This doctoral research work aims for a detailed investigation of lithium-ion batteries and their ageing, in particular for the Nickel Manganese Cobalt Oxide (NMC) battery chemistry, by the development of advanced temperature and ageing dependent electrochemical-thermal modelling.
In this work two types of NMC batteries are studied: a fresh (or uncycled) and an aged (or cycled) battery cells. The ageing of these batteries is achieved by means of accelerated ageing tests (i.e. repetition of numerous charge and discharge cycles) on individual cells at a cycling temperature equal to 35°C. For the development of the electrochemical-thermal modelling of the battery cells, a sensitivity analysis is carried out in order to determine the sensitivity of the parameters values not disclosed by the manufacturers, nor known from the literature and further not measurable in-house. Implementation of estimation techniques for parameters that are not known, though sensitive is hence achieved.
A comprehensive characterisation for parameters that are measurable in-house is further systematically completed on both uncycled and cycled electrodes samples, by means of: X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Equilibrium Potential test, Cyclic Voltammetry (CV), Galvanostatic Intermittent Titration Technique (GITT), Electrochemical Impedance Spectroscopy (EIS), Entropy coefficient and Activation Energy tests.
The assessment of the advanced coupled electrochemical-thermal modelling of the battery cells by means of validation tests, is with this work, accomplished for the first time under both ambient and cycling temperatures. These being based on both WLTC (Worldwide harmonized Light duty driving Test Cycle) and Fast Charging (CCCV-NP) as application-oriented dynamic current profiles.