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

Despite the promising features of Li 7 La 3 Zr 2 O 12 (LLZO) as a solid electrolyte (SE), its air handleability and compatibility with Li metal have been overlooked. This study reports on a Li 2 CO 3 -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 Li 2 CO 3 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 ∼3.43 μm wetted Li metal with the lowest capacity ratio of negative to positive electrode (∼0.176) demonstrates outstanding electrochemical performance. This demonstration will suggest a new direction for advancing high-energy-density solid-state Li metal batteries.