As the holy grail anode, lithium (Li) metal has attracted considerable interest in developing next-generation high-energy–density batteries. However, Li dendrites due to the poorly protected solid electrolyte interphase (SEI) during the Li plating process largely limit the Li application. Here, we report an effective electrolyte additive, i.e., 2,2,2-Trifluoroethyl trifluoroacetate (2,2,2-TFTF) as highly efficient inhibitor against growth of Li dendrites by facile mediation of SEI layer. DFT calculations and a series of characterization results indicate that the additive greatly favors formation of more protective SEI layer on the Li anode and homogeneous Li deposition. Strikingly, with 4% additive, the Li|Li cell showed a long cycle life of 750 h and the Li|Cu cell afforded an ultrahigh Coulombic efficiency (CE) of 99.7%. Moreover, the Li|LFP cell with 4% additive exhibited high-capacity retention and better rate performance, especially at 5C. The additive 2,2,2-TFTF offers a nontraditional option for high-performance lithium metal batteries with simplicity and saving.