Electro-reduction of nitrogen aided by lithium offers a new route for ammonia synthesis. In this novel approach, the first step of lithium plating plays a determining role in faradaic efficiency (FE) of the electro-synthesis process. It was found that the simple addition of cesium salt in a conventional organic electrolyte enhanced Li plating performance (FE of 82.3% for ammonia synthesis) to a substantial extent. This improvement appeared to have a lot to do with a Cs-caused change in morphology of Li deposit, which brought about the suppression of parasitic side reactions between metallic Li and propylene carbonate. This study proves that FE enhancement can be made possible via a simple change in electrolyte composition, an approach that is collectively called electrolyte engineering, and this approach can serve as effective means for making the best of Li-mediated ammonia synthesis. (C) 2018 The Electrochemical Society.