Three-Electrode Setups for Lithium-Ion Batteries II. Experimental Study of Different Reference Electrode Designs and Their Implications for Half-Cell Impedance Spectra

Electrochemical Impedance Spectroscopy (EIS) is a well-established technique for investigating the loss processes that take place in lithium-ion batteries with different characteristic time constants. Three-electrode setups are needed to separate the contributions of working electrode (WE) and counter electrode (CE), but often suffer from measurement artifacts. This paper is the second part of a two-part paper dealing with the roots of these distortions: (I) electrochemical and (II) geometric asymmetry. The first part presents a theoretical examination by FEM simulation and the second part details the corresponding real-world measurements. The simulation results were confirmed: electrochemical and geometric asymmetry lead to artifacts for point-like reference electrodes but not for mesh reference electrodes. The geometric characteristics of the mesh reference electrode are crucial (thin wire and an open weave are essential). Furthermore, a possible realization of a mesh reference electrode setup is presented, using an aluminum mesh coated with Li4Ti5O12 powder as reference electrode. This combination was then validated by additionalmeasurements in symmetric cells. Additionally, the benefits of using the proposed setup for recording quasi-equilibrium potential curves and for performing rate capability experiments are demonstrated. (C) The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License All rights reserved.