Search

Competitive all solid-state batteries (ASSBs) require particulate, ternary composite cathodes, consisting of a ceramic active material, ceramic solid-state electrolyte (SSE) and an electrical conductor, to achieve high energy densities. Firmly bonded contacts between the active material and SSE are necessary to obtain fast Li-ion transfer, so that sintering processes are unavoidable. Since the sintering temperatures of oxidic ceramic SSEs, such as Li1+xAlxTi2-x(PO4)3 (LATP), are above 950 °C, decomposition and mixed phase formation take place during sintering with active materials, so a reduction of the SSE's sintering temperature is necessary. This study investigates the impact of Li3PO4 (3, 5 and 10 vol%) as a sintering additive on the sintering behaviour, microstructure and electrical properties of LATP. The obtained liquid phase sintering results in the acceleration of the densification process, so that the start of sinter neck formation and shrinkage could be reduced by 50 °C and 150 °C, respectively. Effects related to the sintering process, such as LiTiOPO4 and AlPO4 formation, densification, grain size distribution and crack formation, are correlated with the electrical properties. Microscopic effects like changes in the lattice stoichiometry and nature of the grain boundary as well as macroscopic effects like pores, grain sizes and cracks have an influence on the percolation network for Li-ion migration. Finally, the addition of Li3PO4 to LATP results in a high ionic conductivity of ca. 2 × 10-4 S cm-1 along with a reduced sintering temperature of 800 °C.

The sequential production process of thin-film solid-state batteries (TF-SSB) requires high temperatures up to 700 °C in order to achieve crystallized cathode films with high capacities and ceramic electrolytes with high ionic conductivities. This presents challenges for thermal interfacial stability between the electrode and electrolyte as well as electrode and substrate. Interdiffusion processes between the substrate and electrode at elevated temperatures are critical and may explain the low utilization of cathode active materials in TF-SSBs. This study examines the interdiffusion that occur between LiMn2O4 (LMO) thin films and the flexible stainless steel (StSt) substrate. Grazing incidence X-ray diffraction spectroscopy, time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal that during the crystallization at 600 °C and 700 °C, LMO undergoes lithium and manganese depletion whereas elements from the substrate (Fe, Cr, Al, Pt) diffuse into the LMO spinel structure. The combination of these effects, which are exacerbated by the higher crystallization temperature, results in a significant capacity loss during galvanostatic cycling. Various interlayers, including gold, platinum and indium tin oxide (ITO) were tested as conductive interdiffusion barriers. The use of ITO, unlike gold and platinum, as a barrier layer essentially prevents the interdiffusion, leading to an improved discharge capacity of 4.2 mA h cm-2 (600 °C) and 5.1 mA h cm-2 (700 °C). The results indicate that ITO is an effective interdiffusion barrier on flexible StSt current collector foils, which can enable higher performance TF-SSBs as well as cost effective roll-to-roll manufacturing.

Recycling of lithium-ion batteries will become imperative in the future, but comprehensive and sustainable processes for this are still rather lacking. Direct recycling comprising separation of the black mass components as a key step is regarded as the most seminal approach. This paper contributes a novel approach for such separation, that is fractionation in a tubular centrifuge. An aqueous dispersion of cathode materials (lithium iron phosphate, also referred to as LFP, and carbon black) serves as exemplary feed to be fractionated, desirably resulting in a sediment of pure LFP. This paper provides a detailed study of the commonly time-dependent output of the tubular centrifuge and introduces an approach aiming to achieve constant output. Therefore, three different settings are assessed, constantly low, constantly high and an increase in rotational speed over time. Constant settings result in the predictable unsatisfactory time-variant output, whereas rotational speed increase proves to be able to maintain constant centrate properties. With further process development, the concept of fractionation in tubular centrifuges may mature into a promising separation technique for black mass in a direct recycling process chain.

In der vorliegenden Dissertation - Kathoden für Metall-Luft Batterien - steht die Komponente Gasdiffusionselektrode (GDE) – oftmals auch als Luft-Kathode bezeichnet – einer wässrigen Metall-Luft Batterie im Fokus. Ziel dieser Arbeit ist die Synthese und Charakterisierung verschiedener Katalysatorsysteme für die Sauerstoffreduktion und -evolution. Dabei soll auf die Verwendung von Edelmetallen verzichtet und der Einsatz von verfügbaren und günstigen Materialien bzw. Herstellungsprozessen favorisiert werden. Auf Basis von bekannten Materialklassen sollen repräsentative Katalysatoren synthetisiert und ihre katalytischen Aktivitäten für die Sauerstoffreduktion und -evolution bestimmt werden. Im Detail wird eine mögliche Korrelation der strukturellen Eigenschaften der Katalysatoren auf die katalytische Aktivität untersucht. Auf Basis dieser Erkenntnisse sollen die Katalysatoren modifiziert werden, um die katalytischen Eigenschaften weiter zu optimieren. Um einen geschlossenen Entwicklungszyklus in dieser Arbeit realisieren zu können, wird parallel ein kostengünstiger und skalierbarer Herstellungsprozess von GDEs entwickelt. Ein weiteres Ziel dieser Arbeit ist es, Konzepte für sekundäre Zink-Luft Energiespeicher zu erarbeiten und deren Umsetzung zu untersuchen. Dabei kommen die zuvor entwickelten Katalysatoren zum Einsatz. Die vorliegende Arbeit gliedert sich, nach der Darlegung der relevanten Grundlagen mit Stand der Wissenschaft und Technik, in vier Teilkapitel, in denen die einzelnen Ziele adressiert sind. Dies sind die Erforschung reiner Katalysatoren und hybrider Katalysatoren sowie die Etablierung eines Herstellungsprozesses für GDEs und die Implementierung dieser in sekundäre Zink-Luft Energiespeicher. Die experimentellen Grundlagen befinden sich im darauffolgenden Kapitel., The dissertation - Cathodes for metal-air batteries - focuses on the component gas diffusion electrode (GDE) - often referred to as air-cathode - of an aqueous metal-air battery. The aim of this work is the synthesis and characterization of different catalyst systems for the oxygen reduction reaction and oxygen evolution reaction. Instead of precious metals, available and cheap materials as well as low cost manufacturing processes are favored. Based on known material classes, representative catalysts will be synthesized and their catalytic activities for the oxygen reduction and evolution will be analyzed. In detail, a possible correlation of the structural properties of the catalysts with the catalytic activity is investigated. Based on these findings, the catalysts should be modified to further optimize the catalytic activity. In order to realize a closed development cycle in this thesis, a cost-effective and scalable manufacturing process for GDEs is being developed in parallel. Another goal of this work is to develop concepts for secondary zinc-air energy storage systems and to investigate their implementation. The present work is divided into four subchapters, in which the individual goals are addressed. These include research of pure catalysts and hybrid catalysts, as well as the establishment of a manufacturing process for GDEs and their implementation in secondary zinc-air energy storage systems.

Herein, we investigated the synthesis of a bifunctional catalyst particle system for aqueous metal-air batteries. To target a system which possesses both, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) capabilities, g-MnO2 microparticles were combined with NiFe layered double hydroxides (LDH) to a core-shell system. NiFe-LDH can be optimized in its constituency to yield a very low onset potential (at 10 mA cm−2) for the oxygen evolution reaction of only 569 mV vs. Hg/HgO. We investigated different coating processes (in-situ precipitation coating and sonochemical assisted coating) in order to create a bifunctional system of LDH shell@g-MnO2 core. It was found that the overall catalytic functionality of the bifunctional system strongly depends on the coating process, as this ultimately determines the surface nature and thus the behavior in ORR and OER reactions, respectively, of this core-shell system.