Compared with a conventional lithium-ion battery, all-solid-state battery exhibits excellent safety, which is the one of drawbacks of the conventional lithium-ion battery. The Garnet electrolyte Li₇La₃Zr₂O₁₂ (LLZO), as the typical representative of solid electrolyte, shows outstanding safety and electrochemical stability.

During the process of this work, the LLZO underwent the changes from micro-sized particles, nano-particles slurry, and the final ultrathin film. The micro-sized particles was obtained by the conventional solid state reaction. Nanoscale LLZO slurry was prepared using high energy ball-milling technology, with the addition of 1-Methyl-2-pyrrolidinone, LiN(CF₃SO₂)₂, SPEEK-PSI-Li and Piuronic®F127. The LLZO ultrathin electrolyte film was obtained by the method of wet coating and drying out the solvent of LLZO slurry.

The as-prepared LLZO ultrathin film, with a thickness of several micrometers, was applied in the cell of Li/LLZO/LFPO. At room temperature, the battery showed a capacity of 160.4 mAh g^-1 for the first discharge, which was about 94.4% of the theoretical capacity value. After 100 cycles, the cell provided a discharge capacity of 136.8 mAh g^-1. At 60 ℃, the battery presented more stable electrochemical performance. The capacity loss during the cycles form the 2^nd to 100^th was only 0.06% (0.7 mAh g^-1). The excellent performance could be attributed to the ultrathin solid electrolyte film.