Rechargeable solid-state Na metal batteries (SSNMB) can offer high operational safety and energy density. However, poor solid–solid contact between the electrodes and the electrolyte can dramatically increase interfacial resistance and Na dendrite formation, even at low current rates. Therefore, we developed a carbon-fiber-supported liquid Na–K alloy anode that ensures close anode–electrolyte contact, enabling superior cycle stability and rate capability. We then demonstrated the first cryogenic transmission electron microscopy (cryo-TEM) characterization of an SSNMB, capturing the evolution of solid–electrolyte interphase (SEI) and revealing both crystalline and amorphous phases, which could facilitate ion transport and prevent continuous side reactions. By enhancing contact between the Na–K alloy and solid-state electrolyte, these symmetric cells are capable of cycling for over 800 h without notable increased polarization and enable an unprecedented critical current density (CCD) at 40 mA cm^–2. Our liquid Na–K alloy approach offers a promising strategic avenue toward commercial SSNMBs.

中文翻译：

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用于高性能固态钠金属电池的钠钾合金负极

可充电固态钠金属电池 (SSNMB) 可以提供高操作安全性和能量密度。然而，即使在低电流速率下，电极和电解质之间不良的固-固接触也会显着增加界面电阻和钠枝晶的形成。因此，我们开发了一种碳纤维支撑的液态 Na-K 合金负极，可确保负极与电解质的紧密接触，从而实现出色的循环稳定性和倍率性能。然后，我们首次展示了 SSNMB 的低温透射电子显微镜 (cryo-TEM) 表征，捕获了固体电解质界面 (SEI) 的演变并揭示了结晶相和非晶相，这可以促进离子传输并防止连续的副反应。通过增强Na-K合金与固态电解质之间的接触，^–2。我们的液态 Na-K 合金方法为商业 SSNMB 提供了一条有前途的战略途径。