Improving the graphite/electrolyte interface in lithium-ion battery for fast charging and low temperature operation: Fluorosulfonyl isocyanate as electrolyte additive

Nowadays, the demand for high energy density, fast-charging and wide-temperature range lithium-ion batteries has increased significantly. The Solid Electrolyte Interphase (SEI)protecting layer, formed at the interface between the graphite anode and the electrolyte is a key parameter for fast kinetics and wide temperature operation, especially to enable fast charge of cells including graphite anodes. In this work, fluorosulfonyl isocyanate (FI)is used as a novel SEI film forming electrolyte additive for graphite anode. Due to its high reduction potential (above 2.8 V vs. Li+/Li), FI is reduced prior to the carbonate-based electrolyte, yielding a conductive SEI on the surface of the graphite. The SEI is made of a thick and protective inorganic inner layer that prevents the growth of the outer organic layer. As a result, the resistance of the graphite/electrolyte interface is dramatically decreased. Therefore, Li/graphite cells with 2 wt% FI exhibit excellent rate performance at room temperature (20 °C)and low temperature (0 °C and −20 °C), compared to those with the reference liquid electrolyte (LP30).