To provide a plate-like nickel-containing oxyhydroxide suitable as a positive electrode active material for a primary battery, having high filling property and giving a high-capacity battery, and a method for producing the same.

The plate-like nickel-containing oxyhydroxide is obtained as follows: a nickel-containing hydroxide represented by general formula: NiM(OH)2, an alkali metal hydroxide and water, or the nickel-containing hydroxide, an alkali metal hydroxide, an inorganic chloride and water are mixed; the resultant mixture is melted by heating, held at 100-180°C for ≥3 h and cooled; the resultant solid is brought into contact with water to obtain a plate-like nickel-containing hydroxide; slurry of the plate-like nickel-containing hydroxide having slurry concentration of 50-1,000 g/L is formed; and an aqueous solution containing sodium hypochlorite or calcium hypochlorite in an amount corresponding to 1.2-2.5 times the chemical equivalent required to oxidize the divalent nickel in the plate-like nickel-containing hydroxide to trivalent nickel is added to the slurry.

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