Effect of Variation in Anion Type and Glyme Length on the Nanostructure of the Solvate Ionic Liquid/Graphite Interface as a Function of Potential

Atomic force microscope (AFM) force curves are used to probe the effect of anion species and glyme length on the nanostructure of the solvate ionic liquid (SIL)/highly ordered pyrolytic graphite (HOPG) interface as a function of applied potential. At all potentials, the lithium tetraglyme bis(trifluoromethylsulfonyl)imide (Li(G4)TFSI)/HOPG is more structured than lithium tetraglyme bis(perfluoroethylsulfonyl)imide (Li(G4)BETI)/HOPG because [BETI](-) has greater conformational flexibility. The Li(G3) trifluoroacetate (TFA)/HOPG interface is even more disordered because [TFA](-) coordinates strongly to the lithium ion, leading to a high concentration of free glyme. The Li(G3)TFSI/HOPG interface is more structured than the Li(G4)TFSI/HOPG interface because the longer glyme increases the molecular flexibility of the complex cation. The Li(G1)(2)TFSI/HOPG interface has weak interfacial structure because monoglyme is poorly coordinating so the free glyme concentration is high. Despite Li(G3)TFSI, Li(G4)TFSI, and Li(G4)BETI being good SILs (meaning the free glyme concentration is low), application of a negative potential to the HOPG surface leads to the desolvation of Li+ from the glyme at the surface.