In comparison to current lithium-ion-batteries with graphite anode, batteries with lithium metal electrodes possess a higher theoretical energy and power density. Therefore lithium metal electrodes offer a high market potential for electric vehicles suppliers and battery manufacturers as they help to further increase the range of electric vehicles. Some key features of metal lithium electrodes are the growth of a protective layer between electrode and electrolyte (Solid Electrolyte Interphase, SEI) and the growth of lithium dendrites during cycling. The growth of the SEI leads to increased internal resistance, resulting in a decrease in cell performance until battery failure occurs. The dendrites pose a serious safety hazard due to the potential penetration of the separator that would initiate a short circuit with the counter electrode. Both the SEI and dendrite growth will be investigated and modeled in this work.
In the future, the implemented software can be used in hardware-in-the-loop test benches for the verification of algorithms in battery management systems and replace expensive, time consuming and insufficiently reproducible tests on real batteries. Battery management systems (for example in electric vehicles) are used to monitor and control complex battery packs and can use the changing battery state as an indicator to infer changing SEI and dendrite growth. The knowledge of the battery condition and the residual value of the battery system allows the removal of faulty and damaged battery cells from the battery pack compound to preventing accidents.
The aim of this work is to use the empirical findings and parameters obtained from the experimental procedures to model these processes on a physical-electrochemical basis. A prerequisite for the development of the mathematical model of the new energy storage devices with metal lithium electrodes is the experimental analysis characterizing the electrochemical and chemical properties of the metal lithium electrode and its behavior within the energy storage device. Therefore, the lithium metal electrodes will be investigated with various analytical methods. The growth of lithium dendrites during cycling will be determined using an optical in-situ test cell with a light microscope. The growth of the solid electrolyte interphase will be investigated by electrochemical impedance spectroscopy (EIS) and electrochemical quartz microbalance (EQCM).