ZnO materials of various shapes and sizes were synthesized by a facile hydrothermal method using amine chelates like ethylenediamine (en), diethylenetriamine (dien), and triethylenetetramine (trien) as additives. The synthesized ZnO powders were used in Zn/Ni electrochemical cells to investigate how the size and shape of ZnO can influence the Zn/Ni cell performance. Special attention was given to Zn dendrite growth on the negative electrode, and the cells were constructed as follows: Ni(s) | Zn (OH)4 2- (aq, 0.5 mol in 6 M KOH) | Ni(OH)2(s) | Ni(s). As a result, the largest-sized ZnO active material, made using the dien chelate, had the best cell performance because dien could affect the formation of the Zn dendrite and suppress its growth. However, the other cells with smaller-sized particles could not suppress dendrite growth. Therefore, the reversibility of the redox reaction, particularly the anodic reaction (Zn(s) → Zn2+ (aq)), was inhibited because the large Zn dendrite growth made Zn ion diffusion more difficult, and resulted in poorer performance. Hence, the diffusion rate of Zn ions was slower the larger the Zn dendrite was. The cell using DIEN, ZnO material synthesized with dien, had the highest retention of efficiency, and the best cell performance.