Process data acquisition in electrical treatment of lithium-ion batteries

Li-ion batteries are bound to be a fundamental instrument to accommodate for the energy transition, thanks to their ability to store energy in an efficient way and to release it on demand. Being complex systems, modeling and supervising their performance is not easy. One way to achieve this goal is to observe the impedance, which determines the cell voltage response to a current stimulus depending on the frequency of the latter. Being dependent on frequency, the impedance is not a single value, but rather a collection of values, also called a spectrum, whose shape and variations over time are able to provide information on aging, quality and defects. Given these premises, this work objective was to develop a procedure to study the impedance spectrum of prismatic battery cells. Electrochemical Impedance Spectroscopy was performed in order to obtain the impedance spectra and the results were used to fit a number of equivalent circuits, whose parameters values and variation from one cell to another were interpreted to get insights on the cells performance and characteristics. The major part of the computations and result finding was performed through the aid of Python programming language, alongside open source and publicly available program libraries. The first step consisted in a literature research on Li-ion batteries working principles, materials and manufacturing processes, to get a basic understanding of the core working principles. After that, the literature was consulted once more, focusing on measuring techniques, equivalent circuit models theory and regression strategies. With the knowledge thus acquired, various equivalent circuit models and regression strategies were tested and compared. Finally, the methods developed were applied to analyze pristine prismatic cells and to test a possible application of the same methods on a three electrodes coin cell architecture.