Stable Sodium Metal Batteries Enabled by Encapsulation and Alloying-Induced Amorphization
Sodium metal batteries are promising for large-scale energy storage due to sodium's abundance and low cost, but their commercialization is hindered by dendrite growth and low utilization of sodium metal anodes. Here, we report a yolk-shell structure with gold nanoparticles (Au NPs) confined in hollow carbon nanospheres (Au@HCN) as a robust seeding/hosting interphase. The encapsulation isolates Au NPs from direct electrolyte contact, mitigating parasitic reactions, while the void space accommodates volume changes during alloying. Notably, electrochemical testing reveals that Au NPs undergo alloying-induced amorphization upon sodiation, forming a Na-Au amorphous alloy that enhances sodiophilicity and ensures uniform Na nucleation. This amorphous phase, confirmed by ex situ X-ray absorption spectroscopy and transmission electron microscopy, reduces nucleation overpotential and promotes dendrite-free deposition. The Au@HCN electrode achieves a high Coulombic efficiency of 99.8% over 500 cycles at 1 mA cm−2 and a long cycle life of over 2000 hours at 0.5 mA cm−2 in symmetric cells. Full cells paired with Na3V2(PO4)3 cathodes deliver a specific capacity of 105 mAh g−1 with 92% retention after 500 cycles. This work provides a rational design for stable sodium metal anodes through encapsulation and alloying-induced amorphization, offering a pathway for practical sodium metal batteries.