Micro-nano Cu2Se as a stable and ultralong cycle life anode material for sodium-ion batteries

Transition metal selenides have received great attention as promising anode materials for sodium-ion batteries (SIBs). However, it still faces the change of volume and structure, which reduces the rate performance and cycle stability in cycle process. The design of micro-nano hierarchical structure is an important method to improve the structural stability and reaction kinetics in discharge-charge process. In this study, the micro-nano Cu2Se is synthesized using a simple solvothermal and annealing treatment method, and it shows excellent electrochemical performance as anode material for SIBs. It exhibits excellent rate capacity (373.8 mAh g−1 at 0.1 A g−1 and 303.48 mAh g−1 when the current density is increased to 10 A g−1) and cycling stability (250.3 mAh g−1 after 4000 cycles at 5 A g−1, achieving 85.80% for retention rate). In addition, the deep reaction mechanism of Cu2Se has been explored through ex situ XRD and HRTEM.