Large Area, Rapid Spray Plasma Processed Amorphous Lithium Lanthanum Zirconium Oxide Thin-Film Electrolytes for Solid State Batteries

Lithium lanthanum zirconium oxide (LLZO) and other solid-state electrolyte (SSE) materials are widely heralded for their high lithium ionic conductivity, low electrical conductivity, and stability against lithium metal. However, the difficulty in manufacturing solid electrolytes, especially in the thin film geometry, has hindered widespread deployment. Multiple critical challenges need to be solved to produce low-cost SSEs for solid-state batteries at-scale: reproducibility of the thin-film deposition to achieve dense mixed-metal oxides, the intrinsic reactivity of lithiated metal oxides to environmental species like water and carbon dioxide that result in the formation of secondary surface phases like Li₂CO₃, and the necessity of low-throughput and energy-intensive curing steps.<br/><br/>Here, we present a rapid spray plasma process to manufacture large-area thin-film LLZO SSEs for solid state batteries. The LLZO is first generated via blade coating to form an oxide network. The oxide is then cured and densified in one step at 3.6 cm/min linear processing speed by a nitrogen plasma discharged into a low-humidity, ambient pressure environment. Plasma allows for a reduction in processing time by orders of magnitude compared with many traditional vacuum-based thin film routes owing to the combination of radical ions, ultraviolet photons, and heat present in the curing process along with the lack of vacuum. The resulting amorphous phase LLZO thin films have low carbonate contamination, high ionic conductivity of 1x10^-5 S/cm at room temperature, low surface and through-plane defect density, and surface roughness of &lt;40 nm. This work is a step toward the high-throughput manufacturing of LLZO for solid state batteries.