Enhancing aluminum–air anode energy density via interfacial activity–film synergy enabled by a subgrain-network microstructure in alkaline media

This work proposes a microstructure–interface strategy to enable high-efficiency and low-cost Al anodes for alkaline Al–air batteries using a cold-deformed Al–0.5Mg–0.1Bi–0.1In alloy. Controlled annealing induces a sequential evolution from dislocation-cell rearrangement and annihilation to subgrain coalescence and, ultimately, coarse equiaxed grains, yielding four representative microstructures quantified by electron backscatter diffraction and transmission electron microscopy. Although Mg–Bi precipitates undergo staged dissolution and spheroidization, the electrochemical response is governed mainly by defect-mediated transport, micro-galvanic heterogeneity, and discharge-product film evolution. Multiscale tests (OCP, Tafel, EIS, and H 2 evolution) show that the subgrain-network architecture provides the most balanced interface, combining low self-corrosion, suppressed intergranular/exfoliation corrosion, and the highest working voltage over practical current densities. Consequently, this architecture delivers the highest energy density of 3404.5 mWh g -1 at 40 mA cm -2 , whereas grain coarsening accompanied by the dissipation of stored deformation energy (stored defect energy, dominated by dislocation-related contributions) promotes product accumulation and discharge instability under high-rate ion exchange. At industrial scale, a TMI-SN anode achieves 4063 mWh g -1 with 150 h sustained discharge in 6 M NaOH + 0.05 M Na 2 SnO 3 , reducing the energy cost to 0.96 USD kWh -1 .