An Oxygen-Tolerant Lamellar Spacing Window for Eutectic Al–Cu Anodes in Aqueous Aluminum–Manganese Batteries
Abstract
Rechargeable aluminum batteries in aqueous electrolytes have promise due to safety, cost, and abundance considerations; however, the metal-anode negative electrodes suffer from oxide/hydroxide films, hydrogen evolution, dissolved oxygen corrosion, and non-uniform stripping/plating morphologies. The central design challenge is whether the lamellar period of the eutectic Al--Cu alloy can be engineered to meet the oxygen-normalized criterion of both symmetric-cell reversibility and full-cell energy utilization with a hydrated aluminum manganese oxide cathode. The set of electrodes under investigation includes eutectic \AlCu{} lamellar periods of 180, 280, 420, 650, and 1100 nm, as well as pure Al and monolithic \AltwoCu{} electrodes; all are tested in aqueous 2 M \OTF{} electrolyte at dissolved oxygen concentrations of 0.13, 1.5, 5.0, and 13.6 mg L$^{-1}$. It is found that the choice of optimal structure cannot be reduced to maximizing the Al/\AltwoCu{} interfacial density. The 180 nm electrode shows maximum interfacial density but higher sensitivity to oxygen-facilitated cathodic side reactions, while 650 and 1100 nm electrodes have problems related to increased Al diffusion distances and passivation-induced polarization. The 280 nm lamellar period results in the most effective performance: the overpotential in low-oxygen concentration environment decreases from 53 to 38 mV in comparison with the 420 nm electrode reference case, the charge transfer resistance reduces from 160 to 112 $\Omega$, stable stripping/plating increases from 2000 to 3000 h, and a full-cell based on \AlMnO{} cathode delivers a capacity of 492 mAh g$^{-1}$ at 0.1 A g$^{-1}$, 215 mAh g$^{-1}$ at 5 A g$^{-1}$, energy density of 706 Wh kg$^{-1}$, and maintains 88\% after 600 cycles. The key result is that the lamellar Al--Cu alloy should be engineered into a specific range of oxygen tolerance between 240 and 330 nm.