JP-7857252-B2 - Positive electrode active material, positive electrode, and lithium secondary battery

Inventors

• リム ラ ナ
• チョン ヒョン ス
• リム キョン ミン
• キム ソウン キョン
• パク ウン ヒ

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

20230614

Priority Date

20221027

Claims (15)

1. A bimodal type positive electrode active material comprising a first lithium manganese oxide and a second lithium manganese oxide having different average particle sizes, The difference in average particle size between the first lithium manganese oxide and the second lithium manganese oxide is 3 μm or more. The first lithium manganese oxide and the second lithium manganese oxide are lithium-rich lithium manganese oxides in which a phase belonging to the C2/m space group and a phase belonging to the R3-m space group are in solid solution. The manganese content in the total metal elements excluding lithium present in the first lithium manganese oxide and the second lithium manganese oxide is 50 mol% or more and less than 80 mol%. The average particle size of the first lithium manganese oxide is 2 μm to 6 μm. The average particle size of the second lithium manganese oxide is 7 μm to 14 μm. The first lithium manganese oxide and the second lithium manganese oxide are each independently represented by the following chemical formula 1-1 , A positive electrode active material wherein the manganese content (mol%) relative to the total transition metal in the first lithium manganese-based oxide is smaller than the manganese content (mol%) relative to the total transition metal in the second lithium manganese-based oxide . [Chemical formula 1-1] rLi 2 MnO 3-b″ X′ b″ ・(1-r)Li a′ M1 x′ M2 y′ O 2-b′ X b′ (Here, M1 is Ni , M2 is at least one selected from Mn , Co, Al, P, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd . X and X' are halogens capable of substituting at least a portion of the oxygen present in the lithium manganese oxide, (0 < r ≤ 0.7, 0 <a' ≤ 1, 0 ≤ b' ≤ 0.1, 0 ≤ b'' ≤ 0.1, 0 <x' ≤ 1, 0 ≤ y'< 1, 0 <x' + y' ≤ 1)
2. The main peak in the volume-based particle size distribution graph for the first lithium manganese oxide (x-axis: particle size (μm), Y-axis: volume %) is located between 1 μm and 8 μm. The positive electrode active material according to claim 1, wherein the main peak of the volume-based particle size distribution graph (x axis: particle size (μm), Y axis: volume %) for the second lithium manganese-based oxide is located between 6 μm and 24 μm.
3. The positive electrode active material according to claim 1, wherein the first lithium manganese-based oxide and the second lithium manganese-based oxide in the positive electrode active material are present in a weight ratio of 10:90 to 80:20.
4. The positive electrode active material according to claim 1, wherein the first lithium manganese-based oxide and the second lithium manganese-based oxide each independently contain at least one selected from nickel, cobalt, and manganese.
5. The first lithium manganese oxide and the second lithium manganese oxide are each independently lithium manganese oxides containing nickel and manganese. The positive electrode active material according to claim 1, wherein the manganese content (mol%) relative to the total transition metals present on the surface of the first lithium manganese-based oxide is smaller than the manganese content (mol%) relative to the total transition metals present on the surface of the second lithium manganese-based oxide.
6. The positive electrode active material according to claim 1, wherein at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide is a core-shell particle exhibiting at least one concentration gradient selected from nickel and manganese from the center to the surface.
7. The positive electrode active material according to claim 6 , wherein the core-shell particles exhibit a gradient in which the concentration of nickel increases from the center to the surface and the concentration of manganese decreases.
8. The first lithium manganese-based oxide is a core-shell particle exhibiting a concentration gradient of at least one selected from nickel and manganese from the center toward the surface. The positive electrode active material according to claim 1, wherein the second lithium manganese oxide is a particle in which the concentrations of nickel and manganese are constant from the center to the surface, or which exhibits a concentration gradient having a smaller slope than the concentration gradient that appears in the first lithium manganese oxide.
9. The positive electrode active material according to claim 1, wherein a barrier layer exists on at least a portion of the surface of at least one of the first lithium manganese-based oxide and the second lithium manganese-based oxide.
10. The first lithium manganese-based oxide is a core-shell particle exhibiting a concentration gradient from the core to the shell of at least one selected from nickel and manganese. The positive electrode active material according to claim 9 , wherein a barrier layer is present on at least a portion of the surface of the shell.
11. The second lithium manganese oxide is a particle in which the concentrations of nickel and manganese are constant from the center to the surface, or which exhibits a concentration gradient having a smaller slope than the concentration gradient that appears in the first lithium manganese oxide. The positive electrode active material according to claim 9 , wherein a barrier layer is present on at least a portion of the surface of the second lithium manganese-based oxide.
12. The positive electrode active material according to claim 9 , wherein the barrier layer comprises an oxide containing at least one selected from a metallic element, a metalloid element, and phosphorus (P).
13. The positive electrode active material according to claim 9, wherein the barrier layer comprises at least one selected from a first oxide represented by the following chemical formula 2, a second oxide represented by the following chemical formula 3, and a third oxide represented by the following chemical formula 4 . [Chemical formula 2] Li c B d M3 e Of (Here, M3 is at least one selected from Ni, Mn, Co, Al, Nb, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd. (0 ≤ c ≤ 8, 0 < d ≤ 8, 0 ≤ e ≤ 8, 2 ≤ f ≤ 13) [Chemical formula 3] Li g M4 h O i (Here, M4 is at least one selected from Ni, Mn, Co, Al, Nb, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd. (Except when g and h are both 0, where 0 ≤ g ≤ 8, 0 ≤ h ≤ 8, and 2 ≤ i ≤ 13.) [Chemical formula 4] Li j M5 k (P l O m ) n (Here, M5 is at least one selected from Ni, Mn, Co, Al, Nb, B, Si, Ti, Zr, Ba, K, Mo, Fe, Cu, Cr, Zn, Na, Ca, Mg, Pt, Au, Eu, Sm, W, Ce, V, Ta, Sn, Hf, Gd, and Nd. (Except when j and k are both 0, where 0 ≤ j ≤ 10, 0 ≤ k ≤ 8, 0 < l ≤ 4, 0 < m ≤ 10, and 0 < n ≤ 13)
14. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 13 .
15. A lithium secondary battery using the positive electrode described in claim 14 .

Description

This invention relates to a positive electrode active material, a positive electrode, and a lithium secondary battery containing the same. More specifically, the invention relates to a bimodal type positive electrode active material, a positive electrode, and a lithium secondary battery containing the same, which can improve the low energy density per unit volume of lithium-rich lithium manganese oxides, prevent the deterioration of the electrochemical properties of the lithium secondary battery, including rate characteristics, due to excess lithium and manganese present in the lithium manganese oxide, and in particular prevent the deterioration of the lifespan of the lithium secondary battery by suppressing or mitigating the leaching of transition metals from the lithium manganese oxide. A battery stores electricity 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 electrode active material and the negative electrode active material, and by filling the space between the positive and negative electrodes with an organic electrolyte or 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 formed by the combination of Ni, Co, Mn, or Al. 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 advantages such as 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, a large amount of Li by-products is generated depending on the degree of deepening of such cation mixing. These Li by-products mostly consist of LiOH and Li₂CO₃ , which may 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 by-products increases the swelling phenomenon of the cell, which reduces its lifespan characteristics. Various candidate materials have been proposed to compensate for the shortcomings of these conventional cathode active materials. As an example, research is underway to use lithium-rich lithium-manganese oxides, which contain an excess amount of manganese (Mn) among the transition metals, and whose lithium content exceeds the total content of the transition metals, as positive electrode active materials for lithium-ion secondary batteries. Such lithium-rich lithium-manganese oxides are also called lithium-rich layered oxides (OLOs). While the aforementioned OLO theoretically has the advantage of exhibiting high capacity under high-voltage operating conditions, in practice, its relatively low electrical conductivity is due to the excess amount of Mn contained in the oxide. This results in a disadvantage: lithium secondary batteries using OLO have poor rate characteristics. Thus, poor rate characteristics lead to problems such as a decrease in charge/discharge capacity and life efficiency (cycle capacity retention) during the charge-discharge cycle of the lithium secondary battery. Furthermore, due to its material properties, OLO has a high porosity within its particles, resulting in the disadvantage of a low energy density per unit volume. To address the aforementioned problems, research has been ongoing to modify the composition of OLO, but currently, such attempts have not reached a commercialization level. For the sake of easier understanding of this invention, certain terms are defined in this application for convenience. Unless otherwise defined in this application, the scientific and technical terms used herein have meanings that are generally understood by those with ordinary skill in the art. Furthermore, unless otherwise specified in the context, singular terms should be understood to include their plural forms, and plural terms should be understood to include their singular forms. The following describes in more de