From blocker to booster: Harnessing garnet surface chemistry for advanced solid-state electrolytes

Garnet electrolytes with high ionic conductivity and electrochemical stability are widely used as fillers to fabricate composite solid electrolytes (CPEs) within polymer matrices. However, the performance of CPEs is significantly influenced by the surface characteristics of the garnet electrolyte. Herein, the impact of garnet surface characteristics on CPEs was systematically investigated and a conversion from a typically unstable and Lewis basic surface to a more stable Lewis acidic surface was realized, which is shown to be more conductive to the improved performance of CPEs. By simultaneously removing the Li₂CO₃ layer and applying a Li-Al-O coating, the influence of surface characteristics on CPEs was investigated. The Lewis acid Li-Al-O surface coating not only promotes lithium salt dissociation, improving the ionic conductivity and ionic transfer number, but also prevents the reformation of the passive Lewis basic Li₂CO₃ layer. Compared to garnet with a Lewis basic Li₂CO₃ surface, the garnet modified with a Lewis acid Li-Al-O coating enhances CPEs, which exhibit an improved critical current density of 1.0 mA·cm⁻² and highly stable lithium symmetric cell cycling for 400 h at 0.2 mA·cm⁻². This research highlights the importance of surface chemistry in the design of high-performance solid-state batteries and presents a strategic modification approach for garnet-based CPEs.