Nickel oxyhydroxide (NiOOH) as the raw positive electrode materials for alkaline Zn-NiOOH batteries was obtained by chemical oxidation of spherical beta-Ni(OH)(2). The effects of preparation conditions on the oxidation state of Ni in products were systematically investigated by changing the KOH concentration, molar ratio of K2S2O8/beta-Ni(OH)(2), oxidation time and temperature. The physical properties, storage stability and electrochemical performance of NiOOH with Ni oxidation state from 2.95 to 3.55 were also studied. The results show that the gamma-NiOOH content, the degree of breakage and the specific surface area of spherical particles increase whereas the beta-NiOOH content, the tap density and the specific discharge capacity decrease as the oxidation state of Ni in NiOOH increases. The NiOOH with Ni oxidation state of 3.55 is pure gamma phase, which contains intercalated K and H2O. In addition, NiOOH with high Ni oxidation state, which includes gamma-NiOOH phase on the powder surfaces, has better storage stability in alkaline electrolyte than pure (beta-NiOOH with Ni oxidation state of about 3. (C) 2007 Published by Elsevier B.V.