Lithium Deposition from a Piperidinium-based Ionic Liquid: Rapping Dendrites on the Knuckles

Using cyclic voltammetry (CV), in-situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM) the initial stages of lithium deposition on Au(111) from a solution of lithium bis(trifluoromethylsulfonyl)imide in the commercially available ionic liquid 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPipTFSI) were investigated. We could identify three distinct cathodic peaks in the potential range from 0 to -2.5V (vs. Pt quasi-reference electrode), corresponding to different lithium deposition modes. While in the potential region of the under-potential deposition (UPD) (-1.2 to -1.8V) the growth of monoatomic high islands (300-370pm) takes place, Li bulk deposition occurs at potentials <-2.3V. Finally, the third peak at 0V, which only appears after a previous bulk deposition, is connected to a strand-like growth of lithium at (111) terraces with a uniform orientation over the whole substrate. Interestingly, once reaching a step-edge, the one-dimensional growth continues into the electrolyte, indicating the initial stages of Li dendrite formation.