Nickel-based lithium metal composite oxides, their preparation methods and lithium secondary batteries

Abstract

This article discloses a nickel-based lithium metal composite oxide, a method for preparing the same, and a lithium secondary battery including a positive electrode comprising the same. The nickel-based lithium metal composite oxide comprises: secondary particles comprising aggregates of primary particles, wherein the nickel content in the nickel-based lithium metal composite oxide is 50 mol% or more based on the total transition metal content in the nickel-based lithium metal composite oxide; the secondary particles include large secondary particles having a particle size of 10 μm or larger and small secondary particles having a particle size of 5 μm or smaller, and the nickel content in the large secondary particles is greater than the nickel content in the small secondary particles.

Description

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2020-0080492, filed on June 30, 2020, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] One or more embodiments of this disclosure relate to nickel-based lithium metal composite oxides, methods for preparing the same, and lithium secondary batteries including a positive electrode comprising the same. Background Technology

[0004] With the advancement of portable electronic and communication devices, there is a great need to develop lithium secondary batteries with high energy density.

[0005] When lithium metal composite oxides are used as the positive electrode active material for lithium secondary batteries, the cracking of the active material can be suppressed or reduced even during extrusion when large and small secondary particles are mixed, thus exhibiting excellent performance and enabling the manufacture of lithium secondary batteries with high energy density.

[0006] In the manufacture of lithium metal composite oxides comprising a mixture of large and small secondary particles, heat treatment processes are performed simultaneously for both the large and small secondary particles. However, because the large and small secondary particles have different characteristics, when they are heat-treated simultaneously, either the large or small secondary particles may be over-sintered or incompletely sintered, resulting in performance degradation or reduction. Accordingly, the large and small secondary particles are heat-treated separately, and then the heat-treated mixture is heat-treated separately. However, because performing multiple heat treatment processes as described above complicates the preparation of the positive electrode active material and increases its preparation cost, improvements in this regard would be beneficial. Summary of the Invention

[0007] One or more embodiments of this disclosure provide nickel-based lithium metal composite oxides with improved structural stability.

[0008] One or more embodiments provide a method for preparing nickel-based lithium metal composite oxides at low cost through a simplified process.

[0009] One or more embodiments provide a lithium secondary battery including a positive electrode comprising a nickel-based lithium metal composite oxide to have improved efficiency and lifespan.

[0010] Further aspects of the implementation will be set forth in part in the description which follows, and will be apparent in part from the description, or may be learned by practice of the embodiments of this disclosure presented.

[0011] According to one or more embodiments, a nickel-based lithium metal composite oxide includes: secondary particles comprising an aggregate of primary particles, wherein the nickel content in the nickel-based lithium metal composite oxide is 50 mol% or more based on the total content of transition metals in the nickel-based lithium metal composite oxide, the secondary particles comprising large secondary particles having a particle size of 10 μm or larger and small secondary particles having a particle size of 5 μm or smaller, and the nickel content in the large secondary particles is greater than the nickel content in the small secondary particles.

[0012] In the differential capacity dQ / dV charge / discharge differential curve of a lithium secondary battery having a positive electrode including a nickel-based lithium metal composite oxide, the ratio (A2 / A1) of the discharge peak intensity (A2) to the charging peak intensity (A1) at a voltage of 4.1V to 4.25V and a current of 1C can be 1.1 or greater.

[0013] According to one or more embodiments, a method for preparing a nickel-based lithium metal composite oxide includes: mixing a large-particle nickel-based metal hydroxide having a nickel content of 50 mol% or more based on the total transition metal content in the large-particle nickel-based metal hydroxide, a small-particle nickel-based metal hydroxide having a nickel content of 50 mol% or more based on the total transition metal content in the small-particle nickel-based metal hydroxide, and a lithium precursor to obtain a precursor mixture; and heat-treating the precursor mixture to obtain the aforementioned nickel-based lithium metal composite oxide.

[0014] According to one or more embodiments, a lithium secondary battery includes: a positive electrode comprising a nickel-based lithium metal composite oxide; a negative electrode; and an electrolyte inserted between the positive electrode and the negative electrode. Attached Figure Description

[0015] Certain embodiments of this disclosure, as well as other aspects and features, will become more apparent from the following description taken in conjunction with the accompanying drawings, wherein:

[0016] Figure 1 A graph illustrating the dQ / dV charge / discharge differential curves after one cycle of the lithium secondary batteries in Manufacturing Example 1 and Comparative Manufacturing Examples 1 and 2.

[0017] Figure 2 A graph illustrating the dQ / dV charge / discharge differential curves after 30 cycles of the lithium secondary batteries in Manufacturing Example 1 and Comparative Manufacturing Example 2.

[0018] Figure 3 A graph illustrating the dQ / dV charge / discharge differential curves after 50 cycles of the lithium secondary batteries in Manufacturing Example 1 and Comparative Manufacturing Example 2.

[0019] Figure 4A graph illustrating the dQ / dV charge / discharge differential curves after 1 cycle, 30 cycles, and 50 cycles of the lithium secondary battery of Manufacturing Example 1.

[0020] Figure 5 To illustrate the dQ / dV charge / discharge differential curves of the lithium secondary battery in Comparative Manufacturing Example 2 after 1 cycle, 30 cycles, and 50 cycles.

[0021] Figure 6 The image shows the X-ray diffraction analysis of the composite positive electrode active material obtained according to Example 1.

[0022] Figure 7 A schematic diagram illustrating the structure of a lithium secondary battery according to an embodiment;

[0023] Figure 8 A graph illustrating manufacturing examples 1 and 2 and comparing the lifespan characteristics of the lithium secondary battery in manufacturing example 1; and

[0024] Figure 9 A diagram illustrating the charging / discharging characteristics of the button batteries manufactured according to Manufacturing Example 1 and Comparative Manufacturing Example 1. Detailed Implementation

[0025] Reference will now be made in more detail to embodiments of this disclosure, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, embodiments may take different forms and should not be construed as limited to the description set forth herein. Accordingly, embodiments are described below only by reference to the figures to explain aspects of the embodiments described herein. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerated items. Expressions such as “at least one”, when preceding a list of elements, modify the entire list of elements rather than a single element of the list.

[0026] The following description, with reference to the accompanying drawings, will be more detailed about nickel-based lithium metal composite oxides, methods for their preparation, and lithium secondary batteries having a positive electrode including the same.

[0027] Embodiments of this disclosure provide a nickel-based lithium metal composite oxide comprising: secondary particles comprising an aggregate of primary particles, wherein the nickel content (e.g., amount) in the nickel-based lithium metal composite oxide is 50 mol% or more based on the total content of transition metals in the nickel-based lithium metal composite oxide; the secondary particles comprise large secondary particles having a particle size of 10 μm or greater and small secondary particles having a particle size of 5 μm or less, and the nickel content (e.g., amount) in the large secondary particles is greater than the nickel content (e.g., amount) in the small secondary particles. The particle size mentioned herein may be an average particle size, such as, for example, a median particle size or a D50 particle size, which indicates that 50% of the particles in a volumetric distribution of particle size have a larger particle size and 50% of the particles in a volumetric distribution of particle size have a smaller particle size.

[0028] When the particles are spherical, the term "average particle size" for secondary particles can be the median diameter (D50), and when the particles are non-spherical, "average particle size" refers to the length of the major axis. In this specification, "D50" refers to the particle size corresponding to 50% of the volume relative to the cumulative particle distribution arranged from smallest to largest size. Unless otherwise defined herein, the distribution is cumulative in order from smallest to largest particle size. In a curve, when the total number of particles is 100%, it refers to the value of the particle size corresponding to 50% of the smallest particles. The average particle size (D50) can be measured by methods well known to those skilled in the art, for example, by a particle size analyzer (HORIBA), LA-950 laser particle size analyzer, laser diffraction particle size analyzer, scanning electron microscope (SEM), or transmission electron microscope (TEM). As another method, it can be measured using a measuring device utilizing dynamic light scattering methods, performing data analysis, calculating the number of particles in each particle size range, and thereby calculating the average particle size (D50). The D50 value is readily available. For example, the average particle size can be measured using a particle size distribution (PSD) meter and / or by scanning electron microscopy (SEM). The long axis length can be measured by SEM.

[0029] In nickel-based lithium metal composite oxides, the nickel content (e.g., amount) is 60 mol% or more, 75 mol% or more, or 75 mol% to 99 mol%, based on the total content of transition metals in the nickel-based lithium metal composite oxide.

[0030] In the differential capacity (dQ / dV) charge / discharge differential curve of a lithium secondary battery having a positive electrode including a nickel-based lithium metal composite oxide, the ratio (A2 / A1) of the discharge peak intensity (A2) to the charging peak intensity (A1) at a voltage of 4.1V to 4.25V and a current of 1C can be 1.1 or greater.

[0031] At voltages ranging from 3.0V to 4.3V, for example, at voltages ranging from 3.0V to 4.25V, the dQ / dV charge / discharge differential curves are obtained.

[0032] The dQ / dV charge / discharge differential curve (see...) Figures 1 to 5 In the figure, V represents the voltage of the lithium metal at the negative electrode, and Q represents the charge / discharge capacity of the lithium secondary battery. Furthermore, in the dQ / dV charge / discharge differential curve, the X-axis represents the voltage V, and the Y-axis represents the value obtained by differentiating the charge / discharge capacity from the voltage (dQ / dV).

[0033] Lithium secondary batteries with excellent capacity characteristics using nickel-based lithium metal composite oxides can be manufactured by heat-treating large-particle nickel-based lithium metal composite oxide precursors, small-particle nickel-based lithium metal composite oxide precursors, and lithium precursors.

[0034] Because the large-particle and small-particle nickel-lithium metal composite oxide precursors have different characteristics, they are first sintered separately. Then, these precursors are mixed with a lithium precursor and undergo a second sintering process to obtain the desired nickel-lithium metal composite oxide. Thus, the sintering process is performed three times to obtain the nickel-lithium metal composite oxide, resulting in the desired improvement in manufacturing costs and complexity.

[0035] Therefore, without being limited by any particular mechanism or theory, the inventors have prepared embodiments of this disclosure to provide nickel-based lithium metal composite oxides with good structural stability and good capacity characteristics, wherein the nickel-based lithium metal composite oxides are prepared by the following process: simultaneously (e.g., concurrently) heat-treating a large-particle nickel-based lithium metal composite oxide precursor, a small-particle nickel-based lithium metal composite oxide precursor, and a lithium precursor once, while controlling the particle size and nickel content (e.g., amount) of the large-particle nickel-based lithium metal composite oxide precursor and the small-particle nickel-based lithium metal composite oxide precursor within a set or predetermined range.

[0036] The precursors for large-particle nickel-based lithium metal composite oxides are, for example, large-particle nickel-based metal hydroxides, and the precursors for small-particle nickel-based lithium metal composite oxides are, for example, small-particle nickel-based metal hydroxides.

[0037] Based on the total transition metal content in large-particle nickel hydroxides, the nickel content (e.g., amount) in the large-particle nickel hydroxides is 50 mol% or more, 60 mol% or more, 75 mol% or more, or 75 mol% to 99 mol%. Based on the total transition metal content in small-particle nickel hydroxides, the nickel content (e.g., amount) in the small-particle nickel hydroxides is 50 mol% or more, 60 mol% or more, 75 mol% or more, or 75 mol% to 99 mol%.

[0038] The difference between the nickel content (e.g., amount) in large-particle nickel-based metal hydroxides and the nickel content (e.g., amount) in small-particle nickel-based metal hydroxides is 10 mol% or more, 11 mol% or more, 11 mol% to 24 mol%, for example 11 mol% to 20 mol%, 11 mol% to 18 mol%, or 12 mol% to 16 mol%. For example, the amount of nickel in large-particle nickel-based metal hydroxides may be 10 mol% or more, 11 mol% or more, 11 mol% to 24 mol%, for example 11 mol% to 20 mol%, 11 mol% to 18 mol%, or 12 mol% to 16 mol% greater than the amount of nickel in small-particle nickel-based metal hydroxides. When the difference in nickel content (e.g., amount) between the large-particle nickel-based lithium metal composite oxide precursor and the small-particle nickel-based lithium metal composite oxide precursor falls within the above range, nickel-based lithium metal composite oxides with good structural stability and good energy density can be obtained.

[0039] The difference in nickel content (e.g., amount) between large and small secondary particles in the nickel-based lithium metal composite oxide obtained from the precursor remains equal to the difference in nickel content (e.g., amount) between the large and small nickel-based lithium metal composite oxide precursors. Therefore, in some embodiments, the difference between the amount of nickel in the large and small secondary particles in the nickel-based lithium metal composite oxide is the same as or substantially the same as the difference between the amount of nickel in the large and small nickel-based lithium metal composite oxide precursors.

[0040] The difference in nickel content (e.g., amount) between large and small secondary particles in a nickel-based lithium metal composite oxide is 10 mol% or more, 11 mol% or more, for example, 11 mol% to 20 mol%, 11 mol% to 18 mol%, or 12 mol% to 16 mol%. For example, in a nickel-based lithium metal composite oxide, the amount of nickel in the large secondary particles may be 10 mol% or more, 11 mol% or more, for example, 11 mol% to 20 mol%, 11 mol% to 18 mol%, or 12 mol% to 16 mol% greater than the amount of nickel in the small secondary particles. When the difference in nickel content (e.g., amount) between the large and small secondary particles is within the above range, a nickel-based lithium metal composite oxide with good structural stability and good energy density can be obtained by simultaneously (e.g., concurrently) heat-treating both the large-particle and small-particle nickel-based lithium metal composite oxide precursors used to obtain these particles.

[0041] Based on the total transition metal content (e.g., amount) in the large secondary particles, the nickel content (e.g., amount) in the large secondary particles is 85 mol% to 99 mol%, 85 mol% to 95 mol%, or 88 mol% to 95 mol%. Further, based on the total transition metal content (e.g., amount) in the small secondary particles, the nickel content (e.g., amount) in the small secondary particles is 75 mol% to 89 mol%, 80 mol% to 85 mol%, or 75 mol% to 85 mol%.

[0042] The particle size of the large-particle nickel-lithium metal composite oxide precursor is 10 μm to 17 μm, for example, 12 μm to 15 μm. Further, the particle size of the small-particle nickel-lithium metal composite oxide precursor is 2 μm to 5 μm, for example, 3 μm to 4 μm. The large secondary particles contained in the nickel-lithium metal composite oxide obtained from such precursor have particle sizes of 10 μm or larger, 12 μm or larger, 14 μm or larger, 15 μm or larger, for example, 12 μm to 17 μm.

[0043] In this embodiment, the particle size of the large secondary particles is, for example, 10 μm to 15 μm, or 12 μm to 17 μm. Further, the particle size of the small secondary particles is 2 μm to 5 μm, or 3 μm to 4 μm.

[0044] When the particle sizes of large and small secondary particles are within the above ranges, nickel-lithium metal composite oxides with good structural stability and good energy density can be obtained by simultaneously (e.g., concurrently) heat-treating both large and small nickel-lithium metal composite oxide precursors. Based on the total content (e.g., amount) of 100 parts by weight of both large and small nickel-lithium metal composite oxide precursors, the content (e.g., amount) of the large nickel-lithium metal composite oxide precursor is 30 to 90 parts by weight, 50 to 90 parts by weight, 60 to 90 parts by weight, or 80 to 90 parts by weight.

[0045] In the nickel-based lithium metal composite oxide of this disclosure, the content (e.g., amount) of large secondary particles is 30 to 90 parts by weight, 50 to 90 parts by weight, 60 to 90 parts by weight, or 80 to 90 parts by weight, based on the total content (e.g., amount) of large and small secondary particles per 100 parts by weight.

[0046] When the mixing weight ratio of large secondary particles to small secondary particles is within the above range, nickel-lithium metal composite oxides with good structural stability and good energy density can be obtained by simultaneously (e.g., concurrently) heat-treating both large-particle and small-particle nickel-lithium metal composite oxide precursors.

[0047] In a lithium secondary battery having a positive electrode containing a nickel-based lithium metal composite oxide according to an embodiment, in the dQ / dV charge / discharge differential curve at a voltage of 4.1V to 4.25V and a current of 1C, the ratio (A2 / A1) of the discharge peak intensity (A2) to the charging peak intensity (A1) is 1.1 or greater, for example, 1.1 to 1.5. The charging and discharging peaks occur at a current of 1C and a voltage of 4.1V to 4.25V.

[0048] The charging and discharging conditions for lithium secondary batteries with a positive electrode are as follows.

[0049] Charge the lithium-ion battery with a constant current of 1C until the voltage reaches 4.3V, then charge it with a constant voltage until the current reaches 0.05C. After a pause of approximately 10 minutes, discharge the fully charged battery with a constant current of 1C until the voltage reaches 3V. Repeat this cycle several times and evaluate the results.

[0050] After 1 to 100 charge / discharge cycles, after 1 to 80 charge / discharge cycles, or after 1 to 50 charge / discharge cycles, the dQ / dV charge / discharge differential curves are obtained. The charge / discharge cycles can be repeated, for example, a total of 50 cycles.

[0051] The charging peak appears at a voltage of 4.17V to 4.25V, for example, 4.19V, and the discharging peak appears at a voltage of 4.14V to 4.17V, for example, 4.16V.

[0052] The differential capacity (dQ / dV) charge / discharge differential curve describes the capacity characteristics of ions applied to the positive electrode active material through voltage operation. The position, intensity difference, and area of ​​the main peak can vary depending on the type, variety, and / or physical properties of the positive electrode active material.

[0053] The differential capacity (dQ / dV) illustrates the results of measuring the dQ / dV distribution by applying 1C discharge conditions to the lithium-ion battery of this disclosure, which includes a positive electrode comprising a nickel-based lithium metal composite oxide and a lithium metal negative electrode. The nickel-based lithium metal composite oxide may include, for example, lithium nickel cobalt aluminum oxide (NCA).

[0054] In the dQ / dV distribution, three to six main peaks appear, for example, five main peaks. In this case, the peak appearing at approximately 3.65 V corresponds to the main peak of NCA, which involves the phase transition from hexagonal to monoclinic crystal systems. Furthermore, the peak appearing at voltages ranging from 4.1 V to 4.25 V indicates structural changes due to the degradation of NCA.

[0055] In the dQ / dV distribution, the ratio (A2 / A1) of the discharge peak intensity (A2) to the charging peak intensity (A1) is 1.1 to 1.5. The amount of electrical energy stored in the lithium secondary battery can be determined by the charging peak intensity, and the amount of structural change can be determined by the discharge peak intensity. When the ratio (A2 / A1) of the discharge peak intensity (A2) to the charging peak intensity (A1) is within the above range, this ratio (A2 / A1) relates to the difference in Ni content (e.g., amount) between large and small particles and the difference in Co content (e.g., amount) between large and small particles. Furthermore, when this ratio (A2 / A1) is within this range, the NCA has a low surface resistance, and thus, when using an NCA with low surface resistance, a lithium secondary battery with excellent high-temperature life and storage characteristics can be manufactured.

[0056] The dQ / dV charge / discharge differential curve is used for a lithium secondary battery after 1 to 50 charge / discharge cycles, for example, after 1 charge / discharge cycle, after 30 charge / discharge cycles, or after 50 charge / discharge cycles. The evaluation conditions for the charge / discharge cycles are as described in Evaluation Example 1 further below in this text.

[0057] In the dQ / dV charge / discharge differential curve of the nickel-based lithium metal composite oxide according to the embodiment, the charging peak that appears at a voltage of 3.5 V to 3.8 V has a gentle slope.

[0058] The nickel-based lithium metal composite oxide may be a compound represented by Formula 1.

[0059] Formula 1

[0060] Li ,

[0065] (Ni 1-x-y-z Co x M y M' z )O2

[0061] In Formula 1, M is manganese (Mn), aluminum (Al), or a combination thereof, M' is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), or a combination thereof, and 0.95 ≤ a ≤ 1.3, 0 < x < 0.5, 0 < y < 0.5, 0 ≤ z < 0.5, and 0 < x + y + z ≤ 0.5 are satisfied.

[0062] The sum of x + y + z is, for example, 0.01 to 0.2, 0.01 to 0.12, 0.04 to 0.1, or 0.04 to 0.08.

[0063] In the compound of Formula 1, based on the total content of transition metals in the nickel-based lithium metal composite oxide, the content (e.g., amount) of nickel is 50 mol% or more, which is greater than the content (e.g., amount) of each transition metal such as cobalt, M, and M'. When a positive electrode containing such a nickel-based lithium metal composite oxide is used, a lithium secondary battery having lithium diffusivity, high conductivity (e.g., high conductance), and a higher capacity at the same voltage can be manufactured.

[0064] In Formula 1, 0.95 ≤ a ≤ 1.3 and 0 < x ≤ 0.3 can be satisfied, and 0 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.05, and 0.5 ≤ (1 - x - y - z) ≤ 0.95 can be satisfied. In Formula 1, a can be 1 to 1.1, x can be 0.05 to 0.3 or 0.05 to 0.1, y can be 0.05 to 0.3, and z can be 0 or 0.001 to 0.01.

[0065] According to the implementation method, z is 0 in Equation 1.

[0066] For example, the compound of formula 1 can be Li 1.1 Ni 0.92 Co 0.05 Al 0.03 O2, LiNi 0.8 Co 0.1 MnAl 0.1 O2, LiNi 0.85 Co 0.1 Al 0.05 O2, Li 1.1 Ni 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.1 Mn 0.05 O2, Li 1.1 Ni 0.94 Co 0.03 Mn 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.94 Co 0.03 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and / or LiNi 0.96 Co 0.02 Al 0.02 O2, etc.

[0067] According to the embodiments, the large secondary particles are compounds of Formula 1, wherein 0.88 ≤ (1-xyz) ≤ 0.95, 0.01 ≤ x ≤ 0.08, 0.001 ≤ y ≤ 0.05, and 0 ≤ z ≤ 0.01. Further, the small secondary particles are compounds of Formula 1, wherein 0.75 ≤ (1-xyz) ≤ 0.85, 0.01 ≤ x ≤ 0.15, 0.001 ≤ y ≤ 0.05, and 0 ≤ z ≤ 0.01.

[0068] According to the embodiments, the large secondary particles are compounds represented by Formula 1-1, and the small secondary particles are compounds represented by Formula 1-2.

[0069] Equation 1-1

[0070] Li a (Ni 1-x-y-z Cox Al y M z O2

[0071] In Equation 1-1, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), or a combination thereof, and satisfies 0.95≤a≤1.3, 0.88≤(1-xyz)≤0.95, 0.01≤x≤0.08, 0.001≤y≤0.05, and 0≤z≤0.01.

[0072] In Equation 1-1, the following conditions are met: 0.88≤(1-xyz)≤0.96, 0.01≤x≤0.08, 0.001≤y≤0.05, and 0≤z≤0.01.

[0073] Formula 1-2

[0074] Li a (Ni 1-x-y-z Co x Al y M z O2

[0075] In Equations 1-2, M is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), or a combination thereof, and satisfies 0.95≤a≤1.3, 0.75≤(1-xyz)≤0.85, 0.01≤x≤0.05, 0.001≤y≤0.05, and 0≤z≤0.01.

[0076] In equation 1-2, the following conditions are met: 0.75≤(1-xyz)≤0.85, 0.01≤x≤0.05, 0.001≤y≤0.05, and 0≤z≤0.01.

[0077] For example, the large secondary particles in Equation 1-1 can be Li 1.1 Ni 0.92 Co 0.05 Al 0.03 O2, LiNi 0.94 Co 0.03 Al 0.03 O2, LiNi 0.88 Co 0.08 Al 0.04 O2, LiNi 0.88 Co 0.06 Al 0.06 O2, LiNi 0.90 Co 0.05 Al0.05 O2 and / or LiNi 0.96 Co 0.02 Al 0.02 O2, etc., and the smaller secondary particles of Formula 1-2 can be LiNi 0.8 Co 0.15 Al 0.05 O2 and / or LiNi 0.75 Co 0.20 Al 0.05 O2, etc.

[0078] The specific surface area of ​​the large secondary particles is 0.1 m². 2 / g to 1m 2 / g, for example 0.3m 2 / g to 0.8m 2 / g, and the specific surface area of ​​the small secondary particles is 2m². 2 / g to 15m 2 / g, for example 2m 2 / g to 10m 2 / g. Specific surface area can be the BET specific surface area measured by the Brunauer-Emmett-Teller (BET) method. When the specific surface areas of large and small secondary particles are within the above range, positive electrodes and lithium secondary batteries with excellent capacity, lifespan, and high-temperature storage characteristics can be manufactured.

[0079] The compound of Formula 1 has a structure in which primary particles aggregate to form spherical secondary particles, and the average particle size of the secondary particles is from 1 μm to 25 μm, for example, from 5 μm to 25 μm.

[0080] The following describes a method for preparing the composite positive electrode active material according to the embodiments.

[0081] According to embodiments of this disclosure, nickel-based metal hydroxide as large secondary particles, nickel-based metal hydroxide as small secondary particles, and a lithium precursor are mixed to obtain a precursor mixture. The precursor mixture is then heat-treated to obtain a composite positive electrode active material.

[0082] Nickel-based metal hydroxides are precursors to nickel-based lithium metal composite oxides.

[0083] The particle size of nickel-based metal hydroxides as large secondary particles is 10 μm or larger, for example, 12 μm to 17 μm, and the particle size of nickel-based metal hydroxides as small secondary particles is 5 μm or smaller, for example, 2 μm to 5 μm.

[0084] Nickel hydroxides can be compounds represented by Formula 2.

[0085] Formula 2

[0086] (Ni 1-x-y-z Co x M y M' z )(OH)2

[0087] In Formula 2, M is manganese (Mn), aluminum (Al), or a combination thereof, M' is boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), or a combination thereof, and 0 < x < 0.5, 0 < y < 0.5, 0 ≤ z < 0.5, and 0 < x + y + z ≤ 0.5 are satisfied.

[0088] In Formula 2, 0 < x ≤ 0.3, 0 ≤ y ≤ 0.5, and 0 ≤ z ≤ 0.05 are satisfied. In Formula 2, x + y + z is from 0.01 to 0.25, for example, from 0.04 to 0.25.

[0089] The nickel-based metal hydroxide may be a compound represented by Formula 2-1.

[0090] Formula 2-1

[0091] (Ni 1-x-y-z Co x Al<000009l>M z )(OH)2

[0092] In Formula 2-1, M is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), and 0 < x < 0.5, 0 < y < O.5, 0 ≤ z < 0.5, and 0 < x + y + z ≤ 0.50 are satisfied.

[0093] In Formula 2-1, for example, 0 < x ≤ 0.3, 0 ≤ y ≤ 0.5, and ० ≤ z ≤ 0.05 are satisfied. In Formula 2-1, x + y + z is from 0.01 to 0.25, for example, from 0.04 to 0.25.

[0094] The nickel-based metal hydroxide according to the embodiment is, for example, Ni 0.92 Co 0.05 Al[[ID=I47]] 0.03 (OH)2, Ni 0.94 Co 0.03 Al 0.03 (OH)2, Ni 0.88 Co 0.06 Al 0.06 (OH)2, Ni 0.96 Co 0.02 Al 0.02(OH)2, Ni 0.93 Co 0.04 Al 0.03 (OH)2, Ni 0.8 Co 0.15 Al 0.05 O2(OH)2, Ni 0.75 Co 0.20 Al 0.05 (OH)2, Ni 0.92 Co 0.05 Mn 0.03 (OH)2, Ni 0.94 Co 0.03 Mn 0.03 (OH)2, Ni 0.88 Co 0.06 Mn 0.06 (OH)2, Ni 0.96 Co 0.02 Mn 0.02 (OH)2, Ni 0.93 Co 0.04 Mn 0.03 (OH)2, Ni 0.8 Co 0.15 Mn 0.05 O2(OH)2, Ni 0.75 Co 0.20 Mn 0.05 (OH)2 or combinations thereof.

[0095] In this specification, the composition of large and small nickel-based metal hydroxides is controlled to correspond to the composition of large and small nickel-based lithium metal composite oxides.

[0096] As a lithium precursor, lithium hydroxide, lithium fluoride, lithium carbonate, Li₂COOH, or mixtures thereof are used, for example. The content (e.g., amount) of the lithium precursor is controlled such that the molar ratio (Li / M) of lithium to nickel hydroxide in the lithium precursor is greater than 0.95, for example greater than 1.0, for example 1.05 to 1.3, for example 1.1 to 1.2.

[0097] According to embodiments of this disclosure, the transition metal of the nickel-based metal hydroxide can refer to a mixture of Ni, Co, Mn, M, and M' in Formula 2. The content (e.g., amount) of the lithium precursor and the content (e.g., amount) of the nickel-based metal hydroxide are stoichiometrically controlled to enable the preparation of the nickel-based lithium metal composite oxide of Formula 1.

[0098] Mixing can be dry mixing and can be carried out using mixers or the like.

[0099] Heat treatment is performed in an oxidizing gas atmosphere.

[0100] Oxidizing gas atmospheres use oxidizing gases, such as oxygen and / or air, and, for example, the oxidizing gas consists of 10 vol% to 20 vol% oxygen and / or air and 80 vol% to 90 vol% inert gas.

[0101] Heat treatment is performed appropriately or suitably within a range below the densification temperature, while a reaction occurs between the lithium precursor and the nickel-based metal hydroxide. Here, the densification temperature refers to the temperature at which crystallization is adequately achieved, allowing the active material to realize its charge capacity. Heat treatment is performed at temperatures between 650°C and 800°C, 700°C and 750°C, for example, between 700°C and 720°C.

[0102] The heat treatment time varies depending on factors such as the heat treatment temperature.

[0103] The mixing weight ratio of nickel hydroxide as large secondary particles to nickel hydroxide as small secondary particles is 9:1 to 8:2.

[0104] Nickel hydroxides as large secondary particles and nickel hydroxides as small secondary particles can be prepared according to any suitable method commonly used in the art. In some embodiments, nickel hydroxides as large secondary particles and nickel hydroxides as small secondary particles can be prepared by performing substantially the same process, differing only in the reaction time of the nickel hydroxide precursor (raw material) and the drying process of the product obtained after the reaction.

[0105] In the case of large-particle nickel hydroxide, the reaction time for obtaining the nickel hydroxide is, for example, in the range of about 90 hours to about 130 hours, and the drying process is carried out at temperatures of about 180°C to about 200°C, about 185°C to about 200°C, about 190°C to about 200°C, for example, about 200°C. In the case of small-particle nickel hydroxide, compared with large-particle nickel hydroxide, the reaction time of the precursor (raw material) of small-particle nickel hydroxide is reduced, and is, for example, about 20 hours to about 30 hours, for example, about 20 hours to about 28 hours. The drying process of the product after the reaction is carried out at a temperature in the range of about 200°C to about 220°C.

[0106] When the method for preparing nickel-based lithium metal composite oxides according to the embodiments is used, positive electrode active materials with high capacity, improved charge / discharge efficiency and lifetime can be obtained.

[0107] The following describes a method for manufacturing a lithium secondary battery, including a positive electrode containing a nickel-based lithium metal composite oxide as the positive electrode active material, a negative electrode, a non-aqueous electrolyte containing a lithium salt, and a separator.

[0108] A positive electrode and a negative electrode are prepared by separately applying and drying a composition for forming a positive electrode active material layer and a composition for forming a negative electrode active material layer on a current collector. A composition for forming the positive electrode active material is prepared by mixing a positive electrode active material, a conductive agent, a binder, and a solvent. The positive electrode active material according to the embodiment is used as the positive electrode active material.

[0109] In some embodiments, an adhesive is added in an amount of 1 to 50 parts by weight as a component that facilitates adhesion between the active material and the conductive agent, and to the current collector, based on 100 parts by weight of the total weight of the positive electrode active material. Non-limiting examples of adhesives may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various suitable copolymers. The amount (e.g., amount) of the adhesive is 2 to 5 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material. When the amount (e.g., amount) of the adhesive is within the above range, the adhesion between the active material layer and the current collector is good.

[0110] There are no particular limitations on conductive agents, as long as they are conductive (e.g., electrically conductive) without causing chemical changes to the battery (e.g., undesirable chemical changes), and examples may include graphite, such as natural graphite and / or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; fluorides; metal powders, such as aluminum powder and nickel powder; conductive whiskers (e.g., electrically conductive whiskers), such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0111] Based on the total weight of 100 parts by weight of the positive electrode active material, the content (e.g., amount) of the conductive agent is from 2 to 5 parts by weight. When the content (e.g., amount) of the conductive agent is within the above range, the final electrode has excellent conductivity characteristics (e.g., excellent electrical conductivity).

[0112] Non-limiting examples of solvents may include N-methylpyrrolidone. The solvent content (e.g., amount) is from 100 parts by weight to 3000 parts by weight, based on 100 parts by weight of the positive electrode active material. When the solvent content (e.g., amount) is within the above range, the operation for forming the active material layer is straightforward.

[0113] The positive electrode current collector has a thickness of 3 μm to 500 μm and is not particularly limited, as long as it has high conductivity (e.g., high electrical conductivity) without causing chemical changes (e.g., undesirable chemical changes) in the battery. Non-limiting examples may include current collectors made of stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum and / or stainless steel surface-treated with carbon, nickel, titanium, and / or silver. The adhesion of the positive electrode active material to the current collector can be increased by forming fine irregularities on its surface, and various suitable forms, such as films, sheets, foils, meshes, porous bodies, foams, and / or nonwoven fabrics, are possible.

[0114] Individually, the negative electrode active material, binder, conductive agent, and solvent are mixed to prepare a composition for forming the negative electrode active material layer.

[0115] The negative electrode active material is a material capable of absorbing and desorbing lithium ions. Non-limiting examples of negative electrode active materials may include carbon-based materials, such as graphite and carbon, lithium metal and its alloys, and silicon oxide-based materials. Silicon oxide is used according to embodiments of this disclosure.

[0116] Non-limiting examples of binders may include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polymers wherein polyacrylic acid and its hydrogens are substituted with Li, Na and / or Ca, and various suitable copolymers. The binder is added in an amount of 1 to 50 parts by weight based on the total weight of 100 parts by weight of the negative electrode active material. As a non-limiting example of such a binder, the same binder used in the positive electrode may be used.

[0117] The composition used to form the active material layer of the negative electrode may further include a conductive agent (e.g., an electrical conductivity agent). There are no particular limitations on the conductive agent, as long as it is conductive (e.g., electrical conductivity) without causing a chemical change to the battery, and examples may include graphite, such as natural graphite and / or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; fluorides; metal powders, such as aluminum powder and nickel powder; conductive whiskers (e.g., electrical conductivity whiskers), such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives. The conductive agent may be, for example, carbon black, and, for example, may be carbon black having an average particle size of tens of nanometers.

[0118] Based on the total weight of 100 parts by weight of the negative electrode active material layer, the content (e.g., amount) of the conductive agent can be from 0.01 parts by weight to 10 parts by weight, from 0.01 parts by weight to 5 parts by weight, or from 0.1 parts by weight to 2 parts by weight.

[0119] The composition used to form the active material layer of the negative electrode may further include a thickener. As a thickener, at least one selected from carboxymethyl cellulose (CMC), carboxyethyl cellulose, starch, regenerated cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and polyvinyl alcohol may be used.

[0120] Based on 100 parts by weight of the negative electrode active material, the solvent content (e.g., amount) is between 100 parts by weight and 3000 parts by weight. When the solvent content (e.g., amount) is within the above range, the operation for forming the negative electrode active material layer is easy. The same type or kind of material as used in the manufacture of the positive electrode can be used as the solvent.

[0121] Negative electrode current collectors are typically manufactured with a thickness ranging from 3 μm to 500 μm. There are no particular limitations on negative electrode current collectors, provided they possess high conductivity (e.g., high electrical conductivity) without causing chemical changes (e.g., undesirable chemical changes) in the battery. Non-limiting examples include current collectors made of stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, and / or silver, as well as current collectors made of aluminum-cadmium alloys. Similar to positive electrode current collectors, negative electrode current collectors can increase the adhesion of the negative electrode active material by forming fine irregularities on their surface, and various suitable forms, such as films, sheets, foils, meshes, porous bodies, foams, and / or nonwoven fabrics, are possible.

[0122] Insert the separator between the positive and negative electrodes prepared according to the above process.

[0123] The separator has a pore size of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. For example, olefin polymers, such as polypropylene and / or polyethylene, are used as separators; and / or sheets made of glass fiber and / or nonwoven fabrics. Solid electrolytes can also act as separators when solid electrolytes, such as polymers, are used as the electrolyte.

[0124] Non-aqueous electrolytes containing lithium salts include both non-aqueous electrolytes and lithium salts. Non-aqueous electrolytes include non-aqueous electrolyte solutions, organic solid electrolytes, and / or inorganic solid electrolytes.

[0125] Non-limiting examples of non-aqueous electrolytes may include proton-inert organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, methyl propionate, and ethyl propionate.

[0126] Non-limiting examples of organic solid electrolytes may include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyester sulfides, polyvinyl alcohol, and polyvinylidene fluoride.

[0127] Non-limiting examples of inorganic solid electrolytes may include lithium (Li) nitrides, halides and sulfates, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH and Li3PO4-Li2S-SiS2.

[0128] Non-limiting examples of lithium salts that are readily soluble in non-aqueous electrolytes include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi and (FSO2)2NLi.

[0129] Figure 7 A schematic cross-sectional view illustrating the structure of a lithium secondary battery according to an embodiment.

[0130] See Figure 7The lithium secondary battery 21 includes a positive electrode 23, a negative electrode 22, and a separator 24. The positive electrode 23, negative electrode 22, and separator 24 are wound or folded to be housed in a battery casing 25. Subsequently, an organic electrolyte is injected into the battery casing 25 and sealed with a capping fitting 26 to complete the lithium secondary battery 21. The battery casing 25 can be a cylindrical casing, a rectangular casing, and / or a thin-film casing, etc. For example, the lithium secondary battery 21 can be a large thin-film battery. The lithium secondary battery 21 can be a lithium-ion battery. The separator 24 can be located between the positive electrode 23 and the negative electrode 22 to form a battery cell structure. After the battery cell structures are laminated in a binary battery structure, the laminated battery cell structures are impregnated with an organic electrolyte, and the resulting product is housed in a bag and sealed to complete the lithium-ion polymer battery. Furthermore, multiple battery cell structures are stacked to form a battery pack, which can be used in all electrical appliances requiring high capacity and high output. For example, the battery pack can be used in laptops, smartphones, and / or electric vehicles, etc.

[0131] Furthermore, because lithium-ion batteries exhibit excellent storage stability, longevity, and high rate capability at high temperatures, they can be used in electric vehicles (EVs). For example, lithium-ion batteries can be used in hybrid electric vehicles, such as plug-in hybrid electric vehicles (PHEVs).

[0132] Embodiments of this disclosure will be described in more detail with reference to the following examples and comparative examples. However, these examples are set forth to illustrate embodiments of this disclosure, and the scope of this disclosure is not limited thereto.

[0133] Preparation of nickel-based metal hydroxides

[0134] Preparation Example 1: Preparation of Large Particle Nickel Metal Hydroxides

[0135] Nickel hydroxides (Ni) are obtained by the co-precipitation method further described below. 0.94 Co 0.03 Al 0.03 (OH)2).

[0136] Ammonia water is introduced into the reactor, and the pH of the mixture in the reactor is adjusted using added sodium hydroxide. Simultaneously, the feedstock of nickel hydroxide is stoichiometrically controlled to obtain the composition of the final product. Next, while stirring, the introduction of the feed solution is stopped until the desired size is achieved, and a drying process is performed to obtain the target product. These processes will be described in more detail below.

[0137] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O), used as raw materials for nickel-based metal hydroxides, were dissolved in distilled water in a molar ratio of 94:3:3 to prepare a mixed solution. To form a complex compound, diluted solutions of ammonia (NH4OH) and sodium hydroxide (NaOH) were prepared as precipitants. Subsequently, the mixed solutions of the metal raw materials, ammonia, and sodium hydroxide were introduced separately into the reactor. Sodium hydroxide was added to maintain the pH inside the reactor. The reaction was then carried out for approximately 95 hours with stirring, after which the introduction of the raw material solutions was stopped.

[0138] The slurry solution in the reactor was filtered and washed with high-purity distilled water, then dried in a hot air furnace at 200°C for 24 hours to obtain large-particle nickel hydroxide (Ni) with a particle size (D50) of approximately 12 μm. 0.94 Co 0.03 Al 0.03 (OH)2) powder.

[0139] Preparation Example 2: Preparation of Small Particle Nickel Metal Hydroxides

[0140] Small-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 3 μm were obtained in essentially the same manner as in Preparation Example 1. 0.8 Co 0.15 Al 0.05 (OH)2) powder, differing in that the content (e.g., amount) of nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O) is stoichiometrically controlled to obtain small-particle nickel hydroxide (Ni 0.8 Co 0.15 Al 0.05 (OH)2), when drying the precursor, a process of drying in a hot air furnace at 210°C for 24 hours is used instead of drying in a hot air furnace at 200°C for 24 hours, and the reaction time is 25 hours.

[0141] Preparation Example 3: Preparation of Large Particle Nickel Metal Hydroxides

[0142] Large-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 12 μm were obtained in essentially the same manner as in Preparation Example 1. 0.96 Co 0.02 Al 0.02(OH)2) powder, differing in that the content (e.g., amount) of nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and aluminum sulfate (Al2(SO4)3·H2O) is stoichiometrically controlled to obtain large-particle nickel-based metal hydroxides (Ni 0.96 Co 0.02 Al 0.02 (OH)2).

[0143] Preparation Example 4: Preparation of Large Particle Nickel Metal Hydroxides

[0144] Large-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 10 μm were obtained in essentially the same manner as in Preparation Example 1. 0.94 Co 0.03 Al 0.03 (OH)2) powder, rather than large-particle nickel hydroxides (Ni) with a particle size of approximately 12 μm (D50). 0.94 Co 0.03 Al 0.03 (OH)2) powder, the difference is that the reaction time is changed to about 90 hours while stirring.

[0145] Preparation Example 5: Preparation of Large Particle Nickel Metal Hydroxides

[0146] Large-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 17 μm were obtained in essentially the same manner as in Preparation Example 1. 0.94 Co 0.03 Al 0.03 (OH)2) powder, rather than large-particle nickel hydroxides (Ni) with a particle size of approximately 12 μm (D50). 0.94 Co 0.03 Al 0.03 (OH)2) powder, the difference being the introduction of sodium hydroxide to maintain the pH inside the reactor, and the reaction time being changed to approximately 130 hours while stirring.

[0147] Preparation Example 6: Preparation of Small Particle Nickel Metal Hydroxides

[0148] Small-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 2 μm were obtained in essentially the same manner as in Preparation Example 2. 0.8 Co 0.15 Al 0.05 (OH)2) powder, rather than small particles of nickel hydroxide (Ni) with a particle size of about 3 μm (D50). 0.8 Co 0.15 Al 0.05The (OH)2) powder differs in that sodium hydroxide is introduced to maintain the pH inside the reactor, and the reaction time is changed to about 22 hours while stirring.

[0149] Preparation Example 7: Preparation of Small Particle Nickel Metal Hydroxides

[0150] Small-particle nickel hydroxides (Ni) with a particle size (D50) of approximately 5 μm were obtained in essentially the same manner as in Preparation Example 2. 0.8 Co 0.15 Al 0.05 (OH)2) powder, rather than small particles of nickel hydroxide (Ni) with a particle size of about 3 μm (D50). 0.8 Co 0.15 Al 0.05 (OH)2) powder, the difference being the introduction of sodium hydroxide to maintain the pH inside the reactor, and the reaction time being changed to approximately 28 hours while stirring.

[0151] Preparation of nickel-based lithium metal composite oxides

[0152] Example 1

[0153] The large-particle nickel hydroxide powder with a particle size of about 12 μm obtained in Preparation Example 1 and the small-particle nickel hydroxide powder with a particle size of about 3 μm obtained in Preparation Example 2 were mixed at a mixing weight ratio of 80:20.

[0154] In a dry state, a mixture of large and small nickel hydroxide powder particles was mixed with lithium hydroxide (LiOH) at a ratio of 1:1.05 using a Henschel mixer, and then heat-treated at approximately 720°C for 10 hours in an oxygen atmosphere to obtain a nickel-lithium metal composite oxide (LiOH) comprising both large and small secondary particles. 1.05 Ni 0.92 Co 0.05 Al 0.03 O2). The average particle size (D50) of the large secondary particles is about 12 μm, the average particle size (D50) of the small secondary particles is about 3 μm, the mixing weight ratio of the large secondary particles to the small secondary particles is 80:20, and the difference in nickel content (e.g., amount) between the large and small secondary particles is about 14 mol%.

[0155] Example 2

[0156] A nickel-based lithium metal composite oxide comprising large and small secondary particles as shown in Table 1 below was obtained in substantially the same manner as in Example 1, except that the mixing weight ratio of the large nickel-based metal hydroxide powder with a particle size of about 12 μm obtained in Preparation Example 1 and the small nickel-based metal hydroxide powder with a particle size of about 3 μm obtained in Preparation Example 2 was 90:10, and the heat treatment was performed in an oxygen atmosphere at about 720°C for about 10 hours. The D50 of the large secondary particles was about 12 μm, the D50 of the small secondary particles was about 3 μm, the mixing weight ratio of the large and small secondary particles was 90:10, and the difference in nickel content (e.g., amount) between the large and small secondary particles was about 14 mol%.

[0157] Table 1

[0158]

[0159] Examples 3 to 6

[0160] Nickel-based lithium metal composite oxides were obtained in essentially the same manner as in Example 1, except that the heat treatment temperature of the nickel-based metal hydroxides was changed as given in Table 2 below.

[0161] Table 2

[0162]

[0163] Example 7

[0164] Nickel-based lithium metal composite oxides satisfying the conditions in Table 3 below were obtained in essentially the same manner as in Example 1, except that large-particle nickel-based metal hydroxides (Ni) were used in Preparation Example 3. 0.96 Co 0.02 Al 0.02 (OH)2), instead of the large-particle nickel hydroxide with a particle size (particle size) of about 12 μm as in Preparation Example 1.

[0165] Table 3

[0166]

[0167] Example 8

[0168] Nickel-based lithium metal composite oxides satisfying the conditions in Table 4 below were obtained in essentially the same manner as in Example 1, except that large-particle nickel-based metal hydroxides of Preparation Example 4 and small-particle nickel-based metal hydroxides of Preparation Example 2 were used.

[0169] Example 9

[0170] Nickel-based lithium metal composite oxides satisfying the conditions in Table 4 below were obtained in essentially the same manner as in Example 1, except that large-particle nickel-based metal hydroxides of Preparation Example 5 and small-particle nickel-based metal hydroxides of Preparation Example 2 were used.

[0171] Example 10

[0172] Nickel-based lithium metal composite oxides satisfying the conditions in Table 4 below were obtained in essentially the same manner as in Example 1, except that large-particle nickel-based metal hydroxides of Preparation Example 1 and small-particle nickel-based metal hydroxides of Preparation Example 6 were used.

[0173] Example 11

[0174] Nickel-based lithium metal composite oxides satisfying the conditions in Table 4 below were obtained in essentially the same manner as in Example 1, except that large-particle nickel-based metal hydroxides of Preparation Example 1 and small-particle nickel-based metal hydroxides of Preparation Example 7 were used.

[0175] Table 4

[0176]

[0177]

[0178] Comparative Example 1

[0179] Nickel-based lithium metal composite oxides were obtained in essentially the same manner as in Example 1, except that Ni 0.94 Co 0.03 Al 0.03 (OH)₂ was used to prepare large-particle nickel hydroxide in Example 1 and Ni in Example 3. 0.96 Co 0.02 Al 0.02 (OH)2) is used as a small-particle nickel-based metal hydroxide.

[0180] Comparative Example 2

[0181] In a dry state, the large-particle nickel-based metal hydroxide powder of Preparation Example 1 was mixed with lithium hydroxide (LiOH) at a molar ratio of 1:1.05 using a Henschel mixer, and then subjected to an initial heat treatment at approximately 740°C for approximately 10 hours in an oxygen atmosphere to obtain nickel-based lithium metal composite oxide as large secondary particles. The D50 of the large secondary particles was approximately 12 μm.

[0182] Separately, small nickel-based metal hydroxide powder with a particle size of 3 μm from Preparation Example 3 was mixed with lithium hydroxide (LiOH) at a mixing molar ratio of 1:1.01 using a Henschel mixer under dry conditions, and then subjected to a secondary heat treatment at approximately 680°C for approximately 10 hours in an oxygen atmosphere to obtain nickel-based lithium metal composite oxide as small secondary particles. The D50 of the small secondary particles was approximately 3 μm.

[0183] Large and small secondary particles are mixed in a ratio of 80:20 and subjected to a third heat treatment at approximately 700°C to obtain a nickel-based lithium metal composite oxide comprising both large and small secondary particles.

[0184] According to Comparative Example 2, three heat treatment processes are required, resulting in significant manufacturing costs and time in obtaining NCA. Therefore, this method is practically difficult to apply.

[0185] Manufacturing of lithium secondary batteries

[0186] Manufacturing Example 1

[0187] A lithium secondary battery was manufactured using the nickel-based lithium metal composite oxide secondary particles obtained according to Example 1 as the positive electrode active material.

[0188] Using a mixer, a mixture of 96g of secondary nickel-lithium metal composite oxide particles obtained according to Example 1, 2g of polyvinylidene fluoride, 47g of N-methylpyrrolidone as a solvent, and 2g of carbon black as a conductive agent was defoamed to prepare a uniformly dispersed slurry for forming a positive electrode active material layer.

[0189] Using a scraper, the slurry prepared according to the above process is applied onto aluminum foil to form a thin electrode plate, and then the thin electrode plate is dried at 135°C for 3 hours or longer, rolled and dried in a vacuum to prepare a positive electrode.

[0190] A 2032-type button cell is manufactured using a positive electrode and a lithium metal counter electrode, which serves as the positive electrode. A separator (approximately 16 μm thick) made of porous polyethylene (PE) membrane is inserted between the positive electrode and the lithium metal counter electrode, and an electrolyte is injected to manufacture the 2032-type button cell. In this case, a solution in which 1.1 M LiPF6 is dissolved in a solvent (wherein ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a 3:5 volume ratio) is used as the electrolyte.

[0191] The following is the formation process for button batteries manufactured according to the above process.

[0192] In the first charge / discharge cycle, after a 10-hour pause, the button battery is charged at a constant current of 0.2C until the voltage reaches 4.25V, and then charged at a constant voltage until the current reaches 0.05C. After a pause of approximately 10 minutes, the fully charged button battery is discharged at a constant current of 0.2C until the voltage reaches 3V (first cycle). Subsequently, in the second charge / discharge cycle, after a 10-hour pause, the button battery is charged at a constant current of 0.2C until the voltage reaches 4.25V, and then charged at a constant voltage until the current reaches 0.05C. After a pause of approximately 10 minutes, the fully charged button battery is discharged at a constant current of 0.2C until the voltage reaches 3V (second cycle).

[0193] Manufacturing Examples 2 to 11

[0194] The lithium secondary battery was manufactured in essentially the same manner as in Manufacturing Example 1, except that one of the nickel-based lithium metal composite oxides of Examples 2 to 11 was used instead of the nickel-based lithium metal composite oxide of Example 1.

[0195] Comparison of manufacturing examples 1 and 2

[0196] The lithium secondary battery was manufactured in essentially the same manner as in Manufacturing Example 1, except that one of the nickel-based lithium metal composite oxides of Comparative Examples 1 and 2 was used instead of the nickel-based lithium metal composite oxide of Example 1.

[0197] Evaluation Example 1: dQ / dV Analysis

[0198] In the button batteries manufactured in Manufacturing Example 1 and Comparative Manufacturing Examples 1 and 2, the charging / discharging characteristics were evaluated using a charging / discharging machine (model: TOYO-3100, manufactured by TOYO Corporation).

[0199] The process of evaluating charge / discharge characteristics is described in more detail below.

[0200] Each button cell battery is charged at a constant current of 1C until the voltage reaches 4.3V, and then charged at a constant voltage until the current reaches 0.05C. After a pause of approximately 10 minutes, the fully charged button cells are discharged at a constant current of 1C until the voltage reaches 3V (first cycle). These charge / discharge cycles are repeated for a total of 50 cycles.

[0201] After 1, 30, and 50 cycles, the ratio (A2 / A1) of the discharge peak intensity (A2) to the charge peak intensity (A1) obtained from the dQ / dV charge / discharge differential curve distribution in the voltage range of 4.1V to 4.25V was examined, and the results are shown in Table 5 below. Figures 1 to 5 middle.

[0202] The charging peak occurs at voltages between 4.17V and 4.25V, and the discharging peak occurs at voltages between 4.14V and 4.17V.

[0203] Figure 1 To illustrate the graphs of the dQ / dV charge / discharge differential curves after one cycle in the lithium secondary batteries of Manufacturing Example 1 and Comparative Manufacturing Examples 1 and 2, and Figure 2 The graph illustrates the dQ / dV charge / discharge differential curves after 30 cycles in the lithium secondary batteries of Manufacturing Example 1 and Comparative Manufacturing Example 2.

[0204] Figure 3 To illustrate the graphs of the dQ / dV charge / discharge differential curves after 50 cycles in the lithium secondary batteries of Manufacturing Example 1 and Comparative Manufacturing Example 2, and Figure 4 The graph illustrates the dQ / dV charge / discharge differential curves after 1 cycle, 30 cycles, and 50 cycles in the lithium secondary battery of Manufacturing Example 1. Figure 5 The graph illustrates the dQ / dV charge / discharge differential curves after 1 cycle, 30 cycles, and 50 cycles in the lithium secondary battery of Comparative Manufacturing Example 2.

[0205] Table 5

[0206]

[0207] See Figures 1 to 5 As shown in Table 5, the lithium secondary battery of Manufacturing Example 1 is characterized by an A2 / A1 ratio of 1.1 or greater after 1 cycle, 30 cycles, and 50 cycles, while in the lithium secondary batteries of Comparative Manufacturing Examples 1 and 2, the A2 / A1 ratio is less than 1.0 after 1 cycle, 30 cycles, and 50 cycles. In the lithium secondary battery of Manufacturing Example 1, the A2 / A1 change rate is reduced compared to the lithium secondary batteries of Comparative Manufacturing Examples 1 and 2. The A2 / A1 change rate refers to the ratio of A2 / A1 after 50 cycles to A2 / A1 after 1 cycle. The reduction in the A2 / A1 change rate indicates that the structural changes in the lithium secondary battery of Manufacturing Example 1 due to degradation after charge / discharge cycles are small.

[0208] Evaluation Example 2: X-ray Diffraction Analysis

[0209] For the nickel-lithium metal composite oxide of Example 1, Cu Kα radiation was used. X-ray diffraction analysis was performed on the X'PertPro (PANalytical) instrument. The results of the X-ray diffraction analysis showed... Figure 6 middle.

[0210] See Figure 6 It can be observed that the nickel-lithium metal composite oxide of Example 1 forms an aligned layered structure without impurities (or without detectable levels of impurities).

[0211] Evaluation Example 3: Charge / Discharge Efficiency and Capacity Retention

[0212] In the button batteries manufactured according to Manufacturing Examples 1 to 6 and Comparative Manufacturing Example 1, their charging / discharging efficiency and capacity retention were evaluated using a charging / discharging machine (model: TOYO-3100, manufactured by TOYO Corporation) as follows.

[0213] (1) Charging / discharging efficiency

[0214] Each button cell was charged at 25°C with a constant current of 0.2C until the voltage reached 4.25V, and then charged with a constant voltage until the current reached 0.05C. After a pause of approximately 10 minutes, the fully charged button cells were discharged with a constant current of 0.2C until the voltage reached 3V. These charge / discharge cycles were repeated 50 times, and the charge / discharge efficiency was evaluated.

[0215] (2) Capacity retention rate

[0216] Each coin cell was charged at 45°C with a constant current of 1C until the voltage reached 4.3V, and then charged with a constant voltage until the current reached 0.05C. After a pause of approximately 10 minutes, the fully charged coin cells were discharged with a constant current of 1C until the voltage reached 3V. These charge / discharge cycles were repeated 50 times, and the capacity retention was evaluated.

[0217] The capacity retention rate (CRR) is calculated using Equation 1 below, and the initial charge / discharge efficiency is calculated using Equation 2 below. The characteristics of the capacity retention rate and the initial charge / discharge efficiency are evaluated, and the results are shown in Table 6 below. Figure 8 middle. Figure 8 The capacity retention characteristics of manufacturing examples 1 and 2, as well as comparative manufacturing example 1, are shown.

[0218] Equation 1

[0219] Capacity retention rate [%] = [Discharge capacity at 50th cycle / Discharge capacity at 1st cycle] × 100

[0220] Equation 2

[0221] Initial charge / discharge efficiency = [Discharge voltage of the first cycle / Charge voltage of the first cycle] × 100

[0222] Table 6

[0223]

[0224] See Table 6 and Figure 8 As can be seen, compared with the button cell of Comparative Manufacturing Example 1, the button cells manufactured according to Manufacturing Examples 1 to 6 exhibit improved capacity retention characteristics. Furthermore, as can be seen, compared with the button cell of Comparative Manufacturing Example 1, the button cells of Manufacturing Examples 1 to 6 exhibit improved initial charge / discharge efficiency characteristics.

[0225] The button cell of Comparative Example 2 exhibited excellent capacity retention. However, in the button cell of Comparative Example 2, the positive electrode was produced by separately sintering large and small secondary particles three times, thereby subjecting the nickel-lithium metal composite oxide of Comparative Example 2 to three heat treatment processes. Therefore, the manufacturing process of the nickel-lithium metal composite oxide of Comparative Example 2 required significant manufacturing costs and time. Thus, the method of Comparative Example 2 is practically difficult to apply.

[0226] Furthermore, the charge / discharge characteristics of the button batteries in Manufacturing Examples 7 to 11 were evaluated in essentially the same manner as in evaluating the charge / discharge characteristics of the button battery in Manufacturing Example 1.

[0227] As a result, compared with the charging / discharging characteristics of the button battery in Manufacturing Example 1, the charging / discharging characteristics of the button batteries in Manufacturing Examples 7 to 11 showed a similar level.

[0228] Evaluation Example 4: Charging / Discharging Characteristics

[0229] In the button batteries of Manufacturing Example 1 and Comparative Manufacturing Example 1, the charging / discharging characteristics were evaluated under the following conditions.

[0230] In the evaluation of charge / discharge characteristics, each button cell was charged at a constant current of 0.2C at 25°C until the voltage reached 4.25V, and then charged at a constant voltage until the current reached 0.05C. After a pause of approximately 10 minutes, the fully charged button cells were discharged at a constant current of 0.2C until the voltage reached 3V.

[0231] The evaluation results show that Figure 9 middle.

[0232] like Figure 9 As shown, the charging / discharging characteristics of the button battery in Manufacturing Example 1 are improved compared to those of the button battery in Comparative Manufacturing Example 1.

[0233] The nickel-based lithium metal composite oxide according to embodiments of this disclosure exhibits excellent structural stability. When a positive electrode comprising such a nickel-based lithium metal composite oxide is provided, a lithium secondary battery with improved lifespan and high rate capability can be manufactured.

[0234] It should be understood that the embodiments described herein are to be considered in a descriptive sense only and not for limiting purposes. Descriptions of features or aspects within various embodiments should generally be considered as applicable to other similar features or aspects in other embodiments. Although one or more embodiments have been described with reference to the figures, those skilled in the art will understand that various changes in form and detail may be made therein without departing from the spirit and scope of this disclosure as defined by the appended claims and their equivalents.

Claims

1. A nickel-based lithium metal composite oxide, comprising: secondary particles including an aggregate of primary particles, wherein based on the total content of transition metals in the nickel-based lithium metal composite oxide, the content of nickel in the nickel-based lithium metal composite oxide is 50 mol% or more, the secondary particles include large secondary particles having a particle size of 10 μm or more and small secondary particles having a particle size of 5 μm or less, and the content of nickel in the large secondary particles is greater than the content of nickel in the small secondary particles, wherein the difference between the content of nickel in the large secondary particles and the content of nickel in the small secondary particles is 10 mol% to 24 mol%, wherein, in the differential capacity charge / discharge differential curve of a lithium secondary battery having a positive electrode including the nickel-based lithium metal composite oxide, the ratio of the discharge peak intensity to the charge peak intensity that appears at a voltage of 4.1 V to 4.25 V and a current of 1 C is 1.1 to 1.5, wherein the nickel-based lithium metal composite oxide is a compound represented by Formula 1: Formula 1 Li a (Ni 1-x-y-z Co x M y M' z )O2 wherein, in Formula 1, M is aluminum, M' is boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, zirconium, or a combination thereof, and 0.95 ≤ a ≤ 1.3, 0 < x < 0.5, 0 < y < 0.5, 0 ≤ z < 0.5, and 0 < x + y + z ≤ 0.5 are satisfied.

2. The nickel-based lithium metal composite oxide according to claim 1, wherein the charge peak is a peak that appears at a voltage of 4.17 V to 4.25 V, and the discharge peak is a peak that appears at a voltage of 4.14 V to 4.17 V.

3. The nickel-based lithium metal composite oxide according to claim 1, wherein based on the total content of transition metals in the large secondary particles, the content of nickel in the large secondary particles is 85 mol% to 99 mol%.

4. The nickel-based lithium metal composite oxide according to claim 1, wherein based on the total content of transition metals in the large secondary particles, the content of nickel in the small secondary particles is 75 mol% to 89 mol%.

5. The nickel-based lithium metal composite oxide according to claim 1, wherein the large secondary particles have a particle size of 10 μm to 17 μm.

6. The nickel-based lithium metal composite oxide according to claim 1, wherein the small secondary particles have a particle size of 2 μm to 5 μm.

7. The nickel-based lithium metal composite oxide according to claim 1, wherein based on 100 parts by weight of the total content of the large secondary particles and the small secondary particles, the content of the large secondary particles is 30 parts by weight to 90 parts by weight.

8. The nickel-based lithium metal composite oxide according to claim 1, wherein: the large secondary particles include a compound satisfying 0.88 ≤ (1 - x - y - z) ≤ 0.95, 0.01 ≤ x ≤ 0.08, 0.001 ≤ y ≤ 0.05, 0 ≤ z ≤ 0.01, and 0 < x + y + z ≤ 0.5 in Formula 1, and The small secondary particles include a compound satisfying 0.75 ≤ (1 - x - y - z) ≤ 0.85, 0.01 ≤ x ≤ 0.05, 0.001 ≤ y ≤ 0.05, 0 ≤ z ≤ 0.01, and 0 < x + y + z ≤ 0.5 in Formula 1.

9. The nickel-based lithium metal composite oxide according to claim 1, wherein the large secondary particles include a compound represented by Formula 1-1: Formula 1-1 Li a (Ni 1-x-y-z Co x Al y M z )O2 in, In Formula 1-1, M is boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, zirconium, or a combination thereof, and satisfies 0.95 ≤ a ≤ 1.3, 0.88 ≤ (1 - x - y - z) ≤ 0.96, 0.01 ≤ x ≤ 0.08, 0.001 ≤ y ≤ 0.05, and 0 ≤ z ≤ 0.

01.

10. The nickel-based lithium metal composite oxide according to claim 1, wherein: The small secondary particles include a compound represented by Formula 1-2: Formula 1-2 Li a (Ni 1-x-y-z Co x Al y M z )O2 wherein, in Formula 1-2, M is boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, zirconium, or a combination thereof, and satisfies 0.95 ≤ a ≤ 1.3, 0.75 ≤ (1 - x - y - z) ≤ 0.85, 0.01 ≤ x ≤ 0.05, 0.001 ≤ y ≤ 0.05, and 0 ≤ z ≤ 0.

01.

11. A method for preparing a nickel-based lithium metal composite oxide, the method comprising: mixing the large particle nickel-based metal hydroxide having a nickel content of 50 mol% or more based on the total content of transition metals in the large particle nickel-based metal hydroxide, the small particle nickel-based metal hydroxide having a nickel content of 50 mol% or more based on the total content of transition metals in the small particle nickel-based metal hydroxide, and a lithium precursor to obtain a precursor mixture; and thermally treating the precursor mixture to obtain the nickel-based lithium metal composite oxide according to any one of claims 1 to 10.

12. The method according to claim 11, wherein the thermal treatment of the precursor mixture is carried out at a temperature of 650 °C to 800 °C.

13. The method according to claim 11, wherein the large particle nickel-based metal hydroxide has a higher nickel content than the small particle nickel-based metal hydroxide, and the difference between the nickel content of the large particle nickel-based metal hydroxide and the nickel content of the small particle nickel-based metal hydroxide is 10 mol% or more.

14. The method according to claim 11, wherein based on the total content of transition metals in the large particle nickel-based metal hydroxide, the nickel content in the large particle nickel-based metal hydroxide is 85 mol% to 99 mol%, and based on the total content of transition metals in the small particle nickel-based metal hydroxide, the nickel content in the small particle nickel-based metal hydroxide is 75 mol% to 89 mol%.

15. The method according to claim 11, wherein the lithium precursor includes lithium hydroxide, lithium fluoride, lithium carbonate, Li2COOH, or a mixture thereof.

16. A lithium secondary battery, comprising: A positive electrode including the nickel-based lithium metal composite oxide according to any one of claims 1 to 10; A negative electrode; And the electrolyte inserted between the positive electrode and the negative electrode.

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