Electrochemical behaviour of aluminium in non-aqueous electrolytes over a wide potential range

Abstract

The electrochemical behaviour of aluminium in LiClO₄-propylene carbonate electrolyte is studied by cyclic voltammetry, steady-state polarisation, and ac impedance spectroscopy in the potential range -0.4-4.2 V versus Li/Li⁺. The open-circuit potential of Al is 1.57 V versus Li/Li⁺, which is about 0.2 V above the thermodynamic value of Al due to the presence of a surface passive film. In the positive potential region, Al is fairly stable between 1.57 and 3.5 V versus Li/Li⁺ owing to the presence of the surface film. Nevertheless, the oxidation of Al occurs at potentials > > 3.5 V versus Li/Li⁺. The ac impedance data are analysed by using a non-linear least-squares fitting procedure, and the surface film resistance is found to be between 498 and 1032 kΩ cm^-2. In the potential range 3.6-4.2 V versus Li/Li⁺, there is a breakdown of the passive film as demonstrated by a decrease in its resistance to 1.2-4.8 kΩ cm^-2. This breakdown accompanies anodic oxidation of Al. Thus, there is a possibility of anodic degradation of the Al substrate that is usually used as the current-collector of positive electrodes of Li-ion batteries, if Al is exposed to the electrolyte. In the negative potential region, the deposition of uniform and non-dendritic Li occurs, which can be anodically stripped in a quasi-reversible process with high coulombic efficiency. Diffusion of Li into Al results in the formation of a surface layer of Li-Al alloy, as suggested by X-ray diffraction patterns. The quasi-reversible cathodic deposition and anodic stripping of Li with an exchange current density of 0.16 mA cm^-2 indicates that Al is useful as a negative electrode in Li-batteries.