Novel Preoxidation-Assisted Mechanism to Preciously Form and Disperse Bi₂O₃ Nanodots in Carbon Nanofibers for Ultralong-Life and High-Rate Sodium Storage

Metal oxides, as promising electrode materials for sodium-ion batteries, usually need to be formed by exposure to oxygen, which usually thermally corrodes the carbon material with which they are compounded, reducing their flexibility and electrical conductivity. Herein, we present for the first time a preoxidation-assisted mechanism to prepare bismuth oxide and carbon nanofibers (Bi2O3@C-NFs) by electrospinning, using Bi2S3 nanorods as multifunctional templates. The bismuth could be oxidized by C═O bonds formed through the cyclization reaction in the high-temperature calcination process, effectively avoiding thermal corrosion of carbon in oxygen atmosphere at high temperature. More importantly, the uniformly distributed Bi2O3 nanodots and longitudinal tunnels are formed inside the S- and N-doped carbon nanofibers with the continuous diffusion of Bi generated from the decomposition of Bi2S3 nanorods and the conversion to Bi─O bonds with C═O bonds being broken. Benefiting from the structural and composition merits arising from preoxidation, Bi2O3@C-NFs self-supporting anodes show high specific capacity (439 mAh g-1 at 0.05 A g-1), superior rate performance (243 mAh g-1 at a current density of 20 A g-1), and outstanding cycling stability (211 mAh g-1 after 2000 cycles at 5 A g-1). The effective combination of the well-established electrospinning technology and the preoxidation assisted mechanism provides a new way for the preparation of metal oxide and carbon composites.