Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing the same, positive electrode mixture paste for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery
A positive electrode active material for a nonaqueous electrolyte secondary battery contains a first lithium-metal composite oxide represented by General Formula: Li s1 Ni 1-x1-y1-z1 Co x1 Mn y1 M z1 O 2+α and containing a secondary particle formed of a plurality of flocculated primary particles and either one or both of a first compound containing lithium and boron and a second compound containing lithium and tungsten. Either one or both of the following characteristics (1) and (2) are satisfied: (1) the first compound covers surfaces of the primary particles, and a boron content is at least 0.01% by mass and up to 0.5% by mass relative to the entire positive electrode active material; and (2) the second compound covers the surfaces of the primary particles, and a tungsten content is at least 0.01% by mass and up to 1.0% by mass relative to the entire positive electrode active material.
1. A positive electrode active material for a nonaqueous electrolyte secondary battery, the positive electrode active material comprising:
a first lithium-metal composite oxide represented by General Formula (1): Li s1 Ni 1-x1-y1-z1 Co x1 Mn y1 M z1 O 2+α (where 0≤x1≤0.35, 0≤y1≤0.35, 0≤z1≤0.10, 0.95<s1<1.30, and 0≤α≤0.2; and M is at least one element selected from V, Mg, Mo, Nb, Ti, W, and Al) and containing a secondary particle formed of a plurality of flocculated primary particles; and
either one or both of a first compound containing lithium and boron and a second compound containing lithium and tungsten, wherein
either one or both of the following characteristics (1) and (2) are satisfied, and
a lithium amount eluted when the positive electrode active material is dispersed in water measured by neutralization titration is at least 0.01% by mass and less than 0.4% by mass relative to the entire positive electrode active material:
(1) the first compound covers surfaces of the primary particles, and a boron content is at least 0.01% by mass and up to 0.5% by mass relative to the entire positive electrode active material; and
(2) the second compound covers the surfaces of the primary particles, and a tungsten content is at least 0.01% by mass and up to 1.0% by mass relative to the entire positive electrode active material.
2. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , wherein the positive electrode active material has an average particle diameter of at least 5 μm and up to 30 μm and [(d90−d10)/Average particle diameter] as an indicator indicating a spread of particle size distribution of at least 0.70.
3. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, the method comprising mixing fired powder and either one or both of a compound containing boron and a compound containing tungsten together to obtain a positive electrode active material, wherein
the fired powder is a lithium-metal composite oxide represented by General Formula (2): Li s2 Ni 1-x2-y2-z2 Co x2 Mn y2 M z2 O 2+α′ (where 0≤x2≤0.35, 0≤y2≤0.35, 0≤z2≤0.10, 0.95<s2<1.30, and 0≤α′≤0.2; and M is at least one element selected from V, Mg, Mo, Nb, Ti, W, and Al) and contains a secondary particle formed of a plurality of flocculated primary particles,
a lithium amount eluted when the fired powder is dispersed in water measured by neutralization titration is at least 0.05% by mass and up to 1.0% by mass relative to the entire fired powder, and
the compound containing boron and the compound containing tungsten are solid compounds that do not contain lithium and are capable of reacting with lithium and are mixed such that either one or both of the following conditions (i) and (ii) are satisfied:
(i) a boron content is at least 0.01% by mass and up to 0.5% by mass relative to the entire positive electrode active material; and
(ii) a tungsten content is at least 0.01% by mass and up to 1.0% by mass relative to the entire positive electrode active material.
4. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3 , wherein an amount of either one or both of the compound containing boron and the compound containing tungsten to be mixed is adjusted such that an amount of lithium eluted when the positive electrode active material is dispersed in water measured by neutralization titration is at least 0.01% by mass and less than 0.4% by mass relative to the entire positive electrode active material.
5. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3 , wherein the compound containing boron contains one or more selected from boric acid (H 3 BO 3 ), boron oxide (B 2 O 3 ), ammonium tetraborate tetrahydrate ((NH 4 ) 2 B 4 O 7 .4H 2 O), and ammonium pentaborate octahydrate ((NH 4 ) 2 O.5B 2 O 3 .8H 2 O).
6. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 3 , wherein the compound containing tungsten contains tungstic acid (H 2 WO 4 ).
7. A positive electrode mixture paste for a nonaqueous electrolyte secondary battery, the positive electrode mixture paste comprising the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 .
8. A nonaqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1 , a negative electrode, and a nonaqueous electrolyte solution.