On the electrochemical behavior of aluminum electrodes in nonaqueous electrolyte solutions of lithium salts

We studied the electrochemical behavior of aluminum electrodes in solutions comprising ethylene carbonate (EC)-dimethyl carbonate (DMC) and lithium salts: lithium hexafluorophospate (LiPF₆), lithium perchlorate (LiClO ₄), or lithium bis(oxalato)borate (LiBOB). Under anodic polarization within the potential range of 3.00-4.00 V in these solutions, aluminum electrodes demonstrate a stable behavior due to their passivation by surface films. Aluminum electrodes passivate in EC-DMC/ LiPF₆ and EC-DMC/LiBOB solutions both at 30 and 60°C, whereas these electrodes remain active and corrode in EC-DMC/ LiClO₄ solutions. LiBOB may decompose at anodic potentials, thus forming passive films comprising B₂ O ₃ and metal-oxalate species on the aluminum electrodes polarized to 4.50-5.30 V. Li₂ CO₃, LiF and AlPO₄, and LiCl species were also detected on the electrodes anodically polarized in LiBOB-, LiPF₆ -, and LiClO₄ -containing solutions, respectively. At some conditions, current oscillations can be developed on aluminum electrodes upon their polarization at constant potentials. These oscillations may relate to the successive formation and dissolution of the passivating surface films formed on electrodes. The development of F₂ P (O) O- species due to the polarization of aluminum electrodes in EC-DMC/ LiPF₆ solutions was confirmed by solution NMR studies.