Browsing by Author "Ovaska, Seppo J., Prof., Aalto University, Department of Electrical Engineering and Automation, Finland"
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- Electrical and thermal characterization of large lithium-ion batteries for non-road mobile machinery applications
School of Electrical Engineering | Doctoral dissertation (monograph)(2016) Hentunen, AriCommercial lithium-ion battery modules are commonly used to form battery packs for hybrid and electric non-road mobile machinery. The characterization of batteries is a time-consuming task, because very slow dynamics are present and the characteristics are strongly affected by the state of charge, discharge rate, and temperature. Batteries also exhibit reversible heat generation, which is associated with the entropy change in the electrodes resulting from structural changes caused by the intercalation of lithium ions during charging and discharging. The entropy change characteristics, which can be either exothermic or endothermic, are strongly dependent on the materials and composition of the electrodes, and thus, the entropy change characteristics need to be obtained experimentally. This dissertation proposes efficient and effective methods for the electrical and thermal characterization of lithium-ion batteries. The aim is to reduce the time and effort involved in the experimental testing and parameterization as well as to improve the accuracy of the resulting model. A semi-empirical approach, in which the battery model consists of coupled lumped-parameter electrical and thermal models and the characterization is performed on the basis of current, voltage, and temperature data, is adopted in this dissertation. A systematic methodology is presented for the characterization of the capacity, open-circuit voltage, internal impedance, entropy change, and thermal properties by using only two types of experiments, which can be applied for commercial battery modules: (i) galvanostatic intermittent discharging and charging and (ii) continuous thermal loading. Module-level characterization inherently includes the manufacturing tolerances between the cells in a module as well as the effects of the cooling system into the model. Furthermore, it results in a low-order model that can be scaled for any battery pack configuration. The use of a conventional potentiometric method for entropy change characterization takes several weeks to complete. In this dissertation, a novel entropy change characterization method is presented, which uses the empirical temperature data from the galvanostatic intermittent discharging and charging experiments and the corresponding estimated temperature data to extract the entropy change characteristics. The advantage of the method is that no dedicated characterization experiment is needed. Furthermore, because the entropy change is not dependent on the rate or temperature, the characterization can be performed with the data from several experiments, which improves the accuracy of the results.