From amorphous to crystalline: a universal strategy for structure regulation of high-entropy transition metal oxides.

High-entropy materials (HEMs) exhibit extensive application potential owing to their unique structural characteristics. Structure regulation is an effective strategy for enhancing material performance. However, the fabrication of HEMs by integrating five metal elements into a single crystalline phase remains a grand challenge, not to mention their structure regulation. Herein, an amorphous-to-crystalline transformation route is proposed to simultaneously achieve the synthesis and structure regulation of high-entropy metal oxides (HEMOs). Through a facile hydrothermal technique, five metal sources are uniformly integrated into amorphous carbon spheres, which are transformed to crystalline HEMOs after calcination. Importantly, by controlling ion diffusion and oxidation rates, HEMOs with different structures can be controllably achieved. As an example, HEMO of the five first-row transition metals CrMnFeCoNiO is synthesized through the amorphous-to-crystalline transformation route, and structure regulation from solid spheres to core-shell spheres, and then to hollow spheres, is successfully realized. Among the structures, the core-shell CrMnFeCoNiO exhibits enhanced lithium storage performance due to the component and structural advantages. Our work expands the synthesis methods for HEMs and provides a rational route for structure regulation, which brings them great potential as high-performance materials in energy storage and conversion.