In Situ Constructed Fluorosulfided Interface With Metallic Mo Sites for Robust Anode‐Free Sodium Metal Batteries

ABSTRACT

Anode‑free sodium metal batteries (AFSMBs) are acclaimed for their low‑cost, sustainability, and high energy density. However, achieving highly reversible Na plating/stripping on bare current collectors (CCs) and robust solid electrolyte interphase (SEI) is challenging. Herein, we present a robust fluorosulfided SEI (FS‐SEI) layer with metallic Mo active sites through in situ electrochemical transformation of 2D MoS ₂ coating on the Cu CCs. Specifically, the ingenious 2D MoS ₂ holds short ion transport pathways and large contact active areas during battery operation. Furthermore, MoS ₂ can in situ convert into metallic Mo and Na ₂ S, while catalyzing the dissolution of NaPF ₆ to generate NaF. The in situ formed FS‐SEI film possesses excellent sodiophilicity, high Na ⁺ diffusion, and good electron‐blocking capability, which effectively guides a homogeneous distribution of Na ⁺ flux, accelerates the electrochemical reaction kinetics, and blocks side reactions between electrolyte and electrodes. Benefiting from these advantages, the MoS ₂ @Cu half cells achieve average Coulombic efficiency of 99.85% over 350 cycles at 10 mA cm ⁻² and 10 mAh cm ⁻² . When paired with Na ₃ V ₂ (PO ₄ ) ₃ cathodes, the AFSMBs exhibit excellent rate capability and cycling stability (>97.0% retention). This work offers insights into engineering a stable in situ SEI via 2D sodiophilic architectures, paving the way for developing energy‐dense and durable AFSMBs.