Radio frequency magnetron sputtering of Li7La3Zr2O12 thin films for solid state batteries
Abstract Thin film batteries based on solid electrolytes having a garnet structure like Li7La3Zr2O12 (LLZ) are considered as one option for safer batteries with increased power density. In this work we show the deposition of Ta and Al substituted LLZ thin films on stainless steel substrates by r.f. magnetron sputtering. The thin films were characterized by XRD, SEM and time of flight secondary ion mass spectrometry (ToF SIMS) to determine crystal structure, morphology and element distribution. The substrate temperature was identified to be one important parameter for the formation of cubic garnet structured LLZ thin films. LLZ formation starts at around 650 degC. Single phase cubic thin films were obtained at substrate temperatures of 700 degC and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF SIMS and XRD indicated that this layer consists of g LiAlO2. The combined total ionic conductivity of the g LiAlO2 interlayer and the LLZ thin film (perpendicular to the plane) was determined to be 2.0 x 10 9 S cm 1 for the sample deposited at 700 degC. In plane measurements showed a room temperature conductivity of 1.2 x 10 4 S cm 1 with an activation energy of 0.47 eV for the LLZ thin film.