Urchin‐Like CoSe2 as a High‐Performance Anode Material for Sodium‐Ion Batteries

Urchin‐like CoSe 2 assembled by nanorods has been synthesized via simple solvothermal route and has been first applied as an anode material for sodium‐ion batteries (SIBs) with ether‐based electrolytes. The CoSe 2 delivers excellent sodiation and desodiation properties when using 1 m NaCF 3 SO 3 in diethyleneglycol dimethylether as an electrolyte and cycling between 0.5 and 3.0 V. A high discharge capacity of 0.410 Ah g −1 is obtained at 1 A g −1 after 1800 cycles, corresponding to a capacity retention of 98.6% calculated from the 30th cycle. Even at an ultrahigh rate of 50 A g −1 , the capacity still maintains 0.097 Ah g −1 . The reaction mechanism of the as‐prepared CoSe 2 is also investigated. The results demonstrate that at discharged 1.56 V, insertion reaction occurs, while two conversion reactions take place at the second and third plateaus around 0.98 and 0.65 V. During the charge process, Co first reacts with Na 2 Se to form Na x CoSe 2 and then turns back to CoSe 2 . In addition to Na/CoSe 2 half cells, Na 3 V 2 (PO 4 ) 3 /CoSe 2 full cell with excessive amount of Na 3 V 2 (PO 4 ) 3 has been studied. The full cell exhibits a reversible capacity of 0.380 Ah g −1 . This work definitely enriches the possibilities for anode materials for SIBs with high performance.