Rechargeable lithium ion batteries have been widely used in portable consumer electronic devices, hybrid and full electric vehicles, and emergency power supply systems, because of their high energy density and long lifespan. The lithium ion battery market was approximately $11.8 billion in 2010 and is expected to grow to $53.7 billion in 2020. However, there is an intrinsic safety issue in these batteries because electrolyte contains a flammable organic solvent which may cause fire and/or even explosion. All solid-state lithium ion battery is recognized as next-generation technology for rechargeable power sources due to improved safety, high energy density, and long cycle life. Inorganic solid electrolyte replace liquid one to eliminate flammable components. The major challenge for all solid-state lithium ion batteries is to develop solid electrolytes with high ionic conductivity and good stability against both electrodes. Amorphous lithium lanthanum titanium oxide (LLTO) is very promising as solid electrolyte owing to its high ionic conductivity, good stability, and wide electrochemical stability window. In this work, amorphous LLTO thin films (or powders) were successfully prepared by sol-gel process. The thin films are smooth and crack-free. The microstructure evolution from dried gel film to fired film to annealed film was examined. The microstructure of the annealed film, either amorphous or crystalline, depends on the annealing temperature and time. Theoretical analysis was conducted to understand the microstructure evolution. Induction time determines the longest annealing time without transformation from amorphous to crystalline state. The induction time decreases with annealing temperature until the time approaches a minimum, and after that, the time increases with the temperature. Ion transport properties were investigated by Electrochemical Impedance Spectroscopy (EIS). The plateau at low frequencies results from lithium ion long-range diffusion which contributes to dc conductivity, while the observed frequency dispersion at high frequencies is attributed to short-range forward¨Cbackward hopping motion of lithium ions. The relaxation processes are non-Debye in nature. Amorphous LLTO is compatible with Li metal due to its disordered atomic configuration. Finally, a 3D structure of electrode with amorphous LLTO was successfully prepared. This electrode displays promising electrochemical performance.