In–Li Counter Electrodes in Solid‐State Batteries – A Comparative Approach on Kinetics, Microstructure, and Chemomechanics

Abstract A key challenge for solid‐state batteries is the fabrication of high‐capacity cathodes with high area loading and good rate performance. To reliably quantify the performance of high‐capacity cathodes, electrochemically stable, and high‐rate counter electrodes are essential. Otherwise, a three‐electrode setup is required. In–Li alloy electrodes are used for years in a kind of standard approach, since these seem to offer stable operation. In this comparative study, seven preparation methods for In–Li electrodes are examined, determining their suitability for cathode testing. The microstructure of a planar (i.e., foil) and a particle‐based (i.e., composite) anode configuration is analyzed in more detail. Their rate‐dependent electrode performance as well as electrochemical and chemomechanical reversibility in full‐cell configuration are analyzed. The combined results demonstrate the limitations of In–Li electrodes for high‐capacity testing, especially at high rates, while confirming their suitability for simple lab‐scale testing. Preparation significantly influences the electrode microstructure and kinetics, consequently impacting the performance benchmarks of cathodes. These findings underscore both the challenges involved in applying In–Li counter electrodes and the resulting limited comparability of results from different laboratories.