Na-Sn Alloy Coated by Naf on Carbon Fiber Greatly Improves Performance of Three-Dimensional Sodium Metal Anode

Abstract

Sodium metal holds great promise as anode material in high-energy-density sodium batteries, but it faces critical challenges such as dendrite growth and volume expansion, which can lead to reduced efficiency, internal short circuits, and safety issues in cells. To mitigate these issues, a three-dimensional (3D) composite anode, constructed by coating carbon cloth (CC) as current collector with a Na-Sn alloy and NaF, is developed in this study. NaF stabilizes the SEI, reduces electrolyte corrosion, and homogenizes ion flux, leading to uniform sodium metal deposition. The Na-Sn alloy offers numerous active sites for sodium deposition. The stable carbon clothes can maintain the structure of composite anodes during cycling. Therefore, the composite anode of Na-Sn alloy coated by NaF on carbon cloth obtained by one-step melting process (NaF/Na/Na-Sn@CC) significantly enhances cycling stability compared to traditional sodium metal film anode. In particular, the NaF/Na/Na-Sn@CC demonstrated superior cycling stability, outperforming other samples in both symmetric and full cells with liquid and gel polymer electrolytes.

Keywords: 3D sodium metal anode, Na-Sn alloy, NaF, carbon cloth