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

Abstract

The positive electrode active material of the present invention comprises lithium nickel-based oxide particles in the form of single particles consisting of a single nodule or pseudo-single particles as a complex of 30 or fewer nodules, and a coating containing cobalt formed on the surface of the lithium nickel-based oxide particles, wherein, when the positive electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the XPS (Co / Ni) atomic ratio of Co to Ni is 0.15 or more, when the positive electrode active material is analyzed by Auger electron spectroscopy (AES), the standard deviation of the AES (Co / Ni) atomic ratio of Co to Ni is 0.80 or less, and the residual Li2CO3 content of the positive electrode active material is 0.50% by weight or less.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0042136, filed with the Korean Intellectual Property Office on March 27, 2024, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a positive electrode active material in the form of single particles and / or pseudo-single particles, a method for preparing the same, and a positive electrode and a lithium secondary battery including the positive electrode active material. The positive electrode active material has excellent high-temperature life performance and reduces gas generation. Background Technology

[0004] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive and negative electrodes include active materials capable of inserting and deintercalating lithium ions.

[0005] Lithium transition metal oxides are used as positive electrode active materials in lithium-ion secondary batteries, and research and development of lithium nickel-based oxides, which can easily achieve high-capacity batteries, are being actively pursued among these lithium transition metal oxides. However, the secondary particulate form has the problem of accelerated internal crack formation in the positive electrode active material during charging and discharging.

[0006] To address the aforementioned issues, a technique has been proposed to prepare single-particle rather than secondary-particle positive electrode active materials by increasing the firing temperature during the preparation of lithium nickel cobalt manganese-based oxides.

[0007] In particular, when preparing high-nickel cathode active materials in single-particle form with a Ni molar ratio of over 80 mol% in all transition metals, the surface structure integrity of the cathode active material may be low and the residual lithium concentration may be high due to the high sintering temperature. Typically, surface structure integrity can be improved and the residual lithium concentration reduced by forming a coating on the surface of the lithium nickel-based oxide particles.

[0008] However, if the coating formed on the surface of lithium nickel-based oxide particles is uneven, problems such as reduced high-temperature life performance or increased gas generation may occur when applied to lithium secondary batteries.

[0009] Therefore, there is a need for a technology that can uniformly form a coating on the surface of lithium nickel-based oxide particles, thereby improving high-temperature life performance and reducing gas generation. Summary of the Invention

[0010] Technical issues

[0011] To address the aforementioned problems, the present invention provides a positive electrode active material, a method for preparing the same, and a positive electrode and a lithium secondary battery comprising the positive electrode active material. The positive electrode active material comprises a coating uniformly formed on the surface of a lithium nickel-based oxide and containing cobalt, thereby improving high-temperature lifespan performance and suppressing gas generation.

[0012] Technical solution

[0013] [1] The present invention provides a positive electrode active material, which is a lithium nickel-based oxide particle comprising a single particle composed of a single nodule or a pseudo-single particle as a complex of 30 or fewer nodules and a coating containing 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 XPS (Co / Ni) atomic ratio of Co to Ni is 0.15 or more, when the positive electrode active material is analyzed by Auger electron spectroscopy (AES), the standard deviation of the AES (Co / Ni) atomic ratio of Co to Ni is 0.80 or less, and the residual Li2CO3 content of the positive electrode active material is 0.50% by weight or less.

[0014] [2] In the above [1], the present invention provides a positive electrode active material, wherein the nickel content of the lithium nickel-based oxide particles in all metals other than lithium is 55 mol% or more.

[0015] [3] In [1] or [2] above, the present invention provides a positive electrode active material, wherein the D of the positive electrode active material 50 The range is from 2.0 μm to 10.0 μm.

[0016] [4] In at least one of [1] to [3] above, the present invention provides 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.

[0017] [5] In at least one of [1] to [4] above, the present invention provides a positive electrode active material, wherein the BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 1.5 m 2 / g.

[0018] [6] In at least one of [1] to [5] above, the present invention provides a positive electrode active material, wherein the coating further comprises one or more selected from the group consisting of Mg, Al, Ti, V, Cr, Mn, Zr, Nb, W and B.

[0019] [7] In at least one of [1] to [6] above, the present invention provides a positive electrode active material, wherein the lithium nickel-based oxide particles have a composition represented by Formula 1: [Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In Equation 1 above, M 1 It is selected from at least one of the groups consisting of Mn and Al, M 2 It is selected from at least one of 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 and 0≤e≤0.2.

[0020] [8] The present invention provides a method for preparing a positive electrode active material, the method comprising: mixing a transition metal precursor comprising nickel, cobalt and manganese with a lithium raw material and calcining the mixture once to form a lithium nickel-based oxide in the form of a single particle composed of a single nodule or a pseudo-single particle as a composite of 30 or fewer nodules; and mixing the lithium nickel-based oxide with a cobalt compound and calcining the mixture a second time to form a positive electrode active material comprising a coating comprising cobalt, wherein the lithium nickel-based oxide formed by the first calcination comprises Li2CO3 and LiOH, wherein the ratio of LiOH content to Li2CO3 content is 1.4 or more, and the particle size of the cobalt compound is 1500 nm or less.

[0021] [9] In the above [8], the present invention provides a method for preparing a positive electrode active material, wherein the sum of the LiOH content and the Li2CO3 content of the lithium nickel-based oxide formed by the one-time firing is 0.5% to 2.2% by weight.

[0022]

[10] In [8] or [9] above, the present invention provides a method for preparing a positive electrode active material, wherein the ratio of cobalt compound content to LiOH content in the lithium nickel-based oxide formed by the one-time firing is 2.00 mol% / wt% or more.

[0023]

[11] In at least one of [8] to

[10] above, the present invention provides a method for preparing a positive electrode active material, wherein the ratio of the cobalt compound content to BET in the lithium nickel-based oxide formed by the one-time calcination is 2.5 wt% / (m 2 / g) or above.

[0024]

[12] In at least one of [8] to

[11] above, the present invention provides a method for preparing a positive electrode active material, wherein the secondary firing is carried out at a temperature of 660°C to 740°C.

[0025]

[13] The present invention provides a positive electrode comprising any one of the positive electrode active materials described in [1] to [7] above.

[0026]

[14] The present invention provides a lithium secondary battery comprising the positive electrode described above

[13] .

[0027] Beneficial effects

[0028] The positive electrode active material of the present invention allows (1) the standard deviation of XPS (Co / Ni) as the atomic ratio of Co to Ni during XPS analysis, (2) the standard deviation of AES (Co / Ni) as the ratio of Co content to Ni content during AES analysis, and (3) the residual Li2CO3 content of the positive electrode active material that has the effect of suppressing side reactions with the electrolyte solution (all three of which can be quantified to the uniformity and content of the coating containing cobalt formed on the surface of lithium nickel-based oxide) to meet specific numerical ranges. Therefore, the degradation of the positive electrode active material during the charging / discharging process of lithium secondary batteries and during high-temperature storage can be suppressed, thereby achieving high-temperature life performance and reducing gas generation.

[0029] In the method for preparing the positive electrode active material of the present invention, the lithium nickel-based oxide formed by a single firing contains Li2CO3 and LiOH, and 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 the cobalt compound, and the temperature of the second firing are controlled to improve the uniformity of the coating containing cobalt formed on the surface of the lithium nickel-based oxide, thereby suppressing the side reactions between the lithium nickel-based oxide and the electrolyte solution, so as to achieve high-temperature life performance and reduce gas generation. Detailed Implementation

[0030] The terms and words used in this specification and its claims should not be interpreted according to their ordinary or dictionary meaning, but should be interpreted according to the meaning and concept consistent with the technical idea of ​​the invention, based on the principle that the inventor can adequately define the concept of the terms in order to best describe his / her invention.

[0031] In this invention, a "single particle" refers to a particle composed of a single nodule. In this invention, a "pseudo-single particle" refers to a complex particle formed by fewer than 30 nodules.

[0032] In this invention, a "nodule" refers to a sub-particle unit that constitutes a single particle and a pseudo-single particle. A nodule can be a single crystal without grain boundaries, or a polycrystalline material that appears to lack grain boundaries when observed using a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000. The average particle size of the nodule can be measured as the arithmetic mean of the particle sizes of each nodule measured using a scanning electron microscope (SEM).

[0033] In this invention, a "secondary particle" refers to a particle composed of dozens to hundreds, particularly more than 30, sub-particle units. The sub-particle units constituting a secondary particle are called "primary particles" to distinguish them from nodules, i.e., the sub-particle units constituting single particles and pseudo-single particles.

[0034] The term "particle" as used in this invention may include any one or all of single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0035] In this invention, "D" 50 "" refers to the particle size that accounts for 50% of the volumetric cumulative particle size distribution of the positive electrode active material. 50 It can be measured using laser diffraction. For example, the average particle size (D) 50 The particle size distribution can be measured by the following process: dispersing the positive electrode active material powder in a dispersion medium, then introducing the mixture into a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT 3000), irradiating it with ultrasound at an output of 60W at approximately 28 kHz, thereby obtaining a volumetric cumulative particle size distribution map, and then obtaining the particle size corresponding to 50% of the volumetric cumulative amount.

[0036] In this invention, the "specific surface area" is measured by the BET method. Specifically, it can be calculated using the Belserp-mino II from BEL Japan Co., Ltd. based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0037] In this invention, the presence and content of elements on the surface of lithium nickel-based oxides can be confirmed by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES).

[0038] Specifically, X-ray photoelectron spectroscopy (XPS) can be performed using the Nexsa G2 ESCA system from Thermo Fisher Scientific Co., and Auger electron spectroscopy (AES) can be performed using the PHI 710 device from ULVAC-PHI Co. Specifically, X-ray photoelectron spectroscopy (XPS) can analyze the presence and content of elements at each depth in the cathode active material, while Auger electron spectroscopy (AES) can analyze the uniformity of the coating on the surface of lithium nickel-based oxides.

[0039] The positive electrode active material, the method for preparing the positive electrode active material, and the positive electrode and / or lithium secondary battery of the present invention include at least one of the following disclosed configurations, and may include any combination of the following technically possible configurations.

[0040] Positive electrode active material

[0041] The positive electrode active material of the present invention will be described below.

[0042] The positive electrode active material of the present invention comprises lithium nickel-based oxide particles in the form of single particles composed of a single nodule or pseudo-single particles as a complex of 30 or fewer nodules, and a coating containing cobalt formed on the surface of the lithium nickel-based oxide particles. The positive electrode active material, when analyzed by X-ray photoelectron spectroscopy (XPS), has an XPS (Co / Ni) atomic ratio of Co to Ni of 0.15 or higher; when analyzed by Auger electron spectroscopy (AES), has an AES (Co / Ni) standard deviation of 0.80 or lower; and the residual Li₂CO₃ content of the positive electrode active material is 0.50% by weight or lower.

[0043] Lithium nickel-based oxide particles are either single particles consisting of a single nodule or pseudo-single particles as a composite of 30 or fewer nodules, preferably 2 to 20 nodules, more preferably 2 to 10 nodules. Compared to typical secondary particle forms of lithium nickel-based oxides aggregated with tens to hundreds of primary particles, single-particle and / or pseudo-single-particle forms of lithium nickel-based oxides have higher particle strength and therefore less particle breakage during rolling.

[0044] In addition, the lithium nickel-based oxides of the present invention, in the form of single or pseudo-single particles, have fewer sub-components (i.e., nodules) in their constituent particles, and therefore undergo less change due to the volume expansion and contraction of the particles during charging and discharging, thus significantly reducing the occurrence of internal cracks in the particles.

[0045] The positive electrode active material of the present invention may have a composition in which the nickel content in all metals other than lithium is 55 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more. Ni-based positive electrode active materials have high capacity because the nickel content in the transition metals constituting the positive electrode active material is higher than that in other transition metals; however, due to the presence of unstable Ni on the surface of the positive electrode active material… 3+ and Ni 4+ The presence of ions presents a limitation of structural instability. To address this structural instability, various techniques for modifying the surface of positive electrode active materials are being investigated.

[0046] In particular, when preparing cathode active materials with a nickel content of 80 mol% or more in all metals except lithium, there is a problem that the surface structure integrity of the cathode active material may be low and the concentration of residual lithium may be high due to the high firing temperature. To solve the above problems, a coating can be formed on the surface of lithium nickel-based oxide particles to improve the surface structure integrity and reduce the concentration of residual lithium.

[0047] However, if the coating formed on the surface of lithium nickel-based oxide particles is uneven, problems such as reduced high-temperature life performance or increased gas generation may occur when applied to lithium secondary batteries.

[0048] Therefore, the inventors of this invention have confirmed that if the standard deviations of (1) XPS (Co / Ni) as the atomic ratio of Co to Ni during XPS analysis and (2) AES (Co / Ni) as the ratio of Co content to Ni content during AES analysis meet specific numerical ranges to quantify the uniformity of the coating formed on the surface of lithium nickel-based oxide particles, and if (3) the residual Li2CO3 content of the positive electrode active material meets specific numerical ranges to suppress side reactions between lithium nickel-based oxide particles and electrolyte solution, thereby reducing gas generation, then it has the effect of improving high-temperature life performance and reducing gas generation.

[0049] XPS (Co / Ni), the atomic ratio of Co to Ni in XPS analysis, can be measured by confirming the presence and content of Ni and Co in the region from the surface of the cathode active material to the cobalt-containing coating formed on the surface of the lithium nickel-based oxide. During XPS analysis, since the presence and content of Ni and Co in the entire cobalt-containing coating included in the cathode active material particles can be easily confirmed, XPS (Co / Ni), the atomic ratio of Co to Ni in XPS analysis, can be used as a parameter to indicate the content of the cobalt-containing coating on the surface of the cathode active material.

[0050] XPS (Co / Ni), the atomic ratio of Co to Ni in XPS analysis, can be 0.15 or higher, 0.15 to 0.30, 0.17 to 0.25, or 0.20 to 0.22. A positive electrode active material with an XPS (Co / Ni) ratio less than 0.15 indicates a low content of cobalt-containing coating on the surface, which may result in insufficient protection of the interface between the electrolyte solution and the positive electrode active material with a high nickel (high Ni) composition, thus failing to effectively suppress surface degradation during high-temperature cycling and storage. Therefore, if the XPS (Co / Ni) meets the above range, the cobalt-containing coating on the surface of the positive electrode active material is sufficient, and the coating can adequately protect the interface between the electrolyte solution and the positive electrode active material, thus resulting in excellent high-temperature lifetime performance and high-temperature storage performance. The standard deviation of AES (Co / Ni), the ratio of Co content to Ni content in AES analysis, can be obtained by measuring the D-value of the positive electrode active material powder. 50 Multiple measurement regions, specifically more than 15, or more specifically 15, are selected on the surface of positive electrode active material particles of the same particle size. The value is obtained by measuring the standard deviation of the ratio of Co content to Ni content using Auger electron spectroscopy (AES) in each of the multiple measurement regions. In this case, the multiple measurement regions can be square, circular, or elliptical, etc., but are not limited to these, as long as they are local areas on the surface of the positive electrode active material particles. If the multiple measurement regions are square, the length of one side of the square can be the D of the positive electrode active material powder. 50 The concentrations should be less than 10%, 0.5% to 10%, 1% to 5%, or 1.5% to 4.5%. If these ranges are met, the reliability of the uniformity based on the standard deviation of AES (Co / Ni) is excellent. The spacing between multiple measurement areas can be the D of the positive electrode active material powder. 50 Less than 15%, 5% to 13%, 8% to 12%, or 10%. Alternatively, the spacing between multiple measurement areas can be the D of the positive electrode active material powder. 50 The range is below 1 μm, 0.1 μm to 1 μm, 0.2 μm to 0.7 μm, 0.3 μm to 0.5 μm, or 0.4 μm.

[0051] The standard deviation of AES (Co / Ni), which is the ratio of Co content to Ni content in AES analysis, can confirm the distribution of the Co content to Ni content ratio in local areas rather than the entire surface of the cathode active material particles. Therefore, it can be used as a parameter to indicate the uniformity of the cobalt-containing coating on the surface of the cathode active material.

[0052] The standard deviation of AES (Co / Ni), the ratio of Co to Ni content in AES analysis, can be less than 0.8, less than 0.5, between 0.2 and 0.5, or between 0.25 and 0.35. A standard deviation of AES (Co / Ni) greater than 0.8 indicates an uneven cobalt-containing coating. In this case, even with the same Co content, the Co coating will be thinner on certain surface areas. This can lead to problems such as inadequate protection of the interface between the electrolyte solution and the high-nickel (high-Ni) cathode active material, thus failing to effectively suppress surface degradation during high-temperature cycling and storage. Therefore, if the standard deviation of AES (Co / Ni), the ratio of Co to Ni content in AES analysis, meets the above-mentioned range, a cobalt-containing coating of uniform thickness can be formed on the entire surface of the cathode active material, thereby uniformly protecting the interface between the electrolyte solution and the cathode active material. This results in excellent high-temperature lifetime performance and high-temperature storage performance.

[0053] The residual Li₂CO₃ content of the positive electrode active material can be less than 0.5 wt%, less than 0.4 wt%, or between 0.01 wt% and 0.4 wt%. Positive electrode active materials with a residual Li₂CO₃ content greater than 0.5 wt% may exhibit the following problem: excessively increased side reactions between the lithium nickel-based oxide particles and the electrolyte solution, leading to increased gas generation, which can degrade the performance of lithium-ion batteries. Specifically, even if the standard deviations of XPS (Co / Ni) and AES (Co / Ni) meet the above-mentioned ranges, if the final residual Li₂CO₃ content of the positive electrode active material does not meet these ranges, the amount of gas generated will significantly increase compared to cases where the residual Li₂CO₃ content meets these ranges, thus reducing the performance of lithium-ion batteries. Therefore, if the final residual Li₂CO₃ content of the positive electrode active material meets the above-mentioned ranges, side reactions between the positive electrode active material and the electrolyte solution can be suppressed, thereby reducing gas generation.

[0054] The coating may contain one or more of the following 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 contain a coating 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%.

[0055] The positive electrode active material of the present invention D 50 The diameter can be 2.0 μm to 10.0 μm, 3.0 μm to 7.0 μm, or 3.5 μm to 5.0 μm. If the D of the positive electrode active material of the present invention... 50Meeting the above range allows for the achievement of high energy density and low initial resistance. If the D of the positive electrode active material... 50 If the diameter is less than 2.0 μm, it is difficult to achieve high roll density, which reduces energy density, and if D 50 If the thickness is greater than 10.0 μm, the lithium mobility in the positive electrode active material decreases, which can increase the initial resistance of the lithium secondary battery that includes the positive electrode active material.

[0056] In the positive electrode active material of the present invention, the average particle size of the nodules can be 1 μm to 10 μm, 2 μm to 6 μm, or 3 μm to 5 μm. If the average particle size of the nodules in the positive electrode active material of the present invention meets the above range, high energy density and low initial resistance can be achieved. If the average particle size of the nodules in the positive electrode active material of the present invention is less than 1 μm, the total specific surface area of ​​the positive electrode active material increases, which can increase side reactions with the electrolyte solution, and if the average particle size of the nodules is greater than 10 μm, the lithium mobility decreases, which can reduce the output performance of the battery.

[0057] The BET specific surface area of ​​the positive electrode active material of the present invention can be 0.2 m². 2 / g to 1.5 m 2 / g, preferably 0.3 m 2 / g to 1.2 m 2 / g, 0.4 m 2 / g to 1.0 m 2 / g or 0.4 m 2 / g to 0.8 m 2 / g. If the BET specific surface area of ​​the positive electrode active material is less than 0.2 m² / g. 2 If the value is / g, there is a concern about a reduction in the initial output, and if the BET surface area is greater than 1.5 m², there is also a concern about this. 2 If the BET specific surface area is less than a certain value (e.g.), concerns arise regarding high-temperature lifespan, resistivity increase rate, and gas storage. Therefore, if the BET specific surface area of ​​the positive electrode active material meets the aforementioned value range, excellent output performance and high-temperature durability can be achieved.

[0058] Specifically, the lithium nickel-based oxide can be particles having the composition of Formula 1 below.

[0059] [Formula 1]

[0060] Li a Ni b Co c M 1 d M 2 e O2

[0061] In Equation 1 above, M 1is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al, and M 2 is one or more selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo. The M element is not necessarily included, 2 but if included in an appropriate amount, the M 2 element can play a role in promoting particle growth during firing or improving the stability of the crystal structure.

[0062] a represents the molar ratio of lithium in the lithium nickel-based oxide and can satisfy 1.0 ≤ a ≤ 1.5, 1.0 ≤ a ≤ 1.2, or 1.00 ≤ a ≤ 1.15. If the molar ratio of lithium satisfies the above range, a stable layered crystal structure can be formed.

[0063] b represents the molar ratio of nickel among all metals other than lithium in the lithium nickel-based oxide and can satisfy 0.8 ≤ b < 1.0, 0.85 ≤ b < 1.0, or 0.90 ≤ b < 1. If the molar ratio of nickel satisfies the above range, excellent capacity performance can be exhibited. In particular, if the molar ratio of nickel is 0.90 or more, more excellent capacity performance can be achieved.

[0064] c represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel-based oxide and can satisfy 0 ≤ c ≤ 0.2, 0 < c < 0.2, or 0 < c < 0.18.

[0065] d represents the molar ratio of M among all metals other than lithium in the lithium nickel-based oxide 1 and can satisfy 0 ≤ d ≤ 0.2, 0 < d < 0.2, or 0 < d < 0.18.

[0066] e represents the molar ratio of the M 2 element among all metals other than lithium in the lithium nickel-based oxide and can satisfy 0 ≤ e ≤ 0.2, 0 ≤ e ≤ 0.15, or 0 ≤ e ≤ 0.1.

[0067] Preparation method of positive electrode active material

[0068] Next, a method for preparing the positive electrode active material of the present invention will be described.

[0069] The method for preparing the positive electrode active material of the present invention includes the following steps: mixing a transition metal precursor containing nickel, cobalt, and manganese with a lithium raw material and calcining the mixture once to form a lithium nickel-based oxide in the form of a single particle composed of a single nodule or a pseudo-single particle as a composite of 30 or fewer nodules; and mixing the lithium nickel-based oxide with a cobalt compound and calcining the mixture a second time to form a positive electrode active material including a coating containing cobalt. The lithium nickel-based oxide formed by the first calcination contains Li₂CO₃ and LiOH, wherein the ratio of LiOH content to Li₂CO₃ content is 1.4 or more, and the particle size of the cobalt compound is 1500 nm or less.

[0070] Each step of the preparation method for the positive electrode active material will be described in detail.

[0071] (Steps for preparing transition metal precursors)

[0072] First, a transition metal precursor containing nickel, cobalt, and manganese is mixed with a lithium feedstock and the mixture is calcined once to form a lithium nickel-based oxide in the form of a single particle consisting of a single nodule or a pseudo-single particle as a complex of no more than 30 nodules.

[0073] In this case, the positive electrode active material precursor can be a commercially available precursor, such as nickel cobalt manganese-based hydroxide, or it can be prepared according to precursor preparation methods known in the art (e.g., coprecipitation method).

[0074] For example, preparing a mixture containing nickel (Ni), cobalt (Co), and M 1 A solution containing transition metal cations is prepared by adding a complexing agent containing ammonium cations and an alkaline aqueous solution to the solution containing transition metals to carry out a coprecipitation reaction, thereby preparing a precursor of positive electrode active material.

[0075] Solutions containing transition metals may include nickel-containing raw materials, cobalt-containing raw materials, and M-containing raw materials. 1 Raw materials, and containing M 1 The raw materials can be manganese-containing and / or aluminum-containing.

[0076] Nickel-containing raw materials can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides, and specifically, can be Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel salts of fatty acids, nickel halides, or combinations thereof, but are not limited thereto.

[0077] Cobalt-containing raw materials can be cobalt-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides, specifically Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or combinations thereof, but are not limited to these.

[0078] Manganese-containing raw materials can be, for example, manganese-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, hydroxyoxides or combinations thereof, and specifically, can be manganese oxides (e.g., Mn2O3, MnO2 and Mn3O4), manganese salts (e.g., MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate and fatty acid manganese salts), manganese hydroxyoxides, manganese chloride or combinations thereof, but are not limited thereto.

[0079] Aluminum-containing raw materials can 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.

[0080] Solutions containing transition metals can be obtained by combining nickel-containing raw materials, cobalt-containing raw materials, and M-containing raw materials. 1 The raw materials are added to a solvent, specifically water, or a mixture of water and an organic solvent (e.g., alcohol) that is homogeneous with water, or the raw materials can be prepared by adding an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and an aqueous solution of an M-containing raw material. 1 It is prepared by mixing aqueous solutions of raw materials.

[0081] The complex forming agent containing ammonium cations can be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof, but is not limited thereto. Furthermore, the complex forming agent containing ammonium cations can be used in the form of an aqueous solution, and in this case, water, or a mixture of water and an organic solvent that is homogeneous with water (e.g., alcohols), can be used as the solvent.

[0082] The basic compound can be an alkali metal or alkaline earth metal hydroxide (e.g., NaOH, KOH, or Ca(OH)2), its hydrate, or a combination thereof. The basic compound can also be used in the form of an aqueous solution, and in this case, water, or a mixture of water and an organic solvent that is homogeneous with water (e.g., alcohols), can be used as the solvent.

[0083] An alkaline compound is added to control the pH of the reaction solution, and the amount added can make the pH of the metal solution between 8 and 12.

[0084] The coprecipitation reaction can be carried out in an inert atmosphere (such as in a nitrogen atmosphere or an argon atmosphere) at a temperature ranging from 35°C to 80°C.

[0085] Nickel-cobalt-M is generated using the above method. 1 Hydroxide-containing positive electrode active material precursor particles precipitate in the reaction solution. This is achieved by controlling the composition of nickel-containing, cobalt-containing, and M-containing raw materials. 1 The concentration of the raw materials is such that a nickel (Ni) content of 55 mol% or higher in the total metal content can be prepared as a cathode active material precursor. The precipitated cathode active material precursor particles are separated and dried according to typical methods to prepare the cathode active material precursor.

[0086] After that, the positive electrode active material precursor and lithium raw material can be mixed.

[0087] Lithium raw materials can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or hydroxyoxides, etc., and there are no particular restrictions, as long as they can dissolve in water. Specifically, lithium raw materials can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, or Li₃C₆H₅O₇, etc., and any one of them or a mixture of two or more of them can be used.

[0088] The positive electrode active material precursor and lithium raw material can be mixed in a molar ratio of, for example, about 1:1, about 1:1.05, about 1:1.10, about 1:1.15 or about 1:1.20, but are not limited thereto.

[0089] (Single firing)

[0090] Subsequently, the mixture can be fired once to form a single particle consisting of a single nodule or a pseudo-single particle form of a complex of nodules of 30 or fewer.

[0091] The single-stage firing can be carried out in an air or oxygen atmosphere. The single-stage firing can be performed at temperatures of 600°C to 1000°C, 750°C to 950°C, or 800°C to 900°C. The single-stage firing can last for 4 to 12 hours, 6 to 12 hours, or 8 to 12 hours. If the single-stage firing and duration meet the above ranges, lithium nickel-based oxides can be formed in a single-particle form, not as secondary particles, but as pseudo-single-particle forms consisting of a single nodule or as a complex of 30 or fewer nodules. In the case of single-particle or pseudo-single-particle positive electrode active materials, compared with typical secondary-particle positive electrode active materials, the contact area with the electrolyte solution is smaller, resulting in fewer side reactions with the electrolyte solution, and the particle strength is excellent, thus reducing particle breakage during electrode manufacturing. Therefore, when using single-particle or pseudo-single-particle positive electrode active materials, there are advantages in terms of gas generation and lifetime performance.

[0092] The lithium-nickel-based oxide formed by a single firing comprises Li₂CO₃ and LiOH. The Li₂CO₃ content after the single firing can be less than 1.0 wt%, less than 0.7 wt%, or from 0.3 wt% to 0.5 wt%, and the LiOH content after the single firing can be less than 1.2 wt%, from 0.4 wt% to 1.2 wt%, or from 0.6 wt% to 1.1 wt%. After the single firing, the residual lithium reacts with a Co coating source to form an oxide coating comprising Li and Co. The Li₂CO₃ content indicates the content of lithium in a form with relatively low reactivity with the Co coating source, and the LiOH content indicates the content of lithium in a form with relatively high reactivity with the Co coating source. If necessary, the exhaust system of the firing furnace can be used to control the residual lithium content after the single firing.

[0093] The ratio of LiOH content to Li2CO3 content can be 1.4 or higher, 1.4 to 2.5, or 1.7 to 2.0. Even with the same amount of residual lithium, if the ratio of LiOH, which is highly reactive with the Co coating source, is relatively high, a coating with relatively high uniformity can be formed even when performing Co coating with the same process.

[0094] The sum of the LiOH and Li2CO3 contents in the lithium nickel-based oxide formed by a single firing process can be 0.5 wt% to 2.2 wt%, 0.6 wt% to 2.0 wt%, or 0.7 wt% to 1.7 wt%. If the amount of residual lithium is too high, there is a high probability of excess residual lithium even after Co coating, which may lead to poor slurry stability when preparing storage gases and electrodes. Furthermore, if the amount of residual lithium is too low relative to the Co coating source, it may be difficult to form a suitable Li-Co-O coating, which can limit the effective improvement of high-temperature lifespan.

[0095] The BET specific surface area of ​​lithium nickel-based oxides formed by a single firing process can be 0.2 m². 2 / g to 1.5 m 2 / g, 0.3m 2 / g to 1.2 m 2 / g or 0.4 m 2 / g to 0.8 m 2 / g. If the BET content relative to the Co coating is too high, the coating layer may not cover the entire surface area of ​​the cathode, which can limit the improvement of high-temperature lifetime and performance during high-temperature storage. Conversely, excessive coating may form relative to the specific surface area, which can lead to poor initial resistivity. Where necessary, the BET of lithium nickel-based oxides can be controlled by pulverization methods such as mechanical grinding and sintering conditions.

[0096] (Second firing)

[0097] Next, lithium nickel-based oxide is mixed with a cobalt compound and the mixture is subjected to a second firing to form a positive electrode active material including a cobalt-containing coating. Specifically, the surface of the lithium nickel-based oxide particles is coated with a cobalt compound.

[0098] During the secondary firing process, lithium remaining on the surface of the lithium nickel-based oxide can react with the cobalt in the coating material to form lithium cobalt oxide. If the residual lithium is removed due to the formation of the coating, the washing step for removing residual lithium can be omitted, simplifying the process. Furthermore, typically during the washing process, the oxidation state of Ni on the surface of the positive electrode active material particles changes to electrically inert Ni. +2 This tends to increase resistance, but if the washing process is omitted, the change in the oxidation number of Ni can be minimized, thereby suppressing the increase in resistance.

[0099] Cobalt compounds can be acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, or hydroxyoxides containing cobalt, specifically Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4, Co(SO4)2·7H2O, or combinations thereof, but are not limited thereto.

[0100] The total molar amount of cobalt compound relative to the molar amount of lithium nickel-based oxide can be less than 4.0 mol%, from 0.3 mol% to 4.0 mol%, or from 1.0 mol% to 3.0 mol%. If the content of cobalt compound meets the above numerical range, a coating containing an appropriate amount of cobalt is formed on the surface of the lithium nickel-based oxide particles, thereby suppressing side reactions with the electrolyte solution and thus improving the performance of the lithium secondary battery.

[0101] The particle size of cobalt compounds can be below 1500 nm, 100 nm to 1000 nm, or 200 nm to 500 nm. If the particle size of the cobalt compound meets the above numerical range, the coating uniformity decreases when the particle size of the cobalt compound is greater than 1500 nm, thus limiting its ability to improve high-temperature lifetime and high-temperature storage performance.

[0102] The second firing can be carried out at temperatures of 660°C to 740°C, 680°C to 720°C, or 690°C. The second firing can last for 4 to 12 hours, 6 to 12 hours, or 8 to 12 hours.

[0103] When lithium nickel-based oxides are mixed with cobalt compounds and subjected to a second firing at the above-mentioned temperature and duration, if the second firing temperature is too high, the Co coating material will diffuse excessively into the bulk, resulting in a reduced coating effect. If the second firing temperature is too low, the uniformity of the coating will be reduced. Therefore, the high-temperature life performance can be improved by applying an appropriate second firing temperature.

[0104] The ratio of cobalt compound content to LiOH content in the lithium nickel-based oxide formed by a single firing process can be 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 represents the content of lithium forms with relatively low reactivity to the Co coating source, while the LiOH content represents the content of lithium forms with relatively high reactivity to the Co coating source. Therefore, for the formation of a coating with high uniformity, the LiOH content is more important than the Li₂CO₃ content, and a suitable Li-Co-O coating can be formed if the Co coating content and LiOH ratio are limited within the above ranges.

[0105] The ratio of cobalt compound content to BET in lithium nickel-based oxides formed by a single firing process can be 2.5 wt% / (m 2 / g) or more, 3.0% by weight / (m 2 / g) to 10.0 wt% / (m 2 / g) or 4.0% by weight / (m 2 / g) to 6.0 wt% / (m 2 / g). If the BET content relative to the Co coating is too high, the coating layer may not be able to cover the entire surface area of ​​the cathode, which can limit the improvement of high-temperature lifetime and performance during high-temperature storage. If the BET content relative to the Co coating is too low, too much coating may be formed relative to the specific surface area, which can lead to poor initial resistance performance.

[0106] positive electrode

[0107] The positive electrode of the present invention comprises the positive electrode active material described above. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein 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, its detailed description will be omitted, and in the following text, only the remaining components will be described in detail.

[0108] The positive electrode current collector can include highly conductive metals, and there are no particular limitations, as long as it is non-reactive within the battery's voltage range and the positive electrode active material layer can easily adhere to the positive electrode current collector. Examples of positive electrode current collectors include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, and silver. Furthermore, the positive electrode current collector typically has a thickness from 3 μm to 500 μm, and microscopic irregularities can be formed on its surface to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0109] If necessary, in addition to the positive electrode active material, the positive electrode active material layer may optionally include conductive materials and adhesives.

[0110] In this case, the content of the positive electrode active material can be 80% to 99% by weight, or more specifically 90% to 98% by weight, relative to the total weight of the positive electrode active material layer.

[0111] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause chemical changes in the battery to be constructed. Specific examples may include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of them may be used. The content of the conductive material relative to the total weight of the positive electrode active material layer can be from 0.01% to 10% by weight, preferably from 0.1% to 9% by weight, and more preferably from 0.1% to 5% by weight.

[0112] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, polymers whose hydrogens are substituted with Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0113] In addition to using the aforementioned positive electrode active materials, positive electrodes can be manufactured according to typical positive electrode manufacturing methods. Specifically, a positive electrode can be manufactured by coating a positive electrode slurry composition prepared by dissolving or dispersing the aforementioned positive electrode active materials, as well as optional binders, conductive materials, and dispersants in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0114] The solvent can be any solvent commonly used in the art, and can be dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, etc., and any one or a mixture of two or more of them can be used. Considering the coating thickness and manufacturing yield of the slurry, the amount of solvent to be used is sufficient if the solvent dissolves or disperses the positive electrode active material, conductive material, binder, and dispersant, and subsequently results in a viscosity of the slurry that exhibits excellent thickness uniformity when used for coating in the manufacture of the positive electrode.

[0115] Alternatively, in another method, the positive electrode can also be manufactured by casting a positive electrode slurry composition onto a separate support, and then pressing the film layer obtained by peeling it off from the support onto the positive electrode current collector.

[0116] Lithium secondary batteries

[0117] Next, the lithium secondary battery of the present invention will be described.

[0118] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode disposed facing the positive electrode, a separator between the positive and negative electrodes, and an electrolyte. Since the positive electrode is the same as described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0119] In addition, the lithium secondary battery may optionally include a battery housing for housing electrode assemblies for a positive electrode, a negative electrode and a separator, and a sealing member for sealing the battery housing.

[0120] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on the negative electrode current collector.

[0121] There are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, and silver, and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can typically have a thickness from 3 μm to 500 μm, and as with the positive electrode current collector, microscopic irregularities can be formed on the surface of the current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0122] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0123] As anode active materials, compounds capable of reversibly inserting and deintercalating lithium can be used. Specific examples include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic materials that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides that can be doped and dedoped with lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composites containing metallic and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of them can be used. Additionally, thin films of metallic lithium can be used as anode active materials. Furthermore, low-crystallinity carbon and high-crystallinity carbon can also be used as carbon materials. Representative examples of low-crystallinity carbon may include soft carbon and hard carbon, while representative examples of high-crystallinity carbon may include irregular, plate-like, sheet-like, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch and high-temperature heat-treated carbon (e.g. coke derived from petroleum or coal tar pitch).

[0124] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight.

[0125] Adhesives are components used to facilitate the bonding between conductive materials, active materials, and current collectors, and their addition amount is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0126] Conductive materials are components used to further improve the conductivity of the negative electrode active material, and their content can be from 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight, based on the total weight of the negative electrode active material layer. There are no particular limitations on the conductive materials, as long as they are conductive and do not cause chemical changes in the battery. Examples of conductive materials that can be used include graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorinated carbon; metal powders, such as aluminum powder 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.

[0127] The negative electrode active material layer can be prepared by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing the negative electrode active material and optional binder and conductive material in a solvent, onto a negative electrode current collector and then drying it; or by casting the negative electrode slurry composition onto a separate support and then pressing the film layer peeled off from the support onto the negative electrode current collector.

[0128] Meanwhile, in lithium-ion secondary batteries, the separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a commonly used separator in lithium-ion secondary batteries. In particular, separators with low resistance to ion movement in the electrolyte and excellent moisture retention of the electrolyte solution are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, or ethylene / methacrylate copolymers), or stacked structures having two or more of these layers. Alternatively, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0129] In addition, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte, etc., which can be used to manufacture lithium secondary batteries, but the electrolyte is not limited to these.

[0130] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0131] As organic solvents, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which the ions involved in the electrochemical reaction of the battery can move. Specifically, as organic solvents, the following can be used: 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 solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Preferably, carbonate solvents are preferred, and more preferably, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charging / discharging performance of the battery and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is preferred.

[0132] Any compound can be used as a lithium salt without particular limitation, as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from 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 of the constituent groups, and as a lithium salt, 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., can be used. The lithium salt can be used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, more preferably 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, and lithium ions can move efficiently.

[0133] To improve battery life, suppress capacity reduction, and increase discharge capacity, the electrolyte may contain one or more additives, such as alkyl halogenated carbonates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride. In this case, the additive content can be from 0.1% by weight to 10.0% by weight, based on the total weight of the electrolyte.

[0134] As described above, lithium secondary batteries containing the positive electrode active material of the present invention stably exhibit excellent discharge capacity, output performance and capacity retention, and are therefore suitable for use in portable devices such as mobile phones, laptops, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs).

[0135] Therefore, according to another embodiment of the present invention, a battery module including the above-mentioned lithium secondary battery as a unit cell and a battery pack including the battery module are provided.

[0136] Battery modules or battery packs can be used as power sources for one or more medium to large-sized devices in power tools, electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs), or power storage systems.

[0137] Embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments set forth herein.

[0138] Examples and Comparative Examples

[0139] Example 1

[0140] A transition metal precursor with a Ni:Co:Mn molar ratio of 96:1:3 was mixed with lithium feedstock (LiOH) to achieve a transition metal (Ni+Co+Mn):Li molar ratio of 1:1.2. The mixture was then calcined once at 870°C for 10 hours in a calcining furnace and ground to prepare single-particle lithium nickel-based oxide LiNi. 0.96 Co 0.01 Mn 0.03 O2.

[0141] Subsequently, the calcined product was mixed with 3 mol% Co(OH)2 and then calcined again at 690°C for 10 hours to prepare a single-particle positive electrode active material with a cobalt (Co) coating on its surface.

[0142] Example 2 and Comparative Examples 1 to 7

[0143] The content and size of the cobalt compound used during the preparation of the positive electrode active material powder in Examples 2 and Comparative Examples 1 to 7, as well as the secondary firing temperature, are shown in Table 1 below.

[0144] Specifically, in Comparative Example 1, the difference compared to Example 1 was that the rate of temperature decrease during the first firing was reduced by 20%, resulting in a decrease in LiOH, which is highly reactive with the cobalt compound, and an increase in Li₂CO₃ in the residual lithium content after the first firing. In Comparative Example 2, the difference was that a cobalt compound with a larger particle size than the cobalt compound used in Example 1 was used when preparing the positive electrode active material powder. In Comparative Example 3, the second firing temperature was lowered compared to Example 1, causing the cobalt compound to be pushed to the surface and thus widely distributed on the extreme surface portion, but resulting in reduced uniformity. In Comparative Example 5, the difference compared to Example 1 was that the pulverization intensity after the first firing was increased by 15% to improve BET. This means that the specific surface area of ​​the compound increased relative to the amount of cobalt compound added after the first firing. In Comparative Example 6, the lithium (Li) input ratio during the first firing was increased by 3% compared to Example 1 to intentionally increase the residual lithium content after the first firing. In Comparative Examples 6 and 7, the amount of residual lithium, including LiOH, after a single firing was excessive relative to the amount of cobalt compound added, thereby increasing the amount of residual lithium after coating, which led to an increase in gas generation during high-temperature storage.

[0145] Except as described above, the positive electrode active material powder in single-particle form was prepared in the same manner as in Example 1.

[0146] [Table 1]

[0147] Experimental Example 1

[0148] In Examples 1 and 2 and each of Comparative Examples 1 to 7, single-particle lithium nickel-based oxides were collected after a single firing, and the content of LiOH and Li2CO3 on the surface of the lithium nickel-based oxides was measured. Specifically, the content of LiOH and Li2CO3 on the surface of the lithium nickel-based oxides was measured by pH titration, and a T5 pH meter manufactured by Mettler Toledo Company was used as the pH meter.

[0149] In addition, the lithium nickel-based oxide in single-particle form was collected after a single firing to measure BET. Specifically, the BET of the lithium nickel-based oxide was measured by the BET method, and specifically, it was calculated using the BELSORP-mino II manufactured by BEL Japan Co., Ltd. based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0150] The measurement results are shown in Table 2 below.

[0151] Using the above measurement results, the ratio of LiOH content to Li2CO3 content after one firing, the sum of LiOH content and Li2CO3 content after one firing, the ratio of cobalt compound content to LiOH content after one firing, and the ratio of cobalt compound content to BET in the lithium nickel-based oxide after one firing were calculated. The calculation results are shown in Table 2 below.

[0152] [Table 2]

[0153] Experimental Example 2: XPS Analysis of Positive Electrode Active Materials

[0154] The ratio of Co to Ni content on the surface of the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 7 was measured using X-ray photoelectron spectroscopy (XPS) (Nexsa G2 ESCA system, Thermo Fisher Scientific Co.). The atomic ratio of Co to Ni during XPS analysis is shown in Table 3 below.

[0155] Specifically, the positive electrode active materials in powder form of Examples 1 and 2 and Comparative Examples 1 to 7 were sampled in a holder and measured and processed under the following conditions.

[0156] - X-ray source: Monochromatic Al Kα (1486.6 eV)

[0157] X-ray spot size: 400 μm

[0158] - Operating mode: CAE (Constant Analyzer Energy) mode

[0159] - Full scan: Energy 200 eV, energy step 1 eV

[0160] - Narrow scan: Scan mode, through energy 100 eV, energy step size 0.1 eV.

[0161] - Charge compensation: floodlight gun 1.5 V, 150 μA

[0162] -SF:Al THERMO1

[0163] -ECF: TPP-2M

[0164] -BG Subtraction: Shirley Background

[0165] [Table 3]

[0166] Experimental Example 3: AES Analysis of Positive Electrode Active Materials - Standard Deviation

[0167] Auger electron spectroscopy (AES) was performed using a PHI 710 apparatus manufactured by ULVAC-PHI Co. The positive electrode active material powders of Examples 1 and 2, and Comparative Examples 1 to 7, were sprayed and fixed onto aluminum foil, loaded into an AES chamber, and then three particles with diameters of 3 μm to 5 μm were selected for AEM mapping of the surface of each particle to quantify the standard deviation of Co / Ni for all pixels. In this case, the total number of pixels per particle was greater than 10,000, and the mapping intensity of each element was converted into a quantitative value by reflecting the relative sensitivity factor (RSF) of each element. The mapped image was then converted to Co / Ni to eliminate the influence of height.

[0168] Specifically, measurements and data processing were performed under the following conditions. The results are shown in Table 4 below.

[0169] - Electron energy analyzer: CMA (Cylindrical lens analyzer)

[0170] - Electron beam energy: 10 kV

[0171] -Target current: 1 nA

[0172] [Table 4]

[0173] Experiment Example 4: Measurement of Residual Lithium Content in Positive Electrode Active Materials

[0174] The residual lithium content of each positive electrode active material in Examples 1 and 2 and Comparative Examples 1 to 7 was measured. The measurement results are shown in Table 5 below.

[0175] The residual lithium content on the surface of the positive electrode active material was measured by pH titration, and a T5 pH meter manufactured by Mettler Toledo Company was used as the pH meter. Specifically, 10 g of each positive electrode active material powder prepared in Examples 1 and 2 and Comparative Examples 1 to 7 was stirred in 100 mL of distilled water for 5 minutes, and then the solution was pH titrated while a 0.1 N HCl solution was added to it.

[0176] [Table 5]

[0177] Experimental Example 5: Evaluation of High-Temperature Life Performance and Gas Generation

[0178] The high-temperature life performance and gas generation of lithium secondary battery half-cells manufactured using the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 7 were evaluated.

[0179] <Manufacturing of Lithium Secondary Batteries>

[0180] The positive electrode active material, conductive material (carbon black), and PVDF binder prepared in Examples 1 and 2 and Comparative Examples 1 to 7 were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to prepare a positive electrode slurry. The positive electrode slurry was coated on one surface of an aluminum current collector, dried at 130°C, and then rolled to manufacture the positive electrode.

[0181] Lithium metal is used as the negative electrode, and a separator is inserted between the positive and negative electrodes manufactured by the above method to manufacture an electrode assembly. The electrode assembly is placed inside the battery casing, and then an electrolyte solution is injected into the casing to manufacture a battery cell. The electrolyte solution is prepared as follows: 0.6 M LiPF6 is dissolved in a mixed organic solvent in which ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:2:1, and then 2% by weight of ethylene carbonate (VC) is added.

[0182] Specifically, each lithium-ion secondary battery half-cell was charged and discharged at 0.33 C within a voltage range of 2.5 V to 4.35 V at 45°C, which was set as one cycle. Then, 300 charge and discharge cycles were performed to measure the capacity retention using a cycler manufactured by PNE Co. The measurement results are shown in Table 6 below.

[0183] In addition, each lithium secondary battery manufactured above was charged to 4.25 V at 1 C in CC-CV mode, and then the secondary battery was disassembled to separate the positive electrode. Then, 400 mg of the positive electrode and 15 μL of electrolyte solution were placed in a pouch-type battery casing, and the casing was sealed to manufacture a cell. The cell was stored at 60°C for 8 weeks to measure the cell volume change (Δcell volume, unit: ΔmL / g) before and after high-temperature storage. The cell volume change was measured by placing the cell in water and then measuring the change in water volume. The measurement results are shown in Table 6 below.

[0184] [Table 6]

[0185] As can be confirmed from Table 6 above, the lithium secondary batteries comprising the positive electrode active materials of Examples 1 and 2 respectively have better high-temperature life performance and reduce gas generation compared to the lithium secondary batteries comprising the positive electrode active materials of Comparative Examples 1 to 7 respectively. Specifically, it can be confirmed that compared to the lithium secondary batteries comprising the positive electrode active materials of Examples 1 and 2 respectively, the lithium secondary batteries comprising the positive electrode active materials of Comparative Examples 1 to 3 and 6, which have XPS (Co / Ni) of 0.15 or higher, and the residual Li2CO3 content of the final positive electrode active material of 0.50% by weight or less, but a standard deviation of AES (Co / Ni) greater than 0.8, have poorer high-temperature life performance and higher gas generation. Furthermore, it can be confirmed that, compared with the lithium secondary batteries that include the positive electrode active materials of Examples 1 and 2 respectively, the lithium secondary battery that includes the positive electrode active material of Comparative Example 4, which has a standard deviation of AES (Co / Ni) of 0.8 or more, a residual Li2CO3 content of the final positive electrode active material of 0.50% by weight or less, and XPS (Co / Ni) of less than 0.15, has poor high-temperature life performance and higher gas generation.

[0186] Furthermore, it can be confirmed that, compared with the lithium secondary batteries that include the positive electrode active materials of Examples 1 and 2 respectively, the lithium secondary battery that includes the positive electrode active material of Comparative Example 5, which has a residual Li2CO3 content of less than 0.50% by weight, but XPS (Co / Ni) less than 0.15, and a standard deviation of AES (Co / Ni) of less than 0.8, has poor high-temperature life performance and higher gas generation.

[0187] Furthermore, it can be confirmed that, compared with the lithium secondary batteries that include the positive electrode active materials of Examples 1 and 2 respectively, the lithium secondary battery that includes the positive electrode active material of Comparative Example 7, which has XPS (Co / Ni) of 0.15 or higher, AES (Co / Ni) standard deviation of 0.8 or lower, but the residual Li2CO3 content of the final positive electrode active material is greater than 0.50% by weight, has poor high-temperature life performance and higher gas generation.

Claims

1. A positive electrode active material, comprising: Lithium nickel-based oxide particles, wherein the lithium nickel-based oxide particles are single particles composed of a single nodule or pseudo-single particles as a complex of no more than 30 nodules. as well as A coating formed on the surface of the lithium nickel-based oxide particles and comprising cobalt. in: When the positive electrode active material is analyzed by X-ray photoelectron spectroscopy (XPS), the XPS (Co / Ni) ratio, which is the atomic ratio of Co to Ni, is greater than 0.

15. When the positive electrode active material was analyzed by Auger electron spectroscopy (AES), the standard deviation of the AES (Co / Ni) as the atomic ratio of Co to Ni was less than 0.80; and The residual Li2CO3 content of the positive electrode active material is less than 0.50% by weight.

2. The positive electrode active material according to claim 1, wherein, The lithium nickel-based oxide particles contain more than 55 mol% nickel in all metals except lithium.

3. The positive electrode active material according to claim 1, wherein, The positive electrode active material D 50 The range is from 2.0 μm to 10.0 μm.

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

5. The positive electrode active material according to claim 1, wherein, The BET specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 1.5 m 2 / g.

6. The positive electrode active material according to claim 1, wherein, The coating further comprises one or more elements selected from the group consisting of Mg, Al, Ti, V, Cr, Mn, Zr, Nb, W, and B.

7. The positive electrode active material according to claim 1, wherein, The lithium-nickel-based oxide particles have a composition represented by Formula 1: [Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In Equation 1 above, M 1 It is selected from at least one of the groups consisting of Mn and Al, M 2 It is selected from at least one of 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 and 0≤e≤0.

2.

8. A method for preparing a positive electrode active material, the method comprising: A lithium nickel-based oxide is formed by mixing a transition metal precursor containing nickel, cobalt, and manganese with a lithium feedstock and then calcining the mixture once to form single particles consisting of a single nodule or pseudo-single particles as a composite of fewer than 30 nodules; and The lithium nickel-based oxide is mixed with a cobalt compound and the mixture is then subjected to a second firing to form a positive electrode active material including a cobalt-containing coating. The lithium nickel-based oxide formed by a single firing process comprises Li2CO3 and LiOH, wherein the ratio of LiOH content to Li2CO3 content is 1.4 or higher, and the particle size of the cobalt compound is less than 1500 nm.

9. The method according to claim 8, wherein, The sum of the LiOH content and Li2CO3 content of the lithium nickel-based oxide formed by a single firing process is 0.5% to 2.2% by weight.

10. The method according to claim 8, wherein, The ratio of cobalt compound content to LiOH content in the lithium nickel-based oxide formed by a single firing process is 2.00 mol% / wt% or more.

11. The method according to claim 8, wherein, The ratio of cobalt compound content to BET in the lithium nickel-based oxide formed by a single firing process is 2.5 wt% / (m 2 / g) or above.

12. The method according to claim 8, wherein, The secondary firing is carried out at a temperature of 660°C to 740°C.

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

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

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