Bilayer Dense‐Porous Li₇La₃Zr₂O₁₂ Membranes for High‐Performance Li‐Garnet Solid‐State Batteries

Abstract

Li dendrites form inLi 7 La 3 Zr 2 O 12 (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 .

Intermediate‐Stage Sintered LLZO Scaffolds for Li‐Garnet Solid‐State Batteries

“…In the context of mitigating the issues associated with Li dendrites, as well as aspects of the thickness of LLZO SSEs, the development of porous LLZO in the form of thin membranes has been recently targeted. [ 26–29 ] Such porous design of LLZO appears to address problems, assumed to be the primary reasons for Li dendrites—dynamic volume changes of the Li anode and the formation of voids. [ 30–35 ] On the one hand, the formation of voids during stripping can be mitigated by the larger surface area of the LLZO/Li interface in the scaffold compared to dense LLZO ceramics.…”

“…[23][24][25] Another missing aspect of utmost practical importance for achieving both high gravimetric and volumetric energy densities of Li-garnet solid-state batteries is the established methodology for large-scale fabrication of LLZO SSEs in the form of thin (<50 µm) LLZO membranes.In the context of mitigating the issues associated with Li dendrites, as well as aspects of the thickness of LLZO SSEs, the development of porous LLZO in the form of thin membranes has been recently targeted. [26][27][28][29] Such porous design of LLZO appears to address problems, assumed to be the primary reasons for Li dendritesdynamic volume changes of the Li anode and the formation of While significant progress has been achieved in the field of Li-garnet solidstate batteries, their further development, is hindered by the formation of cavities at the Li 7 La 3 Zr 2 O 12 (LLZO)/Li interface at practically relevant current densities and areal capacities exceeding 1 mA cm −2 and 1 mAh cm −2 . As a result, the cells exhibit limited cycling stability due to the inhomogeneous distribution of the applied current density, and therefore, the formation of Li dendrites.…”

Assessment of Critical Stack Pressure and Temperature in Li‐Garnet Batteries

“…XPS survey spectra, covering the binding energy (BE) range of 0 eV – 1200 eV (XPS), were recorded with a step size of 0.5 eV at a constant pass energy of 280 eV using the Al‐Kα source (power 51 W; beam diameter ≈200 µm). Importantly, considering that the same binding energy position (282.9 eV) of C‐C peaks was observed in each spectrum at different sputtering depths due to constant charging effect on the LLZO sample, [ 42 ] their calibration was not performed. For comparison with literature data, all peak positions of spectra can be shifted forward by 1.9 eV to higher binding energies.…”

Garnet-Based Solid-State Li Batteries with High-Surface-Area Porous LLZO Membranes

“…To address the challenges posed by Li dendrites and the thickness of LLZO solid-state electrolytes (SSEs), recent efforts have focused on the development of thin (30–50 μm) porous LLZO membranes. − This porous design aims to tackle the primary factor assumed to cause Li dendrite formation, which is the occurrence of voids during Li stripping from the Li/LLZO interface. − Specifically, the approach effectively diminishes the void formation by expanding the interface area between LLZO and Li (Figure a,b). Consequently, the amount of Li removed from the interface upon Li stripping is thus drastically reduced, to below that received by the diffusional Li flux toward the Li/LLZO interface, as governed by Fick’s second law.…”