Mixed Cu 2 Se Hexagonal Nanosheets@Co 3 Se 4 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, Cu 2 Se hexagonal nanosheets@Co 3 Se 4 nanospheres mixed structures have been fabricated by a facile two‐step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu 2 Se and the remarkable cycling stability of Co 3 Se 4 , Cu 2 Se@Co 3 Se 4 can exhibit outstanding electrochemical performance as a novel electrode material. The as‐prepared Cu 2 Se@Co 3 Se 4 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 Cu 2 Se@Co 3 Se 4 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 ).