Anode active materials, high tap-density ZnO microspheres, with enhanced volumetric capacity and improved cycling performance for nickel-zinc rechargeable batteries have been synthesized via a novel complexing co-precipitation method. The physical and electrochemical properties of the obtained ZnO microsphere are investigated. Notably, tap-density of the resultant ZnO microspheres can reach 3.00 g cm-3, three times higher than the commercial conventional ZnO. Compared with the conventional ZnO, the obtained ZnO microspheres have demonstrated superior electrochemical properties, including higher volume specific capacity, improved high-rate ability, and better cyclic stability. At rates of 0.2C and 2C, the obtained ZnO microspheres deliver volumetric capacities of ∼1450 and ∼1110 mAh cm-3, respectively, which are about three times higher than those of the conventional ZnO. These performance improvements are attributed to its unique more dense spherical microstructure, thus leading to better reaction reversibility, excellent anti-corrosion ability, lower charge transfer resistance and better inhibiting effect on shape change of the material. Owing to its facile synthesis and outstanding electrochemical properties, this high-density spherical ZnO sample is a promising anode material for fabricating high performance Ni-Zn secondary batteries.