NiCo2Se4 Hierarchical Microflowers of Nanosheets and Nanorods as Pseudocapacitive Mg-Storage Materials

Rechargeable Mg batteries are principally based on a metallic Mg anode and a Mg-storage cathode. Their high safety and low cost make them suitable for next-generation large-scale energy storage applications; however, suitable cathode materials are relatively rare. Herein, two NiCo2Se4 materials with different morphologies, microflowers consisting of nanosheets and nanorods, are prepared and employed as Mg-storage materials. The NiCo2Se4 nanosheets exhibit a Mg-storage capacity of 145 mA h g(-1) for which the charge/discharge reaction mainly occurs between NiCo2Se4 and metallic Ni-0 and Co-0. The thin nanosheet or nanorod structures enable rapid solid-phase Mg2+ diffusion and surface-related pseudocapacitive behaviors, of which the NiCo2Se4 nanosheets deliver a superior rate performance delivering 40 mA h g(-1) at 2000 mA g(-1). Moreover, such a microflower morphology maintains the material integrity during cycling, and NiCo2Se4 nanosheets exhibit a remarkable cyclability for 1000 cycles. This work develops a novel kind of advanced Mg-storage materials via delicate morphology regulation and highlights a novel pseudocapacitance strategy for effective Mg storage.