JP-7857354-B2 - Positive electrode active material and lithium secondary battery containing the same

Inventors

• リー，チャン ウ
• チェ，ムン ホ
• ユ，ヒョン ジョン
• パク，ヤン ナム
• パク，ジュン ベー
• ジェオン，ジェ ウ

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

20240723

Priority Date

20200612

Claims (7)

1. A positive electrode active material composed of a lithium composite oxide comprising primary particles containing at least Li, Ni, and B, and secondary particles formed by aggregation of the primary particles, A coating layer containing a boron-containing oxide is present on at least a portion of the surface of the secondary particles. The content of boron (B) in the lithium composite oxide is 0.09 mol% or more and 0.49 mol% or less. The lithium impurity (LiOH) content in the lithium composite oxide is 11,661 ppm or less. Weight loss was measured under an Ar atmosphere at normal pressure from 25°C to 350°C at a heating rate of 10°C/min, and the starting temperature at which the weight loss (thermal decomposition) peak appeared was 231.2°C or higher. The primary particles are a positive electrode active material represented by the following chemical formula 1. [Chemical formula 1] Li w Ni 1-(x+y+z+z') Co x B y M1 z M2 z' O 2 (Here, M1 is at least one selected from Mn and Al. M2 is at least one selected from Mn, Ba, Ce, Hf, Ta, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu. M1 and M2 are different elements. (0.5 ≤ w ≤ 1.5, 0 ≤ x ≤ 0.50, 0 < y ≤ 0.20, 0 ≤ z ≤ 0.20, 0 ≤ z' ≤ 0.20, 0 < x + y + z + z' ≤ 0.50)
2. The positive electrode active material according to claim 1, wherein the coating layer further comprises at least one metal oxide represented by the following chemical formula 3. [Chemical formula 3] Li d M3 e O f (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 ≤ d ≤ 8, 0 < e ≤ 8, 2 ≤ f ≤ 13)
3. The positive electrode active material according to claim 1, wherein the coating layer is removed from at least a portion of the surface of the secondary particles through washing of the lithium composite oxide with water.
4. The positive electrode active material according to claim 3 , wherein the content of residual boron in the lithium composite oxide after washing with water is 0.3 mol% or less.
5. The positive electrode active material according to claim 1, wherein the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl satisfies the following formula 1. [Formula 1] r<(19,153×x1)+x2 (Here, x1 is the boron content (mol%) in the lithium composite oxide before washing with water. x2 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide before washing with water. r is the amount of LiOH leached from the lithium composite oxide after washing with water (ppm).
6. The positive electrode active material according to claim 1, wherein the amount of LiOH eluted from the positive electrode active material by a neutralization titration method using HCl satisfies the following formula 2. [Formula 2] y1≦r≦y1+(y2×(1-y3)×18,429) (Here, y1 is the amount of LiOH (ppm) calculated from the amount of HCl consumed, which corresponds to the x-axis value of the first peak appearing at the smallest x-axis value in the differential graph obtained by differentiating the pH value with respect to the amount of HCl added by the neutralization titration method for the lithium composite oxide after washing with water. y2 is the boron content (mol%) in the lithium composite oxide before washing with water. y3 is the rate of change in the boron content in the lithium composite oxide before and after washing with water, and has a value greater than 0 and less than or equal to 0.90. r is the amount of LiOH leached from the lithium composite oxide after washing with water (ppm).
7. The positive electrode active material according to claim 3 , wherein the ratio of the porosity of the secondary particles after washing with water to the porosity of the secondary particles before washing with water for the lithium composite oxide is 1.7 or more.

Description

This invention relates to a positive electrode active material containing a lithium composite oxide with improved electrochemical properties and stability, and to a lithium secondary battery containing the same. More specifically, it relates to a positive electrode active material and a lithium secondary battery containing the same, in which electrochemical properties and stability are improved by removing at least a portion of the coating layer and lithium-containing impurities present on the surface of the lithium composite oxide. 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 based on 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. Typical materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. These lithium composite oxides include LiCoO₂ , LiMn₂O₄ , LiNiO₂ , LiMnO₂ , or oxides in which Ni, Co, Mn, or Al are composited, as disclosed in Korean Patent Publication No. 10-2015-0069334 (published June 23, 2015). 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 deepening of this cation mixing , a large amount of Li byproducts will be generated. The majority of these Li byproducts consist of LiOH and Li₂CO₃ , which can cause gelation during the production of the positive electrode paste or generate gas due to repeated charging and discharging after electrode production. In addition, residual Li₂CO₃ among the Li byproducts acts as a cause of increased cell swelling and a decrease in lifespan characteristics. To compensate for these shortcomings, the demand for high-ni cathode active materials with a Ni content of 50% or more has begun to increase as cathode active materials for secondary batteries. However, while such high-ni cathode active materials exhibit high capacity characteristics, the increased Ni content in the cathode active material leads to structural instability due to Li/Ni cation mixing. This structural instability in the cathode active material can cause rapid degradation of lithium secondary batteries not only at high temperatures but also at room temperature. Therefore, the development of cathode active materials that complement the problems of such High-Ni cathode active materials is necessary. This is a schematic diagram of a positive electrode active material according to one embodiment of the present invention, illustrating the process by which a coating layer containing a boron-containing oxide and lithium-containing impurities are removed from the surface of secondary particles.This is a differential graph obtained by neutralization titration before water washing of the lithium composite oxide constituting the positive electrode active material in Example 1, Example 2, and Comparative Example 1. The following describes in more detail the positive electrode active material for lithium secondary batteries with improved electrochemical properties and stability according to the present invention, and the lithium secondary battery containing the same. According to one aspect of the present invention, a positive electrode active material is provided which includes secondary particles formed by the aggregation of multiple primary particles, which are lithium composite oxides capable of lithium intercalation and deintercalation. Here, the primary particle refers to a single grain (grain or crystallite), and the secondary particle refers to an aggregate formed by the aggregation of multiple primary particles. The primary particles may have a rod-like, elliptical, and/or amorphous shape. Voids and/or grain boundaries may exist between the primary particles constituting the secondary particles. For ex