Positive active material and lithium secondary battery including the same

Abstract

The present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode including the same. More specifically, the present invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode including the same, which can reduce lithium impurities without a water washing process by including barium (Ba) and sulfur (S) in the positive electrode active material, and can improve the capacity per unit volume by improving the conductivity of the positive electrode active material.

Description

Technical Field

[0001] This invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode comprising the aforementioned positive electrode active material. More specifically, this invention relates to a positive electrode active material and a lithium secondary battery using a positive electrode comprising the aforementioned positive electrode active material, which, by including barium (Ba) and sulfur (S) in the aforementioned positive electrode active material, can reduce lithium impurities without a water washing process, thereby increasing the capacity per unit volume by improving the conductivity of the positive electrode active material. Background Technology

[0002] A battery is a device that stores electrical energy using materials capable of electrochemical reactions at the positive and negative electrodes. A representative example is the lithium-ion secondary battery, which stores energy by utilizing the chemical potential difference generated during the intercalation and deintercalation of lithium ions between the positive and negative electrodes.

[0003] Lithium-ion rechargeable batteries use materials capable of reversible intercalation / deintercalation of lithium ions as positive and negative active materials, and fill the space between the positive and negative electrodes with organic electrolyte or solid polymer electrolyte.

[0004] As positive electrode active materials, lithium transition metal oxides are mainly used. Representative examples include composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2.

[0005] LiCoO2 is widely used due to its excellent lifespan characteristics and charge / discharge efficiency, but its price competitiveness is limited due to the resource constraints and high cost of cobalt.

[0006] Lithium manganese-based oxides (LiMnO2, LiMn2O4) have the advantages of excellent thermal stability and low cost, but they also have the problems of low capacity and deterioration at high temperatures. LiNiO2-based cathode active materials have the advantage of high discharge capacity, but due to the cation mixing phenomenon between Li and transition metals, their synthesis is difficult, resulting in limitations in rate performance and lifetime characteristics.

[0007] To address these issues, multi-component lithium transition metal oxides such as NCM (Ni-Co-Mn), NCA (Ni-Co-Al), and NCMA (Ni-Co-Mn-Al) have been developed as materials that improve low-rate performance and lifetime characteristics while maintaining the high reversible capacity of LiNiO2.

[0008] Since the reversible capacity increases with the nickel content in these multi-component lithium transition metal oxides, multi-component lithium transition metal oxides with high nickel content are favored in fields requiring high-performance lithium secondary batteries.

[0009] However, with the increase of nickel content in lithium transition metal oxides, cation mixing intensifies, leading to a decrease in crystal structure stability. Furthermore, during the synthesis of the positive electrode active material, unreacted lithium byproducts such as LiOH and Li₂CO₃ tend to remain on the surface of the active material. Increased levels of these unreacted lithium byproducts can cause problems such as gas generation, battery swell, and electrode slurry gelation, ultimately resulting in a decline in the performance of lithium-ion batteries.

[0010] Lithium byproducts are water-soluble and can typically be removed from cathode active materials by calcining the precursor followed by washing with distilled water. This washing process effectively reduces lithium byproducts present in the cathode active materials (especially those on the surface). However, there are concerns that the surface of the cathode active material may be damaged during washing, potentially leading to a decrease in its electrochemical properties and thermal stability. Furthermore, the washing process for removing lithium byproducts requires additional equipment and steps, thus increasing the manufacturing cost of cathode active materials.

[0011] In recent years, with the rapid increase in demand for lithium-ion batteries and the rising price of raw materials, the lithium-ion battery industry is facing intense demands for cost reduction. Under these circumstances, minimizing or eliminating the water washing process, which reduces process efficiency and increases manufacturing costs, has become a crucial technical challenge.

[0012] On the other hand, when the size of the unit particles (primary particles) constituting lithium transition metal oxides is too small, the contact area with the electrolyte increases due to the larger specific surface area. As a result, side reactions with the electrolyte are promoted during repeated charge / discharge cycles, which may lead to excessive gas production inside the battery cell. This gas production can cause problems such as battery cell expansion, increased internal pressure, electrolyte consumption, and reduced lifespan, thus becoming one of the main reasons for impairing battery reliability and safety.

[0013] As a method to reduce the specific surface area of ​​lithium transition metal oxides, one approach has been to induce primary particle growth by increasing the calcination temperature. However, excessively high calcination temperatures can lead to deterioration of the crystal structure and uneven composition, which in turn increases the concentration of unreacted lithium byproducts. As a result, the electrochemical performance of the positive electrode active material may decline. Summary of the Invention

[0014] Technical problems to be solved Recently, with the development of the electric vehicle industry, the lithium-ion battery market has expanded rapidly, and the demand for and performance requirements of the cathode materials used in it are also constantly changing. For example, in the past, LFP-based lithium-ion batteries, which emphasized safety, were mainly used, but recently there has been an increasing trend in the application of nickel-based lithium transition metal oxides, which have higher energy density per unit weight.

[0015] With this trend, the positive electrode active material used in high-performance lithium secondary batteries should not only have high energy density, but also be able to ensure stability and reliability under harsh operating conditions.

[0016] There is a need to develop a positive electrode active material that can effectively induce particle growth without compromising structural stability, thereby reducing the specific surface area and thus reducing the formation of residual lithium and gas generation.

[0017] In particular, if lithium byproducts can be reduced without the need for a water washing process, or if particle growth can be induced without structural degradation, then the problems of gas generation and stability can be solved while preventing damage to the positive electrode active material.

[0018] Accordingly, the present invention aims to provide a positive electrode active material that, by including barium and sulfur in the positive electrode active material, can reduce lithium impurities without the need for a water washing process.

[0019] Furthermore, the present invention aims to provide a positive electrode active material that, by including barium and sulfur, facilitates the growth of unit particles constituting the aforementioned lithium transition metal oxide, thereby reducing the specific surface area of ​​the aforementioned lithium transition metal oxide and suppressing side reactions with the electrolyte.

[0020] Furthermore, the present invention aims to provide a positive electrode active material that, by comprising barium and sulfur, can improve conductivity while suppressing side reactions with the electrolyte.

[0021] Technical solution The present invention for solving the above-mentioned technical problems includes the following inventions.

[0022] [1] A positive electrode active material comprising a lithium transition metal oxide capable of lithium insertion / extraction, wherein the positive electrode active material contains barium and sulfur, wherein the full width at half maximum (FWHM) of the diffraction peaks detected at 2θ = 18.0 to 19.5° by X-ray diffraction analysis using Cu-Kα rays is less than 0.090, and the average crystallite size of the lithium transition metal oxide is 120 nm to 210 nm.

[0023] [2] According to the positive electrode active material described in [1], the ratio ([B+C] / A) of the intensity (A) of the diffraction peak detected at 2θ=18.0~19.5° obtained by X-ray diffraction analysis of Cu-Kα rays to the sum of the intensity (B) of the diffraction peak detected at 2θ=25.5~26.2° and the intensity (C) of the diffraction peak detected at 2θ=28.5~28.9° is 0.005 or more and 0.03 or less.

[0024] [3] The positive electrode active material according to any one of [1] and [2], wherein the lithium transition metal oxide comprises at least one selected from nickel, cobalt, manganese and aluminum.

[0025] [4] According to any one of [1] and [2], the lithium transition metal oxide comprises nickel, cobalt and manganese.

[0026] [5] According to any one of [1] to [4], the lattice of the above-mentioned lithium transition metal oxide is doped with barium.

[0027] [6] According to any one of [1] to [5], the lithium transition metal oxide has at least one of the following forms: a single-particle form consisting of a single unit particle and a secondary-particle form consisting of multiple unit particles aggregated together.

[0028] [7] The positive electrode active material according to any one of [1] to [6] has an average particle size of 1.5 mm, as measured from scanning electron microscopy (SEM) images of the lithium transition metal oxide described above. Up to 7.5 .

[0029] [8] According to any one of [1] to [7], the lithium transition metal oxide has a single-particle morphology, and at least a portion of the surface of the single particle contains barium and sulfur.

[0030] [9] According to any one of [1] to [7], the lithium transition metal oxide has a quasi-single particle morphology formed by the aggregation of 30 or fewer unit particles, and barium and sulfur are present in at least a portion of the surface of the outermost unit particle forming the quasi-single particle, the surface of the unit particle isolated inside the quasi-single particle, and the interface between the unit particles isolated inside the quasi-single particle.

[0031]

[10] The positive electrode active material according to any one of [1] to [9] contains more than 60 mol% nickel relative to all elements other than lithium.

[0032]

[11] According to any one of [1] to

[10] , the above-mentioned lithium transition metal oxide has an average composition represented by the following chemical formula 1.

[0033] [Chemical Formula 1] Li a Ni 1-（b+c+d） Co b M1 c M2 d O2 In the above chemical formula 1, M1 is at least one selected from Mn and Al, M2 is at least one selected from Zr, Na, S, Mg, Ti, B, K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu, and 0.85≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.05, 0 <b+c≤0.40。

[0034]

[12] The positive electrode active material according to any one of [1] to

[11] has a barium content of 200 ppm to 30,000 ppm based on the total weight of the positive electrode active material.

[0035]

[13] The positive electrode active material according to any one of [1] to

[12] has a sulfur content of 500 ppm to 3,000 ppm based on the total weight of the positive electrode active material.

[0036] In addition, the present invention includes other solutions as described below.

[0037]

[14] A positive electrode comprising any one of [1] to

[13] of the positive electrode active material.

[0038]

[15] A lithium secondary battery that uses the positive electrode described in

[14] .

[0039] Beneficial effects According to the present invention, by including barium and sulfur in the positive electrode active material, lithium byproducts can be reduced without the need for a water washing process, thereby improving process efficiency and reducing manufacturing costs.

[0040] Furthermore, according to the present invention, surface damage to the positive electrode active material caused by the water washing process can be prevented, thereby improving the long-term reliability of the electrochemical properties and thermal stability of the positive electrode active material.

[0041] Furthermore, according to the present invention, by including barium and sulfur in the positive electrode active material, it is possible to improve conductivity while suppressing side reactions with the electrolyte. Attached Figure Description

[0042] Figures 1 to 11 The images are SEM images of lithium transition metal oxides contained in the positive electrode active materials according to Examples 1 to 11.

[0043] Figures 12 to 18 The images are SEM images of lithium transition metal oxides contained in the positive electrode active materials of Comparative Examples 1 to 7.

[0044] Figure 19 This is a graph showing the surface energy dispersive spectroscopy (EDS) analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Example 3.

[0045] Figure 20 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Example 11.

[0046] Figure 21 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 1.

[0047] Figure 22 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 5.

[0048] Figure 23 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 6. Detailed Implementation

[0049] To facilitate understanding of the invention, specific terms are defined herein for convenience. Unless otherwise defined herein, scientific and technical terms used in this invention should have the meanings commonly understood by those skilled in the art. Furthermore, unless specifically specified in the context, it should be understood that singular terms also include their plural forms, and plural terms also include their singular forms.

[0050] The positive electrode active material according to the present invention and the lithium secondary battery using the positive electrode comprising the above-described positive electrode active material will be described in more detail below.

[0051] Positive electrode active material In this application, the positive electrode active material includes a lithium transition metal oxide capable of reversible lithium-ion insertion / extraction. Here, lithium transition metal oxide refers to an oxide composed of lithium and a metal element.

[0052] The aforementioned lithium transition metal oxides are composite metal oxides capable of lithium ion insertion / extraction, possessing a layered crystal structure belonging to the R-3m space group. These lithium transition metal oxides with layered crystal structures exhibit characteristic peaks in the XRD diffraction patterns obtained from XRD analysis in the region where 2θ is 18° to 20° (e.g., the region where 2θ = 18.6 ± 1°).

[0053] The aforementioned lithium transition metal oxide may contain at least one selected from nickel, cobalt, manganese, and aluminum.

[0054] The aforementioned lithium transition metal oxides can be lithium nickel-based metal composite oxides containing nickel. To improve low-rate performance and lifetime characteristics while maintaining the high reversible capacity of LiNiO2, the aforementioned lithium transition metal oxides can be multi-component lithium transition metal oxides such as NCM (Ni-Co-Mn), NCA (Ni-Co-Al), and NCMA (Ni-Co-Mn-Al) that further contain cobalt, manganese, and / or aluminum. Furthermore, the aforementioned lithium transition metal oxides can be so-called cobalt-free lithium transition metal oxides that do not contain cobalt.

[0055] The aforementioned lithium transition metal oxides may have an average composition represented by the following chemical formula 1. The average composition of the aforementioned lithium transition metal oxides can be determined by known ICP analysis using inductively coupled plasma spectrometry (ICP).

[0056] [Chemical Formula 1] Li a Ni 1-（b+c+d） Co b M1 c M2 d O2 In the above chemical formula 1, M1 is at least one selected from Mn and Al, M2 is at least one selected from Zr, Na, S, Mg, Ti, B, K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu, and 0.85≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.05, 0 <b+c≤0.40。

[0057] In the above chemical formula 1, 'a', representing the ratio of lithium to all elements other than lithium (Li / Ni+Co+M1+M2) in the above lithium transition metal oxide, can be 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, 0.95 or more, 0.96 or more, 0.97 or more, 0.98 or more, 0.99 or more, 1.00 or more, 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, or 1.05 or more. Furthermore, 'a' can be 1.15 or less, 1.14 or less, 1.13 or less, 1.12 or less, 1.11 or less, 1.10 or less, 1.09 or less, 1.08 or less, 1.07 or less, 1.06 or less, or 1.05 or less. The upper and lower limits of the molar fraction of lithium relative to all elements other than lithium in the aforementioned lithium transition metal oxides can be appropriately selected within the range defined above. When the molar fraction of lithium in the aforementioned lithium transition metal oxides meets the above range, a stable crystal structure can be formed.

[0058] In the above chemical formula 1, 1-(b+c+d), representing the mole fraction of nickel relative to all elements other than lithium (Ni / Ni+Co+M1+M2) in the above lithium transition metal oxide, can be 0.60 or more, 0.65 or more, 0.67 or more, 0.70 or more, 0.72 or more, 0.75 or more, 0.77 or more, 0.80 or more, 0.82 or more, 0.83 or more, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 or more, 0.89 or more, 0.90 or more, 0.91 or more, 0.92 or more, 0.93 or more, 0.94 or more, or 0.95 or more. Furthermore, the above 1-(b+c+d) can be less than 1.0, less than 0.99, less than 0.98, or less than 0.97. The upper and lower limits of the molar fraction of nickel relative to all elements other than lithium in the aforementioned lithium transition metal oxides can be appropriately selected within the range defined above. When the molar fraction of nickel in the aforementioned lithium transition metal oxides meets the above range, a stable crystal structure can be formed and high energy density can be exhibited.

[0059] In the above chemical formula 1, b, representing the molar fraction of cobalt relative to all elements other than lithium (Co / Ni+Co+M1+M2) in the above lithium transition metal oxide, can be less than 0.20, less than 0.19, less than 0.18, less than 0.17, less than 0.16, less than 0.15, less than 0.14, less than 0.13, less than 0.12, less than 0.11, less than 0.10, less than 0.09, less than 0.08, less than 0.07, less than 0.06, less than 0.05, less than 0.04, less than 0.03, or less than 0.02. When the above lithium transition metal oxide is a cobalt-free type, b can be 0. When the above lithium transition metal oxide contains cobalt, b can be greater than 0, greater than 0.01, or greater than 0.02. The upper and lower limits of the molar fraction of cobalt relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within the range that satisfies the above definitions. When the molar fraction of cobalt in the aforementioned lithium transition metal oxide meets the above-mentioned range, a stable crystal structure can be formed and good output characteristics can be exhibited.

[0060] In the above chemical formula 1, the value of c, representing the mole fraction of manganese and / or aluminum relative to all elements other than lithium (M1 / Ni+Co+M1+M2) in the above lithium transition metal oxide, can be less than 0.20, less than 0.19, less than 0.18, less than 0.17, less than 0.16, less than 0.15, less than 0.14, less than 0.13, less than 0.12, less than 0.11, less than 0.10, less than 0.09, less than 0.08, less than 0.07, less than 0.06, less than 0.05, less than 0.04, less than 0.03, or less than 0.02. When the above lithium transition metal oxide contains manganese and / or aluminum, the above c can be greater than 0, greater than 0.01, or greater than 0.02. The upper and lower limits of the mole fraction of manganese and / or aluminum relative to all elements other than lithium in the above lithium transition metal oxide can be appropriately selected within the range that satisfies the above definitions. When the molar fractions of manganese and / or aluminum in the aforementioned lithium transition metal oxides meet the above-mentioned range, a stable crystal structure can be formed.

[0061] Furthermore, when the aforementioned lithium transition metal oxide contains at least one selected from manganese and aluminum, as well as cobalt, the b+c in the aforementioned chemical formula 1 may be less than 0.40, less than 0.37, less than 0.35, less than 0.32, less than 0.30, less than 0.28, less than 0.25, less than 0.23, less than 0.20, less than 0.18, less than 0.15, less than 0.14, less than 0.13, less than 0.12, less than 0.11, less than 0.10, less than 0.09, less than 0.08, less than 0.07, less than 0.06, less than 0.05, or less than 0.04.

[0062] In the above chemical formula 1, M2 refers to a dopant that can exist within the crystal structure of the above lithium transition metal oxide. The above lithium transition metal oxide has a layered crystal structure in which lithium layers containing lithium and transition metal layers containing transition metal are alternately arranged, and the above dopant can be mixed into at least one of the above lithium layers and the above transition metal layers.

[0063] When the above-mentioned lithium transition metal oxide contains a dopant, the d in the above-mentioned chemical formula 1, which represents the mole fraction of the dopant in the above-mentioned lithium transition metal oxide relative to all elements other than lithium (M2 / Ni+Co+M1+M2), can be less than 0.05, less than 0.045, less than 0.04, less than 0.035, less than 0.03, less than 0.025, less than 0.02, less than 0.015, less than 0.01, less than 0.009, less than 0.008, less than 0.007, less than 0.006, less than 0.005, less than 0.004, less than 0.003, less than 0.002, or less than 0.001.

[0064] When the aforementioned lithium transition metal oxide selectively includes a dopant, the dopant may include at least one selected from Na, K, Mg, Ca, Sr, Ba, Rb, B, Ce, Hf, Ta, Cr, F, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu, preferably at least one selected from Mg, Ca, Ba, B, V, Ti, Fe, Zr, Zn, Si, Nb, Mo, W, and Cu, and more preferably at least one selected from Mg, Ca, Ba, B, Ti, Zr, Si, Nb, Mo, and W.

[0065] In addition, the aforementioned lithium transition metal oxides may contain barium as a dopant.

[0066] The types, combinations, and amounts of the aforementioned dopants can be appropriately selected within a range that will not adversely affect the electrochemical characteristics and stability of the aforementioned positive electrode active material.

[0067] The aforementioned dopant can be incorporated into the lithium transition metal oxide by mixing the precursor of the lithium transition metal oxide with a dopant-containing raw material and then subjecting the mixture to heat treatment (calcination). The lithium transition metal oxide can be obtained by mixing the precursor of the lithium transition metal oxide, a lithium raw material (e.g., LiOH, Li₂CO₃, or a combination thereof), and the dopant-containing raw material, followed by heat treatment (calcination). The dopant material can be fluorides, chlorides, carbonates, sulfates, nitrates, phosphates, oxides, and / or hydroxides of the aforementioned dopant.

[0068] The precursor for the aforementioned lithium transition metal oxide can be a hydroxide precursor containing at least one selected from nickel, cobalt, manganese, and aluminum. Furthermore, the aforementioned hydroxide precursor can be a nickel-containing hydroxide precursor, a nickel and cobalt-containing hydroxide precursor, a nickel, cobalt, and manganese-containing hydroxide precursor, a nickel, cobalt, and aluminum-containing hydroxide precursor, or a nickel, cobalt, manganese, and aluminum-containing hydroxide precursor. The aforementioned hydroxide precursor can be synthesized using a metal aqueous solution containing the aforementioned metal elements according to a known co-precipitation method. In this case, the aforementioned lithium transition metal oxide can be obtained by heat treatment (calcination) after mixing the aforementioned hydroxide precursor, a lithium feedstock (e.g., LiOH, Li₂CO₃, or a combination thereof), and the aforementioned dopant-containing feedstock.

[0069] As a precursor for the aforementioned lithium transition metal oxide, an oxide precursor obtained by oxidizing a hydroxide precursor containing at least one selected from nickel, cobalt, manganese, and aluminum can be used. The aforementioned oxide precursor can be obtained by oxidizing the aforementioned hydroxide precursor at a temperature below the main calcination temperature (e.g., below 800°C, below 700°C, below 600°C, or below 500°C). In this case, the aforementioned lithium transition metal oxide can be obtained by heat treatment (calcination) after mixing the aforementioned oxide precursor, a lithium feedstock (e.g., LiOH, Li₂CO₃, or a combination thereof), and the aforementioned dopant-containing feedstock.

[0070] Furthermore, the dopant can be derived from a flux used for the crystal growth of the lithium transition metal oxide. By using the flux during the calcination of the lithium transition metal oxide precursor, crystal growth of the lithium transition metal oxide can be induced. At this time, a portion of the metal elements contained in the flux can be doped into the crystal structure of the lithium transition metal oxide. Elements that can be included in the flux used for the crystal growth of the lithium transition metal oxide include at least one selected from Group 1 elements, Group 2 elements, Ba, Y, Zr, Ce, and Nb.

[0071] The aforementioned positive electrode active material contains barium and sulfur. The content of barium and sulfur in the aforementioned positive electrode active material can be determined by the well-known ICP analysis method using inductively coupled plasma spectrometry (ICP).

[0072] Based on the total weight of the above-mentioned positive electrode active materials, the barium content can be above 600 ppm, above 650 ppm, above 700 ppm, above 750 ppm, above 800 ppm, above 850 ppm, above 900 ppm, above 950 ppm, or above 1,000 ppm. Furthermore, based on the total weight of the aforementioned positive electrode active materials, the barium content may be less than 30,000 ppm, less than 29,000 ppm, less than 28,000 ppm, less than 27,000 ppm, less than 26,000 ppm, less than 25,000 ppm, less than 24,000 ppm, less than 23,000 ppm, less than 22,000 ppm, less than 21,000 ppm, less than 20,000 ppm, less than 19,000 ppm, less than 18,000 ppm, less than 17,000 ppm, less than 16,000 ppm, less than 15,000 ppm, less than 14,500 ppm, less than 14,000 ppm, less than 13,500 ppm, less than 13,000 ppm, or less than 12,500 ppm.

[0073] When the barium content in the aforementioned positive electrode active material is less than 600 ppm, the crystal growth effect caused by barium on the unit particles constituting the aforementioned lithium transition metal oxide may be weak. Therefore, it may be difficult to exhibit the effect of reducing the specific surface area of ​​the aforementioned lithium transition metal oxide to suppress side reactions with the electrolyte.

[0074] On the other hand, when the barium content in the above-mentioned positive electrode active material is greater than 30,000 ppm, as the crystal growth of the unit particles constituting the above-mentioned lithium transition metal oxide increases excessively, the movement distance of lithium ions increases, thereby reducing kinetic characteristics or potentially causing lifespan degradation.

[0075] Based on the total weight of the aforementioned positive electrode active materials, the sulfur content can be 500 ppm or more, 550 ppm or more, 600 ppm or more, 650 ppm or more, 700 ppm or more, 750 ppm or more, or 800 ppm or more. Furthermore, based on the total weight of the aforementioned positive electrode active materials, the sulfur content can be 3,000 ppm or less, 2,900 ppm or less, 2,800 ppm or less, 2,700 ppm or less, 2,600 ppm or less, 2,500 ppm or less, 2,400 ppm or less, 2,300 ppm or less, or 2,250 ppm or less.

[0076] When the sulfur content in the aforementioned positive electrode active material is less than 500 ppm, barium undoped into the lattice of lithium transition metal oxides may have difficulty forming sufficient compounds with sulfur. That is, the amount of barium existing in the form of compounds (e.g., BaSO4) is reduced, thus making it difficult to expect a sufficient improvement in conductivity.

[0077] On the other hand, when the sulfur content in the aforementioned positive electrode active material exceeds 3,000 ppm, the excessive content of sulfur-derived impurities (e.g., Li₂SO₄, Li₂S) raises concerns about decreased stability or promotion of side reactions. Furthermore, these sulfur-derived impurities can form a cathode electrolyte interphase (CEI) layer on the surface of the lithium transition metal oxide, potentially reducing surface kinetic properties. Moreover, an excessive sulfur content in the positive electrode active material can hinder the movement of lithium ions within the lithium transition metal oxide lattice, possibly reducing ionic conductivity.

[0078] The sulfur to barium weight ratio (S / Ba) calculated by ICP analysis for the aforementioned positive electrode active material can be 0.06 or higher, 0.065 or higher, 0.07 or higher, 0.075 or higher, 0.08 or higher, 0.085 or higher, 0.090 or higher, 0.095 or higher, 0.10 or higher, 0.105 or higher, or 0.11 or higher, and can be below 15.0, 14.0 or lower, 13.0 or lower, 12.0 or lower, 11.0 or lower, 10.0 or lower, 9.0 or lower, or 8.0 or higher. Below, 7.0 and below, 6.0 and below, 5.0 and below, 4.5 and below, 4.0 and below, 3.5 and below, 3.0 and below, 2.9 and below, 2.8 and below, 2.7 and below, 2.6 and below, 2.5 and below, 2.4 and below, 2.3 and below, 2.2 and below, 2.1 and below, 2.0 and below, 1.9 and below, 1.8 and below, 1.7 and below, 1.6 and below, 1.5 and below, 1.45 and below, 1.4 and below, 1.35 and below, 1.3 and below, 1.25 and below, or 1.2 and below.

[0079] When the weight ratio of sulfur to barium (S / Ba) calculated by ICP analysis for the above-mentioned positive electrode active material is less than 0.06, the content of barium in the above-mentioned positive electrode active material may be too high, or the content of sulfur may be too low.

[0080] When the barium content in the above-mentioned positive electrode active material is too high, as the crystal growth of the unit particles constituting the above-mentioned lithium transition metal oxide increases excessively, the movement distance of lithium ions increases, thereby reducing the kinetic characteristics or potentially causing a problem of lifespan degradation.

[0081] When the sulfur content in the aforementioned positive electrode active material is too low, barium that is not doped into the lattice of the lithium transition metal oxide may have difficulty forming a sufficient compound with sulfur. That is, the amount of barium existing in the form of compounds (e.g., BaSO4) is reduced, and thus it may be difficult to expect a sufficient improvement in conductivity.

[0082] When the weight ratio of sulfur to barium (S / Ba) calculated by ICP analysis for the above-mentioned positive electrode active material is greater than 15.0, the content of barium in the above-mentioned positive electrode active material may be too low, or the content of sulfur may be too high.

[0083] When the barium content in the aforementioned positive electrode active material is too low, the crystal growth effect of barium on the unit particles constituting the aforementioned lithium transition metal oxide may be weak. Therefore, it may be difficult to demonstrate the effect of reducing the specific surface area of ​​the aforementioned lithium transition metal oxide to suppress side reactions with the electrolyte.

[0084] When the sulfur content in the aforementioned positive electrode active material is excessive, the amount of sulfur-derived impurities (e.g., Li₂SO₄, Li₂S) in the material is also excessive, raising concerns about decreased stability or promotion of side reactions. Furthermore, these sulfur-derived impurities can form a CEI layer on the surface of the lithium transition metal oxide, potentially reducing surface kinetic properties. Moreover, an excessive sulfur content in the positive electrode active material can hinder the movement of lithium ions within the lithium transition metal oxide lattice, possibly reducing ionic conductivity.

[0085] The aforementioned lithium transition metal oxide can have a single-particle morphology consisting of a single unit particle and / or a secondary-particle morphology consisting of multiple unit particles aggregated together. That is, the aforementioned lithium transition metal oxide can be composed of a single particle (also called a single particle), or it can exist as a secondary particle formed by the aggregation of multiple single particles. The multiple single particles constituting the aforementioned secondary particles are respectively referred to as primary particles or unit particles, and the aforementioned secondary particles can be referred to as bulk particles or bulk particles.

[0086] Furthermore, the aforementioned lithium transition metal oxide may have a quasi-monoparticle morphology formed by the aggregation of 30 or fewer, 25 or fewer, 20 or fewer, 15 or fewer, or 10 or fewer unit particles. In this case, the aforementioned lithium transition metal oxide may be referred to as a quasi-monoparticle. The number of unit particles forming the aforementioned quasi-monoparticle may vary depending on the size of the unit particles. For example, the larger the size of the unit particles forming the aforementioned quasi-monoparticle, the fewer the number of unit particles forming the aforementioned quasi-monoparticle.

[0087] Here, when a single-particle lithium transition metal oxide is referred to as a non-agglomerated body and a secondary-particle lithium transition metal oxide is referred to as an aggregate, the aforementioned positive electrode active material may contain aggregates and / or non-agglomerated bodies. For example, the aforementioned positive electrode active material may contain only non-agglomerated lithium transition metal oxides, or only aggregated lithium transition metal oxides. Furthermore, the aforementioned positive electrode active material may exist as an aggregate formed by mixing non-agglomerated lithium transition metal oxides and aggregated lithium transition metal oxides.

[0088] For convenience, in this application, the aforementioned unit particle, the aforementioned single particle, the aforementioned primary particle and the aforementioned secondary particle can all be referred to as lithium transition metal oxide, and since the aforementioned single particle and the aforementioned primary particle are both single particles, they are all referred to as primary particles below.

[0089] The aforementioned primary particles may have rod, elliptical, and / or amorphous shapes. Furthermore, unless specifically intended during the manufacturing process, primary particles of various shapes may exist within the same positive electrode active material. Moreover, the aforementioned primary particles refer to particle units that do not exhibit grain boundaries when observed using a scanning electron microscope at magnification of 5,000 to 20,000 times.

[0090] Furthermore, the aforementioned primary particle can refer to a single grain (or crystallite). The aforementioned single particle and / or the aforementioned primary particle may have a single crystal structure containing a single grain, or may have a polycrystalline structure containing multiple grains.

[0091] In this application, the average particle size of the single particles existing as non-agglomerates and / or the aforementioned primary particles constituting aggregates may be greater than 1.1 mm. 1.15 Above, 1.20 Above, 1.25 Above, 1.30 Above, 1.35 Above, 1.40 Above, 1.45 Above, or 1.50 That's all. Furthermore, the average particle size of the aforementioned primary particles can be 7.5 mm. Below, 7.4 Below, 7.3 Below, 7.2 Below, 7.1 Below, 7.0 Below, 6.9 Below, or 6.8 The upper and lower limits of the average particle size of the primary particles can be appropriately selected within the range defined above.

[0092] The average particle size of the aforementioned primary particles can be calculated as the average of the lengths of the primary particles along their major and minor axes ([major axis length + minor axis length] / 2). The lengths of the primary particles along their major and minor axes can be calculated from SEM images of the non-agglomerated and / or agglomerated bodies.

[0093] In this application, the average particle size of the aforementioned secondary particles existing as an aggregate can be 2.0 mm. Up to 20 2.0 up to 18 2.0 Up to 15 2.0 Up to 12 3.0 Up to 20 3.0 up to 18 3.0 Up to 15 Or 3.0 Up to 12 .

[0094] The average particle size of the aforementioned secondary particles can vary depending on the number of the aforementioned primary particles constituting the secondary particles. The average particle size (D) of the aforementioned secondary particles... 50 The secondary particle size distribution can be determined using laser diffraction. For example, the secondary particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and irradiated with approximately 28 kHz ultrasound at an output power of 60 W. A volumetric particle size distribution curve can then be obtained, and the particle size corresponding to 50% of the volumetric volume can be determined. Alternatively, in other cases, the average particle size of the secondary particles can be calculated as the average particle size confirmed from SEM images.

[0095] As described above, the lithium transition metal oxide has at least one of the following forms: a single-particle form consisting of a single unit particle and a secondary-particle form formed by the aggregation of multiple unit particles. When the lithium transition metal oxide has a secondary-particle form, the secondary particles preferably have a quasi-single-particle form formed by the aggregation of 30 or fewer unit particles. When the lithium transition metal oxide constituting the above-mentioned positive electrode active material has a single-particle form and / or a quasi-single-particle form, by including barium and sulfur in the above-mentioned positive electrode active material, lithium impurities can be reduced without a water washing process, thereby improving the conductivity of the positive electrode active material and increasing the capacity per unit volume.

[0096] The aforementioned secondary particle can be divided into a central portion corresponding to a region relatively close to the center of the secondary particle and a surface portion corresponding to a region close to the outer peripheral surface of the secondary particle.

[0097] Unless otherwise defined in this application, the region defined by a distance within half the average radius of the secondary particle from the center of the secondary particle may be referred to as the central region, and the region defined by a distance within half the average radius of the secondary particle from the outer periphery may be referred to as the surface region.

[0098] Pores, gaps, and / or grain boundaries may exist between the primary particles that constitute the secondary particles.

[0099] For example, the primary particle may form an internal void within the secondary particle by being separated from the adjacent primary particle. This internal void can be a closed pore or an open pore. A closed pore is a void that is isolated within the secondary particle and not connected to its surface, while an open pore is a void that is connected to its surface.

[0100] Furthermore, the aforementioned primary particles can be defined as grain boundaries formed by contact with neighboring primary particles. That is, the aforementioned grain boundaries are boundaries formed by contact between adjacent primary particles, and cannot be interpreted as being contained within the aforementioned primary particles. Therefore, dissimilar metal oxides with different compositions and crystal structures than the aforementioned primary particles can exist along the aforementioned grain boundaries.

[0101] The surface of the secondary particle that is exposed to the outside in the surface portion of the primary particle forms the surface (outer peripheral surface) of the secondary particle.

[0102] At least a portion of the surface of the aforementioned lithium transition metal oxide contains a coating portion comprising barium and sulfur. The coating portion can be defined as the region on the surface of the aforementioned lithium transition metal oxide where barium and sulfur are present. The coating portion may have a morphology that wholly or partially covers the surface of the aforementioned lithium transition metal oxide. Furthermore, the coating portion may have an island-like morphology.

[0103] When the aforementioned lithium transition metal oxide has a single-particle morphology, barium and sulfur may be present in at least a portion of the surface of the single particle. Furthermore, when the aforementioned lithium transition metal oxide has a secondary particle morphology (or quasi-single-particle morphology) formed by the aggregation of multiple unit particles, barium and sulfur may be present in at least a portion of the surface of the outermost unit particle forming the secondary particle, the surface of the isolated unit particles within the secondary particle, and the interfaces between the isolated unit particles within the secondary particle. The barium and sulfur in the aforementioned positive electrode active material may exist in the form of compounds (e.g., BaSO4).

[0104] Furthermore, barium and sulfur may be present in the inner pores or inner gaps formed by the isolation of the unit particles within the aforementioned secondary particles. These inner pores or inner gaps correspond to empty spaces where multiple unit particles do not form direct contact with each other, and compounds containing barium and sulfur can exist in the form of filling these inner pores or inner gaps.

[0105] The interface between isolated unit particles within the aforementioned secondary particles can be defined as a grain boundary. The aforementioned barium and sulfur compounds may be present wholly or partially within the grain boundaries, internal voids, and / or internal interstitial spaces. Furthermore, the aforementioned barium and sulfur compounds may selectively exist in regions adjacent to the surface of the aforementioned secondary particles, or be irregularly distributed within the interior of the aforementioned secondary particles.

[0106] Compounds containing barium and sulfur may be present on the surface of the outermost unit particle forming the secondary particles. These compounds may be present entirely or partially on the surface of the secondary particles. They may also be sporadically distributed on the surface of the secondary particles. Furthermore, these compounds may diffuse from the surface portion of the secondary particles toward the center portion along the grain boundaries, internal voids, and / or internal gaps.

[0107] The aforementioned compounds containing barium and sulfur may be present between the secondary particles. In this case, adjacent secondary particles may exist in a state of mutual adhesion through the aforementioned compounds containing barium and sulfur.

[0108] By including barium and sulfur in the aforementioned positive electrode active material at predetermined amounts, thereby inducing the growth of the unit particles constituting the aforementioned lithium transition metal oxide to an appropriate level, the average grain size of the aforementioned lithium transition metal oxide can be 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 155 nm or more, or 159 nm or more. Furthermore, the average grain size of the aforementioned lithium transition metal oxide can be 210 nm or less, 205 nm or less, 200 nm or less, 195 nm or less, 190 nm or less, or 185 nm or less.

[0109] The aforementioned average grain size can be quantitatively analyzed by Cu-Kα X-ray diffraction (XRD) analysis of the aforementioned lithium transition metal oxide. Specifically, the aforementioned average grain size can be calculated by performing Rietveld refinement on the X-ray diffraction patterns in the 2θ = 10°~120° range obtained from XRD analysis of the cathode active material containing the aforementioned lithium transition metal oxide.

[0110] When the average grain size of the lithium transition metal oxide containing barium and sulfur is less than 120 nm, the crystal growth effect per unit particle of the lithium transition metal oxide may be weak, making it difficult to reduce the specific surface area of ​​the lithium transition metal oxide to suppress side reactions with the electrolyte. When the average grain size of the lithium transition metal oxide containing barium and sulfur is greater than 210 nm, polarization may occur due to increased resistance, and this polarization may cause cracks within the particles, ultimately leading to a reduction in the lifetime of the positive electrode active material.

[0111] The changes in crystal structure caused by the presence of barium and sulfur in the aforementioned positive electrode active material, as well as the forms in which barium and sulfur exist in the aforementioned positive electrode active material, can be confirmed by XRD diffraction analysis of the aforementioned positive electrode active material. The aforementioned XRD diffraction analysis can be performed according to known XRD diffraction analysis methods for the aforementioned positive electrode active material.

[0112] In the diffraction spectrum obtained by X-ray diffraction analysis using Cu-Kα rays, the main diffraction peak detected at 2θ = 18.0~19.5° corresponds to the characteristic peak of the (003) crystal plane belonging to the layered crystal structure of the R-3m space group. The full width at half maximum (FWHM) of the characteristic peak of the (003) crystal plane detected by the above XRD diffraction analysis can vary depending on the content and / or morphology of barium and sulfur in the above positive electrode active material.

[0113] In this application, the full width at half maximum (FWHM) of the diffraction peaks detected at 2θ = 18.0~19.5°, obtained by X-ray diffraction analysis using Cu-Kα rays, can be 0.090 or less, 0.089 or less, 0.088 or less, or 0.0878 or less. Furthermore, the FWHM of the diffraction peaks detected at 2θ = 18.0~19.5° can be 0.070 or more, 0.075 or more, 0.076 or more, 0.077 or more, 0.078 or more, 0.079 or more, or 0.080 or more.

[0114] When the growth of the unit particles constituting the lithium transition metal oxide is induced to an appropriate level by including barium and sulfur in the above-mentioned positive electrode active material at a predetermined content, the full width at half maximum (FWHM) of the diffraction peaks detected at 2θ = 18.0 to 19.5° by X-ray diffraction analysis using Cu-Kα rays is 0.070 or more and 0.090 or less, and the average grain size of the lithium transition metal oxide is 120 nm or more and 210 nm or less.

[0115] When barium and sulfur in the above-mentioned positive electrode active material exist in the form of BaSO4, characteristic peaks of BaSO4 can be detected when the positive electrode active material is subjected to X-ray diffraction analysis. Specifically, characteristic peaks of BaSO4 can be detected at 2θ = 25.5~26.2° and 2θ = 28.5~28.9°.

[0116] By including barium and sulfur in the above-mentioned positive electrode active material at a predetermined content, the growth of the unit particles constituting the above-mentioned lithium transition metal oxide is induced to an appropriate level, and when the undoped barium and sulfur in the lattice of the above-mentioned lithium transition metal oxide appropriately form a compound (BaSO4), the ratio of the intensity (A) of the diffraction peak detected at 2θ=18.0~19.5° to the sum of the intensity (B) of the diffraction peak detected at 2θ=25.5~26.2° and the intensity (C) of the diffraction peak detected at 2θ=28.5~28.9° ([B+C] / A) can be 0.005 or more and 0.03 or less. Furthermore, the intensity ratio of the aforementioned diffraction peaks ([B+C] / A) can be 0.005 or higher and 0.03 or lower, 0.006 or higher and 0.03 or lower, 0.0062 or higher and 0.03 or lower, 0.005 or higher and 0.025 or lower, 0.006 or higher and 0.025 or lower, 0.0062 or higher and 0.025 or lower, 0.005 or higher and 0.02 or lower, 0.006 or higher and 0.02 or lower, 0.0062 or higher and 0.02 or lower, 0.005 or higher and 0.018 or lower, 0.006 or higher and 0.018 or lower, 0.0062 or higher and 0.018 or lower, 0.005 or higher and 0.0178 or lower, 0.006 or higher and 0.0178 or lower, or 0.0062 or higher and 0.0178 or lower.

[0117] The ratio of the intensities of the diffraction peaks ([B+C] / A) depends not only on the relative intensities of the characteristic peaks of the (003) crystal plane belonging to the R-3m space group, but also on the relative intensities of the characteristic peaks of BaSO4.

[0118] By including barium and sulfur in the aforementioned positive electrode active material at predetermined amounts, the growth of the unit particles constituting the aforementioned lithium transition metal oxide is induced to an appropriate level. Consequently, when the relative intensity of the characteristic peaks of the (003) crystal plane belonging to the R-3m space group layered crystal structure becomes relatively weaker, the intensity ratio of the aforementioned diffraction peaks ([B+C] / A) may increase. In this case, when the growth of the unit particles constituting the aforementioned lithium transition metal oxide is over-induced, the intensity ratio of the aforementioned diffraction peaks ([B+C] / A) may be greater than 0.03.

[0119] As the growth of the unit particles constituting the lithium transition metal oxide is over-induced, when the ratio of the intensity of the diffraction peaks ([B+C] / A) is greater than 0.03, the crystal growth of the unit particles constituting the lithium transition metal oxide increases excessively, thereby reducing the kinetic properties or potentially causing lifetime degradation due to polarization.

[0120] When the undoped barium in the lattice of the aforementioned lithium transition metal oxide fails to fully form a compound (BaSO4) with sulfur, or when BaSO4 is absent in the aforementioned positive electrode active material, the intensity ratio of the aforementioned diffraction peaks ([B+C] / A) may be less than 0.005. Furthermore, when the unit particles constituting the aforementioned lithium transition metal oxide fail to grow sufficiently due to insufficient or absent barium and / or sulfur in the positive electrode active material, the intensity ratio of the aforementioned diffraction peaks ([B+C] / A) may be less than 0.005.

[0121] Lithium secondary batteries According to another aspect of the present invention, a positive electrode can be provided comprising a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer may comprise the positive active material according to various embodiments of the present invention. Therefore, the positive active material is the same as described above, and for convenience, its specific description will be omitted hereafter; only the remaining components not mentioned above will be described.

[0122] There are no particular restrictions on the aforementioned positive electrode current collector, as long as it does not induce chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or surface-treated aluminum or stainless steel using carbon, nickel, titanium, silver, etc., can be used. Furthermore, the aforementioned positive electrode current collector typically has 3... Up to 500 The thickness can also be increased by forming fine irregularities on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, it can be used in various forms such as thin film, sheet, foil, mesh, porous body, foam, and non-woven body.

[0123] The aforementioned positive electrode active material layer can be prepared by coating the aforementioned positive electrode current collector with a positive electrode slurry composition comprising the aforementioned positive electrode active material, a conductive material, and, if desired, a binder.

[0124] In this case, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight, relative to the total weight of the positive electrode slurry used to form the positive electrode active material layer. When the positive electrode active material is included in the above content range, excellent capacity performance can be shown, but it is not limited thereto.

[0125] The aforementioned conductive materials are used to impart conductivity to the electrodes, and can be used without restriction in the constructed battery as long as they do not cause chemical changes and possess electronic conductivity. Specific examples include graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One or more mixtures of these materials may be used. The conductive materials may comprise 0.1% to 15% by weight of the aforementioned conductive materials relative to the total weight of the positive electrode slurry used to form the positive electrode active material layer.

[0126] The aforementioned binder enhances the adhesion between multiple positive electrode active material particles and the bonding force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), ethylene-vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof; one or more mixtures thereof may be used. The binder may comprise 0.1% to 15% by weight of the aforementioned binder relative to the total weight of the positive electrode slurry used to form the positive electrode active material layer.

[0127] In addition to utilizing the aforementioned positive electrode active material, the positive electrode can be prepared according to conventional positive electrode preparation methods. Specifically, it can be prepared by coating a positive electrode slurry composition onto a positive electrode current collector and then drying and calendering it. The positive electrode slurry composition is prepared by dissolving or dispersing the aforementioned positive electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent.

[0128] The solvents mentioned above can be solvents commonly used in this technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more mixtures thereof can be used. Considering the coating thickness and preparation yield of the slurry, the amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that exhibits excellent thickness uniformity when coated for the preparation of the positive electrode.

[0129] Furthermore, in another embodiment, the positive electrode can also be prepared by casting the positive electrode slurry composition onto a separate support, and then laminating the thin film obtained by peeling off the support onto the positive electrode current collector.

[0130] Furthermore, according to another aspect of the present invention, an electrochemical device including the aforementioned positive electrode can be provided. Specifically, the aforementioned electrochemical device can be a battery, a capacitor, etc., and more specifically, it can be a lithium secondary battery.

[0131] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and an electrolyte disposed between the positive electrode and the negative electrode. The positive electrode is the same as described above; therefore, for convenience, a detailed description is omitted. The following will only describe the remaining components not previously mentioned.

[0132] The aforementioned lithium secondary battery may optionally include: a battery container for housing the electrode assembly containing the positive electrode, the negative electrode, and the separator; and a sealing component for sealing the battery container.

[0133] The aforementioned negative electrode may include a negative electrode current collector and a layer of negative electrode active material located on the aforementioned negative electrode current collector.

[0134] There are no particular restrictions on the aforementioned negative electrode current collector, as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the aforementioned negative electrode current collector typically has 3... Up to 500 Similar to the thickness of the positive electrode current collector, the bonding force of the negative electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as thin films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0135] The aforementioned negative electrode active material layer can be prepared by coating the aforementioned negative electrode current collector with a negative electrode slurry composition comprising the aforementioned negative electrode active material and conductive material, and selectively including a binder as needed.

[0136] As the aforementioned negative electrode active material, compounds capable of reversible lithium insertion and extraction can be used. Specific examples include carbon materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; and metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; such as SiO₂. βMetal oxides capable of being doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metal compounds and carbon materials, such as Si-C composites or Sn-C composites, may be used, and one or more mixtures thereof may be used. Furthermore, lithium metal films may also be used as the aforementioned negative electrode active material. Both low-crystalline and high-crystalline carbon can be used as carbon materials. Representative low-crystalline carbons are soft carbon and hard carbon, while representative high-crystalline carbons are amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitch, and high-temperature calcined carbons such as petroleum or coal tar pitch-derived cokes.

[0137] Based on the total weight of the negative electrode slurry used to form the negative electrode active material layer, it may contain 80% to 99% of the aforementioned negative electrode active material.

[0138] The aforementioned binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, 0.1% to 10% by weight of the binder can be added based on the total weight of the negative electrode slurry used to form the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0139] The aforementioned conductive material is a component used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode slurry used to form the negative electrode active material layer, up to 10% by weight of the aforementioned conductive material can be added, preferably up to 5% by weight. There are no particular limitations on this conductive material as long as it does not induce chemical changes in the corresponding battery and has conductivity. For example, graphite such as natural graphite or artificial graphite can be used; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorinated carbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0140] In one embodiment, the aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying it. The negative electrode slurry composition is prepared by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material in the solvent. Alternatively, the negative electrode slurry composition can be cast onto a separate support, and then a thin film layer obtained by peeling off the support can be pressed onto the negative electrode current collector.

[0141] On the other hand, in the aforementioned lithium secondary battery, the separator is used to separate the negative electrode and the positive electrode and provide a channel for the movement of lithium ions. Any separator commonly used in lithium secondary batteries can be used without limitation. In particular, it is preferable to have low impedance and excellent electrolyte moisture-holding capacity for ion movement of the electrolyte. Specifically, porous polymer films can be used, for example, porous polymer films prepared using polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separators coated with ceramic components or polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0142] Furthermore, examples of electrolytes used in this invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries, but are not limited to these.

[0143] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0144] As the aforementioned organic solvents, organic solvents that can act as a medium for the movement of ions participating in the electrochemical reaction of the battery can be used without limitation. Specifically, as the aforementioned organic solvents, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate can be used. Carbonate solvents such as carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, which may contain double bonds, aromatic rings, or ether bonds); amides such as dimethylformamide; dioxanes such as 1,3-dioxane; or sulfolane, etc. Among these, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate, etc.) with high ionic conductivity and high dielectric constant, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) that can improve the charge-discharge performance of the battery. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, excellent electrolyte performance can be observed.

[0145] The lithium salts described above can be any compound capable of providing lithium ions for use in lithium secondary batteries. Specifically, the lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. Preferably, the concentration of the lithium salts is used in the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, thus exhibiting excellent electrolyte performance and enabling efficient movement of lithium ions.

[0146] When the electrolyte used herein is a solid electrolyte, such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, etc., solid inorganic electrolytes can be used. Preferably, sulfide solid electrolytes can be used.

[0147] As materials for sulfide-based solid electrolytes, solid electrolytes containing Li, X (where X is at least one selected from P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In) and S can be used. Examples of the aforementioned sulfide-based solid electrolyte materials include Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where X is a halogen element such as I or Cl), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (Where m and n are integers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (Where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.)

[0148] The solid electrolyte, preferably, is a sulfide-based solid electrolyte, which can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0149] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 Li 7-x La3Zr 1-x Nb x O 12 Li 7- 3x La3Zr2Al x O 12 Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, Li3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0150] The aforementioned solid electrolyte can be arranged as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Furthermore, the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the positive electrode active material layer of the positive electrode, or the aforementioned solid electrolyte can be partially contained independently of the aforementioned solid electrolyte layer within the negative electrode active material layer of the negative electrode.

[0151] In addition to the electrolyte components described above, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and increasing battery discharge capacity, the electrolyte may also contain one or more additives such as halogenated alkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, the electrolyte may contain 0.1% to 5% by weight of the aforementioned additives relative to its total weight.

[0152] As described above, lithium secondary batteries containing the positive electrode active material of the present invention stably exhibit excellent discharge capacity, output characteristics and lifespan characteristics, and therefore can be used in portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0153] The lithium secondary battery according to the present invention has no particular limitation on its shape and can be cylindrical, prismatic, pouch-shaped, or coin-shaped, etc. Furthermore, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also preferably as a unit battery in medium or large battery modules comprising multiple battery cells.

[0154] According to another aspect of the invention, a battery module comprising the aforementioned lithium secondary battery as a single unit and / or a battery pack comprising the same can be provided.

[0155] The aforementioned battery module or battery pack can be used as a power tool; an electric vehicle, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or as a power source for one or more medium or large-sized devices in an energy storage system.

[0156] The invention will be described in more detail below by way of examples. However, these examples are merely illustrative and the scope of the invention should not be construed as being limited by these examples.

[0157] Preparation Example 1. Preparation of Positive Electrode Active Material Example 1 (a) A NiCoMn(OH)₂ hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a well-known co-precipitation method. The Ni:Co:Mn molar ratio in the aforementioned hydroxide precursor was designed to be 96:2:2.

[0158] (b) The hydroxide precursor obtained in step (a) above, Ba(OH)2 H2O, LiOH A mixture was prepared by mixing H2O (with a molar ratio of Li / (Ni+Co+Mn+Ba) = 1.02) with Ba(OH)2. H₂O was mixed in at a concentration of 0.1 mol% for all metal elements except lithium in the above mixture. The mixture was then calcined at 830°C for 11 hours under an O₂ atmosphere to obtain lithium transition metal oxide. Specifically, during the calcination process, O₂ was supplied to the calcining furnace at a flow rate of 50 L / min, and the temperature inside the furnace was raised to 830°C for 3 hours, followed by calcination for 11 hours. After calcination, the calcining furnace was allowed to cool naturally.

[0159] Example 2 In addition to using 0.2 mol% Ba(OH)₂ in step (b) above In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0160] Example 3 In addition to using 0.3 mol% Ba(OH)₂ in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0161] Example 4 In addition to using 0.4 mol% Ba(OH)2 in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0162] Example 5 In addition to using 0.5 mol% Ba(OH)2 in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0163] Example 6 In addition to using 0.55 mol% Ba(OH)₂ in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0164] Example 7 In addition to using 0.6 mol% Ba(OH)₂ in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0165] Example 8 In addition to using 0.65 mol% Ba(OH)₂ in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0166] Example 9 In addition to using 0.7 mol% Ba(OH)2 in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0167] Example 10 In addition to using 0.75 mol% Ba(OH)₂ in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0168] Example 11 In addition to using 1.0 mol% Ba(OH)2 in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0169] Comparative Example 1 (a) A NiCoMn(OH)₂ hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a well-known co-precipitation method. The Ni:Co:Mn molar ratio in the aforementioned hydroxide precursor was designed to be 96:2:2.

[0170] (b) The hydroxide precursor obtained in step (a) above and LiOH A mixture was prepared by mixing H₂O (Li / (Ni+Co+Mn) molar ratio = 1.02). The mixture was then calcined at 700°C for 18 hours under an O₂ atmosphere to obtain lithium transition metal oxide. Specifically, during the calcination process, O₂ was supplied to the calcining furnace at a flow rate of 50 L / min, and the temperature inside the furnace was raised to 700°C over 2.5 hours, followed by calcination for 11 hours. After calcination, the calcining furnace was allowed to cool naturally.

[0171] Comparative Example 2 Except that the calcination temperature was set to 730°C in step (b) above, the positive electrode active material was prepared in the same manner as in Comparative Example 1. During the calcination of the above mixture, O2 was supplied to the calcination furnace at a flow rate of 50 L / min, and the temperature in the calcination furnace was raised to 730°C for 2.5 hours, followed by calcination for 11 hours. Then, after calcination was completed, the calcination furnace was allowed to cool naturally.

[0172] Comparative Example 3 Except that the calcination temperature was set to 830°C in step (b) above, the positive electrode active material was prepared in the same manner as in Comparative Example 1. During the calcination of the above mixture, O2 was supplied to the calcination furnace at a flow rate of 50 L / min, and the temperature inside the calcination furnace was raised to 830°C for 3 hours, followed by calcination for 11 hours. Then, after calcination was completed, the calcination furnace was allowed to cool naturally.

[0173] Comparative Example 4 Except that the calcination temperature was set to 1,020°C in step (b) above, the positive electrode active material was prepared in the same manner as in Comparative Example 1. During the calcination of the mixture, O2 was supplied to the calcination furnace at a flow rate of 50 L / min, and the temperature inside the furnace was raised to 1,020°C for 4 hours, followed by calcination for 11 hours. After calcination, the calcination furnace was allowed to cool naturally.

[0174] Comparative Example 5 (a) A NiCoMn(OH)₂ hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a known coprecipitation method. The Ni:Co:Mn molar ratio in the aforementioned hydroxide precursor was designed to be 96:2:2.

[0175] (b) The hydroxide precursor, ZrO2, and LiOH obtained in step (a) above A mixture was prepared by mixing H₂O (with a molar ratio of Li / (Ni+Co+Mn+Zr) = 1.02). ZrO₂ was mixed in at a content of 1.0 mol% for all metal elements except lithium in the mixture. The mixture was then calcined at 850°C for 11 hours under an O₂ atmosphere to obtain lithium transition metal oxide. During the calcination process, O₂ was supplied to the calcining furnace at a flow rate of 50 L / min, and the temperature in the furnace was raised to 850°C for 3 hours before calcination for 11 hours. After calcination, the furnace was allowed to cool naturally.

[0176] Comparative Example 6 (a) A NiCoMn(OH)₂ hydroxide precursor was synthesized using nickel sulfate, cobalt sulfate, and manganese sulfate via a known coprecipitation method. The Ni:Co:Mn molar ratio in the aforementioned hydroxide precursor was designed to be 96:2:2.

[0177] (b) The hydroxide precursor, ZrO2, Al(OH)3, and LiOH obtained in step (a) above A mixture was prepared by mixing H₂O (with a molar ratio of Li / (Ni+Co+Mn+Zr+Al) = 1.02). ZrO₂ was mixed in such that its content was 0.5 mol% of all metal elements except lithium in the mixture, and Al(OH)₃ was mixed in such that its content was 0.5 mol% of all metal elements except lithium in the mixture. The mixture was then calcined at 850°C for 11 hours under an O₂ atmosphere to obtain lithium transition metal oxide. During the calcination process, O₂ was supplied to the calcining furnace at a flow rate of 50 L / min, and the temperature in the furnace was raised to 850°C for 3 hours before calcination for 11 hours. After calcination, the furnace was allowed to cool naturally.

[0178] Comparative Example 7 In addition to using 2.0 mol% of Ba(OH)2 in step (b) above. In addition to H2O, the positive electrode active material was prepared in the same manner as in Example 1.

[0179] Preparation Example 2. Preparation of Lithium Secondary Battery (Half-Cell) A positive electrode slurry was prepared by dispersing 92% by weight of the positive electrode active material prepared according to Preparation Example 1, 4% by weight of artificial graphite, and 4% by weight of polyvinylidene fluoride binder in N-methyl-2-pyrrolidone. The prepared positive electrode slurry was uniformly coated onto a substrate with a thickness of 15 mm. After being applied to an aluminum thin film substrate, it is vacuum dried at 135°C to form a positive electrode.

[0180] For the aforementioned positive electrode, lithium foil is used as the counter electrode, with a thickness of 25 mm. A half-cell was prepared using a porous polyethylene membrane (Celgard 2300) as the separator and an electrolyte in which LiPF6 was present at a concentration of 1.15 M in a solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7.

[0181] Preparation Example 3. Preparation of Lithium Secondary Battery (Full Cell) A positive electrode slurry was prepared by dispersing 90% by weight of the positive electrode active material prepared according to Preparation Example 1, 4.5% by weight of carbon black, and 5.5% by weight of polyvinylidene fluoride binder in N-methyl-2-pyrrolidone. The prepared positive electrode slurry was uniformly coated onto a substrate with a thickness of 15 mm. A positive electrode was prepared by vacuum drying on an aluminum thin film at 135°C.

[0182] For the aforementioned positive electrode, a graphite electrode is used as the counter electrode, with a thickness of 20 mm. A full cell was prepared using a porous polyethylene membrane (Celgard 2300) as the separator and an electrolyte consisting of LiPF6 at a concentration of 1.15 M in a solvent in a volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate of 2:4:4.

[0183] Experimental Example 1. Compositional Analysis of Positive Electrode Active Material The contents (ppm) of barium and sulfur in the positive electrode active materials prepared in Preparation Example 1 were determined by ICP analysis. The ICP analysis was performed using inductively coupled plasma spectrometry (ICP) according to a known method. The contents (ppm) of barium and sulfur determined by the ICP analysis are shown in Table 1 below. Comparative Examples 1 to 6 did not use Ba(OH)₂ in step (b). H2O was used, therefore Ba was not detected in the positive electrode active material (lithium transition metal oxide) of the final product.

[0184] [Table 1]

[0185] nd: Not detected Experimental Example 2. SEM Analysis of Positive Electrode Active Material To confirm the size of the unit particles of each positive electrode active material (lithium transition metal oxide) prepared in Preparation Example 1, SEM images were obtained by scanning electron microscopy. Figures 1 to 11 The images are SEM images of the lithium transition metal oxides contained in the positive electrode active materials of Examples 1 to 11. Figures 12 to 18 The images are SEM images of lithium transition metal oxides contained in the positive electrode active materials of Comparative Examples 1 to 7.

[0186] Reference Figures 1 to 18 It can be confirmed that the positive electrode active materials according to Examples 1 to 11 and the positive electrode active materials according to Comparative Examples 4 to 7 comprise lithium transition metal oxides having at least one of the following forms: a single-particle form consisting of one unit particle and a quasi-single-particle form formed by the aggregation of 30 or fewer unit particles. On the other hand, it can be confirmed that the positive electrode active materials according to Comparative Examples 1 to 3 have a polycrystalline structure with more than 30 unit particles.

[0187] Next, the major and minor axis lengths of the unit particles were measured using an image analyzer program, and the average particle size was calculated by setting the particle size to (major axis length + minor axis length) / 2. The average particle size calculated based on the above SEM analysis is shown in Table 2 below.

[0188] [Table 2]

[0189] Furthermore, surface SEM / EDS analysis was performed on the positive electrode active materials (lithium transition metal oxides) according to Examples 3, 11, 1, 5, and 6, confirming the presence of coating materials on the surface of the aforementioned lithium transition metal oxides.

[0190] Figure 19 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Example 3. Figure 20 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Example 11.

[0191] Figure 21 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 1. Figure 22 This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 5. Figure 23This is a graph showing the surface EDS analysis results of the lithium transition metal oxide contained in the positive electrode active material according to Comparative Example 6.

[0192] Reference Figure 21 It can be confirmed that sulfur remains on the surface of the lithium transition metal oxide according to Comparative Example 1. The sulfur remaining on the surface of the lithium transition metal oxide according to Comparative Example 1 originates from the transition metal sulfate used in the precursor synthesis step, and is most likely Li2SO4 formed by the reaction of lithium impurities with sulfate.

[0193] It can be confirmed that, according to Comparative Example 1, since the lithium transition metal oxide was not washed with water after synthesis, a large amount of sulfur element remains on the surface of the lithium transition metal oxide.

[0194] On the other hand, refer to Figure 19 and Figure 20 It can be confirmed that, similar to Comparative Example 1, sulfur remains on the surface of the lithium transition metal oxide. However, in the cases of Examples 3 and 11, the detection sites of barium and sulfur are almost identical, indicating that barium and sulfur are coated in the form of compounds (e.g., BaSO4). For the positive electrode active materials according to Examples 1 to 11, characteristic diffraction peaks of BaSO4 were observed at 2θ = 25.5–26.2° and 28.5–28.9° in the diffraction spectra obtained by X-ray diffraction analysis using Cu-Kα rays (1.540598 Å).

[0195] On the other hand, refer to Figure 22 and Figure 23 It can be confirmed that, with Figure 19 and Figure 20 Unlike Comparative Examples 5 and 6, the detection locations of aluminum (Al) or zirconium (Zr) with sulfur were inconsistent, particularly in areas where sulfur condensation occurred on the surface. This suggests that the aluminum or zirconium was coated without forming a compound with sulfur. In this case, the residual sulfur on the surface of the lithium transition metal oxides according to Comparative Examples 5 and 6 is likely Li₂SO₄ formed by the reaction of lithium impurities with sulfates.

[0196] Experimental Example 3. XRD Analysis of Positive Electrode Active Material X-ray diffraction (XRD) analysis was performed on each of the positive electrode active materials prepared according to Preparation Example 1 to analyze the crystallographic properties of the coating portion formed on the surface of the lithium transition metal oxide. Specifically, the XRD analysis was performed using a Bruker D8E Endeavor diffractometer utilizing Cu-Kα rays (1.540598 Å).

[0197] The grain size of the aforementioned lithium transition metal oxide was obtained by Rietveld refinement of the diffraction spectrum obtained from the XRD analysis. The diffraction angle θ (rad) and full width at half maximum (FWHM) β (rad) were plotted on a coordinate plane with sinθ as the horizontal axis and βcosθ as the vertical axis within the range of 2θ = 10° to 120°, and the result was calculated from the obtained straight line.

[0198] The XRD analysis results are shown in Table 3 below.

[0199] [Table 3]

[0200] FWHM(003): Full width at half maximum (FWHM) of the diffraction peak detected at 2θ = 18.0–19.5°. (B+C) / A: The ratio of the intensity (A) of the diffraction peak detected at 2θ=18.0~19.5° to the sum of the intensity (B) of the diffraction peak detected at 2θ=25.5~26.2° and the intensity (C) of the diffraction peak detected at 2θ=28.5~28.9°; the intensities (A), (B), and (C) of the diffraction peak detected at 2θ=28.5~28.9° are all obtained by subtracting the background signal from the normalized XRD diffraction pattern based on the intensity (A) of the diffraction peak detected at 2θ=18.0~19.5°.

[0201] Referring to the results in Table 3 above, it can be confirmed that the intensity ratio ([B+C] / A) of the diffraction peaks observed in Comparative Examples 1 to 6 is less than 0.005. This result indicates that BaSO4 is absent because barium (Ba) is not present in the aforementioned positive electrode active material. On the other hand, it can be confirmed that the intensity ratio ([B+C] / A) of the diffraction peaks observed in Comparative Example 7 is greater than 0.03. When the intensity ratio ([B+C] / A) of the aforementioned diffraction peaks is greater than 0.03, the crystal growth of the unit particles constituting the aforementioned lithium transition metal oxide increases excessively, thereby reducing kinetic properties or potentially causing lifetime degradation due to polarization.

[0202] Experimental Example 4. Evaluation of the electrochemical characteristics of lithium secondary batteries (half-cells) For the lithium secondary battery (half-cell) prepared in Preparation Example 2, the volumetric capacity was determined by charge-discharge experiments using a 1C / 1C discharge rate within a driving voltage range of 3.0V to 4.4V at 25°C. The volumetric capacity (mAh / cc) was calculated by multiplying the initial discharge capacity (mAh / g) by the compaction density (g / cc). The compaction density (g / cc) was determined by pressing 3g of each positive electrode active material prepared according to Preparation Example 1 under 4.5 tons of pressure for 5 seconds using a tablet press.

[0203] The results of the above measurements are shown in Table 4 below.

[0204] [Table 4]

[0205] When comparing Examples 1 to 11, which have similar average particle sizes as described in Table 2, with Comparative Examples 4 to 7, it can be confirmed that the volumetric capacity of the lithium secondary battery using the positive electrode active material according to Examples 1 to 11, which has a coating containing barium and sulfur, is greater than that of the lithium secondary battery using the positive electrode active material according to Comparative Examples 4 to 7. Furthermore, it can be confirmed that the volumetric capacity of the lithium secondary battery using the positive electrode active material according to Examples 1 to 11 is greater than that of the lithium secondary battery using the positive electrode active material according to Comparative Examples 1 to 3, which has a polycrystalline structure with more than 30 unit particles.

[0206] Experimental Example 5. Stability Evaluation of Lithium Secondary Batteries (Full Cells) For the lithium secondary battery (full cell) prepared in Preparation Example 3, after 500 charge-discharge cycles at 25°C, a voltage range of 3.0V to 4.3V, and 1C / 1C, using an electrochemical analysis apparatus (TOYO SYSTEM Co., Ltd., Toscat-3100), the volume change of the pouch cell (v1) after 500 charge-discharge cycles relative to the initial pouch cell volume was measured using an electronic hydrometer (SID-220W). Furthermore, after storing the pouch cell (v1) after 500 charge-discharge cycles at 25°C for 4 weeks, the volume increase rate of the pouch cell (v2) after 4 weeks relative to the pouch cell (v1) after 500 charge-discharge cycles was measured.

[0207] The results of the above measurements are shown in Table 5 below.

[0208] [Table 5]

[0209] Referring to the results in Table 5, it can be confirmed that the volume increase rate of the lithium secondary battery (full cell) using the positive electrode active material according to Comparative Example 2 is greater than that of the lithium secondary battery (full cell) using the positive electrode active material according to Example 5. This result is presumably attributed to the presence or absence of barium in the positive electrode active material and the difference in the average particle size per unit particle. Furthermore, it can be confirmed that the volume increase rate of the lithium secondary battery (full cell) using the positive electrode active material according to Comparative Example 4 is greater than that of the lithium secondary battery (full cell) using the positive electrode active material according to Example 5. This result is presumably attributed to the presence or absence of barium in the positive electrode active material.

[0210] Furthermore, it can be confirmed that the volume increase rate of the lithium secondary battery (full cell) using the positive electrode active material according to Comparative Example 7 is greater than that of the lithium secondary battery (full cell) using the positive electrode active material according to Example 5. This result is presumably due to the higher absolute content of barium in the positive electrode active material, and the excessive amount of barium relative to sulfur.

[0211] Experimental Example 6. Analysis of Residual Lithium Impurity Content on the Surface of Positive Electrode Active Material The content of residual lithium impurities on the surface of each positive electrode active material prepared according to Preparation Example 1 was quantitatively analyzed by a known method. Specifically, 5 g of each positive electrode active material prepared according to Preparation Example 1 and 100 g of deionized water were placed in a 300 mL beaker and stirred at 300 rpm for 15 minutes using a magnetic stir bar.

[0212] After filtration using a vacuum flask, 50g of the solution was collected. The collected solution was placed in an autotitrator and titrated automatically with 0.1N HCl according to the Warder Method to determine the values ​​of LiOH and Li2CO3 in the solution.

[0213] The analytical results of the residual lithium are shown in Table 6 below.

[0214] [Table 6]

[0215] Referring to the results in Table 6, it can be confirmed that, given similar average particle sizes of the unit particles constituting lithium transition metal oxides, by including barium and sulfur in predetermined amounts, the lithium impurity content is reduced to below a certain level even without a water washing process. Furthermore, referring to the results of Comparative Examples 5 and 6, it can be confirmed that even when zirconium or aluminum is used instead of barium, the reduction effect on lithium impurities is not as good as in Comparative Example 3.

[0216] On the other hand, referring to the results of Comparative Example 7, it can be confirmed that if the absolute content of barium in the positive electrode active material is high and the content of barium is too high relative to sulfur, the effect of reducing lithium impurities will be reduced.

[0217] The embodiments of the present invention have been described above. However, those skilled in the art can make various modifications and alterations to the present invention by adding, changing, deleting, or adding constituent elements without departing from the spirit of the present invention as described in the claims. These modifications and alterations should also be included within the scope of the claims of the present invention.

Claims

1. A positive electrode active material, comprising a lithium transition metal oxide capable of lithium intercalation / deintercalation, characterized in that, The aforementioned positive electrode active material contains barium and sulfur. The full width at half maximum (FWHM) of the diffraction peaks detected at 2θ = 18.0–19.5° using Cu-Kα X-ray diffraction analysis of the aforementioned positive electrode active material is below 0.

090. The average grain size of the aforementioned lithium transition metal oxides ranges from 120 nm to 210 nm.

2. The positive electrode active material according to claim 1, characterized in that, The ratio ([B+C] / A) of the intensity of the diffraction peak detected at 2θ=18.0~19.5° obtained by X-ray diffraction analysis of Cu-Kα rays is greater than 0.005 and less than 0.

03.

3. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide contains at least one selected from nickel, cobalt, manganese, and aluminum.

4. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxides include nickel, cobalt, and manganese.

5. The positive electrode active material according to claim 1, characterized in that, The lattice of the aforementioned lithium transition metal oxide is doped with barium.

6. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide has at least one of the following forms: a single-particle form consisting of a single unit particle and a secondary-particle form consisting of multiple unit particles aggregated together.

7. The positive electrode active material according to claim 6, characterized in that, The average particle size of the aforementioned lithium transition metal oxide, as measured from SEM images, is 1.5 mm. Up to 7.5 .

8. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide has a single-particle morphology, and at least a portion of the surface of the single particle contains barium and sulfur.

9. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxides have a quasi-single-particle morphology, consisting of fewer than 30 unit particles aggregated together. Barium and sulfur are present in at least a portion of the surface of the outermost unit particle forming the aforementioned quasi-monoparticle, the surface of the isolated unit particle inside the aforementioned quasi-monoparticle, and the interface between the isolated unit particles inside the aforementioned quasi-monoparticle.

10. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide contains more than 60 mol% nickel relative to all elements except lithium.

11. The positive electrode active material according to claim 1, characterized in that, The aforementioned lithium transition metal oxide has an average composition represented by the following chemical formula 1: [Chemical Formula 1] The a Nor 1-（b+c+d） Co b M1 c M2 d O2 In the above chemical formula 1, M1 is at least one selected from Mn and Al. M2 is selected from at least one of Zr, Na, S, Mg, Ti, B, K, Ca, Sr, Ba, Rb, Ce, Hf, Ta, Cr, F, V, Fe, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Ge, Nd, Gd, and Cu. 0.85≤a≤1.15, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.05, 0 <b+c≤0.40。 12. The positive electrode active material according to claim 1, characterized in that, Based on the total weight of the above-mentioned positive electrode active materials, the barium content is between 200 ppm and 30,000 ppm.

13. The positive electrode active material according to claim 1, characterized in that, Based on the total weight of the above-mentioned positive electrode active materials, the sulfur content is between 500 ppm and 3,000 ppm.

14. A positive electrode, characterized in that, Includes the positive electrode active material according to any one of claims 1 to 13.

15. A lithium secondary battery, characterized in that, Use the positive electrode as described in claim 14.

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