Development of anode alloys for aluminum/air batteries: Final report

The electrochemistry of various Al-Li-In, Al-Li-In-Bi, and Al-Mg-Mn-In alloys in 4 M KOH at 50/degree/C has been investigated by delineating the partial anodic and cathodic processes as a function of potential. The Al-Li-In alloys (Group 1) and the Al-Li-In-Bi alloys (Group 2) exhibit high corrosion rates under open circuit conditions and do not display activation phenomena as the potential is swept in the negative to positive direction. Accordingly, these alloys are judged to be unsuitable as fuels for alkaline aluminum/air batteries. The Al-Mn-Mg-In alloys (Group 3) do exhibit activation at potential within the range -1.75 to -1.85 V (vs Hg/HgO, 4 M KOH) as a result of oxidation of manganese from the surface to form a soluble product. These alloys display significantly lower open circuit corrosion rates. All the alloys in this group passivate at more positive potentials, followed by a region over which the current varies nearly linearly with voltage. These same characteristics are exhibited by Alloy BDW (Al-lMg-0.1 In-0.2 Mn), which we investigated previously. However, none of the alloys studied in the present program appears to offer any advantages over Alloy BDW as a fuel for alkaline aluminum/air batteries. We have also continued to analyze various mechanisms tomore » account for the extensive electrochemical impedance data for pure aluminum in 4 M KOH at 25/degree/C. Six mechanisms were explored, including some that involve autocatalytic steps in the aluminum electrodissolution process. None of these mechanisms appears to be capable of accounting for the measured impedance any better than the simple irreversible coupled dissolution/hydrogen ion-atom evolution mechanism reported earlier. 23 refs., 38 figs., 14 tabs.« less