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

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 Li6.25Al0.25La3Zr2O12 (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, sigma(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 Ilia in this study, 330 k.cm(2) the sigma(adh) was 1.1 kPa and at the lowest R-int in this study, 7 cm(2), sigma(adh) was 8 MPa. Furthermore, by optimizing the surface chemistry the wettability of LLZO was enhanced resulting in sigma(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.