In our work we demonstrate a facile, water-free synthesis of amorphous lithium niobate (LiNbO₃) layers. Our developed method also enables the coating of substrates in inert atmosphere with simple, industrial scalable methods. As verification, a 120 nm thin LiNbO₃ layer was deposited on the garnet type lithium ion conductor Li_6.45Al_0.05La₃Zr_1.6Ta_0.4O₁₂ (LLZTO) to improve its interface to lithium metal and reduce dendrite formation. The application of the thin film reduced the interface resistance between LLZTO and lithium metal to 1.02(13) Ω∙cm² and was able to suppress dendrite formation for current densities of up to 0.5 mA/cm². The chemical stability of the LiNbO₃ thin film in contact with Li-metal was verified by SEM, XPS and ToF-SIMS.