Effect of LiNbO3 surface dry-coating on the air stability of Ga-doped LLZO solid electrolytes

Oxide-based garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolytes (SEs) have attracted significant attention as promising candidates for next-generation all-solid-state batteries (ASSBs) with high ionic conductivity of 1 × 10 −3 –10 −4 S cm −1 . However, LLZO is prone to surface degradation upon exposure to H 2 O and CO 2 in the air, leading to the formation of Li 2 CO 3 impurities. This not only reduces the ionic conductivity but also increases interfacial resistance with the electrode, ultimately impairing the electrochemical and mechanical performance of the cell. In this study, we investigated and compared the air stability of LiNbO 3 -coated Ga-LLZO and the pristine Ga-LLZO. According to the Accelerated Durability Test (ADT), the formation of Li 2 CO 3 on the surface of LiNbO 3 -coated Ga-LLZO pellets was suppressed compared to the pristine Ga-LLZO. The total ionic conductivity of the pristine Ga-LLZO was 3.90 × 10 −4 S cm −1 , while the LiNbO 3 -coated Ga-LLZO was 9.17 × 10 −4 S cm −1 . Therefore, the ionic conductivity maintenance rates after ADT were 79 % for the LiNbO 3 -coated Ga-LLZO, compared to only 23 % for the pristine Ga-LLZO. These results demonstrate that surface coating of Ga-LLZO particles with LiNbO 3 effectively suppresses air degradation reactions and significantly contributes to long-term ionic conductivity maintenance and improved air stability. • Dry-coating of LiNbO 3 provides a scalable, solvent-free surface treatment. • The LiNbO 3 -coated Ga-LLZO maintained 79 % of its initial ionic conductivity. • The LiNbO 3 layer suppresses Li 2 CO 3 formation and surface degradation in humid air. • The method enhances the long-term air stability of Ga-doped LLZO solid electrolyte.