Cathode active material for lithium secondary battery, preparation method therefor and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising: a nickel (Ni)-containing layered crystal structured lithium metal oxide in a single-particle form; and a coating layer, which is positioned on the surface of the lithium metal oxide and contains cobalt (Co) and fluorine (F), wherein the coating layer is attached to the surface of the lithium metal oxide and is in an island form comprising a plurality of adhered particles spaced apart from each other, the plurality of adhered particles having a particle size normal distribution index of 0.8 or less.

Description

A positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same. More specifically, the invention relates to a single-particle series positive electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0187966, filed on December 17, 2024, the entire contents of which are incorporated herein by reference.

[0003] 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 cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantage of high operating voltage and excellent capacity characteristics, but it is difficult to apply it commercially to large-capacity batteries due to the high cost and unstable supply of cobalt, which is the raw material. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. Meanwhile, lithium manganese oxide has the problem of poor capacity characteristics despite excellent stability. Accordingly, lithium composite transition metal oxides containing two or more transition metals have been developed to compensate for the problems of lithium transition metal oxides containing Ni, Co, or Mn alone; among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0004] Conventional lithium nickel cobalt manganese oxide was generally in the form of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide in the form of secondary particles with many primary particles aggregated in this manner, there are problems such as particle breakage where primary particles detach during the rolling process in anode manufacturing, and cracks occurring inside the particles during the charge-discharge process. If particle breakage or cracking occurs in the anode active material, the contact area with the electrolyte increases, leading to increased gas generation and active material degradation due to side reactions with the electrolyte, which in turn reduces lifespan characteristics.

[0005] To solve the above problem, a technology has been proposed to manufacture a cathode active material in the form of a single particle rather than a secondary particle by increasing the calcination temperature during the production of lithium nickel cobalt manganese oxide. In the case of a cathode active material in the form of a single particle, the contact area with the electrolyte is smaller compared to conventional cathode active materials in the form of secondary particles, so there are fewer side reactions with the electrolyte, and the particle strength is excellent, resulting in less particle breakage during electrode manufacturing. Therefore, when a cathode active material in the form of a single particle is applied, there are advantages such as reduced gas generation and excellent lifespan characteristics. In addition, there has recently been an increasing demand for high-output, high-capacity batteries, such as those for electric vehicles, and accordingly, there is a trend of gradually increasing the nickel content in the cathode active material (so-called “high nickel”).

[0006] However, high-nickel single-particle lithium metal oxides have a problem in that the safety of the battery is compromised due to the high content of residual lithium (LiOH and / or Li2CO3) remaining on the surface of the lithium metal oxide after calcination. At this time, if a washing process is performed to remove residual lithium, it damages the surface structure of the cathode material and increases the possibility of proton exchange, thereby impairing the electrochemical characteristics such as capacity and output of the cathode material, increasing manufacturing costs of the cathode material, and generating wastewater, which necessitates a separate wastewater treatment facility.

[0007] Accordingly, one objective of the present invention is to provide a positive electrode active material for a lithium secondary battery in which residual lithium is efficiently reduced while excellent electrochemical properties (capacity, etc.) are maintained by forming a coating layer on a lithium metal oxide in the form of a single particle, a method for manufacturing the same, and a lithium secondary battery including the same.

[0008] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery comprising: a lithium metal oxide having a single-particle nickel (Ni)-containing layered crystal structure; and a coating layer located on the surface of the lithium metal oxide and containing cobalt (Co) and fluorine (F), wherein the coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing a plurality of attached particles spaced apart from each other, and the plurality of attached particles have a particle size normal distribution index of 0.8 or less.

[0009] The above plurality of attached particles may have an average sphericity of 0.74 or higher.

[0010] The above plurality of attached particles may have an average aspect ratio of 1.6 or less.

[0011] The above plurality of attached particles may have an average size of 0.14 μm or less.

[0012] The above plurality of attached particles may have an average inter-particle distance of 0.155 μm or less.

[0013] The above positive active material may have a residual lithium content of 3500 ppm or less.

[0014] The above positive active material may have a Li2CO3 content of 2,700 ppm or less in residual lithium.

[0015] The nickel content in the above lithium metal oxide may be 80 mol% or more based on the total molar amount of metal excluding lithium.

[0016] The above lithium metal oxide can be represented by the following chemical formula 1.

[0017] [Chemical Formula 1]

[0018] Li a [Ni x Co y Mn z M w ]O2

[0019] In the above chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or a combination thereof.

[0020]

[0021] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium metal oxide having a layered crystal structure containing nickel (Ni) in a single particle form; and mixing the lithium metal oxide, lithium fluoride (LiF), and cobalt raw materials, and then performing a coating heat treatment to form a coating layer containing cobalt (Co) and fluorine (F); wherein a washing process is not performed after the step of preparing the lithium metal oxide and before the step of forming the coating layer, and the coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing a plurality of attached particles spaced apart from each other, and the plurality of attached particles have a particle size normal distribution index of 0.8 or less.

[0022] The amount of lithium fluoride added may be 0.5 to 1.5 mol% based on the total molar amount of the lithium metal oxide.

[0023] The amount of the above-mentioned cobalt raw material added may be 1.5 to 2.5 mol% based on the total molar amount of the above-mentioned lithium metal oxide.

[0024] The above coating heat treatment can be performed at a temperature of 630 to 720°C.

[0025] The above coating heat treatment can be performed for 4 to 24 hours.

[0026] The above coating heat treatment can be performed in an oxygen (O2) atmosphere.

[0027]

[0028] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0029] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0030] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention has a coating layer containing cobalt and fluorine and has an island shape containing a plurality of attached particles, wherein the particle size distribution of the plurality of attached particles is close to a normal distribution, so that residual lithium can be efficiently reduced while electrochemical properties such as capacity characteristics can be excellently preserved.

[0031] Figure 1 is an SEM image in which the number of island-shaped attached particles and the area ratio of the cathode active material prepared according to Example 1 are calculated and applied through Zero-shot Segmentation.

[0032] Figure 2 is an SEM image in which the number of island-shaped attached particles and the area ratio of the cathode active material prepared according to Comparative Example 1 are calculated and applied through Zero-shot Segmentation.

[0033] Figure 3 is an SEM image in which the number of island-shaped attached particles and the area ratio of the cathode active material prepared according to Comparative Example 2 are calculated and applied through Zero-shot Segmentation.

[0034] Figure 4 is an SEM image in which the number of island-shaped attached particles and area ratio of the cathode active material prepared according to Comparative Example 3 are calculated and applied through Zero-shot Segmentation.

[0035] Figure 5 is a graph showing the process of deriving the normal distribution index of a plurality of attached particles of the positive active material prepared according to Example 1 based on the image of Figure 1.

[0036] Figure 6 is a graph showing the process of deriving the normal distribution index of a plurality of attached particles of the positive active material prepared according to Comparative Example 1 based on the image of Figure 2.

[0037] Figure 7 is a graph showing the process of deriving the normal distribution index of a plurality of attached particles of the positive active material prepared according to Comparative Example 2 based on the image of Figure 3.

[0038] Figure 8 is a graph showing the process of deriving the normal distribution index of a plurality of attached particles of the positive active material manufactured according to Comparative Example 3 based on the image of Figure 4.

[0039] Figure 9 is a graph showing the process of deriving the average sphericity of a plurality of attached particles of the positive electrode active material prepared according to Example 1 based on the image of Figure 1.

[0040] Figure 10 is a graph showing the process of deriving the average sphericity of a plurality of attached particles of a positive electrode active material prepared according to Comparative Example 1 based on the image of Figure 2.

[0041] Figure 11 is a graph showing the process of deriving the average sphericity of a plurality of attached particles of a positive electrode active material prepared according to Comparative Example 2 based on the image of Figure 3.

[0042] Figure 12 is a graph showing the process of deriving the average sphericity of a plurality of attached particles of a positive electrode active material prepared according to Comparative Example 3 based on the image of Figure 4.

[0043] Figure 13 is a graph showing the process of deriving the average aspect ratio of a plurality of attached particles of the positive active material prepared according to Example 1 based on the image of Figure 1.

[0044] Figure 14 is a graph showing the process of deriving the average aspect ratio of a plurality of attached particles of a positive electrode active material prepared according to Comparative Example 1 based on the image of Figure 2.

[0045] Figure 15 is a graph showing the process of deriving the average aspect ratio of a plurality of attached particles of a positive electrode active material prepared according to Comparative Example 2 based on the image of Figure 3.

[0046] Figure 16 is a graph showing the process of deriving the average aspect ratio of a plurality of attached particles of the positive electrode active material prepared according to Comparative Example 3 based on the image of Figure 4.

[0047] Figure 17 is a graph showing the process of deriving the average size of a plurality of attached particles of the positive electrode active material prepared according to Example 1 based on the image of Figure 1.

[0048] Figure 18 is a graph showing the process of deriving the average size of a plurality of attached particles of the positive electrode active material prepared according to Comparative Example 1 based on the image of Figure 2.

[0049] Figure 19 is a graph showing the process of deriving the average size of a plurality of attached particles of the positive electrode active material prepared according to Comparative Example 2 based on the image of Figure 3.

[0050] FIG. 20 is a graph showing the process of deriving the average size of a plurality of attached particles of the positive electrode active material prepared according to Comparative Example 3 based on the image of FIG. 4.

[0051] FIG. 21 is a graph showing the process of deriving the average inter-particle distance of a plurality of attached particles of the positive active material prepared according to Example 1 based on the image of FIG. 1.

[0052] FIG. 22 is a graph showing the process of deriving the average inter-particle distance of a plurality of attached particles of the positive active material prepared according to Comparative Example 1 based on the image of FIG. 2.

[0053] FIG. 23 is a graph showing the process of deriving the average inter-particle distance of a plurality of attached particles of the positive active material prepared according to Comparative Example 2 based on the image of FIG. 3.

[0054] FIG. 24 is a graph showing the process of deriving the average inter-particle distance of a plurality of attached particles of the positive active material prepared according to Comparative Example 3 based on the image of FIG. 4.

[0055] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0056] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0057] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0058] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0059] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0060] In this specification, the term “combination(s) of these” described in the Markush-type expression means one or more mixtures or combinations selected from the group consisting of the components described in the Markush-type expression, and means including any one or more selected from the group consisting of said components.

[0061] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0062]

[0063] 1. Cathode active material

[0064] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium metal oxide in the form of a single particle. The positive electrode active material in the form of a single particle has a smaller specific surface area compared to conventional secondary particles, which reduces the amount of gas generated due to side reactions with the electrolyte, and has a higher particle strength, which can suppress particle breakage during rolling and reduce the occurrence of cracks due to repeated charging and discharging. Accordingly, it has the advantage of having superior lifespan and safety compared to secondary particles, and can achieve high energy density of the electrode.

[0065] In this specification, “single particle” is a term used to distinguish it from cathode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles, which were conventionally used; it is a concept that includes a single particle consisting of one primary particle and aggregate particles of 20 or fewer primary particles. Additionally, “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by the aggregation of tens to hundreds of primary particles through physical or chemical bonding between primary particles without an intentional aggregation or assembly process of the primary particles.

[0066] In addition, “primary particle” refers to the smallest particle unit that is distinguished as a single mass when the cross-section of the positive electrode active material is observed through a scanning electron microscope (SEM), and it may consist of a single crystal grain or multiple crystal grains. In addition, “crystal grain” refers to a distinct region in which atoms within the primary particle form a lattice structure in a specific direction.

[0067] In addition, the nickel content in the lithium metal oxide according to the present invention may be 80 mol% or more based on the total molar amount of metal excluding lithium, and more specifically, 85 mol% or 90 mol% or more. As the nickel content in the lithium metal oxide is included in such a high amount (so-called “high nickel”), it is possible to achieve a high capacity of the battery.

[0068] However, high-nickel single-particle lithium metal oxides have a problem in that the safety of the battery is compromised due to the high content of residual lithium (LiOH and / or Li2CO3) remaining on the surface of the lithium metal oxide after calcination. At this time, if a washing process is performed to remove residual lithium, it damages the surface structure of the cathode material and increases the possibility of proton exchange, thereby impairing the electrochemical characteristics such as capacity and output of the cathode material, increasing manufacturing costs of the cathode material, and generating wastewater, which necessitates a separate wastewater treatment facility.

[0069] Accordingly, the inventors investigated a method to reduce residual lithium in high-nickel single particles while excellently preserving electrochemical properties such as capacity. As a result, they discovered that when a coating layer is formed using cobalt raw material and lithium fluoride (LiF) as coating raw materials without a separate washing process after manufacturing lithium metal oxide in the form of single particles, the residual lithium reacts with the coating raw materials to efficiently reduce the residual lithium while excellently preserving capacity properties, thereby completing the present invention.

[0070] In addition, at this time, the coating layer has an island shape containing multiple attached particles, and it was confirmed that the size distribution of the multiple attached particles is close to a normal distribution.

[0071] In addition, the inventors confirmed that although it is difficult to remove Li2CO3 from residual lithium through a coating reaction because its reaction temperature is relatively higher than that of LiOH, using lithium fluoride as a coating raw material allows for an efficient coating reaction with Li2CO3, resulting in a significant reduction in Li2CO3.

[0072] Hereinafter, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described in more detail.

[0073]

[0074] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention comprises a coating layer containing cobalt (Co) and fluorine (F) disposed on the surface of a lithium metal oxide. The coating layer of the above composition can be obtained by using a cobalt raw material and lithium fluoride as coating raw materials.

[0075] By containing cobalt in the coating layer, residual lithium in the form of LiOH on the surface is reduced, and excellent lifespan, output, and efficiency characteristics can be realized. That is, when a coating layer is formed on a lithium metal oxide substrate, lifespan characteristics are improved, but electrochemical characteristics such as capacity and output are degraded. On the other hand, the cathode active material according to the present invention contains a cobalt-containing coating layer, thereby reducing residual lithium in the form of LiOH and improving electrochemical characteristics such as output and efficiency compared to the substrate, or minimizing the degree of degradation.

[0076] By containing fluorine in the coating layer, residual lithium can be effectively removed. In particular, conventional technology often used lithium raw materials such as LiOH as auxiliary coating raw materials; in this case, while electrochemical characteristics such as capacity are excellently realized, the effect of reducing Li2CO3 in residual lithium is often very poor. On the other hand, the present invention uses lithium fluoride as a coating raw material to incorporate F into the coating layer, and it has been confirmed that in this case, the effect of reducing Li2CO3 in residual lithium is greatly improved. Accordingly, the safety of the battery can be improved.

[0077] In particular, the coating layer according to the present invention is attached to the surface of a lithium metal oxide and is in the form of an island comprising a plurality of attached particles spaced apart from each other.

[0078] For the analysis of attached particles using SEM images, a model such as the Segment-Anything model (SAM) can be utilized to segment the background and attached particle regions from the SEM images. When SEM images are analyzed using the SAM model, multiple candidate attached particle regions are generated as binary masks. In the binary image, the background can be set to 0 and the attached particle candidates to 1. From the candidates for attached particle regions, the number of pixels corresponding to a pixel intensity of 1 on each binary mask can be used to more accurately distinguish between the background and the attached particles through Otsu's segmentation algorithm.

[0079] At this time, the plurality of attached particles classified by the above method have a particle size distribution that is very close to a normal distribution, so the particle size normal distribution index is 0.8 or less, and more specifically, 0.798 or less.

[0080] In this specification, the “particle size normal distribution index” refers to an index that quantitatively measures the degree to which the particle size distribution of a plurality of particles is close to a normal distribution, and the smaller the value, the closer it is to a normal distribution.

[0081] In particular, the inventors confirmed that even if the coating layer contains the same amount of F, when the particle size distribution of the attached particles is controlled to be closer to a normal distribution, the effect of reducing residual lithium (especially Li2CO3) is maximized, and excellent electrochemical properties such as capacity are realized. The inventors believe this is because a particle size distribution of the attached particles approaching a normal distribution implies that the coating reaction is carried out smoothly, which leads to efficient reduction of residual lithium and has a positive effect on electrochemical properties such as capacity. Furthermore, it appears that if the particle size distribution index of the attached particles deviates from a normal distribution, the number of excessively large attached particles may increase. In this case, non-uniform particle growth, such as aggregation (necking) among the attached particles, may be induced, which could lead to a decrease in the residual lithium reduction reaction or lithium ion mobility.

[0082] In this specification, the “particle size normal distribution index” of a plurality of attached particles can be measured by the following method.

[0083] To evaluate whether the data follows a normal distribution, a method was used to calculate the normal distribution index by utilizing a QQ (Quantile-Quantile) plot. To obtain the QQ plot, the theoretical quantiles of each data point were calculated. Specifically, the cumulative distribution function (CDF) of the standard normal distribution was used to calculate the quantiles of the data. After obtaining the QQ plot by plotting the theoretical quantile values ​​on the x-axis and the data values ​​on the y-axis, the residual sum was obtained through linear fitting and utilized as the particle size normal distribution index.

[0084] The normal distribution index of the particle size of the coating layer within the above range can be achieved by appropriately controlling the input amounts of coating raw materials, the coating heat treatment temperature, and the time during coating.

[0085]

[0086] In addition, the plurality of attached particles may have an average sphericity of 0.74 or higher, and more specifically, 0.75 or 0.76 or higher. The inventors have confirmed that even if the coating layer contains the same amount of F, when the average sphericity of the attached particles is maximized, the effect of reducing residual lithium (especially Li2CO3) is maximized, and electrochemical properties such as capacity are excellently realized. The inventors believe that this is because as the sphericity of the attached particles improves, a uniform arrangement between the attached particles becomes possible, and the residual lithium reduction reaction and lithium ion mobility are improved.

[0087] In this specification, “sphericity” refers to a numerical expression of the degree to which a particle is close to being spherical, and is defined as the value obtained by dividing the circumference of a circle having the same area as the particle projection shape by the actual circumference of the particle projection shape using a flow-type particle analysis device.

[0088] In this specification, the “average sphericity” of a plurality of attached particles can be measured by the following method.

[0089] In the above divided attached particle binary mask, the average of each attached particle's circularity calculated as 4*pi*A / perimeter^2 can be obtained (ranging from 0 to 1, with values ​​closer to 1 indicating a circle).

[0090] - A: Area (number of pixels)

[0091] - Perimeter: The number of pixels corresponding to the outline of the attached particle

[0092]

[0093] In addition, the above plurality of attached particles may have an average aspect ratio of 1.6 or less, and more specifically, 1.595 or less. The inventors have confirmed that even if the coating layer contains the same amount of F, when the average aspect ratio of the attached particles is minimized, the effect of reducing residual lithium (especially Li2CO3) is maximized and electrochemical properties such as capacity are excellently realized. The inventors believe that this is because, as the aspect ratio of the attached particles decreases, the phenomenon of necking between attached particles is suppressed, thereby suppressing the growth of non-uniform attached particles, and in this case, the residual lithium reduction reaction and lithium ion mobility are improved.

[0094] In this specification, the “aspect ratio” of a particle refers to the ratio of the length of the longest side to the shortest side visible when the particle is observed as a 2D image.

[0095] In this specification, the “average aspect ratio” of a plurality of attached particles can be measured by the following method. It can be obtained by calculating the average of the aspect ratios of each attached particle derived from the width-to-height ratio of the smallest circumscribed rectangle in the divided attached particle binary mask.

[0096]

[0097] In addition, the plurality of attached particles may have an average size of 0.14 μm or less, and more specifically, 0.136 μm or less. The inventors have confirmed that even if the coating layer contains the same amount of F, when the average size of the attached particles is minimized, the effect of reducing residual lithium (especially Li2CO3) is maximized and electrochemical properties such as capacity are excellently realized. The inventors believe that this is because, as the average size of the attached particles decreases, the phenomenon of aggregation (necking) between the attached particles is suppressed, thereby suppressing the growth of non-uniform attached particles, and in this case, lithium ion mobility is improved.

[0098] In this specification, the “size” of an attached particle refers to the length of the longest side visible when the particle is observed as a 2D image.

[0099] In this specification, the “average size” of a plurality of attached particles can be measured by the following method.

[0100] In the above divided attachment particle binary mask, the size of each attachment particle can be obtained by determining the number of pixels corresponding to pixel intensity 1 and then calculating the average of them.

[0101]

[0102] In addition, the average inter-particle distance of the plurality of attached particles may be 0.155 μm or less, and more specifically, 0.15 μm or less. The inventors have confirmed that even if the coating layer contains the same amount of F, excellent electrochemical properties such as capacity are achieved when the average inter-particle distance of the attached particles is minimized. The inventors believe that this is because charge and lithium ion movement are carried out more efficiently as the inter-particle distance decreases.

[0103] In this specification, the “average inter-particle distance” of a plurality of attached particles can be measured by the following method.

[0104] It can be obtained by calculating the center of gravity point for each of the above-mentioned divided attached particle binary masks, calculating the nearest neighbor distance for each center of gravity point, and calculating the average of them.

[0105] As mentioned above, the positive electrode active material according to the present invention effectively reduces the residual lithium content, so it may be 3500 ppm or less, and more specifically, 3200 ppm or less.

[0106] In addition, the cathode active material according to the present invention effectively reduces Li2CO3 among residual lithium, so the Li2CO3 content may be 2700 ppm or less, and more specifically, 2500 ppm or less.

[0107] As the residual lithium content decreases, gas generation and battery swelling caused by side reactions between the residual lithium and the electrolyte can be suppressed, thereby significantly improving the safety of the battery.

[0108]

[0109] The lithium metal oxide according to the present invention can be represented more specifically by the following chemical formula 1.

[0110] [Chemical Formula 1]

[0111] Li a [Ni x Co y Mn z M w ]O2

[0112] In the above chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or a combination thereof.

[0113] In the lithium metal oxide of Chemical Formula 1 above, lithium may be included in an amount corresponding to a, i.e., 0.8 ≤ a ≤ 1.3. If a is too small, the capacity may decrease, and if a is too large, the strength of the calcined cathode active material may increase, making it difficult to grind, and the amount of gas generated may increase due to an increase in lithium by-products. Considering the effect of improving the capacity characteristics of the cathode active material by controlling the lithium content and the balance of sinterability during the manufacture of the active material, the lithium may more preferably be included in an amount of 0.9 ≤ a ≤ 1.1.

[0114] In the lithium metal oxide of Chemical Formula 1 above, nickel may be included in an amount corresponding to x, i.e., 0.8≤x<1, and more specifically, 0.85≤x<1 or 0.90≤x<1. When the nickel content satisfies the above range, it is possible to achieve a high capacity of the battery.

[0115] In the lithium metal oxide of Chemical Formula 1 above, cobalt may be included in an amount corresponding to y, i.e., 0 ≤ y ≤ 0.2. If the cobalt content is too low, grain size growth may be inhibited and output characteristics may be degraded. If the cobalt content is too high, manufacturing costs may increase and reversible capacity may decrease.

[0116] In the lithium metal oxide of Chemical Formula 1 above, manganese may be included in an amount corresponding to z, i.e., 0 ≤ z ≤ 0.2. If the manganese content is too low, the production cost may increase and the stability of the active material may decrease. If the manganese content is too high, the capacity and output characteristics of the battery may decrease.

[0117] In the lithium metal oxide of Chemical Formula 1 above, the other doping element M may be included in an amount corresponding to w, i.e., 0 ≤ w ≤ 0.2. At this time, M may be Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or a combination thereof. The content of the other doping element may be appropriately selected to achieve the other doping effect.

[0118]

[0119] 2. Method for manufacturing positive electrode active material

[0120] Another embodiment of the present invention provides a method for manufacturing a positive electrode active material for a lithium secondary battery, comprising the steps of: preparing a lithium metal oxide having a layered crystal structure containing nickel (Ni) in a single particle form; and mixing the lithium metal oxide, lithium fluoride (LiF), and cobalt raw materials, and then performing a coating heat treatment to form a coating layer containing cobalt (Co) and fluorine (F); wherein a washing process is not performed after the step of preparing the lithium metal oxide and before the step of forming the coating layer, and the coating layer is attached to the surface of the lithium metal oxide and is in the form of an island containing a plurality of attached particles spaced apart from each other, and the plurality of attached particles have a particle size normal distribution index of 0.8 or less.

[0121] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to another embodiment of the present invention will be described in detail step by step.

[0122]

[0123] First, a lithium metal oxide with a single-particle nickel (Ni)-containing layered crystal structure is prepared.

[0124] More specifically, the above-mentioned single-particle lithium metal oxide can be prepared by preparing a metal precursor, then mixing and calcining the metal precursor and the lithium raw material, and then crushing them.

[0125] The above metal precursor may be, more specifically, a metal hydroxide.

[0126] The above metal precursor may be prepared by co-precipitating a metal-containing solution containing, for example, nickel raw material, manganese raw material, or cobalt raw material by adding a complexing agent-containing solution and a pH adjuster-containing solution.

[0127] The above nickel raw material is not particularly limited as long as it is used in the industry for manufacturing a cathode active material precursor. For example, the above nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, it may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, nickel fatty acid salt, nickel halide, or a combination thereof, but is not limited thereto.

[0128] The above-mentioned cobalt raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above-mentioned cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO₄ 4, It may be CoSO4·7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, or a combination thereof, but is not limited thereto.

[0129] The above manganese raw material is not particularly limited as long as it is used in the industry for the manufacture of cathode active material precursors. For example, the above manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof. Specifically, it may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, and manganese fatty acid, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0130] The above metal-containing solution may be prepared by adding a nickel raw material, a manganese raw material, or a cobalt raw material to a solvent, specifically water, or a mixture of water and an organic solvent that can be uniformly mixed with water (e.g., alcohol).

[0131] The above-mentioned complexing agent-containing solution performs the role of forming a complex, and may include, for example, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof as the complexing agent, but is not limited thereto. Meanwhile, the above-mentioned complexing agent-containing solution may 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 uniformly miscible with water (e.g., alcohol, etc.) may be used as the solvent.

[0132] The above pH-adjusting solution serves as a precipitating agent or a pH regulator and may include alkali compounds such as hydroxides of alkali metals or alkaline earth metals like NaOH, KOH, or Ca(OH)2, their hydrates, or combinations thereof. Meanwhile, the above pH-adjusting solution may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (e.g., alcohol) may be used as the solvent. In this case, the above pH-adjusting solution may be added in an amount such that the pH of the reaction solution becomes 10 to 13.

[0133] The above co-precipitation reaction can be carried out under an inert atmosphere such as nitrogen or argon, at a temperature of 30 to 70°C, and at a pH of 10 to 13.

[0134] By the above process, particles of nickel (or manganese-cobalt) hydroxide are generated and precipitated in the reaction solution. The precipitated precursor particles can be separated by conventional methods, washed, and dried to obtain a precursor. The precursor may be a secondary particle formed by the aggregation of primary particles.

[0135] At this time, the molar ratio of nickel, cobalt, or manganese in the precursor can be controlled by adjusting the concentration of the nickel raw material, the cobalt raw material, or the manganese raw material. That is, the concentrations of the nickel raw material, the cobalt raw material, and the manganese raw material can be controlled so that the molar ratio of nickel, cobalt, or manganese in the final product, the lithium metal oxide, falls within the range according to the present invention.

[0136] The above lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it is soluble in water. Specifically, the above lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof, but is not limited thereto.

[0137] In addition, the above calcination can be performed at a temperature of 800 to 900°C. If the calcination temperature is too low, lithium metal oxide in the form of single particles may not be formed. If the calcination temperature is too high, crystal structure defects due to over-calcination may occur, and electrochemical properties may deteriorate.

[0138] In addition, the above calcination may be performed for 5 to 24 hours. If the calcination time is too short, lithium metal oxide in the form of single particles may not be formed. If the calcination time is too long, crystal structure defects due to over-calcination may occur, and electrochemical properties may deteriorate.

[0139] In addition, the atmosphere during the above firing is not particularly limited, but can be performed, for example, in an oxygen (O2) or air atmosphere.

[0140] The above crushing can be performed according to general crushing processes in the industry, for example, using a jet mill.

[0141]

[0142] Next, the lithium metal oxide, lithium fluoride (LiF), and cobalt raw materials are mixed and then subjected to coating heat treatment to form a coating layer containing cobalt (Co) and fluorine (F).

[0143] The above-mentioned cobalt raw material is not particularly limited as long as it is a cobalt raw material. For example, the above-mentioned cobalt raw material is Co(OH)2, CoCl2, CoO, CoSO4·xH2O, CoSO4·7H2O, (CH3COO)2Co·4H2O, Co(NO3)2·6H2O, (CH3CO2)2Co, CoCO3· x It may be H2O, CO3(PO4)2, or a combination thereof, but is not necessarily limited thereto.

[0144] However, from the perspective of a more desirable implementation of the residual lithium reduction effect due to the formation of a coating layer, the above cobalt raw material may be more suitable as Co(OH)2.

[0145] At this time, the amount of lithium fluoride added may be 0.5 to 1.5 mol% based on the total molar amount of the lithium metal oxide, and more specifically, 0.7 to 1.3 mol%. When the amount of lithium fluoride added satisfies the above range, the residual lithium removal effect is preferably realized, while preventing the action of impurities due to excessive fluoride addition, so that excellent electrochemical characteristics such as the capacity of the cathode active material can be realized. In addition, when the amount of lithium fluoride added satisfies the above range, various physical properties related to attached particles, such as the normal distribution index of particle size of attached particles in the coating layer, can be appropriately realized within the range according to the present invention.

[0146] In addition, the amount of the cobalt raw material added may be 1.5 to 2.5 mol% based on the total molar amount of the lithium metal oxide, and more specifically, 1.7 to 2.3 mol%. When the amount of the cobalt raw material added satisfies the above range, the residual lithium removal effect is preferably realized, while preventing the action of impurities due to excessive cobalt addition, so that excellent electrochemical characteristics such as the capacity of the cathode active material can be realized. In addition, when the amount of the cobalt raw material added satisfies the above range, various physical properties related to attached particles, such as the particle size normal distribution index of the attached particles in the coating layer, can be appropriately realized within the range according to the present invention.

[0147] In addition, the coating heat treatment can be performed at a temperature of 630 to 720°C, and more specifically, at a temperature of 660 to 720°C or 670 to 720°C. If the coating heat treatment temperature is too low, the coating reaction may not proceed smoothly, which may result in a decrease in coating yield, and consequently, a decrease in the effect of reducing residual lithium and preserving electrochemical properties. If the coating heat treatment temperature is too high, it may adversely affect the lithium metal oxide crystal structure, which may actually degrade the electrochemical properties of the cathode active material. Furthermore, when the coating heat treatment temperature satisfies the above range, various physical properties related to attached particles, such as the normal distribution index of particle size of attached particles within the coating layer, can be appropriately realized within the range according to the present invention.

[0148] The above coating heat treatment can be performed for 4 to 24 hours, and more specifically, for 4 to 15 hours or 7 to 13 hours. If the coating heat treatment time is too short, the coating reaction may not proceed smoothly, which may result in a decrease in coating yield, and consequently, a decrease in the effect of reducing residual lithium and preserving electrochemical properties. If the coating heat treatment time is too long, it may adversely affect the lithium metal oxide crystal structure, which may actually degrade the electrochemical properties of the cathode active material. Furthermore, when the coating heat treatment time satisfies the above range, various physical properties related to attached particles, such as the normal distribution index of particle size of attached particles within the coating layer, can be appropriately realized within the range according to the present invention.

[0149] The above coating heat treatment can be performed in an oxygen (O2) atmosphere. Accordingly, the coating reaction can proceed more smoothly, thereby increasing coating efficiency, and consequently, the effect of reducing residual lithium and preserving electrochemical properties can be enhanced. Furthermore, when the coating heat treatment atmosphere is under the above conditions, various physical properties related to attached particles, such as the normal distribution index of particle size of attached particles within the coating layer, can be more appropriately realized within the range according to the present invention.

[0150]

[0151] 3. Anodes and Lithium Secondary Batteries

[0152] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0153] More specifically, the anode may include an anode current collector and an anode active material layer disposed on the anode current collector and comprising the aforementioned anode active material.

[0154] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0155] The above positive active material layer may include a binder and / or a conductive material together with the aforementioned positive active material.

[0156] At this time, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0157] In addition, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes may be used without any particular limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used, but is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 weight percent relative to the total weight of the positive electrode active material layer.

[0158] The above-mentioned anode can be manufactured according to a conventional anode manufacturing method, except for using the above-mentioned anode active material.

[0159] Specifically, the anode can be manufactured by applying a composition for forming an anode active material layer, comprising the aforementioned anode active material and optionally a binder, conductive material, or solvent as needed, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0160] The above solvent may be a solvent commonly used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that allows for the dissolution or dispersion of the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0161] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0162]

[0163] Another embodiment of the present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery as described above.

[0164] More specifically, the above lithium secondary battery may include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0165] The above lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0166] The above cathode may include a cathode current collector and a cathode active material layer located on the cathode current collector.

[0167] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0168] The above-mentioned cathode active material layer may optionally include a binder and a conductive material together with the cathode active material. The above-mentioned cathode active material layer may be manufactured, as an example, by applying a composition for forming a cathode active material layer, comprising a cathode active material and optionally a binder and a conductive material, onto a cathode current collector and drying it, or by casting the composition for forming a cathode onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0169] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, the carbon material may include both low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0170] The binder and conductive material mentioned above may be the same as those previously described in the anode.

[0171]

[0172] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It can be used without special restrictions as long as it is typically used as a separator in a lithium secondary battery, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0173]

[0174] The above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0175] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0176] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based 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-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having C2 to C20 structures and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0177] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0178] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate-based compounds like difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexamethylphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0179] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0180] Accordingly, another embodiment of the present invention provides a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same.

[0181] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0182] The embodiments of the present invention will be described in more detail below through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited by the following examples.

[0183]

[0184] Example 1

[0185] (1) Manufacturing of positive electrode active material

[0186] (Preparation of lithium metal oxide) (Ni 0.96 Co 0.03 Mn 0.01 A precursor of the (OH)2 composition and LiOH·H2O were introduced into a mixer and mechanically mixed, and then calcined at a temperature of 850°C for 10 hours under an oxygen (O2) atmosphere to form a lithium metal oxide. Afterwards, the formed cathode active material was pulverized through a jet-mill process to form a single-particle lithium metal oxide.

[0187] After (coating), the lithium metal oxide was mixed with 1 mol% of lithium fluoride (LiF) based on the total molar amount of the lithium metal oxide and 2 mol% of cobalt hydroxide (Co(OH)2) based on the total molar amount of the lithium metal oxide, and then the coating heat treatment was performed at a temperature of 700°C for 10 hours under an O2 atmosphere to form a cobalt and fluorine-containing coating layer on the surface of the lithium metal oxide.

[0188] (2) Lithium secondary battery manufacturing

[0189] The slurry for electrode manufacturing was prepared by mixing the above-prepared cathode active material, conductive material (carbon black, Denka black), and binder (PVDF, KF1100) in a ratio of 96.5 : 1.5 : 2 wt%, and adding NMP (N-Methyl-2-pyrrolidone) to adjust the viscosity so that the solid content was approximately 30%. The prepared slurry was coated onto a 20 µm thick Al foil using a doctor blade and then dry-rolled. The electrode loading amount was 15.4 mg / cm². 2 It was, and the rolled density (25℃, 20kN) was 3.6 g / cm³ 3 It was.

[0190] A coin cell was manufactured using an electrolyte of 1M LiPF6 in EC:DMC:EMC=3:4:3 (vol%) with 3.0 vol% of VC added relative to the total amount of the electrolyte, a PP separator, and a lithium anode (200 μm, Honzo metal).

[0191]

[0192] Comparative Example 1

[0193] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the coating step, 1 mol% of lithium hydroxide (LiOH·H2O) based on the total molar amount of lithium metal oxide was used instead of lithium fluoride.

[0194]

[0195] Comparative Example 2

[0196] A positive electrode active material and a lithium secondary battery were prepared in the same manner as in Example 1, except that in the coating step, 2 mol% of lithium fluoride (LiF) based on the total molar amount of lithium metal oxide was used.

[0197]

[0198] Comparative Example 3

[0199] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that lithium fluoride (LiF) was not used as the coating raw material in the coating step.

[0200]

[0201] Table 1 below summarizes the process conditions of the examples and comparative examples.

[0202] Coating Raw Material and Input Amount (mol%) Coating Heat Treatment LiF LiOH·H2OCo(OH)2 Temperature (°C) Time (h) Atmosphere Example 1 10 2700 10O2 Comparative Example 10 12700 10O2 Comparative Example 2 20 2700 10O2 Comparative Example 3 00 2700 10O2

[0203] Tables 2 to 4 below summarize the results of the evaluation of the physical properties of the cathode active material and the electrochemical characteristics of the lithium secondary battery according to Experimental Example 2 and Experimental Example 3 described below.

[0204] Attached Particles Mophology Particle Size Normal Distribution Exponential Mean Roundness Mean Aspect Ratio Mean Size (um) Mean Inter-particle Distance (um) Example 1 0.79 46 0.76 86 1.59 0.13 45 0.14 82 Comparative Example 15.37 20.61 39 2.21 20.20 14 0.51 36 Comparative Example 20.83 110.73 76 1.60 60.14 10.158 Comparative Example 36.19 10.62 98 2.04 10.21 28 0.40 83

[0205] Residual Lithium Content (ppm) LiOH Li2CO3 Total Example 1 677 2430 3107 Comparative Example 1 459 40 3845 27 Comparative Example 2 540 279 936 39 Comparative Example 3 103 728 68 3905

[0206] Electrochemical Characteristics Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Initial Efficiency (mAh / g) Example 1 239.9 207 86.3 Comparative Example 1 241.6 209.5 86.7 Comparative Example 2 240.2 206.8 86.1 Comparative Example 3 242.2 209.1 86.3

[0207] Experimental Example 1: Evaluation of SEM Images of Anode Active Material

[0208] The number of island-shaped attached particles and the area ratio of the cathode active materials prepared according to Example 1 and Comparative Examples 1 to 3 were calculated and observed in SEM (scanning electron microscope) images applied through Zero-shot Segmentation, and these are shown in Figures 1 to 4, respectively.

[0209] Referring to FIGS. 1 to 4, it was confirmed that the positive active materials of the examples and comparative examples exhibited a single particle form. In addition, it was confirmed that a plurality of attached particles were attached to the surface of the single particles in an irregular dot shape (i.e., an island-type coating layer).

[0210]

[0211] Experimental Example 2: Evaluation of Physical Properties of Anode Active Material

[0212] [Distinguishing attached particle regions in the image]

[0213] A model such as the Segment-Anything model (SAM) can be used to segment the background and attached particle regions from SEM images. When SEM images are analyzed using the SAM model, multiple candidate attached particle regions are generated as binary masks. In the binary image, the background can be set to 0 and the candidate attached particles to 1. From the candidate attached particle regions, the number of pixels corresponding to a pixel intensity of 1 on each binary mask can be used to more accurately distinguish the background and the attached particles through Otsu's segmentation algorithm.

[0214] (1) Evaluation of normal distribution index of particle size of attached particles

[0215] The “particle size normal distribution index” of multiple attached particles was measured by the following method.

[0216] To evaluate whether the data follows a normal distribution, a method was used to calculate the normal distribution index by utilizing a QQ (Quantile-Quantile) plot. To obtain the QQ plot, the theoretical quantiles of each data point were calculated. Specifically, the cumulative distribution function (CDF) of the standard normal distribution was used to calculate the quantiles of the data. After obtaining the QQ plot by plotting the theoretical quantile values ​​on the x-axis and the data values ​​on the y-axis, the residual sum was obtained through linear fitting and utilized as the particle size normal distribution index.

[0217] (2) Evaluation of the average sphericity of attached particles

[0218] The “average sphericity” of multiple attached particles was measured by the following method.

[0219] In the above-described divided attached particle binary mask, the average of each attached particle's circularity calculated as 4*pi*A / perimeter^2 was obtained (ranging from 0 to 1, with values ​​closer to 1 indicating a circle).

[0220] - A: Area (number of pixels)

[0221] - Perimeter: The number of pixels corresponding to the outline of the attached particle

[0222] (3) Evaluation of average aspect ratio of attached particles

[0223] The “average aspect ratio” of multiple attached particles was measured by the following method.

[0224] In the above-described divided attached particle binary mask, the average of the aspect ratios of each attached particle, derived from the width-to-height ratio of the minimum circumscribed rectangle, was calculated.

[0225] (4) Evaluation of average size of attached particles

[0226] The “average size” of multiple attached particles was measured by the following method.

[0227] In the above divided attachment particle binary mask, the size of each attachment particle was determined by the number of pixels corresponding to pixel intensity 1, and then the average of these was calculated.

[0228] (5) Evaluation of average inter-particle distance between attached particles

[0229] The “average inter-particle distance” of multiple attached particles was measured by the following method.

[0230] The centroid point was calculated for each of the above-mentioned divided attached particle binary masks, the nearest neighbor distance was calculated for each centroid point, and the average was obtained.

[0231] (6) Evaluation of residual lithium

[0232] After adding distilled water to the cathode active material, residual lithium was extracted using a stirrer, and the cathode active material powder and extract were separated using a filtering device. Subsequently, the residual lithium was evaluated by measuring the extract through neutralization titration using a Metrohm potentiometer.

[0233]

[0234] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0235] (1) Evaluation of initial capacity and initial efficiency

[0236] After fabricating a lithium secondary battery half cell, it was aged at 25°C for 12 hours, and then a charge-discharge test was performed at 25°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.25V with a constant current of 0.1C. Then, the voltage was switched to a constant voltage, and charging continued until the terminal current reached 0.05C. After a 10-minute rest time following charging, the battery was discharged until it reached 2.5V with a constant current of 0.1C and a reference capacity of 200 mAh / g.

[0237]

[0238] Referring to Tables 1 to 5, in the case of Example 1, in which lithium fluoride and cobalt hydroxide were used as coating raw materials and the coating process conditions, such as the amount of lithium fluoride input, were appropriately controlled, it was confirmed that the various physical properties related to the attached particles, such as the normal distribution index of the particle size of the attached particles within the coating layer, were appropriately realized within the range according to the present invention. At this time, it was confirmed that the total residual lithium content was low, and in particular, the effect of reducing residual lithium in Li2CO3 was excellent. In addition, it was confirmed that the capacity characteristics (initial discharge capacity) of the battery also showed a good level.

[0239] On the other hand, in the case of Comparative Example 1, when conventionally commonly used lithium hydroxide was used instead of lithium fluoride, it was confirmed that the normal distribution index of the particle size of the attached particles was too large and was very far from the normal distribution, and it was also confirmed that other physical properties related to the attached particles deviated significantly from the range according to the present invention. In addition, it was confirmed that the total residual lithium reduction effect was degraded compared to the example, and in particular, the Li2CO3 residual lithium reduction effect was significantly lower compared to the example.

[0240] In the case of Comparative Example 2, as a result of the excessive amount of lithium fluoride input, it was confirmed that the particle size normal distribution index was larger than that of Example 1, causing the attached particles to deviate somewhat from the normal distribution, and that other physical properties related to the attached particles also fell outside the range according to the present invention. Furthermore, it was confirmed that the total residual lithium reduction effect and the Li2CO3 residual lithium reduction effect deteriorated compared to the example. Additionally, it was confirmed that the battery capacity characteristics deteriorated compared to the example.

[0241] In the case of Comparative Example 3, as a result of using only cobalt hydroxide as the coating raw material, it was confirmed that the normal distribution index of the particle size of the attached particles was too large and was very far from the normal distribution, and it was also confirmed that other physical properties related to the attached particles deviated significantly from the range according to the present invention. In addition, it was confirmed that the total residual lithium reduction effect and the Li2CO3 residual lithium reduction effect deteriorated compared to the examples.

[0242]

[0243] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

[0244] Therefore, the substantive scope of the present invention shall be defined by the appended claims and their equivalents.

Claims

1. A lithium metal oxide having a single-particle nickel (Ni)-containing layered crystal structure; and a coating layer located on the surface of the lithium metal oxide and containing cobalt (Co) and fluorine (F), comprising The above coating layer is attached to the surface of a lithium metal oxide and is in the form of an island containing a plurality of attached particles spaced apart from each other, and The above plurality of attached particles are positive electrode active materials for lithium secondary batteries having a particle size normal distribution index of 0.8 or less.

2. In Paragraph 1, The above plurality of attached particles are positive electrode active materials for lithium secondary batteries having an average sphericity of 0.74 or higher.

3. In Paragraph 1, The above plurality of attached particles are positive electrode active materials for lithium secondary batteries having an average aspect ratio of 1.6 or less.

4. In Paragraph 1, The above plurality of attached particles are positive electrode active materials for lithium secondary batteries having an average size of 0.14 μm or less.

5. In Paragraph 1, The above plurality of attached particles are a positive electrode active material for a lithium secondary battery having an average inter-particle distance of 0.155 μm or less.

6. In Paragraph 1, A positive electrode active material for a lithium secondary battery having a residual lithium content of 3,500 ppm or less.

7. In Paragraph 1, A positive electrode active material for a lithium secondary battery having a Li2CO3 content of 2,700 ppm or less in residual lithium.

8. In Paragraph 1, A positive electrode active material for a lithium secondary battery in which the nickel content in the above lithium metal oxide is 80 mol% or more based on the total molar amount of metal excluding lithium.

9. In Paragraph 1, The above lithium metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Co y Mr z M w ]O2 In the above chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, x+y+z+w=1, and M is Zr, Al, B, Y, Ti, Nb, W, V, Cr, Mo, Ta, Fe, Cu, Zn, Ga, Ge, Ru, Rh, Sn, Sb, Re, Ir, Pt, Pb, Bi, Na, K, Rb, Cs, Ca, Sr, Ba, Mg, Si, Sc, or a combination thereof.

10. A step of preparing a lithium metal oxide with a layered crystal structure containing nickel (Ni) in a single-particle form; and The method includes the step of mixing the lithium metal oxide, lithium fluoride (LiF), and cobalt raw materials, and then performing a coating heat treatment to form a coating layer containing cobalt (Co) and fluorine (F). A washing process is not performed after the step of preparing the lithium metal oxide and before the step of forming the coating layer, and A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the coating layer is attached to the surface of a lithium metal oxide and is in the form of an island containing a plurality of attached particles spaced apart from each other, and the plurality of attached particles have a particle size normal distribution index of 0.8 or less.

11. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the amount of lithium fluoride added is 0.5 to 1.5 mol% based on the total molar amount of the lithium metal oxide.

12. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the amount of the above-mentioned cobalt raw material input is 1.5 to 2.5 mol% based on the total molar amount of the above-mentioned lithium metal oxide.

13. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above coating heat treatment is performed at a temperature of 630 to 720℃.

14. In Paragraph 10, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above coating heat treatment is performed for 4 to 24 hours.

15. In Paragraph 10, The above coating heat treatment is a method for manufacturing a positive electrode active material for a lithium secondary battery, which is performed in an oxygen (O2) atmosphere.

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