With increasing demand for energy storage, obtaining aqueous electrolytes that are incombustible, low cost, and conveniently assembled in air with high ionic conductivity has become a dominant focus. Herein, we report the successful synthesis of ultrathin Cu-MOF@δ-MnO₂ nanosheets in a controllable way for 2.0 V aqueous electrolyte-based electrochemical capacitors that involve activated carbon. From electrochemical performance tests, the electrode results in a large increase in the performance of an asymmetric supercapacitor, which involves activated carbon, in an operating voltage window from 0 V to 2.0 V in aqueous electrolyte, with a high specific capacitance of 340 F g⁻¹ at a current density of 1.0 A g⁻¹, and cycling stability for 6000 cycles with only a 5% drop in the initial capacitance. The superior performance during the charging–discharging process is attributed to the existence of a film, which can prevent electronic conduction while allowing ionic conduction.