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JP-7857469-B2 - Positive electrode active material and lithium secondary battery using it

JP7857469B2JP 7857469 B2JP7857469 B2JP 7857469B2JP-7857469-B2

Inventors

  • ムン チェ ウォン
  • ユ ヒュン ジョン
  • パク ジュン ペ
  • チェ ムン ホ

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
20250409
Priority Date
20210331

Claims (10)

  1. A positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation/deintercalation, The molar ratio of Ni to all metal elements other than lithium in the lithium composite oxide is 0.6 or more. The ratio of peak intensities attributed to the (003) plane and the (104) plane obtained from X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide satisfies the following equation 2: The positive electrode active material exhibits a weight loss rate of 0.91% or less when heated to 810°C at a heating rate of 10°C/min under an Ar atmosphere at normal pressure. [Formula 2] 0.630≦I(104)/I(003)≦0.698
  2. A positive electrode active material comprising a layered lithium composite oxide capable of lithium intercalation/deintercalation, The molar ratio of Ni to all metal elements other than lithium in the lithium composite oxide is 0.6 or more. The ratio of peak intensities attributed to the (003) plane and the (101) plane obtained from X-ray diffraction analysis using Cu-Kα rays for the lithium composite oxide satisfies the following equation 3: The positive electrode active material exhibits a weight loss rate of 0.91% or less when heated to 810°C at a heating rate of 10°C/min in an Ar atmosphere at normal pressure. [Formula 3] 0.379≦I(101)/I(003)≦0.421
  3. The positive electrode active material according to claim 1 or 2, wherein the lithium ion diffusion pathway formed within the lithium composite oxide is formed parallel to the long axis direction of the lithium composite oxide.
  4. The lithium ion diffusion pathway formed within the lithium composite oxide is formed parallel to the (003) plane, as described in claim 1 or 2 of the positive electrode active material.
  5. The positive electrode active material according to claim 1 or 2, wherein the lithium ion diffusion pathway formed within the lithium composite oxide is formed to direct at least one crystal plane selected from the (012) plane, the (101) plane, and the (104) plane.
  6. The lithium composite oxide is the positive electrode active material according to claim 1 or 2, represented by the following chemical formula 1. (Chem.1) Li a Ni 1-(b+c+d+e) Co b M1 c M2 d M3 e Of (Here, M1 is at least one selected from Mn and Al. M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr. M1 to M3 are different from each other. (0.90 ≤ a ≤ 1.15, 0 ≤ b ≤ 0.20, 0 ≤ c ≤ 0.10, 0 ≤ d ≤ 0.05, 0 ≤ e ≤ 0.05, 1.0 ≤ f ≤ 2.0.)
  7. The lithium composite oxide contains at least one primary particle, The positive electrode active material according to claim 1 or 2, wherein, in a cross-sectional SEM image of the lithium composite oxide, the density of grain boundaries calculated by the following formula 5 for primary particles lying on a hypothetical straight line crossing the center of the lithium composite oxide is 0.50 or less. [Formula 5] Grain boundary density = (Number of interface surfaces between primary particles on the imaginary straight line / Number of primary particles on the imaginary straight line)
  8. The positive electrode active material is an aggregate of multiple lithium composite oxides, each consisting of at least one primary particle. The positive electrode active material according to claim 1 or 2, wherein, in the aggregate, the proportion of lithium composite oxides in which the density of crystal grain boundaries calculated by the following formula 5 is 0.50 or less for primary particles that lie on a hypothetical straight line crossing the center of the lithium composite oxide in a cross-sectional SEM image of the lithium composite oxide is 30% or more. [Formula 5] Grain boundary density = (Number of interface surfaces between primary particles on the imaginary straight line / Number of primary particles on the imaginary straight line)
  9. The present invention further includes a coating layer covering at least a portion of the surface of the lithium composite oxide, The positive electrode active material according to claim 1 or 2, wherein the coating layer comprises at least one oxide represented by the following chemical formula 2. (Case 2) Li a A b O c (Here, A is at least one selected from Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd. 0 ≤ a ≤ 10, 0 ≤ b ≤ 8, 2 ≤ c ≤ 15.
  10. The positive electrode active material according to claim 1 or 2, wherein the ratio of peak intensities attributed to the (003) plane and the (110) plane obtained from X-ray diffraction analysis using Cu-Kα rays on the lithium composite oxide (I(110)/I(003)) is 0.149 or more and 0.172 or less.

Description

This invention relates to a positive electrode active material and a lithium secondary battery using it, in which the lithium ion diffusion pathways within the lithium composite oxide constituting the positive electrode active material are formed to point towards specific crystal planes, and the growth of the crystal planes pointed towards by the lithium ion diffusion pathways is improved. 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 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. Among the 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 exhibit high discharge capacity battery characteristics, but their synthesis is difficult due to cation mixing problems between Li and transition metals, and consequently, there are significant problems with their rate characteristics. Furthermore, depending on the degree of cation mixing, a large amount of Li byproducts are generated. Most of these Li byproducts consist of LiOH and Li₂CO₃ compounds , which cause gelation during the production of the positive electrode paste and lead to gas generation as charging and discharging progresses after electrode production . Residual Li₂CO₃ not only increases the swelling phenomenon of the cell and reduces the number of cycles, but also causes the battery to swell. To compensate for these shortcomings, the demand for high-Ni type cathode active materials with a Ni content of 50% or more has begun to increase. However, while such high-Ni type 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 cathode active materials can cause rapid degradation of lithium-ion batteries not only at high temperatures but also at room temperature. On the other hand, in recent years, cathode active materials containing not only polycrystalline lithium composite oxides but also single-crystal lithium composite oxides have been proposed (Journal of The Electricochemical Society, Volume 164, Number 7, A1534-A1544 (published May 23, 2017)). The aforementioned document discloses that a lithium composite oxide with a single-crystal structure having a crystallite size of 2-3 μm (LiNi 0.5 Mn 0.3 Co 0.2 O 2 ) exhibits some improved stability compared to a lithium composite oxide with a polycrystalline structure of the same composition. However, if the firing temperature is excessively increased or the firing time is excessively extended in order to single-crystallize the lithium composite oxide constituting the positive electrode active material, the cation mixing phenomenon mentioned above may increase. In particular, when cation mixing increases in single-crystal lithium composite oxides, an excess amount of lithium composite oxide having a quasi-safe phase or Rock-salt phase may be formed in addition to the intended layered structure. The presence of an excess of lithium composite oxide with phases other than the layered structure can lead to degradation of the positive electrode active material, which is an aggregate of these phases. Such degradation of the positive electrode active material can cause a decrease in capacity and a reduction in lifespan. Therefore, there are clear limitations to providing a single-crystal structured cathode active material simply by increasing the firing temperature of the lithium composite oxide constituting the cathode active material. Figures 1 and 2 are schematic diagrams illustrating cross-sectional images of lithium composite oxides contained in positive electrode active materials according to various embodiments of the present invention.Figures 1 and 2 are schematic diagrams illustrating cr