Ceramic solid state-electrolytes attract significant attention due to their intrinsic safety and, in the case of the garnet type Li_6.45Al_0.05La₃Zr_1.6Ta_0.4O₁₂ (LLZO), the possibility to use Li-metal anodes to provide high energy densities on a cell and battery level. However, one of the major obstacles hindering their wide-spread application is the translation and optimization of production processes from laboratory to industrial scale. Even though the plausibility of manufacturing components and cells via wet processing routes like tape casting and screen printing has been shown, the impact of the sensitivity of LLZO to air and protic solvents due to Li⁺/H⁺-exchange is not fully understood yet. An uncontrolled alteration of the powder surface results in poorly reproducible processing characteristics and electrochemical performance of the final battery components and full cells. This knowledge gap is the cause of the large performance variations reported across different research labs worldwide and is unacceptable for up-scaling to industrial level. To close this gap, the influence of the Li⁺/H⁺-exchange taking place at various steps in the manufacturing process was systematically investigated in this study. For the first time, this allowed a mechanistic understanding of its impact on the processability itself and on the resulting electrochemical performance of a free-standing LLZO separator. The importance of a close control of the pre-treatment and storage conditions of LLZO, as well as contact time with the solvent could be extracted for each step of the manufacturing process. As a result, we were able to optimize the processing of thin, dense, free standing LLZO separators and significantly improve the total Li-ion conductivity to 3.90 × 10⁻⁴ S cm⁻¹ and the critical current density to over 300 μA cm⁻² without making structural changes to separator or the starting material. These findings do not only enable a deeper understanding and control over the manufacturing process, but also show potential for further improvement of cell concepts already existing in literature.

An evaluation of the environmental impact of manufacturing an oxide all-solid-state lithium battery with economic cell design.

To make ceramic based all-solid-state batteries competitive for the battery market, a shift from the separator supported cell-design for lab cells to a scalable, cathode-supported one is necessary to improve the energy density. Using tape casting, we were able to demonstrate for the first time all-ceramic free-standing LiCoO₂ (LCO)/Li_6.45Al_0.05La₃Zr_1.6Ta_0.4O₁₂ (LLZO) mixed cathodes with high capacities and active material utilization. Further morphology engineering by introduction of a sequential layer casting enabled us to tailor the microstructure of the mixed cathodes resulting in opposite concentration gradients for the active material and the electrolyte over the thickness of the cathode. With this optimized microstructure, we were able to increase the discharge capacity of the free-standing mixed cathodes to 2.8 mA h cm⁻² utilizing 99% of the theoretical capacity. For the oxide garnet-based system, both the scalable fabrication method and the achieved electrochemical performance demonstrates industrial relevance for the first time. Additionally, the obtained free-standing cathodes have sufficient mechanical stability to allow the application of hybrid and ultra-thin separators to further increase the energy density on the full cell level.

Lithium aluminium titanium phosphate Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is a promising and intensively studied solid electrolyte for the development of ceramic solid-state batteries. LATP has competitive Li-ion conductivity at room temperature, very high oxidation stability, is non-flammable, cheap and environmentally friendly. LATP can be produced in large quantities by a solution-assisted solid-state process, which can be easily scaled up for industrial applications. We show that LATP synthesis can be further simplified, reducing synthesis time, lowering energy consumption, and most importantly, reducing the environmental footprint. The core of this approach is the use of AlPO₄ as Al source instead of aluminium acetate. This reduces the use of H₃PO₄ in the reaction and reduces the amount of organic components, resulting in a CO₂-free synthesis. In addition, our approach allows for direct sintering without the need for high-energy calcination steps, reducing CO₂ emissions by 48% during processing. The resulting LATP exhibits very high phase purity and a homogenous microstructure, resulting in a total ionic conductivity of 0.62 mS·cm⁻¹ at room temperature with an activation energy of 0.33 eV.

Sodium–ion batteries are emerging as strong competition to lithium–ion batteries in certain market sections. While these cells do not use critical raw materials, they still feature a liquid electrolyte with all its inherent safety issues, like high flammability and toxicity. Alternative concepts like oxide-ceramic-based all-solid-state batteries feature the highest possible safety while still maintaining competitive electrochemical performance. However, production technologies are still in their infancy, especially for Na all-solid-state batteries, and need to be urgently developed to enable solid-state-battery technology using only abundant raw materials. In this study, the additive-free production of freestanding, undoped NaSICON separators via tape-casting is demonstrated, having an extremely high total Na-ion conductivity of up to 2.44 mS·cm⁻¹ at room temperature. Nevertheless, a strong influence of sample thickness on phase purity as well as electrochemical performance is uncovered. Additionally, the effect of self-coating of NaSICON during high-temperature treatment was evaluated as a function of thickness. While advantageous for increasing the stability against Na-metal anodes, detrimental consequences are identified when separator thickness is reduced to industrially relevant values and mitigation measures are postulated.