Pulse-fitting - A novel method for the evaluation of pulse measurements, demonstrated for the low frequency behavior of lithium-ion cells

摘要

The impedance of a commercial lithium ion cell (2 Ah) is evaluated over a wide frequency range of 10(-5) Hz < f < 10(2) Hz using a new approach. The so-called pulse-fitting method (PFM) derives the cell impedance from time domain measurements, which are transferred into frequency data by a using a newly developed evaluation algorithm in combination with the distribution of relaxation times (DRT). The time constants of the individual polarization processes taking place during charging/discharging were analyzed at 20 different state-of-charge levels at 23 degrees C in a wide frequency range spanning from 10(-5) Hz < f < 10(2) Hz. The pulse-fitting method seems to be especially useful for monitoring the change of individual polarization losses in the course of time, as self-discharge effects can be sorted out. (C) 2016 Elsevier B.V. All rights reserved.