Advancements in modern technology has led to increasing demand for high-capacity batteries. Lithium metal batteries have high specific capacity and are a promising candidate for post lithium-ion batteries. Traditional organic electrolytes have poor compatibility with lithium metal batteries. Ionic liquids (IL) with the addition of co-solvents have shown promised in lithium metal battery systems. In this work, 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ([Pyr14][TFSI]) was selected for its large electrochemical window and methyl propionate (MP) for its low viscosity and melting point. The IL/MP mixture with 0.8m LiTFSI maintained a large electrochemical window (>5V), extended liquid range of the IL and noticeably improved conductivity (from 0.56 mS/cm for 0.8m LiTFSI in [Pyr14][TFSI] to 11 mS/cm for 0.8m LiTFSI in a mixture of 1 to 7 mole ratio of [Pyr14][TFSI] to MP at 25°C). Also, we have identified that the addition of cyclic carbonate is important to increase the columbic efficiency for lithium deposition and stripping.