A fluorinated amide molecule with two functional segments, namely, an amide group with a high donor number to bind lithium ions and a fluorine chain to expel carbonate solvents and mediate the formation of LiF, was designed to regulate the interfacial chemistry. As expected, the additive preferably appears in the first solvation sheath of lithium ions and is electrochemically reduced on the anode, and thus an inorganic-rich solid electrolyte interphase is generated. The morphology of deposited lithium metal evolves from brittle dendrites into a granular shape. Consequently, the Li||LiFePO4 cell shows an excellent capacity retention of 92.7% at a high rate of 5 C after 800 cycles. Besides, the Li||LiNi0.8Co0.1Mn0.1O2 cell succeeds to maintain 98.1% of the initial capacity after 100 cycles at 1 C. Our designing of N,N-diethyl- 2,3,3,3-tetrafluoropropionamide (denoted as DETFP) highlights the importance of a "high donor number" and may shed light on the design principles of electrolytes for high performance batteries.
Keywords: SEI; additive; fluorinated amide; lithium metal batteries.