Powder Aerosol Deposition and Electrochemical Characterization of 30 µm thick LLZO Solid Electrolyte as a Separator Layer for Solid-State Batteries

Garnet-type Li$_7$La$_3$Zr$_2$O$_{12}$ (LLZO) is a promising solid electrolyte (SE) for solid-state batteries (SSBs). However, identifying a suitable processing method to allow dense film fabrication without high sintering temperatures remains challenging. Powder aerosol deposition method (PAD, a.k.a. ADM) enables the fabrication of dense LLZO films at room temperature. To date, studies on PAD-LLZO films primarily addressed the electrical properties in terms of conductivity, while their cycling performance remains largely unexplored. In this study, we show that PAD-LLZO films can be used for the reversible transport of lithium with current densities up to 0.41 mA cm$^{−2}$ with no thermal post-treatment of pristine films after deposition, albeit at high overvoltage. A mild annealing at 400 °C is performed to reduce microstrain, which is known to lead to high overvoltage during cycling in the as-deposited state. Higher ionic conductivities are achieved after annealing, while the cycling stability deteriorates. These phenomena are attributed to reduced compressive stress as well as microstrain after annealing of the PAD-LLZO films with a nanocrystalline microstructure. ... mehrBased on these assumptions, we propose a possible strategy to improve cycling stability by adapting a post-treatment process to reduce the volume fraction of grain boundaries by controlled grain growth.