Electrochemical Studies of the Lithium Deposition on Au(111) from a Piperidinium-Based Ionic Liquid

For large-scale applications of modern lithium ion batteries, e.g.in electric car applications, thermal stability has to be absolutely ensured. Further, the required increasing power density of modern batteries demands for a larger electric potential of the cell. Room-temperature ionic liquids (RTILs) satisfy these requirements, as they provide low vapour pressure and high thermal stability combined with large electrochemical windows and good ionic conductivities [1,2]. However, internal short circuits due to the formation of lithium dendrites is one of the major issues of modern batteries, but the knowledge of this dendrite formation from RTILs is rather poor. Since an in-depth understanding of these processes is highly desirable we carried out extensive studies regarding the initial stages of lithium deposition from RTILs on single crystal electrodes.

Lithium was electrodeposited on a Au(111) substrate from the solution of lithium bis(trifluoromethylsulfonyl)imide in the commercially available RTIL 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide. Electrochemical investigations were carried out by means of cyclic voltammetry (CV) and the initial stages of metal deposition were followed by in-situscanning tunnelling microscopy (STM). As additional and independent characterization method, Electrochemical Quartz Crystal Microbalance (EQCM) measurements were performed to determine the actual adsorbate species with high accuracy.

We found, that three cathodic peaks appear in the potential range of −0.5 to −2.5 V vs. a Pt pseudo-reference electrode. Each one seems to be related to the deposition of lithium according to the EQCM measurement. This is also in accordance with the in-situ STM investigations, which confirm Li-deposition in various morphologies within this potential range. Further, a strand-like growth of a lithium species on the gold terraces can be recognized in the potential regime of the first cathodic peak. After applying a potential in the order of the second cathodic peak the growth of islands of one monolayer height takes place on the electrode surface. The third peak at very negative potential coincides with a three dimensional growth of lithium.

[1]           M. C. Buzzeo, R. G. Evans, R. G. Compton, ChemPhysChem 5 (2004) 1106.

[2]           R. Hagiwara, T. Hirashige, T. Tsuda, Y. Ito, J. Electrochem. Soc. 149 (2002) D1.