Positive electrode active material for non-aqueous electrolyte secondary batteries, production process therefor, and non-aqueous electrolyte secondary battery
A positive electrode active material for a non-aqueous electrolyte secondary battery, which enables a non-aqueous electrolyte secondary battery to achieve great battery characteristics, and a process for producing the material, as well as a non-aqueous electrolyte secondary batter. Provided is a positive electrode active material for a non-aqueous electrolyte secondary battery, where secondary particles of lithium-nickel-cobalt-manganese composite oxide particles are composed of outer-shell parts with a high manganese concentration and central parts with a low manganese concentration, which are lower in manganese concentration than the outer-shell parts, primary particles constituting the outer-shell parts of the secondary particles with the high manganese concentration are composed of outer peripheral parts with a low manganese concentration and inner parts with a high manganese concentration, and the ratio of the manganese concentration in the inner part to the manganese concentration in the outer peripheral part is 1.5 to 2.5 in the primary particles.
1. A positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material comprising hexagonal lithium-nickel-cobalt-manganese composite oxide particles represented by the general formula: Li 1+s Ni x Co y Mn z M t O 2
wherein:
s, x, y, z, and t in the formula fall within the ranges of: −0.05≤s≤0.20; 0.1≤x≤0.7; 0.1≤y≤0.5; 0.1≤z≤0.5; and 0≤t≤0.05, and x, y, z, and t meet x+y+z+t=1,
M in the formula represents one or more additive elements selected from the group consisting of Ca, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W,
the lithium-nickel-cobalt-manganese composite oxide particles have a layered structure comprising secondary particles with aggregated primary particles,
the secondary particles each comprises an outer-shell part that has a high manganese concentration and a central part that has a low manganese concentration that is lower than the high manganese concentration in the outer-shell part of the secondary particle,
the primary particles constitute the outer-shell parts of the secondary particles,
each of the primary particles comprises an outer peripheral part that has a low manganese concentration and an inner part that has a high manganese concentration, and
a ratio of the high manganese concentration in the inner part of the primary particle to the low manganese concentration in the outer peripheral part of the primary particle is in a range of from 1.5 to 2.5.
2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein a ratio of the low manganese concentration in the central part of the secondary particle to the high manganese concentration in the outer-shell part of the secondary particle is 0.3 to 0.7.
3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode active material is 3 μm to 20 μm in average particle size.
4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the primary particles are 0.2 μm to 0.5 μm in average particle size.
5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode active material has a breadth of a particle size distribution, [(d90−d10)/average particle size], that is 0.60 or less.
6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the secondary particles have voids in the central parts of the secondary particles.
7. A process for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1
the process comprises:
a crystallization step of obtaining nickel-cobalt-manganese composite hydroxide particles represented by the general formula: Ni x Mn z M t (OH) 2+α , wherein x, y, z, and t in the formula fall within the ranges of: 0.1≤x≤0.7; 0.1≤y≤0.5; 0.1≤z≤0.5; and 0≤t≤0.05, x, y, z, and t meet x+y+z+t=1, and M in the formula represents one or more additive elements selected from the group consisting of Ca, Mg, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W;
a mixing step of mixing the nickel-cobalt-manganese composite hydroxide particles with a lithium compound such that a ratio of the atom number of lithium will be in a range of from 0.95 to 1.20 with respect to a total of the atom numbers of metal elements other than lithium, thereby providing a lithium mixture; and
a calcining step in an oxidizing atmosphere including: (i) elevating a temperature of the lithium mixture from room temperature to a temperature in a range of from 400° C. to 550° C. over 0.5 hours to 1.5 hours and keeping the elevated temperature for 1 hour to 5 hours, and (ii) further elevating the temperature of the lithium mixture to a temperature in a range of from 850° C. to 950° C. over 0.5 hours to 1.0 hour and keeping the elevated temperature for 1 hour to 5 hours, thereby forming the lithium-nickel-cobalt-manganese composite oxide particles.
8. The process for producing the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7 , the process further comprising, before the mixing step, a heat treatment step of applying a heat treatment at a temperature in a range of from 105° C. to 150° C. to the nickel-cobalt-manganese composite hydroxide particles.
9. The process for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7 , the process further comprising a grinding step of grinding the lithium-nickel-cobalt-manganese composite oxide particles obtained in the calcining step.
10. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode is the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 .