The poor anode/electrolyte compatibility and dendrite growth have discouraged the development of solid-state sodium-metal batteries (SSSMBs). Here, a self-formed interphase with a unique Fe valence gradient is designed to stabilize the anode interface of Na₃Zr₂Si₂PO₁₂ solid electrolyte. This interphase consists of a Fe- and NaF-containing outer layer near the Na anode and a Fe²⁺/Fe³⁺-rich inner layer, which are in situ formed upon contacting Na with a sodiophilic α-Fe₂O_3-xF_x interlayer specially coated on Na₃Zr₂Si₂PO₁₂. The NaF and Fe prevents continuous reduction reactions and homogenize the electric filed, while the iron oxide gradient layer offers buffering Na storage during plating, further suppressing dendrite growth. Benefiting from the dynamically stable, low-impedance and dendrite-free interface, the symmetric cells achieve a 20-fold reduction in interfacial resistance and a fourfold enhancement in critical current density (CCD) at 25 °C, and powered a high CCD of 1.9 mA cm^-2 and a 1000-h cycle life at 1 mA cm^-2 at 80 °C. The corresponding SSSMBs based on Na₃V₂(PO₄)₃ cathodes deliver a capacity retention rate of 96% over 120 cycles at 1 C. This robust interface design supports one of the best electrochemical performances ever reported and offers a comprehensive solution to stabilize the Na₃Zr₂Si₂PO₁₂/Na interface toward practical SSSMBs.

中文翻译：

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用于无枝晶固态钠金属电池的具有铁价梯度的自形成氟化中间相

较差的阳极/电解质兼容性和枝晶生长阻碍了固态钠金属电池（SSSMB）的发展。在此，设计了具有独特Fe价梯度的自形成界面来稳定Na ₃ Zr ₂ Si ₂ PO ₁₂固体电解质的阳极界面。该中间相由靠近 Na 阳极的含 Fe 和 NaF 的外层和富含 Fe ²⁺ /Fe ^{3+的内层组成，这些内层是在 Na 与亲钠 α-Fe} ₂ O _3-x接触时原位形成的F _x中间层专门涂覆在Na ₃ Zr ₂ Si ₂ PO ₁₂上。 NaF和Fe可防止连续还原反应并使电场均匀化，而氧化铁梯度层在电镀过程中提供缓冲Na存储，进一步抑制枝晶生长。得益于动态稳定、低阻抗和无枝晶的界面，对称电池在 25 °C 下实现了界面电阻降低 20 倍、临界电流密度 (CCD) 提高四倍，并为 1.9 的高 CCD 提供动力mA cm ^{-2和 80 °C 下 1 mA cm -2 的}1000 小时循环寿命。基于 Na ₃ V ₂ (PO ₄ ) ₃阴极的相应 SSSMB 在 1 C 下经过 120 次循环后容量保持率为 96%。这种强大的界面设计支持有史以来报道的最佳电化学性能之一，并提供了全面的解决方案来稳定Na ₃ Zr ₂ Si ₂ PO ₁₂ /Na界面走向实用的SSSMB。