Coated Nickel Hydroxide Powder for Positive Electrode Active Material of Alkaline Secondary Battery, and Production Method Therefor

Abstract

The pH of a suspension of a nickel hydroxide powder is kept at 8 to 11.5, and an aqueous cobalt salt solution and an aqueous alkali, solution are supplied to the suspension while the ratio of the supply rate ρ of the aqueous cobalt salt solution to the product of the supply width d of the aqueous cobalt salt solution in a direction orthogonal to the flow direction of the suspension and the flow velocity v of the suspension in a contact portion between the suspension and the aqueous cobalt salt solution, that is, ρ/(d×v) is controlled to be 3.8×10−4 mol/cm2 or less to coat the surface of nickel hydroxide particles with cobalt hydroxide. Then, the pH of a slurry of the cobalt-hydroxide-coated nickel hydroxide powder is adjusted to 12.5 or higher, and oxygen is supplied to the slurry so that the total amount of oxygen supplied per mole of cobalt in the coating is 30 l/mol or more to oxidize cobalt hydroxide.

1 - 6 . (canceled) 
     
     
         7 . A coated nickel hydroxide powder for a positive electrode active material of alkaline secondary battery comprising nickel hydroxide powder particles whose surface is coated with a cobalt compound mainly containing cobalt oxyhydroxide or a mixture of cobalt oxyhydroxide and cobalt hydroxide,
 wherein the coated nickel hydroxide powder is produced by a method comprising: a coating step in which an aqueous cobalt salt solution and an aqueous alkali solution are supplied to a stirred suspension obtained by dispersing a nickel hydroxide powder in water to form, on a surface of nickel hydroxide particles, a coating mainly containing cobalt hydroxide crystallized out by neutralization; and an oxidation step in which oxygen is supplied to a stirred slurry of the nickel hydroxide particles having the coating formed thereon to oxidize cobalt hydroxide in the coating,   wherein a valence of cobalt in the coating is 2.5 or more and an amount of cobalt contained in the coating is 90 mass % or more with respect to a total mass of metal elements contained in the coating,   and wherein when 20 g of the coated nickel hydroxide powder is shaken in a closed container for 1 hour, an amount of the coating peeled off is 20 mass % or less of a total mass of the coating.   
     
     
         8 . The coated nickel hydroxide powder for a positive electrode active material of alkaline secondary battery according to  claim 7 , wherein an upper limit of the valence of cobalt in the coating is 3.