Four symmetric compounds deriving from the alkyl chain containing tripropyl phosphate were designed and synthesized by varying substitution of fluorine in the side chains and added as co-solvents to yield 10%, 20% and 30% concentrated electrolyte formulations. The formulated electrolytes were physicochemically and electrochemically characterized and compared to a state-of-the-art organic carbonate-based electrolyte in regard to the flammability as well as any occurring trade-off in cycling performance. The addition of phosphates resulted in superior flammability behavior of the electrolyte as the flammability could be severely reduced with increased concentration of the phosphates. As the addition of such phosphate compounds to the electrolyte usually comes with a trade-off in cycling performance, electrochemical behavior was thoroughly investigated regarding ionic conductivity, anodic stability limit and cycling stability in lithium metal and lithium ion cells. The influence of the varying fluorine content as well as position of the substituted fluorine was determined and discussed. The tripropyl phosphate derivatives showed very promising cycling results hand in hand with a significant improvement achieved regarding the flammability of the electrolyte. (C) 2018 The Electrochemical Society.