Fluorinated imine modulating efficient sulfur redox kinetics and a stable solid electrolyte interphase in lithium–sulfur batteries

Abstract

The shuttle effect of lithium polysulfides (LiPSs) and the instability of the solid electrolyte interphase (SEI) lead to lithium dendrite growth and severe corrosion of lithium anodes (Li-anodes) for lithium–sulfur (Li–S) batteries. Herein, we introduce phenyl-1-(4-(trifluoromethyl)phenyl)ethan-1-imine (PTPEI), a fluorinated Schiff base molecule, as a novel dual-function electrolyte additive to enhance the sulfur redox kinetics at the cathode side. Simultaneously, it facilitates the formation of a dense, robust, and stable SEI enriched with lithium fluoride (LiF) on the anode side. With theoretical calculations, we reveal that molecular structure regulation strengthening van der Waals forces between PTPEI and LiPSs facilitates charge transfer by affecting the highest occupied molecular orbital (HOMO) level and improves the role of the PTPEI molecule catalyst in accelerating the sulfur redox kinetics. Furthermore, we demonstrate that the Schiff base molecular configuration facilitates the decomposition of PTPEI and expedites the formation of a stable LiF-enriched SEI, effectively protecting the Li-anode during cycling. As a result, the Li–S cell with PTPEI delivers an initial discharge capacity of 1190.9 mA h g⁻¹ with a capacity decay rate of 0.90% per cycle at 0.1C for 50 cycles at a high sulfur loading of 5.5 mg cm⁻² and low E/S ratio of 8 μL mg⁻¹.