Key Takeaways & Executive Findings
- •• • HEANCF current collector enables 80% capacity retention after 600 cycles at 1 C in full cells, outperforming conventional carbon nanofiber (NCF) which fails at high rates (0 mAh/g at 5 C vs. 75 mAh/g for HEANCF). • • Ah-level pouch cells achieve ~200 Wh kg−1 energy density with 87% capacity retention over 150 cycles at 0.5 C, demonstrating commercial viability for high-energy applications. • • DFT and MD simulations confirm reduced desolvation energy and enhanced Na+ adsorption at the HEA/NCF heterointerface, leading to dendrite-free deposition and stable SEI. • • The scalable electrospinning-pyrolysis synthesis route ensures uniform HEA nanoparticle distribution and structural integrity after cycling, as evidenced by SEM, supporting industrial scale-up.
Abstract
Anode-free sodium metal batteries (AF-SMBs) are promising for high-energy, low-cost energy storage, but suffer from interfacial instability due to sluggish Na+ kinetics and non-uniform deposition. Here, we report a scalable electrospinning-pyrolysis route to anchor FeCoNiCuMn high-entropy alloy (HEA) nanoparticles on N-doped carbon nanofibers (HEANCF). Density functional theory (DFT) calculations reveal high binding energy toward Na atoms, facilitating desolvation and adsorption. A built-in electric field (BIEF) arises from work function differences, driving electron redistribution and guiding uniform Na+ diffusion. The heterostructure also shows strong affinity for PF6− anions, promoting NaF-rich SEI formation that suppresses electron tunneling and parasitic reactions. Full cells with Na3V2(PO4)3 cathodes achieve 80% capacity retention after 600 cycles at 1 C. Ah-level pouch cells deliver ~200 Wh kg−1 and retain 87% capacity after 150 cycles at 0.5 C. This work establishes a coherent interfacial-kinetics framework for practical AF-SMBs.
1. Introduction
Conventional sodium metal batteries face critical bottlenecks: uncontrolled dendritic growth and volume changes fracture the solid-electrolyte interphase (SEI), causing electrolyte depletion and short circuits. Anode-free configurations eliminate excess anode mass to maximize energy density, but the absence of a Na reservoir intensifies interfacial instability, leading to irreversible plating/stripping, continuous SEI degradation, and sluggish Na+ kinetics. Prior strategies—electrolyte optimization, separator modification, or artificial SEI—have only partially mitigated these issues, as most current collectors exhibit poor Na affinity, resulting in high nucleation barriers and limited reversibility.
This work introduces a heterostructured current collector comprising FeCoNiCuMn high-entropy alloy nanoparticles anchored on N-doped carbon nanofibers (HEANCF). The work function difference between HEA and NCF induces a built-in electric field that drives electron redistribution, enhances Na+ adsorption, and promotes lateral ion diffusion, enabling uniform, dendrite-free deposition. DFT and MD simulations confirm reduced desolvation energy and improved interfacial kinetics. The resulting SEI is NaF-rich, suppressing electron tunneling and parasitic reactions. Full cells with NVP cathodes deliver 80% capacity retention after 600 cycles at 1 C, and Ah-level pouch cells achieve ~200 Wh kg−1 with 87% retention over 150 cycles at 0.5 C, setting a new benchmark for practical AF-SMBs.
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Saisai Qiu, Haolin Zhu, Qiang Wu, Jiayue Peng, Canfu Zhang, Shijie Cheng, Jia Xie (2026). Work-function-engineered high-entropy alloy/carbon nanofibers direct Na+ transport for stable anode-free sodium batteries. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3942-2
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Frequently Asked Questions
What is the specific failure mechanism of conventional carbon nanofiber (NCF) current collectors in anode-free sodium batteries, and how does HEANCF overcome it?
NCF exhibits poor sodiophilicity, leading to high nucleation overpotential and non-uniform Na deposition, which causes dendritic growth and SEI fracture. HEANCF introduces FeCoNiCuMn HEA nanoparticles that create a built-in electric field due to work function differences, enhancing Na+ adsorption and promoting lateral diffusion. This results in uniform, dendrite-free deposition, as evidenced by stable cycling (80% retention after 600 cycles at 1 C) versus rapid capacity decay for NCF (0 mAh/g at 5 C).
How does the built-in electric field (BIEF) at the HEA/NCF interface influence the solid electrolyte interphase (SEI) composition and stability?
The BIEF drives electron redistribution, which enhances the affinity for PF6− anions, promoting their preferential decomposition. This leads to a NaF-rich SEI that is mechanically robust and electronically insulating, suppressing electron tunneling and parasitic reactions. The stable SEI contributes to the high capacity retention (87% after 150 cycles at 0.5 C in pouch cells) and low interfacial resistance observed in electrochemical impedance spectroscopy.
What are the scalability and cost implications of the electrospinning-pyrolysis synthesis route for HEANCF?
The electrospinning-pyrolysis method is scalable and cost-effective, as it uses readily available precursors and standard equipment. The uniform distribution of HEA nanoparticles and structural integrity after cycling (confirmed by SEM) indicate reproducibility and durability, making it suitable for industrial production. The achieved energy density of ~200 Wh kg−1 in pouch cells demonstrates commercial viability for high-energy battery applications.
How does the rate capability of NVP||HEANCF compare to state-of-the-art anode-free sodium batteries, and what are the limiting factors at high C-rates?
NVP||HEANCF delivers 75 mAh/g at 5 C, whereas NCF-based cells fail (0 mAh/g). This superior rate performance is attributed to enhanced Na+ kinetics and reduced desolvation energy at the heterointerface. At high rates, the limiting factor is likely mass transport in the electrolyte and electrode, but the HEANCF architecture mitigates these issues by promoting fast interfacial charge transfer, as evidenced by stable voltage plateaus even at 5 C.
What is the long-term cycling stability of HEANCF in anode-free full cells, and what degradation mechanisms are observed after extended cycling?
NVP||HEANCF full cells retain 85.2%, 80%, and 75% capacity after 400, 600, and 1000 cycles at 1 C, respectively. Post-cycling SEM shows intact fiber networks and uniform HEA distribution, indicating excellent mechanical stability. The gradual capacity fade is likely due to slow SEI growth and electrolyte consumption, but the NaF-rich SEI minimizes parasitic reactions, enabling extended cycle life compared to conventional systems.
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