JP-2026075618-A - Positive electrode active material and lithium secondary battery containing the same

Abstract

[Problem] To provide a positive electrode active material with improved resistance to strain caused by volume contraction/expansion of unit particles due to repeated charging and discharging, and a lithium secondary battery containing the same. [Solution] The positive electrode active material contains a lithium transition metal oxide in the form of a single particle consisting of one unit particle and/or a similar single-particle form in which 30 or fewer unit particles are aggregated. By reducing the intergranular cracks and intragranular cracks present in the positive electrode active material, it is possible to enable a lithium secondary battery using the positive electrode active material to exhibit stable electrochemical properties for a long period of time. [Selection Diagram] Figure 1

Inventors

• リュ、ムンファ
• ムン、チェウォン
• チョン、ヒョンス
• イム、ラナ
• シン、ジェフン

Assignees

• エコプロ ビーエム カンパニー リミテッド

Dates

Publication Date

20260508

Application Date

20251021

Priority Date

20241022

Claims (14)

1. It contains lithium transition metal oxides that allow for lithium intercalation/deintercalation, The lithium transition metal oxide has at least one form selected from a single-particle form consisting of one unit particle and a similar single-particle form in which 30 or fewer unit particles are aggregated. A positive electrode active material in which the ratio (a1/a) of the total crack area (a1) present on the surface of the unit particle to the surface area (a) of the unit particle observed from a surface SEM image of the lithium transition metal oxide is 10% or less.
2. When the radius of the unit particle measured from the cross-sectional SEM image of the unit particle is denoted as r, The positive electrode active material according to claim 1, wherein the number of surface cracks where the distance (d) from the center of the unit particle is (2/3)r < d is greater than the number of central cracks where the distance (d) from the center of the unit particle is 0 ≤ d ≤ (2/3)r.
3. When r1 is defined as the length of the major axis measured from the surface shape of the unit particle observed from the surface SEM image of the lithium transition metal oxide, The positive electrode active material according to claim 1, wherein the ratio (a2/a) of the total surface area (a) of the unit particle observed from a surface SEM image of the lithium transition metal oxide to the total surface area (a) of the unit particle, where the distance (d1) from the outermost edge of the unit particle is d1 ≤ (1/4)r1, is 5% or less.
4. When the length of the minor axis measured from the surface shape of the unit particle observed from the surface SEM image of the lithium transition metal oxide is denoted as r2, The positive electrode active material according to claim 1, wherein the ratio (a3/a) of the total surface area (a) of the unit particle observed from a surface SEM image of the lithium transition metal oxide to the total surface area (a) of the unit particle, where the distance (d2) from the outermost edge of the unit particle is d2 ≤ (1/3)r2, is 9% or less.
5. The lithium transition metal oxide comprises lithium and a transition metal. The positive electrode active material according to claim 1, wherein the nickel content in the transition metal is 50 mol% or more.
6. The positive electrode active material according to claim 1, wherein the average particle size (D 50 ) of the lithium transition metal oxide present in the single-particle form is 2.0 μm or more and 10.0 μm or less.
7. The positive electrode active material according to claim 1, wherein the average particle size (D 50 ) of the lithium transition metal oxide existing in the aforementioned similar single-particle form is 3.0 μm or more and 20.0 μm or less.
8. The positive electrode active material according to claim 1, wherein the number of unit particles observed from the surface SEM image of the lithium transition metal oxide existing in the aforementioned similar single-particle morphology is 20 or less.
9. The surface shape of the unit particle observed from the surface SEM image of the lithium transition metal oxide has a long axis and a short axis, The positive electrode active material according to claim 1, wherein the average length of the major axis of the unit particle is 2.0 μm or more and 10.0 μm or less.
10. The surface shape of the unit particle observed from the surface SEM image of the lithium transition metal oxide has a long axis and a short axis, The positive electrode active material according to claim 1, wherein the average value of the length of the short axis of the unit particle is 1.0 μm or more and less than 10.0 μm.
11. The positive electrode active material according to claim 1, wherein the content of alkali metals and alkaline earth metals in the lithium transition metal oxide, excluding lithium, is 0.1 mol% or more and 5.0 mol% or less.
12. The lithium transition metal oxide is represented by the following chemical formula 1, and is the positive electrode active material according to claim 1: [Chemical formula 1] Li a Ni 1-(b+c+d+e) Co b Mn c M1 d M2 e O 2 In the aforementioned chemical formula 1, M1 is at least one selected from Na, K, Mg, Ca, Sr, Ba, and Rb. M2 is at least one selected from B, Ce, Hf, Ta, Cr, F, Al, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu. 0.85 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.20, 0 ≤ c ≤ 0.20, 0.001 ≤ d ≤ 0.05, 0 ≤ e ≤ 0.10, and 0.5 ≤ 1 - (b + c + d + e) < 1.0.
13. A positive electrode comprising the positive electrode active material described in any one of claims 1 to 12.
14. A lithium secondary battery using the positive electrode described in claim 13.

Description

This invention relates to a positive electrode active material and a lithium secondary battery containing the same. More specifically, the invention relates to a positive electrode active material comprising a lithium transition metal oxide in the form of a single particle consisting of one unit particle and/or a similar single-particle form in which 30 or fewer unit particles are aggregated, thereby enabling a lithium secondary battery using the positive electrode active material to exhibit stable electrochemical properties for a long period of time. Batteries store electricity by using electrochemically reactive materials at the positive and negative electrodes. A typical example of such a battery is the lithium-ion secondary battery, which stores electrical energy through the difference in chemical potential that occurs when lithium ions intercalate/deintercalate at the positive and negative electrodes. The aforementioned lithium secondary battery is manufactured by using materials capable of reversible intercalation/deintercalation of lithium ions as the positive and negative electrode active materials, and by filling the space between the positive and negative electrodes with an organic electrolyte or a polymer electrolyte. Lithium transition metal oxides are used as positive electrode active materials in lithium secondary batteries, and composite oxides such as LiCoO₂ , LiMn₂O₄ , LiNiO₂ , and LiMnO₂ are being studied as examples. Of the aforementioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifespan characteristics and charge/discharge efficiency. However, it has the disadvantage of being expensive due to the resource limitations of cobalt used as a raw material, thus limiting its price competitiveness. Lithium manganese oxides such as LiMnO₂ and LiMn₂O₄ have the advantages of excellent thermal safety and low cost, but they have the drawbacks of low capacity and poor high-temperature performance. LiNiO₂ -based cathode active materials have the advantage of exhibiting high discharge capacity, but they are not only difficult to synthesize due to the active cation mixing of Li and Ni, but the synthesized cathode active materials also have the problem of very poor rate characteristics and lifetime characteristics. As a result, in order to improve the low rate characteristics and lifetime characteristics while maintaining the high reversible capacity of LiNiO2 , ternary lithium transition metal oxides such as NCM (Ni-Co-Mn) and NCA (Ni-Co-Al), or quaternary lithium transition metal oxides such as NCMA (Ni-Co-Mn-Al), have been developed in which some of the nickel is replaced with cobalt, manganese, and/or aluminum. Since the reversible capacity decreases as the nickel content in such ternary or quaternary lithium transition metal oxides decreases, research to increase the nickel content in lithium transition metal oxides has been actively conducted recently. Incidentally, as the nickel content in lithium transition metal oxides increases, the cation mixing within the crystal structure increases, leading to decreased stability and an increase in the content of unreacted lithium impurities such as LiOH and Li₂CO₃ on the surface. Furthermore, many lithium transition metal oxides have a secondary particle morphology in which multiple primary particles are aggregated. The more primary particles that make up the secondary particles, the larger the specific surface area. As the specific surface area of the lithium transition metal oxide increases, repeated charging and discharging can cause strain (strain) to accumulate due to random volume contraction/expansion of the primary particles, potentially leading to cracks (grain boundary cracks) between adjacent primary particles. These grain boundary cracks within the secondary particles reduce connectivity between adjacent primary particles, interfering with the lithium ion transport mechanism. Additionally, increasing the exposed surface area of the primary particles can lead to increased side reactions with the electrolyte, potentially causing a rapid decrease in the stability of the positive electrode active material. Therefore, in order to solve the aforementioned problems of grain boundary cracks, there have recently been attempts to induce the growth of primary particles through high-temperature firing and reduce the specific surface area of lithium transition metal oxides. However, when the growth of primary particles is induced through high-temperature firing, while grain boundary cracks tend to decrease, there is a problem of increased cracks in the primary particles. The cracks present in the primary particles include intragranular cracks located inside the primary particles and surface cracks located on the surface of the primary particles. Similar to the grain boundary cracks, surface cracks located on the surface of the primary particles can increase the exposed surface area of the primary particles, whic