Corrosion/Passivation Behavior of Concentrated Ionic Liquid Electrolytes and Its Impact on the Li-Ion Battery Performance

The corrosion/passivation phenomenon of Al and stainless steel (SS) with an ionic liquid-based electrolyte N -methyl- N -propyl-piperidinium bis(fluorosulfonyl)imide (PMpipFSI)-LiFSI was systematically studied by cyclic voltammetry, and its impact on the battery performance was evaluated in NMC532/Li cell. Our results showed that these electrolytes could eliminate the Al corrosion due to their capability of forming a passivation layer during the first anodic scan after 3 V vs Li + /Li. In contrast, no passivation behavior was observed for SS electrode, and the corrosion reaction was kinetically suppressed when the lithium salt concentration increases. We demonstrated that while 1 M LiFSI-PMpipFSI extensively corrodes SS in a NMC532/Li cell, the 5 M electrolyte does not and actually enables the normal cycling of the cell both using SS-2032-coin cells. Further, when an Al-coated coin cells were used, the Coulombic efficiency dramatically improved from 90% to >99.9% with superior capacity retention at both room temperature and 55°C.