Effects of sulfate and nitrate anions on aluminum corrosion in slightly alkaline solution

The corrosion mechanisms and kinetics of AA1085 in Li₂SO₄ and LiNO₃ aqueous rechargeable lithium-ion battery electrolytes were investigated at pH 11 using chronoamperometry. The corrosion kinetics of AA1085 is controlled by the electrolyte concentration level and the anodic potentials. AA1085 is susceptible to crystallographic pitting corrosion in Li₂SO₄ electrolytes. The rates of pit nucleation and pit growth both decreased at higher Li₂SO₄ concentrations or at lower anodic potentials. AA1085 passivates against pitting corrosion in LiNO₃ electrolytes due to the formation of a thick, uniform corrosion product layer. The growth rate of the passive film was slightly enhanced by increasing the electrolyte concentration and anodic potentials. X-ray photoelectron spectroscopy spectra showed the formation of a thin sulfate-incorporated passive film on the electrode, which comprises Al₂(SO)₄18H₂O, Al(OH)SO₄ and Al(OH)₃, before the occurrence of pitting growth in 2 M Li₂SO₄ electrolyte. The thick corrosion product layer formed in 5 M LiNO₃ electrolyte was composed of Al(OH)₃ and AlOOH. Raman spectroscopy on deionized water, LiOH solution, Li₂SO₄ and LiNO₃ electrolytes depicted changes of solution structure with increasing electrolyte concentration. The influence of extrinsic and intrinsic factors on the corrosion kinetics of AA1085 in Li₂SO₄ and LiNO₃ electrolytes at pH 11 are discussed in detail.