Lobato,Killian Paulo KiernanPestana ,Santo Giuseppe Coccoluto2026-02-132026-02-132025http://hdl.handle.net/10400.5/117071Tese de mestrado, Engenharia da Energia e Ambiente , 2025, Universidade de Lisboa, Faculdade de CiênciasThis study is motivated by the need for energy storage to achieve Sustainable Development Goals related to clean energy integration and to balance the consumption and production of variable renewable sources. Lithium iron-phosphate (LFP) is a recently commercialized battery with long lifespan and lower energy density compared to other lithium technologies, ideal for stationary storage systems. It has been proven that their electrochemical behavior is temperature dependent, highlighting the need to control temperature to observe changes in performance. The objective of this dissertation is to develop a temperature-controlled setup to investigate LFP degradation during cycling, by studying the electrochemical performance at different temperatures through Electrochemical Impedance Spectroscopy (EIS), and by identifying trends in the Equivalent Circuit Model (ECM) and impedance to determine the ageing of the LFP. The methods involved standard cycling according to specifications, combined with EIS at every 10% SOC. This allowed monitoring of parameters obtained by fitting the data to an electrical circuit. Measurements were performed on eight batteries at 11 SOC levels, across five temperatures (0–20°C), and four ageing stages (10–450 cycles). The capacity evolution during cycling showed no fade, indicating that the conditions were nondamaging for the LFP cells. The obtained spectra, with the selected ECM, were successfully fitted, except for the data at 100% SOC. Outliers were identified in the spectra and the ECM parameters. The analysis indicated the temperature dependence of Warburg admittance and Charge Transfer Resistance, with Warburg admittance elevated and Charge Transfer Resistance decreasing, alongside slight variations with SOC and cycling. In contrast, the Series Resistance provided indications of degradation, increasing with cycling while showing no temperature dependence. Further research is needed to include a higher number of cycles, accelerated degradation rates, and alternative ECMs for fitting, to achieve a more comprehensive understanding of the battery’s electrochemical degradation mechanisms.application/pdfengElectrochemical Impedance Spectroscopy (EIS)Lithium iron-phosphate (LFP)Equivalent Circuit Model (ECM)Temperature dependencemaster thesis204176050