In Situ Investigation of Lithium Metal-Solid Electrolyte Anode Interfaces with ToF-SIMS

Solid-state batteries with a lithium metal anode (LMA) are promising candidates for the next generation of energy storage systems with high energy and power density. However, successful implementation of the LMA requires deeper insight into the lithium metal-solid electrolyte (Li|SE) interface. Since lithium is highly reactive, reaction products form when it comes into contact with most solid electrolytes (SEs) and the resulting interphase can have detrimental effects on cell performance. To better understand the formation of interphases, Li|SE interfaces are studied with time-of-flight secondary-ion mass spectrometry (ToF-SIMS), which provides chemical information with high sensitivity in 2D as well as 3D and is a valuable complement to commonly used techniques. To investigate the interphase, lithium is deposited in situ on SE pellets either through lithium vapor deposition or electrochemical lithium plating. Subsequent depth profiling provides information about the stability of the Li|SE interface and about the microstructure of the formed interphase. At the Li|Li6PS5Cl interface of lithium metal with argyrodite-type Li6PS5Cl, an apparently covering Li2S-rich layer is found as major part of the interphase. Independent of the deposition method, a combination of ToF-SIMS and atomic force microscopy indicates a thickness of about 250 nm for the Li2S-rich interlayer.