Positive electrode for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery
A positive electrode for nonaqueous electrolyte secondary batteries includes a positive electrode current collector and a positive electrode mix layer, formed on the current collector, containing a positive electrode active material. The positive electrode active material mainly contains a lithium transition metal oxide in which the molar ratio of nickel (Ni) to a transition metal component is 20% or more. The positive electrode mix layer contains a plurality of pores and has a first peak of a logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the pore diameter D is less than 1 μm and a second peak of the logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the pore diameter D is 1 μm or more in a pore distribution determined by mercury intrusion porosimetry. According to this configuration, a nonaqueous electrolyte secondary battery having excellent output characteristics can be provided.
1. A positive electrode for nonaqueous electrolyte secondary batteries, comprising a positive electrode current collector and a positive electrode mix layer, formed on the current collector, containing a positive electrode active material,
wherein the positive electrode active material mainly contains a lithium transition metal oxide in which the molar ratio of nickel (Ni) to a transition metal component is 20% or more and
the positive electrode mix layer contains a plurality of pores and has a first peak of a logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the pore diameter D is less than 1 μm and a second peak of the logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the pore diameter D is 5 μm or more in a pore distribution determined by mercury intrusion porosimetry,
wherein the plurality of pores corresponding to the second peak are regularly formed on a surface of the positive electrode mix layer.
2. The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 , wherein the ratio (D2/D1) of a second mode diameter D2 corresponding to the second peak to a first mode diameter D1 corresponding to the first peak is fifty times or more.
3. The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 , wherein, in the lithium transition metal oxide, the molar ratio of nickel (Ni) to the transition metal component is 35% or more.
4. The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 , wherein the maximum rate of change in cell volume of the lithium transition metal oxide at a charge cut-off potential between zero charge and 4.3 V (vs. Li/Li+) is 1.5% or less.
5. The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 , wherein the lithium transition metal oxide contains tungsten (W).
6. The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 , wherein the positive electrode mix layer contains at least one of a phosphate compound and a tungsten oxide.
7. A nonaqueous electrolyte secondary battery comprising:
the positive electrode according claim 1 ;
a negative electrode; and
a nonaqueous electrolyte.
8. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 1 , wherein the second peak of the logarithmic differential pore volume distribution (dV/dlogD) appears in the range where the pore diameter D is 19 μm or more.
9. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 1 , wherein the pores corresponding to the second peak are grooves.
10. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 9 , wherein the grooves are formed at a substantially same interval.
11. A positive electrode for nonaqueous electrolyte secondary batteries comprising a positive electrode current collector and a positive electrode mix layer formed on the positive electrode current collector,
wherein the positive electrode mix layer includes:
a plurality of positive electrode active material particles formed on the positive electrode current collector,
a plurality of cavities, which are present between a certain particle of the positive electrode active material particles and other particles of the positive electrode active material particles contacting the certain particle, and which have a first peak of a logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where a diameter D of each of the plurality of cavities is less than 1 μm and,
a plurality of pores, which have openings in a surface of the positive electrode mix layer, and which have a second peak of the logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the diameter D of each of the plurality of pores is 5 μm or more,
wherein the plurality of positive electrode active material particles mainly contains a lithium transition metal oxide in which the molar ratio of nickel (Ni) to a transition metal component is 20% or more.
12. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 11 , wherein the diameter D of each of the plurality of cavities is smaller than a diameter of each of the plurality of positive electrode active material particles.
13. A positive electrode for nonaqueous electrolyte secondary batteries comprising a positive electrode current collector and a positive electrode mix layer formed on the positive electrode current collector,
wherein the positive electrode mix layer includes:
a plurality of positive electrode active material particles formed on the positive electrode current collector,
a plurality of cavities, which are present between a certain particle of the positive electrode active material particles and other particles of the positive electrode active material particles contacting the certain particle, and which have a first peak of a logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where a diameter D is less than 1 μm and,
a plurality of grooves formed in the positive electrode mix layer, and which have a second peak of the logarithmic differential pore volume distribution (dV/dlogD) that appears in the range where the diameter D is 5 μm or more,
wherein the plurality of positive electrode active material particles mainly contains a lithium transition metal oxide in which the molar ratio of nickel (Ni) to a transition metal component is 20% or more.
14. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 13 , the diameter D of each of the plurality of cavities is smaller than a particle diameter of each of the plurality of positive electrode active material particle.
15. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 13 , wherein each of the plurality of grooves have substantially a same width.
16. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 13 , wherein each of the plurality of grooves extend in substantially the same direction.
17. The positive electrode for nonaqueous electrolyte secondary batteries according to claims 13 , wherein the plurality of grooves are formed at substantially equal intervals.