KR-20260065526-A - POSITIVE ELECTRODE ACTIVE MATERIAL, ELECTRODE, AND BATTERY

Abstract

The positive electrode active material includes secondary particles. The secondary particles include a plurality of primary particles. Each of the plurality of primary particles includes an olivine-type phosphate compound. The cross-section of the secondary particles consists of a center and an outer periphery. The relationship “0.8 ≤ φ2/φ1” is satisfied. “φ1” represents the porosity in the center. “φ2” represents the porosity in the outer periphery.

Inventors

• 마하라 다카노리
• 에구치 다츠야
• 기미지마 다케시

Assignees

• 도요타 지도샤（주）

Dates

Publication Date

20260508

Application Date

20251024

Priority Date

20241101

Claims (9)

1. Includes secondary particles, The above secondary particle comprises a plurality of primary particles, and Each of the plurality of primary particles comprises an olivine-type phosphate compound, and The cross-section of the above secondary particle consists of a central part and an outer periphery, and 0.8≤φ2/φ1 The relationship is satisfied, The above φ1 represents the porosity in the center, and also, The above φ2 represents the porosity in the outer periphery, a positive electrode active material.
2. In Article 1, 1≤φ2/φ1<2 Positive electrode active material in which the relationship is satisfied.
3. In Article 2, 1.2≤φ2/φ1≤1.5 Positive electrode active material in which the relationship is satisfied.
4. In any one of paragraphs 1 to 3, 20%<φ1<30% The relationship is satisfied, The above porosity represents the fraction of the total area of pores within a measurement area relative to the area of a measurement area set within a cross-sectional image of the secondary particle, and A positive electrode active material in which the porosity is calculated by considering the portion having a luminance of 1/3 or less of the average value of the luminance of the entire cross-sectional image as a void, and also considering the portion having a luminance exceeding 1/3 as a portion other than a void.
5. In any one of paragraphs 1 to 3, The minimum circumscribed circle of the cross-section of the above secondary particle has a radius of D, A positive electrode active material, wherein the center is circular, including the center of the minimum circumscribed circle, and also having a radius of 0.5D.
6. In any one of paragraphs 1 to 3, The above olivine-type phosphate compound comprises at least one selected from the group consisting of lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate, and is a positive electrode active material.
7. It includes a positive polar layer, and also, The above positive electrode layer is an electrode comprising a positive electrode active material described in any one of claims 1 to 3.
8. A battery comprising the electrode described in claim 7.
9. In Article 8, A battery having a bipolar structure.

Description

Positive electrode active material, electrode, and battery The present disclosure relates to a positive electrode active material, an electrode, and a battery. Japanese Patent Publication No. 2015-056223 discloses a positive electrode active material having a porosity of 33 vol% or more and 48 vol% or less of secondary particles. Olivine-type phosphate compounds are being developed as positive electrode active materials. Olivine-type phosphate compounds tend to have low rate characteristics. Conventionally, regarding secondary particles (assemblies), it has been proposed to improve electronic conductivity by nano-forming primary particles or carbon coating primary particles. However, there is still room for improvement in the rate characteristics of the battery. The objective of the present disclosure is to improve rate characteristics. The technical configuration and effects of the present disclosure are described below. However, the mechanism of action includes presumptions. 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 comprises secondary particles. The secondary particles comprise 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 consists of a center and an outer periphery. The relationship “0.8 ≤ φ2/φ1” is satisfied. “φ1” represents the porosity in the center. “φ2” represents the porosity in the outer periphery. Conventionally, in secondary particles of olivine-type phosphate compounds, the porosity in the center tends to increase. Although the detailed mechanism is unclear, the influence of the primary particles, such as nano-particle formation and carbon coating, is thought to be a factor. Consequently, the porosity ratio “φ2/φ1” of the outer periphery relative to the center is, for example, 0.5 or less. This time, it was discovered that rate characteristics are improved when the porosity ratio “φ2/φ1” is 0.8 or higher. It is believed that as the porosity ratio “φ2/φ1” increases, the electrolyte becomes easier to diffuse from the outer periphery of the secondary particle toward the center. As a result, it is believed that the rate characteristics are improved. 2. The positive electrode active material described in “1” above may include, for example, the following composition. The relationship “1 ≤ φ 2 / φ 1 < 2” is satisfied. Since the porosity of the outer periphery is equal to or greater than the porosity of the center, further improvement in rate characteristics is expected. 3. The positive electrode active material described in “1” or “2” above may include, for example, the following composition. The relationship “1.2 ≤ φ2/φ1 ≤ 1.5” is satisfied. As the porosity of the outer periphery exceeds the porosity of the center, further improvement in rate characteristics is expected. 4. The positive electrode active material described in any one of items “1” to “3” above may include, for example, the following composition. The relationship “20% < φ1 < 30%” is satisfied. The porosity represents the fraction of the total area of voids within a measurement area relative to the area of a measurement area set within a cross-sectional image of a secondary particle. A portion having a brightness of 1/3 or less relative to the average brightness value of the entire cross-sectional image is considered as a void. Additionally, a portion having a brightness exceeding 1/3 is considered as a portion other than a void, thereby calculating the porosity. There is also an aspect that energy density decreases as the porosity of secondary particles increases. When the relationship “20% < φ1 < 30%” is satisfied, there tends to be a good balance between rate characteristics and energy density. 5. The positive electrode active material described in any one of items “1” to “4” above may include, for example, the following composition. The minimum circumscribed circle of the cross-section of the secondary particle has a radius of D. The center is a circle that includes the center of the minimum circumscribed circle and also has a radius of 0.5D. 6. The positive electrode active material described in any one of claims 1 to 4 above may include, for example, the following composition. The olivine-type phosphate compound comprises at least one selected from the group consisting of 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 comprises a positive electrode layer. The positive electrode layer comprises a positive electrode active material described in any one of claims "1" to "6" above. The positive electrode layer may be rephrased as a "positive electrode active material layer," a "positive electrode composite layer," etc. The