Abstract <p>Leveraging the synergistic effects between manganese dioxide (MnO₂) and activated carbon (AC), coupled with the high-gravity process intensification principle, MnO₂ electrode materials with enhanced electrochemical performance exhibit broad application prospects. However, the application effects and enhancement mechanisms of the two processes for preparing MnO₂–AC composites, grinding-based composite, and <i>in situ</i> composite remain unclear under a high-gravity field. This study compared and analyzed these two processes using a rotating packed bed (RPB) to reveal the composite synergistic mechanism of MnO₂ and AC under the special field. The results indicated that <i>δ</i>-MnO₂ particles could be prepared in the high-gravity-grinding composite process. After preparing the grinding-based composite with AC, the interphase forces were weak, and the distribution of MnO₂ was uneven. Nevertheless, the introduction of AC still effectively increased the specific surface area of the MnO₂–AC composite, enhancing its specific capacitance by 24% compared with that of single <i>δ</i>-MnO₂. Conversely, when the high-gravity <i>in situ</i> composite process was employed, owing to the strong bonding between Mn²⁺ and the carboxyl groups on the AC surface, the distribution of MnO₂ was improved, and the interphase contact area increased. The specific capacitance of the prepared material was 17% higher than that of the material prepared by the grinding method. The charge transfer resistance was also significantly reduced, and the cycling stability was further enhanced. Moreover, the as-assembled MnO₂–AC//MnO₂–AC capacitor exhibits a high energy density of 21.9 Wh kg^–1. The high-gravity-<i>in situ</i> composite process established in this study provides a new strategy for developing other AC-based composite electrode materials.</p> Graphical Abstract <p></p>