Zinc-ion batteries (ZIBs) have emerged as promising energy storage devices owing to their intrinsic safety, low cost, and environmental friendliness. However, sluggish ion transport kinetics remain a major challenge limiting their practical application. Herein, porous MnO₂ was synthesized via a self-assembly-assisted hydrothermal process to facilitate ion transport. Electrochemical measurements demonstrate that porous MnO₂ delivers a high specific capacity of 207 mAh g⁻¹ at 0.2 A g⁻¹ after 100 cycles, significantly outperforming Mn₂O₃ (85 mAh g⁻¹) and MnO (28 mAh g⁻¹). Furthermore, the charge–storage mechanism of porous MnO₂ was systematically investigated, revealing that the capacity is predominantly governed by the MnO₂ dissolution/deposition mechanism. This work provides new insights into the rational design of high-performance manganese oxide cathodes for aqueous ZIBs.