Deposition and Dissolution Mechanism of Lithium on Aluminum Substrate

Deposition and dissolution mechanism of lithium on the aluminum substrate has been investigated by electrochemical impedance spectroscopy (EIS) and x-ray photoelectron spectroscopy (XPS). Every impedance diagram obtained during deposition and dissolution periods consists of two loops. The diameter of the high-frequency loop is almost constant regardless of the amount of deposition or dissolution, while the magnitude of the low-frequency loop decreases with increasing deposition period, and increases with increasing dissolution period. XPS results showed a surface film, which consists of an outer LiF layer and an inner LiOH-Li2O layer, forms on the Li-Al alloy. Thickness of the LiOH-Li2O layer increases with dissolution period. The mathematical analysis of a model mechanism suggests that the high-frequency loop of the impedance diagram may correspond to both the charge-transfer resistance and the resistance of the LiF layer. The low-frequency loop may comprise the diffusion process of Li+ in the LiOH-Li2O layer, the coverage relaxation of the adsorbed species Liads and Li+ ads, and the alloying process of Li-Al.