Electrochemical and Physicochemical Properties of PYR14-FSI Based Electrolytes with LiFSI

Abstract

N-methyl-N-butylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid (PY14FSI)-based electrolytes with LiFSI have been characterized in terms of conductivity, viscosity, thermal phase behavior, electrochemical and thermal stability. The results indicate a high conductivity for the pure ionic liquid and those containing LiFSI. The addition of salt lowers the melting temperature of the electrolyte mixture and, for some of the electrolytes, the conductivity is superior to 10-5 S cm-1 at -40{degree sign}C and up to 3.7 mS cm-1 at 25{degree sign}C. For the more conductive electrolyte at room temperature ((1-x) PY14FSI-(x) LiFSI (x = 0.10)), lithium metal has been cycled for more than 200 cycles at 20{degree sign}C with little overpotential relative to the Li0/Li+ couple, showing that the passivation layer on the surface of lithium is stable and allows reversible lithium deposition. One drawback of these electrolytes is the low thermal degradation temperature, which is lower than that of the pure IL, which may be attributed to impurities in the commercially available LiFSI.