Lithium-ion batteries (LIBs) employing solid-state electrolytes are considerably safer and might potentially generate a higher energy density compared. The goal of this thesis is to investigate the synthesis and stability of doped Li₇La₃Zr₂O₁₂ (LLZO). The reason of adopting LLZO is to presents a high conductivity, good electrochemical stability against metallic lithium. The investigation method involves preparing LLZO powder, pressing it to pellets, sintering the pellets at 1230 ºC and coating metal electrodes on them, followed by the measurement of the lithium ionic conductivity through Electrochemical Impedance Spectroscopy, Scanning Electron Microscopy, and X-ray diffraction. Doping has proven to be an effective way to improve the lithium ionic conductivity. In our research, multi-doped LLZO with Al and Ta and F presented the highest conductivity σ = 1.67×10-4 Scm-1 at room temperature. Our study suggests that the adoption may lead to a significant increase in the lithium ionic conductivity of LLZO solid-state electrolyte.