Max Planck Institutes Stuttgart Library

Promising cathode materials for fluoride-ion batteries (FIBs) are 3d transition metal containing oxides with Ruddlesden-Popper-type structure. So far, multi-elemental compositions were not investigated, but could alternate electrochemical performance similar to what had been found for cathode materials for lithium-ion batteries. Within this study, we investigate RP type La2Ni0.75Co0.25O4.08 as an intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4.08 during fluoride intercalation / de-intercalation by ex-situ X-ray diffraction, which showed that F- insertion leads to transformation of the parent phase to three different phases. Changes in Ni and Co oxidation states and coordination environment were examined by X-ray absorption spectroscopy and magnetic measurements in order to understand the complex reaction behaviour of the phases in detail, showing that the two transition metals behave differently in the charging and discharging process. Under optimized operating conditions, a cycle life of 120 cycles at a critical cut-off capacity of 40 mAh g-1 against Pb/PbF2 was obtained, which is one of the highest observed for intercalation electrode materials in FIBs so far. The average Coulombic efficiencies ranged from 85% to 90%. Thus, La2Ni0.75Co0.25O4.08 could be a promising candidate for cycling-stable high-energy cathode materials for all-solid-state FIBs

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It is found that at a critical value of the magnetic field in which a system of composite fermions becomes completely spin-polarized, the temperature dependence of the electronic spin polarization is a linear function at low temperatures. It is shown that the slope of this dependence is determined by the Fermi energy of the composite fermions. This made it possible to measure the Fermi energy and the Zeeman splitting of the composite fermions. A large amplification of the spin splitting of composite fermions for complete spin polarization of the system is found. This makes it possible to measure the strength of the interaction between composite fermions.

Digital imaging and analysis methods are applied to the quantitative study of microstructural changes which occur during hot‐pressing of yttria‐doped silicon nitride. Effects of processing changes upon the grain growth and microstructural anisotropy are described. Relationships between grain cross‐sectional area and mechanical properties are established. It was found that, over the range of processing conditions used, increases in grain size correlated strongly with an increase in fracture toughness. The grain size distribution broadened significantly with hot‐press time, resulting in reduced flexural strength. Although no significant change in the mean grain shape factor was observed, the variance in shape factor decreased as the hot‐press time was extended.

This subsession encompassed two talks, one by Prof. Strudel and one by Dr. Dyson, and four posters (Fredholm et al., Huis in’t Veld et al., Rudy et al., Mertens et al.). These contributions were not intended to span the entire field, but have instead thrown spotlights onto selected aspects related to theoretical and practical limits of high temperature materials. The topics addressed can be grouped into four main areas which will be reviewed in turn. It should be emphasized that this contribution is not intended to be a summary of the contents of the talks and posters but is instead a series of reflections based on subjective impressions gathered by the rapporteur.