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 ).