Manufacturing method for positive electrode active material and lithium secondary battery

Abstract

To provide a manufacturing method for high-performance nickel-based positive electrode active material in which the high capacity is achieved, the surface characteristic is excellent, the content of residual lithium is low, the pellet density is high, the long life characteristic is achieved, the process cost is reduced, and the process property and productivity are increased.SOLUTION: A manufacturing method for a positive electrode active material includes mixing a nickel-based precursor and a first lithium raw material, performing a first thermal process at 500°C to 750°C to manufacture a primary burned product, mixing the primary burned product and a second lithium raw material, and performing a second thermal process at 650°C to 850°C to manufacture a positive electrode active material in a secondary particle form including lithium nickel composite oxide, in which a plurality of primary particles are aggregated. The molar ratio (L1) of lithium of the first lithium raw material to the entire metal in the nickel-based precursor is 0.2 to 0.9. The molar ratio (L2) of lithium of the second lithium raw material to the entire metal excluding lithium from the primary burned product is 0.1 to 0.8. In addition, 0.9≤L1+L2≤1.1 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material and a lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries, which have high energy density yet are easy to carry, are widely used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. Recently, active research has been conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] Various cathode active materials have been investigated to realize lithium secondary batteries suitable for these applications. Among these, lithium-nickel oxide, lithium-nickel manganese-cobalt composite oxide, lithium-nickel cobalt-aluminum composite oxide, and lithium-cobalt oxide are the most commonly used cathode active materials. Nickel-based cathode active materials, which contain nickel as the primary transition metal, have been actively developed recently due to their high capacity. However, they suffer from various limitations, such as structural degradation during charge / discharge, surface side reactions with the electrolyte, and degradation due to particle cracking. In particular, nickel-based cathode active materials suffer from the problem of increased unreacted lithium on the surface during heat treatment, as the nickel content increases. To remove this unreacted lithium and control surface properties, a cleaning process is required. However, this process can result in the loss of lithium within the cathode active material, resulting in a decrease in capacity or degradation of physical properties. To restore performance, the lost lithium must be replenished, and the cleaning process and the need for lithium raw material replenishment significantly increase material processing costs. Therefore, there is a need for research into methods for producing high-performance nickel-based positive electrode active materials that achieve high capacity while improving surface properties. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a novel method for producing a high-performance nickel-based positive electrode active material that achieves high capacity, excellent surface properties, low residual lithium content, high pellet density, and long life characteristics, and that reduces processing costs and increases processability and productivity. [Means for solving the problem]

[0005] In one embodiment of the present invention, the method includes: mixing a nickel-based precursor and a first lithium raw material, and performing a first heat treatment at 500°C to 750°C to produce a first fired product; and mixing the first fired product and a second lithium raw material, and performing a second heat treatment at 650°C to 850°C to produce a cathode active material in the form of secondary particles formed by agglomeration of a plurality of primary particles containing a lithium nickel-based composite oxide, wherein the molar ratio of lithium in the first lithium raw material to the total metal of the nickel-based precursor (L 1 ) is 0.2 to 0.9, and the molar ratio of lithium in the second lithium raw material to the total metals excluding lithium in the first fired product (L 2 ) is 0.1 to 0.8, and 0.9≦L 1 +L 2 ≦1.1

[0006] In another embodiment of the present invention, there is provided a positive electrode active material prepared by the above method.

[0007] In yet another embodiment of the present invention, there is provided a lithium secondary battery including a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. [Effects of the Invention]

[0008] According to a method for manufacturing a positive electrode active material according to an embodiment of the present invention, it is possible to reduce processing costs, increase processability and productivity, and provide a high-performance nickel-based positive electrode active material that has high capacity and long life characteristics, excellent surface properties, a low residual lithium content, and a high pellet density. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 is a scanning electron microscope (SEM) image of a first fired product of an example. [Figure 6] 1 shows the results of Rietveld X-ray diffraction refinement of the primary fired product of the example. [Figure 7] 1 is a SEM image of a final positive electrode active material in the form of secondary particles according to an embodiment of the present invention. [Figure 8] 1 is a SEM image of a final positive electrode active material in the form of secondary particles according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Although the present invention may be embodied in many different forms, it is not limited to the embodiments set forth herein.

[0011] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0012] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0013] It should be understood that the terms "comprise," "include," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0014] In the drawings, thicknesses of various layers and regions are exaggerated for clarity, and similar parts are designated by the same reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on" or "above" another part, this includes not only the case where it is "directly on" another part, but also the case where there is another part between them. Conversely, when a part is said to be "directly on" another part, it means that there is no other part between them.

[0015] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0016] The average particle size can be measured by a method well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope or a scanning electron microscope. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, counting the number of particles for each particle size range through data analysis, and then calculating the average particle size. Unless otherwise defined, the average particle size is the diameter (D) of particles whose cumulative volume is 50% by volume in the particle size distribution. 50 ) and, unless otherwise defined, the average particle size is the diameter (D) of the particle that makes up 50% of the cumulative volume in the particle size distribution obtained by measuring the size (diameter or length of the major axis) of 20 or more particles randomly selected from a scanning electron microscope image. 50 ) can be taken as the average particle size.

[0017] Here, "or" is not to be construed in an exclusive sense; for example, "A or B" is to be construed as including A, B, A+B, etc.

[0018] The term "metal" is understood to include general metals, transition metals, and metalloids (semimetals).

[0019] Method for producing positive electrode active material In one embodiment, a method for producing a positive electrode active material is provided, which includes: (i) mixing a nickel-based precursor and a first lithium source and performing a first heat treatment at 500°C to 750°C to produce a first fired product; and (ii) mixing the first fired product and a second lithium source and performing a second heat treatment at 650°C to 850°C to produce a positive electrode active material in the form of secondary particles formed by aggregation of a plurality of primary particles containing a lithium nickel-based composite oxide. Here, the molar ratio of lithium in the first lithium source to the total metal of the nickel-based precursor (L 1 ) is 0.2 to 0.9, and the molar ratio of lithium in the second lithium raw material to the total metals excluding lithium in the first fired product (L 2 ) is 0.1 to 0.8, and 0.9≦L 1 +L 2 ≦1.1. Here, the positive electrode active material can be expressed as a positive electrode active material for lithium secondary batteries, and can be expressed as a nickel-based positive electrode active material.

[0020] The manufacturing method may be a no-wash method that does not include a washing step. In other words, it may be a novel method that effectively reduces unreacted lithium on the surface of a cathode active material and strengthens the surface structure without washing the cathode active material or intermediate products during the manufacturing process of a cathode active material. According to one embodiment, the washing step can be omitted, thereby reducing processing costs and simplifying and easily changing the synthesis paradigm of nickel-based cathode active materials. Furthermore, by adding the lithium raw material in two or more batches, the raw material input amount during sintering can be increased, thereby improving productivity. Furthermore, adding the lithium raw material in separate batches effectively alleviates the problem of raw material aggregation, thereby increasing process yield and improving productivity. According to the above method, it is easy to adjust the content relationship, such as setting an excessive lithium molar ratio, in the second heat treatment process, and it is possible to add coating raw materials, which facilitates surface modification of the cathode active material and further strengthens the surface structure. Furthermore, the above method allows the production of high-quality secondary particle-like cathode active materials with uniform shape and size. The cathode active material prepared by the above method can control the surface residual lithium to about 2000 ppm or less, has uniform particle shape and size, clean particle surface, and small BET specific surface area, which is advantageous for improving electrode plate density and electrolyte impregnation speed. Such cathode active material can achieve high capacity and long life characteristics, and can also achieve excellent performance under high temperature and high voltage conditions.

[0021] According to one embodiment, a method for manufacturing a positive electrode active material is characterized in that lithium materials are added at least twice, for example, in step (i) by adding a first lithium material and in step (ii) by adding a second lithium material. Here, the molar ratio of lithium in the first lithium material to the total metal of the nickel-based precursor (L 1 ) is 0.2 to 0.9, for example, 0.3 to 0.8, 0.4 to 0.7, 0.5 to 0.7, or 0.5 to 0.6. In addition, the molar ratio of lithium in the second lithium raw material to the total metals excluding lithium in the primary fired product (L 2) is 0.1 to 0.8, and can be, for example, 0.2 to 0.7, 0.3 to 0.6, 0.4 to 0.6, or 0.4 to 0.5. 1 +L 2 The sum of these means the molar ratio of lithium to all metals excluding lithium in the final positive electrode active material, and the range is 0.9≦L 1 +L 2 ≦1.1, 0.95≦L 1 +L 2 ≦1.05, 0.9≦L 1 +L 2 ≦1.0, 0.9≦L 1 +L 2 ≦0.995, or 1.0≦L 1 +L 2 ≦1.1. In this case, L 1 >L 2 As another example, L 1 ≦L 2 It can also be designed to satisfy L 1 and L 2 By appropriately adjusting the amount of the cations and the heat treatment temperature, a nickel-based positive electrode active material that achieves high capacity and long life can be effectively obtained.

[0022] The nickel-based precursor may include, for example, a nickel-based hydroxide, a nickel-based oxide, or a combination thereof. The nickel-based hydroxide may be synthesized, for example, by a coprecipitation reaction, and the nickel-based oxide may be synthesized by firing the nickel-based hydroxide in an oxidizing atmosphere.

[0023] The nickel-based precursor is represented by, for example, Chemical Formula 11 or Chemical Formula 12. [Chemical formula 11] Ni x11 M 11 y11 M 12 z11 (OH)2

[0024] In the above formula 11, 0.7≦x11<1, 0 <y11≦0.3、0≦z11≦0.3、0.9≦x11+y11+z11≦1.1であり、M 11and M 12 is each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr.

[0025] In Chemical Formula 11, 0.7 ≦ x11 ≦ 0.99, 0.01 < y11 ≦ 0.3, 0 ≦ z11 ≦ 0.3, or 0.8 ≦ x11 ≦ 0.99, 0.01 < y11 ≦ 0.2, 0 ≦ z11 ≦ 0.2, or 0.85 ≦ x11 < 1, 0 < y11 ≦ 0.15, 0 ≦ z11 ≦ 0.15, or 0.9 ≦ x11 < 1, 0 < y11 ≦ 0.1, 0 ≦ z11 ≦ 0.1 may be satisfied.

[0026] [Chemical Formula 12] Ni x12 M 13 y12 M 14 z12 O 2-b12 X b12

[0027] In the above Chemical Formula 12, 0.7 ≦ x12 < 1, 0 < y12 ≦ 0.3, 0 ≦ z12 ≦ 0.3, 0.9 ≦ x12 + y12 + z12 ≦ 1.1, and 0 ≦ b12 ≦ 0.1, and M 13 and M 14 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0028] In Chemical Formula 12, 0.7 ≦ x12 ≦ 0.99, 0.01 < y12 ≦ 0.3, 0 ≦ z12 ≦ 0.3, or 0.8 ≦ x12 ≦ 0.99, 0.01 < y12 ≦ 0.2, 0 ≦ z12 ≦ 0.2, or 0.85 ≦ x12 < 1, 0 < y12 ≦ 0.15, 0 ≦ z12 ≦ 0.15, or 0.9 ≦ x12 < 1, 0 < y12 ≦ 0.1, 0 ≦ z12 ≦ 0.1 may be satisfied.

[0029] According to one embodiment, the nickel-based precursor may be a secondary particle-type precursor formed by agglomeration of a plurality of primary particles, and may have a particle size identical to or similar to the particle size of the secondary particles of the final cathode active material. For example, at least some or all of the primary particles of the nickel-based precursor may be acicular. That is, according to one embodiment, a method may be used in which a secondary particle-type cathode active material is obtained by using a precursor having a particle size identical to or similar to the particle size of the final cathode active material and performing an appropriate calcination process. According to one embodiment, a cathode active material with improved agglomeration may be synthesized by minimizing the amount of lithium used in each synthesis step of the precursor, calcined product, and final product. The synthesis may be performed under generally mild conditions, resulting in a cathode active material with uniform size and shape and a clean surface.

[0030] The average particle size (D 50 ) is 5 μm to 25 μm, and may be, for example, 8 μm to 20 μm, 10 μm to 18 μm, 12 μm to 16 μm, or 5 μm to 15 μm. When the size of the precursor satisfies the above range, the capacity can be increased while improving the processability. For example, when the size of the precursor is too small, dispersion becomes difficult and the processability decreases, and when it is too large, the capacity may decrease. Here, the average particle size (D 50 ) can be obtained by measuring the size of 20 or so random particles through a scanning electron microscope (SEM) image to obtain a particle size distribution, and the size of the particles whose cumulative volume is 50% by volume can be taken as the average particle size.

[0031] For example, the average particle size (D 50 ) and the average particle size of the final positive electrode active material (D 50 ) is about 1 μm or less or 0.5 μm or less, for example, 0 μm to 1 μm, or 0.01 μm to 0.5 μm.

[0032] The nickel-based precursor may further contain zirconium in addition to nickel. That is, the nickel-based precursor may be a hydroxide or oxide containing nickel and zirconium. That is, a zirconium-doped nickel-based precursor may be used as the nickel-based precursor. Here, zirconium acts as a dopant and also functions as a grain growth promoter during the heat treatment process. When a zirconium-doped nickel-based precursor is used, it promotes grain growth, allowing for the efficient synthesis of a positive electrode active material at a lower temperature than conventional synthesis methods. This also suppresses particle aggregation and improves productivity. Conventional alkaline grain growth promoters and fluxes have the problem of remaining after firing, acting as resistance within the positive electrode and reducing lifespan. However, when a zirconium-doped nickel-based precursor is used as a raw material, impurities do not remain on the surface of the positive electrode active material particles, thereby improving lifespan characteristics. In one embodiment, by using a zirconium-doped nickel-based precursor, a high-nickel-based positive electrode active material can be effectively produced at a relatively low firing temperature and in a simple manner without adding an alkali-based grain growth accelerator or flux, thereby improving productivity and economy.

[0033] The first lithium source may be, for example, lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, or a combination thereof, for example, anhydrous lithium hydroxide. The first lithium source and the second lithium source may be the same or different, for example, they may be the same.

[0034] When anhydrous lithium hydroxide is used as the lithium raw material, the amount of raw material charged in the synthesis process of the cathode active material can be increased, improving production per hour, and the amount of unnecessary gas and moisture generated during heat treatment can be reduced, improving processability and improving the quality of the cathode active material.In addition, by eliminating the input of unnecessary heavy materials such as H2O, the heat treatment yield can be increased, improving productivity.

[0035] As an example, the anhydrous lithium hydroxide (LiOH) has an average particle size (D 50 After drying, lithium hydroxide hydrate (LiOH·HO) with an average particle size (D 50 The anhydrous lithium hydroxide can be produced by pulverizing the starting material, lithium hydroxide hydrate, so that the average particle size (D) is about 3 μm to 30 μm. The anhydrous lithium hydroxide can be produced by pulverizing once after drying, without pulverizing before drying. The drying can be carried out, for example, under vacuum conditions at a temperature range of 50°C to 200°C for 0.5 to 20 hours. 50 ) is, for example, about 450 μm to 550 μm, 480 μm to 500 μm, and the average particle size (D 50 ) may be about 3 μm to 25 μm or about 5 μm to 20 μm.

[0036] According to this method for producing anhydrous lithium hydroxide, the process for obtaining anhydrous lithium salt is simple, optimal process conditions can be maintained, and the conversion rate to Li2CO3 is reduced to 5% or less, making it possible to obtain high-purity anhydrous lithium hydroxide. After anhydrous lithium hydroxide is pulverized, the powder's fluidity rapidly decreases, making it generally very difficult to perform additional processing after pulverization. For example, when drying after pulverization, the heat generated during drying causes the fine particles to become entangled and tightly agglomerate, necessitating an additional pulverization process. However, the high agglomeration strength of the particles makes pulverization difficult. Furthermore, as the number of processes increases, the conversion rate to Li2CO3 increases due to the increase in specific surface area, making it difficult to obtain high-quality anhydrous lithium hydroxide. According to one embodiment of the method for producing anhydrous lithium hydroxide, anhydrous lithium hydroxide is dried under specific conditions and then pulverized once to a specific size, making the process simple and allowing for the production of high-quality anhydrous lithium hydroxide. Furthermore, additional processing steps can be easily performed after pulverization.

[0037] The first heat treatment is performed at a temperature ranging from 500°C to 750°C. By performing the first heat treatment within this temperature range, the primary sintered product can have an appropriately low degree of crystallinity. Furthermore, the hexagonal and cubic crystal structures ensure numerous lithium channels, which enhances reactivity with the second lithium source and facilitates effective particle growth. The cathode active material produced under these temperature conditions exhibits excellent surface properties, uniform shape and size, low residual lithium content, and high pellet density. When the first heat treatment temperature exceeds 750°C, a primary sintered product having a different crystal structure and physical properties from the primary sintered product according to one embodiment is synthesized. However, the degree of crystallinity of the sintered product is relatively high, which reduces reactivity with lithium during secondary sintering, making it difficult to obtain a high-quality cathode active material.

[0038] The first heat treatment can be carried out within a temperature range of, for example, 550°C to 750°C, 600°C to 750°C, 650°C to 750°C, or 700°C to 750°C. The first heat treatment temperature may be lower than the second heat treatment temperature, which will be described later. The first heat treatment can be carried out for 6 to 12 hours, or 8 to 12 hours, in an oxidizing atmosphere. When the first heat treatment is carried out within the above temperature range and conditions, a positive electrode active material having excellent surface properties, uniform shape and size, high pellet density, and a low residual lithium content can be effectively produced.

[0039] In one embodiment, a zirconium raw material can be mixed with the nickel-based first lithium raw material. Zirconium in the zirconium raw material can function as a dopant and a grain growth promoter. The addition of the zirconium raw material promotes grain growth, allowing for the effective synthesis of a positive electrode active material at a lower temperature than conventional synthesis methods. This also suppresses particle aggregation and improves productivity. While conventional alkaline grain growth promoters and fluxes remain after firing, acting as resistance within the positive electrode and reducing lifespan, the use of a zirconium raw material as a dopant for the positive electrode active material prevents them from remaining on the surface of the positive electrode active material particles, thereby improving lifespan characteristics. In one embodiment, the use of a zirconium raw material allows for the effective synthesis of a high-nickel positive electrode active material at a relatively low firing temperature and with a simple method without the addition of an alkaline grain growth promoter or flux, thereby improving productivity and cost efficiency.

[0040] The zirconium content of the zirconium source material is 0.01 mol % to 1 mol %, for example, 0.01 mol % to 0.9 mol %, 0.05 mol % to 0.7 mol %, 0.1 mol % to 0.5 mol %, or 0.1 mol % to 0.3 mol %, based on the total weight of the nickel-based precursor and the zirconium source material (100 mol %). The zirconium content of the zirconium source material is 0.01 wt % to 1 wt %, for example, 0.01 wt % to 0.9 wt %, 0.05 wt % to 0.7 wt %, 0.1 wt % to 0.5 wt %, or 0.1 wt % to 0.3 wt %, based on the total weight of the nickel-based precursor and the zirconium source material (100 mol %). When the zirconium content satisfies the above range, secondary particles of uniform size can be effectively produced at low temperatures.

[0041] The zirconium source is a compound containing zirconium, and may be, for example, zirconium oxide (ZrO2).

[0042] According to one embodiment, the method for manufacturing a cathode active material does not require a pulverization process, which means grinding artificial micro-scale particles, because the degree of agglomeration after the first heat treatment is low. However, it may include a coarse pulverization and crushing process (a process for removing secondary particle powder) for minimal air transport. The crushing process alone can reduce the D of the precursor to a difference of 0.01 μm to 0.5 μm. 50 It is possible to realize a positive electrode active material having the above structure.

[0043] The primary fired product obtained by the first heat treatment may contain a lithium nickel-based composite oxide and may be in the form of secondary particles formed by agglomeration of a plurality of primary particles. The average particle size (D 50 ) may have the same or similar size as the final positive electrode active material, for example, 5 μm to 25 μm, 8 μm to 20 μm, 10 μm to 18 μm, 12 μm to 16 μm, or 5 μm to 15 μm. For example, the average particle size (D 50 ) and the average particle size of the final positive electrode active material (D 50 ) is about 1 μm or less or 0.5 μm or less, for example, 0 μm to 1 μm, or 0.01 μm to 0.5 μm.

[0044] Furthermore, the lithium-nickel composite oxide of the first-sintered product may have a hexagonal crystal structure and a cubic crystal structure. For example, the first-sintered product may contain 60% to 95%, 70% to 95%, or 75% to 90% hexagonal crystal structure by volume, and 5% to 40%, 5% to 30%, or 10% to 25% cubic crystal structure by volume. In this case, the first-sintered product has high reactivity with the second lithium source, which is advantageous for the growth of uniformly sized secondary particles, effectively reducing residual lithium on the surface of the final positive electrode active material. The crystal structure of the first-sintered product can be analyzed, for example, by X-ray diffraction Rietveld analysis.

[0045] The second lithium source may be, for example, lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, or a combination thereof, and an example thereof may be anhydrous lithium hydroxide. The first lithium source and the second lithium source may be the same or different, for example, they may be the same. The molar ratio of lithium in the second lithium source to the total metals excluding lithium in the primary fired product (L 2 ) is in the range of 0.1 to 0.8 as described above, and can be, for example, 0.2 to 0.7, 0.3 to 0.6, 0.4 to 0.6, or 0.4 to 0.5. 2 By appropriately adjusting the amount of lithium, a high-performance positive electrode active material having a high lithium soluble capacity and a low content of residual lithium on the surface can be produced.

[0046] The second heat treatment is characterized by being carried out at a temperature range of 650°C to 850°C, for example, 700°C to 830°C or 750°C to 810°C. The second heat treatment can be carried out in an oxidizing atmosphere for 10 to 16 hours or 12 to 16 hours. By carrying out the second heat treatment under the above conditions, secondary particles with uniform size can be produced, and a positive electrode active material with high lithium soluble capacity and low residual lithium content on the surface can be obtained.

[0047] According to one embodiment, the surface of the positive electrode active material particles can be coated in a simple manner by mixing the coating material with the first sintered product and the second lithium material. The coating material may contain, for example, one or more elements selected from Al, B, Co, Mg, V, Zn, and Zr. The content of the coating element varies depending on the type of element, but may be, for example, 0.1 wt % to 5 wt %, or 0.5 wt % to 3 wt %, based on 100 wt % of the total metals excluding lithium in the positive electrode active material. This coating process is different from the conventional wet coating process in which the sintered product is washed, the coating material is added, and then the sintered product is dried and heat-treated. Instead, this coating process may be a simple dry coating method without a washing process.

[0048] In addition, by heat-treating the second lithium material and the coating material together, an ideal grain boundary coating can be achieved at the grain boundary between the internal and external interfaces of the secondary particles. That is, the coating process effectively forms a coating layer on the surface of the secondary particles and a grain boundary coating on the surface of the primary particles inside the secondary particles, thereby producing a cathode active material with greater structural stability and excellent life characteristics. The coating layer and the grain boundary coating can include Al, B, Co, Mg, V, Zn, Zr, or a combination thereof.

[0049] For example, the method for manufacturing the cathode active material may include mixing the primary sintered product with a second lithium source and a cobalt source and then performing a second heat treatment, thereby manufacturing a cathode active material with improved life characteristics. Here, the content of cobalt as a coating element may be 0.1 wt% to 3 wt%, or 0.5 wt% to 2 wt%, based on 100 wt% of the total metals in the cathode active material excluding lithium.

[0050] According to one embodiment, the method for preparing a cathode active material may further include a pulverization process after the second heat treatment. The application of mild pulverization increases pulverization productivity. The pulverization may be performed using, for example, a colloidal mill, a mild jet mill, or a mild air classifier mill.

[0051] The produced cathode active material contains a lithium-nickel-based composite oxide and is in the form of secondary particles formed by agglomeration of a plurality of primary particles. The produced cathode active material may exhibit a layered crystal structure, unlike primary sintered products that exhibit, for example, a hexagonal crystal structure or a cubic crystal structure. The lithium-nickel-based composite oxide is represented, for example, by Chemical Formula 1. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M2 z1 O 2-b1 X b1

[0052] In the above chemical formula 1, 0.8≦a1≦1.2, 0.7≦x1<1, 0 <y1≦0.3、0≦z1≦0.3、0.9≦x1+y1+z1≦1.1、および0≦b1≦0.1であり、M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0053] The lithium nickel-based composite oxide is specifically represented by the following formula 2 or 3. [Chemical formula 2] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0054] In the above chemical formula 2, 0.9≦a2≦1.2, 0.7≦x2<1, 0 <y2≦0.3、0≦z2≦0.3、0.9≦x2+y2+z2≦1.1、および0≦b2≦0.1であり、M 3 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0055] In Chemical Formula 2, 0.8≦x2≦0.99, 0.01≦y2≦0.2, and 0≦z2≦0.2, or 0.9≦x2≦0.99, 0.01≦y2≦0.1, and 0≦z2≦0.1.

[0056] [Chemical formula 3] Li a3 Ni x3 Co y3 M4 z3 M 5 w3 O 2-b3 X b3

[0057] In the formula 3, 0.9≦a3≦1.2, 0.7≦x3≦0.98, 0.01≦y3≦0.29, 0.01≦z3≦0.29, 0≦w3≦0.29, 0.9≦x3+y3+z3+w3≦1.1, and 0≦b3≦0.1; M 4 is Al, Mn or a combination thereof, and M 5 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0058] In Chemical Formula 3, 0.8≦x3≦0.98, 0.01≦y3≦0.19, 0.01≦z3≦0.19, and 0≦w3≦0.19, or 0.9≦x3≦0.98, 0.01≦y3≦0.09, 0.01≦z3≦0.09, and 0≦w3≦0.09.

[0059] As mentioned above, high-nickel cathode active materials require a cleaning process due to the excessive amount of residual lithium generated on the particle surface during the synthesis process. Ideally, the cleaning process would remove only the lithium compounds present on the surface of the cathode active material particles, such as Li2CO3 and LiOH. However, this process also removes the active lithium from within the cathode active material, potentially reducing reversible capacity and performance due to changes in the crystalline structure and phase shifts. For example, as lithium dissolves, a form such as lithium-nickel-oxide can change to a form such as nickel-oxide, forming NiO. This causes a reduction reaction in which the oxidation state of Ni decreases from 3+ to 2+. Compounds such as NiO cannot be converted back to lithium-containing compounds, resulting in a reduction in reversible capacity and a potential degradation in overall performance due to the promotion of side reactions between the cathode active material particle surface and the electrolyte. To address this issue, a process is required to restore the deteriorated surface by adding additional lithium after the cleaning process. However, adding lithium can cause additional side reactions and increase processing costs.

[0060] In contrast, a novel method for manufacturing a cathode active material according to one embodiment does not include a cleaning step, thereby eliminating the problem of performance degradation due to cleaning, while reducing the residual lithium content on the surface to 2000 ppm or less, thereby manufacturing a cathode active material with excellent surface properties. The residual lithium content on the surface of the cathode active material may be, for example, 2000 ppm or less, 1900 ppm or less, or 1800 ppm or less.

[0061] The average particle size (D 50 ) is 5 μm to 25 μm, and may be 8 μm to 20 μm, 10 μm to 18 μm, 12 μm to 16 μm, or 5 μm to 15 μm. 90 -D 10 ) / D 50 The average particle size (D 50) can be obtained by measuring the size of 20 or more random particles from an SEM image to obtain a particle size distribution, and the size of the particle whose cumulative volume is 50% by volume can be taken as the average particle size. 90 is the particle size at which the cumulative volume is 90% by volume in the particle size distribution, and D 10 is the size of the particles whose cumulative volume is 10% by volume.

[0062] In addition, the positive electrode active material may exhibit a low specific surface area. For example, the positive electrode active material may have a BET specific surface area of ​​0.2 to 0.7 m 2 / g, or 0.3 to 0.6 m 2 / g.

[0063] The positive electrode active material has a low specific surface area and a clean surface, which allows it to achieve a high pellet density. For example, the pellet density of the positive electrode active material may be 3.0 to 3.6 g / cc, or 3.2 to 3.4 g / cc. A lithium secondary battery using such a positive electrode active material can achieve a high energy density. The pellet density can be measured as follows. 3 g of the positive electrode active material is weighed and placed in a mold (area: 1.298 cm). 2 ) and slowly fit the mold bar into the mold body. The mold set is placed in a hydraulic press and pressed at 3 tons for 30 seconds, after which the height is measured and the pellet density can be measured.

[0064] The tap density of the positive electrode active material is 1.2 to 2.2 g / cc, for example, 1.4 to 2.0 g / cc. The tap density can be measured using a tap density measuring device (TAP-2S, Logan Instruments Co.), for example, by filling a 100 cc measuring cylinder with 50 cc of positive electrode active material powder, tapping the cylinder back and forth at a height of 3 mm per second 1,000 times, and then dividing the mass by the volume.

[0065] The positive electrode active material has a peak intensity ratio of (003) to (104) in XRD analysis, which is I (003) / I (104) is 1 or more, 1.15 or more, or 2 or more, for example, 1.15 to 1.35, or 1.2 or 1.35.

[0066] Meanwhile, in one embodiment, the method may further include mixing the cathode active material obtained by the second heat treatment with a coating material and performing a third heat treatment. This allows the desired coating to be formed on the surface of the cathode active material in a simple manner without a cleaning process. The coating material may contain, for example, one or more elements selected from Al, B, Co, Mg, V, Zn, and Zr. In this case, the content of the coating element is not particularly limited, but may be, for example, 0.1 wt % to 5 wt % or 0.5 wt % to 3 wt % relative to 100 wt % of all metals in the final cathode active material excluding lithium.

[0067] For example, a method for manufacturing a cathode active material according to an embodiment may include mixing the cathode active material obtained by the second heat treatment with a boron source and performing a third heat treatment for 2 to 8 hours at a temperature range of about 250° C. to 450° C., thereby manufacturing a cathode active material with improved life characteristics. Here, the boron content may be 0.01 wt % to 0.5 wt %, or 0.05 wt % to 0.3 wt %, based on 100 wt % of the total metals excluding lithium in the final cathode active material.

[0068] positive electrode In one embodiment, a positive electrode for a lithium secondary battery is provided, including the above-described positive electrode active material. For example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer including the above-described positive electrode active material. The positive electrode active material layer may further include other types of positive electrode active materials in addition to the above-described positive electrode active material, and may optionally further include a binder, a conductive material, or a combination thereof.

[0069] binder The binder serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon.

[0070] Conductive material The conductive material is used to impart electrical conductivity to the electrode, and any material that is electron-conductive and does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0071] The content of the binder and the conductive material may be 0.5% by weight to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0072] The positive electrode current collector may be made of Al, but is not limited to this.

[0073] The positive electrode according to an embodiment may achieve a high mixture density. For example, the electrode plate density of the positive electrode active material layer in the final rolled positive electrode may be 3.35 to 3.85 g / cc, or 3.45 to 3.75 g / cc. The application of the positive electrode active material according to an embodiment is advantageous in achieving such a positive electrode density, and a positive electrode satisfying the above-mentioned range of positive electrode density is suitable for realizing a high-capacity, high-energy-density lithium secondary battery.

[0074] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the positive electrode, the negative electrode, and the electrolyte described above. For example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0075] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 1 illustrating a cylindrical battery, FIG. 2 illustrating a prismatic battery, and FIGS. 3 and 4 illustrating pouch battery types. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be immersed in an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0076] negative electrode The negative electrode may include a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder, a conductive material, or a combination thereof.

[0077] Negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0078] Examples of the material capable of reversibly inserting / desorbing the lithium ions include carbon-based negative electrode active materials, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0079] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0080] As the material capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. Examples of the Si-based negative electrode active material include silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof. Examples of the Sn-based negative electrode active material include Sn, SnO2, an Sn alloy, or a combination thereof.

[0081] The silicon-carbon composite may be a composite of silicon and amorphous carbon. 50 ) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles, and the surfaces of the silicon particles may be coated with amorphous carbon. For example, it may include secondary particles (cores) formed by granulating primary silicon particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0082] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core including crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0083] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 to 50% by weight and the amorphous carbon content may be 50 to 90% by weight, based on 100% by weight of the silicon-carbon composite.Alternatively, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 to 50% by weight, the crystalline carbon content may be 10 to 70% by weight, and the amorphous carbon content may be 20 to 40% by weight, based on 100% by weight of the silicon-carbon composite.

[0084] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) can be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, or in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation can be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0085] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio can be 1:99 to 90:10 by weight ratio.

[0086] Binder The binder serves to well adhere the negative electrode active material particles to each other and also well adhere the negative electrode active material to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder or a combination thereof can be used.

[0087] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide or a combination thereof.

[0088] The water-based binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0089] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0090] The dry binder can be a fiberizable polymeric material such as polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0091] Conductive material The conductive material is used to impart conductivity to the electrode and can be any material that is electron-conductive and does not cause chemical changes in the battery. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0092] The content of the negative electrode active material may be 95% to 99.5% by weight, and the content of the binder may be 0.5% to 5% by weight, relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0093] current collector The negative electrode current collector can include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0094] electrolyte The electrolyte for a lithium secondary battery can be, for example, an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0095] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reactions of the battery can migrate, and can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0096] Examples of carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol. Examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0097] The non-aqueous organic solvent may be used alone or in combination of two or more kinds. When a mixture of two or more kinds is used, the mixing ratio may be appropriately adjusted depending on the desired battery performance, which is widely understood by those skilled in the art.

[0098] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0099] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0100] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0101] Representative examples of the ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0102] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0103] The concentration of the lithium salt is preferably within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate ion conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0104] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more of these. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0105] The separator may include a porous substrate and a coating layer including an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0106] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0107] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0108] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0109] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D 50 ) is 1 nm to 2000 nm, and can be, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0110] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a coating layer containing an organic material and a coating layer containing an inorganic material.

[0111] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0112] Examples of the present invention and comparative examples are described below. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0113] Example 1 Example Manufacturing of positive electrode active materials Average particle size (D 50 ) is about 12 μm. 0.94 Co 0.04 Mn 0.02(OH)2) was mixed with anhydrous lithium hydroxide and ZrO2 as the first lithium raw material and subjected to a first heat treatment at 750°C for 12 hours. At this time, the molar ratio of lithium to the total metal of the nickel hydroxide (L 1 The first lithium raw material was mixed so that the ratio of Zr to ZrO2 was 0.6. ZrO2 was also mixed so that the Zr content was 0.125% by weight, relative to the total weight of the entire metal in the nickel hydroxide and Zr in ZrO2, which was 100% by weight.

[0114] An SEM image of the first-sintered product obtained by the first heat treatment is shown in Figure 5, and the results of XRD Rietveld refinement are shown in Figure 6. Referring to Figure 5, the first-sintered product was in the form of secondary particles formed by the aggregation of multiple primary particles, with sizes ranging from approximately 11 μm to 13 μm. Referring to Figure 6, it was confirmed that the first-sintered product had 85.4% hexagonal crystal structure and 14.6% cubic crystal structure.

[0115] The first fired product was mixed with anhydrous lithium hydroxide as the second lithium raw material and cobalt oxide as the coating raw material, and the second heat treatment was carried out at 780 °C for 16 hours. At this time, the molar ratio of lithium in the second lithium raw material to the total metal excluding lithium in the first fired product (L 2 ) was set to 0.45, and the cobalt content was designed to be 0.5 to 3.0 wt% relative to 100 wt% of the total metal excluding lithium and cobalt in the coating raw material in the primary fired product.

[0116] A secondary particle-shaped positive electrode active material was obtained through a second heat treatment. SEM images of the final positive electrode active material are shown in Figures 7 and 8. Referring to Figures 7 and 8, it can be seen that a secondary particle-shaped positive electrode active material with very uniform particle size and a clean surface was effectively produced. Furthermore, XRD Rietveld refinement of the final positive electrode active material confirmed that it was synthesized with a 100% hexagonal crystal structure.

[0117] Residual lithium and XRD analysis The residual lithium content of each of the primary fired products and the final cathode active materials of the above examples was analyzed by pH titration, and the half-widths of the (003) and (104) planes, and the ratios of the peak intensity of the (003) plane to the peak intensity of the (104) plane were analyzed by XRD analysis. The results are shown in Table 1 below.

[0118] [Table 1]

[0119] Referring to Table 1 above, the residual lithium content of the final cathode active material was confirmed to be at a level of 1512 ppm. In the example, a high-nickel cathode active material was synthesized and a very low residual lithium content was observed even though the washing process was omitted.

[0120] Also, referring to Table 1, the final positive electrode active material was analyzed by XRD. (003) / I (104) It can be seen that the ratio is 1.331.

[0121] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited to these, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of symbols]

[0122] 100 Lithium secondary battery 10 positive electrode 11 Positive electrode lead tab 12 Positive terminal 20 negative electrode 21 Negative electrode lead tab 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode tab 71 Positive electrode tab 72 Negative electrode tab

Claims

1. A method for producing a positive electrode active material, mixing a nickel-based precursor and a first lithium raw material, and subjecting the mixture to a first heat treatment at 500°C to 750°C to produce a primary fired product; mixing the primary fired product and the second lithium raw material, and subjecting the mixture to a second heat treatment at 650°C to 850°C to produce a cathode active material in the form of secondary particles formed by agglomeration of a plurality of primary particles containing a lithium nickel-based composite oxide; Including, The molar ratio of lithium in the first lithium source to the total metal in the nickel-based precursor (L 1 ) is 0.2 to 0.9, and the molar ratio of lithium in the second lithium raw material to the total metals excluding lithium in the first fired product (L 2 ) is 0.1 to 0.8, and 0.9≦L 1 +L 2 ≦1.

1.

2. L 1 is 0.4 to 0.7, and L 2 The method for producing a positive electrode active material according to claim 1, wherein is 0.3 to 0.

6.

3. L 1 >L 2 The method for producing a positive electrode active material according to claim 1 , which satisfies the above.

4. L 1 ≦L 2 The method for producing a positive electrode active material according to claim 1 , which satisfies the above.

5. The method for producing a positive electrode active material according to claim 1 , wherein the nickel-based precursor is represented by Chemical Formula 11 or Chemical Formula 12. [Chemical formula 11] Ni x11 M 11 y11 M 12 z11 (OH) 2 (In the above chemical formula 11, 0.7≦x11<1, 0<y11≦0.3, 0≦z11≦0.3, 0.9≦x11+y11+z11≦1.1, and M 11 and M 12 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr. [Chemical formula 12] Yes x12 M 13 y12 M 14 z12 Oh 2-b12 X b12 (In the chemical formula 12, 0.7≦x12<1, 0<y12≦0.3, 0≦z12≦0.3, 0.9≦x12+y12+z12≦1.1, and 0≦b12≦0.1; M 13 and M 14 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from F, P, and S.

6. The nickel-based precursor is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 ) is 5 μm to 25 μm, The average particle size (D 50 ) and the average particle size (D 50 2. The method for producing a positive electrode active material according to claim 1, wherein the difference between the thickness of the first electrode and the thickness of the second electrode is 1 μm or less.

7. 2. The method for producing a positive electrode active material according to claim 1, wherein the first lithium source and the second lithium source include anhydrous lithium hydroxide.

8. The first heat treatment is performed in an oxidizing atmosphere at a temperature of 650°C to 750°C for 6 hours to 12 hours, The method for producing a positive electrode active material according to claim 1 , wherein the first heat treatment temperature is lower than the second heat treatment temperature.

9. When mixing the nickel-based precursor and the first lithium source, a zirconium source is mixed together; 2. The method for producing a positive electrode active material according to claim 1, wherein the zirconium content of the zirconium raw material is 0.01% by weight to 1% by weight, relative to 100% by weight of the total of all metals in the nickel-based precursor and zirconium in the zirconium raw material.

10. The primary fired product is in the form of secondary particles formed by agglomeration of a plurality of primary particles, and the average particle diameter (D 50 2. The method for producing a positive electrode active material according to claim 1, wherein the thickness of the first electrode layer is 5 μm to 25 μm.

11. 2. The method for producing a positive electrode active material according to claim 1, wherein the primary fired product contains a lithium-nickel-based composite oxide, and the lithium-nickel-based composite oxide contains 60% by volume to 95% by volume of a hexagonal crystal structure and 5% by volume to 40% by volume of a cubic crystal structure.

12. 2. The method for producing a positive electrode active material according to claim 1, wherein the second heat treatment is performed in an oxidizing atmosphere at a temperature of 750° C. to 810° C. for 10 to 16 hours.

13. When mixing the first fired product with the second lithium raw material, the coating raw material is mixed together, 2. The method of claim 1, wherein the coating raw material contains one or more elements selected from the group consisting of Al, B, Co, Mg, V, Zn, and Zr.

14. The method for producing a positive electrode active material according to claim 1 , wherein the method does not include a step of washing the positive electrode active material.

15. The method for producing a positive electrode active material according to claim 1 , wherein the produced lithium nickel composite oxide of the positive electrode active material is represented by Chemical Formula 1. [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 (In the above Chemical Formula 1, 0.8≦a1≦1.2, 0.7≦x1<1, 0<y1≦0.3, 0≦z1≦0.3, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr, and X is one or more elements selected from F, P, and S.

16. The average particle size (D 50 ) is 5 μm to 25 μm, and the BET specific surface area is 0.2 to 0.7 m 2 / g, and the content of residual lithium on the surface is 2000 ppm or less, the method for producing a positive electrode active material according to claim 1 .

17. 2. The method for producing a positive electrode active material according to claim 1, wherein the produced positive electrode active material has a pellet density of 3.0 g / cc to 3.6 g / cc and a tap density of 1.2 g / cc to 2.2 g / cc.

18. 2. The method for producing a positive electrode active material according to claim 1, wherein the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane in X-ray diffraction analysis of the produced positive electrode active material is 1.15 or more.

19. The method further includes mixing the prepared positive electrode active material with a coating raw material and performing a third heat treatment; 2. The method of claim 1, wherein the coating raw material contains one or more elements selected from the group consisting of Al, B, Co, Mg, V, Zn, and Zr.

20. A positive electrode active material produced by the method according to any one of claims 1 to 19.

21. A positive electrode comprising the positive electrode active material according to claim 20. negative electrode, and an electrolyte.

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