Positive electrode active material, method for preparing same, and positive electrode and lithium secondary battery comprising same

Abstract

A positive electrode active material according to the present invention comprises: lithium-nickel-based oxide particles each in the form of a single particle, composed of one single nodule, or quasi-single particles, which are a composite of 30 or fewer nodules; and a cobalt-containing coating layer formed on the surface of the lithium-nickel-based oxide particles, wherein XPS (Co / Ni), which is the atomic ratio of Co to Ni when the positive electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), is 0.15 or more, the standard deviation of AES (Co / Ni), which is the atomic ratio of Co to Ni when the positive electrode active material is analyzed by Auger electron spectroscopy (AES), is 0.15 or more, and the content of residual Li2CO3 in the positive electrode active material is 0.50 wt% or less.

Description

Positive electrode active material, method for producing same, positive electrode and lithium secondary battery including same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0042136, filed March 27, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a cathode active material in the form of single particles and / or pseudo-single particles having excellent high-temperature life characteristics and a gas generation reduction effect, a method for producing the same, and a cathode and a lithium secondary battery including the same.

[0005]

[0006] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0007] Lithium composite transition metal oxides are used as cathode active materials in lithium secondary batteries. Among these, lithium nickel oxides, which facilitate the implementation of large-capacity batteries, are being actively researched and developed. However, the secondary particle form has the problem of exacerbating cracking within the cathode active material during charge and discharge.

[0008] To solve the above problems, a technology was proposed to manufacture a positive electrode active material in the form of a single particle rather than a secondary particle by increasing the sintering temperature during the manufacture of lithium nickel cobalt manganese oxide.

[0009] In particular, when manufacturing a high-Ni single-particle cathode active material in which the molar ratio of Ni among the total transition metals is 80 mol% or more, the surface structure of the cathode active material may be low and the concentration of residual lithium may be high due to the high sintering temperature. In general, the surface structure completion can be improved and the concentration of residual lithium can be reduced through a coating layer formed on the surface of lithium nickel-based oxide particles.

[0010] However, when the coating layer formed on the surface of the lithium nickel-based oxide particles is not uniform, there are problems such as poor high-temperature life characteristics or increased gas generation when applied to lithium secondary batteries.

[0011] Therefore, a technology is needed to uniformly form a coating layer on the surface of lithium nickel oxide particles to improve high-temperature life characteristics and reduce gas generation.

[0012]

[0013] The present invention is intended to solve the above problems, and provides a cathode active material capable of improving high-temperature life characteristics and suppressing gas generation by including a cobalt-containing coating layer uniformly formed on the surface of a lithium nickel-based oxide, a method for producing the same, a cathode active material including the same, and a lithium secondary battery.

[0014]

[0015] [1] The present invention provides a positive electrode active material comprising a lithium nickel-based oxide particle in the form of a single particle consisting of one single nodule or a quasi-single particle consisting of a composite of 30 or fewer nodules; and a coating layer comprising cobalt formed on the surface of the lithium nickel-based oxide particle; wherein, when the positive electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of Co to Ni, XPS (Co / Ni), is 0.15 or more, and when the positive electrode active material is analyzed by Auger electron spectroscopy (AES), the standard deviation of the atomic ratio of Co to Ni, AES (Co / Ni), is 0.80 or less, and the positive electrode active material has a residual Li2CO3 content of 0.50 wt% or less.

[0016] [2] The present invention provides a positive electrode active material in the above [1], wherein the lithium nickel-based oxide particles have a nickel content of 55 mol% or more among all metals excluding lithium.

[0017] [3] In the present invention, in the above [1] or [2], the positive electrode active material is D 50 A positive electrode active material having a diameter of 2.0㎛ to 10.0㎛ is provided.

[0018] [4] The present invention provides a positive electrode active material, wherein, in at least one of the above [1] to [3], the average particle diameter of the nodules of the positive electrode active material is 1 µm to 10 µm.

[0019] [5] In the present invention, in at least one of the above [1] to [4], the positive electrode active material has a BET specific surface area of ​​0.2 m 2 / g to 1.5m 2 / g, provides a positive electrode active material.

[0020] [6] The present invention provides a positive electrode active material, wherein in at least one of the above [1] to [5], the coating layer further includes at least one selected from the group consisting of Mg, Al, Ti, V, Cr, Mn, Zr, Nb, W, and B.

[0021] [7] The present invention provides a positive electrode active material, wherein in at least one of the above [1] to [6], the lithium nickel-based oxide has a composition represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Li a Ni b Co c M 1 d M 2 e O2

[0024] In the above chemical formula 1, M 1 At least one selected from the group consisting of Mn and Al, and M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 1.0≤a≤1.5, 0.8≤b≤1.0, 0≤c≤0.2, 0≤d≤0.2, 0≤e≤0.2.

[0025] [8] The present invention provides a method for producing a positive electrode active material, comprising the steps of: mixing a transition metal precursor containing nickel, cobalt, and manganese and a lithium raw material, and performing a first firing to form a lithium nickel-based oxide in the form of a single particle consisting of one single nodule or a composite of 30 or fewer nodules; and mixing the lithium nickel-based oxide with a cobalt compound, and performing a second firing to form a positive electrode active material including a coating layer containing cobalt; wherein the lithium nickel-based oxide formed by the first firing includes Li2CO3 and LiOH, and a ratio of the LiOH content to the Li2CO3 content is 1.4 or more, and the particle size of the cobalt compound is 1500 nm or less.

[0026] [9] The present invention provides a method for manufacturing a positive electrode active material, wherein the lithium nickel oxide formed by the first calcination in the above [8] has a sum of LiOH content and Li2CO3 content of 0.5 wt% to 2.2 wt%.

[0027]

[0010] The present invention provides a method for producing a positive electrode active material, wherein, in the lithium nickel-based oxide formed by the first calcination in the above [8] or [9], the ratio of the cobalt compound content to the LiOH content is 2.00 mol% / wt% or more.

[0028]

[0011] The present invention, in at least one of the above [8] to

[0010] , the lithium nickel-based oxide formed by the first calcination has a ratio of the cobalt compound content to BET of 2.5 wt% / (m 2 / g) provides a method for manufacturing a positive electrode active material.

[0029]

[0012] The present invention provides a method for producing a positive electrode active material, wherein, in at least one of the above [8] to

[0011] , the secondary firing is performed at a temperature of 660°C to 740°C.

[0030]

[0013] The present invention provides a positive electrode comprising a positive electrode active material according to any one of the above [1] to [7].

[0031]

[0014] The present invention provides a lithium secondary battery including a positive electrode according to the above

[0013] .

[0032]

[0033] The cathode active material according to the present invention can suppress degradation of the cathode active material during the charge / discharge process and high-temperature storage of a lithium secondary battery, thereby realizing high-temperature life characteristics and a gas generation reduction effect by ensuring that (1) the atomic ratio of Co to Ni in XPS analysis, which can quantify the uniformity and content of a coating layer including cobalt formed on the surface of a lithium nickel-based oxide, the standard deviation of (2) AES (Co / Ni), which is the ratio of the content of Co to Ni in AES analysis, and (3) the residual Li2CO3 content of the cathode active material, which has the effect of suppressing side reactions between electrolytes, satisfy specific numerical ranges.

[0034] The method for manufacturing a cathode active material according to the present invention is such that the lithium nickel-based oxide formed by the first firing includes Li2CO3 and LiOH, and by controlling the content of LiOH and Li2CO3 after the first firing, the BET of the lithium nickel-based oxide after the first firing, the content and size of cobalt compounds, and the second firing temperature, the uniformity of the coating layer including cobalt formed on the surface of the lithium nickel-based oxide is improved, thereby suppressing side reactions between the lithium nickel-based oxide and the electrolyte, and realizing high-temperature life characteristics and a gas generation reduction effect.

[0035]

[0036] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0037] In the present invention, a "single particle" is a particle composed of one single nodule. In the present invention, a "quasi-single particle" means a composite particle formed of 30 or fewer nodules.

[0038] In the present invention, "nodule" means a sub-particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed under a field of view of 5000 to 20000 times using a scanning electron microscope (SEM). The average particle diameter of the nodule may be measured as the arithmetic mean value of the particle diameters of each nodule measured using a scanning electron microscope (SEM).

[0039] In the present invention, "secondary particle" means a particle formed by the aggregation of tens to hundreds, specifically more than 30, sub-particle unit bodies. To distinguish it from nodules, which are sub-particle units constituting single particles and pseudo-single particles, the sub-particle units constituting secondary particles are called "primary particles."

[0040] The expression "particle" used in the present invention may include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0041] In the present invention, "D 50 " means the particle size based on 50% of the volume cumulative particle size distribution of the positive electrode active material. The above D 50 can be measured using a laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0042] In the present invention, the “specific surface area” is measured by the BET method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0043] In the present invention, the presence or absence and content of elements on the surface of lithium nickel-based oxide can be confirmed through X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analysis.

[0044] Specifically, X-ray photoelectron spectroscopy (XPS) can be performed using a Nexsa G2 ESCA system from Thermo Fisher Scientific, and Auger electron spectroscopy (AES) can be performed using a PHI 710 device from ULVAC-PHI. Specifically, X-ray photoelectron spectroscopy (XPS) can be used to analyze the presence and content of elements at each depth in the positive electrode active material, and Auger electron spectroscopy (AES) can be used to analyze the uniformity of the coating layer on the surface of the lithium nickel oxide.

[0045]

[0046] The cathode active material, the method for producing the cathode active material, the cathode, and / or the lithium secondary battery according to the present invention comprise at least one of the following disclosed configurations, and may comprise any combination between technically possible configurations among the following configurations.

[0047]

[0048] positive electrode active material

[0049] Hereinafter, the positive electrode active material according to the present invention will be described.

[0050]

[0051] The cathode active material according to the present invention is a cathode active material including a lithium nickel-based oxide particle in the form of a single particle consisting of one single nodule or a quasi-single particle which is a composite of 30 or fewer nodules; and a coating layer including cobalt formed on the surface of the lithium nickel-based oxide particle; wherein, when the cathode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the atomic ratio of Co to Ni, XPS (Co / Ni), is 0.15 or more, and when the cathode active material is analyzed by Auger electron spectroscopy (AES), the standard deviation of the atomic ratio of Co to Ni, AES (Co / Ni), is 0.80 or less, and the cathode active material has a residual Li2CO3 content of 0.50 wt% or less.

[0052]

[0053] The lithium nickel-based oxide particles are in the form of single particles consisting of one single nodule or pseudo-single particles consisting of a composite of 30 or fewer, preferably 2 to 20, and more preferably 2 to 10 nodules. Such lithium nickel-based oxide particles in the form of single particles and / or pseudo-single particles have higher particle strength than lithium nickel-based oxide particles in the form of existing secondary particles in which tens to hundreds of primary particles are aggregated, and thus particle breakage is reduced during rolling.

[0054] In addition, in the case of the lithium nickel-based oxide in the form of single particles or pseudo-single particles according to the present invention, since the number of sub-components (i.e., nodules) constituting the particles is small, the change due to volume expansion and contraction of the primary particles during charge and discharge is small, and accordingly, the occurrence of cracks inside the particles is also significantly reduced.

[0055]

[0056] The positive electrode active material according to the present invention may have a composition in which the content of nickel among all metals excluding lithium is 55 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more. The Ni-based positive electrode active material has a high capacity because the content of nickel among the transition metals constituting the positive electrode active material is higher than that of other transition metals, but has unstable Ni present on the surface of the positive electrode active material. 3+ , Ni 4+ There is a limitation of structural instability due to ions. To address this structural instability, various technologies are being studied to modify the surface of the positive electrode active material.

[0057] In particular, when manufacturing a single particle cathode active material in which the nickel content is 80 mol% or more among all metals excluding lithium, there was a problem that the surface structure of the cathode active material was low due to the high sintering temperature and the concentration of residual lithium could be high. To improve this, the surface structure completion can be improved and the concentration of residual lithium can be reduced through a coating layer formed on the surface of the lithium nickel-based oxide particle.

[0058] However, when the coating layer formed on the surface of the lithium nickel-based oxide particles is not uniform, there are problems such as poor high-temperature life characteristics or increased gas generation when applied to lithium secondary batteries.

[0059]

[0060] Accordingly, the inventors of the present invention confirmed that when (1) the standard deviation of XPS (Co / Ni), which is the atomic ratio of Co to Ni during XPS analysis, and (2) AES (Co / Ni), which is the atomic ratio of Co to Ni during AES analysis, satisfies a specific numerical range in order to quantify the uniformity of the coating layer formed on the surface of lithium nickel-based oxide particles, and (3) the residual Li2CO3 content of the positive electrode active material satisfies a specific numerical range in order to suppress side reactions between lithium nickel-based oxide particles and electrolyte and reduce the amount of gas generated, there is an effect of improving the high-temperature life characteristics and the amount of gas generated.

[0061] The atomic ratio of Co to Ni in the XPS analysis, XPS (Co / Ni), can be measured by checking the presence and content of Ni and Co in the region from the surface of the positive electrode active material to the coating layer including cobalt formed on the surface of the lithium nickel-based oxide. Since it is easy to check the presence and content of Ni and Co in the entire coating layer including cobalt included in the positive electrode active material particles in the XPS analysis, the atomic ratio of Co to Ni in the XPS analysis, XPS (Co / Ni), can serve as a parameter indicating the content of the cobalt-containing coating layer on the surface of the positive electrode active material.

[0062] The atomic ratio of Co to Ni, XPS (Co / Ni), in the XPS analysis may be 0.15 or more, 0.15 to 0.30, 0.17 to 0.25, or 0.20 to 0.22. The positive electrode active material having the XPS (Co / Ni) of less than 0.15 means that the content of the cobalt-containing coating layer on the surface is low, and the interface between the electrolyte and the positive electrode active material having a high-nickel (High-Ni) composition cannot be properly protected, which may cause a problem in that surface degradation cannot be effectively suppressed during high-temperature cycling and high-temperature storage. Therefore, when the XPS (Co / Ni) satisfies the above-mentioned range, the content of the cobalt-containing coating layer on the surface of the positive electrode active material is sufficient, so that the coating layer can sufficiently protect the interface between the electrolyte and the positive electrode active material, and thus the high-temperature life characteristics and high-temperature storage characteristics can be excellent. The standard deviation of AES (Co / Ni), which is the ratio of Co content to Ni in the AES analysis, is D of the positive electrode active material powder. 50 The standard deviation of the ratio of Co to Ni content may be obtained by selecting a plurality of measurement areas, specifically 15 or more, more specifically 15, on the surface of positive electrode active material particles having the same particle size, and measuring the standard deviation of the ratio of Co to Ni content by Auger electron spectroscopy (AES) measured in each of the plurality of measurement areas. At this time, the plurality of measurement areas may have a shape such as a square, a circle, an ellipse, etc., but is not limited thereto, and a local area on the surface of the positive electrode active material particle is sufficient. When the plurality of measurement areas are square, the length of one side of the square may be 10% or less, 0.5% to 10%, 1% to 5%, or 1.5% to 4.5% of the D50 of the positive electrode active material powder. When the above range is satisfied, the reliability of the uniformity according to the standard deviation value of the AES (Co / Ni) may be excellent. The plurality of measurement areas may be mutually D50 of the positive electrode active material powder. 50The distance may be 15% or less, 5 to 13%, 8 to 12%, or 10% of the positive electrode active material powder. Alternatively, the plurality of measurement areas may have a distance of D of the positive electrode active material powder. 50 It may have a distance of 1㎛ or less, 0.1 to 1㎛, 0.2 to 0.7㎛, 0.3 to 0.5㎛, or 0.4㎛.

[0063] The standard deviation of AES (Co / Ni), which is the ratio of Co content to Ni in the above AES analysis, can confirm the distribution of the ratio of Co content to Ni in a local area rather than the entire surface of the positive electrode active material particle, and therefore can serve as a parameter indicating the uniformity of the cobalt-containing coating layer on the surface of the positive electrode active material.

[0064] The standard deviation of AES(Co / Ni), which is the ratio of Co content to Ni during the above AES analysis, may be 0.8 or less, 0.5 or less, 0.2 to 0.5, or 0.25 to 0.35. A cathode active material having a standard deviation of AES(Co / Ni) exceeding 0.8 means that the cobalt-containing coating layer on the surface is not uniform. In this case, even if a Co coating with the same content is applied, the Co coating may be thinly applied to a specific surface area, and the interface between the electrolyte and the cathode active material with a high-nickel (High-Ni) composition in that area cannot be properly protected, which may cause a problem in that surface degradation cannot be effectively suppressed during high-temperature cycling and high-temperature storage. Therefore, when the standard deviation of AES (Co / Ni), which is the ratio of Co content to Ni during the AES analysis, satisfies the above-mentioned range, a cobalt-containing coating layer on the surface of the positive electrode active material can be formed with a uniform thickness over the entire surface, so that the interface between the electrolyte and the positive electrode active material can be uniformly protected, and thus, high-temperature life characteristics and high-temperature storage characteristics can be excellent.

[0065] The residual Li2CO3 content of the positive electrode active material may be 0.5 wt% or less, 0.4 wt% or less, or 0.01 wt% to 0.4 wt%. The positive electrode active material having a residual Li2CO3 content of more than 0.5 wt% has a problem in that the side reaction between the lithium nickel-based oxide particles and the electrolyte may excessively increase, resulting in increased gas generation, which may deteriorate the performance of the lithium secondary battery. Specifically, even if the standard deviations of the XPS (Co / Ni) and AES (Co / Ni) satisfy the above numerical range, if the residual Li2CO3 content of the final positive electrode active material does not satisfy the above numerical range, the amount of gas generation may significantly increase compared to when the residual Li2CO3 content satisfies the above numerical range, which may deteriorate the performance of the lithium secondary battery. Therefore, if the residual Li2CO3 content of the final positive electrode active material satisfies the above-described range, the side reaction between the positive electrode active material and the electrolyte may be suppressed, thereby reducing the amount of gas generation.

[0066]

[0067] The coating layer may include at least one selected from the group consisting of Mg, Al, Ti, V, Cr, Mn, Zr, Nb, W, and B, preferably Co and Al, and more preferably Co. Specifically, the positive electrode active material may include the coating layer in an amount of 0.18 wt% to 2.5 wt%, 0.5 wt% to 2.0 wt%, or 1.0 wt% to 1.8 wt%.

[0068]

[0069] The positive electrode active material according to the present invention is D 50 The D of the positive electrode active material according to the present invention may be 2.0 μm to 10.0 μm, 3.0 μm to 7.0 μm, or 3.5 μm to 5.0 μm. 50 When the above range is satisfied, high energy density and low initial resistance characteristics can be realized. D of the positive electrode active material 50If it is less than 2.0㎛, it is difficult to implement high rolling density and the energy density may be low, and D 50 If it exceeds 10.0㎛, lithium mobility in the positive electrode active material may decrease, which may increase the initial resistance of the lithium secondary battery containing it.

[0070]

[0071] The cathode active material according to the present invention may have an average particle size of nodules of 1 µm to 10 µm, 2 µm to 6 µm, or 3 µm to 5 µm. When the average particle size of the nodules of the cathode active material according to the present invention satisfies the above range, high energy density and low initial resistance characteristics can be realized. When the average particle size of the nodules of the cathode active material according to the present invention is less than 1 µm, the overall specific surface area of ​​the cathode active material may increase, which may increase electrolyte side reactions, and when the average particle size of the nodules exceeds 10 µm, lithium mobility in the cathode active material may decrease, which may deteriorate the output characteristics of the battery.

[0072]

[0073] The positive electrode active material according to the present invention has a BET specific surface area of ​​0.2 m 2 / g to 1.5m 2 / g, preferably 0.3m 2 / g to 1.2m 2 / g, 0.4m 2 / g to 1.0m 2 / g, or 0.4m 2 / g to 0.8m 2 / g. The BET specific surface area of ​​the positive electrode active material is 0.2 m 2 If it is less than / g, there is a concern about initial output reduction, and if the BET surface area is less than 1.5m 2 / g exceeds, there are concerns about high-temperature life, resistance increase rate, and storage gas. Therefore, if the BET specific surface area of ​​the positive electrode active material satisfies the above numerical range, excellent performance in terms of output performance and high-temperature durability can be realized.

[0074]

[0075] Specifically, the lithium nickel-based oxide may be a particle having a composition as represented by the following chemical formula 1.

[0076] [Chemical Formula 1]

[0077] Li a Ni b Co c M 1 d M 2 e O2

[0078] In the above chemical formula 1, M 1 is Mn, Al or a combination thereof, preferably Mn or a combination of Mn and Al, and M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo. M 2 Although elements are not essential, when included in appropriate amounts, they can promote grain growth during firing or play a role in improving crystal structure stability.

[0079] The above a represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 1.0≤a≤1.5, 1.0≤a≤1.2, or 1.00≤a≤1.15. When the molar ratio of lithium satisfies the above range, a stable layered crystal structure can be formed.

[0080] The above b represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.8≤b<1.0, 0.85≤b<1.0, or 0.90≤b<1. When the molar ratio of nickel satisfies the above range, excellent capacity characteristics are exhibited, and in particular, when the molar ratio of nickel is 0.90 or more, even better capacity characteristics can be realized.

[0081] The above c represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and 0≤c≤0.2, 0 <c<0.2, 또는 0<c<0.18일 수 있다.

[0082] The above d is M of all metals except lithium in lithium nickel oxide. 1 It represents the molar ratio of , 0≤d≤0.2, 0 <d<0.2, 또는 0<d<0.18일 수 있다.

[0083] The above e is M of all metals except lithium in lithium nickel oxide. 2 It represents the molar ratio of elements, and can be 0≤e≤0.2, 0≤e≤0.15, or 0≤e≤0.1.

[0084]

[0085] Method for manufacturing positive electrode active material

[0086] Next, a method for manufacturing the positive electrode active material of the present invention will be described.

[0087]

[0088] A method for manufacturing a cathode active material according to the present invention comprises the steps of: mixing a transition metal precursor containing nickel, cobalt, and manganese and a lithium raw material, and performing a first firing to form a lithium nickel-based oxide in the form of a single particle consisting of one single nodule or a quasi-single particle which is a composite of 30 or fewer nodules; and mixing the lithium nickel-based oxide with a cobalt compound, and performing a second firing to form a cathode active material including a coating layer containing cobalt. The lithium nickel-based oxide formed by the first firing includes Li2CO3 and LiOH, and a ratio of the LiOH content to the Li2CO3 content is 1.4 or more, and the particle size of the cobalt compound is 1500 nm or less.

[0089]

[0090] Each step of the method for manufacturing a positive electrode active material is described in detail.

[0091]

[0092]

[0093] (Transition metal precursor preparation step)

[0094] First, a lithium raw material is mixed with a transition metal precursor containing nickel, cobalt, and manganese and calcined for the first time to form a lithium nickel oxide in the form of a single particle consisting of one single nodule or a quasi-single particle complex consisting of 30 or fewer nodules.

[0095] At this time, the positive electrode active material precursor may be purchased and used as a commercially available precursor such as nickel-cobalt-manganese hydroxide, or may be manufactured according to a precursor manufacturing method known in the art, such as a co-precipitation method.

[0096] For example, nickel (Ni), cobalt (Co) and M 1 After preparing a transition metal-containing solution containing an ammonium cation, a complex forming agent containing an ammonium cation and a basic aqueous solution are added to the transition metal-containing solution to cause a co-precipitation reaction, thereby preparing a positive electrode active material precursor.

[0097] The above transition metal-containing solution contains nickel-containing raw materials, cobalt-containing raw materials, M 1 It may contain the raw material, and the above M 1 The containing raw material may be a manganese-containing raw material and / or an aluminum-containing raw material.

[0098] The nickel-containing raw material may be, for example, a nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be, but is not limited to, Ni(OH)2, NiO, NiOOH, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, fatty acid nickel salts, nickel halides or combinations thereof.

[0099] The cobalt-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be, but is not limited to, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4, Co(SO4)2ㆍ7H2O or a combination thereof.

[0100] The manganese-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide or a combination thereof, and specifically, may be, but is not limited to, manganese oxides such as Mn2O3, MnO2, Mn3O4; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylic acid salts, manganese citrate, manganese fatty acid salts; manganese oxyhydroxide, manganese chloride or a combination thereof.

[0101] The aluminum-containing raw material may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3 aluminum halides or combinations thereof.

[0102] Transition metal containing solution contains nickel containing raw material, cobalt containing raw material and M 1 It is manufactured by adding the raw material containing nickel to a solvent, specifically, water, or a mixed solvent of an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water, or an aqueous solution of a raw material containing nickel, an aqueous solution of a raw material containing cobalt, and M 1 It may be manufactured by mixing the raw materials contained therein.

[0103] The ammonium cation-containing complex forming agent may be, but is not limited to, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof. Meanwhile, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, and in this case, the solvent may be water, or a mixture of water and an organic solvent (specifically, alcohol, etc.) that can be uniformly mixed with water.

[0104] The basic compound may be a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. The basic compound may also be used in the form of an aqueous solution, in which case the solvent may be water, or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.).

[0105] The basic compound is added to adjust the pH of the reaction solution, and can be added in an amount such that the pH of the metal solution becomes 8 to 12.

[0106] The co-precipitation reaction can be carried out in an inert atmosphere such as nitrogen or argon, at a temperature range of 35°C to 80°C.

[0107] Nickel-cobalt-M by the above process 1 The positive electrode active material precursor particles of hydroxide are generated and precipitated in the reaction solution. Nickel-containing raw material, cobalt-containing raw material and M 1 By controlling the concentration of the contained raw material, a positive electrode active material precursor having a nickel (Ni) content of 55 mol% or more among the total metal content can be manufactured. The precipitated positive electrode active material precursor particles can be separated and dried according to a conventional method to manufacture a positive electrode active material precursor.

[0108]

[0109] Afterwards, the positive electrode active material precursor and the lithium raw material can be mixed.

[0110] The lithium raw material may include lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and any one of these or a mixture of two or more thereof may be used.

[0111] The positive electrode active material precursor and the lithium source material may be mixed in a molar ratio of, for example, but not limited to, about 1:1, about 1:1.05, about 1:1.10, about 1:1.15, or about 1:1.20.

[0112]

[0113] (1st firing)

[0114] Thereafter, the mixture may be subjected to primary calcination to form a lithium nickel oxide in the form of a single particle consisting of one single nodule or a quasi-single particle complex consisting of 30 or fewer nodules.

[0115] The above first firing can be performed in an air or oxygen atmosphere. The above first firing can be performed at a temperature of 600°C to 1000°C, 750°C to 950°C, or 800°C to 900°C. The above first firing can be performed for 4 hours to 12 hours, 6 hours to 12 hours, or 8 hours to 12 hours. When the above first firing and time satisfy the above ranges, a lithium nickel-based oxide in the form of a single particle or a composite of 30 or fewer nodules, which is a single particle rather than a secondary particle, can be formed. In the case of a cathode active material in the form of a single particle or a quasi-single particle, the contact area with the electrolyte is smaller than that of a conventional secondary particle type cathode active material, so that the side reaction with the electrolyte is less, and the particle strength is excellent, so that the particle breakage is less during electrode manufacture. Therefore, when applying a cathode active material in the form of a single particle or pseudo-single particle, there is an advantage of excellent gas generation and life characteristics.

[0116] The lithium nickel-based oxide formed by the first calcination includes Li2CO3 and LiOH, and the Li2CO3 content after the first calcination may be 1.0 wt% or less, 0.7 wt% or less, or 0.3 wt% to 0.5 wt%, and the LiOH content after the first calcination may be 1.2 wt% or less, 0.4 wt% to 1.2 wt%, or 0.6 wt% to 1.1 wt%. After the first calcination, the residual lithium reacts with the Co coating source to form a coating layer of an oxide series containing Li and Co, and the Li2CO3 content refers to the content of a lithium form having relatively low reactivity with the Co coating source, and the LiOH content refers to the content of a lithium form having relatively high reactivity with the Co coating source. If necessary, the residual lithium content after the first calcination can be controlled by a supply and exhaust device of the calciner.

[0117]

[0118] The ratio of the LiOH content to the Li2CO3 content may be 1.4 or more, 1.4 to 2.5, or 1.7 to 2.0. Even if the same amount of residual lithium content exists, if the ratio of LiOH, which is relatively highly reactive with the Co coating source, is high, a coating layer with relatively higher uniformity can be formed even if the Co coating is performed in the same process.

[0119] The lithium nickel-based oxide formed by the first calcination may have a sum of LiOH content and Li2CO3 content of 0.5 wt% to 2.2 wt%, 0.6 wt% to 2.0 wt%, or 0.7 wt% to 1.7 wt%. If the residual lithium is too much, there is a high possibility that the residual lithium will remain in excess even after Co coating, resulting in poor slurry stability when producing storage gas and electrodes. In addition, if the residual lithium is too insufficient compared to the Co coating source, it may be difficult to form an appropriate Li-Co-O series coating layer, which may limit the implementation of effective high-temperature life improvement.

[0120] The BET of the lithium nickel oxide formed by the above first calcination is 0.2 m 2 / g to 1.5m 2 / g, 0.3m 2 / g to 1.2m 2 / g, or 0.4m 2 / g to 0.8m 2 / g. If the BET is too high compared to the Co coating content, the coating layer may not cover the entire surface area of ​​the anode, which may limit the improvement of performance during high-temperature life and high-temperature storage. Conversely, if the coating layer is excessively formed compared to the specific surface area, the initial resistance performance may be inferior. The BET of the lithium nickel-based oxide can be adjusted by a grinding method such as a mechanical milling method and firing conditions, as needed.

[0121]

[0122] (Secondary firing)

[0123] Next, the lithium nickel-based oxide is mixed with a cobalt compound and subjected to secondary calcination to form a positive electrode active material including a coating layer containing cobalt. Specifically, the surface of the lithium nickel-based oxide particles is coated with a cobalt compound.

[0124] In the above secondary firing, the lithium remaining on the surface of the lithium nickel-based oxide and the cobalt of the coating material can react to produce lithium cobalt oxide. If the residual lithium is removed by forming the coating layer, the washing process for removing the residual lithium can be omitted, thereby simplifying the process. In addition, in the process of performing the washing process, the oxidation number of Ni on the surface of the positive electrode active material particles is generally electrically inactive Ni. +2 There is a tendency for the resistance to increase as it changes, but if the washing process is omitted, the change in the Ni oxidation number can be minimized, which can have the effect of suppressing the increase in resistance.

[0125] The above cobalt compound may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, may be Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4, Co(SO4)2ㆍ7H2O or a combination thereof, but is not limited thereto.

[0126] The total molar number of the cobalt compound may be mixed at 4.0 mol% or less, 0.3 mol% to 4.0 mol%, or 1.0 mol% to 3.0 mol% relative to the molar number of the lithium nickel-based oxide. When the content of the cobalt compound satisfies the above numerical range, a coating layer containing an appropriate amount of cobalt is formed on the surface of the lithium nickel-based oxide particles, thereby suppressing side reactions between electrolytes and improving the performance of the lithium secondary battery.

[0127] The particle size of the cobalt compound may be 1500 nm or less, 100 nm to 1000 nm, or 200 nm to 500 nm. When the particle size of the cobalt compound satisfies the above numerical range, if the cobalt compound particle size is larger than 1500 nm, the coating uniformity decreases, which limits the improvement of high-temperature lifespan and high-temperature storage performance.

[0128] The secondary firing may be performed at a temperature of 660°C to 740°C, 680°C to 720°C, or 690°C. The secondary firing may be performed for 4 to 12 hours, 6 to 12 hours, or 8 to 12 hours.

[0129] As a result of secondary firing by mixing lithium nickel-based oxide with a cobalt compound under the above temperature and time, if the secondary firing temperature is too high, the Co coating material diffuses excessively into the bulk, reducing the coating influence, and if the secondary firing temperature is too low, the uniformity of the coating layer decreases. Therefore, by applying an appropriate secondary firing temperature, the high-temperature life characteristics can be improved.

[0130]

[0131] The lithium nickel-based oxide formed by the first calcination may have a ratio of the cobalt compound content to the LiOH content of 2.00 mol% / wt% or more, 2.50 mol% / wt% or more, or 2.70 mol% / wt% to 3.50 mol% / wt%. The Li2CO3 content refers to the content of a lithium form that has relatively low reactivity with the Co coating source, and the LiOH content refers to the content of a lithium form that has relatively high reactivity with the Co coating source. Therefore, in order to form a coating layer with high uniformity, the LiOH content is more important than the Li2CO3 content, and when the Co coating content and the LiOH ratio are limited within the above range, an appropriate Li-Co-O series coating layer is formed.

[0132] The lithium nickel oxide formed by the first calcination has a ratio of the cobalt compound content to BET of 2.5 wt% / (m 2 / g) or more, 3.0 wt% / (m 2 / g) to 10.0 wt% / (m 2 / g), or 4.0 wt% / (m 2 / g) to 6.0 wt% / (m 2 / g). If the BET is too large compared to the Co coating content, the coating layer may not cover the entire surface area of ​​the anode, which may limit the improvement of performance during high-temperature life and high-temperature storage. If the BET is too small compared to the Co coating content, an excessive coating layer may be formed compared to the specific surface area, which may result in poor initial resistance performance.

[0133]

[0134] anode

[0135] The positive electrode according to the present invention comprises the positive electrode active material of the present invention described above. Specifically, the positive electrode comprises a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material of the present invention. Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0136]

[0137] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is easily adhered to by the positive electrode active material layer and does not react within the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0138]

[0139] The above positive electrode active material layer may optionally include a conductive material and a binder, together with the positive electrode active material, as needed.

[0140] At this time, the positive electrode active material may be included in an amount of 80% to 99% by weight, more specifically 90% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0141]

[0142] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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 tubes such as carbon nanotubes; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.01 wt% to 10 wt%, preferably 0.1 wt% to 9 wt%, and more preferably 0.1 wt% to 5 wt%, based on the total weight of the positive electrode active material layer.

[0143]

[0144] The above binder serves to improve 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), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer.

[0145]

[0146] The above-mentioned positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode slurry composition, prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder, a conductive agent, and a dispersant in a solvent as needed, is applied onto a positive electrode current collector, followed by drying and rolling.

[0147] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0148]

[0149] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling the resulting film from the support, and laminating the resulting film onto a positive electrode current collector.

[0150]

[0151] lithium secondary battery

[0152] Next, a lithium secondary battery according to the present invention will be described.

[0153]

[0154] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description thereof will be omitted, and only the remaining components will be specifically described below.

[0155] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0156]

[0157] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0158] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0159]

[0160] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0161] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof 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 alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibers, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch derived cokes.

[0162] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt%, 82 wt% to 99 wt%, or 84 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0163]

[0164] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0165]

[0166] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be included in an amount of 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include 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 fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0167]

[0168] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support, and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0169]

[0170] Meanwhile, 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 any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0171]

[0172] In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

[0173] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0174] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may 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; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0175]

[0176] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - At least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0177]

[0178] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10.0 wt% based on the total weight of the electrolyte.

[0179]

[0180] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0181] 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.

[0182] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0183]

[0184] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0185]

[0186] Examples and Comparative Examples

[0187] Example 1

[0188] The transition metal precursor with a molar ratio of Ni:Co:Mn of 96:1:3 and the lithium raw material (LiOH) were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.2, and then first calcined at 870℃ for 10 hours in a calcination furnace, and milled to obtain lithium nickel-based oxide LiNi in the form of single particles. 0.96 Co 0.01 Mn 0.03 O2 was manufactured.

[0189] Afterwards, the above-mentioned sintered material was mixed with 23 mol% of Co(OH) and then sintered a second time at 690°C for 10 hours to produce a single particle type positive electrode active material powder having a coating layer containing cobalt (Co) formed on the surface.

[0190] Example 2 and Comparative Examples 1 to 7

[0191] The content and size of the cobalt compound applied in the manufacture of the positive electrode active material powder in Example 2 and Comparative Examples 1 to 7, and the secondary firing temperature are shown in [Table 1] below.

[0192] Specifically, in the case of Comparative Example 1, there is a difference in that the speed of the temperature reduction section during the first firing was lowered by 20% compared to Example 1, thereby reducing LiOH, which is highly reactive with the cobalt compound, and increasing Li2CO3 among the residual lithium content ratios after the first firing. In the case of Comparative Example 2, there is a difference in that a cobalt compound having a larger particle size than the cobalt compound applied in Example 1 was used when manufacturing the positive electrode active material powder. In the case of Comparative Example 3, compared to Example 1, the second firing temperature was lowered, so that the cobalt compound was pushed toward the surface and distributed in large quantities on the polar surface, but the uniformity decreased along with it. In the case of Comparative Example 5, there is a difference in that the crushing strength after the first firing was increased by 15% compared to Example 1, thereby increasing the BET. This means that the specific surface area of ​​the compound after the first firing increases relative to the amount of cobalt compound introduced. In the case of Comparative Example 6, the lithium (Li) input ratio during the first firing was increased by 3% compared to Example 1, thereby intentionally increasing the residual lithium content after the first firing. In the case of Comparative Examples 6 and 7, the residual lithium including LiOH after the first firing was excessively large compared to the amount of cobalt compound input, so that the residual lithium remaining after coating also increased, resulting in an increase in the amount of gas generated during high-temperature storage.

[0193] Except for the above, a single particle type positive electrode active material powder was manufactured in the same manner as in Example 1.

[0194] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Cobalt compound content [mol%] 3 2 2 2 2 2 2 3 Cobalt compound particle size [nm] 4 0 4 0 4 0 3 0 0 4 0 4 0 4 0 4 0 4 0 4 0 4 0 4 0 2 sintering temperature [℃] 6 9 0 6 9 0 6 9 0 6 5 0 7 5 0 6 9 0 6 9 0 6 9 0

[0195] Experimental Example 1

[0196] In Examples 1 to 2 and Comparative Examples 1 to 7, lithium nickel oxide particles were collected after the first calcination, and the LiOH and Li2CO3 contents on the surface of the lithium nickel oxide were measured. Specifically, the LiOH and Li2CO3 contents on the surface of the lithium nickel oxide were measured through pH titration, and a T5 from Mettler Toledo was used as a pH meter.

[0197] In addition, after the first calcination, lithium nickel oxide in the form of single particles was collected and the BET was measured. Specifically, the BET of the lithium nickel oxide is measured by the BET method, and can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan.

[0198] The measurement results are shown in [Table 2] below.

[0199]

[0200] Using the above measurement results, the ratio of the LiOH content to the Li2CO3 content after the first calcination, the sum of the LiOH content and the Li2CO3 content after the first calcination, the ratio of the cobalt compound content to the LiOH content after the first calcination, and the ratio of the cobalt compound content to the BET of the lithium nickel-based oxide after the first calcination were calculated. The calculation results are shown in [Table 2] below.

[0201] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 LiOH content after the 1st firing [wt%] 1.10.60.30.60.60.60.61.11.2 Li2CO3 content after the 1st firing [wt%] 0.50.30.60.30.30.30.30.50.7 BET of lithium nickel oxide after the 1st firing [m 2 / g]0.50.50.50.50.50.50.9 ... 2 / g)]6.04.04.04.04.04.04.02.24.06.0

[0202] Experimental Example 2: XPS Analysis of Positive Electrode Active Material

[0203] The ratio of Co and Ni element contents [unit: at%] on the surface of the positive electrode active materials of Examples 1 to 2 and Comparative Examples 1 to 7 was measured using X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific, Nexsa G2 ESCA system). The atomic ratio of Co to Ni, XPS (Co / Ni), during XPS analysis is shown in [Table 3] below.

[0204] Specifically, the positive electrode active materials in powder form of Examples 1 to 2 and Comparative Examples 1 to 7 were sampled in a holder, and measured and data processed under the following conditions.

[0205] - X-ray source: Monochromated Al Kα (1486.6eV)

[0206] - X-ray spot size: 400㎛

[0207] - Operation mode: CAE (Constant Analyzer Energy) mode

[0208] - Survey scan: pass energy 200eV, energy step 1eV

[0209] - Narrow scan: scanned mode, pass energy 100eV, energy step 0.1eV

[0210] - Charge compensation: flood gun 1.5V, 150㎂

[0211] - SF: Al THERMO1

[0212] - ECF: TPP-2M

[0213] - BG subtraction: Shirley background

[0214] XPS(Co / Ni)Example 10.22Example 20.20Comparative Example 10.18Comparative Example 20.21Comparative Example 30.23Comparative Example 40.09Comparative Example 50.12Comparative Example 60.18Comparative Example 70.22

[0215] Experimental Example 3: AES Analysis of Positive Electrode Materials - Standard Deviation

[0216] Auger electron spectroscopy (AES) was performed using a PHI 710 device from ULVAC-PHI. The positive active material powders of Examples 1 to 2 and Comparative Examples 1 to 7 were sprayed on aluminum foil and fixed, and then loaded into the AES chamber. Three particles with a particle diameter of 3 to 5 μm were selected, and the surface of each particle was AEM mapped to quantify the Co / Ni standard deviation of the entire pixel. At this time, the total number of pixels for one particle was 10,000 or more, and the element-specific RSF (Relative sensitivity factor) was reflected in the element-specific mapped intensity to convert it to a quantitative value, and the mapping image was converted to Co / Ni to exclude the effect of height.

[0217] Specifically, measurements and data processing were performed under the following conditions. The results are shown in [Table 4] below.

[0218] - Electron energy analyzer: CMA (Cylindrical Mirror Analyzer)

[0219] - Electron Beam Energy: 10kV

[0220] - Target Current: 1nA

[0221] Standard deviation of AES(Co / Ni) Example 10.33 Example 20.28 Comparative Example 10.90 Comparative Example 21.10 Comparative Example 31.00 Comparative Example 40.30 Comparative Example 50.85 Comparative Example 60.90 Comparative Example 70.35

[0222] Experimental Example 4: Measurement of Residual Lithium Content in Positive Electrode Active Material

[0223] The residual lithium content of the positive electrode active materials of Examples 1 to 2 and Comparative Examples 1 to 7 was measured. The measurement results are shown in [Table 5] below.

[0224] The residual lithium content present on the surface of the positive electrode active material was measured through pH titration, using a T5 pH meter from Mettler Toledo. Specifically, 10 g of each of the positive electrode active material powders manufactured in Examples 1 to 2 and Comparative Examples 1 to 7 was stirred in 100 mL of distilled water for 5 minutes, and then a 0.1 N HCl solution was added to the solution, thereby performing pH titration.

[0225] Residual Li2CO3 content [wt%] Example 10.40 Example 20.30 Comparative Example 10.30 Comparative Example 20.27 Comparative Example 30.27 Comparative Example 40.27 Comparative Example 50.27 Comparative Example 60.45 Comparative Example 70.65

[0226] Experimental Example 5: Evaluation of High-Temperature Lifetime Characteristics and Gas Emission

[0227] The high-temperature life characteristics and gas generation amount were evaluated for lithium secondary battery half cells manufactured as follows using the positive electrode active materials of Examples 1 to 2 and Comparative Examples 1 to 7.

[0228] <Manufacturing of Lithium Secondary Batteries>

[0229] The positive electrode active material, conductive material (carbon black), and PVDF binder manufactured in Examples 1 to 2 and Comparative Examples 1 to 7, respectively, were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to manufacture a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode.

[0230] Lithium metal was used as the negative electrode, and a separator was interposed between the positive and negative electrodes manufactured by the above-described method to manufacture an electrode assembly, which was then placed inside a battery case, and an electrolyte was injected into the case to manufacture a battery cell. The electrolyte was manufactured by dissolving 0.6 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:2:1 by volume, and adding 2 wt% of vinylene carbonate (VC).

[0231]

[0232] Specifically, the high-temperature life characteristics were measured by charging and discharging each lithium secondary battery half cell at 0.33C at 45°C in a voltage range of 2.5 V to 4.35 V for 300 cycles, with one cycle being considered as charging and discharging, and then measuring the capacity retention rate using a PNE cycler. The measurement results are shown in [Table 6] below.

[0233] In addition, the amount of gas generation was measured by charging each lithium secondary battery manufactured above in CC-CV mode 1C until 4.25 V, then disassembling the secondary battery to separate the positive electrode. Then, 400 mg of the positive electrode and 15 μL of electrolyte were placed in a pouch-type battery case and sealed to manufacture a cell, and the cell was stored at 60°C for 8 weeks, and the cell volume change (△Cell volume, unit: △mL / g) before and after high-temperature storage was measured. The cell volume change was measured by placing the cell in water and measuring the volume change of the water. The measurement results are shown in [Table 6] below.

[0234] Capacity retention rate [%]Gas generation amount [mL / g]Example 192.50.16Example 292.60.17Comparative example 189.50.75Comparative example 287.50.75Comparative example 388.60.72Comparative example 488.90.80Comparative example 587.80.78Comparative example 688.80.85Comparative example 791.50.79

[0235] Through the above [Table 6], it can be confirmed that the lithium secondary batteries including the positive electrode active materials of Examples 1 to 2 have superior high-temperature life characteristics and have the effect of reducing gas generation compared to the lithium secondary batteries including the positive electrode active materials of Comparative Examples 1 to 7. Specifically, it can be confirmed that the lithium secondary batteries including the positive electrode active materials of Comparative Examples 1 to 3 and 6, in which the XPS (Co / Ni) is 0.15 or more, the residual Li2CO3 content of the final positive electrode active material is 0.50 wt% or less, but the standard deviation of AES (Co / Ni) exceeds 0.8, have inferior high-temperature life characteristics and have high gas generation compared to the lithium secondary batteries including the positive electrode active materials of Examples 1 to 2. In addition, the standard deviation of AES (Co / Ni) is 0.8 or more, the residual Li2CO3 content of the final positive electrode active material is 0.50 wt% or less, but the XPS (Co / Ni) is 0.15 It can be confirmed that the lithium secondary battery including the positive electrode active material of Comparative Example 4, which is less than 100%, has poor high-temperature life characteristics and a high amount of gas generation compared to the lithium secondary batteries including the positive electrode active materials of Examples 1 and 2.

[0236] In addition, it can be confirmed that the lithium secondary battery including the cathode active material of Comparative Example 5, which satisfies that the residual Li2CO3 content of the final cathode active material is 0.50 wt% or less, but has XPS (Co / Ni) of less than 0.15 and a standard deviation of AES (Co / Ni) of 0.8 or less, has poor high-temperature life characteristics and a high gas generation amount compared to the lithium secondary batteries including the cathode active materials of Examples 1 and 2.

[0237] In addition, it can be confirmed that the lithium secondary battery including the cathode active material of Comparative Example 7, which satisfies that XPS (Co / Ni) is 0.15 or more and the standard deviation of AES (Co / Ni) is 0.8 or less, but the residual Li2CO3 content of the final cathode active material exceeds 0.50 wt%, has inferior high-temperature life characteristics and a high amount of gas generation compared to the lithium secondary batteries including the cathode active materials of Examples 1 and 2.

Claims

A cathode active material comprising: lithium nickel-based oxide particles in the form of single particles consisting of 1.1 single nodules or quasi-single particles consisting of 30 or fewer nodules; and a coating layer including cobalt formed on the surface of the lithium nickel-based oxide particles; When analyzing the above positive electrode active material by X-ray photoelectron spectroscopy (XPS), the atomic ratio of Co to Ni, XPS (Co / Ni), is 0.15 or more, When analyzing the above positive electrode active material by Auger electron spectroscopy (AES), the standard deviation of AES (Co / Ni), which is the atomic ratio of Co to Ni, is 0.80 or less, The above positive electrode active material is a positive electrode active material having a residual Li2CO3 content of 0.50 wt% or less.

2. In claim 1, The above lithium nickel-based oxide particles are a cathode active material having a nickel content of 55 mol% or more among all metals excluding lithium.

3. In claim 1, The above positive electrode active material is D 50 A positive electrode active material having a diameter of 2.0㎛ to 10.0㎛.

4. In claim 1, A positive electrode active material, wherein the average particle size of the nodules of the positive electrode active material is 1 µm to 10 µm.

5. In claim 1, The above positive electrode active material has a BET specific surface area of ​​0.2 m 2 / g to 1.5m 2 / g, positive electrode active material.

6. In claim 1, A positive electrode active material, wherein the coating layer further comprises at least one selected from the group consisting of Mg, Al, Ti, V, Cr, Mn, Zr, Nb, W, and B.

7. In claim 1, The above lithium nickel-based oxide is a positive electrode active material having a composition represented by the following chemical formula 1. [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 At least one selected from the group consisting of Mn and Al, and M 2 is at least one selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo, and 1.0≤a≤1.5, 0.8≤b≤1.0, 0≤c≤0.2, 0≤d≤0.2, 0≤e≤0.

2.

8. A step of mixing a transition metal precursor including nickel, cobalt, and manganese and a lithium raw material and performing a first calcination to form a lithium nickel-based oxide in the form of a single particle consisting of one single nodule or a composite of 30 or fewer nodules; and A step of mixing the lithium nickel-based oxide with a cobalt compound and performing secondary firing to form a positive electrode active material including a coating layer containing cobalt; The lithium nickel-based oxide formed by the first calcination includes Li2CO3 and LiOH, and the ratio of the LiOH content to the Li2CO3 content is 1.4 or more, A method for producing a positive electrode active material, wherein the particle size of the above cobalt compound is 1500 nm or less.

9. In claim 8, A method for producing a positive electrode active material, wherein the lithium nickel-based oxide formed by the first calcination has a sum of LiOH content and Li2CO3 content of 0.5 wt% to 2.2 wt%.

10. In claim 8, A method for producing a positive electrode active material, wherein the lithium nickel-based oxide formed by the first calcination has a ratio of the cobalt compound content to the LiOH content of 2.00 mol% / wt% or more.

11. In claim 8, The lithium nickel oxide formed by the first calcination has a ratio of the cobalt compound content to BET of 2.5 wt% / (m 2 / g) A method for manufacturing a positive electrode active material.

12. In claim 8, A method for producing a positive electrode active material, wherein the secondary firing is performed at a temperature of 660°C to 740°C.

13. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 7.

14. A lithium secondary battery comprising the positive electrode of claim 13.