Bilayer Dense-Porous Li₇ La₃ Zr₂ O₁₂ Membranes for High-Performance Li-Garnet Solid-State Batteries

Li dendrites form in Li₇ La₃ Zr₂ O₁₂ (LLZO) solid electrolytes due to intrinsic volume changes of Li and the appearance of voids at the Li metal/LLZO interface. Bilayer dense-porous LLZO membranes make for a compelling solution of this pertinent challenge in the field of Li-garnet solid-state batteries (SSB). Lithium is thus stored in the pores of the LLZO, thereby avoiding i) dynamic changes of the anode volume and ii) the formation of voids during Li stripping due to increased surface area of the Li/LLZO interface. The dense layer then additionally reduces the probability of short circuits during cell charging. In this work, a method for producing such bilayer membranes utilizing sequential tape-casting of porous and dense layers is reported. The minimum attainable thicknesses are 8-10 µm for dense and 32-35 µm for porous layers, enabling gravimetric and volumetric energy densities of Li-garnet SSBs of 279 Wh kg^-1 and 1003 Wh L^-1 , respectively. Bilayer LLZO membranes in symmetrical cell configuration exhibit high critical current density up to 6 mA cm^-2 and cycling stability of over 160 cycles at a current density of 0.5 mA cm^-2 at an areal capacity limitation of 0.25 mAh cm^-2 .