Li₇La₃Zr₂O₁₂-PEO Composite Electrolytes and the Role of Interface Resistance

Composite electrolytes consisting of both polymer and ceramic solid state electrolytes have recently received more attention because of their potential to combine high ionic conductivity, facile interface formation and simplified processing compared to conventional ceramic processing routes. Ceramics (e.g. Li7La3Zr2O12 (LLZO)) show high ionic conductivity, but processing the materials into thin membranes is challenging. Energy consuming sintering steps are necessary to obtain dense specimen. In addition, ceramics are brittle, posing further challenges on subsequent processing steps. Polymer electrolytes (e.g. based on poly(ethylene oxide) (PEO)) are facile to prepare by tape casting method and offer flexibility; however, ionic conductivities are lower compared to inorganic materials. Hence, combining both materials forming a composite electrolyte may be a solution. Here, we present the preparation of composite electrolytes consisting of LLZO and PEO based polymer electrolyte with high weight fractions of LLZO. The composites are investigated with regard to their electrochemical properties, paying special attention to the interface between ceramic and polymer. A model system is used to determine the interface resistance between LLZO and PEO as a function polymer electrolyte composition using both experimental and computational methods.