The development of cathode materials is an effective way to improve the electrochemical performance of zinc-ion batteries (ZIBs). Herein, Ni²⁺-doped MnO₂/graphene nanocomposites (denoted as NMO/rGO) are synthesized by hydrothermal and mechanical ball milling methods as cathode materials for ZIBs. The NMO/rGO electrode shows a super capacity, excellent rate performance, and good cycling stability. The specific discharge capacity can reach 431.5 mAh g⁻¹ at 0.1 A g⁻¹. Moreover, the specific capacity retention rate is 56% after 2200 cycles at 2 A g⁻¹. The excellent electrochemical performance is attributed on the one hand to the stable insertion of Ni²⁺, which affects the MnO bond and weakens the electrostatic interaction between MnO₂ and Zn²⁺ and on the other hand, the strong interaction (MnOC bond) is formed between NMO and rGO through ball milling, which improves the electrical conductivity and mitigates the volume expansion. Notably, mechanical ball milling can also introduce oxygen vacancies for MnO₂, thus increasing the active sites for redox reactions and significantly improving the electrochemical performance of the materials.