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

Abstract

The present invention relates to a cathode active material for lithium secondary battery, comprising: a lithium metal oxide having a layered crystal structure containing nickel (Ni) in the form of single particles; and a coating layer covering the entire surface of the lithium metal oxide and containing an aluminum (Al) compound, wherein the aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3.

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] In addition, the demand for high-power, high-capacity batteries, such as those for electric vehicles, is increasing recently, and accordingly, the nickel content in the cathode active material is gradually increasing (so-called "high nickel"). When the nickel content in the cathode active material increases, the initial capacity characteristics are improved, but when charge and discharge are repeated, the highly reactive Ni +4 There is a problem that a large amount of ions are generated, causing structural collapse of the positive electrode active material, which increases the rate of deterioration of the positive electrode active material, resulting in a decrease in life characteristics and battery safety.

[0006] To address the above issues, a technique has been proposed for producing single-particle cathode active materials, rather than secondary particles, by increasing the sintering temperature during the production of lithium nickel cobalt manganese oxide. Single-particle cathode active materials have a smaller contact area with the electrolyte than conventional secondary-particle cathode active materials, resulting in less side reactions with the electrolyte. Furthermore, their superior particle strength reduces particle breakage during electrode production. Therefore, the application of single-particle cathode active materials offers the advantages of reduced gas generation and superior cycle life.

[0007] However, in order to grow high-nickel single-particle lithium transition metal oxide into a cathode active material with a particle size of several microns, sintering at high temperatures and for a long time is required. At this time, if sintering at high temperatures and for a long time is performed, defects in the layered crystal structure due to oversintering occur, and since it is manufactured at a relatively high sintering temperature, a rock salt phase is formed on the particle surface, which increases the surface resistance and reduces the mobility of lithium ions. This decrease in lithium ion mobility primarily reduces the capacity characteristics, and secondarily causes an imbalance in lithium ion movement, which causes crystal structure deformation and particle cracking, resulting in a problem of reduced life characteristics such as an increase in resistance as the cycle progresses.

[0008] Furthermore, high-nickel cathode materials typically have a high content of residual lithium (LiOH and / or Li2CO3) remaining on their surfaces after manufacturing. Therefore, a washing process is typically performed to remove this residual lithium, which can compromise battery safety. However, this washing process damages the cathode surface structure, increases the likelihood of proton exchange, and thus degrades electrochemical properties such as capacity and output. Furthermore, it increases the cost of cathode manufacturing, and generates wastewater, necessitating the need for separate wastewater treatment facilities.

[0009]

[0010] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery, which is a lithium metal oxide in the form of a single particle, which reduces residual lithium and improves capacity and lifespan characteristics, a method for producing the same, and a lithium secondary battery including the same.

[0011]

[0012] 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 the form of a single particle and a coating layer covering the entire surface of the lithium metal oxide and containing an aluminum (Al) compound, wherein the aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3.

[0013] The average thickness of the above coating layer may be 0.1 to 0.65 nm.

[0014] The average difference between the maximum thickness and the minimum thickness of the above coating layer may be 0.5 nm or less.

[0015] The above lithium metal oxide may have a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) of 1.514 or more when analyzing an X-ray diffraction pattern.

[0016] The content of aluminum element in the above positive electrode active material may be 550 to 4000 ppm based on the total weight of the positive electrode active material.

[0017] The above LiAlO2 may be amorphous.

[0018] The above Al2O3 may be amorphous.

[0019] The above positive electrode active material may have a residual lithium content of 33500 ppm or less.

[0020] 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.

[0021] The above lithium metal oxide can be represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Li a [Ni x Co y Mn zM w ]O2

[0024] 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.

[0025]

[0026] 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 forming a coating layer containing an aluminum compound on the lithium metal oxide by an atomic layer deposition method, 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 aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3.

[0027] The above atomic layer deposition can be performed in 1 to 7 cycles.

[0028] One cycle of the above atomic layer deposition may include a step of supplying an aluminum-containing gas onto the lithium metal oxide to adsorb the aluminum-containing gas onto the lithium metal oxide; and a step of supplying and reacting a reactant onto the lithium metal oxide on which the aluminum-containing gas is adsorbed.

[0029] The amount of the aluminum-containing gas supplied may be 0.2 to 1.6 wt% based on the total weight of the lithium metal oxide.

[0030] The supply amount of the above reactant may be 0.002 to 0.01 wt% based on the total weight of the lithium metal oxide.

[0031] The above atomic layer deposition can be performed at a temperature of 150 to 300°C.

[0032] The above atomic layer deposition can be performed at a pressure of 1 to 10 torr.

[0033]

[0034] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0035] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0036]

[0037] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery is a lithium metal oxide in the form of a single particle, and since a very thin and homogeneous aluminum (Al) coating layer is coated without a separate washing process after a firing process, not only is residual lithium reduced, but capacity and life characteristics can be improved.

[0038] In addition, the cathode active material for a lithium secondary battery according to one embodiment of the present invention can reduce residual lithium without a washing process, so that there is no problem with wastewater treatment of the washing solution, thereby reducing process costs.

[0039]

[0040] Figure 1 is a SEM image of a positive electrode active material manufactured according to Example 1.

[0041]

[0042] 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 only 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0047] 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.

[0048] 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.

[0049]

[0050] 1. Positive active material

[0051] 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.

[0052] 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, which has 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 50 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.

[0053] Additionally, "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, "crystal grain" refers to a distinct region in the form of a lattice structure in which atoms within a primary particle form a lattice structure with a certain direction.

[0054] Additionally, the content of nickel in the lithium metal oxide according to the present invention may be 80 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.

[0055] However, in order to grow high-nickel single-particle lithium transition metal oxide into a cathode active material with a particle size of several microns, sintering at high temperatures and for a long time is required. At this time, if sintering at high temperatures and for a long time is performed, defects in the layered crystal structure due to oversintering occur, and since it is manufactured at a relatively high sintering temperature, a rock salt phase is formed on the particle surface, which increases the surface resistance and reduces the mobility of lithium ions. This decrease in lithium ion mobility primarily reduces the capacity characteristics, and secondarily causes an imbalance in lithium ion movement, which causes crystal structure deformation and particle cracking, resulting in a problem of reduced life characteristics such as an increase in resistance as the cycle progresses.

[0056] Furthermore, high-nickel cathode materials typically have a high content of residual lithium (LiOH and / or Li2CO3) remaining on their surfaces after manufacturing. Therefore, a washing process is typically performed to remove this residual lithium, which can compromise battery safety. However, this washing process damages the cathode surface structure, increases the likelihood of proton exchange, and thus degrades electrochemical properties such as capacity and output. Furthermore, it increases the cost of cathode manufacturing, and generates wastewater, necessitating the need for separate wastewater treatment facilities.

[0057] Accordingly, in a lithium secondary battery cathode active material according to one embodiment of the present invention, after manufacturing a lithium metal oxide in the form of a single particle, aluminum is coated using an atomic layer deposition process instead of a water-rinsing process. Accordingly, the deterioration of electrochemical characteristics such as the capacity of the cathode active material due to the water-rinsing process can be prevented, and the process cost can be reduced because there is no problem with the treatment of the water-rinsing solution wastewater. In addition, since the aluminum coating is performed using the atomic layer deposition process, a coating layer can be coated on the entire surface of the lithium metal oxide particles with a very thin and uniform thickness, so that not only the life characteristics can be improved, but also the capacity characteristics can be improved by minimizing the increase in resistance due to the formation of the coating layer.

[0058] More specifically, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention includes a coating layer that covers the entire surface of a lithium metal oxide and contains an aluminum (Al) compound. That is, the coating layer is a conformal type coating layer that evenly covers the entire surface of a single particle, and accordingly, compared to an island type coating layer, the effect of improving the structural stability of the positive electrode active material and the effect of reducing residual lithium are better implemented, so that the effect of improving the lifespan and safety of the positive electrode active material can be preferably implemented. Meanwhile, the conformal type coating layer can be implemented by performing coating using an atomic layer deposition process.

[0059] At this time, the aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 may be 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3, and more specifically, 28 to 40 wt%. The content of LiAlO2 within the above range may be a greater content than when the coating process is performed after performing the washing process after producing the lithium metal oxide. That is, when the washing process is performed after producing the lithium metal oxide, the residual lithium (LiOH and / or Li2CO3) on the surface is reduced, and the content of LiAlO2 in the coating layer is lowered. However, the present invention performs the coating process without performing the washing process, so that the content of LiAlO2 in the coating layer can be derived within the above range. At this time, when the content of LiAlO2 satisfies the above range, the effects of reducing the residual lithium of the positive electrode active material and improving the capacity and lifespan characteristics can be preferably implemented.

[0060] Meanwhile, the weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer can be confirmed through X-ray photoelectron spectroscopy (XPS) analysis of the surface of the positive electrode active material.

[0061]

[0062] In addition, the average thickness of the coating layer may be 0.1 to 0.65 nm, and more specifically, 0.38 to 0.65 nm. When the average thickness of the coating layer satisfies the above range, the effects of reducing residual lithium and improving capacity and lifespan characteristics of the positive electrode active material can be preferably implemented.

[0063] Meanwhile, the average thickness of the coating layer can be obtained by controlling the number of cycles of the atomic layer deposition process, the temperature at which the atomic layer deposition process is performed, the amount of aluminum-containing gas supplied per cycle, the amount of reactant supplied per cycle, etc. This will be described in more detail in the method for manufacturing a positive electrode active material described below.

[0064] In addition, the average thickness of the coating layer can be measured by the following method. First, the thickness of the coating layer for one positive electrode active material particle (single particle) can be calculated by analyzing a cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material particle, randomly selecting 10 locations on the surface of the positive electrode active material particle, and then calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the coating layer can be calculated by calculating the average of the coating layer thicknesses measured in the same manner as above for 20 random positive electrode active material particles among the positive electrode active material powder.

[0065]

[0066] In addition, the average difference between the maximum and minimum thicknesses of the coating layer may be 0.5 nm or less. That is, since the coating layer according to the present invention is manufactured through an atomic layer deposition coating process, the thickness uniformity of the coating layer can be improved. Accordingly, the resistance of the coating layer can be reduced, and the effects of improving the capacity and lifespan characteristics of the positive electrode active material can be more preferably implemented.

[0067] Meanwhile, the average of the difference between the maximum and minimum thicknesses of the coating layer can be obtained by controlling the number of cycles of the atomic layer deposition process, the temperature at which the atomic layer deposition process is performed, the amount of aluminum-containing gas supplied per cycle, the amount of reactant supplied per cycle, etc. This will be described in more detail in the method for manufacturing a positive electrode active material described below.

[0068] In addition, the average of the difference values ​​between the maximum thickness and the minimum thickness of the coating layer can be measured by the following method. First, the difference value between the maximum thickness and the minimum thickness for one positive electrode active material particle (single particle) can be calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material particle, calculating the maximum thickness and the minimum thickness of the entire coating layer surrounding the active material particle, and obtaining the difference value. Next, the average of the difference values ​​between the maximum thickness and the minimum thickness of the coating layer can be calculated by calculating the average of the coating layer thicknesses measured in the same manner as above for 20 random positive electrode active material particles among the positive electrode active material powders.

[0069]

[0070] In addition, the content of the aluminum element in the positive electrode active material may be 550 to 4000 ppm based on the total weight of the positive electrode active material, and more specifically, may be 1600 to 4000 ppm. When the content of the aluminum element in the positive electrode active material satisfies the above range, the overall properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. Accordingly, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0071] Meanwhile, in this specification, the content of aluminum element in the positive electrode active material can be measured through ICP (inductively coupled plasma spectrometry) component analysis.

[0072]

[0073] In addition, the lithium metal oxide may have a ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) of 1.514 or more when analyzing the X-ray diffraction pattern of the lithium metal oxide. The ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) when analyzing the X-ray diffraction pattern of the lithium metal oxide may be used as a measure of the so-called cation mixing ratio. At this time, a larger I(003) / I(104) peak intensity ratio may mean a smaller cation mixing ratio. Cation mixing refers to a phenomenon in which transition metal cations in a transition metal layer are partially substituted into the lithium layer in a layered crystal structure lithium metal oxide, that is, a structure in which lithium layers and transition metal layers are alternately laminated. At this time, the ratio of the substituted transition metal cations in the lithium layer is referred to as the cation mixing ratio. In particular, nickel ions, which have similar ionic radii to lithium ions, are representative transition metals substituted into the lithium layer. At this time, if the cation mixing ratio of the lithium metal oxide is too large, the mobility of lithium ions in the lithium layer may be reduced, thereby deteriorating the capacity and life characteristics of the battery. Therefore, the lithium metal oxide according to the present invention has an I(003) / I(104) peak intensity ratio that satisfies the above range, so that the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented. In particular, the inventors of the present invention confirmed that when all conditions of the coating process according to the present invention are satisfied, the I(003) / I(104) peak intensity ratio is appropriately implemented within the above range.

[0074] In addition, the LiAlO2 may be amorphous, and the Al2O3 may be amorphous. Since the aluminum compounds LiAlO2 and Al2O3 in the coating layer are amorphous, lithium ion mobility may be improved, so that the capacity and output characteristics of the positive electrode active material may be more preferably implemented. The amorphousness of the aluminum compound can be confirmed through TEM (transmission electron microscope) image analysis or X-ray diffraction pattern analysis for the positive electrode active material.

[0075]

[0076] Meanwhile, the positive electrode active material according to the present invention can have a residual lithium content of 33,500 ppm or less, and more specifically, 10,000 ppm or less, by coating the aluminum coating layer as described above. Accordingly, gas generation and battery swelling caused by side reactions between residual lithium and the electrolyte can be suppressed, thereby improving battery safety.

[0077]

[0078] The lithium metal oxide according to the present invention can be more specifically represented by the following chemical formula 1.

[0079] [Chemical Formula 1]

[0080] Li a [Ni x Co y Mn z M w ]O2

[0081] 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.

[0082] 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.

[0083] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, i.e., 0.8≤x<1. When the nickel content satisfies the above range, high capacity of the battery can be achieved.

[0084] 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.

[0085] 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.

[0086] 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≤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 implement other doping effects.

[0087]

[0088] 2. Method for manufacturing positive electrode active material

[0089] 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 forming a coating layer containing an aluminum compound on the lithium metal oxide by an atomic layer deposition method, 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 aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3.

[0090] 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.

[0091]

[0092] First, lithium metal oxide with a layered crystal structure containing nickel (Ni) in the form of single particles is prepared.

[0093] 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.

[0094] The above metal precursor may more specifically be a metal hydroxide.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] Additionally, the sintering may be performed at a temperature of 750 to 1000°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.

[0107] Additionally, the above-mentioned calcination can be performed for 5 to 20 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, resulting in poor electrochemical properties.

[0108] 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.

[0109] 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.

[0110]

[0111] At this time, the washing process may not be performed after the step of preparing the lithium metal oxide and before the step of forming the coating layer. The washing process is usually performed to remove residual lithium remaining on the surface of the synthesized lithium metal oxide. However, the washing process may damage the surface structure of the positive electrode active material, thereby reducing the electrochemical characteristics such as capacity, output, and lifespan of the positive electrode active material. Therefore, the present invention can replace the washing process with a coating process described below to achieve the effect of reducing residual lithium. Accordingly, the effect of reducing residual lithium and the effect of preserving the electrochemical characteristics of the positive electrode active material can be simultaneously implemented.

[0112]

[0113] Next, a coating layer containing an aluminum compound is formed on the lithium metal oxide using an atomic layer deposition method.

[0114] At this time, the atomic layer deposition can be performed for 1 to 7 cycles, and more specifically, for 3 to 7 cycles. When the number of cycles performed during atomic layer deposition satisfies the above range, various properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. Accordingly, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0115] More specifically, one cycle of the above atomic layer deposition may include a step of supplying an aluminum-containing gas onto the lithium metal oxide to adsorb the aluminum-containing gas onto the lithium metal oxide; and a step of supplying and reacting a reactant onto the lithium metal oxide on which the aluminum-containing gas is adsorbed.

[0116] At this time, the supply amount of the aluminum-containing gas may be 0.2 to 1.6 wt% based on the total weight of the lithium metal oxide, and more specifically, 0.3 to 1.0 wt%. When the supply amount of the aluminum-containing gas satisfies the above range, aluminum coating can be appropriately performed in atomic layer units per cycle. Accordingly, various physical properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. In addition, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0117] The supply amount of the above reactant may be 0.002 to 0.01 wt% based on the total weight of the lithium metal oxide. When the supply amount of the reactant satisfies the above range, aluminum coating can be appropriately performed in atomic layer units per cycle. Accordingly, various physical properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. In addition, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0118] The above aluminum-containing gas may be, for example, trimethoxy aluminum (Tri Methoxy Aluminum, TMA).

[0119] The reactant may be, for example, water (H2O) or ozone (O3).

[0120] The above atomic layer deposition can be performed at a temperature of 150 to 300°C. When the atomic layer deposition performing temperature satisfies the above range, the reaction of the aluminum-containing gas and the reactant occurs smoothly, so that the aluminum coating layer can be easily formed. Accordingly, various physical properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. In addition, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0121] The above atomic layer deposition can be performed at a pressure of 1 to 10 torr. When the performing pressure during atomic layer deposition satisfies the above range, the reaction between the aluminum-containing gas and the reactant occurs smoothly, so that the aluminum coating layer can be easily formed. Accordingly, various physical properties of the positive electrode active material, such as the content of LiAlO2 based on the total weight of LiAlO2 and the Al2O3, the average thickness of the coating layer, and the average of the difference between the maximum thickness and the minimum thickness of the coating layer, can be appropriately implemented within the range according to the present invention. In addition, the effect of improving the capacity and life characteristics of the positive electrode active material can be more preferably implemented.

[0122]

[0123] 3. Cathode ray and lithium secondary battery

[0124] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0125] 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.

[0126] 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, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134]

[0135] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0136] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0137] The above lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] The above binder and conductive material may be the same as those described above for the positive electrode.

[0143]

[0144] 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.

[0145]

[0146] 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.

[0147] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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).

[0152] 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.

[0153] 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.

[0154]

[0155] 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.

[0156]

[0157] Example 1

[0158] (1) Manufacturing of positive electrode active material

[0159] (Preparation of lithium metal oxide) LiNi 0.88 Co 0.095 Mn 0.025 Lithium metal oxide in the form of single particles with an O2 composition was prepared.

[0160] At this time, no separate washing process was performed after lithium metal oxide synthesis.

[0161] (Coating) The atomic layer deposition reactor used a fluidized bed type, and low vacuum conditions were maintained so that the reaction temperature was 150 to 300℃ and the pressure inside the chamber was 1 to 10 torr. Trimethylaluminum (TMA, Al(CH3)3) was used as an aluminum-containing gas as a precursor, and water (H2O) was used as a reactant.

[0162] The lithium metal oxide prepared above was introduced into an atomic layer deposition reactor, and TMA was injected together with N2 gas to cause chemical adsorption and saturation of the lithium metal oxide base material, and then H2O was injected again to cause a chemical reaction to form an aluminum compound-containing coating layer. In addition, the amount of TMA introduced per cycle was 0.5 wt% based on the total weight of the lithium metal oxide, and the amount of H2O introduced per cycle was 0.005 wt% based on the total weight of the lithium metal oxide.

[0163] This series of processes is called 1 cycle, and a total of 1 cycle was performed.

[0164] (2) Lithium secondary battery manufacturing

[0165] 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.

[0166] 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).

[0167]

[0168] Example 2

[0169] 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 the number of atomic layer deposition cycles was set to 2.

[0170]

[0171] Example 3

[0172] 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 the number of atomic layer deposition cycles was set to 4.

[0173]

[0174] Example 4

[0175] 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 the number of atomic layer deposition cycles was set to 6.

[0176]

[0177] Comparative Example 1

[0178] After preparing the lithium metal oxide, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the coating process was not performed.

[0179]

[0180] Comparative Example 2

[0181] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a washing process using distilled water was performed before performing the coating process after preparing the lithium metal oxide.

[0182]

[0183] Comparative Example 3

[0184] 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 the number of atomic layer deposition cycles was set to 8.

[0185]

[0186] Table 1 below summarizes the process conditions of examples and comparative examples.

[0187] TMA input amount (weight%) based on the total weight of lithium metal oxide in 1 cycle H2O input amount (weight%) based on the total weight of lithium metal oxide in 1 cycle Whether or not washing process is performed Number of atomic layer deposition cycles Comparative example 1--Non-washing-Comparative example 20.50.005 Washing 1 Example 10.50.005 Non-washing 1 Example 20.50.005 Non-washing 2 Example 30.50.005 Non-washing 4 Example 40.50.005 Non-washing 6 Comparative example 30.50.005 Non-washing 8

[0188]

[0189] Tables 2 and 3 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.

[0190] Coating layer average thickness (nm) Difference between maximum and minimum thickness of coating layer average (nm) LiAlO2 / Al2O3+LiAlO2 weight ratio (%) Al element content (ppm) LiOH (ppm) Li2CO3 (ppm) Total (ppm) I (003) / I (104) Peak intensity ratio Comparative example 1---027,4746,44433,9181.5138 Comparative example 20.120.12950118,2344,50322,7371.5248 Example 10.160.0616.566226,9896,35033,3391.5259 Example 20.320.1326.11,22020,4456,22326,6681.5246Example 30.40.1529.12,1446,5772,4509,0271.5313Example 40.580.2735.93,7224,5561,9826,5381.5149Comparative Example 30.781.341.34,2304,1022,2346,3361.5060

[0191] Initial charge capacity (mAh / g) Initial discharge capacity (mAh / g) Initial efficiency (%) Capacity retention rate (45℃30cycle, %) Comparative example 1219.7193.988.393.3 Comparative example 2220.3195.388.792.5 Exemplary example 1221.5196.788.893.6 Exemplary example 2220.3197.889.894 Exemplary example 3222.5197.588.893.8 Exemplary example 4221.3194.387.893.4 Comparative example 3219.3191.287.293.1

[0192]

[0193] Experimental Example 1: Evaluation of SEM images of positive electrode active materials

[0194] The SEM (scanning electron microscope) image of the positive electrode active material manufactured according to Example 1 was observed and is shown in Fig. 1.

[0195] Referring to Fig. 1, it was confirmed that the positive electrode active material of Example 1 was in the form of a single particle, and multiple spaced coated particles were not observed on the particle surface, confirming that the coating layer was of a conformal type that evenly covered the entire particle surface.

[0196]

[0197] Experimental Example 2: Evaluation of the properties of positive electrode active materials

[0198] (1) Evaluation of average thickness of coating layer

[0199] First, the thickness of the coating layer for a single positive electrode active material particle (single particle) was calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material particle, randomly selecting 10 locations on the surface of the positive electrode active material particle, and calculating the average value of the coating layer thickness at the selected locations. Next, the average thickness of the coating layer was calculated by calculating the average of the coating layer thicknesses measured in the same manner as above for 20 random positive electrode active material particles among the positive electrode active material powders.

[0200] (2) Average evaluation of the difference between the maximum and minimum thickness of the coating layer

[0201] First, the difference between the maximum and minimum thickness for a single positive electrode active material particle (single particle) was calculated by analyzing the cross-sectional TEM image after FIB (Focused Ion Bean) milling of the positive electrode active material particle, calculating the maximum and minimum thickness of the entire coating layer surrounding the positive electrode active material particle, and obtaining the difference value. Next, the average of the difference between the maximum and minimum thickness of the coating layer was calculated by calculating the average of the coating layer thicknesses measured in the same manner as above for 20 random positive electrode active material particles among the positive electrode active material powders.

[0202] (3) Evaluation of the weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer

[0203] The weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer was evaluated through X-ray photoelectron spectroscopy (XPS) analysis of the surface of the positive electrode active material.

[0204] (4) Evaluation of Al element content in positive electrode active material

[0205] The Al element content in the cathode active material was evaluated through ICP (inductively coupled plasma spectroscopy) component analysis.

[0206] (5) Evaluation of residual lithium content

[0207] 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.

[0208] (6) Evaluation of I(003) / I(104) peak intensity ratio

[0209] The I(003) / I(104) peak intensity ratio was evaluated by X-ray diffraction pattern analysis.

[0210]

[0211] Experimental Example 3: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0212] (1) Initial capacity and initial efficiency evaluation

[0213] 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.

[0214] (2) Evaluation of high temperature capacity retention rate (45℃, 30 cycles)

[0215] After fabricating a lithium secondary battery half-cell, it was charged to 4.25 V at a constant current of 0.5 C at 45°C, then switched to a constant voltage and charged until the end current reached 0.05 C. After a rest time of 10 minutes after charging, it was discharged at a constant current of 1.0 C until it reached 2.5 V. Under these charge-discharge cycle conditions, 30 charge-discharge cycles were performed, and the capacity retention rate of the 30th cycle was calculated compared to the first cycle.

[0216]

[0217]

[0218] Referring to Table 1, in Examples 1 to 4 in which the overall coating process conditions according to the present invention, such as the number of atomic layer deposition cycles, the amount of TMA and H2O injected into the lithium metal oxide during 1 cycle, and non-performance of the washing process, were controlled, it was confirmed that the average thickness of the coating layer, the weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer, and other physical properties were appropriately obtained within the range according to the present invention. As a result, it was confirmed that the residual lithium content was reduced compared to Comparative Example 1, which is a lithium metal oxide base material, and the capacity (initial discharge capacity) and lifespan (capacity retention rate) characteristics were improved.

[0219] On the other hand, in the case of Comparative Example 1, which is a lithium metal oxide base material, it was confirmed that the residual lithium content was too high and the capacity and life characteristics were deteriorated compared to the examples.

[0220] In the case of Comparative Example 2, as a result of performing the washing process, it was confirmed that the weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer was lower than in the example, and the content of Al element in the positive electrode active material was reduced. It appears that the decrease in the content of Al element is the result of the reaction between the residual lithium and the aluminum source not occurring smoothly during the coating process reaction. In addition, it was confirmed that the capacity and life characteristics of the battery were lower than in the example.

[0221] In the case of Comparative Example 3, as a result of the number of atomic layer deposition cycles being too high, the average thickness of the coating layer was obtained to be too large, the average difference between the maximum thickness and the minimum thickness of the coating layer was too large, so the coating homogeneity was poor, the weight ratio of LiAlO2 to the total weight of LiAlO2 and Al2O3 in the coating layer was obtained to be too large, and the I(003) / I(104) peak intensity ratio was obtained to be smaller than in the example, so it could be confirmed that the cation mixing ratio was large. In addition, it could be confirmed that the capacity and life characteristics of the battery were lower than in the example.

[0222] Meanwhile, when comparing the examples in more detail, it was confirmed that in the case of examples 3 and 4, where the number of atomic layer deposition cycles was more appropriately controlled, the residual lithium content was more preferably implemented at 10,000 ppm or less.

[0223]

[0224] 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.

[0225] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium metal oxide having a layered crystal structure containing nickel (Ni) in the form of a single particle, and a coating layer covering the entire surface of the lithium metal oxide and containing an aluminum (Al) compound, A cathode active material for a lithium secondary battery, wherein the aluminum compound comprises LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3.

2. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average thickness of the coating layer is 0.1 to 0.65 nm.

3. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the average of the difference between the maximum thickness and the minimum thickness of the coating layer is 0.5 nm or less.

4. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery, wherein the ratio of the peak intensity of the (003) plane to the peak intensity of the (104) plane (I(003) / I(104)) when analyzing an X-ray diffraction pattern is 1.514 or more.

5. In paragraph 1, A cathode active material for a lithium secondary battery, wherein the content of aluminum element in the cathode active material is 550 to 4000 ppm based on the total weight of the cathode active material.

6. In paragraph 1, The above LiAlO2 is an amorphous cathode active material for lithium secondary batteries.

7. In paragraph 1, The above Al2O3 is an amorphous cathode active material for lithium secondary batteries.

8. In paragraph 1, A cathode active material for a lithium secondary battery having a residual lithium content of 33,500 ppm or less.

9. 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.

10. 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.

11. A step for preparing a lithium metal oxide having a layered crystal structure containing nickel (Ni) in the form of a single particle; and Comprising a step of forming a coating layer containing an aluminum compound on the lithium metal oxide by an atomic layer deposition method, After the step of preparing the lithium metal oxide, the washing process is not performed before the step of forming the coating layer. The above aluminum compound includes LiAlO2 and Al2O3, and the content of the LiAlO2 is 12 to 40 wt% based on the total weight of the LiAlO2 and the Al2O3. A method for manufacturing a cathode active material for a lithium secondary battery.

12. In paragraph 11, A method for manufacturing a cathode active material for a lithium secondary battery, wherein the above atomic layer deposition is performed for 1 to 7 cycles.

13. In paragraph 12, One cycle of the above atomic layer deposition is A step of supplying an aluminum-containing gas onto the lithium metal oxide to adsorb the aluminum-containing gas onto the lithium metal oxide; and Comprising a step of supplying and reacting a reactant on a lithium metal oxide on which the aluminum-containing gas is adsorbed. A method for manufacturing a cathode active material for a lithium secondary battery.

14. In Article 13 A method for producing a cathode active material for a lithium secondary battery, wherein the amount of the aluminum-containing gas supplied is 0.2 to 1.6 wt% based on the total weight of the lithium metal oxide.

15. In paragraph 13, A method for producing a cathode active material for a lithium secondary battery, wherein the amount of the reactant supplied is 0.002 to 0.01 wt% based on the total weight of the lithium metal oxide.

16. In paragraph 11, A method for producing a cathode active material for a lithium secondary battery, wherein the above atomic layer deposition is performed at a temperature of 150 to 300°C.

17. In paragraph 11, A method for producing a cathode active material for a lithium secondary battery, wherein the above atomic layer deposition is performed at a pressure of 1 to 10 torr.

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

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

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