A composite cathode active material, a cathode and a lithium battery that include the composite cathode active material, and a method of preparing the composite cathode active material are provided. The composite cathode active material includes: a core including a lithium transition metal oxide; and a shell arranged along a surface of the core, wherein the shell includes at least one first metal oxide represented by M.sub.aO.sub.b (where 0<a≤3, 0<b<4, when a is 1, 2, or 3, b is not an integer); a first carbon-based material; and a second carbon-based material, where the at least one first metal oxide is arranged in a matrix of the first carbon-based material, M is at least one metal selected from among Groups 2 to 13, 15, and 16 of the Periodic Table of Elements, and the second carbon-based material includes fibrous carbon having an aspect ratio of greater than or equal to 10.

A mixed conductor, a method of preparing the same, and a cathode, a lithium-air battery, and an electrochemical device each including the mixed conductor. The mixed conductor is represented by Formula 1 and having electronic conductivity and ionic conductivity:

Li.sub.xMO.sub.2-δ  Formula 1 wherein, in Formula 1, M is a Group 4 element, a Group 5 element, a Group 6 element, a Group 7 element, a Group 8 element, a Group 10 element, a Group 11 element, a Group 12 element, or a combination thereof, and 0<x<1 and 0≤δ≤1 are satisfied.

A mixed conductor represented by Formula 1:
A.sub.4±xTi.sub.5−yG.sub.zO.sub.12−δ  Formula 1 wherein, in Formula 1, A is a monovalent cation, G is at least one of a monovalent cation, a divalent cation, a trivalent cation, a tetravalent cation, a pentavalent cation, or a hexavalent cation, with the proviso that G is not Ti or Cr, wherein 0<x<2, 0.3<y<5, 0<z<5, and 0<δ≤3.

A positive electrode active material for a non-aqueous electrolyte secondary battery is provided. The positive electrode active material includes a layer-structured, nickel-containing lithium transition metal complex oxide. The lithium transition metal complex oxide contains titanium and niobium in a chemical composition thereof, and has a ratio of a total number of moles of titanium and niobium relative to a total number of moles of metals excluding lithium in the chemical composition of 0.04 or less.

Provided is a positive electrode active material for a nonaqueous electrolyte secondary battery including a LiNi composite oxide having low internal resistance and excellent thermal stability. The positive electrode active material is obtained by performing a water washing process using a water spray on a LiNi composite oxide powder obtained by a firing step until the filtrate has an electric conductivity of 30 to 60 mS/cm, and then dried, where the LiNi composite oxide is represented by the composition formula (1): Li.sub.bNi.sub.1-aM1.sub.aO.sub.2, where M1 represents at least one kind of element selected from transition metal elements other than Ni, group 2 elements, and group 13 elements, and 0.01≤a≤0.5, and 0.85≤b≤1.05.

A nickel lithium ion battery positive electrode material having a concentration gradient, and a preparation method therefor. The material is a core-shell material having a concentration gradient, the core material is a material having a high content of nickel, and the shell material is a ternary material having a low content of nickel. The method comprises: synthesizing a material precursor having a high content of nickel by means of co-precipitation, co-precipitating a ternary material solution having a low content of nickel outside the material precursor having a high content of nickel, aging, washing, and drying to form a composite precursor in which the low nickel material coats the high nickel material, adding a lithium source, grinding, mixing, calcining, and cooling to prepare a high nickel lithium ion battery positive electrode material. The obtained material has regular morphology, uniform coating, narrow particle size distribution range, gradient distribution of the concentration of the nickel element, high content of the nickel element in the core, and low content of the nickel element in the shell; the nickel element in the core guarantees the specific capacity of the material, and the shell coating material maintains the stability of the structure of the material, so as to improve the safety of the material in the charge and discharge process, and improve the cycle and rate performance of the material.

The present invention relates to a lithium composite metal oxide which satisfies the requirements (1) and (2) described below. Requirement (1): The ratio of the half width A of the diffraction peak within the range of 2θ=64.5±1° to the half width B of the diffraction peak within the range of 2θ=44.4±1°, namely A/B is from 1.39 to 1.75 (inclusive) in powder X-ray diffractometry using a Cu-Kα ray. Requirement (2): The ratio of the volume-based 90% cumulative particle size (D.sub.90) to the volume-based 10% cumulative particle size (D.sub.10), namely D.sub.90/D.sub.10 is 3 or more.

A lithium metal complex oxide powder satisfies requirements (1) to (3): Requirement (1): Composition Formula (I) is satisfied, Li[Li.sub.x(Ni.sub.(1−y−z−w)Co.sub.yMn.sub.zM.sub.w).sub.1−x]O.sub.2 . . . (I) (where M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, W, B, Mo, Nb, Zn, Sn, Zr, Ga, La, and V, and −0.1≤x≤0.2, 0≤y≤0.4, 0≤z≤0.4, and 0≤w≤0.1 are satisfied). Requirement (2): an average primary particle diameter is 1 μm or more and 7 μm or less. Requirement (3): R1/Ra, which is a ratio of the average primary particle diameter represented by R1 to an average crystallite diameter represented by Ra, is more than 5.0 and 20 or less.

A method for producing a lithium-containing composite oxide, the method including: a first step of preparing a lithium hydroxide; a second step of heating a hydroxide containing nickel and a metal M1 other than lithium and nickel to 300° C. or higher and 800° C. or lower, to obtain a composite oxide containing the nickel and the metal M; a third step of mixing the lithium hydroxide and the composite oxide, to obtain a mixture; a fourth step of compression-molding the mixture, to obtain a molded body; and a fifth step of baking the molded body at 600° C. or higher and 850° C. or lower, to obtain a baked body.

The present invention provides a secondary battery-use active material that allows for an improvement in thermal stability after charge and discharge are repeated. The secondary battery-use active material of the present invention includes a cathode active material that includes (A) a main phase and a sub-phase, (B) the main phase containing a first lithium compound represented by Li.sub.aNi.sub.bM.sub.cAl.sub.dO.sub.e (where M is an element such as cobalt, and 0.8<a<1.2, 0.45≦b≦1, 0≦c≦1, 0≦d≦0.2, 0<e≦1.98, (c+d)>0, and (b+c+d)≦1), and (C) the sub-phase containing a second lithium compound that contains lithium, aluminum, and oxygen as constituent elements.