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EP-4456200-B1 - SECONDARY BATTERY POSITIVE ELECTRODE, PRODUCTION METHOD THEREFOR, AND SECONDARY BATTERY

EP4456200B1EP 4456200 B1EP4456200 B1EP 4456200B1EP-4456200-B1

Inventors

  • HARADA, Maho
  • NAKAYAMA, TAKAHITO

Dates

Publication Date
20260506
Application Date
20221220

Claims (16)

  1. A positive electrode for a secondary battery, comprising: a positive electrode current collector; and a positive electrode active material layer supported on the positive electrode current collector, wherein the positive electrode active material layer contains active material particles, a binder, and a thermal decomposable additive, and the thermal decomposable additive includes an acetamidobenzoic acid.
  2. The positive electrode for a secondary battery according to claim 1, wherein at least part of the thermal decomposable additive is present as particles having a particle diameter of 10 µm or more, in the positive electrode active material layer.
  3. The positive electrode for a secondary battery according to claim 2, wherein in a cross-sectional observation of the positive electrode active material layer, 5 or more particles of the thermal decomposable additive having a particle diameter measured according to the description of 10 µm or more are observed in a rectangular field of view defined by a length 300 µm in a plane direction of the positive electrode active material layer multiplied by a thickness of the positive electrode active material layer.
  4. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein a content of the acetamidobenzoic acid in the positive electrode active material layer is 0.1 mass% or more and 5 mass% or less.
  5. The positive electrode for a secondary battery according to any one of claims 1 to 4, wherein, when a cross section of the positive electrode active material layer is analyzed using a scanning electron microscope and an electron probe microanalyzer, an area of a portion where the acetamidobenzoic acid is present is 0.5 area% or more and 27 area% or less in a rectangular field of view defined by a length 300 µm in a plane direction of the positive electrode active material layer multiplied by a thickness T of the positive electrode active material layer.
  6. The positive electrode for a secondary battery according to any one of claims 1 to 5, wherein an acetic acid component is contained in an amount of 500 µg or more and 5000 µg or less per 1 gram of the thermal decomposable additive.
  7. The positive electrode for a secondary battery according to any one of claims 1 to 6, wherein the thermal decomposable additive covers part of surfaces of the active material particles.
  8. The positive electrode for a secondary battery according to any one of claims 1 to 7, wherein the thermal decomposable additive is more distributed near an outermost surface of the positive electrode active material layer than near a surface facing the positive electrode current collector of the positive electrode active material layer.
  9. The positive electrode for a secondary battery according to claim 8, wherein 1.35≤ Pt/Pb measured according to the description is satisfied, where when a thickness of the positive electrode active material layer is denoted by T, the Pb represents a presence probability of the thermal decomposable additive present in a region from a surface of the positive electrode current collector to 0.5T in the positive electrode active material layer, and the Pt represents a presence probability of the thermal decomposable additive present in a region from a position at 0.5T from the surface of the positive electrode current collector to the outermost surface in the positive electrode active material layer.
  10. The positive electrode for a secondary battery according to any one of claims 1 to 9, wherein the active material particles include a lithium-containing transition metal oxide, the lithium-containing transition metal oxide contains a lithium-nickel oxide including lithium and Ni and having a layered rock-salt type crystal structure, and a proportion of Ni in metal elements other than Li contained in the lithium-nickel oxide is 50 at.% or more.
  11. The positive electrode for a secondary battery according to claim 10, wherein the lithium-nickel oxide is represented by a formula: Li α Ni x1 M1 x2 M2 (1-x1-x2) O 2+β , where the element M1 is at least one selected from the group consisting of V, Co, and Mn, the element M2 is at least one selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb, 0.95 ≤ α ≤ 1.05 , − 0.05 ≤ β ≤ 0.05 , 0.5 ≤ x 1 < 1 , 0 ≤ x 2 ≤ 0.5 , and 0 < 1 − x 1 − x 2 ≤ 0.5 .
  12. The positive electrode for a secondary battery according to any one of claims 1 to 11, wherein the binder is at least one selected from the group consisting of a fluorocarbon resin and a hydrogenated nitrile butadiene rubber.
  13. A secondary battery, comprising: the positive electrode for a secondary battery of any one of claims 1 to 12; a negative electrode; a lithium-ion conductive electrolyte; and a separator interposed between the positive electrode and the negative electrode.
  14. A method for producing a positive electrode for a secondary battery, the method comprising steps of: preparing a positive electrode slurry containing active material particles, a binder, a thermal decomposable additive, and a dispersion medium; preparing a positive electrode current collector; applying the positive electrode slurry onto a surface of the positive electrode current collector, to form an applied film; drying the applied film, to form an unrolled layer; and rolling the unrolled layer, to form a positive electrode active material layer, wherein the thermal decomposable additive includes an acetamidobenzoic acid, and the dispersion medium includes an organic solvent.
  15. The method for producing a positive electrode for a secondary battery of claim 14, wherein at least part of the thermal decomposable additive is present as particles having a particle diameter measured according to the description of 10 µm or more, in the positive electrode slurry.
  16. The method for producing a positive electrode for a secondary battery according to claim 14 or 15, wherein 1.35 ≤ Pt / Pb measured according to the description is satisfied, where when a thickness of the positive electrode active material layer is denoted by T, the Pb represents a presence probability of the thermal decomposable additive present in a region from a surface of the positive electrode current collector to 0.5T in the positive electrode active material layer, and the Pt represents a presence probability of the thermal decomposable additive present in a region from a position at 0.5T from the surface of the positive electrode current collector to an outermost surface in the positive electrode active material layer.

Description

[Technical Field] The present disclosure mainly relates to a positive electrode for a secondary battery. [Background Art] For a secondary battery, as its energy density is increased, improvement in safety is required. In particular, it is important to reduce the heat generation due to internal short circuit. When the battery has internal short circuit, even though the shorted portion is small, the Joule heat generated by short-circuit current melts the separator, to form a larger shorted portion. When the shorted portion expands and the short-circuit current increases, the battery temperature rises acceleratingly. The higher the energy density of the secondary battery is, the more the Joule heat generated by short-circuit current increases. Patent Literature 1 proposes a positive electrode active material comprising a composite oxide mainly composed of lithium and nickel and having a layered crystal structure, which is a powder having an element composition represented by a general formula: LiaNi1-b-cM1bM2cO2, where 0.95 ≤ a ≤ 1.05, 0.01 ≤ b ≤ 0. 10, and 0.10 ≤ c ≤ 0.20 (here, M1 is one or more elements selected from Al, B, Y, Ce, Ti, Sn, V, Ta, Nb, W, and Mo, and M2 is one or more elements selected from Co, Mn, and Fe), and is characterized by that when the powder is pressure-molded, an electrical conductivity σ at 25 °C of a powder compact at a compression density of 4.0 g/cm3 is within the range of 5 × 10-2 ≥ σ ≥ 5×10-4 [S/cm]. [Citation List] [Patent Literature] Patent Literature 1: Japanese Laid-Open Patent Publication No. 2000-315502 [Summary of Invention] [Technical Problem] Patent Literature 1 discloses that, according to the above positive electrode active material, the thermal stability in a charged state can be improved, and even when an internal short circuit occurs in the battery, the Joule heat generation by short-circuit current can be suppressed, easily leading to ensured safety. However, when controlling the electrical conductivity of the powder compact as in Patent Literature 1, the battery ends up in having a high resistance as a whole, causing a deterioration in battery performance. Moreover, the solution in Patent Literature 1 is specialized for a composite oxide mainly composed of lithium and nickel, and is poor in versatility. [Solution to Problem] One aspect of the present disclosure relates to a positive electrode for a secondary battery, including: a positive electrode current collector; and a positive electrode active material layer supported on the positive electrode current collector, wherein the positive electrode active material layer contains active material particles, a binder, and a thermal decomposable additive, and the thermal decomposable additive includes an acetamidobenzoic acid. Another aspect of the present disclosure relates to a secondary battery, including: the above-described positive electrode for a secondary battery; a negative electrode; a nonaqueous electrolyte; and a separator interposed between the positive electrode and the negative electrode. Still another aspect of the present disclosure relates to a method for producing a positive electrode for a secondary battery, the method including steps of: preparing a positive electrode slurry containing active material particles, a binder, a thermal decomposable additive, and a dispersion medium; preparing a positive electrode current collector; applying the positive electrode slurry onto a surface of the positive electrode current collector, to form an applied film; drying the applied film, to form an unrolled layer; and rolling the unrolled layer, to form a positive electrode active material layer, wherein the thermal decomposable additive includes an acetamidobenzoic acid, and the dispersion medium includes an organic solvent. [Advantageous Effects of Invention] According to the present disclosure, while suppressing an increase in the resistance at room temperature, it is possible to increase the resistance at high temperature when an internal short circuit occurs in the battery. Therefore, both high safety and good battery performance can be achieved. While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. [Brief Description of Drawing] [FIG. 1] A schematic longitudinal cross-sectional view of the internal structure of a secondary battery according to an embodiment of the present disclosure. [Description of Embodiments] Embodiments of a positive electrode for a secondary battery according to the present disclosure and a secondary battery using the positive electrode will be described below by way of examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values and materials are