Key Takeaways & Executive Findings
- •• • Au@HCN yolk-shell structure confines Au nanoparticles in hollow carbon nanospheres, achieving a high Coulombic efficiency of 99.8% over 500 cycles at 1 mA cm−2, addressing dendrite growth and low utilization for practical sodium metal anodes. • • Alloying-induced amorphization of Au upon sodiation forms a Na-Au amorphous alloy, which enhances sodiophilicity and reduces nucleation overpotential, as evidenced by ex situ XAS and TEM, enabling uniform Na deposition. • • The void space in the yolk-shell design accommodates volume expansion during alloying, mitigating mechanical stress and ensuring structural stability over 2000 hours of cycling in symmetric cells at 0.5 mA cm−2. • • Full cells with Na3V2(PO4)3 cathodes deliver a specific capacity of 105 mAh g−1 with 92% capacity retention after 500 cycles, demonstrating practical viability for high-energy sodium metal batteries.
Abstract
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.
1. Introduction
Commercial lithium-ion batteries face limitations in lithium resources and energy density, prompting the need for next-generation storage systems. Sodium-based batteries offer low cost and abundance, but their anodes suffer from dendrite growth and low utilization. Sodium metal anodes, with high theoretical capacity (1165 mAh g−1) and low redox potential (−2.71 V vs. SHE), are promising yet hindered by safety and efficiency issues. Strategies like electrolyte modification and 3D scaffolds have been explored, but host-less Na nucleation remains uncontrolled. The design of sodiophilic nucleation seeds is critical to regulate Na+ flux and ensure uniform deposition.
Metal-based seeds (Au, Sn, Zn) enhance sodiophilicity via alloying, but suffer from volume expansion and parasitic reactions. Downsizing seeds mitigates volume changes but increases aggregation and side reactions. Spatial confinement via yolk-shell structures can stabilize seeds and isolate them from electrolyte, yet fundamental issues persist: the influence of seed distribution, alloying behavior at nanoscale, and quantification of Na affinity at alloy interfaces. This work introduces Au nanoparticles confined in hollow carbon nanospheres (Au@HCN), which undergo alloying-induced amorphization, providing a robust seeding/hosting interphase that navigates homogeneous Na nucleation and stable cycling.
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QU Changzhen, YANG Jiaying, HAN Yimeng, PENG Xu, XU Xiaosa, KASKEL Stefan, SANAD Moustafa M.S., SHENOUDA Atef Y., ZHUANG Rong, XU Fei (2026). Stable Sodium Metal Batteries Enabled by Encapsulation and Alloying-Induced Amorphization. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4349-9
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Frequently Asked Questions
What is the failure mechanism of Au@HCN electrodes under high current densities or deep cycling?
The yolk-shell design accommodates volume changes via void space, and the amorphous Na-Au alloy maintains sodiophilicity. At 1 mA cm−2, Coulombic efficiency remains 99.8% over 500 cycles, indicating stable performance. However, at higher current densities or deeper cycling, potential degradation could arise from cumulative volume changes or loss of electrical contact, though specific data beyond 500 cycles are not provided.
How does the cost of Au@HCN compare to conventional sodium metal anode hosts, and is it scalable?
Gold is expensive, but the loading is minimal (Au NPs confined in carbon). The synthesis uses template-free methods, potentially scalable. However, cost parity with cheaper hosts (e.g., carbon) is not quantified. For large-scale storage, cost reduction via alternative metals or lower Au loading may be necessary.
What is the role of the amorphous Na-Au alloy in reducing nucleation overpotential, and how is it characterized?
The amorphous alloy provides abundant sodiophilic sites, reducing nucleation overpotential. Ex situ XAS and TEM confirm amorphization after sodiation. This amorphous phase likely enhances Na+ adsorption and uniform nucleation, as evidenced by stable cycling and high CE.
How does the Au@HCN electrode perform in full-cell configurations with practical cathode loadings?
Full cells with Na3V2(PO4)3 cathodes deliver 105 mAh g−1 with 92% retention after 500 cycles, indicating compatibility. However, cathode loading and areal capacity are not specified, which are critical for practical energy density.
What are the long-term cycling stability and rate capability of Au@HCN symmetric cells?
Symmetric cells cycle over 2000 hours at 0.5 mA cm−2, demonstrating excellent stability. Rate capability data are not provided, but the high CE and low overpotential suggest good performance at moderate rates.
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