<p>High-entropy oxides (HEOs) have emerged as a frontier in electrochemical energy storage, driven by their exceptional compositional tunability and robust crystal frameworks. In this study, spinel (CrMnFeCoNi)₃O₄ nanopowder are prepared by co-precipitation method, especially the effect of different precipitants on the average size of the produced HEOs and then their electrochemical performance are studied in detail. Benefiting from the dual role of Na₂CO₃ as both a structure-directing and in-situ pore-forming agent, the resulting HEO powder exhibits a refined particle size (242&#xa0;nm), thereby significantly boosting its electrochemical activity. The synthesized HEO delivered a specific capacitance of 572&#xa0;F g^− 1 at a current density of 1&#xa0;A g^− 1. Kinetic analysis indicates that dispersal behavior dominated the charge storage process. The assembled HEO//AC asymmetric supercapacitor delivers a wide voltage window of 1.5&#xa0;V, demonstrating a high specific capacitance of 225.2&#xa0;F g^− 1 at 1&#xa0;A g^− 1, along with a capacity retention of 56% after 10,000 cycles at 5&#xa0;A g^− 1. Furthermore, the device yields an energy density of 70.4&#xa0;W h kg^− 1 at a power energy of 751&#xa0;W kg^− 1. This study not only demonstrates the effectiveness of co-precipitation method to synthesize the HEOs, but also confirms the great potential of the produced (CrMnFeCoNi)₃O₄ nanopowders as electrode materials for high–performance supercapacitor.</p>