Ionic mass transfer during electrochemical dissolution of Li metal in PC electrolyte solution

A Li metal anode was electrochemically dissolved in propylene carbonate (PC) containing 0.5 M lithium perchlorate (LiClO4) and the development of the Li+ concentration profile measured in situ by holographic interferometry. As the electrochemical cell configurations both a horizontal anode-over-cathode configuration, with the anode facing upward, and a vertical configuration of the parallel planar electrodes were employed. At low current densities (<2 mA cm−2) no shifting of the interference fringes was observed in either configuration during the initial stage of current passage. Such an incubation period has been observed also during cathodic Li electrodeposition from PC solutions, but in anodic Li dissolution the amount of electricity consumed during the incubation period was found to be appreciably less than in electrodeposition. This incubation phenomenon in electrochemical dissolution may be related to the existence of a solid-electrolyte interface layer on the Li metal surface in PC. The Li+ ion mass transfer rate measured after the incubation period agreed with that expected assuming one-dimensional diffusion in stagnant LiClO4 solution, away from the upward facing horizontal anode. In the case of a vertical plane anode, natural convection of the electrolytic solution was induced by the accumulation of LiClO4 at the anode. The mass transfer rate of Li+ ion measured after incubation was in reasonable agreement with natural convection boundary layer theory.