Nanoconfinement of Ultrasmall Bismuth in Hard Carbon Enables Ultrahigh-Capacity Sodium-Ion Batteries at Low Temperatures

Alloy-type anodes, particularly bismuth (Bi), are promising for low-temperature sodium-ion batteries (SIBs) due to their high operating potentials and fast Na⁺ transport. However, challenges such as significant volume changes during cycling hinder their performance.

To address this, we preemptively stabilize Bi by exploiting Bi³⁺-induced ionic bridging with xanthan gum to construct a homogeneous precursor network, followed by carbon locking of sub-10 nm Bi nanoparticles within a hard-carbon scaffold. This design reduces particle migration, mitigates alloying-induced pulverization, and preserves critical Bi–C interfacial contact. The resulting Bi@HC anode shows ultrahigh reversible specific capacity of 520 mAh g^–1 at 0.1 A g^–1 and long-term stability.