A dual-layer solid electrolyte interphase enhances interfacial chemistry stability in aqueous aluminium metal batteries

Aqueous aluminum metal batteries (AAMBs) have garnered significant attention owing to the abundance of aluminum, high volumetric energy density (8040 mAh cm- 3, approximately four times that of lithium metal anodes), and chemical inertness. However, profound issues such as surface corrosion and the side reaction of hydrogen evolution severely impede the advancement of AAMBs. Here, we report the in-situ formation of a dense inorganic AlF3 + Al/Zn-CO3 + flexible carbon shell solid-electrolyte interface (SEI) on the surface of an Al electrode through hydrothermal and electrochemical activation in a dilute aqueous solution of Al(OTf)3-Zn (NO3)2. Experimental evidence demonstrates that the electrically insulating Al/Zn-NO3 layer initially forms on the Al negative electrode surface through self-polymerization reactions of Al with Zn2+ and NO3 - under sealed heating conditions. Subsequent electrochemical activation leads to the decomposition of CF3SO3- to form conductive AlF3 + Al/Zn-CO3, while in situ generation of a flexible carbon layer occurs internally on the surface. The inorganic inner layer facilitates the diffusion of Al ions, while the organic carbon shell suppresses water permeation and maintains the stability of the SEI structure. The in-situ formed SEI enables the Al//Ti battery to achieve a high Coulombic efficiency (CE) of 98.9 % over 100 cycles. Constructing the Al//beta-MnO2 battery yields a high energy density of 216 Wh kg- 1, with the capacity retention remaining stable at 83.6 % after 700 cycles.