Abstract: A compound having a layered structure that is used for a positive electrode active material for a lithium ion secondary battery achieves both a high energy density and a high cyclability. The positive electrode active material for a lithium ion secondary battery contains a compound having a layered structure belonging to a space group R-3m, in which the compound having a layered structure is represented by a compositional formula: Li1+aM1O2+? wherein M1 represents a metal element or metal elements other than Li, and contains at least Ni, ?0.03?a?0.10, and ?0.1<?<0.1, a proportion of Ni in M1 is larger than 70 atom %, and a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%, and a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less.

Abstract: A positive electrode active material includes a primary particle represented by Compositional Formula (1): Li1+xNiyCozM1?x?y?zO2 ??(1), where x is a number satisfying a relation represented by an expression ?0.12?x?0.2; y is a number satisfying a relation represented by an expression 0.7?y?0.9; z is a number satisfying a relation represented by an expression 0.05?z?0.3; and M is at least one element selected from the group consisting of Mg, Al, Ti, Mn, Zr, Mo, and Nb; or a secondary particle into which the primary particle aggregates. The primary particle or the secondary particle includes a free lithium compound in a weight proportion of 0.1% or more and 2.0% or less, and the weight of lithium hydroxide in the free lithium compound is 60% or less of the weight of lithium carbonate in the free lithium compound.

Abstract: An object of the present invention is to provide lithium ion secondary batteries having cycle characteristics as well as high energy density and rate characteristics during high-potential charging of a layered compound. The following is provided, a positive electrode active material for lithium ion secondary batteries, comprising particles each having: a core part comprising a lithium metal composite oxide; and a surface layer part comprising a lithium metal composite oxide having a composition differing from that in the core part, the surface layer part being formed on the surface of the core part, wherein both the core part and the surface layer part have a layered structure, the surface layer part contains Ni, Mn, and Li, and Ni/Mn mole ratio in the surface is less than 1.

Abstract: The objective of the present invention is to provide a lithium ion secondary battery, the charged state of which can be detected from the battery voltage with high accuracy, and which is able to achieve a high capacity in a high-potential range. This objective can be achieved by a cathode active material for lithium ion secondary batteries, which is composed of a lithium transition metal oxide containing Li and metal elements including at least Ni and Mn, and which is characterized in that: the atomic ratio of Li to the metal elements satisfies 1.15<Lil(metal elements)<1.5; the atomic ratio of Ni to Mn satisfies 0.334<Ni/Mn?1; and the atomic ratio of Ni and Mn to the metal elements satisfies 0.975?(Ni+Mn)/(metal elements)?1.

Abstract: Provided is a method for manufacturing a cathode electrode material, including the step of performing calcination of a mixture of lithium carbonate and a compound containing Ni, and capable of mass-producing a cathode electrode material including a lithium composite oxide with high Ni concentration industrially. The manufacturing method includes a mixture step of mixing lithium carbonate and a compound including Ni, and a calcination step of performing calcination of a mixture obtained in the mixture step under oxidizing atmosphere to obtain a lithium composite compound with high Ni concentration. The calcination step includes: a first heat treatment step to obtain a first precursor; a second heat treatment step of performing heat treatment of the first precursor to obtain a second precursor; and a third heat treatment step of performing heat treatment of the second precursor to obtain the lithium composite compound.

Abstract: A compound having a layered structure that is used for a positive electrode active material for a lithium ion secondary battery achieves both a high energy density and a high cyclability. The positive electrode active material for a lithium ion secondary battery contains a compound having a layered structure belonging to a space group R-3m, in which the compound having a layered structure is represented by a compositional formula: Li1+aM1O2+?wherein M1 represents a metal element or metal elements other than Li, and contains at least Ni, ?0.03?a?0.10, and ?0.1<?<0.1, a proportion of Ni in M1 is larger than 70 atom %, and a site occupancy of a transition metal or transition metals at a 3a site obtained by structural analysis by a Rietveld method is less than 2%, and a content of residual lithium hydroxide in the positive electrode active material is 1 mass % or less.

Abstract: A positive electrode active material includes a primary particle represented by Compositional Formula (1): Li1+xNiyCozM1?x?y?zO2 (1), where x is a number satisfying a relation represented by an expression ?0.12?x?0.2; y is a number satisfying a relation represented by an expression 0.7?y?0.9; z is a number satisfying a relation represented by an expression 0.05?z?0.3; and M is at least one element selected from the group consisting of Mg, Al, Ti, Mn, Zr, Mo, and Nb; or a secondary particle into which the primary particle aggregates. The primary particle or the secondary particle includes a free lithium compound in a weight proportion of 0.1% or more and 2.0% or less, and the weight of lithium hydroxide in the free lithium compound is 60% or less of the weight of lithium carbonate in the free lithium compound.