Cation-Structure Effects on Zinc Electrodeposition and Crystallographic Orientation in Ionic Liquids

The electrochemical behavior of Zn deposition in room temperature ionic liquids consisting of bis(trifluoromethanesulfonyl)amide (TFSA(-)) combined with N-propyl-N-methylpyrrolidinium (Pyr(1,3)(+)) or 1-ethyl-3-methylimidazolium (EMI+) was investigated in terms of their physicochemical properties and dissolved Zn2+ species. The effect of cation structure was examined not only on the macroscopic morphologies, but also on the microscopic aspects of crystallographic orientation of Zn deposits obtained from [Zn(TFSA)(2)](0.1)[Cation-TFSA](0.9). Electron backscattered diffraction revealed that the crystal grains grown in Pyr(1,3)-TFSA at the current density of 0.5 mA cm(-2) were much finer, compared with the sizes of those in EMI-TFSA. This is probably because Pyr(1,3) cations inhibit the surface diffusion of Zn adatoms, thus preventing growth in a specific plane direction. It was found that higher reversibility on Zn stripping needs larger crystal grains rather than polycrystalline with fine grains. The obtained results will contribute greatly to the realization of longer life batteries using Zn without resource constraints.

Automated summary

The electrochemical behavior of Zn deposition in different ionic liquids was studied. The results showed that the cation structure of the ionic liquid affects the macroscopic morphology and crystallographic orientation of the Zn deposits. The N-propyl-N-methylpyrrolidinium cation inhibits the surface diffusion of Zn adatoms, resulting in smaller crystal grain sizes. Larger crystal grains are beneficial for the reversibility of the Zn stripping process.