Positive electrode active material and method for producing a positive electrode active material

Abstract

To provide a positive electrode active material with improved high-temperature lifetime characteristics and resistance characteristics, and a method for producing a positive electrode active material. [Solution] The present invention relates to a positive electrode active material comprising a lithium transition metal oxide in the form of secondary particles formed by the aggregation of primary particles, which contains 70 mol% or more nickel (Ni) among the total metals other than lithium, and a coating layer containing B formed on the lithium transition metal oxide, wherein the average aspect ratio of the primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0, a positive electrode active material, a method for producing the positive electrode active material, a positive electrode containing the positive electrode active material, and a lithium secondary battery.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0111848 filed on August 24, 2021, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a positive electrode active material, a positive electrode including the positive electrode active material, a lithium secondary battery, and a method for manufacturing the positive electrode active material.

Background Art

[0003] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, a high voltage, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

[0004] As the positive electrode active material of a lithium secondary battery, a lithium transition metal oxide is used. Among them, lithium cobalt oxide of LiCoO2, which has a high operating voltage and excellent capacity characteristics, is mainly used. However, LiCoO2 has very poor thermal characteristics due to the destabilization of the crystal structure by delithiation, and is also expensive, so there is a limit to its large-scale use as a power source in fields such as electric vehicles.

[0005] As materials to be used in place of the LiCoO2, lithium manganese composite metal oxides (such as LiMnO2 or LiMn2O4), lithium iron phosphate compounds (such as LiFePO4), or lithium nickel composite metal oxides (such as LiNiO2) have been developed. Among them, research and development on lithium nickel composite metal oxides, which have a high reversible capacity of about 200 mAh / g and are easy to realize a large-capacity battery, have been more actively carried out. However, the LiNiO2 has inferior thermal stability compared with LiCoO2. When an internal short circuit occurs due to external pressure or the like in the charged state, there is a problem that the positive electrode active material itself is decomposed, causing battery rupture and ignition. Therefore, as a method for maintaining the excellent reversible capacity of LiNiO2 and improving its low thermal stability, LiNi 1-α Co α O2 (α = 0.1 to 0.3) or lithium nickel cobalt metal oxides in which part of nickel is substituted with Mn, Co, or Al have been developed.

[0006] However, in the case of the lithium nickel cobalt metal oxide, there is a problem of low capacity. In order to increase the capacity of the lithium nickel cobalt metal oxide, a method of increasing the content of nickel contained in the lithium nickel cobalt metal oxide has been studied. In this case, due to the presence of unreacted residual lithium on the surface, a water washing process is essential. The water washing process causes surface defects of the positive electrode active material, resulting in a decrease in the battery life characteristics.

[0007] In order to solve this problem, conventionally, a method of forming a coating layer on the surface of the positive electrode active material at a low temperature after washing the positive electrode active material with water has been studied, but there are still limitations in terms of improving the high-temperature life characteristics and resistance characteristics.

[0008] Therefore, the development of a positive electrode active material with improved high-temperature life characteristics and resistance characteristics is required.

Summary of the Invention

Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a positive electrode active material having improved high-temperature life characteristics and resistance characteristics, and a method for producing the positive electrode active material.

[0010] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

Means for Solving the Problems

[0011] In order to solve the above problems, the present invention provides a positive electrode active material, a method for producing a positive electrode active material, a positive electrode, and a lithium secondary battery.

[0012] (1) The present invention provides a positive electrode active material comprising a lithium transition metal oxide containing 70 mol% or more of nickel (Ni) among all metals other than lithium and having a secondary particle form in which primary particles are aggregated, and a coating layer containing boron (B) formed on the lithium transition metal oxide, wherein the average aspect ratio of the primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0.

[0013] (2) In the above (1), the present invention provides a positive electrode active material in which the lithium transition metal oxide has a composition represented by the following Chemical Formula 1. [Chemical Formula 1] Li x Ni a1 Co b1 Mn c1 Al d1 B e1 M 1 f1 O2 In the Chemical Formula 1, M 1 is one or more selected from Zr, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba, 0.90 ≦ x ≦ 1.12, 0.70 ≦ a1 ≦ 1.0, 0 ≦ b1 ≦

[0014] (3) The present invention provides a method for producing a positive electrode active material, comprising the steps of (A) producing a calcined product by primary calcining a reaction mixture containing a positive electrode active material precursor containing 70 mol% or more nickel (Ni) of the total metal at a primary calcination temperature; (B) producing a lithium transition metal oxide by mixing the calcined product with a first boron-containing raw material and secondary calcining at a secondary calcination temperature; and (C) forming a coating layer by mixing the lithium transition metal oxide with a second boron-containing raw material and heat-treating it, wherein the ratio of the primary calcination temperature to the secondary calcination temperature is 0.7 to 0.9.

[0015] (4) The present invention provides a method for producing a positive electrode active material, wherein the positive electrode active material precursor has a composition represented by the following chemical formula 2-1 or chemical formula 2-2, as described in (3) above. [Chemical formula 2-1] Ni a2 Co b2 Mn c2 M 1 d2 (OH)2 [Chemical formula 2-2] Ni a2 Co b2 Mn c2 M 1 d2 O.OH In the aforementioned chemical formulas 2-1 and 2-2, M 1 is one or more selected from Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, Ce, Hf, F, P, S, and La. 0.70≦a2≦1.0, 0≦b2≦0.30, 0≦c2≦0.30, 0≦d2≦0.10.

[0016] (5) The present invention provides a method for producing a positive electrode active material in which, in (3) or (4) above, the reaction mixture further comprises an aluminum-containing raw material.

[0017] (6) The present invention provides a method for producing a positive electrode active material in any one of (3) to (5) above, wherein the primary firing temperature is 300°C to 750°C.

[0018] (7) The present invention provides a method for producing a positive electrode active material in any one of (3) to (6) above, wherein the first boron-containing raw material is one or more selected from H3BO3, H4BO4, B2O3, LiBO2, Li2B4O7, B4C, AlBO2, and AlB2O4.

[0019] (8) The present invention provides a method for producing a positive electrode active material in any one of (3) to (7) above, wherein the secondary firing temperature is 500°C to 900°C.

[0020] (9) The present invention provides a method for producing a positive electrode active material in any one of (3) to (8) above, wherein the second boron-containing raw material is one or more selected from H3BO3, H4BO4, B2O3, LiBO2, Li2B4O7, B4C, AlBO2, and AlB2O4.

[0021] (10) The present invention provides a method for producing a positive electrode active material in any one of (3) to (9) above, wherein the second boron-containing raw material is mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the lithium transition metal oxide.

[0022] (11) The present invention provides a method for producing a positive electrode active material in any one of (3) to (10) above, wherein the heat treatment temperature is 200°C to 400°C.

[0023] (12) The present invention provides a positive electrode comprising a positive electrode active material according to (1) or (2) above.

[0024] (13) The present invention provides a lithium secondary battery including a positive electrode according to (12) above. [Effects of the Invention]

[0025] According to the present invention, when the positive electrode active material contains 70 mol% or more nickel (Ni) among the total metals other than lithium, and comprises a lithium transition metal oxide in the form of secondary particles formed by the aggregation of primary particles, and a coating layer containing B formed on the lithium transition metal oxide, and the average aspect ratio of the primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0, the battery containing this exhibits excellent high-temperature life characteristics and resistance characteristics.

[0026] According to the present invention, when manufacturing a positive electrode active material, if a specific amount of the first boron-containing raw material is added in a secondary firing step after primary firing, and firing is performed under conditions where the primary firing temperature and the secondary firing temperature satisfy a specific ratio, the primary particles present on the surface of the manufactured positive electrode active material can have a specific aspect ratio. [Brief explanation of the drawing]

[0027] [Figure 1] This figure shows an SEM image of the positive electrode active material manufactured in Example 1 and a table showing the average aspect ratio of primary particles present on the surface of the positive electrode active material. [Figure 2] This figure shows an SEM image of the cathode active material manufactured in Example 2 and a table showing the average aspect ratio of primary particles present on the surface of the cathode active material. [Figure 3] This figure shows an SEM image of the positive electrode active material manufactured in Comparative Example 1 and a table showing the average aspect ratio of primary particles present on the surface of the positive electrode active material. [Figure 4] This figure shows an SEM image of the positive electrode active material manufactured in Comparative Example 2 and a table showing the average aspect ratio of primary particles present on the surface of the positive electrode active material. [Figure 5] This figure shows an SEM image of the positive electrode active material manufactured in Comparative Example 3 and a table showing the average aspect ratio of primary particles present on the surface of the positive electrode active material. [Figure 6] This figure shows an SEM image of the positive electrode active material manufactured in Comparative Example 4 and a table showing the average aspect ratio of primary particles present on the surface of the positive electrode active material. [Figure 7]This figure shows an SEM image of the cathode active material manufactured in Comparative Example 5 and a table showing the average aspect ratio of primary particles present on the surface of the cathode active material. [Modes for carrying out the invention]

[0028] The present invention will now be described in more detail to facilitate understanding of it. Hereinafter, terms and words used in this specification and in the claims will not be interpreted to be limited to their ordinary or dictionary meanings, but rather to be interpreted in a way that is consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0029] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the existence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

[0030] In this specification, the term "on top of" means not only when one configuration is formed directly on top of another, but also when a third configuration is interposed between these configurations.

[0031] In this specification, "primary particle" means the smallest particle unit recognized when observing the positive electrode active material via a scanning electron microscope (SEM), and "secondary particle" means a secondary structure formed by the aggregation of multiple primary particles.

[0032] positive electrode active material The positive electrode active material according to the present invention contains 70 mol% or more nickel (Ni) among the total metals other than lithium, and comprises a lithium transition metal oxide in the form of secondary particles formed by the aggregation of primary particles, and a coating layer containing boron (B) formed on the lithium transition metal oxide, wherein the average aspect ratio of the primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0. The inventors of the present invention have found that in this case both high-temperature lifetime characteristics and resistance characteristics are improved, and have completed the present invention.

[0033] In this invention, the average aspect ratio of primary particles present on the surface of the positive electrode active material was obtained by the following method. First, using the ImageJ program, the shape of one primary particle to be measured was selected from the SEM image of the positive electrode active material (selected using the ImageJ program's tools). Then, the Shape Descriptors were checked in Analyze's Set Measure and the measurement was performed to obtain the ratio of the major axis to the minor axis passing through the center of an ellipse fitted to the shape of the primary particle. Aspect ratios were obtained for several dozen primary particles for each positive electrode active material, and their average was calculated and defined as the average aspect ratio of the primary particles.

[0034] The positive electrode active material according to the present invention not only includes a coating layer containing boron (B), but also satisfies an average aspect ratio of 1.8 to 6.0 of primary particles present on the surface of the lithium transition metal oxide, and can improve high-temperature life characteristics and resistance characteristics with minimal loss in the capacity and output characteristics of a battery containing it. The average aspect ratio of primary particles present on the surface of the lithium transition metal oxide can be 1.8 or higher, 1.9 or higher, 2.0 or higher, 2.1 or higher, 3.0 or lower, 4.0 or lower, 5.0 or lower, or 6.0 or lower, from the viewpoint of further improving the performance of the battery.

[0035] On the other hand, if the average aspect ratio of primary particles present on the surface of the lithium transition metal oxide is less than 1.8, the proportion of (001) surfaces with stable surface energy decreases, leading to a problem of reduced high-temperature life characteristics and resistance characteristics of the battery. Furthermore, if the average aspect ratio of primary particles present on the surface of the lithium transition metal oxide is greater than 6.0, the surfaces on which lithium can move are limited, resulting in a problem of reduced battery capacity and output characteristics.

[0036] The aforementioned coating layer may be a coating layer containing compounds such as boron oxide or Li-BO solid solution.

[0037] According to the present invention, the lithium transition metal oxide can have a composition represented by the following chemical formula 1 in terms of improving the capacity of the battery.

[0038] [Chemical formula 1] Li x Ni a1 Co b1 Mn c1 Al d1 B e1 M 1 f1 O2

[0039] In the aforementioned chemical formula 1, M 1 is one or more selected from Zr, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba. 0.90≦x≦1.12, 0.70≦a1≦1.0, 0≦b1≦0.30, 0≦c1≦0.30, 0≦d1≦0.20, 0 <e1≦0.20、0≦f1≦0.10、a1+b1+c1+d1+e1+f1=1である。

[0040] The above a1 refers to the atomic fraction of nickel among the metal elements other than lithium in the positive electrode active material, and in terms of improving the battery capacity, it can be 0.70 or more, 0.80 or more, 0.85 or more, 0.95 or less, 0.98 or less, or 1.0 or less.

[0041] The above b1 refers to the atomic fraction of cobalt among the metal elements other than lithium in the positive electrode active material, and can be 0 or more, greater than 0, 0.01 or more, 0.10 or less, 0.20 or less, or 0.30 or less.

[0042] The aforementioned c1 refers to the atomic fraction of manganese among the metal elements other than lithium in the positive electrode active material, and can be 0 or greater, greater than 0, 0.01 or greater, 0.10 or less, 0.20 or less, or 0.30 or less.

[0043] The aforementioned d1 refers to the atomic fraction of aluminum among the metal elements other than lithium in the positive electrode active material, and can be 0 or greater, greater than 0, 0.01 or greater, 0.05 or less, 0.10 or less, or 0.20 or less. Specifically, in terms of improving structural stability, lifespan, and thermal stability, d1 can be greater than 0, 0.01 or greater, 0.05 or less, 0.10 or less, or 0.20 or less.

[0044] The above e1 refers to the atomic fraction of boron among the metal elements other than lithium in the positive electrode active material, and can be greater than 0, 0.005 or more, 0.01 or more, 0.05 or less, 0.10 or less, or 0.20 or less.

[0045] The aforementioned f1 is M, which is one of the metal elements other than lithium in the positive electrode active material. 1 This refers to the atomic fraction, which can be greater than or equal to 0, less than or equal to 0.05, or less than or equal to 0.10.

[0046] Method for manufacturing positive electrode active material The method for producing a positive electrode active material according to the present invention comprises the steps of: (A) producing a calcined product by primary calcining a reaction mixture containing a positive electrode active material precursor containing 70 mol% or more nickel (Ni) of the total metal and a lithium-containing raw material at a primary calcination temperature; (B) producing a lithium transition metal oxide by mixing the calcined product with a first boron-containing raw material and secondary calcining at a secondary calcination temperature; and (C) forming a coating layer by mixing the lithium transition metal oxide with a second boron-containing raw material and heat-treating it, wherein the first boron-containing raw material is mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the calcined product, and the ratio of the primary calcination temperature to the secondary calcination temperature is 0.7 to 0.9.

[0047] The inventors have found that when a specific amount of the first boron-containing raw material is added in a secondary firing step after primary firing during the production of a positive electrode active material, and when firing is performed under conditions where the primary firing temperature and secondary firing temperature satisfy a specific ratio, the primary particles present on the surface of the produced positive electrode active material can have a specific aspect ratio. Furthermore, they have found that in batteries to which a positive electrode active material produced by the positive electrode active material production method of the present invention is applied, the initial resistance, high-temperature life characteristics, and resistance characteristics are all improved.

[0048] A positive electrode active material produced by the method for producing a positive electrode active material according to the present invention can be the positive electrode active material according to the present invention described above. That is, it can be a positive electrode active material comprising a lithium transition metal oxide in the form of secondary particles formed by the aggregation of primary particles, which contains 70 mol% or more nickel (Ni) among the total metals other than lithium, and a coating layer containing B formed on the lithium transition metal oxide, wherein the average aspect ratio of the primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0.

[0049] The method for producing the positive electrode active material according to the present invention will be described in more detail below, step by step.

[0050] (A) Step Step (A) is a step in which a reaction mixture containing a positive electrode active material precursor containing 70 mol% or more nickel (Ni) of the total metal and a lithium-containing raw material is subjected to primary calcination to produce a calcined product.

[0051] According to the present invention, the positive electrode active material precursor may have a composition represented by the following chemical formula 2-1 or chemical formula 2-2.

[0052] [Chemical formula 2-1] Ni a2 Co b2 Mn c2 M 1 d2 (OH)2

[0053] [Chemical formula 2-2] Ni a2 Co b2 Mn c2 M 2 d2 O.OH

[0054] In the aforementioned chemical formulas 2-1 and 2-2, M 2 is one or more selected from Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba. 0.70≦a2≦1.0, 0≦b2≦0.30, 0≦c2≦0.30, 0≦d2≦0.10, and a2+b2+c2+d2=1.

[0055] The above a2 refers to the atomic fraction of nickel among the metal elements in the precursor, and in terms of improving the battery capacity, it can be 0.70 or more, 0.80 or more, 0.85 or more, 0.95 or less, 0.98 or less, or 1.0 or less.

[0056] The above b2 refers to the atomic fraction of cobalt among the metal elements in the precursor, and can be 0 or greater, greater than 0, 0.01 or greater, 0.10 or less, 0.20 or less, or 0.30 or less.

[0057] The aforementioned c2 represents the atomic fraction of manganese among the metal elements in the precursor, and can be 0 or greater, greater than 0, 0.01 or greater, 0.10 or less, 0.20 or less, or 0.30 or less.

[0058] The aforementioned d2 is M among the metal elements in the precursor. 2 This refers to the atomic fraction, which can be greater than or equal to 0, less than or equal to 0.05, or less than or equal to 0.10.

[0059] According to the present invention, the reaction mixture may further contain an aluminum-containing raw material in addition to the lithium-containing raw material and the cathode active material precursor. The aluminum-containing raw material may be one or more selected from Al(OH)3, Al2O3, AlF3, AlBr3, AlPO4, AlCl3, Al(NO)3, Al(NO3)3·9H2O, Al2(SO4)3·H2O, Al(H2PO4)3, C2H5O4Al, Al(SO)4, NaAlO2, Al2CoO4, LaAlO3, and MgAl2O4. In this case, the aluminum-containing raw material has a low melting point, allowing aluminum to diffuse uniformly, be abundantly and uniformly present on the surface side of the lithium transition metal oxide, and facilitate uniform doping of Al to the transition metal sites. Furthermore, cation mixing can be suppressed to impart structural stability and improve lifetime and thermal stability.

[0060] On the other hand, the reaction mixture does not contain boron-containing raw materials. If the reaction mixture contains boron-containing raw materials, that is, if the boron-containing raw materials are mixed in during the primary firing rather than the secondary firing, the desired crystal growth will not occur, and the lifetime characteristics and resistance characteristics at high temperatures cannot be improved.

[0061] The lithium-containing raw material may include one or more selected from lithium hydroxide hydrate, lithium carbonate, and lithium hydroxide. Specifically, the lithium-containing raw material may be lithium hydroxide hydrate, and more specifically, LiOH·H2O. In this case, the reactivity between the precursor with a high atomic fraction of nickel among the metal elements in the precursor and the lithium-containing raw material can be improved.

[0062] The positive electrode active material precursor and the lithium-containing raw material can be mixed in a molar ratio of 1:1.0 to 1:1.10, specifically 1:1.03 to 1:1.09, and more specifically 1:1.05 to 1:1.09. If the lithium-containing raw material is mixed in a ratio below the above range, the volume of the positive electrode active material produced may decrease. If the lithium-containing raw material is mixed in a ratio exceeding the above range, a large amount of unreacted Li will remain as a by-product, which may result in a decrease in volume and separation of positive electrode active material particles after calcination (induction of aggregation of positive electrode active material).

[0063] According to the present invention, the primary firing temperature can be 300°C to 750°C. Specifically, the primary firing temperature can be 300°C or higher, 400°C or higher, 500°C or higher, 740°C or lower, or 750°C or lower. When the primary firing temperature is within the above range, the primary particles present on the surface of the manufactured positive electrode active material can have a specific aspect ratio.

[0064] The primary firing can be carried out in an oxygen atmosphere. For example, the primary firing may be carried out in an oxygen atmosphere containing 90% or more by volume of oxygen, specifically 95% or more by volume. In this case, a calcined product having a structurally stable phase can be formed.

[0065] The primary firing can be carried out for 2 to 10 hours. Specifically, the primary firing may be carried out for 2 hours or more, 3 hours or more, 4 hours or more, 6 hours or less, 8 hours or less, or 10 hours or less. When the primary firing time is within the above range, firing can be carried out uniformly without variation in firing location. The primary firing time is the time during which the primary firing temperature is maintained, and is the time excluding the time to raise the temperature to the temperature for primary firing and the time to cool down to room temperature after primary firing.

[0066] The calcined product contains unreacted residual lithium on its surface, but the amount of such residual lithium can be minimized through steps (B) and (C) according to the present invention.

[0067] (B) Step Step (B) is a step in which the calcined product manufactured in step (A) is mixed with a first boron-containing raw material and secondary calcined at a secondary calcination temperature to produce a lithium transition metal oxide. Here, the amount of the first boron-containing raw material is 0.1 to 2.0 parts by weight per 100 parts by weight of the calcined product, and the ratio of the primary calcination temperature to the secondary calcination temperature is 0.7 to 0.9.

[0068] In the present invention, in step (B) above, by mixing the first boron-containing raw material in a specific amount and performing secondary firing under conditions where the primary firing temperature and secondary firing temperature satisfy a specific ratio, the primary particles present on the surface of the resulting positive electrode active material have an average aspect ratio within a specific range, thereby improving both the high-temperature life characteristics and resistance characteristics of the secondary battery containing the positive electrode active material.

[0069] According to the present invention, the first boron-containing raw material can be one or more selected from H3BO3, H4BO4, B2O3, LiBO2, Li2B4O7, B4C, AlBO2, and AlB2O4. Specifically, the first boron-containing raw material can be H3BO3, B2O3, and more specifically, H3BO3. In this case, the melting point of the first boron-containing raw material is low, and a uniform coating layer can be formed.

[0070] The first boron-containing raw material can be mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the calcined product, specifically in amounts of 0.1 parts by weight or more, 0.2 parts by weight or more, 0.315 parts by weight or more, 1.26 parts by weight or less, 1.5 parts by weight or less, and 2.0 parts by weight or less. When the content of the first boron-containing raw material is within the above range, crystal growth on the surface of the positive electrode active material can be controlled, and the high-temperature life characteristics and resistance characteristics of the battery to which the positive electrode active material is applied can be improved.

[0071] On the other hand, if the content of the first boron-containing raw material is less than 0.1 parts by weight per 100 parts by weight of the calcined product, crystal growth on the surface of the positive electrode active material is not controlled, and if it exceeds 2.0 parts by weight, there is a problem of reduced capacity and resistance characteristics of the battery containing the positive electrode active material.

[0072] Furthermore, the mixing of the lithium transition metal oxide and the first boron-containing raw material can be done by dry mixing. This has the advantage of minimizing impurities compared to wet mixing.

[0073] On the other hand, if the ratio of the primary firing temperature to the secondary firing temperature is less than 0.7, the primary firing temperature is relatively low, and even if the primary firing is completed, a crystalline structure is not formed. As a result, during secondary firing, a large amount of boron diffuses into the cathode material, inhibiting crystal growth between the transition metals, and thus the desired crystalline structure cannot be obtained. Furthermore, if the ratio of the primary firing temperature to the secondary firing temperature is greater than 0.9, the primary firing temperature is relatively high, and the amount of boron that diffuses into the cathode material, where a crystalline structure has already been formed, is small, making it impossible to obtain the desired crystalline structure. Consequently, the average aspect ratio of the primary particles cannot satisfy 1.8 to 6.0, leading to problems with reduced high-temperature life characteristics and resistance characteristics of batteries to which the positive electrode active material is applied.

[0074] According to the present invention, the secondary firing temperature can be 500°C to 900°C. Specifically, the secondary firing temperature can be 500°C or higher, 700°C or higher, 750°C or higher, 820°C or lower, 850°C or lower, or 900°C or lower. When the secondary firing temperature is within the above range, boron affects the crystal growth of primary particles, and a positive electrode active material can be produced in which the average aspect ratio of primary particles present on the surface of the lithium transition metal oxide is 1.8 to 6.0.

[0075] The aforementioned secondary calcination may be carried out in an oxygen atmosphere in order to efficiently calcin the calcined product containing hydroxide groups into a lithium transition metal oxide having a layered structure. For example, the secondary calcination may be carried out in an oxygen atmosphere containing 90% or more by volume of oxygen, specifically 95% or more by volume.

[0076] The secondary firing can be performed for 2 to 10 hours. Specifically, the secondary firing can be performed for 2 hours or more, 3 hours or more, 4 hours or more, 6 hours or less, 8 hours or less, or 10 hours or less. When the secondary firing time is within the above range, firing can be performed uniformly without variation depending on the firing location. The secondary firing time is the time during which the secondary firing temperature is maintained, and is the time excluding the time it takes to raise the temperature to the temperature for secondary firing and the time it takes to cool down to room temperature after secondary firing.

[0077] Furthermore, step (B) may further include step (b1) of washing and drying after secondary firing.

[0078] The aforementioned washing is a process for removing unreacted residual lithium, and involves mixing the calcined product immediately after secondary calcination with a washing solution for washing, and then separating the calcined product from the washing solution.

[0079] The aforementioned washing solution may be, but is not limited to, water, ethanol, or the like.

[0080] The washing solution can be mixed with 100 parts by weight of the fired product in an amount of 60 to 200 parts by weight, specifically, 60 parts by weight or more, 80 parts by weight or more, 150 parts by weight or less, or 200 parts by weight or less. When the content of the washing solution is within the above range, surface damage to the fired product can be prevented and residual lithium present on the surface can be easily removed.

[0081] The aforementioned drying process is a step to remove moisture from the fired product that has contained moisture after the washing process, and may involve vacuum drying the fired product separated from the washing solution at 100°C to 150°C. Here, the separation can be carried out using a reduced pressure filter having an average pore size of 1 to 50 μm.

[0082] The lithium transition metal oxide produced by step (B) above may contain 70 mol% or more nickel (Ni) among the total metals other than lithium, and may be a lithium transition metal oxide in the form of secondary particles formed by the aggregation of primary particles, and specifically may have a composition represented by the following chemical formula 1.

[0083] [Chemical formula 1] Li x Ni a1 Co b1 Mn c1 Al d1 B e1 M 1 f1 O2

[0084] In the aforementioned chemical formula 1, M 1 is one or more selected from Zr, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba. 0.90≦x≦1.12, 0.70≦a1≦1.0, 0≦b1≦0.30, 0≦c1≦0.30, 0≦d1≦0.20, 0 <e1≦0.20、0≦f1≦0.10、a1+b1+c1+d1+e1+f1=1である。

[0085] The above a1 refers to the atomic fraction of nickel among the metal elements other than lithium in the positive electrode active material, and in terms of improving the battery capacity, it can be 0.70 or more, 0.80 or more, 0.85 or more, 0.95 or less, 0.98 or less, or 1.0 or less.

[0086] The above b1 refers to the atomic fraction of cobalt among the metal elements other than lithium in the positive electrode active material, and can be 0 or more, greater than 0, 0.01 or more, 0.10 or less, 0.20 or less, or 0.30 or less.

[0087] The aforementioned c1 refers to the atomic fraction of manganese among the metal elements other than lithium in the positive electrode active material, and can be 0 or greater, greater than 0, 0.01 or greater, 0.10 or less, 0.20 or less, or 0.30 or less.

[0088] The aforementioned d1 refers to the atomic fraction of aluminum among the metal elements other than lithium in the positive electrode active material, and can be 0 or greater, greater than 0, 0.01 or greater, 0.05 or less, 0.10 or less, or 0.20 or less. Specifically, in terms of improving structural stability, lifespan, and thermal stability, d1 can be greater than 0, 0.01 or greater, 0.05 or less, 0.10 or less, or 0.20 or less.

[0089] The above e1 refers to the atomic fraction of boron among the metal elements other than lithium in the positive electrode active material, and can be greater than 0, 0.005 or more, 0.01 or more, 0.05 or less, 0.10 or less, or 0.20 or less.

[0090] The aforementioned f1 is M, which is one of the metal elements other than lithium in the positive electrode active material. 1This refers to the atomic fraction, which can be greater than or equal to 0, less than or equal to 0.05, or less than or equal to 0.10.

[0091] (C) Step Step (C) is a step in which the lithium transition metal oxide produced in step (B) is mixed with a second boron-containing raw material and heat-treated to form a coating layer.

[0092] (C) A coating layer containing boron is formed on the lithium transition metal oxide in step (C). Specifically, a coating layer containing compounds such as boron oxide and Li-BO solid solution is formed on the surface of the lithium transition metal oxide. By forming the coating layer on the lithium transition metal oxide, side reactions with the electrolyte and other components can be suppressed, thereby preventing deterioration of the battery life characteristics.

[0093] According to the present invention, the second boron-containing raw material can be one or more selected from H3BO3, H4BO4, B2O3, LiBO2, Li2B4O7, B4C, AlBO2, and AlB2O4. Specifically, the second boron-containing raw material can be H3BO3, B2O3, and more specifically, H3BO3. In this case, the melting point of the boron-containing raw material is low, and a uniform coating layer can be formed.

[0094] According to the present invention, the second boron-containing raw material can be mixed with 100 parts by weight of the lithium transition metal oxide in an amount of 0.1 to 2.0 parts by weight, specifically 0.1 parts by weight or more, 0.2 parts by weight or more, 0.235 parts by weight or more, 1.14 parts by weight or less, 1.5 parts by weight or less, and 2.0 parts by weight or less. When the content of the second boron-containing raw material is within the above range, not only is a coating layer formed uniformly, but a coating layer of appropriate thickness is also formed, and when the manufactured positive electrode active material is applied to a battery, the battery life characteristics can be improved.

[0095] On the other hand, the mixing of the lithium transition metal oxide and the boron-2-containing raw material can be done by dry mixing. This has the advantage of minimizing impurities compared to wet mixing.

[0096] According to the present invention, the heat treatment temperature can be 200°C to 400°C. Specifically, the heat treatment temperature can be 200°C or higher, 250°C or higher, 260°C or higher, 330°C or lower, 350°C or lower, or 400°C or lower. When the heat treatment temperature is within the above range, a coating layer is uniformly formed on the lithium transition metal oxide, and when applied to a battery, the battery life characteristics can be improved.

[0097] positive electrode Furthermore, the present invention provides a positive electrode containing the positive electrode active material. The positive electrode can be a positive electrode for a lithium secondary battery.

[0098] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to the present invention.

[0099] Here, the positive electrode active material is as described above, and a detailed explanation will be omitted. Below, only the remaining components will be described in detail.

[0100] 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., can be used. The positive electrode current collector can also typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0101] The positive electrode active material layer may contain, together with the positive electrode active material, a conductive material and, if necessary, a selective binder.

[0102] In this case, the positive electrode active material can be included in an amount of 80 to 99% by weight, more specifically 85 to 98.5% 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.

[0103] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes 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 alone or a mixture of two or more can be used. The conductive material may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0104] The binder plays a role in improving adhesion between positive electrode active material particles and 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be included in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0105] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by coating a positive electrode active material layer-forming composition, which is prepared by dissolving or dispersing the positive electrode active material and, selectively, a binder and a conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0106] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0107] Alternatively, the positive electrode can also be manufactured by casting the positive electrode active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0108] Lithium-ion rechargeable battery Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element can be a battery, a capacitor, and more specifically, a lithium secondary battery.

[0109] 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 remaining components will be described in detail below.

[0110] 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.

[0111] 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.

[0112] 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 can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0113] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0114] 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. β Examples include metallic oxides that can be doped and dedoped with lithium, 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, and 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. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. 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.

[0115] The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0116] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and is usually added in an amount of 0.1% to 10% by weight relative to 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0117] The conductive material is a component for further improving the conductivity of the negative electrode active material and can 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. Such a conductive material is not particularly limited as long as it does not cause chemical changes in the battery and is conductive, and 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 can be used.

[0118] For example, the negative electrode active material layer can be manufactured by coating a negative electrode active material layer-forming composition, 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 by casting the negative electrode active material layer-forming composition onto another support, peeling it off this support, and then laminating the resulting film onto the negative electrode current collector.

[0119] 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, but those with low resistance to ion movement of the electrolyte and excellent moisture-absorbing capacity for the electrolyte are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, 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 can be selectively used as single-layer or multi-layer structures.

[0120] 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.

[0121] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0122] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned 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), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcohol 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 can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can 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, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 allows the electrolyte to exhibit excellent performance.

[0123] The lithium salt can be any compound capable of providing lithium ions for use in a lithium secondary battery, without any particular limitations. 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, etc. 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 this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0124] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds including 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, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additive may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0125] The lithium secondary battery according to the present invention can achieve a ratio of over 98.0% to 98.5% of the 30th cycle capacity retention rate (30th cycle capacity retention rate) when the charge-discharge cycle is repeated 30 times at a constant current of 0.33C at 45°C and in the range of 3.0 to 4.25V, and the discharge capacity is measured at the 30th cycle to the discharge capacity of the first cycle.

[0126] Furthermore, the lithium secondary battery according to the present invention can maintain a ratio of 120.0% or less (30th cycle resistance increase rate) to the DCIR obtained by dividing the voltage drop (ΔV) over 60 seconds by the current in the 30th discharge cycle, when performing 30 charge-discharge cycles at 45°C and in the range of 3.0 to 4.25V with a constant current of 0.33C.

[0127] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention exhibit excellent high-temperature life characteristics and resistance characteristics in a stable manner, making them useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0128] Therefore, 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.

[0129] 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.

[0130] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0131] 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 preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0132] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0133] Examples Example 1 (An example in which the ratio of the primary firing temperature to the secondary firing temperature is 0.75) Ni 0.88 Co 0.05 Mn 0.07 (OH)2 and Al(OH)3 were mixed in a molar ratio of 1:0.02, and LiO·H2O was further mixed in so that the molar ratio of Li:transition metal (Ni+Co+Mn+Al) was 1.06:1 to prepare the reaction mixture. The reaction mixture was subjected to primary calcination at 600°C for 5 hours under an oxygen atmosphere to produce the calcined product (LiNi 0.86 Co 0.05 Mn 0.07 Al 0.02 They manufactured (containing O2).

[0134] The calcined product was mixed with H3BO3 in a weight ratio of 100:0.63, and the mixture was secondary-fired at 800°C for 5 hours under an oxygen atmosphere to produce a fired product. The fired product was mixed with water in a weight ratio of 100:120, washed with water for 5 minutes, filtered under reduced pressure, and then vacuum-dried at 130°C to produce a lithium transition metal oxide (LiNi 0.85 Co 0.05 Mn 0.07 Al 0.02 B 0.01 O2 was manufactured.

[0135] Next, the lithium transition metal oxide and H3BO3 were mixed in a weight ratio of 100:0.57, and the mixture was heat-treated at 300°C for 4 hours under an oxygen atmosphere to produce a positive electrode active material on which a coating layer containing B was formed on the surface.

[0136] Example 2 (An example in which the ratio of the primary firing temperature to the secondary firing temperature is 0.88) The cathode active material was manufactured using the same method as in Example 1, except that the primary firing was performed at 700°C instead of 600°C.

[0137] Comparative Example 1 (A comparative example in which the ratio of the primary firing temperature to the secondary firing temperature is 0.50) The positive electrode active material was manufactured using the same method as in Example 1, except that the primary calcination was performed at 400°C instead of 600°C.

[0138] Comparative Example 2 (A comparative example in which the ratio of the primary firing temperature to the secondary firing temperature is 0.63) The cathode active material was manufactured using the same method as in Example 1, except that the primary firing was performed at 500°C instead of 600°C.

[0139] Comparative Example 3 (A comparative example in which the ratio of the primary firing temperature to the secondary firing temperature is 0.94) The cathode active material was manufactured using the same method as in Example 1, except that the primary calcination was performed at 750°C instead of 600°C.

[0140] Comparative Example 4 (Comparative example in which H3BO3 was mixed during the primary firing instead of the secondary firing) Ni 0.88 Co 0.05 Mn 0.07 Mix (OH)2 and Al(OH)3 in a molar ratio of 1:0.02, then further mix LiOH·H2O so that the molar ratio of Li:transition metal (Ni+Co+Mn+Al) is 1.06:1, and add H3BO3 to this mixture. 0.88 Co 0.05 Mn 0.07 A reaction mixture was prepared by further mixing (OH)2 to 0.9 parts by weight per 100 parts by weight. The reaction mixture was subjected to primary calcination at 600°C for 5 hours under an oxygen atmosphere to produce a calcined product.

[0141] The calcined product was subjected to secondary calcination at 800°C for 5 hours under an oxygen atmosphere to produce a fired product. The fired product and water were mixed in a weight ratio of 100:120, washed with water for 5 minutes, subjected to reduced pressure filtering, and then vacuum dried at 130°C to produce a lithium transition metal oxide.

[0142] Next, the lithium transition metal oxide and H3BO3 were mixed in a weight ratio of 100:0.57, and the mixture was heat-treated at 300°C for 4 hours under an oxygen atmosphere to produce a positive electrode active material on which a coating layer containing B was formed on the surface.

[0143] Comparative Example 5 (Comparative example in which the primary boron-containing raw material was not mixed during secondary firing) Ni 0.88 Co 0.05 Mn 0.07 (OH)2 and Al(OH)3 were mixed in a molar ratio of 1:0.02, and LiO·H2O was further mixed in so that the molar ratio of Li:transition metal (Ni+Co+Mn+Al) was 1.06:1 to prepare the reaction mixture. The reaction mixture was subjected to primary calcination at 600°C for 5 hours under an oxygen atmosphere to produce a calcined product.

[0144] The calcined product was subjected to secondary calcination at 800°C for 5 hours under an oxygen atmosphere to produce a fired product. The fired product and water were mixed in a weight ratio of 100:120, washed with water for 5 minutes, subjected to reduced pressure filtering, and then vacuum dried at 130°C to produce a lithium transition metal oxide.

[0145] Next, the lithium transition metal oxide and H3BO3 were mixed in a weight ratio of 100:0.57, and the mixture was heat-treated at 300°C for 4 hours under an oxygen atmosphere to produce a positive electrode active material on which a coating layer containing B was formed on the surface.

[0146] Experimental Example 1: Confirmation of the average aspect ratio of primary particles present on the surface of the positive electrode active material. SEM(FEI TM Using a FEG250 (manufactured by the company), SEM images of the positive electrode active materials for each of Examples 1 and 2 and Comparative Examples 1 to 5 were obtained and analyzed to confirm the average aspect ratio of the primary particles present on the surface of each positive electrode active material. The results are shown in Table 1 below.

[0147] The average aspect ratio of primary particles present on the surface of the positive electrode active material was obtained using the following method. First, using the ImageJ program, the shape of one primary particle to be measured was selected from the SEM image of the positive electrode active material (selected using the ImageJ program's tools). Then, the Shape Descriptors were checked in Analyze's Set Measure and the measurement was performed to obtain the ratio of the major axis to the minor axis passing through the center of an ellipse fitted to the shape of the primary particle. Aspect ratios were obtained for 17 to 21 primary particles for each positive electrode active material, and the average was calculated and defined as the average aspect ratio of the primary particles.

[0148] Figures 1 to 7 show, in order, SEM images of the cathode active materials produced in Examples 1 and 2 and Comparative Examples 1 to 5, and tables showing the average aspect ratio of primary particles present on the surface of the cathode active materials.

[0149] [Table 1]

[0150] Experimental Example 2: Evaluation of Lithium-ion Battery Characteristics The positive electrode active material, conductive material (carbon black), and binder (polyvinylidene fluoride) prepared in Examples 1 and 2 and Comparative Examples 1 to 5 were mixed in an NMP solvent in a weight ratio of 96:2:2 to produce a positive electrode forming composition. The positive electrode forming composition was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode. Lithium metal was used as the negative electrode.

[0151] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive electrode and the lithium metal negative electrode manufactured as described above. After positioning the electrode assembly inside a battery case, an electrolyte was injected into the case to manufacture a lithium secondary battery half-cell. Here, the electrolyte used was a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMD), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, in which 1.0 M LiPF6 was dissolved.

[0152] For each lithium secondary battery half-cell manufactured as described above, CC / CV mode charging was performed at 25°C with a constant current of 0.1C up to 4.25V, followed by CC mode discharge (constant current of 0.1C) until the voltage reached 3V. The initial charge capacity, initial discharge capacity, and initial efficiency were measured and are shown in Table 2 below.

[0153] Furthermore, for each lithium secondary battery half-cell manufactured as described above, the capacity of the lithium secondary battery was measured by repeating the charge-discharge cycle 30 times at a constant current of 0.33C in the range of 3.0 to 4.25V at 45℃. In particular, the ratio of the discharge capacity after the 30th cycle to the discharge capacity after the 1st cycle was defined as the capacity retention rate, and this is shown in Table 2 below. Also, the ratio of the DCIR obtained by dividing the voltage drop (ΔV) over 60 seconds in the 30th discharge cycle by the current to the DCIR obtained by dividing the voltage drop (ΔV) over 60 seconds in the 1st discharge cycle by the current was defined as the resistance increase rate, and this is also shown in Table 2 below.

[0154] [Table 2]

[0155] Referring to Table 2 above, it can be confirmed that in the case of batteries using the positive electrode active materials of Examples 1 and 2, an initial efficiency equivalent to that of Comparative Examples 1 to 5 is achieved, the capacity retention rate at high temperatures is high, and the resistance increase rate is low, thus preventing battery degradation at high temperatures and demonstrating remarkably excellent high-temperature life characteristics.

[0156] In other words, the present invention shows that, during the production of a positive electrode active material, by adding a first boron-containing raw material in a secondary firing step after primary firing, and performing firing under conditions where the primary firing temperature and secondary firing temperature satisfy a specific ratio, the primary particles present on the surface of the manufactured positive electrode active material can have a specific aspect ratio. Furthermore, it shows that in batteries to which a positive electrode active material manufactured by the positive electrode active material manufacturing method of the present invention is applied, both the capacity retention rate at high temperatures and the resistance increase rate at high temperatures can be improved.

Claims

1. A lithium transition metal oxide containing 70 mol% or more nickel (Ni) among all metals other than lithium, in the form of secondary particles formed by the aggregation of primary particles, The lithium transition metal oxide is formed on a coating layer containing B, A positive electrode active material having an average aspect ratio of 1.8 to 6.0 for primary particles present on the surface of the lithium transition metal oxide.

2. The lithium transition metal oxide has the composition represented by the following chemical formula 1, [Chemical formula 1] Li ｘ Ni ａ１ Co ｂ１ Mn ｃ１ Al ｄ１ B ｅ１ M １ ｆ１ O ２ In the aforementioned chemical formula 1, M １ is one or more selected from Zr, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba. The positive electrode active material according to claim 1, wherein 0.90 ≤ x ≤ 1.12, 0.70 ≤ a1 ≤ 1.0, 0 ≤ b1 ≤ 0.30, 0 ≤ c1 ≤ 0.30, 0 ≤ d1 ≤ 0.20, 0 < e1 ≤ 0.20, 0 ≤ f1 ≤ 0.10, and a1 + b1 + c1 + d1 + e1 + f1 = 1.

3. (A) A step of producing a calcined product by primary calcining a reaction mixture containing a positive electrode active material precursor with nickel (Ni) of 70 mol% or more of the total metal and a lithium-containing raw material at a primary calcination temperature, (B) A step of mixing the calcined product with a first boron-containing raw material and performing secondary calcination at a secondary calcination temperature to produce a lithium transition metal oxide, (C) The process includes the step of mixing the lithium transition metal oxide with a second boron-containing raw material and heat-treating it to form a coating layer. The first boron-containing raw material is mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the calcined product. A method for producing a positive electrode active material, wherein the ratio of the primary firing temperature to the secondary firing temperature is 0.7 to 0.

9.

4. The positive electrode active material precursor has a composition represented by the following chemical formula 2-1 or the following chemical formula 2-2, [Chemical formula 2-1] Ni ａ２ Co ｂ２ Mn ｃ２ M ２ ｄ２ (OH) ２ [Chemical formula 2-2] Ni ａ２ Co ｂ２ Mn ｃ２ M ２ ｄ２ O・OH In the aforementioned chemical formulas 2-1 and 2-2, M ２ is one or more selected from Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, and Ba. A method for producing a positive electrode active material according to claim 3, wherein 0.70 ≤ a² ≤ 1.0, 0 ≤ b² ≤ 0.30, 0 ≤ c² ≤ 0.30, 0 ≤ d² ≤ 0.10, and a² + b² + c² + d² = 1.

5. The method for producing a positive electrode active material according to claim 3, wherein the reaction mixture further comprises an aluminum-containing raw material.

6. The method for producing a positive electrode active material according to claim 3, wherein the primary firing temperature is 300°C to 750°C.

7. The first boron-containing raw material is H ３ BO ３ H ４ BO ４ , B ２ O ３ LiBO ２ Li ２ B ４ O ７ , B ４ C, AlBO ２ and AlB ２ O ４ A method for producing a positive electrode active material according to claim 3, wherein the active material is one or more selected from the following.

8. The method for producing a positive electrode active material according to claim 3, wherein the secondary firing temperature is 500°C to 900°C.

9. The second boron-containing raw material is H ３ BO ３ H ４ BO ４ , B ２ O ３ LiBO ２ Li ２ B ４ O ７ , B ４ C, AlBO ２ and AlB ２ O ４ A method for producing a positive electrode active material according to claim 3, wherein the active material is one or more selected from the following.

10. The method for producing a positive electrode active material according to claim 3, wherein the second boron-containing raw material is mixed in an amount of 0.1 to 2.0 parts by weight per 100 parts by weight of the lithium transition metal oxide.

11. The method for producing a positive electrode active material according to claim 3, wherein the temperature of the heat treatment is 200°C to 400°C.

12. A positive electrode comprising the positive electrode active material described in claim 1.

13. A lithium secondary battery comprising the positive electrode described in claim 12.

Images