The Zn(solvents)$_x^{2+}$, with high desolvation energy barriers, leads to the formation of H$^+$ and partial desolvated Zn$^{2+}$ simultaneously intercalated into the MnO$_2$ cathode. A single-atom Ni catalyst on nitrogen-doped carbon (SANi-NC) is introduced to achieve stepwise atom-level catalytic desolvation of Zn(H2O)$_x^{2+}$, which enables more insertion of Zn$^{2+}$, thereby achieving high-performance Zn–MnO$_2$ batteries.