Surface reactions and performance of non-aqueous electrolytes with lithium metal anodes

Six electrolytes were investigated for lithium metal battery applications. The electrolytes were composed of combinations of four different salts (LiPF6, LiB(C2O4)2, LiI and LiN(SO2CF3)2) and three different solvents (PC, DME, and 1,3-dioxolane). All six electrolytes had conductivities >3 mS cm−1 at temperatures from −20 to 40 °C. Electrochemical impedance spectroscopy (EIS) and linear polarization, both at room temperature and low temperature (−8 °C), provided congruent results. The LiI-based electrolyte had the lowest film resistance, while 0.7 M LiB(C2O4)2–PC:DME (1:1) had the highest impedance. The presence of 1,3-dioxolane in electrolytes provided lower impedance with LiB(C2O4)2 but higher resistance with LiPF6-based electrolytes. NMR analysis of electrolytes after thermal abuse indicate that LiN(SO2CF3)2-based electrolytes are the most thermally stable. SEM analysis suggests that surface modification and impedance changes are correlated.