Lithium dendrites have become a roadblock in the realization of solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk defects in crystalline electrolytes such as the garnet Li7La3Zr2O12 (LLZO) facilitates the growth of these hazardous lithium filaments. Here we explore the amorphous phase of LLZO as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against lithium metal, and high electronic insulation. By tuning the lithium stoichiometry, the ionic conductivity can be increased by 4 orders of magnitude while retaining a negligible electronic conductivity. In symmetric cells, plating-stripping shows no signs of lithium penetration up to 3.2 mA cm−2. The dense conformal nature of the films enables microbatteries with an electrolyte thickness of only 70 nm, which can be cycled at 10C for over 500 cycles. The application of this material as a coating on crystalline LLZO lowers the interface resistance and increases the critical current density. The effectiveness of the amorphous Li-La-Zr-O as dendrite blocking layer can accelerate the development of better solid-state batteries.

Lithium garnet Li₇La₃Zr₂O₁₂ (LLZO) electrolyte is a potential candidate for the development of solid-state batteries with lithium metal as high-capacity anode. But ceramic LLZO in the form of pellets or polycrystalline films can still suffer from lithium dendrite penetration because of surface and bulk inhomogeneities and grain boundaries with non-negligible electronic conductivity. In contrast, the amorphous phase of LLZO (aLLZO) possesses a grain-boundary-free microstructure with moderate ionic conductivity (10^-7 S cm^-1) and high electronic insulation (10^-14 S cm^-1), which in the form of thin coatings can offer resistance to lithium dendrite growth. We explore the electrochemical properties and applications of aLLZO ultrathin films prepared by sputtering deposition. The defect-free and conformal nature of the films enables microbatteries with an electrolyte thickness as low as 70 nm, which withstand charge-discharge at 0.2 mA cm^-2 for over 500 cycles. In Li/aLLZO/Li symmetric cells, plating-stripping at current densities up to 3.2 mA cm^-2 shows no signs of lithium penetration. Finally, we show that the application of aLLZO as a coating on LLZO ceramic pellets significantly impedes the formation of Li dendrites.

Lithium metal dendrites have become a roadblock in the realization of next-generation solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk inhomogeneities with non-negligible electronic conductivity in crystalline electrolytes such as the lithium garnet Li7La3Zr2O12 (LLZO) facilitates the growth of lithium filaments, posing a critical safety risk. Here we explore the amorphous phase of LLZO (aLLZO) as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against metallic lithium, and high electronic insulation. We demonstrate that by tuning the lithium stoichiometry in sputtered aLLZO films, the ionic conductivity can be increased up to 10-7 S cm-1 while retaining an ultralow electronic conductivity of 10-14 S cm-1. In Li/aLLZO/Li symmetric cells, plating-stripping results in no degradation of the films and current densities up to 3.2 mA cm-2 can be applied with no signs of lithium penetration. The defect-free and conformal nature of the films enables microbatteries with an electrolyte thickness as low as 70 nm, which withstand charge-discharge at 0.2 mA cm-2 for over 500 cycles. Finally, we demonstrate that the application of aLLZO as a coating on crystalline LLZO lowers the interface resistance and significantly impedes the formation of lithium dendrites, increasing the critical current density of a symmetric cell up to 1.3 mA cm-2 at room temperature and without external pressure. The effectiveness of the amorphous Li-La-Zr-O as lithium dendrite blocking layer can accelerate the development of more powerful and safer solid-state batteries.

Lithium metal dendrites have become a roadblock in the realization of next-generation solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk inhomogeneities with non-negligible electronic conductivity in crystalline electrolytes such as the lithium garnet Li₇La₃Zr₂O₁₂ (LLZO) facilitates the growth of lithium filaments, posing a critical safety risk. Here we explore the amorphous phase of LLZO (aLLZO) as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against metallic lithium, and high electronic insulation. We demonstrate that by tuning the lithium stoichiometry in sputtered aLLZO films, the ionic conductivity can be increased up to 10^-7 S cm^-1 while retaining an ultralow electronic conductivity of 10^-14 S cm^-1. In Li/aLLZO/Li symmetric cells, plating-stripping results in no degradation of the films and current densities up to 3.2 mA cm^-2 can be applied with no signs of lithium penetration. The defect-free and conformal nature of the films enables microbatteries with an electrolyte thickness as low as 70 nm, which withstand charge-discharge at 0.2 mA cm^-2 for over 500 cycles. Finally, we demonstrate that the application of aLLZO as a coating on crystalline LLZO lowers the interface resistance and significantly impedes the formation of lithium dendrites, increasing the critical current density of a symmetric cell up to 1.3 mA cm^-2 at room temperature and without external pressure. The effectiveness of the amorphous Li-La-Zr-O as lithium dendrite blocking layer can accelerate the development of more powerful and safer solid-state batteries.<div></div>

Lithium garnet Li₇La₃Zr₂O₁₂ (LLZO) electrolyte is a potential candidate for the development of solid-state batteries with lithium metal as high-capacity anode. But ceramic LLZO in the form of pellets or polycrystalline films can still suffer from lithium dendrite penetration because of surface and bulk inhomogeneities and grain boundaries with non-negligible electronic conductivity. In contrast, the amorphous phase of LLZO (aLLZO) possesses a grain-boundary-free microstructure with moderate ionic conductivity (10^-7 S cm^-1) and high electronic insulation (10^-14 S cm^-1), which in the form of thin coatings can offer resistance to lithium dendrite growth. We explore the electrochemical properties and applications of aLLZO ultrathin films prepared by sputtering deposition. The defect-free and conformal nature of the films enables microbatteries with an electrolyte thickness as low as 70 nm, which withstand charge-discharge at 0.2 mA cm^-2 for over 500 cycles. In Li/aLLZO/Li symmetric cells, plating-stripping at current densities up to 3.2 mA cm^-2 shows no signs of lithium penetration. Finally, we show that the application of aLLZO as a coating on LLZO ceramic pellets significantly impedes the formation of Li dendrites.