Hollow urchin-like NiCo2O4 microspheres (∼3 μm) with a large specific surface area (158.57 m2 g−1) have been synthesized by a facile template-free hydrothermal method and a morphology evolution mechanism of “bundles-solid spheres-hollow urchin-like microspheres” was proposed.

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The urchin-like NiCo 2 O 4 material was prepared by a one-step hydrothermal method. The optimal synthetic conditions were systematically investigated by an orthogonal test method and single factor of hydrothermal time to evaluate the influence of sample morphology and electrochemical performance. The synthesis conditions for preparing NiCo 2 O 4 with different morphologies were systematically studied. In the single factor experiment, when the hydrothermal time is 6, 12, 16, and 24 hours, the corresponding morphologies are urchin-like (NCO-U), flower-like (NCO-F), sheet-like (NCO-S), and block-like (NCO-B), respectively. The element content of the prepared materials under different synthesis conditions was tested by an inductive-coupled plasma emission spectrometer, and an interesting phenomenon was found. As the reaction time