Lithium composite metal oxide and nonaqueous electrolyte secondary battery

1. A lithium composite metal oxide comprising Li and at least one transition metal element, wherein

at least one lithium composite metal oxide particle constituting the lithium composite metal oxide has both hexagonal and monoclinic crystal structures,

the amount (mol) of Li is 1.4 or more and 1.7 or less based on the total amount (mol) of the transition metal elements,

the monoclinic crystal structure is a crystal structure belonging to the space group C2/m, the hexagonal crystal structure is a crystal structure belonging to the space group R-3m, and

the lithium composite metal oxide comprising Li and at least one transition metal element is a lithium composite metal oxide comprising Li and at least one element selected from Ni, Co, Mn and Fe.

2. A lithium composite metal oxide comprising Li, Ni and M (where, M represents one or more kinds of transition metal elements selected from the group consisting of Mn, Co and Fe), having a diffraction peak (diffraction peak A) at an angle 2θ in a range from 20° to 23° in a powder X-ray diffraction pattern of a lithium composite metal oxide which is obtained by powder X-ray diffraction measurement made in the condition that CuKα is used as a radiation source and the measurement range of the diffraction angle 20θ is in a range from 10° to 90°,

wherein the amount (mol) of Li is 1.4 or more and 1.7 or less based on the total amount (mol) of the transition metal elements, at least one lithium composite metal oxide particle constituting the lithium composite metal oxide has both hexagonal and monoclinic crystal structures, the monoclinic crystal structure is a crystal structure belonging to the space group C2/m, and the hexagonal crystal structure is a crystal structure belonging to the space group R-3m.

3. The lithium composite metal oxide according to claim 2 , wherein the intensity of the diffraction peak A is 3 or more and 10 or less when the diffraction peak (diffraction peak B) having the maximum intensity is set to 100 in said powder X-ray diffraction pattern.

4. The lithium composite metal oxide according to claim 2 , having the hexagonal crystal structure and an a-axis lattice constant in Rietveld analysis of the crystal structure is 2.840 Å or more and 2.851 Å or less.

5. The lithium composite metal oxide according to claim 3 , having the hexagonal crystal structure and an a-axis lattice constant in Rietveld analysis of the crystal structure is 2.840 Å or more and 2.851 Å or less.

6. A lithium composite metal oxide comprising Li and at least one transition metal element, wherein

at least one lithium composite metal oxide particle constituting the lithium composite metal oxide has both hexagonal and monoclinic crystal structures,

the amount (mol) of Li is 1.4 or more and 1.7 or less based on the total amount (mol) of the transition metal elements,

the monoclinic crystal structure is a crystal structure belonging to the space group C2/m, the hexagonal crystal structure is a crystal structure belonging to the space group R-3m, and

the lithium composite metal oxide comprising Li and at least one transition metal element is a lithium composite metal oxide comprising Li, Ni and M (where, M represents one or more kinds of transition metal elements selected from the group consisting of Mn, Co and Fe).

7. The lithium composite metal oxide according to claim 6 , wherein the amount (mol) of Li is 1.4 or more and 1.7 or less based on the total amount (mol) of Ni and M.

8. The lithium composite metal oxide according to claim 6 , wherein the amount (mol) of M exceeds 0 and is 0.9 or less based on the total amount (mol) of Ni and M.

9. The lithium composite metal oxide according to claim 6 , wherein the amount (mol) of Co is 0 or more and 0.4 or less based on the total amount (mol) of M.

10. The lithium composite metal oxide according to claim 6 , wherein M is Mn and/or Co.

11. The lithium composite metal oxide according to claim 6 , wherein M is Mn.

12. A positive electrode active material for a nonaqueous electrolyte secondary battery comprising the lithium composite metal oxide of claim 6 .

13. A positive electrode for a nonaqueous electrolyte secondary battery comprising the positive electrode material for a nonaqueous electrolyte secondary battery of claim 12 .

14. A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery of claim 13 .

15. The nonaqueous electrolyte secondary battery according to claim 14 , further comprising a separator.

16. The nonaqueous electrolyte secondary battery according to claim 15 , wherein the separator is made of a laminated porous film obtained by laminating a heat-resistant layer containing a heat-resistant resin and a shut-down layer containing a thermoplastic resin.

17. A method for charging and discharging a nonaqueous electrolyte secondary battery, charging the nonaqueous electrolyte secondary battery of claim 14 at a voltage which reaches a maximum voltage ranging from 4.0 V to 5.0 V and discharging at a voltage which drops to a minimum voltage ranging from 2.0 V to 3.0 V at a temperature ranging from 40° C. to 70° C.

18. The method for charging and discharging a nonaqueous electrolyte secondary battery according to claim 17 , charging and discharging the nonaqueous electrolyte secondary battery of claim 14 by a method including the following steps (1) and (2) at a temperature ranging from 40° C. to 70° C.:

(1) charging the nonaqueous electrolyte secondary battery at a voltage which reaches a maximum voltage ranging from 4.3 V to 4.8 V and discharging at a voltage which drops to a minimum voltage ranging from 2.0 V to 3.0 V; and

(2) charging the nonaqueous electrolyte secondary battery at a voltage which reaches a maximum voltage ranging from 4.0 V to 4.4 V and discharging at a voltage which drops to a minimum voltage ranging from 2.0 v to 3.0 V.

19. A nonaqueous electrolyte secondary battery charged and discharged by the method for charging and discharging a nonaqueous electrolyte secondary battery of claim 17 .