Positive electrode material powder, method for preparing the same, and lithium

Abstract

The present invention provides a positive electrode material powder including lithium nickel-based oxide particles represented by the following Chemical Formula 1, and having a single crystallization degree represented by mathematical formula (1) of the present invention of 1.85 to 3.00. [Chemical Formula 1] LiaNibCocM1dM2eO2 in the above Chemical Formula 1, M1 is Mn, Al, or a combination thereof, M2 is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.80 < = a < = 1.20, 0.80 < = blt, 0.80 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = 1, 0lt; clt; ct; 0.45, 0 lt; dlt; 0.45, 0 < = e < = 0.20.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0124865, filed on September 19, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to cathode material powder, its preparation method, and lithium secondary batteries comprising the same. More specifically, this invention relates to cathode material powder capable of improving high-temperature characteristics, its preparation method, and lithium secondary batteries comprising the same. 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 cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium-ion batteries. Among these, lithium cobalt oxide has the advantages of high driving voltage and excellent capacity characteristics; however, due to the high price and unstable supply of cobalt as a raw material, it is difficult to commercialize lithium cobalt oxide for use in high-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifetime performance. Meanwhile, lithium manganese oxide has excellent stability, but suffers from poor capacity characteristics. Therefore, to overcome the limitations of lithium transition metal oxides containing only Ni, Co, or Mn, lithium composite transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in electric vehicle batteries.

[0006] Conventional lithium nickel cobalt manganese oxides typically exist as spherical secondary particles, aggregated from tens to hundreds of primary particles. However, when using lithium nickel cobalt manganese oxides in the form of secondary particles formed by the aggregation of a large number of primary particles, particle breakage is prone to occur during the rolling process in the manufacture of the positive electrode, and there is a problem of internal cracks forming within the particles during charging and discharging. When the particles of the positive electrode active material break or crack, the contact area with the electrolyte increases, thus increasing gas generation and active material degradation caused by side reactions with the electrolyte, leading to a decrease in lifespan performance.

[0007] Meanwhile, the demand for high-power and high-capacity batteries (such as those used in electric vehicles) has been increasing in recent years, leading to a trend of increasing electrode density to manufacture high-capacity batteries. However, while increasing electrode density improves capacity characteristics, it also increases the generation of fine powder due to particle breakage during electrode compression, thus increasing the reaction area with the electrolyte. This results in the drawback of electrolyte decomposition and degradation of the surface structure of the active material during charge and discharge.

[0008] To address the aforementioned issues, a technique has been proposed to prepare single-particle, rather than secondary-particle, cathode active materials during the preparation of lithium nickel cobalt manganese oxides. Compared to conventional cathode active materials in secondary-particle form, single-particle cathode active materials have a smaller contact area with the electrolyte, resulting in fewer side reactions with the electrolyte. Therefore, the use of single-particle cathode active materials offers advantages such as less gas generation and superior lifetime characteristics.

[0009] However, the problem with conventional cathode active materials in single-particle form is that they generate a large amount of gas at high temperatures or have poor lifetime characteristics. Summary of the Invention

[0010] Technical issues

[0011] To address the aforementioned problems, one aspect of the present invention provides a cathode material powder that produces less gas at high temperatures and exhibits excellent lifetime characteristics, a method for preparing the same, and a lithium secondary battery comprising the same.

[0012] Technical solution

[0013] [1] The present invention provides a cathode material powder comprising lithium nickel oxide particles represented by the following chemical formula 1, and having a degree of monocrystallization of 1.85 to 3.00 represented by the following mathematical formula (1).

[0014] [Chemical Formula 1]

[0015] Li a Ni b Co c M 1 d M 2 e O2

[0016] In the above chemical formula 1, M 1 M is Mn, Al, or a combination thereof, M 2 The element is selected from one or more elements in the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.80 ≤ a ≤ 1.20, 0.80 ≤ b < 1, 0 <c<0.45,0<d<0.45,0≤e≤0.20。

[0017] Mathematical formula (1): Degree of single crystallinity =

[0018] In the above mathematical formula (1), A k The area of ​​the kth grain is measured by ion milling of an electrode made using the cathode material powder, followed by analysis of the cross-section of the electrode by electron backscatter diffraction (EBSD), where n is the total number of grains measured by electron backscatter diffraction (EBSD) analysis, which is between 200 and 500.

[0019] [2] In the above [1], the above chemical formula 1 can be represented by the following chemical formula 1-1.

[0020] [Chemical Formula 1-1]

[0021] Li a1 Ni b1 Co c1 Mn d1 Al d2 M 2 e1 O2

[0022] In the above chemical formula 1-1, M 2 It can be one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and it can be 0.85≤a1≤1.20, 0.80≤b1<1, 0 <c1<0.18,0<d1<0.18,0<d2<0.15,0≤e1≤0.20,0<d1+d2<0.33。

[0023] [3] In [1] or [2] above, the positive electrode material powder may have a particle size of 0.40 μm. 2 / g to 0.75 m 2 Specific surface area per g.

[0024] [4] In at least one of [1] to [3] above, the cathode material powder may have a calendering density of 2.9 g / cc to 3.2 g / cc.

[0025] [5] In at least one of [1] to [4] above, when the cathode material powder is pressurized with 9 tons, the production rate of fine powder with a particle size of less than 1 μm can be less than 6% by volume.

[0026] [6] In at least one of [1] to [5] above, the positive electrode material powder may have an average particle size (D) of 2 μm to 5 μm. 50 ).

[0027] [7] In at least one of [1] to [6] above, the degree of monocrystallization of the cathode material powder, as expressed by mathematical formula (1), is 2.0 to 2.5.

[0028] [8] The present invention provides a method for preparing a positive electrode material powder of at least one of [1] to [7] above, the method comprising the following steps: (S1) mixing a positive electrode active material precursor and a lithium source, and then calcining the mixture once; and (S2) calcining the calcined product obtained by the first calcination a second time, wherein the first calcination is carried out at 850°C to 960°C for 10 to 20 hours, and the second calcination sequentially includes a first holding period at 720°C to 850°C, a second holding period at 900°C to 970°C, and a third holding period at 720°C to 850°C, and the positive electrode active material precursor has a nickel content of 80 mol% or more in all metals except lithium.

[0029] [9] In the above [8], the first firing can be carried out at 870°C to 960°C for 10 to 15 hours.

[0030]

[10] In [8] or [9] above, the first retention period and the third retention period can be maintained independently for 5 to 10 hours.

[0031]

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

[10] above, the second holding period may be maintained for 5 minutes to 60 minutes.

[0032]

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

[11] above, the total firing time of the secondary firing can be 10 hours to 15 hours.

[0033]

[13] The present invention provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte comprising a positive electrode material powder containing at least one of the above [1] to [7].

[0034] Beneficial effects

[0035] The cathode material powder of the present invention is characterized in that the degree of monocrystallization, as expressed by mathematical formula (1), is in the range of 1.85 to 3.00. In the case of lithium secondary batteries using cathode material powders with a degree of monocrystallization of less than 1.85 or greater than 3.00, as expressed by mathematical formula (1), the amount of gas generated during high-temperature storage is large, and the high-temperature life characteristics are reduced.

[0036] On the other hand, when a lithium secondary battery is used with a cathode material powder having a monocrystallinity that satisfies the above-mentioned range of the present invention, both high-temperature life characteristics and high-temperature storage characteristics are excellent. Attached Figure Description

[0037] Figure 1 This is a SEM image of a cross-section of an electrode manufactured using the positive electrode material powder prepared in Example 1 of the present invention.

[0038] Figure 2 This is a SEM image of a cross-section of an electrode manufactured using the positive electrode material powder prepared in Example 2 of the present invention.

[0039] Figure 3 This is a SEM image of a cross-section of an electrode manufactured using the positive electrode material powder prepared in Comparative Example 2 of the present invention.

[0040] Figure 4 It is a SEM image of a cross-section of an electrode made using the positive electrode material powder prepared in Example 1 of the present invention, and the image was obtained by performing EBSD analysis.

[0041] Figure 5 It is a SEM image of a cross-section of an electrode made using the positive electrode material powder prepared in Example 2 of the present invention, and the image was obtained by performing EBSD analysis.

[0042] Figure 6 The image is a cross-sectional SEM image of an electrode manufactured using the cathode material powder prepared in Comparative Example 2 of the present invention, and the image was obtained by performing EBSD analysis. Detailed Implementation

[0043] The invention will be described in more detail below.

[0044] It should be understood that the terms or words used in this specification and claims should not be construed as having the meanings defined in commonly used dictionaries, but should be interpreted as having meanings and concepts consistent with the technical ideas of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best interpret the invention.

[0045] In this invention, a "grain" is a particle unit with the same crystal orientation and is considered to be the smallest particle unit of a single block in an electron backscatter diffraction (EBSD) distribution (map) image. The size of the grain can be measured by analyzing the EBSD distribution map.

[0046] In this invention, "single particle" refers to a particle consisting of a single nodule, and "quasi-single particle" refers to a complex particle consisting of 30 or fewer nodules.

[0047] "Nodules" are sub-particle units that make up single particles and quasi-single particles. They can be single crystals without grain boundaries or polycrystalline particles that do not appear to have grain boundaries when observed with a scanning electron microscope at 5,000 to 20,000x magnification.

[0048] In this invention, "secondary particles" refer to particles formed by the aggregation of multiple (e.g., dozens to hundreds) primary particles. Specifically, secondary particles can be aggregates of 50 or more primary particles.

[0049] In this invention, "particle" is a concept that includes any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0050] In this invention, the "specific surface area" is measured by the BET method, specifically calculated using the Belserp-mini II of BEL Japan Co., Ltd. from the amount of nitrogen adsorbed at liquid nitrogen temperature (77K).

[0051] In this invention, "average particle size D" 50 "" refers to the particle size representing 50% of the volumetric cumulative particle size distribution of the cathode material powder, which can be measured using laser diffraction. For example, the average particle size D can be measured in the following way. 50 The cathode material powder is dispersed in a dispersion medium, and then the mixture is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac MT3000) to be irradiated with ultrasound at an output of 60 W at approximately 28 kHz to obtain a volumetric cumulative particle size distribution map, and then the particle size corresponding to 50% of the cumulative volume is obtained.

[0052] As a result of repeated research into developing cathode materials with excellent high-temperature properties, the inventors have discovered that if the ratio of the sum of the squares of the grain areas of the cathode material powder to the sum of its grain areas satisfies a specific relationship, excellent high-temperature properties can be achieved, and thus the present invention has been completed.

[0053] The present invention will be described in detail below.

[0054] The cathode material powder, its preparation method, and the lithium secondary battery comprising the present invention comprise at least one of the following disclosed compositions, and may comprise any combination of the following technically possible compositions.

[0055] Positive electrode material powder

[0056] The cathode material powder of the present invention will be described below.

[0057] The degree of monocrystallization of the cathode material powder of the present invention, as expressed by the following mathematical formula (1), is 1.85 to 3.00.

[0058] Mathematical formula (1): Degree of single crystallinity =

[0059] In the above mathematical formula (1), A kThe area of ​​the k-th grain is measured by ion milling of an electrode made using the aforementioned cathode material powder, followed by analysis of the electrode's cross-section using electron backscatter diffraction (EBSD), and A k It is based on μm 2 The value measured in units. Specifically, A k The value can be obtained through the software of the EBSD device. Additionally, A k 2 A was obtained through the above method k The square of , and refers to the square of the area of ​​the k-th grain.

[0060] Meanwhile, A, substituted into mathematical expression (1) k and A k 2 It is a dimensionless number excluding units.

[0061] n is the total number of grains measured by electron backscatter diffraction (EBSD) analysis, and can be 200 to 500, preferably 250 to 450, more preferably 300 to 400. If the measured total number of grains is too small, it does not represent the trend of grain size in the entire cathode material powder, while if it is too large, it may reduce the measurement accuracy.

[0062] Electron backscatter diffraction (EBSD) analysis is a method that measures crystal phases and crystal orientations using the diffraction pattern of a sample and analyzes crystallographic information based on the measurement results. If the sample is tilted at a large angle relative to the incident direction of the electron beam in a scanning electron microscope, the incident electron beam is scattered within the sample, resulting in a diffraction pattern appearing on the surface of the sample; this is called an electron backscatter diffraction pattern (EBSP). The electron backscatter diffraction pattern responds to the crystal orientation of the region irradiated by the electron beam, and therefore can be used to accurately measure the crystal orientation of the sample, obtaining an EBSD inverse pole figure (IPF) for individual grains with the same crystal orientation. Furthermore, EBSD software can be used for image analysis of the IPF plots to obtain information such as grain size, shape, and orientation.

[0063] In this invention, for EBSD analysis of cathode material powder, an electrode for EBSD analysis is fabricated using the cathode material powder to be analyzed. The fabricated electrode is then cut by ion milling, and an electron beam is irradiated onto the cross-section of the cut electrode for EBSD analysis. Specifically, the electrode for EBSD measurement can be fabricated by mixing the cathode material powder to be analyzed, a conductive material, and a binder in N-methylpyrrolidone to prepare an electrode slurry, applying the electrode slurry onto an aluminum current collector, and then drying it. Simultaneously, a rolling process is not performed when fabricating the electrode for EBSD analysis. This is because if a rolling process is performed, the cathode active material particles may deform or break.

[0064] Figures 4 to 6 The image shows an IPF plot obtained by EBSD analysis of the cross-section of electrodes manufactured using the positive electrode material powders of Examples 1 to 2 and Comparative Example 2 described later. Figures 4 to 6 As shown, EBSD analysis can be used to obtain images of individual grain unit partitions.

[0065] According to the inventors' research, if the degree of monocrystallization represented by the above mathematical formula (1) meets a specific range, the effect of simultaneously improving high-temperature storage and high-temperature lifespan characteristics can be obtained.

[0066] The degree of single crystallinity, as expressed by the above mathematical formula (1), is 1.85 to 3.00. The degree of single crystallinity is preferably 1.9 to 2.8, and more preferably 2.0 to 2.5. The above mathematical formula (1) is obtained by dividing the sum of the squares of the grain areas that appear during EBSD analysis by the sum of the grain areas. If the above mathematical formula (1) is less than 1.85, the reaction area of ​​the cathode material powder reacting with the electrolyte increases, thereby accelerating electrolyte decomposition and surface structure deterioration, resulting in problems with deterioration of high-temperature storage characteristics and lifetime characteristics. If the above mathematical formula (1) is greater than 3.00, the movement distance of lithium ions diffuse into the particles increases, thereby deteriorating lithium mobility. Therefore, there is an imbalance of lithium ions between the inside and outside of the particles during charge and discharge, resulting in problems with deterioration of high-temperature storage characteristics and lifetime characteristics. Therefore, it has been found that if a lithium secondary battery is manufactured by using cathode material powder that meets the above range, both high-temperature storage characteristics and high-temperature lifetime characteristics are excellent.

[0067] The degree of single crystallinity represented by the above mathematical formula (1) can be controlled by various methods, but it can preferably be controlled according to the number of moles of nickel contained in the lithium nickel oxide particles and the type of raw materials used in the preparation of cathode material powder, mixing ratio, firing steps, firing temperature, firing time, firing atmosphere, etc.

[0068] Meanwhile, the cathode material powder of the present invention includes lithium nickel-based oxide particles represented by Chemical Formula 1 below.

[0069] [Chemical Formula 1]

[0070] Li a Ni b Co c M 1 d M 2 e O2

[0071] In Chemical Formula 1 above, M 1 is Mn, Al, or a combination thereof, preferably a combination of Mn or Mn and Al, more preferably a combination of Mn and Al.

[0072] M 2 is one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, preferably one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Sr, W, and Nb, more preferably one or more selected from the group consisting of Ti, Mg, Al, Zr, and Y. The M 2 element is not necessarily included, 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.

[0073] a represents the molar ratio of lithium in the lithium nickel-based oxide particles and can satisfy 0.80 ≤ a ≤ 1.20, 0.90 ≤ a ≤ 1.10, or 0.95 ≤ a ≤ 1.15. When the molar ratio of lithium satisfies the above range, a stable layered crystal structure can be formed.

[0074] b represents the molar ratio of nickel in all metals other than lithium in the lithium nickel-based oxide particles and can satisfy 0.80 ≤ b < 1, 0.82 ≤ b < 1, or 0.85 ≤ b < 1. If the molar ratio of nickel satisfies the above range, excellent capacity characteristics are exhibited, and particularly, if the molar ratio of nickel is 0.80 or more, even more excellent capacity characteristics can be achieved, while if the molar ratio of nickel is less than 0.80, there is a problem that it is difficult to achieve the single crystallinity represented by the above mathematical formula (1).

[0075] c represents the molar ratio of cobalt in all metals other than lithium in the lithium nickel-based oxide particles and can satisfy 0 < c < 0.45, 0 < c < 0.40, 0 < c < 0.20, or 0 < c < 0.18.

[0076] d represents M in all metals other than lithium in the lithium nickel-based oxide particles 1The molar ratio of the elements, and can satisfy 0 < d < 0.45, 0 < d < 0.40, 0 < d < 0.33, 0 < d < 0.25, 0 < d < 0.20, or 0 < d < 0.18.

[0077] e represents M in all metals other than lithium in the lithium nickel oxide particles 2 The molar ratio of the elements, and can satisfy 0 ≤ e ≤ 0.20, 0 ≤ e ≤ 0.15, or 0 ≤ e ≤ 0.10.

[0078] More preferably, the above Chemical Formula 1 can be represented by the following Chemical Formula 1-1.

[0079] [Chemical Formula 1-1]

[0080] Li a1 Ni b1 Co c1 Mn d1 Al d2 M 2 e1 O2

[0081] In the above Chemical Formula 1-1, M 2 can be one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and can be 0.80 ≤ a1 ≤ 1.20, 0.80 ≤ b1 < 1, 0 < c1 < 0.18, 0 < d1 < 0.18, 0 < d2 < 0.15, 0 ≤ e1 ≤ 0.20, 0 < d1 + d2 < 0.33. Preferably, 0.80 ≤ a1 ≤ 1.20, 0.82 ≤ b1 < 1, 0 < c1 < 0.15, 0 < d1 < 0.15, 0 < d2 < 0.10, 0 ≤ e1 ≤ 0.10, 0 < d1 + d2 < 0.25. More preferably, 0.80 ≤ a1 ≤ 1.20, 0.85 ≤ b1 < 1, 0 < c1 < 0.15, 0 < d1 < 0.15, 0 < d2 < 0.10, 0 ≤ e1 ≤ 0.10, 0 < d1 + d2 < 0.25. If the lithium nickel oxide particles have the composition of Chemical Formula 1-1, the structural stability and capacity characteristics of the positive electrode active material are excellent.

[0082] Meanwhile, the positive electrode material powder may further include a coating layer formed on the surface of the lithium nickel oxide particles and containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

[0083] If a coating is present on the surface of lithium nickel oxide particles, the contact between the electrolyte and the lithium nickel oxide particles is suppressed by the coating. As a result, it can have the effect of reducing the dissolution of transition metals or the generation of gases due to side reactions with the electrolyte.

[0084] Meanwhile, the lithium nickel oxide particles can be single particles consisting of a single nucleus and / or quasi-single particles as a composite of 30 or fewer nuclei, preferably 2 to 20 nuclei, more preferably 2 to 10 nuclei, or can be in a form including the above. Preferably, the cathode material powder of the present invention can be composed of a combination of cathode active material particles in the form of single particles and quasi-single particles. This is because if the number of nuclei constituting the cathode active material particles is greater than 30, particle breakage increases during electrode manufacturing, and internal cracking increases due to the volume expansion / contraction of the nuclei during charging and discharging, which may reduce the effect of improving high-temperature lifetime characteristics and high-temperature storage characteristics.

[0085] Meanwhile, the specific surface area of ​​the cathode material powder can be 0.40 m². 2 / g to 0.75 m 2 / g, preferably 0.45 m 2 / g to 0.70 m 2 / g, more preferably 0.50 m 2 / g to 0.70 m 2 / g. If the above BET specific surface area range is met, side reactions with the electrolyte can be appropriately reduced to decrease gas generation and improve the high-temperature life characteristics of the battery.

[0086] Meanwhile, the rolling density of the cathode material powder can be from 2.9 g / cc to 3.2 g / cc, preferably from 2.95 g / cc to 3.1 g / cc. If the above-mentioned rolling density of the cathode material powder is met, excellent energy density can be ensured, and particle breakage that occurs during electrode rolling can be prevented to appropriately reduce side reactions with the electrolyte, thereby improving the battery's lifespan and stability characteristics.

[0087] Meanwhile, when the cathode material powder is pressurized with 9 tons, the generation rate of fine powder smaller than 1 μm can be less than 6% by volume, preferably less than 5% by volume, and more preferably less than 3% by volume. Since the surface side reactions of the cathode active material are mainly caused by the generation of fine powder of the cathode active material, if a large amount of fine powder smaller than 1 μm is generated, the side reactions with the electrolyte may be aggravated, which may reduce the lifetime characteristics and storage characteristics at high temperatures.

[0088] Meanwhile, the average particle size (D) of the cathode material powder 50The average particle size (D) of the cathode material powder can be from 2 μm to 5 μm, preferably from 2.5 μm to 4.5 μm, more preferably from 3 μm to 4 μm, and even more preferably from 3.3 μm to 3.7 μm. 50 () is the particle size when the cumulative volume appearing in the volume-cumulative particle size distribution measured by laser diffraction is 50%. In this case, if the average particle size (D) of the cathode material powder 50 If the above range is met, the initial capacity and output characteristics of the battery can be excellent.

[0089] Method for preparing cathode material powder

[0090] Next, the method of the present invention for preparing cathode material powder will be described.

[0091] The method for preparing cathode material powder according to the present invention includes: (S1) mixing a cathode active material precursor and a lithium source, and then calcining the mixture once; and (S2) calcining the calcined product obtained by the first calcination a second time, wherein the first calcination is carried out at 850°C to 960°C for 10 to 20 hours, and the second calcination sequentially includes a first holding period at 720°C to 850°C, a second holding period at 900°C to 970°C, and a third holding period at 720°C to 850°C, and wherein the cathode active material precursor has a nickel content of 80 mol% or more in all metals except lithium.

[0092] The cathode material powder of the present invention can be prepared by appropriately controlling the type of raw materials, mixing ratio, firing steps, firing temperature, firing atmosphere, etc.

[0093] Each step of the invention will be described in detail below.

[0094] (Step S1)

[0095] This involves mixing the positive electrode active material precursor and the lithium source, and then calcining the mixture once, with the calcination taking place at 850°C to 960°C for 10 to 20 hours.

[0096] The nickel content in the precursor of the positive electrode active material is 80 mol% or more in all metals except lithium. Preferably, the nickel content in all metals except lithium can be 82 mol% or more, and more preferably, the nickel content in all metals except lithium can be 85 mol% or more. If the nickel content in the precursor of the positive electrode active material is less than 80 mol%, a large amount of heat is required to ensure crystallinity as the nickel content decreases and the content of other elements increases. Therefore, a high firing temperature is necessary to increase the degree of monocrystallization. Therefore, if the nickel content in the precursor of the positive electrode active material is less than 80 mol%, it is difficult to control the degree of monocrystallization, as expressed by mathematical formula (1), within the firing temperature range of the present invention. Even if the positive electrode active material powder is prepared by the first firing and second firing of the present invention, it is difficult to achieve excellent high-temperature storage characteristics and lifetime characteristics.

[0097] In addition, the positive electrode active material precursor can be a commercially available precursor, such as nickel cobalt manganese hydroxide, nickel cobalt manganese aluminum hydroxide, etc., or it can be prepared according to precursor preparation methods known in the art (e.g., co-precipitation).

[0098] For example, a solution containing transition metals, including cations of nickel (Ni), cobalt (Co), and manganese (Mn), is prepared. Then, the solution containing transition metals is added together with a complex forming agent containing ammonium cations and an alkaline aqueous solution to carry out a co-precipitation reaction, thereby preparing a precursor for a positive electrode active material. If necessary, the solution containing transition metals may also contain cations of aluminum (Al).

[0099] Solutions containing transition metals may include nickel-containing raw materials, cobalt-containing raw materials, and manganese-containing raw materials, and may also include aluminum-containing raw materials if necessary.

[0100] Nickel-containing raw materials can be, for example, nickel-containing acetates, nitrates, sulfates, halides, sulfides, hydroxides, oxides, hydroxyoxides, etc., and can specifically 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.

[0101] 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.

[0102] 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 such as Mn2O3, MnO2 and Mn3O4, manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylic acid, manganese citrate and fatty acid manganese salts, manganese hydroxyoxide, manganese chloride or combinations thereof, but are not limited thereto.

[0103] 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, but are not limited thereto.

[0104] Solutions containing transition metals can be prepared by adding nickel-containing, cobalt-containing, manganese-containing, and aluminum-containing raw materials to a solvent, specifically water or a mixture of water and an organic solvent (e.g., alcohol) that can be uniformly mixed with water, or by mixing an aqueous solution of nickel-containing raw materials, an aqueous solution of cobalt-containing raw materials, and a manganese-containing raw material.

[0105] The ammonium cation-containing complex forming agent can be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or combinations thereof, but is not limited thereto. Furthermore, the ammonium cation-containing complex forming agent can be used in the form of an aqueous solution, in which case a mixture of an organic solvent (e.g., an alcohol) and water that is homogeneous with water can be used as the solvent.

[0106] Basic compounds can be hydroxides of alkali metals or alkaline earth metals, such as NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Basic compounds can also be used in the form of aqueous solutions, in which case a mixture of an organic solvent (e.g., an alcohol) and water that is homogeneous with water can be used as the solvent.

[0107] An alkaline compound is added to control the pH of the reaction solution; the amount added is such that the pH of the metal solution is between 8 and 12.

[0108] The coprecipitation reaction can be carried out in an inert atmosphere (such as in a nitrogen atmosphere, argon atmosphere, etc.) at a temperature of 35°C to 80°C.

[0109] Through the above process, nickel-cobalt-manganese hydroxide or nickel-cobalt-manganese-aluminum hydroxide precursor particles are generated and precipitated in the reaction solution. By controlling the concentrations of nickel-containing, cobalt-containing, manganese-containing, and aluminum-containing raw materials, a precursor with a nickel (Ni) content of 55 mol% or higher in the total metal content can be prepared. The precipitated precursor particles are separated using conventional methods and dried to prepare the precursor.

[0110] Lithium raw materials can be lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, 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, Li₃C₆H₅O₇, etc., and any one of them or a mixture of two or more of them can be used.

[0111] Mixing can be carried out through solid-phase mixing or liquid-phase mixing. If the components are mixed by solid-phase mixing, the firing process can be carried out without a separate drying process, while if the components are mixed by liquid-phase mixing, the firing process is carried out after the mixed components are spray-dried.

[0112] In addition, if necessary, raw materials can be mixed and doped.

[0113] As doping materials, oxides, hydroxides, sulfides, hydroxy oxides, halides, or mixtures thereof of one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo can be used.

[0114] A single firing can be carried out in an air or oxygen atmosphere.

[0115] The single firing can be carried out at a temperature of 850°C to 960°C, preferably 860°C to 960°C, and more preferably 870°C to 960°C. By firing within the above temperature range, cathode material powder with improved crystallinity and thus improved structural stability can be prepared, and an appropriate degree of monocrystalline structure can be obtained by controlling the grain area measured on the cross-section of the electrode made using the cathode material powder to an appropriate value.

[0116] Furthermore, a single firing process can last from 10 to 20 hours, preferably from 10 to 18 hours, and more preferably from 10 to 15 hours. If the firing time is less than 10 hours, the crystallinity is poor, resulting in reduced structural stability, and particle growth cannot be fully achieved, leading to low monocrystallization. In addition, if the firing time exceeds 20 hours, the battery's output characteristics deteriorate due to over-firing.

[0117] (Step S2)

[0118] The method includes a second firing of the fired product obtained by a single firing, wherein the second firing sequentially includes a first holding period at 720°C to 850°C, a second holding period at 900°C to 970°C, and a third holding period at 720°C to 850°C. The firing can be carried out in an air or oxygen atmosphere.

[0119] The secondary firing involves maintaining the second holding period at a higher temperature than the first and third holding periods, thus allowing for appropriate control of the monocrystalline degree of the cathode material powder. Specifically, by including a second holding period for a short duration of heat treatment at a higher temperature than the first and third holding periods, the monocrystalline degree of particles that are growing unevenly due to insufficient heat can be increased, making it possible to prepare cathode material powder with an appropriate monocrystalline degree. Furthermore, if the first to third holding periods are included in a single firing rather than a secondary firing, it may be difficult to obtain an appropriate monocrystalline degree.

[0120] The temperatures for the first and third holding periods can each be independently between 720°C and 850°C, preferably between 730°C and 840°C, or more preferably between 750°C and 830°C, and the temperatures for the first and third holding periods can be the same. If the above ranges are met, high-temperature life and high-temperature storage performance can be improved due to excellent surface structure stability, and the capacity characteristics, output characteristics, and high-temperature life characteristics of the battery can be improved due to less particle agglomeration.

[0121] The temperature for the second holding period can be 900°C to 970°C, preferably 910°C to 960°C, and more preferably 920°C to 950°C. If the above range is met, sufficient heat can be used to grow particles, thereby solving the problem of uneven particle growth caused by insufficient heat, and thus improving the high-temperature life characteristics and high-temperature storage characteristics of the battery.

[0122] The first holding period can be maintained for 5 to 10 hours, preferably 6 to 10 hours, or more preferably 7 to 9 hours. If the above range is met, the particles can agglomerate in an appropriate amount, thereby satisfying the desired monocrystallization range.

[0123] The second holding period can be maintained for 5 to 60 minutes, preferably 10 to 50 minutes, or more preferably 10 to 40 minutes. If the above range is met, the problem of uneven particle growth can be solved, thus achieving an appropriate range of monocrystalline degree.

[0124] The third holding period can be maintained for 5 to 10 hours, preferably 6 to 10 hours, or more preferably 7 to 9 hours. If the above range is met, the particles can agglomerate in an appropriate amount, thereby satisfying the desired monocrystallization range.

[0125] The total firing time for the second firing can be 10 to 15 hours, preferably 10 to 14 hours, or more preferably 10 to 13 hours. If the above range is met, the surface structure stability can be fully achieved, thereby improving the surface structure durability, and the particles will not excessively agglomerate with each other, thus improving the electrochemical characteristics of the battery.

[0126] If necessary, the fired products that have undergone secondary firing and the coating raw materials can be mixed and heat-treated to form a coating.

[0127] The coating can be formed by methods known in the art. For example, wet coating methods, dry coating methods, plasma coating methods, atomic layer deposition (ALD), etc., can be used.

[0128] Wet coating can be carried out, for example, by adding a suitable solvent such as ethanol, water, methanol, or acetone to the calcined product and the coating material that has undergone two firings, and then mixing the mixture until the solvent is removed.

[0129] Dry coating is a method of mixing lithium composite transition metal oxides and coating materials in a solid phase without solvents, for example, by using a grinding mill or mechanical fusion method.

[0130] The coating material can be an oxide, hydroxide, hydroxyoxide, carbonate, sulfate, halide, sulfide, acetate, carboxylate, or combination thereof containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Zr, Sr, W, Ta, Nb, and Mo.

[0131] positive electrode

[0132] Next, the positive electrode of the present invention will be described.

[0133] The positive electrode of the present invention comprises a positive electrode active material layer containing the positive electrode material powder of the present invention. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode material powder. Since the positive electrode material powder has been described above, the description of the positive electrode material powder will be omitted, and the components other than the positive electrode material powder will be described below.

[0134] In the positive electrode, there are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, and silver can be used. Moreover, the positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector 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.

[0135] In addition, the positive electrode active material layer may include conductive materials and binders together with the aforementioned positive electrode material powder.

[0136] 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 materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; 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 these may be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material is typically 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0137] The adhesive is used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, 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 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0138] The positive electrode can be manufactured according to conventional methods used for manufacturing positive electrodes. For example, the positive electrode can be manufactured by mixing positive electrode materials, binders and / or conductive materials in a solvent to prepare a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, and then drying and calendering it.

[0139] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water, and any one or a mixture of two or more of these can be used. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, while considering the coating thickness and preparation yield of the slurry, and to give the slurry a viscosity that exhibits excellent thickness uniformity during subsequent coating to manufacture the positive electrode.

[0140] In another method, the positive electrode can be manufactured by casting a positive electrode slurry onto a separate support, and then pressing a film layer peeled off from the support onto a positive electrode current collector.

[0141] Lithium secondary batteries

[0142] Next, the lithium secondary battery of the present invention will be described.

[0143] The lithium secondary battery of the present invention includes a positive electrode of the present invention, specifically, a positive electrode containing the positive electrode material powder of the present invention. More specifically, the lithium secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte. More specifically, the lithium secondary battery may include a positive electrode, a negative electrode arranged opposite to the positive electrode, a separator between the positive and negative electrodes, and an electrolyte, wherein the positive electrode is the same as described above. Furthermore, the lithium secondary battery may optionally further include a battery casing for housing electrode assemblies of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery casing.

[0144] (negative electrode)

[0145] 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.

[0146] 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, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or 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 like the positive electrode current collector, fine irregularities can be formed on its surface 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.

[0147] In addition to the negative electrode active material, the negative electrode active material layer may optionally include an adhesive and a conductive material.

[0148] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples can include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metal compounds 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; and metal oxides that can be doped and de-doped with lithium, such as SiO₂. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a complex of metal compounds and carbonaceous materials, such as Si-C complex or Sn-C complex, and any one of them or a mixture of two or more thereof may be used.

[0149] Furthermore, lithium metal films can be used as anode active materials. Additionally, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include irregular, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, liquid crystal pitch, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon, such as coke derived from petroleum or coal tar pitch.

[0150] The conductive material is used to impart conductivity to the electrode. 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. Specific examples may include: graphite, such as natural or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or fibers such as copper, nickel, aluminum, and silver; 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 these may be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material is typically 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0151] The adhesive is used to improve the bonding between particles of the negative electrode active material and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, 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 negative electrode active material layer, the adhesive content may be 1 to 30% by weight, preferably 1 to 20% by weight, more preferably 1 to 10% by weight.

[0152] As an example, the negative electrode active material layer can be prepared by coating a negative electrode slurry containing a negative electrode active material and optionally a binder and conductive material onto a negative electrode current collector and then drying it; or by casting the negative electrode slurry onto a separate support and then pressing the film layer peeled off from the support onto the negative electrode current collector.

[0153] (Septum)

[0154] Meanwhile, in lithium-ion secondary batteries, the separator separates the negative and positive electrodes and provides 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. Separators with high electrolyte retention capacity and low resistance to electrolyte ion movement are particularly preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer), or stacked structures of two or more layers thereof. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0155] (electrolytes)

[0156] 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.

[0157] Specifically, electrolytes can include organic solvents and lithium salts.

[0158] As organic solvents, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating 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 hydrocarbon 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), or propylene carbonate (PC); alcohol solvents, such as ethanol or isopropanol; nitriles, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) are more preferred, as they can improve the charge and discharge performance of the battery.

[0159] Any compound can be used as a lithium salt without particular limitation, as long as it can provide lithium ions for use in lithium secondary batteries. Specifically, 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 as lithium salts. Lithium salts are preferred in concentration ranges from 0.1 to 5.0 M, preferably from 0.1 M to 3.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0160] To improve battery life performance, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also include additives. For example, additives may be used alone or in combination with the following substances: alkyl halogenated carbonate compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride, etc., but additives are not limited to these. Based on the total weight of the electrolyte, the content of additives may be 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

[0161] As described above, lithium secondary batteries comprising the cathode material powder of the present invention stably exhibit excellent discharge capacity, output characteristics and capacity retention, and are therefore applicable to portable devices (e.g., mobile phones, laptops, digital cameras, etc.) and electric vehicles (e.g., hybrid electric vehicles (HEVs)).

[0162] Therefore, another embodiment of the present invention provides a battery module comprising a unit cell of the lithium secondary battery and a battery pack comprising the battery module.

[0163] The battery module or battery pack can be used as a power source for one or more large or medium-sized devices in power tools, electric vehicles (including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs)) or energy storage systems.

[0164] The 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.

[0165] Example 1

[0166] Nickel-cobalt-manganese-aluminum hydroxide powder with a molar ratio of Ni:Co:Mn:Al of 85:7:6:2 was mixed with lithium hydroxide to make the molar ratio of transition metal (Ni+Co+Mn+Al):Li 1:1.04. The mixture was then calcined at 950°C for 12 hours.

[0167] Subsequently, the cathode material powder is prepared by performing the following operations in sequence: the sintered product obtained by the first sintering is held at 820°C for 5 hours for a first holding period, held at 950°C for 10 minutes for a second holding period, and held at 820°C for 5 hours for a third holding period.

[0168] Example 2

[0169] Except for a single firing at 870°C for 12 hours, and a second firing by sequentially holding the fired mixture at 805°C for 5 hours, holding it at 950°C for 10 minutes, and holding it at 805°C for 5 hours, the cathode material powder was prepared in the same manner as in Example 1.

[0170] Comparative Example 1

[0171] Nickel-cobalt-manganese-aluminum hydroxide powder with a molar ratio of Ni:Co:Mn:Al of 85:7:6:2 was mixed with lithium hydroxide to make the molar ratio of transition metal (Ni+Co+Mn+Al):Li 1:1.04. The mixture was then sintered at 830°C for 22 hours to prepare cathode material powder.

[0172] Comparative Example 2

[0173] Except for a single calcination at 950°C for 20 hours, the cathode material powder was prepared in the same manner as in Comparative Example 1.

[0174] Comparative Example 3

[0175] Nickel-cobalt-manganese-aluminum hydroxide powder with a molar ratio of Ni:Co:Mn:Al of 85:7:6:2 was mixed with lithium hydroxide to make the molar ratio of transition metal (Ni+Co+Mn+Al):Li 1:1.04. The mixture was then calcined at 950°C for 8 hours, followed by calcination at 800°C for 8 hours to prepare cathode material powder.

[0176] Comparative Example 4

[0177] Except for a single firing at 965°C for 10 hours and a firing at 860°C for 10 hours, the cathode material powder was prepared in the same manner as in Comparative Example 3.

[0178] Comparative Example 5

[0179] Nickel-cobalt-manganese-aluminum hydroxide powder with a molar ratio of Ni:Co:Mn:Al of 85:7:6:2 was mixed with lithium hydroxide to make the molar ratio of transition metal (Ni+Co+Mn+Al):Li 1:1.04. The cathode material powder was then prepared by calcining the mixture by holding it at 920°C for 8 hours, holding it at 950°C for 10 minutes, and then holding it at 920°C for 8 hours.

[0180] Comparative Example 6

[0181] Except for a single firing at 950°C for 12 hours, and a second firing by sequentially holding the fired mixture at 820°C for 5 hours, holding it at 990°C for 5 minutes, and holding it at 820°C for 5 hours, the cathode material powder was prepared in the same manner as in Example 1.

[0182] Comparative Example 7

[0183] Except for a single firing at 950°C for 12 hours, and a second firing by sequentially holding the fired mixture at 820°C for 5 hours, holding it at 890°C for 20 minutes, and holding it at 820°C for 5 hours, the cathode material powder was prepared in the same manner as in Example 1.

[0184] Comparative Example 8

[0185] Except that the nickel-cobalt-manganese-aluminum hydroxide powder with a molar ratio of Ni:Co:Mn:Al of 75:5:18:2 was mixed with lithium hydroxide to make the molar ratio of transition metal (Ni+Co+Mn+Al):Li 1:1.04, the cathode material powder was prepared in the same manner as in Example 1.

[0186] The preparation methods of Examples 1 and 2 and Comparative Examples 1 to 8 are summarized and shown in Table 1 below.

[0187] Table 1

[0188] Experimental Example 1: Measurement of average particle size, BET specific surface area, particle breakage and calendering density

[0189] (average particle size (D) 50 )Measurement)

[0190] 0.03 g of each cathode material powder prepared in Examples 1 and 2 and Comparative Examples 1 to 8 were dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (Microtrac MT 3000). Subsequently, ultrasonic waves at approximately 28 kHz were irradiated onto the powder with an output of 60 W to measure the average particle size (D) of each cathode material powder. 50 The measurement results are shown in Table 2 below.

[0191] (BET specific surface area measurement)

[0192] In addition, 3 g of positive electrode material powder prepared by Examples 1 and 2 and Comparative Examples 1 to 8 were collected and then measured by BELSORP Co-mini II using the BET method. The measurement results are shown in Table 2 below.

[0193] (Particle breakage measurement)

[0194] In addition, 5 g of cathode material powder prepared by Examples 1 and 2 and Comparative Examples 1 to 8 were placed in a cylindrical metal mold with a diameter of 4 cm, pressurized under a pressure of 9 tons, and then the volumetric cumulative particle size distribution (PSD) was measured to determine the yield of fine powder with a particle size of less than 1 μm. The yield of fine powder with a particle size of less than 1 μm was converted to volume % for the total volume of cathode material powder and is shown in Table 2.

[0195] (Caulking density measurement)

[0196] In addition, the calendering density was measured using a HANTECH HLP-AC12-T. Specifically, 5 g of cathode material powder prepared by Examples 1 and 2 and Comparative Examples 1 to 8 were placed in a cylindrical metal mold with a diameter of 4 cm, pressurized under a pressure of 2 tons, and then the height of the pressurized mold was measured by vernier calipers to obtain the calendering density, which is shown in Table 2.

[0197] Experimental Example 2: EBSD Analysis and Single Crystallinity Measurement

[0198] Electrode slurries were prepared by mixing the positive electrode material powders prepared in Examples 1 and 2 and Comparative Examples 1 to 8, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) at a weight ratio of 95:2.5:2.5. The electrode slurry was coated on one surface of an aluminum current collector and then dried at 130°C to prepare an electrode for EBSD analysis. No calendering was performed during the manufacture of the positive electrode.

[0199] The positive electrode was transversely cut using an ion milling apparatus (HITACHI IM-500, accelerating voltage 6 kV), and SEM images were obtained using a FE-SEM (JEOL JSM7900F) equipped with an electron backscatter diffraction (EBSD) analyzer. EBSD analysis was performed on the SEM images at an accelerating voltage of 15 kV and a WD of 15 mm, at a scale of approximately 400 + / - 10 grains.

[0200] By using EBSD analysis, the area of ​​each grain observed on each positive electrode cross section was measured and substituted into mathematical formula (1) to calculate the degree of monocrystallization. The measurement results are shown in Table 2 below.

[0201] also, Figures 1 to 3 SEM images of cross-sections of electrodes fabricated using the cathode material powders of Examples 1 and 2 and Comparative Example 2 are shown. Figures 4 to 6EBSD analysis images of cross sections of electrodes manufactured using the cathode material powders of Examples 1 and 2 and Comparative Example 2 are shown.

[0202] Table 2

[0203] As can be confirmed from Table 2 above, it can be seen that Examples 1 and 2 meet the above-mentioned degree of monocrystallization compared with Comparative Examples 1 to 8.

[0204] <Manufacturing of Lithium Secondary Batteries>

[0205] The positive electrode material powders prepared in Examples 1 and 2 and Comparative Examples 1 to 8, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) at a weight ratio of 95:2.5:2.5 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 calendered to manufacture the positive electrode.

[0206] Artificial graphite as the negative electrode active material, carbon black as the conductive material, and SBR-CMC as the binder are mixed in a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry. The negative electrode slurry is then coated on one surface of a copper current collector, dried at 100°C, and then calendered to manufacture the negative electrode.

[0207] A separator is inserted between the positive and negative electrodes to create an electrode assembly, which is then placed inside a battery casing. An electrolyte is then injected into the casing to create a lithium-ion secondary battery. The electrolyte is prepared by dissolving 1 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 1:2 volume ratio.

[0208] Experiment Example 3: Evaluation of High-Temperature Storage Characteristics

[0209] The lithium-ion secondary batteries manufactured as described above were each charged to 4.2 V at 0.5 C in CC-CV mode, and then the secondary batteries were disassembled to separate the positive electrode. The positive electrode and 200 μl of electrolyte were then placed in a pouch-type battery casing, and the casing was sealed to manufacture a cell. The cell was stored at 65°C for 8 weeks to measure the change in cell volume (Δcell volume, unit: ΔmL) 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 3.

[0210] Experiment Example 4: Evaluation of High-Temperature Lifetime Characteristics

[0211] The lithium secondary batteries manufactured as described above were each charged to 4.2 V at 1 C in CC-CV mode at 45°C and discharged to 2.5 V at a constant current of 2 C. This was set as one cycle, and then 100 charge-discharge cycles were performed to measure capacity retention in order to evaluate high-temperature lifetime characteristics. The measurement results are shown in Table 3.

[0212] Table 3

[0213] As can be confirmed from Table 3 above, the batteries using cathode material powders of Examples 1 and 2, whose monocrystallinity meets the scope of the present invention using mathematical formula (1), are superior to the batteries using cathode material powders of Comparative Examples 1 to 8 in terms of high-temperature life characteristics and high-temperature storage characteristics.

Claims

1. A cathode material powder comprising lithium nickel oxide particles represented by the following chemical formula 1, and having a degree of monocrystalline solidity of 1.85 to 3.00 as represented by the following mathematical formula (1): [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 in, In the above chemical formula 1, M 1 M is Mn, Al, or a combination thereof, M 2 The element is selected from one or more elements in the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.80 ≤ a ≤ 1.20, 0.80 ≤ b < 1, 0 <c<0.45,0<d<0.45,0≤e≤0.20, Mathematical formula (1): Degree of single crystallinity = In the above mathematical formula (1), A k The area of ​​the kth grain is measured by ion milling of an electrode made using the cathode material powder, followed by analysis of the cross-section of the electrode by electron backscatter diffraction (EBSD), where n is the total number of grains measured by electron backscatter diffraction (EBSD) analysis, which is between 200 and 500.

2. The positive electrode material powder as described in claim 1, wherein, The above chemical formula 1 is represented by the following chemical formula 1-1: [Chemical Formula 1-1] Li a1 Ni b1 Co c1 Mr d1 Al d2 M 2 e1 O2 In the above chemical formula 1-1, M 2 The element is selected from one or more of the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and 0.85 ≤ a1 ≤ 1.20, 0.80 ≤ b1 < 1, 0 <c1<0.18,0<d1<0.18,0<d2<0.15,0≤e1≤0.20,0<d1+d2<0.33。 3. The positive electrode material powder as described in claim 1, wherein, The positive electrode material powder has a particle size of 0.40 μm. 2 / g to 0.75m 2 Specific surface area per g.

4. The positive electrode material powder as described in claim 1, wherein, The cathode material powder has a calendering density of 2.9 g / cc to 3.2 g / cc.

5. The positive electrode material powder as described in claim 1, wherein, When the cathode material powder is pressurized with 9 tons, the production rate of fine powder with a particle size of less than 1 μm is less than 6% by volume.

6. The positive electrode material powder as described in claim 1, wherein, The cathode material powder has an average particle size D of 2 μm to 5 μm. 50 .

7. The positive electrode material powder as described in claim 1, wherein, The degree of monocrystallization of the cathode material powder, as expressed by mathematical formula (1), is 2.0 to 2.

5.

8. A method for preparing the cathode material powder of claim 1, the method comprising the following steps: (S1) The positive electrode active material precursor and the lithium source are mixed, and then the mixture is calcined once; and (S2) The fired product obtained by the first firing is subjected to a second firing. in: The first firing is carried out at 850°C to 960°C for 10 to 20 hours; The secondary firing process sequentially includes a first holding period at 720°C to 850°C, a second holding period at 900°C to 970°C, and a third holding period at 720°C to 850°C; and The positive electrode active material precursor has a nickel content of more than 80 mol% in all metals except lithium.

9. The method of claim 8, wherein, The first firing is carried out at 870°C to 960°C for 10 to 15 hours.

10. The method of claim 8, wherein, The first retention period and the third retention period are maintained independently for 5 to 10 hours.

11. The method of claim 8, wherein, The second holding period is 5 to 60 minutes.

12. The method of claim 8, wherein, The total firing time for the second firing is 10 to 15 hours.

13. A lithium secondary battery, comprising: A positive electrode comprising the positive electrode material powder of claim 1; negative electrode; Diaphragm; and Electrolytes.

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