The aim of my project at the Storage of Electrochemical Energy section of the TU Delft is to improve the performance and uncover the electrolytic hurdles of the widely used Na-beta”-alumina solid electrolyte within Sodium semi solid-state batteries at Room Temperature. Na-beta”-alumina could be an interesting candidate to replace volatile and flammable organic electrolytes, seeing as it is not flammable and made of abundant elements. It would be a safer, with potential for mass-production due to the abundancy and low costs of the required materials. However, to make working electrolyte pellets, high sintering temperatures are needed for a high density. The material would be a lot more interesting if it could be used without such high sintering temperatures and reasonable conductivity at room temperature. The aim of this thesis is to investigate whether the point-contact problem is solid-state electrolytes can be circumvented by varying the solid electrolyte particle size in combination with liquid addition and various potential concepts. Regarding our conclusions, we can affirm that the mechanically pressed BASE electrolyte pellet concept performs worse than the slurry electrolyte concept. This is related to the improved slurry contact, as well as the increased point contacts for the pellet in combination with a suspected lower ionic liquid coverage. We can also conclude that the electrolyte resistance is lowered with organic electrolyte or ionic liquid addition. The evidence space-charge of has yet to be demonstrated for our components, as smaller particles resulted in lower conductivity and capacitance, regardless of the various series and concepts experimented with. Finally, the Na+ diffusion was better for bigger particles for all three liquid additions.

Diffusivities and lithium distributions in Li₆PS₅X (X = Cl, Br, I) and Li₇PX₆ (X = S, Se) are investigated by means of molecular dynamics simulations. The best lithium conduction is found in Li₆PS₅Cl with diffusivity of over 1 S/cm at 600 K. The halide rich Li₅PS₄Cl₂ shows promising results with diffusivity of over 2 S/cm at 600 K, performing better in simulations than the existing compounds.

Simulations show a beneficent effect of chlorine and bromine disorder on anion sites, opening lithium pathways in the neighborhood and enabling higher conductivities. No significant influence of vacancies on the diffusivity of lithium in these materials can be reported. Lithium jump rates in both material families are in the order of 10¹⁰ s^-1, while Li₆PS₅Cl and Li₅PS₄Cl₂ show the highest jump rates of respectively 2.10·10¹¹ s^-1 and 2.14·10¹¹ s^-1 at 600 K.