Lithiumbatterien für stationäre und mobile Anwendungen : Benchmarking und experimentelle Umsetzung

摘要

In order to reduce the anthropogenic greenhouse gas emission, a conversion of the electric energy supply towards renewable energies is mandatory. Therefore it is necessary to introduce novel electrochemical energy storages. The development of a model which evaluates the application specific potential of lithium batteries and their components is the goal of this work. Additionally, the most promising research areas are to be derived and experimentally validated. The work approach is based on the derivation of a benchmarking model, which enables an evaluation of anodes, cathodes, electrolytes and passive components used in lithium batteries for battery and hybrid electric vehicles as well as a stationary photovoltaic battery system. Based on an extensive literature study, limiting and accessible characteristics for the requirements: energy density, power density, safety, lifetime, costs and raw materials are defined for the different components. They build the fundament of the following benchmarking process. The developed benchmarking model enables a systematic, quantitative and application specific evaluation of the considered components. Thus, the poor safety characteristics together with a comparably low volumetric energy density make sulfur cathodes unsuitable for all contemplated applications. Lithium and tin anodes as well as the Co and Ni based cathodes: LiCoO2, LiNiO2, LiNi0,8Co0,15Al0,05O2 and LiNi0,33Mn0,33Co0,33O2 cannot be used as well, due to their insufficient safety properties. The anode material Li4Ti5O12 is inapplicable in stationary systems because of its low cost and reserve evaluation factors. Organic respectively inorganic solid state electrolytes have a low ionic conductivity respectively a comparably high contact resistance during cycling. They are therefore not suited to be used in large scaled cells for the considered applications. An increase of the energy density of state of the art systems for battery electric vehicles by 100% is possible in cells based on silicon anodes together with high-capacity or high-voltage cathodes. Substitution of silicon with carbon anodes decreases the energy density, but increases the lifetime evaluation of resulting cells considerably. Cell concepts based on LiFePO4 and Li4Ti5O12 promise a high power density in combination with a high safety and lifetime evaluation. They are therefore interesting candidates for batteries in hybrid electric vehicles. The application of TiO2 anodes with LiFePO4 cathodes in lifetime, raw material and cost optimized cells is most interesting for stationary systems. The degradation process of conventional organic carbonate based electrolytes with high-voltage cathodes has not been completely understood, yet. Based on the experimental evaluation of a derived aging model, it is possible to show that the oxidation of the electrolyte has to be considered, if it is unstable against the cathode potential. The process has diffusion controlled kinetics and occurs even after the formation of the initial surface layers on the electrode. The utilization of electrolytes which are stable at high anodic potentials are suitable to increase both safety and lifetime of cells with high-voltage cathodes. The characterization of electrolytes based on novel ionic liquids with a 5 cyanotetrazolide anion enables their evaluation according to the derived benchmarking model. Thus, the electrolyte class offers comparably high power densities, safety evaluation factors and a sufficient anodic stability window for the application with high-voltage cathodes.