Provided are a positive electrode active material that can provide a nonaqueous electrolyte secondary battery having high energy density and excellent output characteristics, a nickel-manganese composite hydroxide as a precursor thereof, and methods for producing these. A nickel-manganese composite hydroxide is represented by General Formula (1): Ni.sub.xMn.sub.yM.sub.z(OH).sub.2+α and contains a secondary particle formed of a plurality of flocculated primary particles. The nickel-manganese composite hydroxide has a half width of a diffraction peak of a (001) plane of at least 0.35° and up to 0.50° and has a degree of sparsity/density represented by [(a void area within the secondary particle/a cross section of the secondary particle)×100](%) within a range of greater than 10% and up to 25%.

Provided are a positive electrode active material that can provide a nonaqueous electrolyte secondary battery having high energy density and excellent output characteristics, a nickel-manganese composite hydroxide as a precursor thereof, and methods for producing these. A nickel-manganese composite hydroxide is represented by General Formula (1): Ni.sub.xMn.sub.yM.sub.z(OH).sub.2+α and contains a secondary particle formed of a plurality of flocculated primary particles. The nickel-manganese composite hydroxide has a half width of a diffraction peak of a (001) plane of at least 0.35° and up to 0.50° and has a degree of sparsity/density represented by [(a void area within the secondary particle/a cross section of the secondary particle)×100](%) within a range of greater than 10% and up to 25%.

A positive active material for a rechargeable lithium battery includes a first positive active material including a secondary particle including at least two agglomerated primary particles, where at least one part of the primary particles has a radial arrangement structure, as well as a second positive active material having a monolith structure, wherein the first and second positive active materials may each include nickel-based positive active materials and the surface of the second positive active material is coated with a boron-containing compound. Further embodiments provide a method of preparing the positive active material, and a rechargeable lithium battery including a positive electrode including the positive active material.

Disclosed is a cathode active material for secondary batteries comprising at least one compound selected from the following formula 1:
(1−s−t)[Li(Li.sub.aMn.sub.(1−a−x−y)Ni.sub.xCo.sub.y)O.sub.2]*s[Li.sub.2CO.sub.3]*t[LiOH]  (1)
wherein 0<a<0.2, 0<x<0.9, 0<y<0.5, a+x+y<1, 0<s<0.03, and 0<t<0.03; and a, x and y represent a molar ratio, and a and t represent a weight ratio. The cathode active material has long lifespan at room temperature and high temperatures and provides superior stability, although charge and discharge are repeated at a high current.

A battery 2 includes an outer can 10 and an electrode group 22 that is housed in the outer can 10 together with an alkaline electrolytic solution, in which a positive electrode 24 included in the electrode group 22 includes a positive electrode substrate and a positive electrode mixture supported on the positive electrode substrate, the positive electrode mixture includes nickel hydroxide and a positive electrode additive, the positive electrode additive includes a titanium oxide particle having an anatase-type crystal structure, the titanium oxide particle has an average primary particle size of 5 nm or more and 10 nm or less and a BET specific surface area of 230 m.sup.2/g or more and 360 m.sup.2/g or less, and includes 0.1% by mass or more of niobium, and a rate of addition of the titanium oxide relative to the nickel hydroxide is 0.1% by mass or more and 1.0% by mass or less.

A process for producing nickel particles comprises the steps of: melting a nickel source to produce a melt; and powderizing molten nickel contained in the melt by an atomization method comprising atomizing a gas or an aqueous medium onto the melt, thereby producing nickel particles having purity of 90% or more. In the production process, it is also possible to melt a metal that is more likely to be oxidized than nickel together with the nickel source and then remove an oxide of the metal which is produced as the result of the melting.

A process for producing nickel particles comprises the steps of: melting a nickel source to produce a melt; and powderizing molten nickel contained in the melt by an atomization method comprising atomizing a gas or an aqueous medium onto the melt, thereby producing nickel particles having purity of 90% or more. In the production process, it is also possible to melt a metal that is more likely to be oxidized than nickel together with the nickel source and then remove an oxide of the metal which is produced as the result of the melting.

Disclosed is a cathode active material for secondary batteries comprising one or more compounds having a layered-crystal structure, represented by the following Formula 1, wherein a transition metal layer contains Li, in an amount lower than 20%, based on a total amount of a transition metal site, and a ratio of Ni positioned in a lithium layer, that is, a cation mixing ratio is 1% to 4.5%, based on a total amount of a lithium site in the lithium layer to stably support the layered-crystal structure: (1-s-t)[Li(Li.sub.aMn.sub.(1-a-x-y)Ni.sub.xCo.sub.y)O.sub.2]*s[Li.sub.2CO.sub.3]*t[LiOH] (1), wherein 0<a<0.2; 0<x<0.9; 0<y<0.5; a+x+y<1; 0<s<0.03; and 0<t<0.03. The cathode active material exhibits long lifespan and superior stability at room temperature and high temperatures in spite of repeated charge and discharge at a high current.

A process for producing a metal oxide powder proceeds by spray pyrolysis, in which a mixture comprising ammonia and an aerosol which is obtained by atomizing a solution containing a metal compound by means of an atomization gas is introduced into a high-temperature zone of a reaction space and reacted in an oxygen-containing atmosphere therein and the solids are subsequently separated off.

A process for producing a metal oxide powder proceeds by spray pyrolysis, in which a mixture comprising ammonia and an aerosol which is obtained by atomizing a solution containing a metal compound by means of an atomization gas is introduced into a high-temperature zone of a reaction space and reacted in an oxygen-containing atmosphere therein and the solids are subsequently separated off.