Active material excelling in high-voltage characteristics

1. An active material having a lamellar rock-salt structure comprising a superficial layer including the outermost surface of the active material,

wherein the outermost surface is a high manganese portion;

the active material present in a location other than where the high manganese portion exists is expressed by a general formula, Li a Ni b Co c Mn d D e O f (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0≤“e”<1, “D” is at least one element selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1);

the high manganese portion is made of a metallic oxide including Ni, Co and Mn at least and of which the composition ratio between Ni, Co and Mn is expressed by Ni:Co:Mn =b2:c2:d2 (where “b2”+“c2”+“d2”=1,0<“b2”<1, 0<“c2”<“c”, and “d”<“d2”<1); and

a layer of the high manganese portion having a thickness “s 1 ” (nm) falling in such a range as 0<“s 1 ”<20, wherein, if the active material exhibits a concentration gradient over the entire region from the center to the surface, the high manganese portion is excluded from the concentration gradient.

2. A production process for the active material or lithium composite metallic oxide as set forth in claim 1 , the production process comprising any of following Treatments 1 through 4 carried out to a material having a lamellar rock-salt structure, and expressed by a general formula, Li a Ni b Co c Mn d D e O f (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0 ≤“e”<1, “D” is at least one element selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1):

(Treatment 1) comprising the steps of:

1-1) readying an acidic metallic salt aqueous solution;

1-2) mixing the metallic salt aqueous solution with a material expressed by the aforementioned general formula;

1-3) mixing a liquid obtained at said step 1-2) with an ammonium-phosphate salt aqueous solution; and

1-4) isolating the aforementioned material from another liquid obtained at said step 1-3);

(Treatment 2) comprising the steps of:

2-1) readying an ammonium-phosphate salt aqueous solution;

2-2) mixing the ammonium-phosphate salt aqueous solution with a material expressed by the aforementioned general formula;

2-3) mixing a liquid obtained at said step 2-2) with an acidic metallic salt aqueous solution; and

2-4) isolating the aforementioned material from another liquid obtained at said step 2-3);

(Treatment 3) comprising the steps of:

3-1) readying an aqueous solution of an ammonium-phosphate salt, or an aqueous solution of a metallic salt and an ammonium-phosphate salt;

3-2) mixing the aqueous solution with a material expressed by the aforementioned general formula; and

3-3) isolating the aforementioned material from a liquid obtained at said step 3-2); or (Treatment 4) comprising the steps of:

4-1) readying an acidic metallic salt aqueous solution, and an ammonium-phosphate salt aqueous solution, respectively;

4-2) mixing water with a material expressed by the aforementioned general formula;

4-3) mixing a liquid obtained at said step 4-2), said acidic metallic salt aqueous solution, and said ammonium-phosphate salt aqueous solution one another; and

4-4) isolating the aforementioned material from another liquid obtained at said step 4-3).

3. A lithium-ion secondary battery comprising the active material as set forth in claim 1 .

4. The active material according to claim 1 , wherein a first superlattice-structure portion exists in the superficial layer, the first superlattice-structure portion exhibiting a seven-set averaged value “n” of intensity ratios being less than 0.9 when the intensity ratios are computed in seven sets by dividing a minimum value of three continuous integrated intensities of an image, which is obtained by observing identical 3b sites in said lamellar rock-salt structure from a <1-100> orientation with a high-angle scattering annular dark-field scanning transmission electron microscope, by a maximum value of the three continuous integrated intensities.

5. The active material according to claim 1 , wherein the lamellar rock-salt crystal structure comprises a heterogeneous stain η c , in the crystalline c-axis direction and a heterogeneous strain η in the all-round direction.

6. An active material having a lamellar rock-salt structure, and expressed by a general formula, Li a Ni b Co c Mn d D e O f (where 0.2≤“a”≤1, “b”+“c”+“d”+“e”=1, 0 ≤“e”<1, “D” is at least one element selected from the group consisting of Li, Fe, Cr, Cu, Zn, Ca, Mg, Zr, S, Si, Na, K and Al, and 1.7≤“f”≤2.1); and

the active material comprising a first superlattice-structure portion in an active-material superficial layer thereof, the first superlattice-structure portion exhibiting a seven-set averaged value “n” of intensity ratios being less than 0.9 when the intensity ratios are computed in seven sets by dividing a minimum value of three continuous integrated intensities of an image, which is obtained by observing identical 3b sites in said lamellar rock-salt structure from a <1-100>orientation with a high-angle scattering annular dark-field scanning transmission electron microscope, by a maximum value of the three continuous integrated intensities.