Lithium mixed metal oxide and positive electrode active material
Disclosed is a lithium mixed metal oxide which is useful for a positive electrode active material that is capable of providing a nonaqueous electrolyte secondary battery having more excellent cycle characteristics, in particular, more excellent cycle characteristics during high-temperature operation at 60 DEG C. or the like. Specifically disclosed is a lithium mixed metal oxide represented by the following formula (A). Li x (Mn 1-y-z Ni y Fe z )O 2 (A) (In the formula, x is not less than 0.9 and not more than 1.3; y is 0.46 or more and less than 0.5; and z is 0 or more and less than 0.1.) Also disclosed are: a positive electrode active material which comprises the lithium mixed metal oxide; a positive electrode which comprises the positive electrode active material; and a nonaqueous electrolyte secondary battery which comprises the positive electrode.
1. A lithium mixed metal oxide represented by the following formula (A):
Li x (Mn 1-y-z Ni y Fe z )O 2 (A)
wherein x is a value in the range of not less than 0.9 and not more than 1.3, y is a value in the range of not less than 0.46 and less than 0.5, and z is a value in the range of not less than 0 and less than 0.1,
wherein a mean value of particle diameters of lithium mixed metal oxide constituent primary particles is in the range of not less that 0.01 μm and not more than 0.5 μm, and
wherein a mean value of particle diameters of lithium mixed metal oxide secondary particles is not less than 0.1 μm and not more than 3 μm.
2. The lithium mixed metal oxide according to claim 1 , wherein the value of (1-y-z) is larger than that of y in said formula (A).
3. The lithium mixed metal oxide according to claim 1 , wherein z is a value in the range of not less than 0.02 and not more than 0.07 in said formula (A).
4. A positive electrode active material comprising the lithium mixed metal oxide according to claim 1 .
5. A positive electrode comprising the positive electrode active material according to claim 4 .
6. A nonaqueous electrolyte secondary battery comprising the positive electrode according to claim 5 .
7. The nonaqueous electrolyte secondary battery according to claim 6 , which further comprises a separator.
8. The nonaqueous electrolyte secondary battery according to claim 7 , wherein the separator is a separator comprising a laminated film which has a heat-resistant porous layer and a porous film laminated to each other.
9. A process for producing a lithium mixed metal oxide represented by the following formula (A):
Li x (Mn1 -y-z Ni y Fe z )O 2 (A),
wherein x is a value in the range of not less than 0.9 and not more than 1.3, y is a value in the range of not less than 0.46 and less than 0.5, and z is a value in the range of not less than 0 and less than 0.1,
which process comprises the following steps (1), (2) and (3) in this order:
(1) the step of bringing an aqueous solution containing Ni, Mn, Fe and Cl into contact with an alkali to obtain a coprecipitate slurry,
(2) the step of obtaining a coprecipitate from the coprecipitate slurry, and
(3) the step of obtaining the mixed metal oxide by subjecting a mixture obtained by mixing the coprecipitate, a lithium compound, and optionally an inactive flux to calcination by keeping the mixture at a temperature of less than 900° C.