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CN-122000351-A - Positive electrode active material, electrode, and battery

CN122000351ACN 122000351 ACN122000351 ACN 122000351ACN-122000351-A

Abstract

The present disclosure relates to a positive electrode active material, an electrode, and a battery. An object of the present disclosure is to improve magnification characteristics. A positive electrode active material includes secondary particles. The secondary particles include a plurality of primary particles. Each of the plurality of primary particles comprises an olivine-type phosphate compound. The cross section of the secondary particles is composed of a central portion and an outer peripheral portion. Satisfies the relation of phi 2/phi 1 which is more than or equal to 0.8. "φ 1" represents the porosity of the center portion. "φ 2" represents the porosity of the outer peripheral portion.

Inventors

  • Ma Yuanlongde
  • EGUCHI TATSUYA
  • KIMIJIMA TAKEYUKI

Assignees

  • 丰田自动车株式会社

Dates

Publication Date
20260508
Application Date
20251029
Priority Date
20241101

Claims (9)

  1. 1. A positive electrode active material includes secondary particles, The secondary particles comprise a plurality of primary particles, Each of a plurality of the primary particles comprises an olivine-type phosphate compound, The cross section of the secondary particles is composed of a central part and an outer peripheral part, Satisfies the relationship of phi 2/phi 1 which is less than or equal to 0.8, The phi 1 represents the porosity of the central portion, and And phi 2 represents the porosity of the outer peripheral portion.
  2. 2. The positive electrode active material according to claim 1, Satisfies the relation of 1≤phi.2/phi.1 < 2.
  3. 3. The positive electrode active material according to claim 2, Satisfies the relation of phi 2/phi 1 less than or equal to 1.2 and less than or equal to 1.5.
  4. 4. The positive electrode active material according to any one of claim 1 to 3, Satisfies the relationship of 20% < phi 1 < 30%, The porosity represents a fraction of a total area of pores in a measurement region set in a cross-sectional image of the secondary particles relative to an area of the measurement region, The porosity is calculated by considering a portion having a luminance of 1/3 or less with respect to the average value of the luminance of the entire cross-sectional image as a void and a portion having a luminance exceeding 1/3 as a portion other than the void.
  5. 5. The positive electrode active material according to any one of claim 1 to 3, The radius of the smallest circumscribed circle of the cross section of the secondary particle is D, The center portion is a circle including the center of the minimum circumscribed circle and having a radius of 0.5D.
  6. 6. The positive electrode active material according to any one of claim 1 to 3, The olivine-type phosphate compound includes at least one selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.
  7. 7. An electrode comprising a positive electrode layer, and The positive electrode layer contains the positive electrode active material according to any one of claims 1 to 3.
  8. 8. A battery comprising the electrode of claim 7.
  9. 9. The battery of claim 8, having a bipolar structure.

Description

Positive electrode active material, electrode, and battery Technical Field The present disclosure relates to a positive electrode active material, an electrode, and a battery. Background Japanese patent application laid-open No. 2015-056223 discloses a positive electrode active material in which the porosity of the secondary particles is 33% by volume or more and 48% by volume or less. Disclosure of Invention As the positive electrode active material, an olivine-type phosphate compound was developed. Olivine-type phosphate compounds have a tendency to have low rate characteristics. Conventionally, in secondary particles (granules), it has been proposed to improve electron conductivity by nanoparticle of primary particles, carbon coating of primary particles, or the like. However, there is room for improvement in the rate characteristics of the battery. An object of the present disclosure is to improve magnification characteristics. The technical scheme and the operational effects of the present disclosure are explained below. However, the mechanism of action includes estimation. The mechanism of action does not limit the technical scope of the present disclosure. 1. One aspect of the present disclosure is a positive electrode active material. The positive electrode active material contains secondary particles. The secondary particles include a plurality of primary particles. Each of the plurality of primary particles comprises an olivine-type phosphate compound. The cross section of the secondary particles is composed of a central portion and an outer peripheral portion. Satisfies the relation of phi 2/phi 1 which is more than or equal to 0.8. "φ 1" represents the porosity of the center portion. "φ 2" represents the porosity of the outer peripheral portion. Conventionally, secondary particles of olivine-type phosphate compounds tend to have a higher porosity in the center. The detailed mechanism is not yet clear, but is considered to be an influence of nanoparticle formation of primary particles, carbon coating, and the like. Therefore, conventionally, the porosity ratio "Φ2/Φ1" of the outer peripheral portion to the central portion is, for example, 0.5 or less. It has been found that by having a porosity ratio "phi 2/phi 1" of 0.8 or more, the rate characteristics are improved. It is considered that the electrolyte is easily diffused from the outer peripheral portion to the central portion of the secondary particles by increasing the porosity ratio "phi 2/phi 1". As a result, it is considered that the rate characteristics are improved. 2. The positive electrode active material according to the above "1" may include the following embodiments, for example. Satisfies the relation of '1≤phi.2/phi 1<2'. Further improvement of the rate characteristics can be expected by setting the porosity of the outer peripheral portion to be equal to or greater than the porosity of the central portion. 3. The positive electrode active material described in "1" or "2" may contain the following components, for example. Satisfies the relation of phi 2/phi 1 less than or equal to 1.5 which is less than or equal to 1.2. Further improvement in the rate characteristics can be expected by the porosity of the outer peripheral portion exceeding the porosity of the central portion. 4. The positive electrode active material according to any one of the above "1" to "3" may include, for example, the following. The relation of '20% < phi 1< 30%' is satisfied. The porosity represents the fraction of the total area of pores in the measurement region set in the cross-sectional image of the secondary particles relative to the area of the measurement region. A portion having a luminance of 1/3 or less with respect to the average value of the luminance of the entire cross-sectional image is regarded as an aperture. Further, the porosity was calculated by regarding a portion having a luminance exceeding 1/3 as a portion other than the pore. If the porosity of the secondary particles becomes high, the energy density is also reduced. When the relationship of "20% < Φ1<30%", there is a tendency that the balance between the rate characteristics and the energy density is good. 5. The positive electrode active material according to any one of the above "1" to "4" may include, for example, the following. The radius of the smallest circumcircle of the secondary particle cross section is D. The center portion is a circle including the center of the smallest circumscribed circle and having a radius of 0.5D. 6. The positive electrode active material according to any one of the above "1" to "4" may include, for example, the following. The olivine-type phosphate compound includes at least one selected from lithium iron phosphate (LFP), lithium Manganese Phosphate (LMP), and lithium manganese iron phosphate (LMFP). 7. One aspect of the present disclosure is an electrode. The electrode includes a positive electrode layer. The positive electrode layer contains th