Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery
The positive electrode active material for a lithium ion secondary battery contains a lithium-nickel-manganese composite oxide, in which metal elements constituting the lithium-nickel-manganese composite oxide include lithium, nickel, manganese, cobalt, titanium, niobium, and optionally zirconium, an amount of substance ratio of the elements is represented as Li:Ni:Mn:Co:Zr:Ti:Nb=a:b:c:d:e:f:g (provided that, 0.97≤a≤1.10, 0.80≤b≤0.88, 0.04≤c≤0.12, 0.04≤d≤0.10, 0≤e≤0.004, 0.003<f≤0.030, 0.001<g≤0.006, and b+c+d+e+f+g=1), in the amount of substance ratio, (f+g)≤0.030 and f>g are satisfied.
1. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material comprising a lithium-nickel-manganese composite oxide having a hexagonal layered structure and configured by secondary particles with a plurality of aggregated primary particles,
wherein metal elements constituting the lithium-nickel-manganese composite oxide include lithium (Li), nickel (Ni), manganese (Mn), cobalt (Co), titanium (Ti), niobium (Nb), and optionally zirconium (Zr),
an amount of substance ratio of the metal elements is represented as Li:Ni:Mn:Co:Zr:Ti:Nb=a:b:c:d:e:f:g (provided that, 0.97≤a≤1.10, 0.80≤b≤0.88, 0.04≤c≤0.12, 0.04≤d≤0.10, 0≤e≤0.004, 0.003<f≤0.030, 0.001<g≤0.006, and b+c+d+e+f+g=1),
in the amount of substance ratio, (f+g)≤0.030 and f>g are satisfied,
niobium is segregated at a grain boundary between primary particles of the lithium-nickel-manganese composite oxide, and
an amount of lithium to be eluted in water when the positive electrode active material is immersed in water is 0.20% by mass or less with respect to the entire positive electrode active material.
2. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the amount of substance ratio of the metal elements is represented as Li:Ni:Mn:Co:Zr:Ti:Nb=a:b:c:d:e:f:g (provided that, 0.97≤a≤1.10, 0.80≤b≤0.88, 0.04≤c≤0.12, 0.04≤d≤0.10, 0≤e≤0.004, 0.003<f≤0.030, 0.003≤g≤0.006, and b+c+d+e+f+g=1).
3. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein an amount of lithium eluted in water when the positive electrode active material is immersed in water is 0.10% by mass or less with respect to the whole positive electrode active material.
4. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a niobium concentration at the grain boundary between primary particles, as determined by point analysis using STEM-EDX, with respect to a niobium concentration inside primary particles of the lithium-nickel-manganese composite oxide is 1.3 times or more.
5. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a titanium concentration at the grain boundary between primary particles, as determined by point analysis using STEM-EDX, with respect to a titanium concentration inside primary particles of the lithium-nickel-manganese composite oxide is less than 1.3 times.
6. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein [(D90−D10)/Mv] indicating a particle size distribution width calculated by D90, D10 and a volume average particle size (Mv) in a particle size distribution by a laser diffraction scattering method is 0.80 or more and 1.20 or less.
7. The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein a volume average particle size Mv is 8 μm or more and 20 μm or less.
8. A lithium ion secondary battery comprising: a positive electrode; a negative electrode; and a non-aqueous electrolyte, the positive electrode containing the positive electrode active material for a lithium ion secondary battery according to claim 1 .