Solid Electrolyte Interphase Film on Lithium Metal Anode in Mixed-Salt System

Abstract

The effect of electrolyte salt on the solid electrolyte interphase (SEI) is discussed with respect to improvement of the lithium metal anode. Lithium bis(fluorosulfonyl)imide (LiFSI) and lithium nitrate (LiNO3) were dissolved together in dimethyl sulfoxide (DMSO), in which the ratios of LiNO3:LiFSI (x:100-x mol%) were in the range of 0<x<100. Electrochemical lithium plating/stripping was tested for various x-values. A LiNO3 single salt electrolyte yielded small polarizations in the initial cycles; however, the polarization became larger with the cycle number. A LiFSI single salt electrolyte showed larger polarizations, but maintained an almost constant magnitude during all cycles. LiNO3 and LiFSI salt-mixtures gave better cycle performance with low and stable polarizations compared to the single salt electrolytes. X-ray photoelectron spectroscopy (XPS) analyses revealed that LiNO3 gave a Li2O-rich SEI membrane, while LiFSI gave a LiF-rich membrane. For LiNO3 and LiFSI salt-mixtures, the ratio of these components changed according to the x value. The use of multiple lithium salts is thus an effective way to control the SEI properties and improve the cycle performance of a lithium metal anode.