Interfaces in Composite All-solid-state Cathodes: Advanced Characterization and Optimization

All-solid-state-batteries (ASBs) with sulfide, polymer or oxide solid electrolytes offer a promising alternative
to lithium ion batteries (LiBs) with liquid electrolytes. According to current research, sulfide-based ASBs are
the best-performing of this class. For all types of ASBs, however, central problems still have to be solved.
The project therefore combines the competencies of TIT (Tokyo Institute of Technology), KIT (Karlsruhe
Institute of Technology) and JLU (Justus-Liebig-University) for sulfide electrolytes. Specific objectives aim
to clarify low conductivities in the electrolyte and charge transfer losses at the interface between cathode
and electrolyte. At the KIT, Institute for Applied Materials - Electrochemical Technologies (IAM-ET), model systems prepared by the partners are analyzed with the help of
electrochemical impedance spectroscopy and electron microscopic methods. The mutually supportive
expertise in the fields is fostered by a constant exchange of young researchers and in this way contributes
to a better qualitative and quantitative understanding of the above-mentioned questions.

Fundamental questions regarding the chemical, microstructural and electrochemical properties of solidstate
electrolytes for Li+ ion batteries are addressed by preparing (TIT/Kanno and JLU/Janek) and
investigating various model systems with different analytical tools (JLU/Janek and KIT/Ivers-Tiffée). The
complexity of these model systems thereby increases step-by-step, from electrolyte samples to the most
complex design composed of all relevant cell components. The geometrical dimensions are kept as simple
as possible and the variation in cell chemistry and cell layer design as comprehensively as possible. Key to
the success will be the careful chemical, structural and microstructural characterization of composites in
parallel to advanced impedance characterization – aiming for the full electrical modelling of ASBs.
Complementary, in-situ measurements of the Li distribution in composite cathodes on a mesoscopic scale
are addressed. This requires an ongoing improvement of the performance of composite cathodes in oxide
(FZJ/Finsterbusch), sulfide (TIT/Suzuki) and polymer (WWU/Wiemhöfer) based ASBs and the development
of a temperature-controlled sample holder (QST/Satoh and FZJ/Finsterbusch). If successful, the knowledge
gained by ion beam measurements on ASBs can be transferred to various types of conventional and next
generation lithium ion batteries. The experimental results are continuously communicated to the partners
and are integrated into the development of models, materials and manufacturing techniques.