A Eutectic Aluminum-Tin Alloy Substrate for Anode-Free Na Battery

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 (Al₂O₃). 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 Na₃V₂(PO₄)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.