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Probing Mechanical Properties of Solid-Electrolyte Interphases on Li Nuclei by In Situ AFM


 Mechanical properties of solid-electrolyte interphases (SEIs) play pivotal roles in maintaining reversible cycling of Li metal anodes. However less attention has been paid to the integration of different types of SEIs on Li nuclei, and precise characterization of mechanical properties of SEIs is challenging. Here, we employ combined in-situ atomic force microscopy (AFM) based nanoindentation and peak force quantitative nanomechanics (QNM) methods to explore the structure, thickness, and Young’s moduli of three types of SEIs which may appear in “anode-free” Li metal batteries, and correlate mechanical properties with chemical and/or electrochemical origins. Results show that SEIs formed by electrochemical reduction bear conventional double layer structures and are much thicker, with smaller Young’s moduli, compared to inorganic-organic hybrid SEIs formed with chemical reactions. In-situ AFM monitoring of morphology evolution shows that coexistence of different kinds of SEIs on individual Li nuclei, even with apparently minor differences in thickness and Young’s moduli, could result in breakage of SEI shells upon dissolution of Li nuclei. Our work reveals the importance of integration of types of SEIs on Li nuclei and demonstrates the advantage of combined use of nanoindentation and QNM methods in understanding the cause mechanical point of view.