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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, the cathode active material comprising: a lithium metal oxide having a nickel (Ni)-containing layered crystal structure in a single particle form; and a coating layer disposed on the surface of the lithium metal oxide and containing cobalt (Co) and fluorine (F), wherein in X-ray photoelectron spectroscopy (XPS) analysis of O1s on the outermost surface of the cathode active material, a first peak appears in a binding energy range of 530 eV to 532 eV, a second peak appears in a binding energy range of 528.5 eV to 529.5 eV, and the ratio of the height of the first peak to the height of the second peak (first peak / second peak) is from 3 to 3.5.

Description

Positive electrode active material for lithium secondary batteries, method for producing the same, and lithium secondary batteries comprising the same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same, and more specifically, to a positive electrode active material for a single-particle lithium secondary battery, a method for producing the same, and a lithium secondary battery comprising the same.

[0002]

[0003] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMnO4), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high price of cobalt, which is the raw material, and its supply are unstable, making it difficult to commercially apply it to large-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient cycle life characteristics. Meanwhile, lithium manganese oxide has excellent stability but has the problem of poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to complement the problems of lithium transition metal oxides containing only Ni, Co, or Mn. Among these, lithium nickel cobalt manganese oxides containing Ni, Co, and Mn are widely used in the field of electric vehicle batteries.

[0004] Conventional lithium nickel cobalt manganese oxides are generally in the form of spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxides formed in the form of secondary particles formed by agglomeration of many primary particles, there is a problem in that the primary particles are easily broken during the rolling process during the manufacture of the positive electrode, and cracks occur inside the particles during the charge and discharge process. When the positive electrode active material particles are broken or cracked, the contact area with the electrolyte increases, which increases the generation of gases and degradation of the active material due to side reactions with the electrolyte, and this causes problems in that the life characteristics are reduced.

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

[0006] However, high-nickel single-particle lithium metal oxides have a high content of residual lithium (LiOH and / or Li2CO3) remaining on the surface of the lithium metal oxide after calcination, which compromises the safety of the battery. At this time, performing a washing process to remove the residual lithium can damage the surface structure of the cathode material, increase the possibility of proton exchange, and thus impair electrochemical properties such as capacity and output of the cathode material. Furthermore, this can increase the cost of cathode material manufacturing and generate wastewater, necessitating the need for separate wastewater treatment facilities.

[0007]

[0008] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery, which efficiently reduces residual lithium while maintaining excellent electrochemical characteristics (capacity, etc.) by forming a coating layer on a lithium metal oxide in the form of a single particle, a method for producing the same, and a lithium secondary battery including the same.

[0009]

[0010] One embodiment of the present invention provides a cathode active material for a lithium secondary battery, comprising a lithium metal oxide having a layered crystal structure containing nickel (Ni) in a single particle form and a coating layer disposed on the surface of the lithium metal oxide and containing cobalt (Co) and fluorine (F), wherein when XPS (X-ray photoelectron spectroscopy) analysis is performed on O1s on the outermost surface of the cathode active material, a first peak appears in a region having a binding energy of 530 to 532 eV, a second peak appears in a region having a binding energy of 528.5 to 529.5 eV, and a ratio of the height of the first peak to the height of the second peak (first peak / second peak) is 3 to 3.5.

[0011] The full width at half maximum (FWHM) of the first peak may be 2.5 eV or less.

[0012] When analyzing XPS (X-ray photoelectron spectroscopy) for F1s on the outermost surface of the above-mentioned positive electrode active material, a third peak may appear in the region with a binding energy of 683 to 686 eV.

[0013] The full width at half maximum (FWHM) of the third peak may be 1.65 eV or less.

[0014] The above coating layer is attached to the surface of the lithium metal oxide and may be in the form of an island including a plurality of attached particles spaced apart from each other.

[0015] The average coverage of the above coating layer may be 18 to 30 area% based on the total surface area of ​​the single particle.

[0016] The average number of the above-mentioned attached particles may be 240 to 300.

[0017] The above positive electrode active material may have a residual lithium content of 3500 ppm or less.

[0018] The above positive electrode active material may have a Li2CO3 content of residual lithium of 2700 ppm or less.

[0019] The content of nickel in the above lithium metal oxide may be 80 mol% or more based on the total mole number of metals excluding lithium.

[0020] The above lithium metal oxide can be represented by the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Li a [Ni x Co y Mn z M w ]O2

[0023] 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.

[0024]

[0025] Another embodiment of the present invention provides a method for producing 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 the form of a single particle; and mixing the lithium metal oxide, lithium fluoride (LiF), and a cobalt raw material, 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 amount of lithium fluoride added is 0.5 to 1.5 mol% based on the total mole number of the lithium metal oxide.

[0026] The amount of the cobalt raw material input may be 1.5 to 2.5 mol% based on the total mole number of the lithium metal oxide.

[0027] The above coating heat treatment can be performed at a temperature of 630 to 720°C.

[0028] The above coating heat treatment can be performed for 4 to 24 hours.

[0029] The above coating heat treatment can be performed in an O2 atmosphere.

[0030]

[0031] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0032] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0033]

[0034] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery is formed by calcining a lithium metal oxide in the form of a single particle and then coating it with a cobalt and fluorine-containing coating layer without a separate washing process, thereby reducing residual lithium and simultaneously preserving excellent electrochemical characteristics such as capacity characteristics.

[0035]

[0036] Figure 1 is an SEM image in which the number of island-shaped attached particles and the area ratio of the positive electrode active material manufactured according to Example 1 are calculated using zero-shot segmentation.

[0037] Figure 2 is an SEM image in which the number of island-shaped attached particles and the area ratio of the positive electrode active material manufactured according to Comparative Example 1 are calculated using Zero-shot Segmentation.

[0038] Figure 3 is an SEM image in which the number of island-shaped attached particles and the area ratio of the positive electrode active material manufactured according to Comparative Example 2 are calculated using Zero-shot Segmentation.

[0039] Figure 4 is an SEM image in which the number of island-shaped attached particles and the area ratio of the positive electrode active material manufactured according to Comparative Example 3 are calculated using Zero-shot Segmentation.

[0040] Figure 5 is a graph showing the results of XPS (X-ray Photoelectron Spectroscopy) analysis for F1s on the outermost surface of the positive electrode active material manufactured according to Example 1 and Comparative Examples 1 to 3.

[0041] Figure 6 is a graph showing the results of XPS (X-ray Photoelectron Spectroscopy) analysis for O1s on the outermost surface of the positive electrode active material manufactured according to Example 1 and Comparative Examples 1 to 3.

[0042]

[0043] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0045] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0046] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0047] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0048] In this specification, the term "combination(s) thereof" described in the expression in the Makushi format means one or more mixtures or combinations selected from the group consisting of the components described in the expression in the Makushi format, and means including any one or more selected from the group consisting of said components.

[0049] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0050]

[0051] 1. Positive active material

[0052] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium metal oxide in the form of a single particle. Compared to conventional secondary particles, the cathode active material in the form of a single particle has a smaller specific surface area, which reduces the amount of gas generated by side reactions with the electrolyte. Furthermore, the material has a higher particle strength, which suppresses particle breakage during rolling, and reduces the occurrence of cracks during repeated charging and discharging. Accordingly, the cathode active material has superior lifespan and safety compared to secondary particles, and has the advantage of being able to realize a high energy density of the electrode.

[0053] In this specification, the term “single particle” is used to distinguish it from the secondary particle type positive electrode active material particle formed by the aggregation of tens to hundreds of primary particles that have been commonly used in the past, and is a concept that includes a single particle composed of one primary particle and an aggregate particle of 20 or fewer primary particles. In addition, “secondary particle” means an aggregate, i.e., a secondary structure, formed by the physical or chemical bonding between tens to hundreds of primary particles without an intentional aggregation or assembly process for the primary particles.

[0054] Additionally, the term "primary particle" refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of a positive electrode active material through a scanning electron microscope (SEM), and may be composed of a single crystal grain or multiple crystal grains. Furthermore, the term "crystal grain" refers to a distinct region in which atoms within a primary particle form a lattice structure with a certain orientation.

[0055] In addition, the content of nickel in the lithium metal oxide according to the present invention may be 80 mol% or more, and more specifically, 85 mol% or 90 mol% or more, based on the total mole number of metals excluding lithium. Since the content of nickel in the lithium metal oxide is included at such a high content (so-called “high nickel”), it is possible to achieve high capacity of the battery.

[0056] However, high-nickel single-particle lithium metal oxides have a high content of residual lithium (LiOH and / or Li2CO3) remaining on the surface of the lithium metal oxide after calcination, which compromises the safety of the battery. At this time, performing a washing process to remove the residual lithium can damage the surface structure of the cathode material, increase the possibility of proton exchange, and thus impair electrochemical properties such as capacity and output of the cathode material. Furthermore, this can increase the cost of cathode material manufacturing and generate wastewater, necessitating the need for separate wastewater treatment facilities.

[0057] Accordingly, the inventors of the present invention studied a method for reducing residual lithium in high-nickel single particles while excellently preserving electrochemical characteristics such as capacity. As a result, 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 and the coating raw material undergo a coating reaction, efficiently reducing residual lithium while excellently preserving characteristics such as capacity, thereby completing the present invention.

[0058] In particular, the inventors of the present invention confirmed that, among residual lithium, Li2CO3 is difficult to remove through a coating reaction because its reaction temperature is relatively high compared to LiOH, but when lithium fluoride is used as a coating raw material, an efficient coating reaction occurs with Li2CO3, resulting in a large Li2CO3 reduction effect.

[0059] 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.

[0060]

[0061] A cathode active material for a lithium secondary battery according to one embodiment of the present invention is disposed on the surface of a lithium metal oxide and includes a coating layer containing cobalt (Co) and fluorine (F). The coating layer having the above composition can be obtained by using a cobalt raw material and lithium fluoride as coating raw materials.

[0062] In addition, when the cathode active material for a lithium secondary battery according to one embodiment of the present invention is analyzed by XPS (X-ray photoelectron spectroscopy) for O1s on the outermost surface, a first peak appears in a region having a binding energy of 530 to 532 eV. The first peak may refer to a peak resulting from the combination of oxygen and cobalt.

[0063] In addition, when the cathode active material for a lithium secondary battery according to one embodiment of the present invention is analyzed by XPS (X-ray photoelectron spectroscopy) for O1s on the outermost surface, a second peak appears in a region having a binding energy of 528.5 to 529.5 eV. The second peak may refer to a peak resulting from the bonding of oxygen and fluorine.

[0064] At this time, the cathode active material according to the present invention may have a ratio of the height of the first peak to the height of the second peak (first peak / second peak) of 3 to 3.5, and more specifically, 3.1 to 3.4. If the ratio of the height of the first peak to the height of the second peak is too small, it may be the result of adding too much lithium fluoride as a coating raw material, and in this case, fluorides due to excessive lithium fluoride may act as impurities, deteriorating the electrochemical characteristics of the cathode active material and reducing residual lithium. If the ratio of the height of the first peak to the height of the second peak is too large, it may be the result of adding too little lithium fluoride as a coating raw material, and in this case, the reducing effect of residual lithium due to the adding of lithium fluoride may be minimal.

[0065] In addition, the full width at half maximum (FWHM) of the first peak may be 2.5 eV or less, and more specifically, may be 2.3 to 2.5 eV or 2.4 to 2.5 eV. The full width at half maximum of the first peak within the above range can be obtained when lithium fluoride is appropriately added as a coating raw material within the range according to the present invention. Therefore, when the full width at half maximum of the first peak satisfies the above range, the residual lithium reduction effect and electrochemical characteristics of the positive electrode active material can be preferably implemented.

[0066] In addition, the cathode active material according to the present invention may exhibit a third peak in a region having a binding energy of 684 to 685 eV when analyzed by XPS (X-ray photoelectron spectroscopy) for F1s on the outermost surface. The third peak may be a unique peak that appears when lithium fluoride is used as a coating raw material, and may specifically refer to a peak resulting from the combination of fluorine and oxygen.

[0067] At this time, the full width at half maximum (FWHM) of the third peak may be 1.65 eV or less, and more specifically, 1.60 eV or less. The excessively large full width at half maximum of the third peak may be the result of adding too much lithium fluoride as a coating raw material, resulting in an excessive amount of fluoride impurity phase. In this case, the electrochemical characteristics of the positive electrode active material may deteriorate, and the residual lithium reduction effect may also be reduced.

[0068]

[0069] Meanwhile, the coating layer according to the present invention is attached to the surface of lithium metal oxide and may have an island shape including a plurality of attached particles spaced apart from each other.

[0070] At this time, the average coverage of the coating layer according to the present invention may be 18 to 30 area% based on the total surface area of ​​the single particle, and more specifically, 18.5 to 25 area%. When the average coverage of the coating layer is sufficiently large as in the above range, the effect of reducing residual lithium due to the formation of the coating layer can be preferably implemented. However, if the average coverage of the coating layer is too large, the capacity characteristics may be reduced. At this time, the average coverage of the coating layer in the above range can be obtained by using lithium fluoride as a coating raw material in the manufacturing method and appropriately controlling the input amount of lithium fluoride within the range according to the present invention.

[0071] In this specification, the “average coverage of the coating layer” can be measured by the following methods. First, the “coverage of the coating layer for one positive electrode active material particle” can be obtained by calculating the percentage value of the total area of ​​multiple attached particles to the total particle surface area when the particle surface is observed with a SEM (scanning electron microscope) at 20,000x magnification using a zero-shot segmentation algorithm. At this time, the zero-shot segmentation algorithm refers to an algorithm that classifies which object or area each pixel of an image belongs to, extracts pixels from the image, predicts whether the corresponding pixel belongs to a new class using the characteristics of the extracted pixels, and performs segmentation based on this. Next, the “average coverage of the coating layer” can be obtained by calculating the coverage of each of 20 random positive electrode active material particles in the positive electrode active material powder using the above method and calculating the average value thereof.

[0072] In addition, the average number of attached particles in the coating layer according to the present invention may be 240 to 300, and more specifically, 250 to 280. When the average number of attached particles in the coating layer is sufficiently large as in the above range, the effect of reducing residual lithium due to the formation of the coating layer can be preferably implemented. However, if the average number of attached particles in the coating layer is too large, the capacity characteristics may be reduced. At this time, the average number of attached particles in the coating layer in the above range can be obtained by using lithium fluoride as a coating raw material in the manufacturing method and appropriately controlling the input amount of lithium fluoride within the range according to the present invention.

[0073] In this specification, the “average number of attached particles” can be measured by the following methods. First, the “number of attached particles for one positive electrode active material particle” can be obtained by calculating the total number of multiple attached particles spaced apart from each other when observing the particle surface with a SEM (scanning electron microscope) at 20,000x magnification using a zero-shot segmentation algorithm. At this time, the zero-shot segmentation algorithm is an algorithm that classifies which object or area each pixel of an image belongs to, extracts pixels from an image, and predicts whether the corresponding pixel belongs to a new class using the characteristics of the extracted pixels, and performs segmentation based on this. Next, the “average number of attached particles” can be obtained by calculating the number of attached particles for each of 20 random positive electrode active material particles in the positive electrode active material powder using the above method and calculating the average value thereof.

[0074]

[0075] The positive electrode active material according to the present invention can efficiently reduce residual lithium remaining on the surface after manufacturing lithium metal oxide in the form of single particles through the above-described coating layer, and the residual lithium content can be 3500 ppm or less, and more specifically, 3200 ppm or less.

[0076] In addition, the cathode active material according to the present invention uses lithium fluoride as a coating raw material, so that the removal efficiency of Li2CO3, especially of residual lithium, is improved, and the content of Li2CO3 in the residual lithium can be 2700 ppm or less, and more specifically, 2500 ppm or less.

[0077] As the residual lithium content decreases, gas generation and battery swelling caused by side reactions between residual lithium and the electrolyte can be suppressed, thereby dramatically improving the safety of the battery.

[0078]

[0079] The lithium metal oxide according to the present invention can be more specifically represented by the following chemical formula 1.

[0080] [Chemical Formula 1]

[0081] Li a [Ni x Co y Mn z M w ]O2

[0082] 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.

[0083] In the lithium metal oxide of the above chemical formula 1, lithium may be included in an amount corresponding to a, that is, 0.8≤a≤1.3. If a is too small, the capacity may be reduced, and if a is too large, the strength of the sintered positive electrode active material may be increased, making pulverization difficult, and the amount of gas generated may increase due to an increase in lithium byproducts. Considering the effect of improving the capacity characteristics of the positive electrode active material according to the control of the lithium content and the sinterability balance during the production of the active material, the lithium may be included in an amount of 0.9≤a≤1.1 more preferably.

[0084] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, that is, 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 high capacity of the battery.

[0085] In the lithium metal oxide of the above chemical formula 1, 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 deteriorate. If the cobalt content is too high, manufacturing costs may increase and reversible capacity may decrease.

[0086] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content 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.

[0087] In the lithium metal oxide of the above chemical formula 1, M, which is another doping element, may be included in a content corresponding to w, that is, 0≤w1≤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 implement other doping effects.

[0088]

[0089] 2. Method for manufacturing positive electrode active material

[0090] Another embodiment of the present invention provides a method for producing 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 the form of a single particle; and mixing the lithium metal oxide, lithium fluoride (LiF), and a cobalt raw material, 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 amount of lithium fluoride added is 0.5 to 1.5 mol% based on the total mole number of the lithium metal oxide.

[0091] 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.

[0092]

[0093] First, lithium metal oxide with a layered crystal structure containing nickel (Ni) in the form of single particles is prepared.

[0094] The lithium metal oxide in the form of single particles can be prepared more specifically by preparing a metal precursor, mixing and calcining the metal precursor and lithium raw material, and then crushing the metal precursor.

[0095] The above metal precursor may more specifically be a metal hydroxide.

[0096] The above metal precursor may be manufactured by, for example, adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a metal-containing solution including a nickel raw material, a manganese raw material, or a cobalt raw material, and performing a co-precipitation reaction.

[0097] The above nickel raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the nickel raw material may be a nickel-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, may be NiSO4, NiSO4·6H2O, Ni(OH)2, NiO, NiOOH, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, fatty acid nickel salt, nickel halide, or a combination thereof, but is not limited thereto.

[0098] The above cobalt raw material is not particularly limited as long as it is used in the art for manufacturing a positive electrode active material precursor. For example, the cobalt raw material may be a cobalt-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, CoSO 4, It may be, but is not limited to, CoSO4ㆍ7H2O, Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O or a combination thereof.

[0099] The manganese raw material is not particularly limited as long as it is used in the art for manufacturing a precursor of a cathode active material. For example, the manganese raw material may be a manganese-containing sulfate, acetate, nitrate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically, may be a manganese salt such as MnSO4, MnCO3, Mn(NO3)2, manganese acetate, manganese dicarboxylic acid salt, manganese citrate, and manganese fatty acid salt, manganese oxide such as Mn2O3, MnO2, and Mn3O4, oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0100] 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 (e.g., alcohol, etc.) that can be uniformly mixed with water.

[0101] The above complexing agent-containing solution performs the function of forming a complex, and may include, but is not limited to, NH3, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3 or a combination thereof as the complexing agent. Meanwhile, the complexing agent-containing solution may be used in the form of an aqueous solution, and at this time, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water may be used as the solvent.

[0102] The above pH adjusting agent-containing solution acts as a precipitant or pH adjusting agent, and may include an alkaline compound such as a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. Meanwhile, the pH adjusting agent-containing solution may also be used in the form of an aqueous solution, and at this time, water or a mixture of water and an organic solvent (e.g., alcohol, etc.) that can be uniformly mixed with water may be used as the solvent. At this time, the pH adjusting agent-containing solution may be added in an amount such that the pH of the reaction solution becomes 10 to 13.

[0103] The above coprecipitation reaction can be performed under an inert atmosphere such as nitrogen or argon, can be performed at a temperature of 30 to 70°C, and can be performed at a pH of 10 to 13.

[0104] Nickel (or manganese-cobalt) hydroxide particles are generated through the above process and precipitated within the reaction solution. The precipitated precursor particles can be separated, washed, and dried using conventional methods to obtain the precursor. The precursor may be a secondary particle formed by the agglomeration of primary particles.

[0105] 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, cobalt raw material, or manganese raw material. That is, the concentration of the nickel raw material, cobalt raw material, and manganese raw material can be controlled so that the molar ratio of nickel, cobalt, or manganese in the final product, lithium metal oxide, falls within the range according to the present invention.

[0106] The lithium raw material may be lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, the lithium raw material may be, but is not limited to, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or a combination thereof.

[0107] Additionally, the sintering may be performed at a temperature of 800 to 900°C. If the sintering temperature is too low, lithium metal oxide particles may not be formed. If the sintering temperature is too high, crystal structure defects due to oversintering may occur, resulting in poor electrochemical properties.

[0108] Additionally, the calcination can be performed for 5 to 24 hours. If the calcination time is too short, lithium metal oxide particles may not be formed. If the calcination time is too long, crystal structure defects due to overcalcination may occur, resulting in poor electrochemical properties.

[0109] In addition, the atmosphere during the above firing is not particularly limited, but may be performed in an oxygen (O2) or air atmosphere, for example.

[0110] The above disintegration can be performed according to a disintegration process common in the art, and can be performed using, for example, a jet mill.

[0111]

[0112] Next, the lithium metal oxide, lithium fluoride (LiF), and cobalt raw materials are mixed and then subjected to a coating heat treatment to form a coating layer containing cobalt (Co) and fluorine (F).

[0113] The above cobalt raw material is not particularly limited as long as it is a cobalt raw material. For example, the above 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, but is not necessarily limited to, H2O, Co3(PO4)2 or a combination thereof.

[0114] However, from the perspective of more desirable implementation of the effect of reducing residual lithium due to the formation of a coating layer, Co(OH)2 may be more appropriate as the cobalt raw material.

[0115]

[0116] At this time, the amount of lithium fluoride added may be 0.5 to 1.5 mol% based on the total mole number of lithium metal oxide, and more specifically, 0.7 to 1.3 mol%. If the amount of lithium fluoride added is too small, the effect of removing residual lithium may be reduced. If the amount of lithium fluoride added is too large, the phase of fluoride impurities in the coating layer may increase due to excessive lithium fluoride, which may lower the electrochemical characteristics such as the capacity of the positive electrode active material, and the effect of removing residual lithium may rather deteriorate. In addition, when the amount of lithium fluoride added satisfies the above range, various physical properties related to XPS analysis of the positive electrode active material can be more appropriately implemented within the range according to the present invention.

[0117] In addition, the amount of the cobalt raw material may be 1.5 to 2.5 mol% based on the total mole number of the lithium metal oxide, and more specifically, 1.7 to 2.3 mol%. If the amount of the cobalt raw material is too small, the capacity of the positive electrode active material, the improvement of the lifespan, and the reduction of the residual lithium due to the cobalt coating may be minimal. If the amount of the cobalt raw material is too large, excessive cobalt may act as an impurity, which may lower the capacity of the positive electrode active material. In addition, when the amount of the cobalt raw material satisfies the above range, the various physical properties related to the XPS analysis of the positive electrode active material, the average coverage, and the average number of attached particles can be more appropriately implemented within the range according to the present invention.

[0118] In addition, the coating heat treatment may be performed at a temperature of 630 to 720°C, and more specifically, may be performed 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 occur smoothly, which may lower the coating yield, and thus the residual lithium reduction effect and electrochemical property preservation effect may be reduced. If the coating heat treatment temperature is too high, the lithium metal oxide crystal structure may be adversely affected, which may rather deteriorate the electrochemical properties of the positive electrode active material. In addition, when the coating heat treatment temperature satisfies the above range, various physical properties related to XPS analysis of the positive electrode active material can be more appropriately implemented within the range according to the present invention.

[0119] 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 reduce the coating yield, and thus the effect of reducing residual lithium and preserving electrochemical properties may be reduced. If the coating heat treatment time is too long, the crystal structure of the lithium metal oxide may be adversely affected, which may actually deteriorate the electrochemical properties of the positive electrode active material. In addition, when the coating heat treatment time satisfies the above range, various physical properties related to XPS analysis of the positive electrode active material can be more appropriately implemented within the range according to the present invention.

[0120] The above coating heat treatment can be performed in an O2 atmosphere. Accordingly, the coating reaction can proceed more smoothly, increasing coating efficiency. Consequently, the residual lithium reduction effect and electrochemical property preservation effect can be enhanced. Furthermore, when the coating heat treatment atmosphere is under the above conditions, various properties related to XPS analysis of the positive electrode active material can be more appropriately implemented within the ranges described herein.

[0121]

[0122] 3. Cathode ray and lithium secondary battery

[0123] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0124] More specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and including the positive electrode active material described above.

[0125] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change 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 positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0126] The above-described positive electrode active material layer may include a binder and / or a conductive material together with the above-described positive electrode active material.

[0127] At this time, the binder plays a role of improving the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one kind alone or a mixture of two or more kinds thereof may be used, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0128] And, the conductive material is used to provide conductivity to the electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types among these may be used, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0129] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above positive electrode active material is used.

[0130] Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including the positive electrode active material described above and optionally a binder, a conductive agent, or a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0131] The solvent may be a solvent generally used in the relevant technical field, such as dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0132] Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the resulting film on a positive electrode current collector by peeling it off from the support.

[0133]

[0134] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0135] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0136] The above lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0137] The above negative electrode may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0138] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0139] The negative electrode active material layer may optionally include a binder and a conductive material together with the negative electrode active material. As an example, the negative electrode active material layer may be manufactured by applying a composition for forming a negative electrode active material layer comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying the composition, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the film off from the support.

[0140] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, and Al alloy; metallic oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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.

[0141] The above binder and conductive material may be the same as those described above for the positive electrode.

[0142]

[0143] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries can be used without any particular restrictions. In particular, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0144]

[0145] The above electrolyte may include, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0146] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0147] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0148] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0149] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0150] As described above, a lithium secondary battery including a cathode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0151] Accordingly, another embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

[0152] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0153]

[0154] Hereinafter, embodiments of the present invention will be described in more detail through examples. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0155]

[0156] Example 1

[0157] (1) Manufacturing of positive electrode active material

[0158] (Preparation of lithium metal oxide) (Ni 0.96 Co 0.03 Mn 0.01)(OH)2 precursor and LiOH·H2O were mechanically mixed in a mixer, and then calcined at 850℃ for 10 hours in an oxygen (O2) atmosphere to form lithium metal oxide. Afterwards, the formed positive electrode active material was pulverized through a jet mill process to form lithium metal oxide in the form of single particles.

[0159] (Coating) After that, the lithium metal oxide, 1 mol% of lithium fluoride (LiF) based on the total mole number of lithium metal oxides and 2 mol% of cobalt hydroxide (Co(OH)2) based on the total mole number of lithium metal oxides were mixed, and then a coating heat treatment was performed at a temperature of 700°C for 10 hours in an O2 atmosphere to form a cobalt and fluorine-containing coating layer on the surface of the lithium metal oxide.

[0160] (2) Lithium secondary battery manufacturing

[0161] The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (carbon black, Denka black): binder (PVDF, KF1100) = 96.5:1.5:2 wt%, and the viscosity was adjusted so that the solid content was approximately 30% by adding NMP (N-Methyl-2-pyrrolidone). The manufactured slurry was coated on a 20 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading was 15.4 mg / cm 2 and the rolling density (25℃, 20kN) was 3.6 g / cm 3 It was.

[0162] The electrolyte was 1M LiPF6in EC:DMC:EMC=3:4:3 (vol%), with 3.0 vol% VC added to the total amount of the electrolyte, and a coin cell was manufactured using a PP separator and a lithium negative electrode (200 μm, Honzo metal).

[0163]

[0164] Comparative Example 1

[0165] In the coating step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 1 mol% of lithium hydroxide (LiOH·H2O) based on the total moles of lithium metal oxide was used instead of lithium fluoride.

[0166]

[0167] Comparative Example 2

[0168] In the coating step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 2 mol% of lithium fluoride (LiF) based on the total mole number of lithium metal oxides was used.

[0169]

[0170] Comparative Example 3

[0171] In the coating step, 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 a coating raw material.

[0172]

[0173] Table 1 below summarizes the process conditions of examples and comparative examples.

[0174] Coating raw materials and input amount (mol%)Coating heat treatmentLiFLiOH·H2OCo(OH)2Temperature (℃)Time (h)AtmosphereExample 110270010O2Comparative example 101270010O2Comparative example 220270010O2Comparative example 300270010O2

[0175] Tables 2 to 4 below are tables summarizing the results of evaluating the properties of positive electrode active materials and the electrochemical characteristics of lithium secondary batteries according to Experimental Examples 2 and 3 described below.

[0176] O1s XPS analysisF1s XPS analysisFirst peak appearance position (eV)Second peak appearance position (eV)First peak / second peak height ratioFirst peak half-width (eV)Third peak appearance positionThird peak half-width (eV)Example 1531.1528.93.312.45684.71.55Comparative example 1531.1528.83.712.18--Comparative example 2531.1529.11.352.01684.71.73Comparative example 3531.1528.63.622.23--

[0177] Average number of attached particles Average coverage (area %) Example 1263.64 19.62 Comparative example 121.3 22.64 Comparative example 2222.6 17.25 Comparative example 329.0 4 3.93

[0178] Residual lithium content (ppm) LiOHLi2CO3Total Example 167724303107 Comparative Example 145940384527 Comparative Example 254027993639 Comparative Example 3103728683905

[0179] Electrochemical Characteristics Initial Charge Capacity (mAh / g) Initial Discharge Capacity (mAh / g) Initial Efficiency (mAh / g) Example 1239.920786.3 Comparative Example 1241.6209.586.7 Comparative Example 2240.2206.886.1 Comparative Example 3242.2209.186.3

[0180]

[0181] Experimental Example 1: Evaluation of SEM images of positive electrode active materials

[0182] The number of island-shaped attached particles and area ratio of positive electrode active materials manufactured according to Example 1 and Comparative Examples 1 to 3 were calculated by observing SEM (scanning electron microscope) images applied through zero-shot segmentation, and these are shown in FIGS. 1 to 4, respectively, in that order.

[0183] Referring to FIGS. 1 to 4, it was confirmed that the positive electrode active materials of the examples and comparative examples exhibited a single particle form. In addition, it was confirmed that multiple attached particles were attached to the surface of the single particle in an irregular dot form (i.e., an island-type coating layer).

[0184]

[0185] Experimental Example 2: Evaluation of the properties of positive electrode active materials

[0186] (1) Peak evaluation during XPS (X-ray Photoelectron Spectroscopy) analysis for O1s

[0187] The binding energy peaks (first peak and second peak) for O1s were analyzed during XPS analysis on the surface of the manufactured positive electrode active material. Through this, the occurrence positions of the first and second peaks, the height ratio of the first peak to the second peak, and the half width of the first peak were calculated.

[0188] Figure 6 is a graph showing the results of XPS (X-ray Photoelectron Spectroscopy) analysis for O1s on the outermost surface of the positive electrode active material manufactured according to Example 1 and Comparative Examples 1 to 3.

[0189] (2) Peak evaluation during XPS (X-ray Photoelectron Spectroscopy) analysis for F1s

[0190] The binding energy peak (third peak) was analyzed during XPS analysis for F1s on the outermost surface of the manufactured positive electrode active material. Through this, the expression position and half-width of the third peak were calculated.

[0191] Figure 5 is a graph showing the results of XPS (X-ray Photoelectron Spectroscopy) analysis for F1s on the outermost surface of the positive electrode active material manufactured according to Example 1 and Comparative Examples 1 to 3.

[0192] (3) Residual lithium assessment

[0193] After adding distilled water to the positive electrode active material, the residual lithium was extracted using a stirrer, and the positive electrode active material powder and the extract were separated using a filtering device. The extract was then measured through neutralization titration using a Metrohm potentiometric titrator to evaluate the residual lithium.

[0194] (4) Evaluation of average coverage of coating layer

[0195] The “average coverage of the coating layer” was measured using the following method. First, the “coverage of the coating layer for one positive electrode active material particle” was calculated by calculating the percentage value of the total area of ​​multiple attached particles to the total particle surface area when the particle surface was observed with a SEM (scanning electron microscope) at 20,000x magnification using the zero-shot segmentation algorithm. The zero-shot segmentation algorithm is an algorithm that classifies which object or area each pixel of the image belongs to. It extracts pixels from the image, predicts whether the pixel belongs to a new class using the characteristics of the extracted pixels, and performs segmentation based on this. Next, the “average coverage of the coating layer” was calculated by calculating the coverage of each of 20 random positive electrode active material particles in the positive electrode active material powder using the above method, and calculating the average value of these.

[0196] (5) Evaluation of the average number of attached particles

[0197] The “average number of adhered particles” was measured using the following method. First, the “number of adhered particles per positive electrode active material particle” was calculated by calculating the total number of multiple adhered particles spaced apart from each other when observing the particle surface with a SEM (scanning electron microscope) at 20,000x magnification using the zero-shot segmentation algorithm. The zero-shot segmentation algorithm is an algorithm that classifies which object or area each pixel of the image belongs to. It extracts pixels from the image, predicts whether the pixel belongs to a new class using the characteristics of the extracted pixels, and performs segmentation based on this. Next, the “average number of adhered particles” was calculated by calculating the number of adhered particles for each of 20 random positive electrode active material particles in the positive electrode active material powder using the above method and calculating the average value of these.

[0198]

[0199] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0200] (1) Initial capacity and initial efficiency evaluation

[0201] After fabricating a lithium secondary battery half-cell, it was aged at 25°C for 12 hours and then subjected to a charge-discharge test at 25°C. To evaluate the initial capacity, the reference capacity was set to 200 mAh / g, and the battery was charged to 4.25 V at a constant current of 0.1 C. Then, the battery was switched to a constant voltage and charged until the end current reached 0.05 C. After a 10-minute rest time after charging, the battery was discharged to 2.5 V at a constant current of 0.1 C, using the reference capacity of 200 mAh / g.

[0202]

[0203] Referring to Tables 1 to 5, in Example 1, where lithium fluoride and cobalt hydroxide were used as coating raw materials and the overall coating process conditions, such as the amount of lithium fluoride added, were appropriately controlled, it was confirmed that all physical properties, including the ratio of the height of the first peak to the height of the second peak during XPS analysis, were appropriately implemented within the range according to the present invention. In addition, it was confirmed that the average coverage of the coating layer and the average number of adhered particles within the coating layer were appropriately implemented within the range according to the present invention. In addition, it was confirmed that the residual lithium reduction effect was very excellent, and in particular, the reduction of Li2CO3 was efficiently achieved. In addition, it was confirmed that the capacity characteristics (initial discharge capacity) of the battery also showed a good level.

[0204] On the other hand, in Comparative Example 1, when lithium hydroxide was used instead of lithium fluoride, it was confirmed that the physical properties, such as the ratio of the height of the first peak to the height of the second peak during XPS analysis, were outside the range according to the present invention. In addition, when lithium fluoride was not used as a coating raw material, it was confirmed that the third peak, which is a unique peak due to the use of lithium fluoride, was not expressed. In addition, it was confirmed that the average coverage of the coating layer and the average number of attached particles within the coating layer were significantly smaller than in the examples. In addition, it was confirmed that the total residual lithium reduction effect was worse than in the examples, and in particular, the Li2CO3 residual lithium reduction effect was significantly lower than in the examples.

[0205] In the case of Comparative Example 2, it was confirmed that the physical properties, such as the ratio of the height of the first peak to the height of the second peak during XPS analysis, were outside the range according to the present invention due to the excessive amount of lithium fluoride input. In addition, it was confirmed that the third peak, which is a unique peak due to the use of lithium fluoride as a coating raw material, was expressed, but the half-width of the third peak was obtained too large. In addition, it was confirmed that the average coverage of the coating layer and the average number of attached particles within the coating layer were somewhat smaller than in the Example. In addition, it was confirmed that the total residual lithium reduction effect and the Li2CO3 residual lithium reduction effect were deteriorated compared to the Example. In addition, it was confirmed that the capacity characteristics of the battery were deteriorated compared to the Example.

[0206] In Comparative Example 3, when only cobalt hydroxide was used as a coating raw material, it was confirmed that the physical properties, such as the ratio of the height of the first peak to the height of the second peak during XPS analysis, were outside the range according to the present invention. In addition, when lithium fluoride was not used as a coating raw material, it was confirmed that the third peak, which is a unique peak due to the use of lithium fluoride, was not expressed. In addition, it was confirmed that the average coverage of the coating layer and the average number of attached particles within the coating layer were significantly smaller than in the examples. In addition, it was confirmed that the total residual lithium reduction effect and the Li2CO3 residual lithium reduction effect were deteriorated compared to the examples.

[0207]

[0208] Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications can be made within the scope of the patent claims, the detailed description of the invention, and the attached drawings, and it is obvious that this also falls within the scope of the present invention.

[0209] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cathode active material comprising a lithium metal oxide having a layered crystal structure containing nickel (Ni) in the form of a single particle and a coating layer containing cobalt (Co) and fluorine (F) arranged on the surface of the lithium metal oxide, When analyzing XPS (X-ray photoelectron spectroscopy) for O1s on the upper surface of the above-mentioned positive electrode active material, a first peak appears in the region where the binding energy is 530 to 532 eV, and a second peak appears in the region where the binding energy is 528.5 to 529.5 eV. A cathode active material for a lithium secondary battery, wherein a ratio of the height of the first peak to the height of the second peak (first peak / second peak) is 3 to 3.

5.

2. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the full width at half maximum (FWHM) of the first peak is 2.5 eV or less.

3. In paragraph 1, A cathode active material for a lithium secondary battery, wherein a third peak appears in a region having a binding energy of 683 to 686 eV when analyzing XPS (X-ray photoelectron spectroscopy) for F1s on the outermost surface of the cathode active material.

4. In paragraph 3, A cathode active material for a lithium secondary battery, wherein the full width at half maximum (FWHM) of the third peak is 1.65 eV or less.

5. In paragraph 1, The above coating layer is attached to the surface of lithium metal oxide and is a cathode active material for a lithium secondary battery in the form of an island including a plurality of attached particles spaced apart from each other.

6. In paragraph 5, A cathode active material for a lithium secondary battery, wherein the average coverage of the coating layer is 18 to 30% based on the total surface area of ​​the single particle.

7. In paragraph 5, A cathode active material for a lithium secondary battery, wherein the average number of the above-mentioned attached particles is 240 to 300.

8. In paragraph 1, A cathode active material for a lithium secondary battery having a residual lithium content of 3500 ppm or less.

9. In paragraph 1, A cathode active material for a lithium secondary battery having a Li2CO3 content of residual lithium of 2700 ppm or less.

10. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the content of nickel in the lithium metal oxide is 80 mol% or more based on the total mole number of metals excluding lithium.

11. In paragraph 1, The above lithium metal oxide is a cathode 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 chemical formula 1, 0.8≤a≤1.3, 0.8≤x<1, 0≤y≤0.2, 0≤z≤0.2, 0≤w≤0.2, and 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.

12. A step for preparing a lithium metal oxide having a layered crystal structure containing nickel (Ni) in the form of a single particle; and It includes a 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). After the step of preparing the lithium metal oxide, the washing process is not performed before the step of forming the coating layer. A method for producing a cathode 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 mole number of lithium metal oxide.

13. In paragraph 12, A method for producing a cathode active material for a lithium secondary battery, wherein the amount of the cobalt raw material input is 1.5 to 2.5 mol% based on the total mole number of the lithium metal oxide.

14. In paragraph 12, 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°C.

15. In paragraph 12, A method for manufacturing a cathode active material for a lithium secondary battery, wherein the above coating heat treatment is performed for 4 to 24 hours.

16. In paragraph 12, A method for manufacturing a cathode active material for a lithium secondary battery, wherein the above coating heat treatment is performed in an O2 atmosphere.

17. A cathode for a lithium secondary battery comprising the cathode active material of clause 1.

18. A lithium secondary battery comprising the positive electrode for a lithium secondary battery of Article 17.

Images