Bulk-type SSLB based on LLZ:Ta achieves high specific areal capacity and operational current densities.

Thin film batteries based on solid electrolytes having a garnet-structure like Li 7 La 3 Zr 2 O 12 (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°C. Single phase cubic thin films were obtained at substrate temperatures of 700°C and higher. At these temperatures an interlayer is formed. Combination of SEM, ToF-SIMS and XRD indicated that this layer consists of γ-LiAlO 2. The combined total ionic conductivity of the γ-LiAlO 2 interlayer and the LLZ thin film (perpendicular to the plane) was determined to be 2.0x10-9 S cm-1 for the sample deposited at 700°C. In-plane measurements showed a room temperature conductivity of 1.2x10-4 S cm-1 with an activation energy of 0.47 eV for the LLZ thin film.

Solid-state lithium batteries comprising a ceramic electrolyte instead of a liquid one enable safer highenergy batteries. Their manufacturing usually requires a high temperature heat treatment to interconnect electrolyte, electrodes, and if applicable, further components like current collectors. Tantalum-substituted Li 7 La 3 Zr 2 O 12 as electrolyte and LiCoO 2 as active material on the cathode side were chosen because of their high ionic conductivity and energy density, respectively. However, both materials react severely with each other at temperatures around 1085 °C thus leading to detrimental secondary phases. Thin-film technologies open a pathway for manufacturing compounds of electrolyte and active material at lower processing temperatures. Two of them are addressed in this work to manufacture thin electrolyte layers of the aforementioned materials at low temperatures: physical vapor deposition and coating technologies with liquid precursors. They are especially applicable for electrolyte layers since electrolytes require a high density while at the same time their thickness can be as thin as possible, provided that the separation of the electrodes is still guaranteed.