Analysis of Three-Electrode Setups for AC-Impedance Measurements on Lithium-Ion Cells by FEM simulations

Electrochemical impedance spectroscopy is a well-established method for investigating electrode processes in lithium-ion cells. Commonly, a three-electrode setup is used, with a reference electrode positioned at the rim of the separator and centered between working and counter electrode. The reliability of this setup is evaluated theoretically by using finite-element calculations and experimentally by using LiFePO4 and lithium-metal electrodes in symmetrical and mixed arrangements measured as half-cells and full-cells. The results show that asymmetries between working and counter electrode arising from electrode misalignment and/or different electrode characteristics, adulterate the reference electrode potential. In consequence, errors such as quantitative scaling factors and cross contamination of electrode impedance response arise and inductive artifacts develop. Furthermore, we assess the impedance distortion quantitatively for different ratios of electrolyte and electrode resistances. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.100202jes] All rights reserved.