A Eutectic Aluminum–Tin Alloy Substrate for Anode‐Free Na Battery

Abstract Due to the abundant availability of Na resources, Na batteries garner significant attention. Anode‐free Na batteries, devoid of active negative materials, are deemed promising candidates for the next generation of high‐energy‐density Na batteries. The cyclic stability of anode‐free Na batteries primarily hinges on the stability of the limited Na supplied by the cathode, and the design of the anode substrate plays a pivotal role. In this study, a cost‐effective aluminum–tin eutectic alloy substrate is developed using a straightforward melting process. In eutectic alloy, tin element is present in its metallic form, which facilitates the disruption of the compactness of the Passivation film (Al 2 O 3 ). Besides, tin metal and tin dioxide on the surface of the eutectic alloy show a strong Na affinity (strong binding energy with Na atom and lower Na nucleation barrier), thereby promoting the uniform nucleation of sodium. This eutectic alloy substrate enables highly reversible Na plating/stripping with an average coulombic efficiency of 99.97%, and the cycle life exceeds 4000 cycles. Coupling with Na 3 V 2 (PO 4 ) 3 , the AlSn‐2%‐NVP full cell exhibits a capacity retention of up to 81% after 100 cycles, significantly outperforming coated carbon aluminum foils and aluminum foils. This study introduces an efficient approach to the anode‐free Na battery.