Abstract
All-solid-state Li-ion batteries (ASSLiB) attracted lots of attention mainly due to their higher safety compared with commercial Li-ion batteries. The research of solid electrolyte is critical for the development of ASSLiB, and among all the candidates of solid electrolyte materials, amorphous Lithium Lanthanum Titanate Oxide (LLTO) is promising because of its outstanding electrochemical stability up to 12V. However, the fundamental relationship among the ionic conductivity, microstructure, and mechanism of Li ion transport is still unrevealed. In this study, both amorphous LLTO thin film and LLTO powder were successfully prepared by sol-gel process. In order to determine the relationship between microstructure and ionic conductivity, various annealing time at 500°C were applied. This work shows that the ionic conductivity increases from 2.32 × 10−8 S/cm to 9.01 × 10−6 S/cm with the annealing time before LLTO starts to crystallize and decreases back to ∼1.6 × 10−9 S/cm after the formation of crystal phase. The absolute value of difference is close to 3 orders of magnitude. Furthermore, the morphology of the thin film changes accordingly, solvent evaporation, surface refinement and crystallization phases would occur sequentially, and this indicates that there is an optimal synthesis condition for the LLTO film. However, the changes of structure, morphology and ionic conductivity does not affect activation energy. This will help researchers to find optimized synthesis condition of amorphous LLTO and potentially search for and design other solid electrolyte materials.
