Non-aqueous electrolyte secondary battery positive electrode and non-aqueous electrolyte secondary battery
Disclosed is a non-aqueous electrolyte secondary battery positive electrode that includes a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode mixture layer contains a positive electrode active material and carbon nanotubes. The positive electrode active material contains a lithium transition metal composite oxide (I) that either comprises secondary particles that are aggregates of primary particles having an average particle size of 1 μm or greater, or is substantially composed of single particles, the lithium transition metal composite oxide (I) having a volume-based median diameter of 0.6 μm to 6 μm, and a lithium transition metal composite oxide (II) that comprises secondary particles that are aggregates of primary particles having an average particle size of less than 1 μm, the lithium transition metal composite oxide (II) having a volume-based median diameter of 3 μm to 25 μm.
1. A non-aqueous electrolyte secondary battery positive electrode, comprising:
a positive electrode core; and
a positive electrode mixture layer disposed on the positive electrode core,
wherein the positive electrode mixture layer contains a positive electrode active material and carbon nanotubes, the positive electrode active material containing:
a lithium transition metal composite oxide (I) that comprises a combination of (i) secondary particles that are aggregates of primary particles having an average particle size of 1 μm or greater, and (ii) particles substantially composed of single particles that are present independently of the secondary particles, the lithium transition metal composite oxide (I) having a volume-based median diameter (D50) of 0.6 μm to 6 μm,
wherein 50% or greater of all particles of the lithium transition metal composite oxide (I) are the (ii) particles substantially composed of single particles that are present independently of the secondary particles, and
a lithium transition metal composite oxide (II) that comprises secondary particles that are aggregates of primary particles having an average particle size of less than 1 μm, the lithium transition metal composite oxide (II) having a volume-based median diameter (D50) of 3 μm to 25 μm
wherein the lithium transition metal composite oxide (II) is a composite oxide represented by a general formula Li a Ni b Co c M1 d M2 e O f (where 0.8≤a≤1.2, b≥0.80, c≤0.15, 0.01≤d≤0.12, 0.001≤e≤0.06, 1≤f≤2, b+c+d+e=1, M1 represents one or more elements selected from Mn and Al, and M2 comprises B and Ti),
wherein each of the lithium transition metal composite oxides (I) and (II) contains Ni in an amount of 80 mol % or more relative to the total number of moles of one or more metal elements excluding Li, and one or more elements selected from group 4 elements, group 5 elements, group 6 elements, and group 13 elements of the periodic table are present on particle surfaces of each of the lithium transition metal composite oxides (I) and (II).
2. The non-aqueous electrolyte secondary battery positive electrode according to claim 1 , wherein the carbon nanotubes comprise both single-walled carbon nanotubes and multi-walled carbon nanotubes.
3. The non-aqueous electrolyte secondary battery positive electrode according to claim 1 , wherein the percentage content of the lithium transition metal composite oxide (I) relative to the mass of the positive electrode active material is 20% by mass to 55% by mass.
4. The non-aqueous electrolyte secondary battery positive electrode according to claim 2 , wherein the ratio of the mass of the single-walled carbon nanotubes to the mass of the positive electrode mixture layer is less than the ratio of the mass of the multi-walled carbon nanotubes to the mass of the positive electrode mixture layer.
5. The non-aqueous electrolyte secondary battery positive electrode according to claim 1 , wherein the lithium transition metal composite oxide (I) is a composite oxide represented by a general formula Li a Ni b Co c M1 d M2 e O f (where 0.8≤a≤1.2, b≥0.80, c≤0.15, 0.01≤d≤0.12, 0.001≤e≤0.06, 1≤f≤2, b+c+d+e=1, M1 represents one or more elements selected from Mn and Al, and M2 represents one or more elements selected from group 4 elements, group 5 elements, group 6 elements, and group 13 elements of the periodic table).
6. The non-aqueous electrolyte secondary battery positive electrode according to claim 5 , wherein in the lithium transition metal composite oxide (I), M2 in the general formula represents one or more elements selected from B and Al.
7. The non-aqueous electrolyte secondary battery positive electrode according to claim 5 , wherein in the lithium transition metal composite oxide (I), M2 in the general formula represents B and Al.
8. The non-aqueous electrolyte secondary battery positive electrode according to claim 1 , wherein the positive electrode mixture layer has a resistance of 15 Ωcm 2 or less.
9. The non-aqueous electrolyte secondary battery positive electrode according to claim 5 ,
wherein in the lithium transition metal composite oxide (II), M2 in the general formula comprises B,
wherein, in the lithium transition metal composite oxide (II) particles having particle diameters that are larger than a volume-based 70% particle diameter (D70) are first particles, and that particles having particle diameters that are smaller than a volume-based 30% particle diameter (D30) are second particles, a molar fraction of B in the first particles (B1) relative to the total number of moles of one or more metal elements excluding Li is greater than a molar fraction of B in the second particles (B2) relative to the total number of moles of one or more metal elements excluding Li.
10. The non-aqueous electrolyte secondary battery positive electrode according to claim 1 , wherein the positive electrode mixture layer is free of particulate conductive material.
11. A non-aqueous electrolyte secondary battery, comprising:
a positive electrode;
a negative electrode; and
a non-aqueous electrolyte,
wherein the positive electrode is the non-aqueous electrolyte secondary battery positive electrode according to claim 1 .