• A novel ZnO/CoNiO2/CoO/C composite with flower-like morphology was synthesized via a cost-effective hydrothermal method and annealing under N2, achieving a high specific capacity of 1435 C·g−1 at 1 A·g−1.
• The composite exhibits excellent rate capability (87.3% retention at 20 A·g−1) and cycling stability (90.5% after 3000 cycles), attributed to synergistic effects of ZnO, CoNiO2, CoO, and carbon.
• An aqueous hybrid supercapacitor device (ZnO/CoNiO2/CoO/C/NF//AC) delivers a high specific energy of 55.9 W·h·kg−1 at 850 W·kg−1, demonstrating practical applicability.
• The oxidation-defect annealing environment is crucial for controlling morphology and composition, offering a promising strategy for preparing mixed metal oxide composites for energy storage.