Understanding the Impacts of Li Stripping Overpotentials at the Counter Electrode by Three-Electrode Coin Cell Measurements.

The evaluation of new materials, interfaces, and architectures for battery applications are routinely conducted in two-electrode coin cell experiments, which although convenient, can lead to misrepresentations of the processes occurring in the cell. Few three-electrode coin cell designs have been reported, but those which have involve complex cell assembly, specialized equipment, and/or cell configurations which vary drastically from the standard coin cell environment. Herein, we present a novel, facile three-electrode coin cell design which can be easily assembled with existing coin cell parts and which accurately reproduces the environment of traditional coin cells. Using this design, we systematically investigated the inaccuracies incurred in two-electrode measurements in both symmetric/asymmetric cells and half-cell experiments by galvanostatic charge/discharge, galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry. From our investigation, we reveal that lithium metal stripping contributes larger overpotentials than its nucleation/plating processes, a phenomenon which is often misinterpreted in two-electrode cell measurements.