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Abstract

Freeze casting is used for the first time to prepare solid electrolyte scaffolds with oriented porosity and dense ceramic walls made of Li 7 La 3 Zr 2 O 12 (LLZO), one of the most promising candidates for solid state battery electrolytes. Processing parameters -such as solvent solidification rate, solvent type, and ceramic particle size -are investigated, focusing on their influence on porosity and ceramic wall density. Dendrite-like porosity is obtained when using cyclohexane and dioxane as solvents. Lamellar porosity is observed in aqueous slurries resulting in a structure with the highest apparent porosity and densest ceramic scaffold but weakest mechanical properties due to the lack of interlamellar support. The use of smaller LLZO particle size in the slurries resulted in lower porosity and denser ceramic walls. The intrinsic ionic conductivity of the oriented LLZ ceramic scaffold is unaffected by the freeze casting technique, providing a promising ceramic scaffold for polymer infill in view of designing new types of ceramic-polymer composites.

A grain-selection template was applied to freeze casting to control nucleation of pore-forming crystals and achieve ceramics with highly aligned pore structures. A polymethylsiloxane preceramic polymer was freeze cast with cyclohexane as a solvent to produce dendritic pores in SiOC. Image analysis and permeability measurements were performed to quantify the influence of various templates on sample properties. Results show that templates increased the percentage of porosity aligned along the freezing axis, from 13.9% without a template to 92.6% with an optimal template. The Darcian permeability constant increased by more than 6-fold, from 3.4 x 10-12 to 2.1 x 10-11 m 2 .