Mixtures of ionic liquid - alkylcarbonates as electrolytes for safe lithium-ion batteries

Mixtures of alkylcarbonate electrolytes with an ionic liquid (IL) and a lithium salt have been studied in order to develop new electrolytes for lithium-ion cells with enhanced safety profiles. In this work the influence of the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (Py14TFSI) on the electrochemical properties of commercial carbonate-based electrolytes, i.e. 1M LiPF6 in EC:DMC (LP30) and in EC:DMC:DEC (LP71) is reported. Four new electrolyte compositions have been prepared and characterized. The addition of the ionic liquid in the electrolyte carbonate-based solution results in (i) an ionic conductivity comparable with that of the pristine IL-free carbonate-based electrolyte, (ii) the enlargement of the electrochemical stability window, and (iii) a large reduction of the self-extinguish time (SET) of the electrolyte mixture when exposed to a free flame. All the newly developed electrolytes have been tested in lithium cells versus LiFePO4 and Li4Ti5O12 electrodes: the cells show good performances in galvanostatic cycling. The best performing electrolyte i.e. LP30/Py14TFSI 70/30 wt/wt has been also successfully tested in a full Li-ion cell realized by coupling LiFePO4 and Li4Ti5O12 electrodes.