Untersuchungen von Polarisationseffekten an Lithium-Ionen-Batterien und deren Einfluss auf Sicherheit, Alterung sowie weiterer anwendungsrelevanter Eigenschaften
FacultiesFakultät für Naturwissenschaften
The aim of this work was to study electrochemical processes in a lithium-ion cell and their impact on the design and dimensioning of the components. This lead to in deeper understanding of the involved single side electrode processes and the consequent optimization of the properties described. For an overall assessment of individual factors on electrochemical processes, a test setup had to be developed which allows a determination of individual electrode potentials. As a result, all tests were carried out with pouch cells and cylindrical cells with reference electrode which were developed during this work. Based on these measurements, electrode polarization (concentration, diffusion, and charge-transfer polarization) which has impact on the involved processes and associated properties of a lithium-ion cell can be investigated. The kinetics of the electrode thereby have significant impact on the overpotential, which in turn has influence on the electrode balancing. Therefore, various factors and their effects on electrode polarization were examined, for example: electrolyte, current, active material, temperature, electrode surface area and electrode preparation. The electrode polarization is influenced by electrolytes applied due to varying ionic conductivity and charge transfer resistance of the SEI (Solid electrolyte interphase). Furthermore the active material of the positive electrode (cathode) has influence on polarization of the negative electrode (anode) as well. For instance, LFP (LiFePO4) induces lower anode polarization compared to NMC (LiNi1/3Mn1/3Co1/3O2 ). This is caused by different deinsertion mechanisms and speeds. With knowledge of the various influences on polarization the electrode balancing could be adapted resulting in a reduced full cell aging behavior. Therefore full cells (18650) with exceptional cycling stability of more than 10.000 full cycles SOH (State of health) > 85 % at a rate of 2C even at low temperatures could be manufactured.
Subject HeadingsLebensdauer [GND]
Lithium ion batteries [LCSH]