Selective facet etching enables dendrite-less molten salt aluminum metal batteries

Aluminum metal batteries represent a promising alternative to lithium batteries for large-scale energy storage due to their high theoretical capacity, cost efficiency and improved safety features. However, a significant challenge lies in the polycrystalline surface nature of aluminum foil anodes, which can result in uneven aluminum deposition and increase the risk of a short circuit during cycling. Here we report a selective facet-etching method to construct a 3D porous aluminum anode (3D-Al) featuring near-single exposed (220) plane on the surface, enabling dendrite-free behavior and ultra-long cycling for aluminum batteries. The chemical etching mechanism is elucidated to showcase selective removal of the (111) and (200) planes, while preserving (220), which induces directional aluminum plating along the (220) plane. Further, the resulting 3D-Al anode possesses abundant pores and cavities, which serve as preferential sites for aluminum deposition, alleviating volume expansion and effectively inhibiting dendrite growth. The assembled 3D-Al||graphite battery displays excellent rate capability and an ultralong lifespan over 13 000 cycles at a high rate of 10.0 A g^-1. This work provides a facile yet effective strategy for suppressing aluminum dendrite formation and establishes a new avenue for advancing high-performance aluminum batteries.