• • Eutectic p-Bi57Sn43@C delivers 470.3 mAh g−1 at 1 C, exceeding typical alloying anodes by >20%, enabling higher energy density Na-ion cells.
• • Capacity retention of 95.2% after 1000 cycles at 20 C demonstrates exceptional long-term stability, critical for grid-scale storage where cycle life dictates levelized cost.
• • Hypo- and hyper-eutectic compositions form dendritic primary phases that increase internal resistance and accelerate structural degradation, highlighting the necessity of eutectic interface engineering.
• • The defect-free eutectic concept reduces volume expansion and maintains microstructural integrity, offering a scalable metallurgical route for binary alloy anodes.