A Novel Strategy to Fabricate β-Bi ₂ O ₃ @C Core-Shell Nanocomposites for Sodium-Ion Batteries and Surface-Enhanced Raman Scattering

Designing multifunctional materials often relies on stabilizing unconventional phases and tailoring their architectures. In this study, a novel one-step calcination approach using Bi 2 Se 3 as a precursor is developed to stabilize the metastable β-Bi 2 O 3 phase at elevated temperatures, thereby forming a unique core-shell β-Bi 2 O 3 @C nanocomposite architecture. In situ carbon coating through citric acid pyrolysis not only preserves the β-Bi 2 O 3 phase but also enhances its electrical conductivity, a factor essential for electrochemical applications. When tested in a half-cell configuration for Na-ion batteries, the β-Bi 2 O 3 @C electrode exhibits stable cycling performance, retaining 182.6 mAh g –1 (∼70% capacity retention after 125 cycles at 100 mA g –1 ), which is competitive among reported β-Bi 2 O 3 -based anodes under comparable testing conditions. The carbon encapsulating the β-Bi 2 O 3 nanoparticles serves as a mechanical buffer that maintains structural integrity against severe volume expansion, while simultaneously providing continuous electron-transport pathways, thereby ensuring long-term stability. Beyond energy storage, the β-Bi 2 O 3 @C nanocomposite demonstrates outstanding performance as a highly sensitive nonplasmonic surface-enhanced Raman scattering substrate, enabling the detection of Rhodamine-6G molecules down to a concentration of 1.8 nM with an enhancement factor of 2.45 × 10 8 compared to normal Raman scattering. This dual-functional β-Bi 2 O 3 @C material thus provides a controlled-synthesis-based platform for sodium-ion storage and ultrasensitive molecular sensing applications.