Ionic Mass Transfer Accompanied with Electrodeposition of Li Metal in Solvate Ionic Liquid

Abstract

Li metal is a promising negative electrode candidate for next-generation rechargeable batteries. However, the non-uniform electrochemical reaction induces dendrite formation during charging operation and dead lithium during discharging operation, respectively. Many researchers tried to control the morphological variation of electrodeposited Li metal by using additives and artificial interface layer. In general, the electrodeposition of metals are governed by the ionic mass transfer rate in the vicinity of the electrode. In this study, we focused on the Li+ ionic mass transfer phenomenon during the electrodeposition and electrochemical dissolution of Li metal in solvate ionic liquid. The solvate ionic liquid is new electrolyte candidate for the batteries. Especially, it is good candidate for Li-S batteries due to the suppression of dissolution of poly-sulfide. However, the mechanism of electrodeposition of Li metal has not been cleared in solvate ionic liquid system. Here, two in-situ techniques were applied to discuss the mechanism of Li metal electrodeposition from the viewpoint of ionic mass transfer. One is the digital holographic interferometry microscope which can visualize the Li+ concentration profile near the electrode. Another is micro-Raman spectroscopy which can detect the bonding of the chemical species in the electrolyte. We would like to discuss the ionic mass transfer phenomenon in the vicinity of the electrode during the electrodeposition and electrochemical dissolution of Li metal in solvate ionic liquid based on these in-situ measurement results.