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

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.