Atomic Layer Deposition of the Solid Electrolyte Garnet Li7La3Zr2O12

Lithium solid electrolytes are a promising platform for achieving high energy density, long-lasting, and safe rechargeable batteries, which could have widespread societal impact. In particular, the ceramic oxide garnet Li7La3Zr2O12 (LLZO) has been shown to be a promising electrolyte due to its stability and high ionic conductivity. Two major challenges for commercialization are the manufacture of thin layers and the creation of stable, low-impedance interfaces with both anode and cathode materials. Atomic layer deposition (ALD) has recently been shown to be a powerful method for depositing both solid electrolytes and interfacial layers to improve the stability and performance at electrode electrolyte interfaces in battery systems. Herein, we present a thermal ALD process for LLZO, demonstrating the ability to tune composition within the amorphous as-deposited film, which is studied using in situ quartz crystal microbalance measurements. Postannealing using a variety of substrates and gas environments was performed, and the formation of the cubic phase was observed at temperatures as low as 555 degrees C, significantly lower than what is required for bulk processing. Additionally, challenges associated with achieving a dense garnet phase due to substrate reactivity, morphology changes, and Li loss under the necessary high-temperature annealing are quantified via in situ synchrotron X-ray diffraction.