Battery and Fuel Cell Technology

All-solid-state Li-batteries (Li-ASBs) promise to alleviate many issues related to the use of organic liquid electrolytes in conventional Li-Ion Batteries since they have the potential to simultaneously increase the energy and power density while offering intrinsic safety and low degradation. They are thus intensely researched worldwide and are of high interest to automotive and portable electronics applications. However, of the many materials and cell chemistries that are explored in fundamental research, successful demonstrations on larger scales are still missing. Of all concepts, oxide based solid electrolytes like the garnet structured Li7La3Zr2O12 (LLZ) in combination with Li-metal anodes and thick mixed cathodes promise the highest theoretical energy densities. To demonstrate functionality in larger cells, two main challenges are currently faced during fabrication and one during operation of such large cells using a Li metal anode. For fabrication, scalable synthesis methods for of LLZ itself and processing technologies for large area cell components need to be investigated. While LLZ can be produced with a variety of methods on lab scale, the authors developed a process that allows for large quantities of high quality powder to be  synthesized using an industrial established process. Subsequent fabrication of high capacity mixed cathodes requires not just electrochemical stability of the materials used, but also chemical stability at the elevated processing temperatures of ASBs. Secondary phase formation at the electrolyte/cathode interface thus poses further challenges in cell manufacturing. During operation of full all-solid-state cells using Li metal anodes, the difficulty of suppressing the growth of Li dendrites is the main challenge. It is thus essential to understand dendrite formation in LLZ on a fundamental level in order to find mitigation strategies, like the application of interlayers a concept successfully invented by the authors.