CoSe2 hollow microspheres, nano-polyhedrons and nanorods as pseudocapacitive Mg-storage materials with fast solid-state Mg2+ diffusion kinetics
Rechargeable Mg battery is an efficient and reliable energy storage technique because of the abundant and dendrite-free metallic Mg anode, but the lack of high-performance cathodes is blocking their development. In this work, CoSe2 with different nanostructures including hollow microspheres (H-CoSe2), nano-polyhedrons (P-CoSe2) and nanorods (R-CoSe2) are fabricated by facile one-step hydrothermal methods, and used as pseudocapacitive electrode for rechargeable Mg batteries. It is observed that R-CoSe2 exhibits the highest reversible capacity of 233 mAh g‒1 at 50 mA g‒1 and an excellent rate capability of 116 mAh g‒1 at 500 mA g‒1, ascribing to the 1D nanorod structure which facilitates the solid-state Mg2+ diffusion. Benefited from the stable hierarchical structure, H-CoSe2 exhibits a superior long-term cycling stability of 350 cycles. Mechanism study indicates the redox reaction reversibly occurs between CoSe2 and metallic Co0. Further investigation demonstrates that the fast solid-state Mg2+ diffusion kinetics and surface-controlled pseudocapacitive behavior enhance the electrochemical performance. This work highlights a novel and efficient Mg-storage strategy of using pseudocapacitive materials, and the performance and solid-state Mg2+ diffusion kinetics of CoSe2 could be optimized by rational structural tailoring.