The present paper aims at discussing the effect of zinc ions in electrolytes on the cycling stability of nickel oxide electrodes for the zinc/nickel single flow battery. It is shown that the presence of zinc in KOH electrolytes decreases the charging voltage to some extent and inhibits changes in the galvanostatic charging curve vs. cycling number as compared to KOH electrolytes with no zinc present. As a result, the discharge capacity of the electrodes basically does not decay even after 500 charge–discharge cycles. The cycling performance of nickel oxide electrodes is enhanced substantially. It is demonstrated that zinc ions in electrolytes may be incorporated into the lattice structure of nickel hydroxides during the cell cycling, forming a composite where the zinc plays a role as an additive and preventing the formation of γ-phase and overcharge.