In Situ Visualizing the Interfacial Failure Mechanism and Modification Promotion of LAGP Solid Electrolyte toward Li Metal Anode

In‐depth understanding the failure process of solid‐state electrolyte (SSE) and providing potential solutions are crucial for the development of solid‐state batteries (SSBs). Typical techniques are powerful to investigate the chemical/electrochemical degradation of SSE. While, mechanical failure, which would undoubtedly affect battery performance, is difficult to detect by normal techniques and lack effective characterizations. Herein, via in situ electrochemical SEM, the dynamic failure process of SSE is observed, revealing the continuously generated side‐reaction layer and the stress‐induced cracks are the main origins. C3N4 (CN) is introduced as the modification layer for Li and SSE. Via in situ scanning electron microscope, Li growth is regulated by CN from dendrite‐like to particulate‐like growth. The properties of electronic transportation and ionic migration in CN are quantitatively measured, and CN promotion mechanism is revealed. Thanks to CN layer, the interfacial side‐reaction is restrained, simultaneously, Li+ flux becomes well‐distributed for dense Li deposition, preventing stress‐induced mechanical failure in SSE. Li symmetrical batteries with CN can endure the maximum current density up to 2.0 mA cm−2 and stably cycle for 3000 h at 300 µA cm−2. This work suggests a promising method to circumvent SSE degradation against Li and open opportunities for future SSBs. This work establishes a powerful in situ scanning electron microscope technique coupled with electrochemical testing system to successfully observe the real‐time dynamic failure process of solid‐state electrolyte and reveal the promotion mechanism in electronic transportation and ionic migration of C3N4 as an interfacial layer in solid‐state batteries toward stable Li anode.