Ceramic membranes made of garnet Li7Zr3La2O12 (LLZO) are promising separators for lithium metal batteries because they are chemically stable to lithium metal and can resist the growth of lithium dendrites. Free-standing garnet separators can be produced on a large scale using tape casting and sintering slurries containing LLZO powder, but the quality of the separators is severely compromized by the protonation of the moisture-sensitive LLZO during processing and the irreversible loss of lithium during sintering. In this work, an approach is presented to mitigate the degradation of the LLZO and produce high quality separators using Li2CO3 as a source of excess lithium. By systematically investigating the effects of Li2CO3 addition during the different steps of the tape casting process and the intricate relationship between the protonation and relithiation of LLZO phase, the formation of highly protonated LLZO during ball milling was identified as the most critical step. It was shown that the addition of minimal amounts of Li2CO3 during wet milling effectively suppresses LLZO protonation and ensure the effectiveness of relithiation during subsequent sintering. Using this modified method, flat LLZO separators with a relative density of 95.3 % were prepared in a simplified process with a significantly reduced excess lithium of only 5 mol % with respect to the stoichiometric LLZO, exhibiting an ionic conductivity of 0.18 mS cm−1 at room temperature and a critical current density of 1 mA cm−2 at 60 °C for lithium stripping/plating.@en

All-solid-state batteries based on the active cathode material LiCoO2 (LCO), a garnet-type Li7La3Zr2O12 (LLZO) electrolyte and a Li-metal anode are attracting a lot of attention as a robust and safe alternative to conventional lithium-ion batteries. The challenges in the practical realization of such cells are related to high-temperature sintering, which compacts the ceramic powder but also leads to undesirable material interactions such as cation interdiffusion and secondary phase formation. Even if high initial capacities can be achieved, the all-inorganic cells suffer from a strong capacity drop due to various degradation phenomena during processing and operation, which are not yet fully understood. In this study, the thermodynamic and kinetic aspects of co-sintering as well as the structural evolution of materials and interfaces during processing and operation of co-sintered LCO-LLZO cathodes are investigated in detail. A thermodynamic model for the interdiffusion of cations is derived and the effects of the diffusion of Al- and Co-ions, which occurs during the processing and cycling of the cells, are investigated. In LLZO, the diffusion of 0.13 Co per formula unit (pfu) has a negligible effect on ionic and electronic conductivity and electrochemical stability. In contrast, the substitution of 0.01 pfu Al and the induced disorder in the layer structure of LCO increases the polarization during cycling. All-inorganic cells fabricated with optimized sintering parameters to minimize interdiffusion between LCO and LLZO show good initial performance but similar degradation during cycling, as the used processing parameters result in a more porous microstructure leading to the development of cracks along the LLZO/LCO interface. The results obtained highlight the inherent instabilities of all-ceramic cathodes with unprotected LCO/LLZO interfaces, which require precise tuning of materials and processing parameters to achieve both high mechanical stability and low interdiffusion.@en

Nanocrystalline cellulose (NCC) is an abundant biogenic nanomaterial with unique properties that enables the efficient synthesis of mesoporous crystalline titania. We significantly enhance the photocatalytic activity of titania thin films by introducing solvothermally synthesized preformed anatase nanoparticles into a sol-gel based biotemplated titania scaffold. The resulting dual source titania thin films containing different amounts of preformed crystalline species were investigated by time-resolved microwave conductivity (TRMC) measurements and tested in the photocatalytic conversion of 4-chlorophenol. The gradual addition of preformed nanoparticles leads to a consistent increase of the mean size of titania crystalline domains, whereas the porosity of the composite is well-preserved due to the shape-persistent nature of the NCC template. Microwave conductivity studies establish increased photoconductivity of the films containing preformed anatase nanoparticles in comparison to that of films made without the nanoparticles. The synergistic features of the dual source titania, namely the improved crystalline properties brought by the preformed nanocrystals in combination with the high surface area provided by the NCC-templated sol-gel titania, result in a very high photocatalytic activity of the films in the photocatalytic decomposition of 4-chlorophenol. In quantitative terms, the dual source titania films prepared with 75% nanoparticles exhibit a first order degradation rate constant of 0.53 h^-1 (1.47 × 10^-4 sec^-1), which strongly outperforms the activity of commercial P90 nanopowder showing a rate constant of 0.17 h^-1 (0.47 × 10^-4 sec^-1) under the same conditions.

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