Mixed Cu2Se Hexagonal Nanosheets@Co3Se4 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, Cu2Se hexagonal nanosheets@Co3Se4 nanospheres mixed structures have been fabricated by a facile two‐step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu2Se and the remarkable cycling stability of Co3Se4, Cu2Se@Co3Se4 can exhibit outstanding electrochemical performance as a novel electrode material. The as‐prepared Cu2Se@Co3Se4 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 Cu2Se@Co3Se4 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). [ABSTRACT FROM AUTHOR]