Nickel oxyhydroxides with various oxidation states prepared by chemical oxidation of spherical β-Ni(OH)2

Nickel oxyhydroxide (NiOOH) as the raw positive electrode materials for alkaline Zn–NiOOH batteries was obtained by chemical oxidation of spherical β-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/β-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 γ-NiOOH content, the degree of breakage and the specific surface area of spherical particles increase whereas the β-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 γ phase, which contains intercalated K and H2O. In addition, NiOOH with high Ni oxidation state, which includes γ-NiOOH phase on the powder surfaces, has better storage stability in alkaline electrolyte than pure β-NiOOH with Ni oxidation state of about 3.