Designing unique 3D nanomaterial structures is an important strategy to improve the energy density and cycle life of supercapacitors. Herein, core-shell heterostructures of copper oxide/cobalt nickel hydroxide were successfully designed and synthesized by a simple in situ growth method and ion etching method. In particular, the multi-layered CoNi-LDH nanosheets can expose many redox active sites, and the crisscross CuO can provide ion transport paths to enhance the conductivity. Benefiting from the synergistic effect of shell and core, CuO/CoNi-LDH-4 h (CuO/CN-4) electrode exhibits outstanding specific capacitance of 1990 F g−1 at 1 A g−1 and excellent cycling stability with 91.4 % capacity retention after 5000 cycles at 50 A g−1, superior to CuO/CN-1, CuO /CN-2, CuO/CN-8, and pure CoNi-LDH. Additionally, Imperata cylindrica derived carbon (ICC) also exhibits excellent specific capacitance (363 F g−1 at 1 A g−1) and cycling performance (111 % after 5000 cycles). Finally, the supercapacitor assembled with CuO/CN-4 as cathode and ICC as anode reflects an energy density of 84.6 Wh kg−1 at the power density of 805.3 W Kg−1, and an unexpected cycling performance of 96.6 % after 10,000 cycles. Furthermore, when two devices are connected in series, a timer can work for more than an hour.