Three-Electrode Setups for Lithium-Ion Batteries

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 Li 4 Ti 5 O 12 powder as reference electrode. This combination was then validated by additional measurements 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.