Innovative L-band electron paramagnetic resonance investigation of solid-state pouch cell batteries

Usually, conventional electron paramagnetic resonance (EPR) spectroscopy and imaging employ a microwave cavity operating at X-band, i.e.,  with an excitation frequency of around 9.6 GHz, and this remains the most popular mode for the magnetic characterization of lithium batteries to date. Here, we provide the first low-frequency EPR investigations with respect to monitoring the metallic lithium structures in solid-state pouch cell batteries. We show that L-band, i.e., a microwave frequency of around 1.01 GHz, is an invaluable method to probe the electrode components directly through a standard pouch cell using aluminum-laminated film for packaging without opening the battery. These results offer a new approach for monitoring the nucleation of micrometric and submicrometric lithium particles, such as dendritic lithium structures, and is an important step in the development of reliable solid-state batteries.