A Nanosheet Array of Cu₂Se Intercalation Compound with Expanded Interlayer Space for Sodium Ion Storage

Abstract Intercalation chemistry/engineering has been widely investigated in the development of electrochemical energy storage. Graphite, as an old intercalation host, is receiving vigorous attention again via a new halogen intercalation. Whereas, exploiting new intercalation hosts and optimizing the intercalation effect still remains a great challenge. This study fabricates a Cu₂Se intercalation compound showing expanded interlayer space and nanosheet array features by using a green growth approach, in which cetyltrimethyl ammonium bromide (CTAB) is inserted into Cu₂Se at an ambient temperature. When acting as an electrode material for sodium‐ion batteries, the Cu₂Se–CTAB nanosheet arrays exhibit excellent discharge capacity and rate capability (426.0 mAh g⁻¹ at 0.1 A g⁻¹ and 238.1 mAh g⁻¹ at 30 A g⁻¹), as well as high capacity retention of ≈90% at 20 A g⁻¹ after 6500 cycles. Benefiting from the porous array architecture, the transport of electrolytes is facilitated on the surface of Cu₂Se nanosheets. In particular, the CTAB intercalated in the interlayer space of Cu₂Se can increase its buffer space, stabilize the polyselenide shuttle, and prevent the fast growth of Cu nanoparticles during its electrochemical process.