Currently, metal–organic frameworks (MOFs) have been attracting great interest as a new kind of electrode material for energy storage devices, because their porous skeleton would benefit the access and transport of electrolytes, and the exposure of metal ions can offer more active sites to electrolytes. In this study, we have successfully fabricated nickel metal–organic framework/carbon nanotube (Ni-MOF/CNT) composites, which show excellent electrochemical performance due to the synergistic effects of the Ni-MOF specific structure and CNTs with high conductivity, achieving a high specific capacitance of 1765 F g⁻¹ at a current density of 0.5 A g⁻¹. To further explore the capacitive performance of the composite electrode, an asymmetric supercapacitor device using Ni-MOF/CNTs as the positive electrode and reduced graphene oxide/graphitic carbon nitride (rGO/g-C₃N₄) as the negative electrode was fabricated, and this device could be operated in a working voltage range of 0–1.6 V based on a complementary potential window in 6 M KOH aqueous electrolyte, delivering a high energy density of 36.6 W h kg⁻¹ at a power density of 480 W kg⁻¹. Moreover, this asymmetric supercapacitor revealed an excellent cycle life along with 95% specific capacitance retention after 5000 consecutive charge–discharge tests. These outstanding performances would make MOFs become one of the most promising candidates for the future high energy storage systems.