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.