Preparation of Structured Garnet LLZO Composite Solid Electrolyte Using Graphene Oxide as a Template

All-solid-state lithium-ion batteries are viewed as a promising candidate for next-generation batteries due to their safety and high energy density. Despite the enhanced safety of these batteries owing to the use of solid-state electrolytes (SSEs), there is still ample room for improvement in terms of their ionic conductivity. Among various types of SSEs, composite solid electrolytes (CSEs) stand out as they combine the benefits of polymer matrix and ceramic fillers. The ionic conductivity and transport behavior of CSEs is strongly influenced by the tortuosity and continuity of the ceramic fillers. Thus, achieving low tortuosity structures with straight, interconnected ion pathways in CSEs is highly desirable but challenging. In this work, we choose the garnet-type Li₇La₃Zr₂O₁₂ (LLZO) as the ceramic filler, because of its high ionic conductivity (10^-4-10^-3 S/cm) at room temperature and its great chemical stability against lithium metal anodes. Additionally, we use poly(ethylene oxide) (PEO) as the polymer matrix to form the CSE. While most aligned ceramic scaffold are made by templating fixed structures, such as wood, cotton, or cellulose, we harness graphene oxide (GO) as a template to fabricate oriented LLZO structures. This method allows us to establish versatile processing techniques for designing distinct ceramic structures with interconnected pathways, including honeycomb and layered structure. Utilizing a uni-directional freeze-drying process, we successfully create interconnected ceramic structures with low tortuosity. Consequently, the corresponding CSE exhibits significantly improved ionic conductivity compared to CSEs with randomly mixed ceramic fillers. Our work provides a promising approach to the realization of CSEs with superior ionic conductivity and further advancing the prospects of safer, more efficient, and higher energy density batteries.