NaF包覆的钠锡合金/碳纤维复合负极的制备和电化学性能

    Preparation and Electrochemical Performance of NaF Coated Sodium-tin Alloy/Carbon Fiber Composite Anode

    • 摘要: 钠金属是一种高比容量的钠电池负极材料,但它面临由于枝晶生长和体积膨胀而导致的库伦效率降低、内部短路等安全问题。本文通过高温熔融的方式,将SnF2包覆的碳布接触熔融钠,SnF2和熔融钠反应形成了NaF与Na-Sn合金,随后将熔融钠通过毛细作用注入碳布中,制备了一种三维钠合金复合负极,旨在改善枝晶生长和体积膨胀问题的。以碳布(Carbon Cloth, CC) 作为集流体,构建NaF和Na-Sn合金分层式的钠合金。NaF可以提高固态电解质界面相(Solid Electrolyte Interphase, SEI) 稳定性,减少电解液腐蚀,均匀化离子通量,钠锡合金为钠沉积提供了许多活性位点,提高钠沉积均匀性,碳布提高了复合负极的结构的稳定性和抑制体积膨胀。因此,NaF包覆的Na-Sn合金/碳布的复合负极(NaF/Na/Na-Sn@CC) 表现出优异的循环稳定性。与传统的钠金属负极相比,复合负极组成的对称电池以更低的过电位稳定循环700 h;组成的全电池在20 C的倍率下稳定循环400圈。

       

      Abstract: Sodium metal is a promising high specific capacity anode material for sodium batteries. However, it faces critical challenges including dendrite growth and volumetric expansion. These issues lead to reduced coulombic efficiency, internal short circuits, and safety problem. This study demonstrates a three-dimensional sodium alloy composite anode fabricated through a high-temperature fusion. SnF2-coated carbon cloth (CC) is contacted with molten sodium, triggering a reaction between SnF2 and molten sodium to form NaF and Na-Sn alloy. Subsequently, the molten sodium infiltrates the carbon cloth via capillary action. The composite anode, using carbon cloth as a current collector, features a hierarchical architecture integrating NaF and Na-Sn alloy. This design aims to mitigate dendritic growth and volume expansion of sodium metal anodes. The NaF layer stabilizes the solid electrolyte interphase (SEI) , mitigates electrolyte corrosion, and homogenizes ion flux distribution. Meanwhile, the Na-Sn alloy provides abundant active sites for sodium deposition, enhancing uniformity of deposition. During cycling, the carbon cloth ensures structural integrity of the composite anode. Consequently, the composite anode of NaF-coated Na-Sn alloy/carbon cloth (NaF/Na/Na-Sn@CC) demonstrates exceptional cycling stability. Compared with conventional sodium metal anodes, symmetric cells with composite anodes exhibit stable cycling for 700 hours with a significantly low overpotential. The full cells with the composite anodes enable stable cycling over 400 cycles at an elevated rate of 20 C.

       

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