High Energy Density Ultra-thin Li Metal Solid-State Battery Enabled by a Li₂CO₃-Proof Garnet-Type Solid Electrolyte

Despite the promising features of Li7La3Zr2O12 (LLZO) as a solid electrolyte (SE), its air handleability and compatibility with Li metal have been overlooked. This study reports on a Li2CO3-proof LLZO (AH-LLZO) SE that exhibits remarkable air handleability in humid environments for months and outstanding Li metal wettability even after long-time air exposure. The formation of the Li-Al-O compounds at both the surface and the grain boundary inside caused by excess Li and Al suppresses not only Li2CO3 formation at the surface but also its propagation because it improves the hydrophobic property of the surface and the grain boundary. Furthermore, AH-LLZO is handled/stored in ambient air and exhibits excellent Li metal wettability that enables an ultra-thin Li metal seeding layer to achieve high energy density. The cell that has similar to 3.43 mu m wetted Li metal with the lowest capacity ratio of negative to positive electrode (similar to 0.176) demonstrates outstanding electrochemical performance. This demonstration will suggest a new direction for advancing high-energy-density solid-state Li metal batteries.