Revealing quasi-1D volume expansion in Na-/K-ion battery anodes: A case study of Sb₂O₃ microbelts

Tailoring a rational structure to control the huge volume variation is practical in regulating alkali-ion battery performance on the basis of the anisotropic properties of crystallized anode materials. Here, a double-serrated orthorhombic antimony oxide (Sb₂O₃) microbelt was prepared by a thermally induced recrystallization/sublimation process. In situ transmission electron microscopy (TEM), in situ X-ray powder diffraction (XRD), and ex situ scanning electron microscopy (SEM) measurements demonstrate that Sb₂O₃ microbelts exhibit a quasi-one-dimensional expansion perpendicular to the belt (along the [100] direction) during sodiation. The unconstrained microbelt surface space can appropriately accommodate the oriented volume variation. Thus, Sb₂O₃ microbelts exhibit enhanced cycling and rate performance in half-cell sodium-ion batteries samples. Via support of reduced graphene oxide (RGO), Sb₂O₃@RGO composites deliver good rate capability (312.3 mAh g⁻¹ at 3 A g⁻¹) for sodium-ion full-cell batteries and good cycling performance (473.9 mAh g⁻¹ at 100 mA g⁻¹ after 100 cycles) for half-cell potassium-ion batteries. In situ Raman measurements reveal that the conversion/alloying-type Sb₂O₃ anode undergoes a fully reversible alloying reaction and partially reversible conversion mechanism, which explains its irreversible capacity during the first cycle. The delicate structural design and clarification of the alkali-ion storage mechanisms facilitate the development of Sb₂O₃ anodes for energy storage applications.