Mixed Cu2 Se Hexagonal Nanosheets@Co3 Se4 Nanospheres for High-Performance Asymmetric Supercapacitors.

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu2 Se hexagonal nanosheets@Co3 Se4 nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu2 Se and the remarkable cycling stability of Co3 Se4 , Cu2 Se@Co3 Se4 can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu2 Se@Co3 Se4 electrode displays high specific capacitance of 1005 F g-1 at 1 A g-1 with enhanced rate capability (56 % capacitance retention at 10 A g-1 ), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g-1 ). An asymmetric supercapacitor is assembled applying the Cu2 Se@Co3 Se4 as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg-1 at 0.74 kW kg-1 ), high power density (21.0 Wh kg-1 at 7.50 kW kg-1 ), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g-1 ).