Nickel-cobalt selenide as high-performance and long-life electrode material for supercapacitor

In this work, a series of Ni_xCo_1-xSe₂ selenides are prepared with x ranging from 0 to 1 and investigated as electrode materials for supercapacitor. The sample Ni_0.6Co_0.4Se₂ shows 1580 and 1205 F g^-1 at 1 and 20 A g^-1, respectively. At 10 A g^-1, 90% capacitance retention is sustained after 20,000 cycles. A Ni_0.6Co_0.4Se₂-based asymmetric supercapacitor (ASC) is assembled and exhibits energy density of 44.1 and 36.8 Wh kg^-1 at power density of 691.3 and 15070.6 W kg^-1 and long stability. Systematic physicochemical/electrochemical analysis reveals that the high active MOOH (M = Ni, Co)/Ni_0.6Co_0.4Se₂ phases generated by electrooxidation act as the actual active materials during the charge storage/release process. The collective effects of large ion-accessible active area, high conductivity and electrochemically active MOOH (M = Ni, Co)/Ni_0.6Co_0.4Se₂ phases convincingly account for the remarkable performance, especially the excellent rate capability and stability.