Positive electrode active substance particles and process for producing the same, and non-aqueous electrolyte secondary battery
The present invention provides positive electrode active substance particles which are improved in charge/discharge capacities, cycle characteristics and thermal stability. The positive electrode active substance particles according to the present invention comprise a compound having at least a crystal system belonging to a space group of R-3m and a crystal system belonging to a space group of C2/m and having a specific peak intensity ratio, in which a content of Mn in the compound is controlled such that a molar ratio of Mn/(Ni+Co+Mn) therein is not less than 0.55; a content of boron in the compound is 0.01 to 1% by weight; a content of fluorine in the compound is 0.01 to 5% by weight; and a content of an element A (at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ca, Fe, Zn, Mo and Bi) in the compound is 0.004 to 9% by weight, and can be produced by calcining a mixture comprising precursor particles comprising Mn and Ni and/or Co, a lithium compound, a boron compound, a fluorine compound and a compound of the element A.
1. A positive electrode active substance particles comprising a compound having at least a crystal system belonging to a space group of R-3m and a crystal system belonging to a space group of C2/m, the compound comprising
a composite oxide comprising at least Li, Mn, and Co and/or Ni, an element A, wherein A is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ca, Fe, Zn, Mo and Bi, boron and fluorine, in which
a molar ratio of Mn to a sum of Ni, Co and Mn [Mn/(Ni+Co+Mn)] therein is not less than 0.56;
a content of the boron in the compound is 0.01 to 1% by weight;
a content of the fluorine in the compound is 0.01 to 5% by weight;
a content of the element A in the compound is 0.004 to 9% by weight; and
a relative intensity ratio [(a)/(b)] of a maximum diffraction peak intensity (a) observed at 2θ=20.8±1° in a powder X-ray diffraction pattern of the positive electrode active substance particles as measured using a Cu-Ka ray to a maximum diffraction peak intensity (b) observed at 2θ=18.6±1° in the powder X-ray diffraction pattern [(a)/(b)] is 0.02 to 0.2,
wherein the positive electrode active substance particles have a molar ratio of Li/(Ni+Co+Mn) of 1.4 to 1.7.
2. The positive electrode active substance particles according to claim 1 , wherein the crystal system belonging to a space group of R-3m includes compounds comprising LiM x Mn 1-x O 2 wherein M is Ni and/or Co; 0<x≦1, and the crystal system belonging to a space group of C2/m includes compounds comprising Li 2 M′ (1-y) Mn y O 3 wherein M′ is Ni and/or Co; 0<y≦1.
3. The positive electrode active substance particles according to claim 1 , wherein the positive electrode active substance particles have a specific surface area of 0.05 to 20 m 2 /g as measured by a BET method.
4. The positive electrode active substance particles according to claim 1 , wherein
the positive electrode active substance particles are in the form of secondary particles produced by aggregating primary particles thereof in which the primary particles have an average primary particle diameter of not more than 5 μm,
the secondary particles have an average secondary particle diameter of 1 to 50 μm, and
the secondary particles have average particle diameters greater than the primary particles.
5. A process for producing the positive electrode active substance particles as defined in claim 1 , comprising any of a step (1) of dry-mixing precursor particles comprising a transition metal, a boron compound, a lithium compound, a fluorine compound and a compound of the element A and then calcining the resulting mixture; a step (2) of wet-mixing a slurry or the like of the precursor particles comprising a transition metal with the boron compound, the fluorine compound and the compound of the element A, drying the obtained wet mixture to obtain dry particles, mixing the dry particles with the lithium compound, and then calcining the resulting mixture; and a step (3) of dry-mixing or wet-mixing the precursor particles comprising a transition metal with the boron compound and the lithium compound, calcining particles of the obtained dry or wet mixture, dry-mixing or wet-mixing the calcined product with the fluorine compound and the compound of the element A, and subjecting particles of the resulting mixture to heat treatment.
6. A non-aqueous electrolyte secondary battery comprising a positive electrode comprising the positive electrode active substance particles as defined in claim 1 .
7. A positive electrode active substance particles comprising a compound having at least a crystal system belonging to a space group of R-3m and a crystal system belonging to a space group of C2/m, the compound comprising
a composite oxide comprising at least Li, Mn, and Co and/or Ni, an element A, wherein A is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ca, Fe, Zn, Mo and Bi, boron and fluorine, in which
a molar ratio of Mn to a sum of Ni, Co and Mn [Mn/(Ni+Co+Mn)] therein is not less than 0.6;
a content of the boron in the compound is 0.01 to 1% by weight;
a content of the fluorine in the compound is 0.01 to 5% by weight;
a content of the element A in the compound is 0.004 to 9% by weight; and
a relative intensity ratio [(a)/(b)] of a maximum diffraction peak intensity (a) observed at 2θ=20.8±1° in a powder X-ray diffraction pattern of the positive electrode active substance particles as measured using a Cu-Ka ray to a maximum diffraction peak intensity (b) observed at 2θ=18.6±1° in the powder X-ray diffraction pattern [(a)/(b)] is 0.02 to 0.2.
8. The positive electrode active substance particles according to claim 7 , wherein the crystal system belonging to a space group of R-3m includes compounds comprising LiM x Mn 1-x O 2 wherein M is Ni and/or Co; 0<x≦1, and the crystal system belonging to a space group of C2/m includes compounds comprising Li 2 M′ (1-y) Mn y O 3 wherein M′ is Ni and/or Co; 0<y≦1.
9. The positive electrode active substance particles according to claim 7 , wherein the positive electrode active substance particles have a molar ratio of Li/(Ni+Co+Mn) of 1.2 to 1.7.
10. The positive electrode active substance particles according to claim 7 , wherein the positive electrode active substance particles have a specific surface area of 2.3 to 20 m 2 /g as measured by a BET method.
11. The positive electrode active substance particles according to claim 7 , wherein the positive electrode active substance particles are in the form of secondary particles produced by aggregating primary particles thereof in which the primary particles have an average primary particle diameter of not more than 5 μm,
the secondary particles have an average secondary particle diameter of 3 to 50 μm, and
the secondary particles have average particle diameters greater than the primary particles.
12. A positive electrode active substance particles comprising a compound having at least a crystal system belonging to a space group of R-3m and a crystal system belonging to a space group of C2/m, the compound comprising
a composite oxide comprising at least Li, Mn, and Co and/or Ni, an element A, wherein A is at least one element selected from the group consisting of Al, Mg, Ti, Zr, Ca, Fe, Zn, Mo and Bi, boron and fluorine, in which
a molar ratio of Mn to a sum of Ni, Co and Mn [Mn/(Ni+Co+Mn)] therein is not less than 0.568;
a content of the boron in the compound is 0.01 to 1% by weight;
a content of the fluorine in the compound is 0.01 to 5% by weight;
a content of the element A in the compound is 0.004 to 9% by weight; and
a relative intensity ratio [(a)/(b)] of a maximum diffraction peak intensity (a) observed at 2θ=20.8±1° in a powder X-ray diffraction pattern of the positive electrode active substance particles as measured using a Cu-Ka ray to a maximum diffraction peak intensity (b) observed at 2θ=18.6±1° in the powder X-ray diffraction pattern [(a)/(b)] is 0.02 to 0.2.
13. The positive electrode active substance particles according to claim 12 , wherein the molar ratio of Mn to a sum of Ni, Co and Mn [Mn/(Ni+Co+Mn)] therein is not less than 0.582.
14. The positive electrode active substance particles according to claim 12 , wherein the crystal system belonging to a space group of R-3m includes compounds comprising LiM x Mn 1-x O 2 wherein M is Ni and/or Co; 0<x≦1, and the crystal system belonging to a space group of C2/m includes compounds comprising Li 2 M′ (1-y) Mn y O 3 wherein M′ is Ni and/or Co; 0<y≦1.
15. The positive electrode active substance particles according to claim 12 , wherein the positive electrode active substance particles have a molar ratio of Li/(Ni+Co+Mn) of 1.2 to 1.7.
16. The positive electrode active substance particles according to claim 12 , wherein the positive electrode active substance particles have a specific surface area of 2.3 to 20 m 2 /g as measured by a BET method.
17. The positive electrode active substance particles according to claim 12 , wherein the positive electrode active substance particles are in the form of secondary particles produced by aggregating primary particles thereof in which the primary particles have an average primary particle diameter of not more than 5 μm,
the secondary particles have an average secondary particle diameter of 3 to 50 μm, and
the secondary particles have average particle diameters greater than the primary particles.