LAUSR

Sb2O3 shows great promise as a high‐capacity anode material for sodium‐ion batteries (SIBs) due to the combined mechanisms of intercalation, conversion, and alloying. In this work, the electrochemical performance and mechanical property of Sb2O3 nanobelts during sodiation/desodiation are revealed by constructing nanoscale solid‐state SIBs in a high‐resolution transmission electron microscopy. It is found that the Sb2O3 nanobelt exhibits an ultrahigh sodiation speed of ≈13.5 nm s−1 and experiences a three‐step sodiation reaction including the intercalation reaction to form NaxSb2O3, the conversion reaction to form Sb, and the alloying reaction to form NaSb. The alloying reaction is found to be reversible, while the conversion reaction is partially reversible. The Sb2O3 nanobelt shows anisotropic expansion and the orientation of the Sb2O3 nanobelt has great influence on the expansion ratio. It is found that the existence of a {010} plane with large d‐spacing in the nanobelt leads to a surprisingly small expansion ratio (≈5%). The morphology of the Sb2O3 nanobelt is well maintained during multiple electrochemical cycles. In situ bending experiments suggest that the sodiated Sb2O3 nanobelts show improved toughness and flexibility compared to pristine Sb2O3 nanobelts. These fundamental studies provide insight into the rational design of anode materials with improved electrochemical and mechanical performance in SIBs.