Positive electrode active material and lithium secondary battery including same

Abstract

The present specification relates to a positive electrode active material and a lithium secondary battery including the same, and more particularly, to a positive electrode active material and a lithium secondary battery including the same, which improve electrochemical characteristics and stability by removing lithium-containing impurities present on the surface of a lithium composite oxide without a water washing process.

Description

Positive electrode active material and lithium secondary battery including the same Technical Field

[0001] This specification relates to a positive electrode active material and a lithium secondary battery including the same, and more specifically, to a positive electrode active material and a lithium secondary battery including the same, which improves electrochemical properties and stability by removing lithium-containing impurities present on the surface of lithium composite oxides without a water washing process. Background Technology

[0002] Batteries use materials capable of electrochemical reactions at the positive and negative electrodes to store electrical energy. As a representative example of such batteries, there are lithium-ion secondary batteries that store electrical energy through the difference in chemical potential during the insertion / extraction of lithium ions at the positive and negative electrodes.

[0003] The aforementioned lithium secondary battery is prepared by using materials capable of reversible lithium-ion insertion / extraction as positive and negative electrode active materials, and filling the space between the positive and negative electrodes with organic or polymer electrolytes.

[0004] Representative materials used as positive electrode active materials in lithium secondary batteries include lithium composite oxides. Examples of such lithium composite oxides include LiCoO2, LiMn2O4, LiNiO2, LiMnO2, or complex oxides of nickel, cobalt, manganese, or aluminum, as disclosed in Korean Patent Publication No. 10-2015-0069334 (published on June 23, 2015).

[0005] Among the aforementioned positive electrode active materials, LiCoO2 is the most widely used due to its excellent lifetime characteristics and charge / discharge efficiency. However, due to the limited resources of cobalt used as a raw material, its price is expensive, thus limiting its price competitiveness.

[0006] Lithium manganese-based oxides such as LiMnO2 and LiMn2O4 have the advantages of excellent thermal stability and low price, but they suffer from small capacity and poor high-temperature performance. In addition, LiNiO2-type cathode active materials exhibit high discharge capacity battery performance, but they are difficult to synthesize due to the problem of cation mixing between lithium and transition metals, resulting in significant problems in rate performance.

[0007] Furthermore, depending on the severity of this cation mixing, a large amount of lithium byproducts are generated. Most of these byproducts consist of compounds of LiOH and Li₂CO₃. Therefore, they can lead to gelation during the preparation of the cathode slurry, or become a source of gas generation due to repeated charge-discharge cycles after electrode fabrication. In addition, the residual Li₂CO₃ in these lithium byproducts increases monomer swelling, thus reducing the electrode's lifespan.

[0008] To compensate for this shortcoming, the demand for nickel-rich cathode active materials with a nickel content of 50% or more has increased as a cathode active material for secondary batteries. However, while these nickel-rich cathode active materials exhibit high capacity characteristics, they also suffer from structural instability caused by the mixing of lithium / nickel cations as the nickel content increases. Due to this structural instability of the cathode active material, lithium secondary batteries degrade rapidly not only at high temperatures but also at room temperature.

[0009] Therefore, it is necessary to develop cathode active materials that can overcome the problems of the aforementioned nickel-rich cathode active materials.

[0010] Existing technical documents

[0011] Patent documents

[0012] (Patent Document 1) Korean Patent Publication No. 10-2015-0069334 (Publication Date: June 23, 2015)

[0013] (Patent Document 2) Korean Patent Publication No. 10-1651338 (Publication Date: August 25, 2016) Summary of the Invention

[0014] Technical issues

[0015] In the lithium secondary battery market, while the growth of lithium secondary batteries for electric vehicles plays a dominant role, the demand for positive electrode active materials used in lithium secondary batteries is also constantly changing.

[0016] For example, the application of nickel-based lithium composite oxides with high energy capacity per unit weight is continuously expanding.

[0017] Therefore, one object of this specification is to provide a positive electrode active material that can improve the electrochemical characteristics and stability of lithium secondary batteries.

[0018] In addition, another object of this specification is to provide a lithium secondary battery using a positive electrode comprising a lithium composite oxide as defined herein.

[0019] The purpose of this specification is not limited to those stated above. Other purposes and advantages not mentioned herein will be understood through the following description and through the embodiments described herein. Furthermore, it will be readily apparent that the purposes and advantages of this specification can be achieved by the means and combinations thereof described in the claims.

[0020] Solution to the problem

[0021] Previously, a technique was proposed to improve the stability of positive electrode active materials by having light elements, such as boron, exist in the form of oxides, thereby reducing surface side reactions of the positive electrode active materials (Korean Patent Publication No. 10-1651338, Publication Date: 2016.08.25).

[0022] However, although side reactions between the positive electrode active material and the electrolyte can be reduced by forming oxides containing the aforementioned light elements on the surface of the positive electrode active material, there is a problem that the content of lithium impurities on the surface of the positive electrode active material increases due to the reaction between the positive electrode active material and the raw material containing the aforementioned light elements.

[0023] The reason for the above problem is that at least a portion of the lithium-containing impurities present on the surface of the positive electrode active material reacts with the raw material containing the light element to be converted into oxides containing the light element. However, the amount of lithium-containing impurities converted into oxides containing the light element is extremely small compared to the amount of lithium-containing impurities generated by the reaction between the positive electrode active material and the raw material containing the light element.

[0024] To solve the above-mentioned technical problems, according to one aspect of this specification, a positive electrode active material is provided, which is a positive electrode active material comprising a lithium composite oxide capable of lithium intercalation and deintercalation, wherein the lithium composite oxide comprises boron and sulfur, and a coating comprising a sulfur compound is present on at least a portion of the surface of the lithium composite oxide.

[0025] In one embodiment, the lithium composite oxide may include at least one transition metal selected from nickel, cobalt, manganese and aluminum.

[0026] Here, the nickel content in the transition metals other than lithium in the above-mentioned lithium composite oxide can be 50 mol% or more.

[0027] In addition, in the above-mentioned lithium composite oxides, the aluminum content can be greater than the boron content.

[0028] On the other hand, in the above-mentioned lithium composite oxide, at least one of aluminum, boron and sulfur can be segregated on the surface of the lithium composite oxide.

[0029] In one instance, the aforementioned chalcogenide compounds may include Li2SO4.

[0030] Here, the 2θ value obtained by Cu-KαXRD analysis of the above-mentioned lithium composite oxide may have a peak value in at least one region selected from the group consisting of 22.1°±0.1°, 22.3°±0.1°, 25.8°±0.1° and 28.3°±0.1°.

[0031] Furthermore, the amount of LiOH dissolved by the aforementioned lithium composite oxide, as determined by neutralization titration with HCl, is less than 3279 ppm.

[0032] On the other hand, the sum of the a-axis lattice constant and the c-axis lattice constant of the aforementioned lithium composite oxide can be less than [a certain value].

[0033] Here, the aforementioned lithium composite oxide can be represented by the following chemical formula 1.

[0034] [Chemical Formula 1]

[0035] Li a Ni 1-(b+c+d+e) M1 b M2 c Al d B e O2

[0036] (Where M1 is at least one selected from Co and Mn, and M2 is at least one selected from Ba, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.20, 0 <d≤0.20,0<e≤0.10)。

[0037] On the other hand, the coating may further include at least one compound represented by the following chemical formula 2.

[0038] [Chemical Formula 2]

[0039] Li x M3 y S w O z

[0040] (Where M3 is selected from at least one of Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, B, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, 0≤x≤8, 0 <y≤8,0≤w≤8,2≤z≤13)。

[0041] According to another aspect of this specification, a method for preparing a positive electrode active material is provided, comprising: step (a), preparing a lithium composite oxide; step (b), coating a solution containing a boron-based compound and a sulfuric acid-based compound onto the surface of the lithium composite oxide; and step (c), calcining at a temperature below 350°C.

[0042] In one embodiment, the sulfuric acid compound may be aluminum sulfate.

[0043] On the other hand, after calcination in step (c) above, the content of unreacted residual LiOH and Li2CO3 can be less than 63.3% relative to the content before calcination.

[0044] According to another aspect of this specification, a lithium secondary battery comprising the above-described positive electrode active material is provided.

[0045] The effects of the invention

[0046] According to this specification, since the lithium composite oxide contained in the above-mentioned positive electrode active material includes boron and sulfur, and a coating containing sulfur compounds is formed on its surface, lithium-containing impurities can be removed, thereby improving electrochemical characteristics and stability.

[0047] In particular, according to this specification, in the additional calcination step of the positive electrode active material, by mixing lithium composite oxide with light element-containing raw materials and sulfuric acid-based raw materials and heat-treating, sulfur compounds can be concentrated on the surface of the particles in the positive electrode active material.

[0048] In addition to the effects described above, the specific effects of the present invention will be described while explaining the specific embodiments. Attached Figure Description

[0049] Figure 1 shows the XRD results of a positive electrode active material according to an embodiment of this specification.

[0050] Figure 2 is a SEM image showing a positive electrode active material according to an embodiment of this specification.

[0051] Figure 3 is a graph showing the characteristics of a positive electrode active material according to an embodiment of this specification.

[0052] Figure 4 is a SEM image showing a positive electrode active material according to an embodiment of this specification.

[0053] Figure 5 illustrates the electrochemical characteristics of a battery comprising a positive electrode active material according to an embodiment of this specification. Detailed Implementation

[0054] Specific terms are defined herein for ease of understanding. Unless specifically defined herein, scientific and technical terms used herein should have the meanings commonly understood by those skilled in the art. Furthermore, it should be understood that, as used herein, the singular form is intended to include the plural form, and vice versa, unless the context clearly indicates otherwise.

[0055] The following describes in more detail the positive electrode active material for lithium secondary batteries with improved electrochemical properties and stability, and lithium secondary batteries including the same.

[0056] Positive electrode active material

[0057] According to one aspect of this specification, the positive electrode active material is a positive electrode active material comprising a lithium composite oxide capable of lithium intercalation and deintercalation, wherein the lithium composite oxide comprises boron and sulfur, and a coating comprising a sulfide compound may be present on at least a portion of the surface of the lithium composite oxide.

[0058] In one instance, the aforementioned lithium composite oxide can exist as secondary particles formed by the aggregation of multiple primary particles, or as a single crystal of primary particles without grain boundaries.

[0059] When the lithium composite oxide contained in the positive electrode active material as defined in this article exists as an aggregate of multiple primary particles, the lithium composite oxide can be referred to as a secondary particle.

[0060] The primary particle mentioned above refers to a single grain (grain or crystallite), while the secondary particle refers to an aggregate formed by the aggregation of multiple primary particles.

[0061] At this point, the primary particles constituting the aforementioned lithium composite oxide can have rod-like, elliptical, and / or irregular shapes. Furthermore, unless specifically designed in the preparation process, primary particles of various shapes can coexist in the same positive electrode active material. Additionally, the aforementioned primary particles refer to particle units that do not exhibit grain boundaries when observed under a scanning electron microscope at magnification of 5000x to 20000x.

[0062] The aforementioned primary particles can consist of a single grain or multiple grains. In this case, the size of the grain can be inferred from the diffraction pattern obtained by XRD analysis of the aforementioned lithium composite oxide, or calculated by substituting the full width at half maximum (FWHM) of the characteristic peaks of the representative crystal planes into the Scherrer equation.

[0063] In the case where the aforementioned lithium composite oxide is a secondary particle form created by the aggregation of multiple primary particles, the primary particles can be separated from adjacent primary particles within the secondary particle to form internal pores. Furthermore, the primary particles can form a surface existing within the secondary particle by contacting the internal pores, rather than forming grain boundaries by contacting adjacent primary particles. On the other hand, the surface of the primary particles existing on the outermost surface of the secondary particle, exposed to external air, forms the surface of the secondary particle. Here, the average particle size of the secondary particles may vary depending on the number of primary particles aggregated, but can be from 1 μm to 30 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm or any two values.

[0064] On the other hand, the term "single crystal" as used in this specification refers to a crystal in which the particles do not contain grains or grain boundaries. Furthermore, "primary particles of a single crystal" refers to particles that exist independently without forming aggregates. Therefore, "lithium-based composite compounds having a single crystal structure" refers to lithium-based composite compounds in which the primary particles are single grains, or particles in which the primary particles do not contain grain boundaries.

[0065] The average major axis length of the aforementioned primary particles is from 0.1 μm to 15 μm, for example, within the range of 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or any two of these values, thereby enabling the achievement of optimal density of the positive electrode prepared using the positive electrode active material according to various embodiments of this specification.

[0066] In one embodiment, the lithium composite oxide may include at least one transition metal selected from nickel, cobalt, manganese and aluminum.

[0067] Here, the nickel content in the transition metals other than lithium in the aforementioned lithium composite oxide can be 50 mol% or more, for example, 50 mol%, 55 mol%, 60 mol%, 65 mol%, 70 mol%, 75 mol%, 80 mol%, 80.5 mol%, 81 mol%, 81.5 mol%, 82 mol%, 82.5 mol%, 83 mol%, 83.5 mol%, 84 mol%, 84.5 mol%, 85 mol%, 85.5 mol%, 86 mol%, 86.5 mol%, 87 mol%, and 87.5 mol%. %, 88 mol%, 88.5 mol%, 89 mol%, 89.5 mol%, 90 mol%, 90.5 mol%, 91 mol%, 91.5 mol%, 92 mol%, 92.5 mol%, 93 mol%, 93.5 mol%, 94 mol%, 94.5 mol%, 95 mol%, 95.5 mol%, 96 mol%, 96.5 mol%, 97 mol%, 97.5 mol%, 98 mol%, 98.5 mol%, 99 mol%, 99.5 mol%, 99.9 mol%, or a range between any two values.

[0068] As mentioned above, nickel-rich cathode active materials with high nickel content suffer from reduced stability and shortened lifespan. Furthermore, a high Li / TM value, representing the ratio of lithium to transition metals (TM), results in a significant amount of lithium residue after calcination. Consequently, gelation easily occurs in the slurry used to prepare the electrode, making battery fabrication difficult.

[0069] Existing methods for removing residual lithium typically involve washing the positive electrode active material with water. However, this washing process can damage the surface of the positive electrode active material, leading to a decrease in battery performance.

[0070] On the other hand, the lithium composite oxide according to one embodiment of this specification can be coated with aluminum-containing and boron-containing raw materials and then heat-treated to remove residual lithium.

[0071] In this process, the aluminum-containing raw material can be incorporated into the lithium composite oxide, thereby adjusting the electrochemical properties and replacing the water washing process to remove residual lithium. Here, the amount of the aluminum-containing raw material can be greater than the amount of the boron-containing raw material. In other words, the aluminum content in the lithium composite oxide can be greater than the boron content.

[0072] On the other hand, the aforementioned lithium composite oxide may contain boron and sulfur, and the coating present in at least a portion of the surface portion of the aforementioned lithium composite oxide may contain sulfur compounds.

[0073] Here, the surface portion of the lithium composite oxide in which the above coating exists can refer to the surface of a single primary particle or the surface of a secondary particle formed by the aggregation of multiple primary particles.

[0074] On the other hand, in the above-mentioned lithium composite oxide, at least one of aluminum, boron and sulfur can be segregated on the surface of the lithium composite oxide.

[0075] Here, the so-called segregation of specific elements refers to a concentration in a specific region of the aforementioned lithium composite oxide that is more than twice the average concentration of the relevant elements in the aforementioned lithium composite oxide.

[0076] In one instance, the clustering of these elements can be calculated from the line sum spectrum obtained by line scanning of devices such as EDS or EDX mounted on SEM or TEM, or by mapping specific elements in SEM or TEM images and identifying them from their density.

[0077] For example, a peak with a height more than twice the average value of an element appears in a line sum spectrum chart, or the density of points of a specific element is more than twice that of a specific element in a specific region of a mapping image, but is not limited to these.

[0078] The aforementioned elemental segregation structure can be formed by coating the lithium composite oxide with raw materials containing sulfur and aluminum, along with boron-containing raw materials, followed by heat treatment. However, if the heat treatment temperature is too high, the elements may diffuse, potentially preventing the formation of the segregation structure. Furthermore, the degree of element diffusion can vary depending on the type of element.

[0079] On the other hand, the segregating elements can form the aforementioned chalcogenide compounds.

[0080] Here, the surface portion can be a predetermined depth, such as 10% of the particle size of the target particle, extending inward from the outermost surface, but is not limited to this.

[0081] In one example, the aforementioned chalcogenide compounds may include Li₂SO₄. Unlike LiOH and Li₂CO₃, which cause gelation of the electrode slurry, Li₂SO₄ is an ion-conducting material that does not have gelation problems, and can improve the electrochemical performance of the aforementioned positive electrode active material.

[0082] The 2θ value obtained by Cu-Kα XRD analysis of the aforementioned lithium composite oxide exhibits a peak value in at least one region selected from the group consisting of 22.1°±0.1°, 22.3°±0.1°, 25.8°±0.1°, and 28.3°±0.1°. Here, the XRD analysis is performed using CuKα rays (… The results obtained.

[0083] In the XRD analysis described above, the peak observed in the region satisfying the 2θ value may indicate a Li2SO4 crystal structure that can improve the electrochemical performance of the positive electrode active material.

[0084] Furthermore, the amount of LiOH dissolved by the aforementioned lithium composite oxide, as determined by neutralization titration with HCl, is less than 3279 ppm. For example, it can be 3275 ppm, 3250 ppm, 3225 ppm, 3200 ppm, 3175 ppm, 3150 ppm, 3125 ppm, 3100 ppm, 3075 ppm, 3050 ppm, 3025 ppm, 3000 ppm, 2975 ppm, 2950 ppm, 2925 ppm, 2900 ppm, 2875 ppm, 2850 ppm, 2825 ppm, 2800 ppm, 2775 ppm, 2750 ppm, 2725 ppm, 2700 ppm, 2675 ppm, 2650 ppm, 2625 ppm, 2600 ppm, 2575 ppm, 2550 ppm, 2525 ppm, 2500 ppm, or any two of these values, or less than 2500 ppm, but is not limited thereto.

[0085] The above-mentioned leaching amount of LiOH is an exemplary value and may vary depending on the composition of the above-mentioned lithium composite oxide.

[0086] Here, the amount of LiOH dissolved can be determined according to the method in the experimental example, or the amount of HCl consumed can be calculated by converting the first peak value that appears at the minimum x-axis value in the differential graph obtained by differentiating the pH value relative to the amount of HCl added by neutralization titration.

[0087] At this point, the above-mentioned neutralization titration method can be used to perform the above-mentioned neutralization titration on 5g of the above-mentioned positive electrode active material, and the amount of LiOH dissolved can be determined by the differential graph of pH change of the amount of HCl added obtained by the above-mentioned neutralization titration method.

[0088] On the other hand, the sum of the a-axis lattice constant and the c-axis lattice constant of the aforementioned lithium composite oxide is less than For example,

[0089] The range between any two values, or less than But it is not limited to this.

[0090] The a-axis and c-axis lattice constants mentioned above are exemplary values ​​and may vary depending on the composition of the lithium composite oxide.

[0091] Here, the aforementioned lithium composite oxide can be represented by the following chemical formula 1.

[0092] [Chemical Formula 1]

[0093] Li a Ni 1-(b+c+d+e) M1 b M2 c Al d B e O2

[0094] (Where M1 is at least one selected from Co and Mn, and M2 is at least one selected from Ba, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.20, 0 <d≤0.20,0<e≤0.10)。

[0095] The value 'a' above represents the molar ratio of lithium to transition metal in the lithium composite oxide, which can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or any two values ​​in between.

[0096] The values ​​b and c above represent the ratio of M1 to M2, and can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or any range between two values.

[0097] Here, M1 and M2 can be selected based on known technologies for positive electrode active materials to impart the desired performance to the lithium composite oxide.

[0098] The d above represents the ratio of the total amount of doped aluminum and aluminum segregated on the surface, and can be 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0. 09, 0.095, 0.10, 0.105, 0.11, 0.115, 0.12, 0.125, 0.13, 0.135, 0.14, 0.145, 0.15, 0.155, 0.16, 0.165, 0.17, 0.175, 0.18, 0.185, 0.19, 0.195, 0.20, or a range between any two values.

[0099] The 'e' above represents the ratio of boron, which can be 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.1, or any two values ​​in between.

[0100] On the other hand, in addition to the aforementioned chalcogenides, the coating may further contain other compounds. These compounds may include, but are not limited to, one of aluminum, boron, and sulfur that segregate on the surface.

[0101] For example, the coating may further include at least one compound represented by the following chemical formula 2.

[0102] [Chemical Formula 2]

[0103] Li x M3 y S w O z

[0104] (Where M3 is selected from at least one of Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, B, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, 0≤x≤8, 0 <y≤8,0≤w≤8,2≤z≤13)。

[0105] The x value above represents the lithium ratio in the above compound, and can be 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, or any two values ​​in between.

[0106] The above y represents the ratio of M3, which can be 0.01, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, or any range between two values.

[0107] Here, M3 can be selected based on known technologies for positive electrode active materials to form a coating with the desired properties on the lithium composite oxide.

[0108] The above w represents the ratio of S, which can be 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, or any range between two values.

[0109] The z above represents the oxygen ratio, which can be 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, or any range between two values.

[0110] In one example, the compound represented by the above chemical formula 2 can be B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, or Li2B8O. 13 Boron-containing oxides, etc.

[0111] In another example, the compound represented by the above chemical formula 2 can be an aluminum-containing oxide such as Al2O3, LiAlO2, or LiAl5O8.

[0112] Alternatively, the compound represented by the above chemical formula 2 can be AlS2O2, LiAlSO, etc., but is not limited to these.

[0113] Preparation method of positive electrode active material

[0114] According to another aspect of this specification, the method for preparing the positive electrode active material may include: step (a), preparing a lithium composite oxide; step (b), coating a solution containing a boron-based compound and a sulfuric acid-based compound onto the surface of the lithium composite oxide; and step (c), calcining at a temperature below 350°C.

[0115] Step (a) above may be a step of preparing a lithium composite oxide containing residual lithium on the surface.

[0116] Here, the above-mentioned lithium composite oxide is prepared by a method including the following steps: step (a1), preparing a hydroxide precursor; and step (a2), mixing the above-mentioned hydroxide precursor prepared in step (a1) with a lithium-containing raw material and then performing a first heat treatment.

[0117] The aforementioned hydroxide precursor may contain nickel. Alternatively, in addition to nickel, the aforementioned hydroxide precursor may further include at least one transition metal element selected from the group consisting of cobalt, manganese, and aluminum.

[0118] The lithium-containing raw material can be selected from LiOH and Li2CO3. Here, the ratio of the number of moles of lithium (Li) in the lithium-containing raw material to the number of moles of transition metal (TM) in the hydroxide precursor, i.e., Li / TM, can be 0.5 to 1.5, for example, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, and 1.5.

[0119] On the other hand, in step (a2) above, at least one raw material selected from the group consisting of Ni, Co, Mn, Al, Ba, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd, and Cu can be further mixed. This allows for the doping and / or coating of the above-mentioned lithium composite oxide with specific elements.

[0120] Furthermore, step (a2) above can be repeated more than once, for example, 1 time, 2 times, or 3 times in separate steps. The types and amounts of raw materials used in this repeated execution can be different.

[0121] Step (b) above is the step of coating the prepared lithium composite oxide from step (a) with a solution containing boron-based compounds and sulfuric acid-based compounds.

[0122] Here, the solution can be a mixed aqueous solution containing boron-based compounds and sulfate-based compounds. Here, the boron-based compounds can be H3BO3, B2O3, Li2O-B2O3, Li3BO3, Li2B4O7, Li2B2O7, or Li2B8O. 13 The mixing amount relative to the lithium composite oxide in step (a) above can be from 0.1 wt% to 1.5 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, or any two values, but is not limited thereto.

[0123] On the other hand, the sulfuric acid compound mentioned above can be aluminum sulfate, and its mixing amount relative to the lithium composite oxide in step (a) above can be from 0.1 mol% to 1 mol%, for example, it can be 0.1 mol%, 0.2 mol%, 0.3 mol%, 0.4 mol%, 0.5 mol%, 0.6 mol%, 0.7 mol%, 0.8 mol%, 0.9 mol%, 1 mol%, or any two of these values, but is not limited thereto.

[0124] Here, the above solution can be applied to the surface of the lithium composite oxide in step (a) by spray coating, but any method that can uniformly apply the solution is not limited.

[0125] Step (c) above refers to the calcination process performed at a temperature less than 350°C, for example, 349°C, 345°C, 340°C, 335°C, 330°C, 325°C, 320°C, 315°C, 310°C, 305°C, 300°C, 295°C, 290°C, 285°C, 280°C, 275°C, 270°C, 265°C, 260°C, 255°C, 250°C, 245°C, 240°C, 235°C, 230°C, 225°C, 220°C, 215°C, 210°C, 205°C, 200°C, or any two of these values. However, it is not limited to this step.

[0126] If the calcination temperature exceeds the above range, certain elements may not agglomerate on the surface but diffuse, thus failing to fully remove residual lithium or making it difficult to form a coating.

[0127] Furthermore, after calcination in step (c) above, the content of unreacted residual LiOH and Li₂CO₃ is less than 63.3% compared to before calcination, for example, 63.3%, 63.2%, 63.1%, 63%, 62.9%, 62.8%, 62.7%, 62.6%, 62.5%, 62.4%, 62.3%, 62.2%, 62.1%, and 62%. The percentage is 61.9%, 61.8%, 61.7%, 61.6%, 61.5%, 61.4%, 61.3%, 61.2%, 61.1%, 61%, 60.9%, 60.8%, 60.7%, 60.6%, 60.5%, 60.4%, 60.3%, 60.2%, 60.1%, 60%, or any two values ​​within a range, or less than 60%.

[0128] According to the above method, unreacted residual lithium can be effectively removed even without a water washing process.

[0129] Lithium secondary batteries

[0130] According to another embodiment of the present invention, the present invention can provide a positive electrode comprising a positive current collector and a positive active material layer formed on the positive current collector. The positive active material layer may comprise lithium composite oxide as the positive active material according to various embodiments of the present invention.

[0131] Therefore, the lithium composite oxide is the same as described previously, and for convenience, its specific description will be omitted. Hereinafter, only the remaining components not previously mentioned will be described. Furthermore, for convenience, the above-described lithium composite oxide will be referred to as the positive electrode active material.

[0132] There are no particular limitations on the aforementioned positive electrode current collector, as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the aforementioned positive electrode current collector typically has a thickness of 3μm to 500μm, and fine irregularities can be formed 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 films, sheets, foils, meshes, porous bodies, foams, and nonwovens.

[0133] 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.

[0134] In this case, the content of the positive electrode active material relative to the total weight of the positive electrode active material layer can be from 80% to 99% by weight, more specifically from 85% to 98.5% by weight. When the positive electrode active material is included in the above content range, excellent capacity characteristics can be exhibited, but it is not limited thereto.

[0135] The aforementioned conductive materials are used to impart conductivity to the electrodes. In the constructed battery, they can be used without restriction 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 total weight of the positive electrode active material layer may range from 0.1% to 15% by weight of the aforementioned conductive materials.

[0136] 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), 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 active material layer.

[0137] 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.

[0138] 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 a mixture of two or more of them 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.

[0139] 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.

[0140] Meanwhile, according to another embodiment of the present invention, an electrochemical device including the above-described positive electrode can be provided. Specifically, the electrochemical device is a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0141] Specifically, the aforementioned lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and a separator and 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 remaining components not previously described will be explained below.

[0142] The aforementioned lithium secondary battery may optionally include: a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separation membrane; and a sealing component for sealing the battery container.

[0143] The aforementioned negative electrode may include a negative current collector and a layer of negative active material located on the aforementioned negative current collector.

[0144] There are no particular limitations 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 surfaces treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the aforementioned negative electrode current collector can typically have a thickness of 3μm to 500μm. Similar to 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.

[0145] 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.

[0146] 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; 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; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), 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. One or more mixtures of these can be used. Furthermore, lithium metal thin films can 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.

[0147] Based on the total weight of the negative electrode active material layer, it may contain 80% to 99% of the aforementioned negative electrode active material.

[0148] The aforementioned binder is a component that facilitates the bonding between the conductive material, the active material, and the current collector. Typically, based on the total weight of the negative electrode active material layer, 0.1% to 10% of the aforementioned binder can be added. 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.

[0149] 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 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.

[0150] 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.

[0151] 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 a mixture of two or more of them 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.

[0152] Furthermore, in the aforementioned lithium secondary battery, the separator membrane is used to separate the negative and positive electrodes and provide a channel for lithium ion movement. Any separator membrane 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 electrolyte ion movement. Specifically, porous polymer films can be used, for example, porous polymer films prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or their two- or more-layered stacked structures. Furthermore, conventional porous nonwoven fabrics can also be used, for example, nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Moreover, to ensure heat resistance or mechanical strength, separator membranes coated with ceramic components and polymeric substances can also be used, selectively in single-layer or multi-layer structures.

[0153] Furthermore, examples of electrolytes used in this invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, but they are not limited to these.

[0154] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0155] As the aforementioned organic solvents, any organic solvent capable of acting 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.

[0156] 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 in the range of 0.1M to 2.0M. If 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.

[0157] 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.

[0158] As a material 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-P₂S-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, Li₂S-P₂S₅-ZmSn (where m and n are integers, and Z is Ge, Zn, or Ga), Li₂S-GeS₂, Li₂S-SiS₂-Li₃PO₄, and Li₂S-SiS₂-Li p MO q (Where p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.)

[0159] The solid electrolyte, preferably, is a sulfide-based solid electrolyte, which can be amorphous, crystalline, or a mixture of amorphous and crystalline states.

[0160] Examples of oxide-based solid electrolytes include Li7La3Zr2O. 12 Li 7-x La3Zr 1-x Nb xO 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, Li 3+x PO 4-x N x (LiPON), Li 2+2x Zn 1-x GeO4 (LISICON), etc.

[0161] The aforementioned solid electrolyte can be arranged as a separate layer (solid electrolyte layer) between the positive and negative electrodes. Alternatively, the aforementioned solid electrolyte can be partially contained in the positive electrode active material layer of the aforementioned positive electrode independently of the solid electrolyte layer, or the aforementioned solid electrolyte can be partially contained in the negative electrode active material layer of the aforementioned negative electrode independently of the aforementioned solid electrolyte layer.

[0162] In addition to the electrolyte components mentioned 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 imidazolidinyl ethers, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 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.

[0163] As described above, lithium secondary batteries containing the positive electrode active material described in this specification consistently exhibit excellent discharge capacity, output characteristics, and lifespan characteristics. Therefore, they can be used in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs).

[0164] The appearance of the lithium secondary battery according to this specification is not particularly limited, but it can be cylindrical, prismatic, pouch-shaped, or coin-shaped, using a can. Furthermore, the lithium secondary battery can be used not only as a battery cell for powering small devices, but also preferably as a unit cell in medium to large battery modules comprising multiple battery cells.

[0165] According to another aspect of this specification, a battery module including a lithium secondary battery as a unit cell and / or a battery pack including the same may be provided.

[0166] The aforementioned battery modules or battery packs can be used as power sources for at least one medium-sized and large device in systems such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0167] Preparation Example 1. Preparation of Positive Electrode Active Material

[0168] Example 1

[0169] (a) Precursor preparation

[0170] An aqueous solution of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O in a molar ratio of 95:2:3, along with NaOH and NH4OH, was added to the reactor while stirring. The reactor temperature was maintained at 45℃, and N2 gas was introduced into the reactor simultaneously to carry out the precursor synthesis reaction. After the reaction was complete, the mixture was washed and dehydrated to obtain Ni. 0.95 Co 0.02 Mn 0.03 Hydroxide precursor composed of (OH)2.

[0171] (b) First heat treatment

[0172] The hydroxide precursor obtained in step (a) above was mixed with LiOH (lithium / metal other than lithium molar ratio = 1.00) and Al(OH)3 as lithium raw materials, such that the aluminum content in the precursor, based on metal elements other than lithium, was 0.5 mol%, thus preparing a mixture. Next, the mixture was heated to 730°C in a calcination furnace under an O2 atmosphere for 6 hours and 10 minutes, and then heat-treated for 10 hours followed by furnace cooling to obtain a primary positive electrode active material containing lithium composite oxide.

[0173] (c) Second heat treatment

[0174] The primary cathode active material obtained in step (b) above was mixed with 1.0 mol% Co(OH)₂ and 1.0 mol% LiOH, based on the cobalt content excluding lithium, to prepare a mixture. The mixture was then heated to 700°C in a calcination furnace under an O₂ atmosphere for 2 hours and heat-treated for 8 hours, followed by furnace cooling, to obtain a secondary cathode active material containing lithium composite oxide.

[0175] (d) Third heat treatment

[0176] Weigh the material to ensure that the H3BO3 content relative to the secondary cathode active material obtained in step (c) is 0.4% by weight, and add deionized water (DIW) to bring the H3BO3 concentration to 7.5% by weight to prepare a solution. Weigh the material to ensure that the Al2(SO4)2 content relative to the secondary cathode active material is 0.25% by weight, and then add Al2(SO4)2 to the above solution. Spray the prepared solution onto the secondary cathode active material in a quantitative manner and mix. Place the mixture in a calcination furnace under an O2 atmosphere and heat it to 300°C for 1 hour, then heat-treat it for 8 hours and cool it in the furnace to obtain a tertiary cathode active material containing lithium composite oxide (average particle size of 14 μm).

[0177] Example 2

[0178] Except for the addition of 0.5 mol% Al2(SO4)2 in step (d), the positive electrode active material was prepared in the same manner as in Example 1.

[0179] Comparative Example 1

[0180] Except for the absence of Al2(SO4)2 in step (d), the positive electrode active material was prepared in the same manner as in Example 1.

[0181] Comparative Example 2

[0182] Except for step (d), in which Al2(SO4)2 was not added and 0.5 mol% (NH4)SO4 was added, the positive electrode active material was prepared in the same manner as in Example 1.

[0183] Comparative Example 3

[0184] Except for changing the calcination temperature of step (d) above to 350°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0185] Comparative Example 4

[0186] Except for changing the calcination temperature of step (d) above to 400°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0187] Comparative Example 5

[0188] Except for changing the calcination temperature of step (d) above to 600°C, the positive electrode active material was prepared in the same manner as in Example 1.

[0189] Experimental Example 1. Determination of Unreacted Residual Lithium in Positive Electrode Active Material

[0190] The amount of unreacted residual lithium dissolved in the primary, secondary, and tertiary positive electrode active materials in Preparation Example 1 was determined by neutralization titration using HCl.

[0191] The content of unreacted residual lithium was determined by pH titration using the amount of 0.1M HCl used to reach pH 4. First, 5g of the positive electrode active material was added to 100ml of DIW and stirred for 15 minutes, then filtered. 50ml of the filtrate was collected, and 0.1M HCl was added. The amount of HCl consumed according to the pH change was measured to determine Q1 and Q2. The dissolution amounts of unreacted LiOH and Li2CO3 were then calculated using the following formula.

[0192] M1 = 23.94 (Molecular weight of LiOH)

[0193] M2 = 73.89 (Li2CO3 molecular weight) SPL value = (sample weight × solution weight) / water weight

[0194] LiOH (wt%) = [(Q1-Q2)×C×M1×100] / (SPL size×1000)

[0195] Li2CO3 (wt%) = [2 × Q2 × C × M2 / 2 × 100] / (SPL size × 1000)

[0196] Using the above method, the amount of unreacted LiOH and Li2CO3 dissolved in the lithium composite oxides prepared in the above examples and comparative examples was determined, and the results are shown in Table 1.

[0197] Table 1

[0198]

[0199] Referring to Table 1, it can be confirmed that sulfate treatment can reduce residual lithium to a level similar to that of water washing. However, ammonium sulfate cannot remove residual lithium, and the reduction effect may vary depending on the different calcination temperatures of the three calcinations.

[0200] Experimental Example 2. Determination of XRD Characteristics of Positive Electrode Active Material

[0201] XRD analysis was performed on Example 1, Comparative Example 1 and Comparative Example 2.

[0202] XRD analysis used Cu-Kα rays ( The results were obtained using a Bruker D8Advance diffractometer and are shown in Figure 1.

[0203] Referring to Figure 1, it can be confirmed from the crystal peaks that Li2SO4 was formed with the application of sulfate-based substances.

[0204] Experimental Example 3. ICP Analysis of Positive Electrode Active Material

[0205] The metal content ratio of the three positive electrode active materials obtained from Preparation Example 1 was determined by ICP analysis and is shown in Table 2 below.

[0206] Table 2

[0207]

[0208] As can be seen from Table 2, when sulfate-based substances are treated, the sulfur (S) content increases, while when aluminum-based substances are treated, the aluminum (Al) content increases.

[0209] Example 4. SEM Analysis of Positive Electrode Active Material

[0210] The SEM image of the lithium composite oxide contained in the positive electrode active material prepared according to the example was obtained using an FE-SEM device and is shown in Figure 2.

[0211] Referring to Figure 2, it can be confirmed that aluminum (Al) and sulfur (S) are concentrated on the surface due to the chemical reaction between sulfate compounds and residual lithium. Considering the aforementioned XRD analysis results, it can be inferred that the sulfur (S) here exists in the form of Li₂SO₄.

[0212] Experimental Example 5. Characteristic Analysis of Positive Electrode Active Materials Based on Calcination Temperature

[0213] To confirm the characteristics of the calcination temperature according to step (d) of the embodiments, the characteristics of the three positive electrode active materials prepared in Examples 1, 3, 4 and 5 were analyzed by the method applicable to Experimental Examples 1 to 4, and the results are shown in Table 3, Figure 3 and Figure 4.

[0214] Table 3

[0215]

[0216] Referring to Figure 3, as the calcination temperature increases in step (d) above, the residual lithium content, the Ni metal occupancy (Niocc.) of the Li 3a sites, the a-axis lattice constant, and the c-axis lattice constant all increase.

[0217] The proportion of Ni metal can be used as a basis for aluminum (Al) doping. Furthermore, due to Al... 3+ Its electronegativity (1.513) is relatively lower than that of Ni. 3+ The electronegativity of Al is 1.695, therefore, when Al is doped, the binding force of the TM-O bond decreases, leading to an increase in the repulsive force between oxygen layers. As a result, both the a-axis and c-axis lattice constants increase.

[0218] Referring to Figure 4, the differences in the composition and crystal structure of aluminum (Al) and sulfur (S) in the surface region can be confirmed according to the calcination temperature.

[0219] Preparation Example 2. Preparation of Lithium Secondary Batteries

[0220] A positive electrode slurry was prepared by dispersing 94% by weight of each of the positive electrode active materials prepared according to Preparation Example 1, 3% by weight of artificial graphite, and 3% by weight of PVDF binder in 3.5 g of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was then uniformly coated onto a 20 μm thick aluminum (Al) film serving as the positive electrode current collector and dried. The film was then rolled to prepare the positive electrode. The positive electrode loading level was 7 mg / cm³. 2 The electrode density is 3.2 g / cm³. 3 .

[0221] In contrast to the aforementioned positive electrode, lithium foil was used as the counter electrode, and a porous polyethylene membrane (Celgard 2300, thickness: 25 μm) was used as the separation membrane. A button cell was prepared using a liquid electrolyte containing ethylene carbonate and ethyl methyl carbonate in a 3:7 volume ratio and LiPF6 at a concentration of 1.15 M through a conventional preparation process.

[0222] Example 6. Evaluation of the electrochemical characteristics of lithium secondary batteries

[0223] The initial charge capacity, initial discharge capacity and initial reversible efficiency of the lithium secondary battery (button cell) prepared according to Preparation Example 2 were determined by performing a charge test under the conditions of 25°C, a voltage range of 2.7V to 4.3V and a discharge rate of 0.05C.

[0224] The results of the above measurements are shown in Table 4 and Figure 5 below.

[0225] Table 4

[0226]

[0227] Referring to the results in Table 4 and Figure 5 above, by forming Li₂SO₄ as a conductive material on the surface, the capacity can be improved compared to Comparative Example 1, which only treats boron (B). Furthermore, in this embodiment, by forming an aluminum coating on the surface, the lifetime characteristics can be improved.

[0228] While the embodiments disclosed in this specification have been described above, those skilled in the art will understand that various modifications and alterations can be made to this specification by adding, modifying, deleting, or supplementing the constituent elements without departing from the spirit of the entire text of the claims, and these modifications and alterations also fall within the scope of the claims of this specification.

Claims

1. A positive electrode active material comprising a lithium composite oxide capable of lithium intercalation and deintercalation, wherein the lithium composite oxide comprises boron and sulfur, and a coating comprising a sulfide compound is present on at least a portion of the surface of the lithium composite oxide.

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

3. The positive electrode active material according to claim 2, characterized in that, In the above-mentioned lithium composite oxide, the content of nickel in the transition metals other than lithium is more than 50 mol%.

4. The positive electrode active material according to claim 2, characterized in that, In the aforementioned lithium composite oxide, the aluminum content is greater than the boron content.

5. The positive electrode active material according to claim 2, characterized in that, In the above-mentioned lithium composite oxide, at least one element selected from aluminum, boron, and sulfur is segregated on the surface portion of the lithium composite oxide.

6. The positive electrode active material according to claim 1, characterized in that, The aforementioned chalcogenide compounds include Li2SO4.

7. The positive electrode active material according to claim 6, characterized in that, The 2θ values ​​obtained by Cu-KαXRD analysis of the above-mentioned lithium composite oxides have peak values ​​in at least one region selected from the group consisting of 22.1°±0.1°, 22.3°±0.1°, 25.8°±0.1° and 28.3°±0.1°.

8. The positive electrode active material according to claim 1, characterized in that, The amount of LiOH dissolved by the above-mentioned lithium composite oxide was less than 3279 ppm, as determined by neutralization titration with HCl.

9. The positive electrode active material according to claim 1, characterized in that, The sum of the a-axis lattice constant and the c-axis lattice constant of the above-mentioned lithium composite oxide is less than 10. The positive electrode active material according to claim 1, characterized in that, The above-mentioned lithium composite oxide is represented by the following chemical formula 1: [Chemical Formula 1]Li a Ni 1-(b+c+d+e) M1 b M2 c Al d B e O2 (wherein, M1 is at least one selected from Co and Mn, M2 is at least one selected from Ba, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, Ge, Nd, Gd and Cu, 0.5≤a≤1.5, 0≤b≤0.20, 0≤c≤0.20, 0 <d≤0.20,0<e≤0.10)。 11. The positive electrode active material according to claim 1, characterized in that, The coating further comprises at least one compound represented by the following chemical formula 2: [Chemical Formula 2]Li x M3 y S w O z (Where M3 is selected from at least one of Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, B, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, P, Eu, Sm, W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd, and Nd, 0≤x≤8, 0 <y≤8,0≤w≤8,2≤z≤13)。 12. A method for preparing a positive electrode active material, characterized in that, include: Step (a) is the step of preparing the lithium composite oxide; step (b) is the step of coating the surface of the lithium composite oxide with a solution containing boron-based compounds and sulfuric acid-based compounds; and step (c) is the step of calcining at a temperature below 350°C.

13. The method for preparing the positive electrode active material according to claim 12, characterized in that, The sulfuric acid compound mentioned above is aluminum sulfate.

14. The method for preparing the positive electrode active material according to claim 12, characterized in that, After calcination in step (c) above, the content of unreacted residual LiOH and Li2CO3 is less than 63.3% relative to the content before calcination.

15. A lithium secondary battery, characterized in that, It includes the positive electrode active material according to any one of claims 1 to 11.

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