Low temperature pulsed laser deposition of garnet Li_6.4La₃Zr_1.4Ta_0.6O₁₂ films as all solid-state lithium battery electrolytes

With its stability against Li and good ionic conductivity, Li₇La₃Zr₂O₁₂ (LLZO) has emerged as a promising electrolyte material for lithium-based solid-state batteries (SSBs). Thin layers of solid electrolyte are needed to enable the practical use of SSBs. We report the first deposition of Li-conductive crystalline Ta-doped LLZO thin films on MgO (100) substrates via pulsed laser deposition. Further, we investigate the impact of laser fluence, deposition temperature (in the 50 °C–700 °C range), and post-deposition annealing on the structural, compositional, and transport properties of the film. We analyze the structure of the deposited films via grazing incident X-ray diffraction, their morphology via scanning electron microscopy, and the composition via depth profiling X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The Li ionic conductivity is investigated via electrochemical impedance spectroscopy. Contrary to previous reports for LLZO films, the crystalline Ta-doped films presents a pure cubic LLZO structure for deposition temperatures as low as 50 °C, with resulting conductivities not significantly influenced by the temperature deposition. Instead, the laser fluence has a major effect on the growth rate of the thin films.