Antimony is one of the most promising high-rate-capability Na- and Li-ion conversion electrode materials, demonstrating extraordinarily high rates of lithiation and sodiation. For example, small isotropic antimony nanocrystals have exhibited stable, reversible, long-term cycling at charge/discharge rates as fast as 20C without significant capacity loss. Herein, we investigate the effect of structural anisotropy on the sodiation of high-capacity, high-power density antimony electrodes fabricated from an engineered set of highly anisotropic, nanostructured antimony electrode materials produced via a supercritical fluid-based synthesis. By controlling reaction conditions, precursor concentration, and ligand choice, the synthesis can be tailored to produce an array of nanostructured antimony electrode materials with a variety of morphologies including platelets, truncated octahedra, and dendritic microstructures. In addition to analyzing the growth processes that promote the supercritical fluid-based synthesis of these anisotropic antimony nanostructures, we discuss how this morphological selectivity can be used to evaluate the effects of structural anisotropy on sodiation and desodiation, and how oxidation and temperature influence the electrochemical alloying process. We hope that a better understanding of the transformations that take place during the high-rate electrochemical alloying of nanostructured antimony will enable the structural optimization of high-rate-capability antimony-based conversion electrodes.