[en] Highlights: • NiO-Co₃O₄ composite was synthesized via a simple hydrothermal process. • The composite showed the microstructure of micro-spheres. • Specific capacitance reached 801 F g⁻¹ at a current density of 1 A g⁻¹. The precursor of NiO-Co₃O₄ composites was synthesized via a simple hydrothermal process. After that, the precursor was calcined at 300 °C for 3 h to obtain the composite powders. The powders calcined at 300 °C showed amorphous, and the powders calcined at 400 °C and 500 °C for comparison showed the composite phase of NiO and Co₃O₄. The composite products showed a microstructure of micro-spheres. For the samples calcined at 300 °C for 3 h, the specific capacitance reached 801 F g⁻¹ at a current density of 1 A g⁻¹.