Novel Production Route for Alloyed Aluminum Anodes of Rechargeable Aluminum Batteries

Alternative battery systems, such as rechargeable aluminum batteries (RABs), offer advantages over state-of-the-art lithium-ion batteries, especially for large-scale energy storage applications. Aluminum is abundant, inexpensive, and provides high gravimetric energy density. In the past, the importance of the aluminum anode for cycling stability in non-aqueous RABs has often been underestimated. With recent advances in cathode performance, a shift towards anode-focused research has emerged. However, the native oxide layer of aluminum causes challenges such as inhomogeneous corrosion, repassivation, and unstable plating/stripping behavior at high current densities. Consequently, most studies concentrate on modifying, substituting, or removing the oxide layer and on suppressing dendrite growth. Zinc alloying has been reported to effectively increase battery performance by altering the native oxide in Al-air batteries. To test whether this observation also applies to battery systems employing non-aqueous electrolytes, anodes of Al 3.5 wt% Zn were produced and subjected to symmetric-cell tests which revealed increased overpotential. Besides the effect of the chemical composition, the influence of surface roughness on battery performance was assessed as well. Subsequently, the focus was placed on aluminum¿magnesium alloys with controlled microstructure. A combined approach was investigated, in which oxide stability is modified through alloying while a porous-like surface is generated by selective etching of a homogeneously distributed secondary phase. Anodes from two alloys (Al¿6Mg¿0.4Mn¿0.2Zr¿0.2Sc and Al¿6Mg¿0.4Mn¿0.3Zr¿0.08Y) with tailored heat treatments were produced, characterized using SEM/EDX, and evaluated in symmetric-cell tests employing AlCl¿/[EMIm]Cl as electrolyte. A significant increase in effective surface area could be achieved by selective etching of magnesium-enriched islands using phosphoric acid. The introduced alloying elements, as well as trace impurities from the commercially pure aluminum base, did not induce cycling instability at current densities of 0.05 mA cm¿² and 0.1 mA cm¿². Compared to 99.99 % pure aluminum foil, which is the current state-of-the-art in literature, the alloyed anodes exhibit a reduction in initial charge-transfer resistance of 88 % and 77 % for the scandium- and yttrium-containing samples, respectively, and achieved stable cycling more rapidly. Electrochemical impedance spectroscopy measurements after cycling revealed only negligible differences in charge-transfer resistance. Further studies are required to evaluate the dendrite-suppression capability at higher current densities and in a full-cell configuration.