Simultaneous Electrochemical Impedance Spectroscopy and Magnetic Resonance Imaging analysis of lithium-ion batteries

Abstract

Electrochemical Impedance Spectroscopy and Magnetic Resonance Imaging (MRI) were measured simultaneously on Lithium-Ion batteries. The motivation for developing this measurement method was the following: While Electrochemical Impedance Spectroscopy provides integral information on processes in the battery, MRI adds spatially resolved information on structures and their changes in the battery on a microscopic length scale. This offers combined and more comprehensive information on microscopic and integral levels. A significant benefit of simultaneous measurement is that the battery is in the same state as well as that it allows continuous measurement of a specific battery thus avoiding replacements and rest times when exchanging parts of the experiments. Comparative measurements of Electrochemical Impedance Spectroscopy, performed in parallel to MRI and outside of the MRI setup, however, require optimal decoupling of the electromagnetic fields involved in both techniques. The current version shows only minor differences in the impedances measured below 20 Hz. On the other hand, images were acquired with and without parallel Electrochemical Impedance Spectroscopy, the images show the same structural features. Differences are on the noise level of the MRI measurement. The combination of results of both techniques allows for a thorough detection and identification of the batteries behavior. For example, in the case of two fresh batteries, increased resistance could be assigned to inhibited ionic transport paths due to a misplaced separator. In aged and defective batteries, the combination of both techniques revealed the loss of electrolyte to be the main source of degradation.