on electrical-induced interface reactions

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A new class of lithium ion thin film batteries will be studied, which exhibits a novel, self-forming reaction layer instead of conventional electrodes. The batteries will be prepared by reactive ion-beam sputtering, using an ultra-thin layer of the well-known network glass LIPON (Lithium Phosphorous Oxynitride) as a solid electrolyte. For deposition of the electrodes a novel, alternative concept will be applied: At the interface between LIPON and a conventional metal, an electrochemical-active interface phase is formed by solid state reaction. This phase serves as an active material on the cathode side, so the deposition of a conventional intercalation cathode is not necessary any more.Currently, the growth process and the properties of this interface phase are only poorly investigated. Nevertheless, recent results of literature and of own work show that it exhibits novel electrochemical properties and that it may help to increase the energy density and the cycle stability of the thin film batteries. Therefore, in a first step of the project, the growth process and the properties of this electrochemical-active phase shall be studied from a fundamental point of view, in case of the model system Pt-LIPON-Ag. It shall be investigated which interface reactions occur and in which way these reactions influence the storage capacity and the cycle stability of the batteries. For this purpose, transmission electron microscopy, cyclic voltammetry, and impedance spectroscopy will be used to investigate the interface reactions in detail. Based on these fundamental studies, a concept shall be developed, to improve the energy density and the cycle stability of the new thin film batteries. For this purpose, new materials will be tested. On the side of the cathode, the use of e.g. Fe, Co, Mg, or V is planed, which may result in an increased energy density. Instead, on the side of the anode, a thin layer of lithium titanium oxide will be used, which may enhance the cycle stability of the batteries.