Hollow-shell structured porous CoSe2 microspheres encapsulated by MXene nanosheets for advanced lithium storage

Cobalt diselenide (CoSe2), a representative transition-metal chalcogenide (TMC), is attracting intensive interest as an anode material for lithium ion batteries (LIBs), in view of its high specific capacity based on the conversion reaction mechanism. However, the huge volume variation and low intrinsic electrical conductivity during the charge/discharge process lead to inferior rate performance and short cycle life of the CoSe2 electrode, which severely hinder its practical application. Herein, novel hollow-shell structured porous CoSe2 microspheres are constructed by selenization of Co-MOFs based on the Kirkendall effect. Furthermore, CoSe2@MXene robust structures, comprised of inner hollow CoSe2 microspheres and an outer MXene flake coating, are fabricated by a facile electrostatic self-assembly method. The as-obtained CoSe2@MXene hybrids possess the combined advantages of the high capacity of CoSe2 hollow spheres and high conductivity of MXene flakes. More importantly, strong chemical interactions (Co–O–Ti covalent bonds) between CoSe2 and oxygen functionalized Ti3C2 MXene are formed at the interface, which could boost the electron/ion transport kinetics and enhance the structural durability of CoSe2@MXene hybrids, resulting in the improvement of rate performance and cycling stability. Consequently, as anode materials for LIBs, the CoSe2@MXene hybrids deliver an admirable reversible capacity of 1051 mA h g−1 at 200 mA g−1, a superior rate capability of 465 mA h g−1 at 5 A g−1, and excellent long-term cycling properties at 1 A g−1 with a capacity of 1279 mA h g−1 after 1000 cycles. The hollow-shell structured porous materials coated by the MXene strategy provide an effective route for designing new anode materials with excellent electrochemical properties.