Self-Template\nConstruction of Hierarchical Bi@C Microspheres\nas Competitive Wide Temperature-Operating Anodes for Superior Sodium-Ion\nBatteries

Huge\nvolume changes of bismuth (Bi) anode leading to rapid capacity\nhindered its practical application in sodium-ion batteries (SIBs).\nHerein, porous Bi@C (P-Bi@C) microspheres consisting of self-assembled\nBi nanosheets and carbon shells were constructed via a hydrothermal\nmethod combined with a carbothermic reduction. The optimized P-Bi@C-700\n(annealed at 700 °C) demonstrates 359.8 mAh g<sup>–1</sup> after 1500 cycles at 1 A g<sup>–1</sup>. <i>In situ/ex\nsitu</i> characterization and density functional theory calculations\nverified that this P-Bi@C-700 relieves the volume expansion, facilitates\nNa<sup>+</sup>/electron transport, and possesses an alloying-type\nstorage mechanism. Notably, P-Bi@C-700 also achieved 360.8 and 370.3\nmAh g<sup>–1</sup> at 0.05 A g<sup>–1</sup> under 0\nand 60 °C conditions, respectively. Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>//P-Bi@C-700 exhibits a capacity of 359.7\nmAh g<sup>–1</sup> after 260 cycles at 1 A g<sup>–1</sup>. These hierarchical microspheres effectively moderate the volume\nfluctuation, preserving structural reversibility, thereby achieving\nsuperior Na<sup>+</sup> storage performance. This self-template strategy\nprovides insight into designing high-volumetric capacity alloy-based\nanodes for SIBs.