Lithium garnet Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> (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<sup>-7</sup> S cm<sup>-1</sup>) and high electronic insulation (10<sup>-14</sup> S cm<sup>-1</sup>), 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<sup>-2</sup> for over 500 cycles. In Li/aLLZO/Li symmetric cells, plating-stripping at current densities up to 3.2 mA cm<sup>-2</sup> 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.
Blocking Lithium Dendrite Growth in Solid-State Batteries with an Ultrathin Amorphous Li-La-Zr-O Solid Electrolyte
