Controllable synthesis of Bi@C nanocomposites for high-performance sodium-ion batteries anodes

When metallic bismuth (Bi) is adopted directly as anode materials for sodium-ion batteries (SIBs), severe volumetric variation emerges during the repeated alloying/dealloying redox reactions. Such structural evolution ultimately triggers electrode structural pulverization and rapid capacity fading of the batteries. Herein, Bi-based metal-organic framework (Bi-MOF) precursors were fabricated via a facile solvothermal strategy. Porous Bi@C composites with tunable morphologies were further synthesized by regulating solvent volume ratios and thermal treatment temperatures. On the one hand, MOF-derived nanoporous carbon frameworks construct abundant conductive pathways for ion and electron migration, thereby boosting the comprehensive electrochemical properties of the as-prepared composites. On the other hand, the electrochemically active Bi species are spatially confined and stabilized within the carbon matrix. This confinement effect efficiently alleviates the inherent volumetric expansion of Bi, and accordingly improves the long-term cycling stability of electrode materials. Among all samples, the optimized Bi@C-100:30-800 electrode delivers superior electrochemical performance. It retains a high reversible specific capacity of 443.6 mAh g -1 after 500 long-term cycles at a current density of 500 mA g -1 . Notably, a reversible specific capacity of 416.5 mAh g -1 can still be achieved after 1000 cycles at 1 A g -1 , accompanied by a coulombic efficiency of 99.9%. Such remarkable electrochemical merits endow the material with promising application potential in advanced sodium-ion batteries.