( Invited ) Correlation of SEI Conductivity with Battery Performance: Insights from Cryo and in Situ TEM

The solid–electrolyte interphase (SEI) plays a crucial role in rechargeable battery performance by preventing parasitic reactions while enabling ion transport. However, its electrical properties remain poorly understood due to the lack of reliable measurement techniques. Here, we integrate in situ TEM with scanning tunneling microscopy (STM) to directly measure SEI electrical conductivity on Cu and Li substrates. Using ion-blocking electrodes, we analyze I–V characteristics, differential conductance, and critical field strength. By investigating SEIs formed in different electrolyte environments, we reveal that SEIs exhibit measurable electrical conductance, contrary to common assumptions. Cryo-TEM imaging and electrochemical tests further correlate SEI electrical properties with microstructure and battery performance, showing that higher conductance SEIs tend to be thicker and degrade electrochemical stability. This study highlights the importance of SEI electrical properties in battery performance and provides a broadly applicable methodology for electrochemical systems.