Correlating the interface resistance and surface adhesion of the Li metal-solid electrolyte interface

Abstract Solid electrolytes could enable stable cycling of metallic Li anodes, which can offer drastic increases to the capacity of Li-ion batteries. However, little is known about the mechanics of the Li-solid electrolyte interface. This study combines electrochemical and mechanical characterization to correlate interface kinetics with adhesive strength. Cubic garnet with the Li 6·25 Al 0·25 La 3 Zr 2 O 12 (LLZO) formulation was selected as a model solid electrolyte based on its high conductivity and stability against Li metal. Symmetric Li-LLZO cells were tested using electrochemical impedance spectroscopy to determine the interfacial resistance, R int , and the adhesive strength of the Li-LLZO interface, σ adh , was measured using a unique tensile test in an inert atmosphere. It was determined that the R int is directly correlated to the adhesive strength of Li on LLZO. At the highest R int in this study, 330   k·cm 2 the σ adh was 1.1 kPa and at the lowest R int in this study, 7 ·cm 2 , σ adh was 8 MPa. Furthermore, by optimizing the surface chemistry the wettability of LLZO was enhanced resulting in σ adh exceeding the ultimate tensile strength of Li metal. The relationship demonstrated provides a deeper understanding of the mechanical properties of the Li-electrolyte interface, which will play an important role in the design of batteries employing metallic Li anodes.