Highly infiltrative micro-sized Cu2Se as advanced material with excellent rate performance and ultralong cycle-life for sodium ion half/full batteries

Appropriate material is the key to improve the energy and power density of sodium ion batteries. Herein, monoclinic Cu2Se is acquired by a facile one-pot solid method using Cu foil and Se power as the raw materials without use of expensive reagents and sophisticated instruments. Cu2Se exhibits preeminent cycling and rate properties. Concretely, Cu2Se represents reversible capacity of 264 and 241 mAh g−1 at 0.1 and 10 A g−1, as well as high capacity retention of ≈100% over 1000 cycles at 1 A g−1. When Cu2Se is applied as anode to assemble full battery with Na3V2(PO4)2F3@rGO, this battery exhibits a largest energy density of 97 Wh kg−1 (with a power density of 117 W kg−1) and a biggest power density of 1180 W kg−1 (with energy density of 59 Wh kg−1) based on the gross mass of cathode and anode active materials. A combination of ex-situ X-ray diffraction, transition electron microscopy tests and first-principle calculations demonstrate a reversible transformation between Cu2Se and Cu exists in the discharge-charge process. Stable solid-electrolyte interface film, highly infiltrative electrode and capacitive Na + storage behaviours are in favor of the excellent property. The preeminent electrochemical performance indicates that Cu2Se is a highly desirable anode material for high-performance sodium ion batteries.