Interface Engineering in Sulfide‐Based All‐Solid‐State Batteries: Insights from Resistance Analysis

All‐solid‐state batteries (ASSBs) are secondary batteries that utilize solid electrolytes (SEs) as lithium conduction carriers. Consequently, they can potentially replace conventional lithium‐ion batteries. To enhance the battery performance, the properties of solid–solid interfaces must be fully understood. However, design guidelines for the formation of solid–solid SE interfaces within electrodes are yet to be formulated. Herein, a resistance analysis is applied to investigate the factors affecting the performance of sulfide‐based SEs with different particle sizes in ASSB electrodes. Conventional alternating current impedance spectroscopy and direct current internal resistance measurements reveal a correlation between the SE particle size and the resistance of the cathode electrode. The optimal SE particle size for the positive electrodes in ASSBs is found to vary with the state of charge (SOC) of the battery. Furthermore, the performance of the positive electrode cell is rate‐limited when the SOC is below 20%. The findings can be used to formulate effective design guidelines for SEs employed in ASSB electrodes.