3D Ni_χCo_1−χ oxides with different morphologies for high-capacity supercapacitors were controllably synthesized via an electrodeposition method combined with a simple post annealing process. The synthesis involves the co-electrodeposition of the bimetallic (Ni, Co) hydroxide precursor on a nickel foam scaffold and subsequent thermal transformation to Ni_χCo_1−χ oxides. The crystalline structure, morphology and electrochemical performance of the 3D Ni_χCo_1−χ oxides can be readily manipulated by simply varying the Co/Ni molar ratio in the electrodeposition electrolyte. With the increase of the Co/Ni molar ratio, the characteristic peak intensities and the signal sites were gradually changed from a NiO crystal dominant structure to NiCo₂O₄ and finally to a Co₃O₄ dominant structure. Moreover, the morphology also can be controlled by adjusting the Co/Ni molar ratio in the electrodeposition electrolyte. In addition, the Ni_0.61Co_0.39 oxide electrode shows a large specific capacitance of 1523.0 F g⁻¹ at 2 A g⁻¹ and 95.30% of that can be retained, even at a high current density of 30 A g⁻¹. The superior rate capability should be attributed to the unique 3D network-like architecture, which can enlarge the liquid–solid interfacial area, facilitate the electron and ion transport, and further increase the utilization of the active material. To demonstrate its practical application, an asymmetric supercapacitor based on the Ni_0.61Co_0.39 oxide electrode as a positive electrode and activated carbon as a negative electrode was fabricated. Owing to the outstanding capacitive behavior of the Ni_0.61Co_0.39 oxide electrode, the asymmetric device delivers a prominent energy density of 36.46 W h kg⁻¹ at a power density of 142 W kg⁻¹, and which holds great promise for potential applications in energy storage.