In Situ Electrochemical Evolution of Amorphous Metallic Borides Enabling Long Cycling Room‐/Subzero‐Temperature Sodium‐Sulfur Batteries

Abstract Room temperature sodium‐sulfur batteries (RT Na‐S) have garnered significant attention for their high energy density and cost‐effectiveness, positioning them as a promising alternative to lithium‐ion batteries. However, they encounter challenges such as the dissolution of sodium polysulfides and sluggish kinetics. Introducing high‐activity electrocatalysts and enhancing the density of active sites represents an efficient strategy to enhance reaction kinetics. Here, an amorphous Ni‐B material that undergoes electrochemical evolution to generate the NiS_x phase within an operational sodium‐sulfur battery, contrasting with the crystalline NiB counterpart is fabricated. Electrochemical cycling facilitated the establishment of an interface between the amorphous Ni‐B and NiS_x, leading to heightened catalytic activity and improved reaction kinetics. Consequently, batteries utilizing the amorphous Ni‐B showcased a notable initial specific capacity of 1487 mAh g⁻¹ at 0.2 A g⁻¹, exhibiting exceptional performance under high current densities of 5 A g⁻¹, in low‐temperature conditions (−10 °C), with high sulfur loading, and in pouch cell configurations.