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

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.