JP-7857456-B2 - Positive electrode active material, positive electrode, and lithium secondary battery

Inventors

• リム ラ ナ
• ヤン エー レウム
• キム ギュン ジュン
• リム キョン ミン
• キム ハイ ビン

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

20250217

Priority Date

20201204

Claims (8)

1. A positive electrode active material comprising a lithium-rich lithium-manganese oxide containing at least lithium, nickel, and manganese, The aforementioned lithium manganese oxide is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group. In the solid solution, there exists a region where the proportion of the phase belonging to the C2/m space group and the phase belonging to the R3-m space group are different. The lithium manganese oxide in the positive electrode active material satisfies the following formula 1, where the concentration of the metal element satisfies the following formula 1. [Formula 1] 0.24≦ M2 /M1 ≦ 0.55 Here, M1 is the total number of moles of metal elements (excluding lithium) in the lithium manganese oxide. M2 is the number of moles of nickel in the lithium manganese oxide, based on the total number of metal elements (excluding lithium).
2. The lithium manganese-based oxide is a core-shell particle comprising a core and a shell covering at least a portion of the surface of the core, Within the core, the phase belonging to the C2/m space group and the phase belonging to the R3-m space group coexist. The positive electrode active material according to claim 1, wherein the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group within the shell is greater than the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group within the core.
3. The positive electrode active material according to claim 2, wherein the concentration of the metal element inside the shell satisfies the following formula 3. [Formula 3] 0.24≦ M4 /M3 ≦ 0.75 Here, M3 is the total number of moles of metal elements (excluding lithium) within the shell. M4 is the number of moles of nickel relative to the total metal elements (excluding lithium) within the shell.
4. The positive electrode active material according to claim 2, wherein the concentration of the metal element inside the shell satisfies the following formula 4. [Formula 4] 0.40≦ M4′ /M3 ′ ≦0.75 Here, M3 ' is the total number of moles of metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the shell. M 4' is the number of moles of nickel relative to the total number of metallic elements (excluding lithium) in the phase belonging to the R3-m space group within the shell.
5. The positive electrode active material according to claim 2, wherein the ratio of the phase belonging to the R3-m space group to the phase belonging to the C2/m space group in the lithium manganese-based oxide has a gradient that increases from the core toward the shell.
6. The lithium manganese oxide is the positive electrode active material according to claim 1, represented by the following chemical formula 1. [Chemical formula 1] rLi 2 MnO 3 (1-r) Li a Ni x Co y Mn z M1 1-(x+y+z) O 2 Here, M1 is at least one selected from Mo, Nb, Fe, Cr, V, Cu, Zn, Sn, Mg, Ru, Al, Ti, Zr, B, Na, K, Y, P, Ba, Sr, La, Ga, Gd, Sm, W, Ca, Ce, Ta, Sc, In, S, Ge, Si, and Bi. 0 < r ≤ 0.8, 0 < a ≤ 1, 0 < x ≤ 1, 0 ≤ y < 1, 0 < z < 1, and 0 < x + y + z ≤ 1.
7. The positive electrode active material according to claim 1, wherein the lithium manganese-based oxide comprises at least one selected from non-aggregated particles containing a single primary particle and secondary particles formed by the aggregation of multiple primary particles.
8. The positive electrode active material according to claim 7 , wherein the average major axis length of the primary particles is 0.1 μm to 20 μm.

Description

This invention relates to a positive electrode active material, a positive electrode, and a lithium secondary battery containing the same. More specifically, it relates to a lithium-rich lithium manganese oxide, which is a solid solution of a phase belonging to the C2/m space group and a phase belonging to the R3-m space group, wherein the lithium manganese oxide contains regions where the proportions of the phases belonging to the C2/m space group and the phases belonging to the R3-m space group differ, thereby mitigating and/or preventing the decrease in stability caused by the excess lithium and manganese present in 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 during the intercalation/deintercalation of lithium ions 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 polymer electrolyte. Lithium composite oxides are used as positive electrode active materials in lithium secondary batteries. Examples include LiCoO₂ , LiMn₂O₄ , LiNiO₂ , LiMnO₂, and composite oxides in which Ni, Co , Mn, or Al are combined, as described 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 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, depending on the degree of deepening of this 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 problems such as gel formation during the production of the positive electrode paste and gas generation as charging and discharging progresses after the electrode is manufactured. Residual Li₂CO₃ not only increases the swelling phenomenon of the cell and reduces the number of cycles, but also causes the battery to swell. Various candidate materials are being discussed 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: the lithium secondary battery using OLO has a low capacity rate. Thus, a low capacity rate leads 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, the decrease in charge/discharge capacity or voltage decay during charge/discharge cycles of lithium secondary batteries using OLO can also be induced by phase transitions due to the migration of transition metals in lithium manganese oxides. For example, in layered crystalline lithium manganese oxides, if a phase transition is induced by unintended migration of transition metals, a spinel or similar crystalline structure may develop entirely and/or partially within the lithium manganese oxide. To address the aforementioned problems, attempts have been made to improve the structure and surface modification of OLO particles, such as adjusting the particle size or coating the surface of the OLO particles. However, these attempts have not yet reached a commercialization level. Korean Published Patent Publication No. 10-2015-0069334 (Published June 23, 2015) Figure 1 shows the TEM analysis results for lithium manganese