FWF - InterBatt - The Nature of Interfaces in All Solid-State Batteries

All solid-state battery (ASSB) systems using ceramic-based electrolytes have the potential to revolutionize the battery consumer market - from electric vehicles, consumer appliances and power tools, to miniaturize rechargeable cells on electronic chips - because of potential benefits in energy density, operable temperature range, and safety in comparison to traditional liquid electrolyte based systems. One of the most promising solid electrolytes to realize ASSBs are Li7La3Zr2O12 garnets and variants (LLZO). LLZO is related to the class of garnets known as gem stones (e.g. almandine) and is one of the most promising solid electrolytes with high Li-ion conductivities and superior stability. Preliminary tests to implement LLZO into ASSBs, however, suggest plenty of room for improvement. High interfacial resistances currently limit the applicability of LLZO. In order to improve LLZO a profound understanding of the key factors related to its properties is highly needed. In previous studies polycrystalline LLZO samples were used. Polycrystalline samples, however, suffer very often from significant compositional inhomogeneities and a strong variation between different samples, even if made in the same batch (or even within one sample). This variation in composition limits the significance of experimental results and therefore the understanding of the underlying processes. These strong compositional variations could be overcome by using large, homogeneous single crystals. In this study, we have the great opportunity to use such single crystals with a size of several inches as a model system to systematically study the chemical and physical processes at the electrode-electrolyte interface and to test approaches to improve the interface with regard to a working device. Furthermore, the impact of chemical and physical inhomogeneities, which are one of the major reasons of failure in liquid electrolyte based lithium ion batteries, will be evaluated by highly sophisticated locally resolved analysis techniques. This will lead to a very accurate description of the LLZO-electrode interface and will provide a deep understanding on the underlying processes, thus creating a kind of roadmap to improvements of the interface for a future working ASSB.