A positive electrode active material for a nonaqueous electrolyte secondary battery includes particles of a lithium-transition metal composite oxide that contains nickel in the composition thereof and has a layered structure. The particles have an average particle size D.sub.SEM based on electron microscopic observation in a range of 1 μm to 7 μm in which a ratio D.sub.50/D.sub.SEM of a 50% particle size D.sub.50 in volume-based cumulative particle size distribution to the average particle size based on electron microscopic observation is in a range of 1 to 4, and a ratio D.sub.90/D.sub.10 of a 90% particle size D.sub.90 to a 10% particle size D.sub.10 in volume-based cumulative particle size distribution is 4 or less.

A positive electrode active material precursor for a lithium secondary battery, in which the following requirements (1) and (2) are satisfied.

Requirement (1): In powder X-ray diffraction measurement using a CuKα ray, α/β that is a ratio of an integrated intensity α of a peak present within a range of a diffraction angle 2θ=19.2±1° to an integrated intensity β of a peak present within a range of a diffraction angle 2θ=33.5±1° is 3.0 or more and 5.8 or less.

Requirement (2): A 10% cumulative volume particle size D.sub.10 obtained from particle size distribution measurement is 2 μm 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 method of producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the method includes preparing nickel-containing composite oxide particles having a ratio .sup.1D.sub.90/.sup.1D.sub.10 of a 90% particle size .sup.1D.sub.90 to a 10% particle size .sup.1D.sub.10 in volume-based cumulative particle size distribution is 3 or less; mixing the composite oxide particles and a lithium compound to obtain a first mixture; subjecting the first mixture to a first heat treatment at a first temperature and a second heat treatment at a second temperature higher than the first temperature to obtain a first heat-treated product; and subjecting the first heat-treated material to a dispersion treatment.

A positive electrode active material that has high capacity and excellent charge and discharge cycle performance for a secondary battery is provided. A positive electrode active material that inhibits a decrease in capacity in charge and discharge cycles is provided. A high-capacity secondary battery is provided. A secondary battery with excellent charge and discharge characteristics is provided. A highly safe or reliable secondary battery is provided. A positive electrode active material contains lithium, cobalt, oxygen, and aluminum and has a crystal structure belonging to a space group R-3m when Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction. In analysis by X-ray photoelectron spectroscopy, the number of aluminum atoms is less than or equal to 0.2 times the number of cobalt atoms.

A lithium deficient cathode active material for lithium-ion batteries is described. More particularly, the lithium deficient cathode active material can have multiphase structures, including both a layered or hexagonal structure (e.g., having an R-3m space group) and a spinel structure (e.g., having a .sub.Fd-m space group). Batteries including the cathode active material and methods of preparing the cathode active material are also described.

A process for preparing a metal oxide-containing powder that comprises conducting spray pyrolysis that comprises aerosolizing a slurry that comprises solidphase particles in a liquid that comprises at least one precursor compound, which comprises one or more metallic elements of at least one metal oxide, to form droplets of said slurry, and calcining the droplets to at least partially decompose the at least one precursor compound and form the metal oxide-containing powder having a non-hollow morphology.

Lithium metal oxides may be regenerated under ambient conditions from materials recovered from partially or fully depleted lithium-ion batteries. Recovered lithium and metal materials may be reduced to nanoparticles and recombined to produce regenerated lithium metal oxides. The regenerated lithium metal oxides may be used to produce rechargeable lithium ion batteries.

A cathode active material contains a compound having a crystal structure of space group FM-3M, represented by composition formula (1), and having a half-width in 2δ of 0.9° or more and 2.4° or less for a (200) diffraction peak in powder X-ray diffraction (XRD): Li.sub.xMe.sub.yO.sub.2. . . (1). In the formula, Me represents one or two or more elements selected from the group consisting of Mn, Nb, Ti, Ni, Co, Fe, Sn, Cu, Mo, Bi, V, and Cr. In addition to this, the following conditions are met: 0.5≦x/y≦3.0; and 1.5≦x+y≦2.3.

The present invention relates to a positive electrode active material having improved capacity characteristic and life cycle characteristic, and a method of preparing the same, and specifically, to a positive electrode active material for a lithium secondary battery, wherein the positive electrode active material comprises a compound represented by Formula 1 above and allowing reversible intercalation/deintercalation of lithium, and from a crystal structure analysis of the positive electrode active material by a Rietveld method in which space group R-3m is used in a crystal structure model on the basis of an X-ray diffraction analysis, the thickness of MO slab is 2.1275 Å or less, the thickness of inter slab is 2.59 Å or greater, and the cation mixing ratio between Li and Ni is 0.5% or less, and a method of preparing the same.