Rapid Li compensation toward highly conductive solid state electrolyte film

Garnet type solid-state electrolytes (SSEs) possess high stability against Li metal, intrinsic safety, and wide electrochemical window. To achieve the all-solid-state batteries (ASSBs) with high gravimetric/volumetric energy density and high power density, flat thin garnet SSEs with a high ionic conductivity of > 10−4 S/cm are required. However, the current fabrication processes are challengeable to maintain both the high ionic conductivity and the flat skeleton due to the severe Li loss during processing and the fragile nature of thin films. Herein, we introduce a rapid Li compensation (RLC) technique that combines the ultra-fast high-temperature sintering (UHS) technique with the tape casting process to produce highly ionic conductive, flat garnet SSE thin films. The freestanding Li6.4La3Zr1.4Ta0.6O12 (LLZTO) thin film with a thickness of 40 µm, fabricated using this technique, displays a surface roughness of 5 µm and a relative density of 95%. After a 10-seconds Li compensation, the compensated LLZTO film displays an ionic conductivity of 4.3 × 10−4 S/cm, 2 times higher than the non-compensated one. As a proof of concept, this RLC technique proposes a new strategy for the fabrication of high-performance ceramic thin films and also lays a solid foundation for the application of ASSBs.