Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, and more specifically to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery, wherein the lithium transition metal oxide comprises a lithium transition metal oxide having a single crystallinity degree (X) of 0.50 to 0.75 according to the following formula 1, and the lithium transition metal oxide is in single-particle form. JPEG2026510385000010.jpg28170 In the above formula 1, a i When the single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the ratio of the cross-sectional area (A) of the single particle. i ) value (A i This means / A).

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0043513 dated April 3, 2023, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material for lithium secondary batteries, a positive electrode containing the same, and a lithium secondary battery. [Background technology]

[0003] In recent years, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries has been rapidly increasing. In particular, lithium-ion batteries are attracting attention as a power source for portable devices due to their light weight and high energy density. Therefore, research and development and efforts to improve the performance of lithium-ion batteries are being actively pursued.

[0004] In a lithium secondary battery, an organic electrolyte or polymer electrolyte is filled between a positive electrode and a negative electrode, both made of an active material capable of lithium ion intercalation and deintercalation. Electrical energy is produced by oxidation and reduction reactions during lithium ion intercalation / deintercalation at the positive and negative electrodes.

[0005] Lithium-ion rechargeable batteries utilize lithium cobalt oxide (LiCoO2), nickel-based lithium transition metal oxides, lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) as positive electrode active materials. Among these, lithium cobalt oxide (LiCoO2) is widely used due to its advantages of high operating voltage and excellent capacity characteristics, and is applied as a positive electrode active material for high voltage applications. However, due to rising cobalt (Co) prices and unstable supply, there are limitations to its large-scale use as a power source in fields such as electric vehicles, increasing the need for the development of alternative positive electrode active materials.

[0006] Therefore, nickel-based lithium transition metal oxides, such as nickel-cobalt-manganese lithium composite transition metal oxides, have been developed in which some of the cobalt (Co) is replaced with nickel (Ni) or other elements.

[0007] On the other hand, conventionally developed nickel-based lithium transition metal oxides have a fine (micro) average particle size (D 50 This is a form of secondary particles formed by the aggregation of fine primary particles having a large specific surface area and low particle strength. Therefore, when an electrode is manufactured using a positive electrode active material containing secondary particles formed by the aggregation of fine primary particles and then rolled, there is a problem of severe particle cracking, resulting in a large amount of gas generation during cell operation and poor stability. In particular, high-content nickel-based (High-Ni) lithium transition metal oxides, in which the nickel (Ni) content is increased to ensure high capacity, have further reduced chemical stability and it is difficult to ensure thermal stability due to the aforementioned structural problems.

[0008] To improve upon the shortcomings of the aforementioned conventional nickel-based lithium transition metal oxides in the form of aggregated secondary particles, the average particle size (D 50 Nickel-based lithium transition metal oxide cathode active materials have been proposed that are in a secondary particle form in which large macro-primary particles are aggregated.

[0009] The nickel-based lithium transition metal oxide cathode active material in the form of secondary particles aggregated from macro primary particles has minimized interfaces of the secondary particles, improving problems such as thermal stability, life degradation due to side reactions during electrochemical reactions, and gas generation.

[0010] On the other hand, high-content nickel-based (High-Ni) lithium transition metal oxide cathode active materials usually undergo a water washing process to reduce the content of lithium impurities remaining on the surface. Such a water washing process is advantageous for reducing gas generation as it removes surface lithium by-products, but it is disadvantageous in terms of life from the perspective of surface damage to the cathode active material particles. In particular, the nickel-based lithium transition metal oxide cathode active material in the form of secondary particles aggregated from macro primary particles has an inherent problem of inferior life characteristics, and when it undergoes a water washing process, its life characteristics deteriorate further, and the resistance increases as charge and discharge progress.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] An object of the present invention is to provide a cathode active material that can improve the initial charge-discharge capacity and efficiency of a battery and reduce the amount of gas generation.

Means for Solving the Problems

[0013] To solve the above problems, the present invention provides a cathode active material, a cathode, and a lithium secondary battery.

[0014] (1) The present invention provides a positive electrode active material containing a lithium transition metal oxide having a crystallinity (X) calculated by the following formula 1 of 0.50 to 0.75, wherein the lithium transition metal oxide is in a single particle form.

[0015]

Number

[0016] In the above formula 1, a i means the value (A i / A) of the cross-sectional area (A i ) of the i-th crystal grain with respect to the cross-sectional area (A) of the single particle when the single particle consists of i crystal grains.

[0017] (2) The present invention provides the positive electrode active material according to (1) above, wherein the crystallinity (X) is 0.60 to 0.75.

[0018] (3) The present invention provides the positive electrode active material according to (1) or (2) above, wherein the average particle diameter (D 50 ) of the single particle is 1.5 μm or more.

[0019] (4) The present invention provides the positive electrode active material according to any one of (1) to (3) above, wherein the BET specific surface area of the single particle is 0.50 m 2 / g or less.

[0020] (5) The present invention provides the positive electrode active material according to any one of (1) to (4) above, wherein the lithium transition metal oxide is represented by the following chemical formula 1.

[0021] [Chemical formula 1] Li(Ni 1-x-y-z Co x Mn y M z )O2

[0022] In the above chemical formula 1, M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo. x, y, and z are atomic fractions of independent elements, where 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 ≤ z < 1, and 0 ≤ x + y + z < 1.

[0023] (6) The present invention also provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described in any one of (1) to (5) above.

[0024] (7) The present invention also provides a lithium secondary battery including the positive electrode for a lithium secondary battery described in (6) above. [Effects of the Invention]

[0025] The positive electrode active material according to the present invention contains a lithium transition metal oxide having a single-particle form and a single-crystallinity degree (X) of 0.50 to 0.75, thereby reducing the generation of fine particles due to particle cracking. When used as a positive electrode active material in a lithium secondary battery, it can improve the initial charge / discharge capacity and efficiency of the battery, reduce gas generation, and significantly improve the stability of the battery. [Brief explanation of the drawing]

[0026] [Figure 1] The images show SEM images of the positive electrode active materials for Example 1 and Comparative Examples 1-3 ((A): Example 1, (B): Comparative Example 1, (C): Comparative Example 2, (D): Comparative Example 3). [Figure 2] This is a reference figure to demonstrate the extraction of particles from an EBSD image, showing that a particle region extracted from a SEM image has been applied to the EBSD image, and that the particle region has been extracted from the EBSD image. [Figure 3] This graph shows the single crystallinity distribution of the positive electrode active materials in Example 1 and Comparative Examples 1-3. [Figure 4] This graph shows the amount of gas generated during storage of monocells using the positive electrode active materials of Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail below to facilitate understanding of it.

[0028] The terms and words used in the description and claims of this invention should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​this invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0029] In the present invention, "primary particle" refers to the smallest particle unit that can be distinguished as a single mass when observing a cross-section of the positive electrode active material using a scanning electron microscope (SEM), and may consist of one crystal grain or multiple crystal grains. In the present invention, the average particle size of the primary particle can be measured by measuring the size of each particle distinguished by the SEM data of the cross-section of the positive electrode active material particles, and then calculating their arithmetic mean.

[0030] In the present invention, "single particle" is a term used to distinguish it from positive electrode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which have been commonly used in the past. The term encompasses a single particle consisting of one primary particle and aggregate particles of 10 or fewer primary particles.

[0031] In this invention, "average particle size (D 50 The average particle size (D) can be defined as the particle size at the 50% reference level of the volume cumulative particle size distribution and can be measured by the laser diffraction method. Specifically, the average particle size (D) 50 ) After dispersing the target particles in a dispersion medium, they are introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000) and irradiated with ultrasound at approximately 28 kHz with an output of 60 W, and the average particle size (D) at the 50% reference level of the cumulative particle volume distribution by particle size measured by the analyzer is determined. 50 It is possible to calculate ).

[0032] In this invention, "single crystal" refers to a crystal in which no grain boundaries are present within the particles.

[0033] In this invention, "crystal grain" refers to a particle unit having substantially the same crystal orientation, and can be measured by EBSD (Electron Backscatter Diffraction). Specifically, it refers to the smallest particle unit displayed with the same hue in an IPF map obtained by EBSD analysis of a cross-section of a positive electrode active material cut by ion milling.

[0034] The present invention will be described in detail below.

[0035] The positive electrode active material of the present invention contains a lithium transition metal oxide having a single crystallinity degree (X) of 0.50 to 0.75 calculated by the following formula 1, and is characterized in that the lithium transition metal oxide is in single-particle form.

[0036]

number

[0037] In the above formula 1, a i When the single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the ratio of the cross-sectional area (A) of the single particle. i ) value (A i This means / A).

[0038] The object of the present invention is to provide a positive electrode active material comprising a lithium transition metal oxide having a single-particle form and satisfying a single-crystallinity degree (X) of 0.50 to 0.75.

[0039] In this invention, the degree of single crystallinity is evaluated and expressed by the parameter represented by Formula 1 above. In this invention, the degree of single crystallinity refers to a value adjusted by the number of crystal grains that make up a single particle and the area of ​​each crystal grain. The higher the area of ​​the specific crystal grain with the largest area within a single particle, the closer the area is to the total area of ​​the single particle, the higher the degree of single crystallinity.

[0040] In other words, the degree of single crystallinity shown in this invention is higher the fewer the number of crystal grains that make up a single particle. If the number of crystal grains is the same, the degree of single crystallinity is higher when a particular crystal grain has a larger area than other crystal grains, rather than when the areas of the crystal grains are similar, and the smaller the difference between that area and the total area of ​​the single particle, the higher the degree of single crystallinity.

[0041] For example, the maximum value of the single crystallinity is 1, which means that one single particle consists of one crystal grain. Also, when one single particle consists of N crystal grains, the single crystallinity varies depending on the area of ​​each crystal grain, but the minimum value of the single crystallinity that can be had when there are N crystal grains is 1 / N, which is when all N crystal grains have the same area. Even when one single particle consists of N crystal grains, if a particular crystal grain has a larger area than the other crystal grains, the single crystallinity will have a value higher than 1 / N. This is because when a particular crystal grain has the largest area, its form is closer to that of a single crystal than when all N crystal grains have the same area.

[0042] From this perspective, the smaller the area of ​​the added crystal grains, the less the degree of single crystallinity decreases. This is because small crystal grains have a small area relative to the total particle area, and therefore have a low impact on the decrease in single crystallinity.

[0043] As shown in Formula 1 above, the lithium transition metal oxide contained in the positive electrode active material of the present invention has a single crystallinity degree represented by Formula 1 of 0.50 to 0.75. Specifically, the lithium transition metal oxide may have a single crystallinity degree represented by Formula 1 of 0.50 or more, 0.51 or more, 0.52 or more, 0.53 or more, 0.54 or more, 0.55 or more, 0.56 or more, 0.57 or more, 0.58 or more, 0.59 or more, or 0.60 or more, and may be 0.65 or less, 0.66 or less, 0.67 or less, 0.68 or less, 0.69 or less, 0.70 or less, 0.71 or less, 0.72 or less, 0.73 or less, 0.74 or less, or 0.75 or less. More specifically, the lithium transition metal oxide may have a single crystallinity degree represented by Formula 1 of 0.60 to 0.75.

[0044] Having a single-crystallinity degree within the above range indicates that the lithium transition metal oxide of the present invention has a single-particle form in which clumping between particles is suppressed. This suppresses particle cracking due to grain boundaries during electrode rolling and cell driving, reduces gas generation, and reduces the grain boundary area in contact with the electrolyte, thereby controlling side reactions with the electrolyte and significantly improving the lifespan of the secondary battery.

[0045] On the other hand, if the degree of single crystallinity is less than 0.50, many particles are often clustered together, which can cause cracking and the generation of fine powder during electrode rolling, and the advantages of single-particle cathode materials, such as suppression of gas generation, are not realized. If the degree of single crystallinity exceeds 0.75, it is usually due to over-calcination or over-grinding, which can lead to problems such as reduced capacity in the case of over-calcination, and increased fine powder and reduced cathode material particle size in the case of over-grinding.

[0046] In the present invention, the single particle has an average particle size (D 50 The diameter may be 1.5 μm or larger, specifically 1.5 μm or larger, 2.0 μm or larger, 2.5 μm or larger, 3.0 μm or larger, 3.5 μm or larger, or 4.0 μm or larger, and may be 4.2 μm or smaller, 4.3 μm or smaller, 4.4 μm or smaller, 4.5 μm or smaller, 5.0 μm or smaller, 5.5 μm or smaller, or 6.0 μm or smaller.

[0047] The positive electrode active material of the present invention has the advantage of having a single-particle form, which suppresses particle cracking and reduces gas generation compared to conventional secondary particles in which primary particles are aggregated. Furthermore, when the average particle size of the single particles is within the above range, side reactions and gas generation due to an increase in specific surface area are suppressed, preventing performance degradation due to volume reduction and decrease in rolling density, while also suppressing an increase in resistance and exhibiting optimal physical properties.

[0048] In the present invention, the single particle has a BET specific surface area of ​​0.50 m². 2 It may be less than or equal to / g, specifically 0.20m 2 / g or more, 0.25m 2 / g or more, 0.30m 2 / g or more, 0.35m 2 / g or more, or 0.40m 2 It may be 0.46m or more 2 / g or less, 0.47m 2 / g or less, 0.48m 2 / g or less, 0.49m 2 Less than / g, or 0.50m 2 It may be less than or equal to / g.

[0049] The positive electrode active material of the present invention contains a lithium composite transition metal oxide that satisfies a specific range of single crystallinity and has few grain boundaries, thus enabling it to have a low BET specific surface area as described above.

[0050] In the present invention, the lithium transition metal oxide may be represented by the following chemical formula 1.

[0051] [Chemical formula 1] Li(Ni) 1-x-y-z Co x Mn y M z )O2

[0052] In the aforementioned chemical formula 1, M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo. x, y, and z are the atomic fractions of independent elements, where 0 ≦ x ≦ 0.2, 0 ≦ y ≦ 0.2, 0 ≦ z < 1, and 0 ≦ x + y + z < 1.

[0053] M is an element substituted for the transition metal site in the oxide represented by Chemical Formula 1, and may include one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo.

[0054] 1 - x - y - z represents the molar ratio of nickel among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0.5 < 1 - x - y - z < 1.0, preferably 0.55 ≦ 1 - x - y - z ≦ 0.95, 0.7 < 1 - x - y - z < 1.0, or 0.75 ≦ 1 - x - y - z ≦ 0.95 may hold.

[0055] x represents the molar ratio of cobalt among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 < x < 0.5, preferably 0.025 ≦ x ≦ 0.35, or 0.025 ≦ x ≦ 0.15 may hold.

[0056] y represents the molar ratio of manganese among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 < y < 0.5, preferably 0.025 ≦ y ≦ 0.35, or 0.025 ≦ y ≦ 0.25 may hold.

[0057] z represents the molar ratio of M among the metal components excluding lithium in the lithium transition metal oxide represented by Chemical Formula 1, and 0 ≦ z ≦ 0.05, preferably 0 ≦ z ≦ 0.02 may hold.

[0058] Further, the positive electrode active material may further include a coating layer formed on the surface. The coating layer may include one or more selected from the group consisting of Co, Al, W, and B, and preferably may include B (boron).

[0059] The coating layer prevents contact between the positive electrode active material and the electrolyte contained in the lithium secondary battery, thereby suppressing the occurrence of side reactions, which further improves the lifespan characteristics and increases the packing density of the positive electrode active material.

[0060] The coating layer may be formed over the entire surface of the positive electrode active material or partially. Specifically, when the coating layer is partially formed on the surface of the positive electrode active material, it may cover 20% or more but less than 100% of the total surface area of ​​the positive electrode active material. If the area of ​​the coating layer is less than 20%, the effect of improving lifespan characteristics and packing density due to the formation of the coating layer is minimal.

[0061] Furthermore, the positive electrode active material of the present invention can be manufactured by a manufacturing method comprising: (S1) preparing a solid-phase raw material mixture containing lithium raw material powder, nickel raw material powder, cobalt raw material powder, and manganese raw material powder such that the molar ratio of lithium to all transition metals is 0.90 to 1.10; (S2) primary calcining the solid-phase raw material mixture and then pulverizing it; and (S3) mixing lithium raw material powder into the result of step (S2) such that the total molar ratio of lithium to all transition metals is 0.95 to 1.10, and then secondary calcining.

[0062] Furthermore, in the above method, the temperature of the secondary firing may be 600 to 900°C, or 650 to 880°C, more preferably 700 to 850°C.

[0063] The lithium transition metal oxide of the present invention is produced by a solid-phase synthesis method using a solid-phase raw material mixture. The solid-phase synthesis method has the advantage of enabling mass production through a relatively simple synthesis process, and is particularly advantageous for the production of high-content nickel NCM with a high nickel content.

[0064] Furthermore, the grinding and mixing process results in smaller and more uniformly mixed raw material particles, allowing for smoother particle growth at lower temperatures and enabling the material to exhibit excellent single crystallinity and sphericity.

[0065] In contrast, when using a process in which a positive electrode active material precursor is prepared first and then used to manufacture a single-particle positive electrode active material slurry, particle growth may not proceed smoothly, resulting in insufficient single-particle formation. This necessitates an over-calcination process, which may lead to a decrease in battery capacity during use due to reasons such as the formation of a rock salt phase. Furthermore, secondary particle morphologies based on the precursor will coexist, making it impossible to achieve the degree of spheroidization and crystallinity targeted by this invention.

[0066] In the present invention, the lithium raw material powder may be, for example, a lithium-containing carbonate (e.g., lithium carbonate), a lithium-containing hydrate (e.g., lithium hydroxide hydrate (LiOH·H2O)), a lithium-containing hydroxide (e.g., lithium hydroxide), a lithium-containing nitrate (e.g., lithium nitrate (LiNO3)), or a lithium-containing chloride (e.g., lithium chloride (LiCl)). Preferably, the first lithium raw material substance may be one or more selected from the group consisting of lithium hydroxide, lithium hydroxide hydrate, and lithium carbonate.

[0067] In the present invention, nickel raw material powder means a raw material powder containing only nickel in order to provide nickel as a transition metal. The nickel raw material powder may be at least one selected from the group consisting of nickel oxide, nickel carbonate, nickel sulfate, nickel hydroxide, nickel phosphate, and nickel nitrate.

[0068] The cobalt raw material powder may be at least one selected from the group consisting of cobalt oxide, cobalt carbonate, cobalt sulfate, cobalt hydroxide, and cobalt phosphate.

[0069] The manganese raw material powder may be at least one selected from the group consisting of manganese dioxide, manganese carbonate, manganese sulfate, and manganese nitrate.

[0070] The solid-phase raw material mixture produced in step (S1) contains lithium raw material powder, nickel raw material powder, cobalt raw material powder, and manganese raw material powder such that the molar ratio of lithium to the total transition metals is 0.90 to 1.10.

[0071] If the molar ratio of lithium is less than 0.90, problems may occur in the formation of the composite transition metal phase by solid-phase synthesis, potentially leading to lithium deficiency, decreased discharge efficiency, and a significant increase in surface resistance. If the mixed molar ratio exceeds 1.10, the residual lithium may increase, potentially leading to a decrease in the performance of the positive electrode active material.

[0072] The aforementioned molar ratio of lithium is a condition controlled to produce a single-particle positive electrode active material having a high degree of single crystallinity, as in the present invention.

[0073] Furthermore, in this invention, in order to produce a positive electrode active material in the form of a single particle with a high degree of single crystallinity, the material can be packed at a packing density of 0.7 cc / g or more during firing. When the packing density is within the above range, the inter-particle distance is shortened during firing, which facilitates particle reaction and growth, thereby increasing the degree of single crystallinity of the positive electrode active material.

[0074] In the present invention, the solid-phase raw material mixture is first calcined and then pulverized.

[0075] The primary firing may be performed at a temperature of 400 to 900°C. When the primary firing temperature is within the above range, it is possible to prevent the reactivity of the lithium raw material powder and the respective transition metal raw material powders in the solid phase raw material mixture from being low, which can lead to an increase in unreacted residual lithium, or to prevent a shortage of lithium inside the positive electrode active material, which can reduce the battery capacity and lifespan. Furthermore, it is possible to suppress localized over-firing phenomena caused by non-uniform reactions during primary firing, which can degrade the performance of the positive electrode active material and reduce the battery capacity and lifespan.

[0076] In the present invention, the solid-phase raw material mixture is first calcined and then pulverized. By pulverizing, the average particle size (D) of the first calcined product is reduced. 50 The particle size can be adjusted to 2-4 μm or 3-4 μm, and the maximum particle size (Dmax) can be adjusted to 30 μm or less or 20 μm or less. This grinding process eliminates clumping of particles during firing, suppressing the generation of macroparticles, and ultimately enabling the production of single particles with a uniform composition of the desired size.

[0077] The positive electrode active material of the present invention can be manufactured by mixing lithium raw material powder with the result of step (S2) such that the total molar ratio of lithium to all transition metals is 0.95 to 1.10, and then performing a secondary calcination.

[0078] If the total molar ratio of lithium to the transition metal is less than 0.95 after mixing the lithium raw materials, problems may occur in the formation of the composite transition metal phase by solid-phase synthesis, potentially leading to lithium deficiency, decreased discharge efficiency, and a significant increase in surface resistance. Furthermore, if the total molar ratio of lithium exceeds 1.10, there is a risk of increased residual lithium and a decrease in the performance of the positive electrode active material.

[0079] In this invention, the secondary firing temperature may be 500-900°C, 600-850°C, or 700-800°C. The secondary firing time may be 5-15 hours, or 7-12 hours.

[0080] By performing secondary calcination within the above range, thermal energy and additional lithium raw materials can be replenished as needed, compensating for the lack of particle growth during primary calcination. Fine particles generated in the grinding process are grown and absorbed, enabling the production of a positive electrode active material with a suitable particle size and high degree of single crystallinity.

[0081] In the present invention, the firing may be carried out in an oxygen or air atmosphere. When firing is carried out in the aforementioned atmosphere, the local oxygen partial pressure increases, improving the crystallinity of the positive electrode active material and making it easier to control the surface phase. In contrast, when firing is carried out in a non-oxidizing atmosphere or an inert gas atmosphere instead of the aforementioned atmosphere, the crystallinity decreases due to the desorption of oxygen during firing, and the surface phase is formed unevenly, making it difficult to control the phase present on the surface.

[0082] Furthermore, the manufacturing method of the present invention may further include a step of washing the positive electrode active material synthesized by the method described above with water.

[0083] For example, by washing the positive electrode active material with a water washing solution (preferably distilled water), lithium by-products present as impurities on the surface of the positive electrode active material can be effectively removed.

[0084] Furthermore, the present invention may further include the step of forming a coating layer. Preferably, the coating layer may contain an element such as B or Co, but is not limited thereto.

[0085] For example, the coating element may form a coating layer on the surface of the positive electrode active material by heat treatment.

[0086] The heat treatment for forming the coating layer may be performed within a temperature range suitable for the coating material to be applied to the surface of the positive electrode active material, specifically, between 100 and 800°C.

[0087] Furthermore, the present invention provides a positive electrode for a lithium secondary battery containing the positive electrode active material.

[0088] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector and containing the positive electrode active material.

[0089] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector usually has a thickness of 3 to 500 μm, and the adhesion strength of the positive electrode active material may be increased by forming fine irregularities on the surface of the current collector. For example, various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics are possible.

[0090] The positive electrode active material layer may contain a conductive material and a binder together with the positive electrode active material.

[0091] In this case, the positive electrode active material may be included in an amount of 80 to 99% by weight, more specifically 85 to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above content range, excellent capacity characteristics can be observed.

[0092] In this case, the conductive material is used to impart conductivity to the electrodes and can be used in the constructed battery without any particular limitations, as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite 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 metal 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 of these may be used alone, or a mixture of two or more. The conductive material may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0093] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or as a mixture of two or more. The binder may be included in an amount of 1 to 30% by weight relative to the total weight of the positive electrode active material layer.

[0094] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except that the positive electrode active material is used. Specifically, the positive electrode composite material, which is prepared by dissolving or dispersing the positive electrode active material and, selectively, a binder and a conductive material in a solvent, can be applied to a positive electrode current collector, followed by drying and rolling. In this case, the types and contents of the positive electrode active material, binder, and conductive material are as described above.

[0095] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone, or a mixture of two or more. The amount of solvent used should be sufficient to dissolve or disperse the cathode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for cathode manufacturing, taking into account the coating thickness and production yield of the slurry.

[0096] Alternatively, the positive electrode may be manufactured by casting the positive electrode composite onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0097] Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0098] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive and negative electrodes, and an electrolyte. As the positive electrode is as described above, a detailed explanation will be omitted, and only the other components will be described in detail below.

[0099] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0100] In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0101] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0102] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0103] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic 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; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites; any one or more mixtures of these can be used. A metallic lithium thin film may also be used as the negative electrode active material. As for the carbon material, both low-crystallinity carbon and high-crystallinity carbon can be used. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0104] The aforementioned negative electrode active material may be present in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0105] The binder is a component that helps to bond the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0106] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, relative to the total weight of the negative electrode active material layer. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, 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.

[0107] For example, the negative electrode active material layer may be manufactured by coating a negative electrode composite material, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it; or it may be manufactured by casting the negative electrode composite material onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0108] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte impregnation ability are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used as single-layer or multi-layer structures.

[0109] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0110] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0111] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, and is not particularly limited. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; 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), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate can be mixed in a volume ratio of about 1:1 to about 1:9 to produce an electrolyte with excellent performance.

[0112] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. Specifically, the lithium salt 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. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0113] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the total weight of the electrolyte.

[0114] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making it useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the electric vehicle field, such as hybrid electric vehicles (HEVs).

[0115] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0116] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0117] The external shape of the lithium secondary battery of the present invention is not particularly limited, but cylindrical, rectangular, pouch-type, or coin-type batteries using a can are possible.

[0118] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0119] Examples The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention to these examples alone.

[0120] Example 1 Li, Ni, Co, Mn, and Al raw materials were added to a mixer in amounts such that the molar ratio of Li:Ni:Co:Mn:Al was 0.97:0.93:0.05:0.01:0.01, and the mixture was mixed and pulverized using a high-energy milling apparatus. The raw materials used were LiOH·H2O, Ni(OH)2, Co3O4, and MnO. 2、 And Al3O4 was used.

[0121] The mixed and pulverized raw materials were packed into a crucible at a density of 0.7 g / cc or higher, and subjected to primary calcination at 810°C for 10 hours under an oxygen atmosphere. The resulting primary calcined product was then pulverized using a pneumatic pulverizer. At this stage, the size of the primary calcined product was D 50 2-4 μm, D max It was adjusted to be >20μm.

[0122] The pulverized primary calcined product and LiOH·H2O were mixed so that the molar ratio of lithium to the transition metal was 1.00. After secondary calcination at 750°C for 5 hours, the mixture was crushed using a pneumatic pulverizer to produce the positive electrode active material.

[0123] Comparative Example 1 (Ni) synthesized using metal sulfate raw materials 0.94 Co 0.05 Mn 0.01 The (OH)2 precursor, LiOH·H2O, and Al2O3 raw materials were mixed in a stirring mixer in amounts such that the molar ratio of Li:(Ni+Co+Mn):Al was 0.97:0.99:0.01. The mixture was then subjected to primary calcination in an electric furnace under an oxygen atmosphere at 810°C for 10 hours, and the resulting primary calcined product was pulverized using a pneumatic pulverizer. At this time, the size of the primary calcined product was D 50 2-4 μm, D max The size was adjusted to be <20 μm.

[0124] The pulverized primary calcined product and LiOH·H2O were mixed so that the molar ratio of lithium to the transition metal was 1.00. After secondary calcination at 750°C for 5 hours, the mixture was crushed using a pneumatic pulverizer to produce the positive electrode active material.

[0125] Comparative Example 2 Li, Ni, Co, Mn, and Al raw materials were added to a mixer in amounts such that the molar ratio of Li:Ni:Co:Mn:Al was 0.97:0.93:0.05:0.01:0.01, and the mixture was then mixed and ground using a high-energy milling apparatus. In this process, LiOH·H2O, Ni(OH)2, Co3O4, MnO2, and Al3O4 were used as raw materials.

[0126] The mixed and pulverized raw materials were packed into a crucible at a density of 0.6 g / cc or higher, and subjected to primary calcination at 810°C for 10 hours under an oxygen atmosphere. The resulting primary calcined product was then pulverized using a mechanical grinding device.

[0127] The crushed primary calcined product and LiOH·H2O were mixed so that the molar ratio of lithium to the transition metal was 1.00, and then the mixture was subjected to secondary calcination at 810°C for 5 hours to produce the positive electrode active material.

[0128] Comparative Example 3 Li, Ni, Co, Mn, and Al raw materials were added to a mixer in amounts such that the molar ratio of Li:Ni:Co:Mn:Al was 0.97:0.93:0.05:0.01:0.01, and the mixture was then mixed and ground using a high-energy milling apparatus. In this process, LiOH·H2O, Ni(OH)2, Co3O4, MnO2, and Al3O4 were used as raw materials.

[0129] The mixed and pulverized raw materials were packed into a crucible at a density of 0.6 g / cc or higher, and subjected to primary firing in an electric furnace under an oxygen atmosphere at 840°C for 10 hours. The resulting primary fired product was then pulverized using a pneumatic pulverizer. At this stage, the size of the primary fired product was D 50 2-4 μm, D max The size was adjusted to be <20 μm.

[0130] The pulverized primary calcined product and LiOH·H2O were mixed so that the molar ratio of lithium to the transition metal was 1.00. After secondary calcination at 780°C for 5 hours, the mixture was crushed using a pneumatic pulverizer to produce the positive electrode active material.

[0131] Experimental Example 1 (1) Particle size The particle size of each cathode active material produced in the examples and comparative examples was measured using a laser diffraction scattering particle size distribution analyzer (model: Partica LA-960V2, manufacturer: Horiba, Ltd.). The minimum particle size, average particle size, and maximum particle size are shown in Table 1 below. N-methylpyrrolidone (NMP) was used as the dispersion medium.

[0132] (2) BET specific surface area Using BELSORP-mini II from Bell Co., Ltd., the specific surface area of ​​each cathode active material produced in the examples and comparative examples was calculated by the BET method from the amount of nitrogen gas adsorbed under liquid nitrogen temperature (77K), and is shown in Table 1 below.

[0133] [Table 1]

[0134] (3) SEM image SEM images of the cathode active materials produced in the examples and comparative examples were obtained using a scanning electron microscope (SEM), and are shown in Figure 1.

[0135] Figure 1(A) is an SEM image of the positive electrode active material of Example 1, (B) is an SEM image of the positive electrode active material of Comparative Example 1, (C) is an SEM image of the positive electrode active material of Comparative Example 2, and (D) is an SEM image of the positive electrode active material of Comparative Example 3.

[0136] Experimental Example 2: Analysis of Single Crystallinity The positive electrode active materials, carbon black conductive material, and PVDF binder prepared in the examples and comparative examples were mixed in NMP solvent in a weight ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to produce a positive electrode. The produced positive electrode was cut using the FIB method to obtain a cross-section of the positive electrode. SEM and EBSD images of the same portion were measured, and the particle morphology and region (obtained from the SEM image) and the cross-section of the crystal grain (obtained from the EBSD image) were obtained in the map. Then, a clustering algorithm was applied to separate the crystal grains within the particles, and the degree of single crystallinity of the positive electrode active material was analyzed using Equation 1 of the present invention. Figure 2 is a reference diagram to show the extraction of particles from an EBSD image, and shows that the particle region extracted from the SEM image is applied to the EBSD image to extract the particle region from the EBSD image.

[0137]

number

[0138] In the above formula 1, a i When the single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the ratio of the cross-sectional area (A) of the single particle. i ) value (A i This means / A).

[0139] The analysis results are shown in Table 2 and Figure 3 below. Figure 3 is a graph showing the single crystallinity distribution of the positive electrode active materials for Example 1 and Comparative Examples 1-3.

[0140] [Table 2]

[0141] Referring to Figures 1 and 3 and Table 2, it can be confirmed that the positive electrode active material of Example 1 has a relatively uniform particle size without any coarse powder formed by the aggregation of many particles, and that it has fewer crystal grains forming single particles and a higher degree of single crystallinity compared to Comparative Examples 1 and 2. Comparative Example 1 showed that particle growth and single crystallinity progressed relatively less compared to the solid-phase synthesized positive electrode active material of Example 1. In Comparative Example 2, the calcination reaction and pulverization did not proceed smoothly, and it was observed that fine and coarse powders were occasionally present, resulting in an uneven particle size and degree of single crystallinity. Comparative Example 3 was a sample in which the degree of single crystallinity was improved by increasing the calcination temperature, and the average particle size increased due to over-calcination.

[0142] Furthermore, while Example 1 and Comparative Examples 1 and 2 showed similar particle sizes, Example 1 exhibited a lower BET specific surface area compared to Comparative Examples 1 and 2. The higher the degree of single crystallinity of the particles, the fewer crystal grains make up a single particle, and the smaller the area of ​​the grain boundary, resulting in a lower BET specific surface area. In other words, despite Example 1 having particle sizes equivalent to or smaller than Comparative Examples 1 and 2, it had a lower BET specific surface area, indicating that it had a relatively higher degree of single crystallinity compared to Comparative Examples 1 and 2.

[0143] Furthermore, the positive electrode active material of Example 1 had a mode single crystallinity of 0.5 to 0.6, which was on average higher than the 0.2 to 0.4 of Comparative Examples 1 and 2. It was also shown that there were more particles with a single crystallinity of 1, which is the maximum value. On the other hand, in Comparative Example 3, although the number of particles with a single crystallinity of 0.8 to 1.0 increased, the electrode properties deteriorated due to over-calcination, as shown in Experimental Example 3 below, and it was not possible to exhibit the desirable properties of a positive electrode material.

[0144] Experimental Example 3 The positive electrode active materials, carbon black conductive material, and PVDF binder prepared in the examples and comparative examples were mixed in an NMP solvent in a ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an Al current collector, dried, and then rolled to produce a positive electrode.

[0145] A lithium metal electrode was used as the negative electrode, and an electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. After positioning the electrode assembly inside a battery case, an electrolyte was injected into the case to manufacture a half-cell. The electrolyte was prepared by dissolving 1.0 M LiPF6 in an organic solvent mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 2:1:2.

[0146] Each half-cell manufactured in this manner was charged at 25°C in CC(0.1C)-CV mode until it reached 4.25V, and then discharged at 0.1C to 3.0V. The initial charge capacity and initial discharge capacity were measured and are shown in Table 3 below. The efficiency is expressed as the percentage of the initial discharge capacity to the initial charge capacity.

[0147] [Table 3]

[0148] Referring to Table 3 above, it can be confirmed that the secondary battery containing the positive electrode active material according to the present invention has improved initial charge / discharge capacity and efficiency.

[0149] Experimental Example 4 The positive electrode active materials, Denka Black conductive material, and PVDF binder prepared in Example 1 and Comparative Example 1 were mixed in an NMP solvent in a ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an Al current collector, dried, and then rolled to produce a positive electrode.

[0150] Next, a negative electrode slurry was prepared by mixing a negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (SBR+CMC) in water in a weight ratio of 95.6:1.5:3.54. The negative electrode slurry was applied to one surface of a Cu current collector, dried, and then rolled to produce a negative electrode.

[0151] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. After positioning the electrode assembly inside a battery case, an electrolyte solution was injected into the case to produce 32 monocells with an electrode size of 3 cm x 4 cm. The electrolyte solution was prepared by dissolving 1.0 M LiPF6 in an organic solvent mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:3:4.

[0152] The 32 monocells were charged at 25°C in CC (0.33C)-CV (0.05C cutoff) mode until they reached 4.25V, after which the positive electrodes were separated. The separated positive electrodes were placed in cell pouches, electrolyte was added, and the pouches were sealed to prepare the samples. The amount of gas generated was measured while the samples were stored at 60°C for 12 weeks. Figure 4 shows a graph of the rate of volume change over the storage period, and Table 4 below shows the amount of gas generated after 12 weeks.

[0153] [Table 4]

[0154] Referring to Figure 4 and Table 4, it can be confirmed that the secondary battery containing the positive electrode active material according to the present invention exhibits a significant reduction in gas generation during high-temperature storage.

[0155] In conclusion, the positive electrode active material according to the present invention contains a lithium transition metal oxide having a single-particle form and a single-crystallinity degree (X) of 0.50 to 0.75, thereby reducing the generation of fine particles due to particle cracking. When used as a positive electrode active material in a lithium secondary battery, it can improve the initial charge / discharge capacity and efficiency of the battery, reduce gas generation, and significantly improve the stability of the battery.

Claims

1. The material contains a lithium transition metal oxide whose single crystallinity (X) according to formula 1 below is 0.50 to 0.

75. A positive electrode active material wherein the lithium transition metal oxide is in the form of a single particle. [Math 1] (In formula 1 above, a ｉ When the single particle consists of i crystal grains, the cross-sectional area of ​​the i-th crystal grain (A) is given by the ratio of the cross-sectional area (A) of the single particle. ｉ The value of (A ｉ (This means / A).

2. The positive electrode active material according to claim 1, wherein the degree of single crystallinity (X) is 0.60 to 0.

75.

3. The average particle size (D) of the single particle ５０ The positive electrode active material according to claim 1, wherein the diameter of the ) is 1.5 μm or more.

4. The BET specific surface area of ​​the aforementioned single particle is 0.50 m². ２ The positive electrode active material according to claim 1, wherein the amount is less than or equal to / g.

5. The positive electrode active material according to claim 1, wherein the lithium transition metal oxide is represented by the following chemical formula 1. [Chemical formula 1] L) １－ｘ－ｙ－ｚ Co ｘ Mn ｙ M ｚ )O ２ (In the above chemical formula 1, M is one or more elements selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo. x, y, and z are the atomic fractions of independent elements, where 0 ≤ x ≤ 0.2, 0 ≤ y ≤ 0.2, 0 ≤ z < 1, and 0 ≤ x + y + z < 1.

6. A positive electrode for a lithium secondary battery, comprising the positive electrode active material described in any one of claims 1 to 5.

7. A lithium secondary battery comprising a positive electrode for a lithium secondary battery as described in claim 6.

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