JP-7857478-B2 - Positive electrode active material and lithium secondary battery containing the same

Inventors

• パク ジュン ペ
• チェ ムン ホ
• ユ ヒュン ジョン

Assignees

• エコプロ ビーエム カンパニー リミテッド

Dates

Publication Date

20260512

Application Date

20250604

Priority Date

20200902

Claims (7)

1. The positive electrode active material is in a bimodal form, containing small-particle first lithium composite oxide and large-particle second lithium composite oxide. The average particle size (D50) of the first lithium composite oxide is 8 μm or less. The average particle size (D50) of the second lithium composite oxide is 8.5 μm or larger. The positive electrode active material is The first coating layer covers at least a portion of the surface of the first lithium composite oxide and includes a first metal oxide, The second coating layer covers at least a portion of the surface of the second lithium composite oxide and includes a second metal oxide, The first lithium composite oxide is a composite particle containing at least one primary particle, The first lithium composite oxide is defined such that the average value of the grain boundary density calculated by the following equation 3 for primary particles arranged on a hypothetical straight line crossing the center of the first lithium composite oxide in a cross-sectional SEM image of the first lithium composite oxide is less than or equal to the average value of the grain boundary density calculated by the following equation 3 for primary particles arranged on a hypothetical straight line crossing the center of the second lithium composite oxide in a cross-sectional SEM image of the second lithium composite oxide. The first metal oxide and the second metal oxide each comprise at least one coating element selected from Co, Al, Mn, Zr, and Nb. When the difference (at%) between the content of the coating element present on the surface of the first lithium composite oxide and the content of the coating element present on the surface of the first coating layer, as determined by SEM/EDS analysis, is called r1, and the difference (at%) between the content of the coating element present on the surface of the second lithium composite oxide and the content of the coating element present on the surface of the second coating layer, as determined by SEM/EDS analysis, is called r2, The aforementioned r1 and r2 are positive electrode active materials that satisfy the following formula 2 . [Formula 3] The density of grain boundaries = (number of interface surfaces between primary particles arranged on the imaginary straight line / number of primary particles arranged on the imaginary straight line) [Formula 2] 0.72≦r2/r1<1.23
2. The first lithium composite oxide is a composite particle containing at least one primary particle, The positive electrode active material according to claim 1, wherein the first lithium composite oxide has a grain boundary density calculated by the following formula 3 for primary particles arranged on a hypothetical straight line crossing the center of the first lithium composite oxide in a cross-sectional SEM image of the first lithium composite oxide, which is 0.75 or less. [Formula 3] The density of grain boundaries = (number of interface surfaces between primary particles arranged on the imaginary straight line / number of primary particles arranged on the imaginary straight line)
3. The first lithium composite oxide has a single-crystal structure, as described in claim 2.
4. The second lithium composite oxide is a composite particle containing at least one primary particle, The positive electrode active material according to claim 1, wherein the second lithium composite oxide has a grain boundary density of 0.90 or more, calculated by the following formula 3 for primary particles arranged on a hypothetical straight line crossing the center of the second lithium composite oxide in a cross-sectional SEM image of the second lithium composite oxide. [Formula 3] The density of grain boundaries = (number of interface surfaces between primary particles arranged on the imaginary straight line / number of primary particles arranged on the imaginary straight line)
5. The positive electrode active material according to claim 1, wherein the first lithium composite oxide and the second lithium composite oxide are represented by the following chemical formula 1. [Chemical formula 1] Li w Ni 1-(x+y+z) Co x M1 y M2 z O 2+α (Here, M1 is at least one selected from Mn and Al. M2 is at least one selected from P, Sr, Ba, B, Ce, Cr, Mn, Mo, Na, K, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W, and Cu. M1 and M2 are different from each other. (0.5 ≤ w ≤ 1.5, 0 ≤ x ≤ 0.50, 0 ≤ y ≤ 0.20, 0 ≤ z ≤ 0.20, 0 ≤ α ≤ 0.02)
6. The positive electrode active material according to claim 1, wherein the first metal oxide and the second metal oxide are each independently represented by the following chemical formula 2. [Chemical formula 2] Li a M3 b O c (Here, M3 is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Gd, and Nd. (0 ≤ a ≤ 10, 0 ≤ b ≤ 8, 2 ≤ c ≤ 13)
7. The positive electrode active material according to claim 6 , wherein M3 is at least one selected from Co, Al, Mn, Zr, and Nb.

Description

This invention relates to a positive electrode active material and a lithium secondary battery containing the same, and more specifically, to a bimodal positive electrode active material comprising a first lithium composite oxide with small particles and a second lithium composite oxide with large particles having different average particle sizes, wherein the invention can prevent a decrease in the electrochemical properties and stability of the positive electrode active material caused by the uneven distribution of a coating layer that coats at least a portion of the surfaces of the small and large particles, a positive electrode containing the positive electrode active material, and a lithium secondary battery using the positive electrode. A battery stores electrical energy by using electrochemically reactive materials at its 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 composite oxides are used as positive electrode active materials in lithium secondary batteries, and examples of composite oxides such as LiCoO₂ , LiMn₂O₄ , LiNiO₂ , and LiMnO₂ are being studied. 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. Furthermore, while LiNiO₂- based cathode active materials exhibit high discharge capacity, their synthesis is difficult due to cation mixing problems between Li and transition metals, resulting in significant problems with their rate characteristics. Furthermore, depending on the degree of cation mixing, a large amount of Li byproducts are generated. Since the majority of these Li byproducts consist of LiOH and Li₂CO₃ compounds , they cause gelation problems during the production of the positive electrode paste and gas generation as charging and discharging progresses after the electrode is manufactured. The residual Li₂CO₃ increases the swelling phenomenon of the cell, reducing the number of cycles and causing the battery to swell. On the other hand, in recent years, to increase the capacity of lithium secondary batteries, bimodal positive electrode active materials, which are mixtures of small and large particles with different average particle sizes, have frequently been used. When small and large particles are mixed, the gaps between the large particles can be filled by the relatively smaller particles, thereby improving the accumulation density of lithium composite oxide per unit volume and increasing the energy density per unit volume. However, when small and large particles are mixed with the coating material and then fired simultaneously, the coating material may be unevenly distributed on the smaller particles, which have a relatively larger specific surface area. This can lead to a coating imbalance between the small and large particles, which can degrade the electrochemical properties and stability of the bimodal positive electrode active material containing the mixed small and large particles. Korean Patent Publication No. 10-2010-0131921 This figure schematically shows a cross-section of a lithium composite oxide used to calculate the density of grain boundaries as defined in this application.This figure schematically shows a cross-section of a lithium composite oxide used to calculate the density of grain boundaries as defined in this application. For the sake of easier understanding of the present invention, certain terms are defined herein for convenience. Unless otherwise defined herein, the scientific and technical terms used herein have the meanings generally understood by a person of ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms are to be understood as including their plural forms, and plural terms are to be understood as including their singular forms. The following will provide a more detailed description of the positive electrode active material and the lithium secondary battery containing the positive electrode active material according to the present invention. According to one aspect of the pre