Post-lithiation: a way to control the ionic conductivity of solid-state thin film electrolyte

Ionic conductivity is pivotal for solid-state battery performance. While the garnet oxide electrolyte Li₇La₃Zr₂O₁₂ (LLZO) boasts high ionic conductivity due to its distinct crystal structure and lithium-ion mobility, lithium loss during fabrication hampers its potential. In this study, we introduce a method that merges synthesis optimization with a post-lithiation process, enhancing LLZO's ionic conductivity. This approach compensates lithium loss with a gas-phase diffusion process, which stabilizes the cubic LLZO phase and amplifies its ionic conductivity by more than three orders of magnitude compared to electrolytes without post-lithiation. Through our comprehensive experimental procedure, we have conclusively determined that the film deposited at 700 °C and subsequently annealed at 700 °C with LiOH exhibits the highest conductivity, with a notable value of 1.11 × 10^-2 S cm^-1 at 200 °C. This is a significant boost compared to the as-deposited film (3.54 × 10^-6 S cm^-1 at 200 °C). Our findings present an additional approach to boosting lithium ion diffusion. The approach employed in this work has the potential to be applicable to films produced through other deposition methods, as it addresses the prevalent issue of lithium loss, a significant barrier to the utilization of lithium-rich thin films.