JP-2026514226-A - Positive electrode active material, positive electrode, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material, and more particularly to a positive electrode and lithium secondary battery that can simultaneously solve the problems of both conventional secondary particles and single particles. The positive electrode active material contains particles such as conventional single particles as primary particles, and also contains secondary particles formed by the aggregation of multiple primary particles. This allows for improved energy density due to superior density characteristics, as well as improved cell characteristics such as increased lifespan and reduced gas generation in lithium secondary batteries.

Inventors

• ジュン・ウク・イ
• ミュン・ギ・ジョン
• ジン・フ・ジョン
• ジュ・キョン・ファン
• ジ・ヨン・イ
• ヒョン・モ・リュ
• クク・ジン・ホ
• サン・ウン・バク
• ジョン・ヒュク・キム
• スン・ボム・チョ

Assignees

• エルジー・ケム・リミテッド

Dates

Publication Date

20260507

Application Date

20240429

Priority Date

20230428

Claims (8)

1. It contains secondary particles formed by the aggregation of multiple primary particles, The aforementioned plurality of primary particles have an average particle size of 1.5 μm or more and 5.0 μm or less, as measured from SEM images, and the particle size of the primary particles is the particle size based on the major axis of the primary particle. The aforementioned secondary particles have an average particle size (D 50 ) of 7.0 μm or more and 20.0 μm or less, as determined by the volume cumulative distribution measured using a laser diffraction particle size analyzer. A positive electrode active material in which, as observed from the electron backscatter diffraction (EBSD) pattern of a SEM image of the cross-section of a secondary particle (measured under the conditions of acceleration voltage 20 kV, WD 16 mm, measurement magnification 5,000x (width 16 μm × height 16 μm), step size 0.025 μm), the cross-sectional size of the secondary particle is within the range of the average particle size (D 50 ), and the number of grain cross-sections confirmed within a unit area of 5 μm × 5 μm within the cross-section of the secondary particle is between 1 and 150.
2. The positive electrode active material according to claim 1, wherein, as observed from the electron backscatter diffraction (EBSD) pattern of a SEM image of the cross-section of a secondary particle (measured under the conditions of acceleration voltage 20 kV, WD 16 mm, measurement magnification 5,000x (width 16 μm × height 16 μm), step size 0.025 μm), in the cross-section of a secondary particle having a size within the range of the average particle size (D 50 ), the number of grain cross-sections confirmed within a unit area of 5 μm horizontal × 5 μm vertical within the cross-section of the secondary particle is 1 or more and 100 or less.
3. The positive electrode active material according to claim 1, comprising a lithium transition metal composite oxide containing nickel, cobalt, and manganese.
4. The positive electrode active material according to claim 1, comprising a lithium transition metal composite oxide containing 60 mol% or more nickel among all transition metals.
5. The positive electrode active material according to claim 1, comprising a lithium transition metal composite oxide having an average composition represented by the following chemical formula 1. [Chemical formula 1] Li x Ni a Co b Mn c M 1 d O 2 (In the above chemical formula 1, M1 is one or more elements selected from the group consisting of Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, V, F, P, S, and Y. (0.9 ≤ x ≤ 1.3, 0.6 ≤ a < 1.0, 0 < b < 0.4, 0 < c < 0.4, 0 ≤ d ≤ 0.2, a + b + c + d = 1.)
6. The positive electrode active material according to claim 1, wherein the plurality of primary particles include single-crystal primary particles.
7. A positive electrode comprising the positive electrode active material described in any one of claims 1 to 6.
8. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, as described in claim 7.

Description

This application claims priority under Korean Patent Application No. 10-2023-0056231 dated April 28, 2023, and Korean Patent Application No. 10-2024-0057080 dated April 29, 2024, and all content disclosed in the documents of said Korean patent applications is incorporated herein by reference. This invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery. In recent years, with the advancement of technologies such as electric vehicles, the demand for high-capacity secondary batteries has increased, leading to active research on high-nickel (High Ni) cathode active materials with superior capacity characteristics. High-nickel positive electrode active materials, formed with a structure of secondary particles formed by the aggregation of primary particles, undergo structural degeneration during charging and discharging of lithium-ion batteries. However, relatively speaking, changes in the lattice structure constant, i.e., volume changes within the unit cell, occur more significantly. Such volume changes can cause cracks in the positive electrode active material. Furthermore, cracks may also occur in the positive electrode active material due to pressure during electrode rolling. The cracks that develop in the high-nickel cathode active material in this way worsen as the lithium secondary battery's charging and discharging cycle progresses. This can lead to the electrolyte failing to make contact with the cracks, or the cracks acting as voids that reduce conductivity, ultimately reducing the battery's lifespan or increasing its resistance. Attempts have been made to manufacture single-particle cathode active materials as a method to minimize crack formation in such secondary particle structures. However, such single-particle cathode active materials have the problem of non-uniform particle size distribution, resulting in a large particle size distribution after grinding. Furthermore, single-particle cathode active materials have a small specific surface area, leading to poor cell resistance characteristics. Therefore, there is a need to develop cathode active materials that can simultaneously solve both the conventional secondary particle problem and the single-particle problem. On the other hand, Korean Patent Registration No. 10-1785262 (Patent Document 1) discloses large-particle secondary particles containing aggregated primary particles, where the secondary particles contain a nickel-based lithium transition metal oxide, the average particle size of the primary particles is 3 to 5 μm, and the average particle size of the secondary particles is 10 to 20 μm. Such large-particle secondary particles, by containing primary particles with an average particle size at the micron level, can improve rolling density and minimize cracks caused by rolling, and the secondary particle structure can improve the specific surface area and cell properties. To manufacture a cathode active material in the form of secondary particles with primary particle sizes at the micron level, as disclosed in Patent Document 1, it is necessary to perform heat treatment at a higher temperature compared to secondary particles with primary particle sizes at the submicron level (less than 1 μm). However, the higher the heat treatment temperature, the more the layered structure of the lithium transition metal composite oxide degenerates into a rock salt structure, causing a decrease in crystallinity, which in turn degrades the performance of the cathode active material. In particular, at high heat treatment temperatures, the degeneration of the layered structure of the lithium transition metal composite oxide into a rock salt structure becomes more severe when nickel is the most fragile element, and the nickel content in the lithium transition metal composite oxide constituting the cathode active material increases. Therefore, conventionally, as a cathode active material in the form of secondary particles with primary particle sizes at the micron level, only mid-nickel (Mid Ni) cathode active materials, in which the nickel content among the transition metals of the lithium transition metal composite oxide is at the 50 mol level, as disclosed in Patent Document 1, were applicable. Furthermore, in high-nickel (High Ni) cathode active materials, which have a high nickel content among the transition metals in lithium transition metal composite oxides and exhibit excellent capacitance characteristics, it was impossible to manufacture cathode active materials in the form of secondary particles with primary particle sizes at the micron level. KR10-1785262B1KR10-2017-0119573A (A) SEM image of the positive electrode active material and (B) SEM image of a cross-section of the positive electrode active material in Example 1.(A) SEM image of the positive electrode active material and (B) SEM image of a cross-section of the positive electrode active material in Example 2.(A) SEM imag