The Li metal / LLZTO interface was formed using similar methods to previous works 2, . Specifically, after heat treatment, the electrolyte discs were removed from the oven. Li metal foil (Alfa Aesar, Ward Hill, Massachusetts, USA) was scraped with a steel spatula to produce a clean metal surface. This Li was then cut into 3 mm diameter pads using a biopsy punch. The Li metal pads were immediately adhered to the LLZTO disk, and the resulting assembly was placed into the oven and baked at 250°C for 1 hour.