 A high-performance nickel cathode material HPMo/Ni(OH)2 for the Ni–Zn cell is developed by using phosphomolybdic acid (HPMo) as a structure-directing agent. Its three-dimensional porous flower-like structure makes the active material possess the advantages of high specific surface areas, rich active sites, easy electrolyte accesses, and fast electron transfer. Combined with these advantages, the Ni–Zn cell of HPMo/Ni(OH)2 as the cathode, ZnO as the anode, exhibits a high specific capacity of 277.5 mAh g− 1 (cut off 1.5 V), and even up to 346.9 mAh g− 1 during deep discharge (cut off 0.5 V) at 2.5 A g− 1. When the ZnO/graphene as the anode, the cycle life of HPMo/Ni(OH)2 can extend to 10,000 at 5 A g− 1. Besides, this is the first time that the three-dimensional nickel hydroxide is produced in large quantities with simple preparation process using phosphomolybdic acid as a structure directing agent. This also provides a new synthesis strategy for the self-assembly of 3D nanomaterials, and presents new prospects for the development of more advanced energy storage materials.