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Solid–state batteries based on Li7La3Zr2O12 (LLZO) garnet electrolyte are a robust and safe alternative to conventional lithium‐ion batteries. However, the large‐scale implementation of ceramic composite cathodes is still challenging due to a complex multistep manufacturing process. A new one‐step route for the direct synthesis of LLZO during the manufacturing of LLZO/LiCoO2 (LCO) composite cathodes based on cheap precursors and utilizing the industrially established tape casting process is presented. It is shown that Al, Ta:LLZO can be formed directly in the presence of LCO from metal oxide precursors (LiOH, La2O3, ZrO2, Al2O3, and Ta2O5) by heating to 1050 °C, eliminating the time‐ and energy‐consuming synthesis of preformed LLZO powders. In addition, performance‐optimized gradient microstructures can be produced by sequential casting of slurries with different compositions, resulting in dense and flat phase‐pure cathodes without unwanted ion interdiffusion or secondary phase formation. Freestanding cathodes with a thickness of 85 µm, a relative density of 95%, and an industrial relevant LCO loading of 15 mg show an initial capacity of 82 mAh g−1 (63% of the theoretical capacity of LCO) in a solid‐state cell with Li metal anodes, which is comparable to conventional LCO/LLZO cathodes and can be further improved in the future. [ABSTRACT FROM AUTHOR]

Oxide-ceramic based electrolytes such as Li 7 La 3 Zr 2 O 12 (LLZO), are one of the most promising solid electrolytes for application in all-solid-state batteries. However, most of its constituents are listed as critical raw materials, highlighting the need to minimize waste during synthesis and processing. Therefore, we investigated the re-use of aged LLZO powder and aged LLZO green foils produced by tape-casting, an industrial processing route suitable for ASSBs. We established a new synthesis route to fully recovery Li-poor LLZO and pyrochlore phase La 2 Zr 2 O 7 by simply adding a Li source during firing. By using recycled LLZO powder in a <200 μm thick cast tape, we were able to prove a similar ionic conductivity of 2.1 × 10−4 S cm−1 at room temperature and a critical current density of 0.75 mA cm−2 at 60 °C compared to fresh powder. This simple and efficient re-synthesis strategy might hold the potential to minimize waste streams of critical raw materials in future industrial production processes of solid-state batteries. • Investigation of re-use of production waste of the solid electrolyte Li 7 La 3 Zr 2 O 12. • Waste powder and tape loses Li and thus forms a pyrochlore phases. • A new processing route was developed to re-introduce the waste directly. • The performance was shown to be almost identical to freshly synthesized powders. • This approach minimizes waste of critical raw materials in future ASB production. [ABSTRACT FROM AUTHOR]