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

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, comprising: a core containing a lithium transition metal oxide doped with boron; and a coating layer disposed on the core and containing boron and cobalt, wherein the total boron content, which is the sum of boron doped in the lithium transition metal oxide and boron contained in the coating layer, is 1200 ppm or less relative to the total weight of the cathode active material, and the cathode active material is composed of single particles.

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] As electric vehicles expand to achieve carbon neutrality and demand for energy storage devices such as ESS for renewable energy sources surges, lithium-ion batteries are becoming an irreplaceable, core energy storage device. In particular, the characteristics of lithium-ion batteries are significantly influenced by their cathode materials, making cathode material research a significant part of lithium-ion battery research.

[0004] Among cathode materials, active research is being conducted on NCM cathode materials, which are nickel-based cathode materials with a layered structure and doped with cobalt and manganese. Previously, much research has focused on secondary particle active materials formed by the agglomeration of primary particles. However, these secondary particle active materials have large surface areas and low particle strength, leading to problems such as cracking and gas generation, which can lead to reduced battery life. Therefore, development of small-particle active materials is moving toward single-particle cathode materials composed of primary particles.

[0005] However, these single-particle cathode materials have a problem in that their electrochemical characteristics (i.e., capacity, initial efficiency, resistance characteristics, etc.) regarding lithium diffusion are bound to be inferior to those of secondary particles because the distance through which lithium ions must diffuse within the cathode material becomes longer.

[0006]

[0007] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery having excellent capacity, initial efficiency and resistance characteristics as a single particle, a method for producing the same and a lithium secondary battery including the same.

[0008]

[0009] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising: a core comprising a lithium transition metal oxide doped with boron; and a coating layer disposed on the core and comprising boron and cobalt; wherein the total boron content, which is the sum of the boron doped into the lithium transition metal oxide and the boron included in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and is composed of single particles.

[0010] The boron doped in the lithium transition metal oxide may be present within a distance of 5 nm inward from the surface of the core.

[0011] The above coating layer may include lithium boron oxide.

[0012] When XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to boron contained in the lithium boron oxide in the coating layer may be 15 wt% or less.

[0013] When XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the content of boron contained in the lithium boron oxide may be 85 wt% or more based on the total boron content in the coating layer.

[0014] When XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the content of boron contained in the boron oxide may be 15 wt% or less based on the total boron content in the coating layer.

[0015] The above coating layer may further contain aluminum.

[0016] The above coating layer may further contain lithium.

[0017] The above lithium transition metal oxide may contain nickel in an amount of 60 mol% or more based on the total mole number of transition metals.

[0018] The above lithium transition metal oxide can be represented by the following chemical formula 1.

[0019] [Chemical Formula 1]

[0020] Li a [Ni x Co y Mn z B w1 M w2 ]O2

[0021] In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0 <w1≤0.2, 0≤w2≤0.2 이고, x+y+z+w1+w2=1이고, M은 Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr 또는 이들의 조합이다.

[0022]

[0023] Another embodiment of the present invention provides a method for manufacturing a cathode material for a lithium secondary battery, comprising the steps of: preparing a transition metal hydroxide; forming a mixture comprising the transition metal hydroxide and a lithium raw material, and then performing a main firing and a post-firing to form a lithium transition metal oxide of single particles; forming a first mixture comprising the lithium transition metal oxide and a cobalt raw material, and then performing a first heat treatment; and forming a second mixture comprising the first heat-treated resultant and a boron raw material, and then performing a second heat treatment.

[0024] The first mixture may further include an aluminum raw material.

[0025] The first mixture may further include a lithium raw material.

[0026] The above first heat treatment can be performed at a temperature of 600 to 720°C.

[0027] The above second heat treatment can be performed at a temperature of 250 to 350°C.

[0028]

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

[0030] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0031]

[0032] A positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can realize excellent capacity, initial efficiency, and resistance characteristics by being coated and doped with boron and coated with cobalt.

[0033]

[0034] Figures 1 and 2 are SEM images of a positive electrode active material manufactured according to Example 4.

[0035] Figure 3 is a TOF-SIMS analysis graph of a positive electrode active material manufactured according to Example 4.

[0036] Figures 4 and 5 are SEM images of the positive electrode active material manufactured according to Comparative Example 4.

[0037] Figure 6 is a TOF-SIMS analysis graph of a positive electrode active material manufactured according to Comparative Example 4.

[0038] Figures 7 and 8 are SEM images of the positive electrode active material manufactured according to Comparative Example 5.

[0039] Figure 9 is a TOF-SIMS analysis graph of a positive electrode active material manufactured according to Comparative Example 5.

[0040] Figure 10 is a graph showing the XPS analysis results of a positive electrode active material manufactured according to Example 4.

[0041] Figure 11 is a graph showing the XPS analysis results of a positive electrode active material manufactured according to Comparative Example 4.

[0042] Figure 12 is a graph showing the XPS analysis results of a positive electrode active material manufactured according to Comparative Example 5.

[0043] Figure 13 is a graph showing a TEM image and an outer EELS analysis result of a positive electrode active material manufactured according to Example 4.

[0044] Figure 14 is a graph showing the capacity characteristics according to the cycle progression of lithium secondary batteries manufactured according to Example 4, Comparative Example 4, and Comparative Example 5.

[0045] Figure 15 is a graph showing voltage-dQ / dV curve analysis of lithium secondary batteries manufactured according to Example 4, Comparative Example 4, and Comparative Example 5.

[0046]

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0052] 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.

[0053] 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.

[0054]

[0055] 1. Positive active material

[0056] One embodiment of the present invention provides a positive electrode active material for a lithium secondary battery, comprising: a core comprising a lithium transition metal oxide doped with boron; and a coating layer disposed on the core and comprising boron and cobalt; wherein the total boron content, which is the sum of the boron doped into the lithium transition metal oxide and the boron included in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and is composed of single particles.

[0057] At this time, the lithium transition metal oxide may have a layered crystal structure.

[0058] In addition, the lithium transition metal oxide may contain nickel in an amount of 60 mol% or more based on the total mole number of transition metals, and more specifically, may contain nickel in an amount of 70, 80, or 90 mol% or more. When the nickel content satisfies the above range, high-capacity characteristics can be realized.

[0059]

[0060] A cathode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single particles.

[0061] 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 agglomeration 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 30 or fewer primary particles. The “secondary particle” refers to an aggregate, i.e., a secondary structure, formed by the physical or chemical bonding between primary particles without an intentional agglomeration or assembly process for the primary particles.

[0062] The above “primary particle” refers to the smallest particle unit that can be distinguished as a single lump when observing the cross-section of the positive electrode active material through a scanning electron microscope (SEM), and may be composed of a single crystal grain or multiple crystal grains.

[0063] Since the cathode active material for a lithium secondary battery according to one embodiment of the present invention is composed of single particles, the particle strength is increased, which can suppress particle breakage during rolling, and the occurrence of cracks between primary particles during repeated charging and discharging can be prevented. In addition, the specific surface area is small, which can reduce the amount of gas generated due to side reactions with the electrolyte. In addition, the rolling density can be increased during electrode manufacturing, which can improve the energy density of the electrode.

[0064] However, in the case of single particle cathode active materials, the electrochemical characteristics (i.e., capacity, output characteristics) related to lithium diffusion are bound to be inferior to those of secondary particles because the distance through which lithium ions must diffuse within the cathode material becomes longer, and there is a problem of structural defects occurring, such as an increase in the amount of nickel cations occupying lithium sites during high-temperature firing for particle growth.

[0065]

[0066] Accordingly, a cathode active material for a lithium secondary battery according to one embodiment of the present invention comprises a lithium transition metal oxide core doped with boron and a coating layer containing boron and cobalt. As boron is coated and doped and cobalt is coated in this manner, excellent capacity, initial efficiency, and resistance characteristics can be realized.

[0067] More specifically, boron doped into the lithium transition metal oxide may exist in a region within a distance of 5 nm inward from the surface of the core. The case where boron is doped into the lithium transition metal oxide core may be a case where it exists evenly throughout the entire region of the core, or a case where it exists locally only in the outer portion of the core. In this case, when boron is doped locally only in the outer portion of the core as in one embodiment of the present invention, the effects of improving capacity, initial efficiency, and resistance characteristics can be more preferably implemented compared to a case where boron exists evenly throughout the entire region of the core. This is believed to be because structural collapse is suppressed during charge and discharge.

[0068] The doping region of boron in these lithium transition metal oxides can be confirmed by dispersing the active material powder in epoxy and molding it to create a protective layer, slicing it thinly and performing ion milling pretreatment, and analyzing the boron EELS (electron energy loss spectroscopy) peak in the TEM (transmission electron microscope) image of the outer part of the oxide.

[0069] Meanwhile, in order for boron to be locally doped and exist only in the outer part of the core, it may be more appropriate to dope by mixing and heat-treating the boron raw material after the lithium transition metal oxide is manufactured, rather than doping during the co-precipitation process for manufacturing the transition metal hydroxide precursor or the sintering process for manufacturing the lithium transition metal oxide. In this case, the reason why boron is doped in a form that exists only locally in the outer part of the core seems to be because boron does not easily diffuse into the interior because it is heat-treated at a low temperature after the NCM layered structure has already been formed. A more specific boron coating and doping method will be described in more detail in the method for manufacturing a cathode active material described below.

[0070] In particular, the total boron content, which is the sum of the boron doped into the lithium transition metal oxide and the boron included in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, and more specifically, may be 1100 or 1000 ppm or less, and may be 200 ppm, 300 ppm, 400 ppm, or 500 ppm or more. If the boron content is too low, the capacity, initial efficiency, and resistance characteristic improvement effects due to coating and doping with boron may be minimal. If the boron content is too high, the content of boron oxide, which is a boron compound in a form that is not desirable for battery performance, may increase in the coating layer, which may rather deteriorate the battery performance. More specifically, as described above, boron may be locally doped and present only in the outer part, which is an area within a distance of 5 nm from the surface of the core. At this time, when the content of boron in the active material increases, boron is doped in a form that exists evenly in the outer part of the core up to a certain level, thereby improving the battery performance. However, excess boron beyond a certain level can no longer be doped into the outer core and remains within the coating layer. This excess doping within the coating layer forms boron oxide, which can actually degrade battery performance. The boron-containing compounds within the coating layer are described in more detail below.

[0071]

[0072] A cathode active material for a lithium secondary battery according to one embodiment of the present invention includes a coating layer including boron and cobalt.

[0073] Boron included in the above coating layer may be present in the coating layer in the form of a boron-containing compound.

[0074] More specifically, the boron-containing compound may include lithium boron oxide and may further include boron oxide as a byproduct.

[0075]

[0076] At this time, when XPS analysis is performed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to the boron contained in the lithium boron oxide in the coating layer may be 15 wt% or less. That is, the more lithium boron oxide and the less boron oxide there is in the boron-containing compound in the coating layer, the more preferably the effects of improving capacity, initial efficiency, and resistance characteristics can be implemented. This appears to be because the conductivity of lithium boron oxide is higher than that of boron oxide.

[0077] More specifically, when XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the content of boron contained in the lithium boron oxide may be 85 wt% or more based on the total boron content in the coating layer.

[0078] The lithium boron oxide is not particularly limited as long as it is a lithium and boron-containing oxide. For example, the lithium boron oxide may be LiBO2, but is not necessarily limited thereto.

[0079] More specifically, when XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the content of boron contained in the boron oxide may be 15 wt% or less based on the total boron content in the coating layer.

[0080] The lithium boron oxide is not particularly limited as long as it is a lithium and boron-containing oxide. For example, the lithium boron oxide may be LiBO2, but is not necessarily limited thereto.

[0081] Meanwhile, the content of lithium boron oxide and boron oxide as boron-containing compounds in the coating layer can be determined depending on the content of boron introduced into the positive electrode active material, and a more detailed description thereof is as described above.

[0082]

[0083] The above coating layer may optionally further include aluminum as needed. When the coating layer includes all of boron, cobalt, and aluminum, the effects of improving capacity, initial efficiency, and resistance characteristics can be more preferably realized.

[0084] The above coating layer may further contain lithium. The lithium may be derived from a lithium raw material added during the formation of the coating layer, as described in the manufacturing method described below.

[0085]

[0086] Meanwhile, as previously mentioned, the lithium transition metal oxide according to the present invention may contain nickel in a high content of 60, 80, or 90 mol% or more. Since the higher the nickel content, the more sensitively the influence of the battery chemical properties is reflected according to the selection of doping elements, coating elements, and coating layer compounds and the control of their contents, it may be particularly important to appropriately implement doping and coating when using a high nickel content active material.

[0087]

[0088] These lithium transition metal oxides can be more specifically represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090] Li a [Ni x Co y Mn z B w1 M w2 ]O2

[0091] In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0 <w1≤0.2, 0≤w2≤0.2 이고, x+y+z+w1+w2=1이고, M은 Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr 또는 이들의 조합이다.

[0092] In the lithium transition metal oxide of the above chemical formula 1, lithium may be included in a content corresponding to a, that is, 0.8≤a≤1.2. 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 a content of 0.9≤a≤1.1 more preferably.

[0093] In the lithium transition metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, that is, 0.6≤x<1, 0.6≤x≤0.97, 0.7≤x≤0.97, 0.80≤x≤0.97, or 0.90≤x≤0.97. If the nickel content is too low, it may be difficult to achieve high capacity of the battery, and if the nickel content is too high, the battery life and safety may be reduced due to a decrease in the structural stability of the active material.

[0094] In the lithium transition metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0≤y≤0.4, 0≤y≤0.3, 0≤y≤0.2, or 0≤y≤0.1. If the cobalt amount is too low, it may be difficult to simultaneously achieve sufficient rate characteristics and high powder density of the active material. If the cobalt amount is too high, the overall cost of the raw material may increase and the reversible capacity may decrease.

[0095] In the lithium transition metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0≤z≤0.4. 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.

[0096] In the lithium transition metal oxide of the above chemical formula 1, boron has a content corresponding to w1, i.e., 0 <w1≤0.2로 포함될 수 있다. 보론 함량이 너무 적으면, 용량, 초기 효율 및 저항 특성 향상 효과가 미미할 수 있다. 보론 함량이 너무 많으면, 코팅층 내 보론 산화물이 과다 형성될 수 있다.

[0097] In the lithium transition metal oxide of the above chemical formula 1, M may be included in a content corresponding to w2, that is, 0≤w2≤0.2. At this time, M is a doping element other than boron, such as Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0098]

[0099] 2. Method for manufacturing positive electrode active material

[0100] Another embodiment of the present invention provides a method for manufacturing a cathode material for a lithium secondary battery, comprising the steps of: preparing a transition metal hydroxide; forming a mixture comprising the transition metal hydroxide and a lithium raw material, and then performing a main firing and a post-firing to form a lithium transition metal oxide of single particles; forming a first mixture comprising the lithium transition metal oxide and a cobalt raw material, and then performing a first heat treatment; and forming a second mixture comprising the first heat-treated resultant and a boron raw material, and then performing a second heat treatment.

[0101] Hereinafter, a method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention will be described in detail step by step.

[0102]

[0103] First, prepare a transition metal hydroxide.

[0104] The above transition metal hydroxide may be prepared by a coprecipitation reaction by adding a complexing agent-containing solution and a pH adjusting agent-containing solution to a transition metal-containing solution including, for example, a nickel raw material and optionally, a cobalt raw material or a manganese raw material, as a precursor of a positive electrode active material.

[0105] 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.

[0106] The above cobalt raw material is not particularly limited as long as it is used in the manufacture of a cathode active material precursor in the art. 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.

[0107] 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.

[0108] The above transition metal-containing solution may be prepared by adding a nickel raw material and optionally a cobalt raw material or a manganese 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.

[0109] 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.

[0110] 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 11 to 13.

[0111] 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 11 to 13.

[0112] Through the above process, nickel-cobalt-manganese (doped element) hydroxide particles are generated 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.

[0113] At this time, the molar ratio of nickel, cobalt, and manganese in the precursor can be controlled by controlling the concentration of nickel raw material, cobalt raw material, and manganese raw material.

[0114] Meanwhile, doping elements other than boron can be doped during the lithium transition metal oxide formation stage. In this case, the doping raw material can be further added during the formation of the mixture and then calcined to dope the doping element into the lithium transition metal oxide.

[0115]

[0116] Next, a mixture containing the above transition metal hydroxide and lithium raw material is formed, and then the main and post-fired processes are performed to form a single particle of lithium transition metal oxide.

[0117] 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.

[0118] The above-mentioned firing can be performed at a temperature of 800 to 900°C and can be performed for 2 to 5 hours.

[0119] The above post-firing can be performed at a temperature of 700 to 820°C and can be performed for 5 to 13 hours.

[0120] The above firing can be performed under an oxygen or air atmosphere. When firing under the above atmosphere, the local oxygen partial pressure increases, which can improve the crystallinity of the positive electrode active material.

[0121] Meanwhile, doping elements other than boron can be doped during the lithium transition metal oxide formation stage. In this case, the doping raw material can be further added during the formation of the mixture and then calcined to dope the doping element into the lithium transition metal oxide.

[0122]

[0123] Next, a first heat treatment is performed after forming a first mixture including the lithium transition metal oxide and cobalt raw material.

[0124] The above cobalt raw material is not particularly limited as long as it is a cobalt-containing compound, but for example, Co3O4, Co(OH)2, Co(NO3) 2, C4H6CoO 4, It can be CoSO4 or a combination thereof.

[0125] The above first mixture may further include an aluminum raw material. At this time, the aluminum raw material is not particularly limited as long as it is an aluminum-containing compound, but for example, Al2O3, Al(OH)3, Al2(SO4) 3, It can be Al(NO3)3, AlCl3 or a combination thereof.

[0126] The first mixture may further include a lithium raw material. At this time, the lithium raw material is not particularly limited as long as it is a lithium-containing compound, but may be, for example, LiOH, LiOH(H2O), Li2CO3, LiF, or a combination thereof.

[0127] The above first heat treatment can be performed at a temperature of 600 to 720°C. If the first heat treatment temperature is too low, there may be a problem in which the coating layer is not properly formed, and if the first heat treatment temperature is too high, there may be a problem in which the surface characteristics deteriorate due to doping rather than formation of the coating layer.

[0128]

[0129] Next, a second mixture containing the first heat-treated resultant and the boron raw material is formed and then subjected to a second heat treatment. Accordingly, boron can be coated and doped as in the above-described embodiment.

[0130] The above boron raw material is not particularly limited as long as it is a boron-containing compound, but may be, for example, B2O3, H3BO3, or a combination thereof.

[0131] The second heat treatment may be performed at a temperature of 250 to 350°C. If the second heat treatment temperature is too low, there may be a problem in which the coating layer is not properly formed, and if the second heat treatment temperature is too high, there may be a problem in which the surface characteristics deteriorate due to doping rather than formation of the coating layer.

[0132] The above second heat treatment can be performed in an oxygen or air atmosphere.

[0133]

[0134] Meanwhile, the method for manufacturing a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention as described above sequentially first coats cobalt, cobalt / aluminum, or cobalt / aluminum / lithium, and then coats boron. Accordingly, the concentration of Ni is high in the NCM core, and the concentration of Ni decreases toward the outside, while the concentrations of Co and B increase, so there is an advantage of less surface deterioration of the active material.

[0135]

[0136] 3. Cathode ray and lithium secondary battery

[0137] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery using the positive electrode active material described above.

[0138] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0139] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0140] In addition, the 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.

[0141]

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151]

[0152] 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] The above binder and conductive material may be the same as those described above for the positive electrode.

[0157]

[0158] 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.

[0159]

[0160] 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.

[0161] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0162] 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.

[0163] 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.

[0164] 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.

[0165]

[0166] 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).

[0167] 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.

[0168] 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.

[0169]

[0170] 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.

[0171]

[0172] Example 1 (500 ppm boron)

[0173] (1) Manufacturing of positive electrode active material

[0174] (plastic) Ni 0.955 Co 0.02 Mn 0.02 Al 0.005(OH)2 transition metal hydroxide was prepared. Thereafter, the prepared transition metal hydroxide and LiOH·H2O were placed in a mixer and mechanically mixed, and then a first calcination process was performed at 850°C for 3.75 hours under an oxygen atmosphere, followed by a second calcination process at 790°C for 9.75 hours to form a single particle of lithium transition metal oxide.

[0175] (First heat treatment) After that, the first mixture was formed by mixing so that Co(OH)2 as a cobalt raw material was 2 mol% based on the total mole number of the lithium transition metal oxide, Al(OH)3 as an aluminum raw material was 0.5 mol%, and LiOH·H2O as a lithium raw material was 0.1 mol%, and then the first heat treatment was performed at 680°C for 5 hours.

[0176] (Second heat treatment) After that, H3BO3 as a boron raw material was mixed into the first heat-treated result so that the content of boron in the active material was 500 ppm to form a second mixture, and then a second heat treatment was performed at 280°C for 5 hours in an oxygen atmosphere.

[0177] (2) Lithium secondary battery manufacturing

[0178] 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) = 96.25:1.65:2.1 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 15 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading was 14.6 mg / cm 2 and the rolling density (25 ℃, 20 kN) was 3.5 g / cm 3 It was.

[0179] 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).

[0180]

[0181] Example 2 (1,000 ppm boron)

[0182] In the second heat treatment step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted so that the content of boron in the active material was 1000 ppm.

[0183]

[0184] Comparative Example 1

[0185] In the second heat treatment step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the heat treatment was performed without adding boron raw material.

[0186]

[0187] Comparative Example 2

[0188] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the second heat treatment step was not performed.

[0189]

[0190] Comparative Example 3 (Boron 1,300 ppm)

[0191] In the second heat treatment step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted so that the content of boron in the active material was 1300 ppm.

[0192]

[0193] Comparative Example 4 (Boron 5,000 ppm)

[0194] In the second heat treatment step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted so that the content of boron in the active material was 1300 ppm.

[0195]

[0196] Comparative Example 5 (Boron 10,000 ppm)

[0197] In the second heat treatment step, a positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amount of boron raw material added was adjusted so that the content of boron in the active material was 1300 ppm.

[0198]

[0199] Experimental Example 1: Evaluation of active material SEM images and TOF-SIMS graphs

[0200] SEM (scanning electron microscope) images and TOF-SIMS (time-of-flight secondary ion mass spectrometry) graphs of the positive electrode active materials manufactured according to Example 4, Comparative Example 4, and Comparative Example 5 are shown in FIGS. 1 to 3 (Example 4), FIGS. 4 to 6 (Comparative Example 4), and FIGS. 7 to 9 (Comparative Example 5).

[0201] Referring to FIGS. 1 to 9, it was confirmed that the positive electrode active materials manufactured according to the examples and comparative examples were in the form of single particles.

[0202] Meanwhile, in the case of Example 4 containing an appropriate amount of boron, it was confirmed that the surface of the lithium transition metal oxide was smoothly coated, but in the case of Comparative Examples 4 and 5 containing an excessive amount of boron, the surface was not smooth and it was confirmed that a lot of by-products were formed. In addition, it was confirmed that when the boron content exceeded a certain amount, the surface became less smooth as the content increased.

[0203] Meanwhile, referring to the TOF-SIMS graph, it was confirmed that as the boron content increased, a large amount of B was detected on the surface.

[0204]

[0205] Experimental Example 2: Evaluation of Coating Layer Components

[0206] In order to evaluate the type and content of boron-containing compounds in the coating layer of the positive electrode active material manufactured according to the examples and comparative examples, XPS (X-ray photoelectron spectroscopy) analysis was performed at a depth of 5 nm from the outermost surface of the active material, and the results are shown in Fig. 10 (Example 4), Fig. 11 (Comparative Example 4), and Fig. 12 (Comparative Example 5). In addition, the type of boron-containing compounds in the coating layer and the content ratio of each boron-containing compound based on the total weight of the coating layer were evaluated through the XPS analysis results, and these are shown in Table 1 below.

[0207] Boron content (ppm) based on total weight of active material XPS analysis results at 5 nm depth from the outermost surface Weight % of B in LiBO2 to total B Weight % of B in BO3 to total B Weight % of B in BO3 to B in LiBO2 Example 1500 ppm 100 % 0 % 0 % Example 21000 ppm 100 % 0 % 0 % Comparative Example 31300 ppm 83.2 % 16.8 % 20.19 % Comparative Example 45000 ppm 31.36 % 68.64 % 218.88 % Comparative Example 510000 ppm 17.22 % 82.78 % 481.24 %

[0208] Referring to FIGS. 10 to 12 and Table 1, it was confirmed that in the case of examples containing an appropriate amount of boron, LiBO2 was mainly detected in the coating layer, and BO3 was not detected.

[0209]

[0210] On the other hand, in the case of the comparative example containing an excessive amount of boron, it was confirmed that LiBO2 decreased and BO3 increased. More specifically, it was confirmed that when the boron content exceeded a certain amount (approximately 1000 to 1200 ppm), the BO3 compound increased as the content increased. This can be interpreted as a result of the fact that when the boron content exceeds a certain amount, it can no longer be doped into the lithium transition metal oxide and remains in the coating layer, forming a BO3 compound as a byproduct.

[0211]

[0212] Experimental Example 3: TEM images and EELS evaluation of active materials

[0213] The TEM (transmission electron microscope) image of the positive electrode active material manufactured according to Example 4 and the EELS (electron energy loss spectroscopy) peak evaluation for the outer part of the lithium transition metal oxide in the TEM image were performed, and the results are shown in Fig. 13.

[0214] More specifically, the active material powder was dispersed in epoxy, molded to create a protective layer, and then sliced ​​into thin pieces and ion milled to measure the EELS boron peak.

[0215] Referring to Fig. 13, it was confirmed that boron not only exists within the coating layer, but also exists by being doped in a region within a distance of 5 nm inward from the surface of the transition metal oxide.

[0216]

[0217] Experimental Example 4: Evaluation of Battery Electrochemical Characteristics

[0218] The electrochemical properties of the positive electrode active materials manufactured according to the examples and comparative examples were evaluated, and the results are shown in Table 2 below and Figures 14 and 15. The specific experimental methods are as follows.

[0219] (1) Initial charge and discharge capacity, initial efficiency evaluation

[0220] The coin-type half-cells manufactured in the examples and comparative examples were aged at room temperature (25°C) for 10 hours, and then a charge / discharge test was conducted.

[0221] Capacity evaluation was conducted with 200 mAh / g as the reference capacity, and the charge / discharge conditions were constant current (CC) / constant voltage (CV) 3.0 V to 4.25 V, with a 1 / 20 C cut-off. The initial charge and discharge capacity and initial efficiency at 0.2 C were evaluated.

[0222] (2) Resistance characteristic evaluation (DC-IR)

[0223] The room temperature initial resistance (DC-IR (Direct current internal resistance)) was calculated by performing one 0.1C charge and 0.1C discharge discharge at 25℃ under constant current-constant voltage conditions of 2.5 V to 4.25 V and 1 / 20 C cut-off, and measuring the voltage value 60 seconds after applying the discharge current at 100% of the 4.25 V charge.

[0224] (3) Life characteristics evaluation (50 cycles)

[0225] The life characteristics of the positive electrode active material were evaluated after 50 cycles under 0.5C charge / 1C discharge conditions at high temperature (45℃).

[0226] (4) Voltage-dQ / dV characteristic evaluation

[0227] The voltage curve obtained after 0.2C initial charge and discharge was differentiated to evaluate the voltage-dQ / dV characteristics, which are shown in Fig. 15.

[0228] Coating layer element Boron content (ppm) 0.2C initial charge capacity (mAh / g) 0.2C initial discharge capacity (mAh / g) Initial efficiency (%) DC-IR (Ω) Life characteristics (50 cycle, %) Example 1B, Co, Al 5 0 0 2 4 5.6 2 17.4 8 8.5 2 2.8 9 3.0 Example 2B, Co, Al 1 0 0 2 4 6.4 2 18.5 8 8.7 2 2.7 9 2.7 Comparative example 1 Co, Al 0 2 4 1.2 2 12.5 8 8.1 2 8.8 9 3.4 Comparative example 2 Co, Al 0 2 4 2.0 2 13.3 8 8.2 14.9 9 1.1 Comparative example 3B, Co, Al 1 3 0 0 2 4 4.0 2 16.4 8 8.7 2 2.7 8 8.6 Comparative example 4B, Co, Comparative Example 5B, Co, Al10000200.5156.478.022.719.5

[0229] Referring to Table 2 and Fig. 14, it was confirmed that the initial capacity, efficiency, resistance characteristics, and life characteristics were overall very excellent in the case of an example in which the coating layer included boron, cobalt, and aluminum, but the content of boron in the active material was appropriately controlled.

[0230] In the case of Comparative Examples 1 and 2, where the coating layer contained Co and Al but no boron, it was confirmed that the initial capacity and efficiency were significantly reduced.

[0231] Meanwhile, in the case of Comparative Examples 3 to 5, where the coating layer includes boron, cobalt, and aluminum, but the boron content is excessive, the initial capacity, efficiency, resistance characteristics, and life characteristics are reduced, and specifically, it was confirmed that these characteristics tend to become increasingly inferior as the boron content increases.

[0232]

[0233] Referring to Fig. 15, it was confirmed that the average charge and discharge voltage itself moved between 4.1 and 4.2 V as the boron content increased from 0 ppm to 1000 ppm. This can be interpreted as a result of the change in the composition of the lithium transition metal oxide itself due to an increase in boron doped into the lithium transition metal oxide as the boron content increased within the boron content range of approximately 1000 ppm.

[0234]

[0235] 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.

[0236] Accordingly, the actual scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A positive electrode active material comprising a core comprising a lithium transition metal oxide doped with boron; and a coating layer disposed on the core and comprising boron and cobalt; The total boron content, which is the sum of boron doped in the lithium transition metal oxide and boron included in the coating layer, is 1200 ppm or less based on the total weight of the positive electrode active material, A cathode active material for a lithium secondary battery, composed of single particles.

2. In paragraph 1, A positive electrode active material for a lithium secondary battery, wherein boron doped in the lithium transition metal oxide exists in a region within a distance of 5 nm inward from the surface of the core.

3. In paragraph 1, The above coating layer is a positive electrode active material for a lithium secondary battery including lithium boron oxide.

4. In paragraph 3, A positive electrode active material for a lithium secondary battery, wherein, when XPS is analyzed at a depth of 5 nm from the outermost surface of the positive electrode active material, the weight ratio of boron contained in the boron oxide to boron contained in the lithium boron oxide in the coating layer is 15 wt% or less.

5. In paragraph 3, A positive electrode active material for a lithium secondary battery, wherein the content of boron contained in the lithium boron oxide is 85 wt% or more based on the total boron content in the coating layer when analyzed by XPS at a depth of 5 nm from the outermost surface of the positive electrode active material.

6. In paragraph 4, A positive electrode active material for a lithium secondary battery, wherein the content of boron contained in the boron oxide is 15 wt% or less based on the total boron content in the coating layer when analyzed by XPS at a depth of 5 nm from the outermost surface of the positive electrode active material.

7. In paragraph 1, The above coating layer is a positive electrode active material for a lithium secondary battery further containing aluminum.

8. In paragraph 1, The above coating layer is a positive electrode active material for a lithium secondary battery further containing lithium.

9. In paragraph 1, The above lithium transition metal oxide is a positive electrode active material for a lithium secondary battery containing nickel in an amount of 60 mol% or more based on the total mole number of transition metals.

10. In paragraph 1, The above lithium transition metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Co y Mr z B w1 M w2 ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.60≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0 <w1≤0.2, 0≤w2≤0.2 이고, x+y+z+w1+w2=1이고, M은 Zr, Al, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr 또는 이들의 조합이다.

11. Step of preparing transition metal hydroxide; A step of forming a mixture containing the above transition metal hydroxide and lithium raw material, and then performing main firing and post-firing to form a single particle of lithium transition metal oxide; A step of performing a first heat treatment after forming a first mixture including the lithium transition metal oxide and cobalt raw material; and Comprising a step of performing a second heat treatment after forming a second mixture containing the first heat-treated result and the boron raw material. Method for manufacturing a cathode material for a lithium secondary battery.

12. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein the first mixture further comprises an aluminum raw material.

13. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein the first mixture further comprises a lithium raw material.

14. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein the first heat treatment is performed at a temperature of 600 to 720°C.

15. In paragraph 11, A method for producing a positive electrode active material for a lithium secondary battery, wherein the second heat treatment is performed at a temperature of 250 to 350°C.

16. In paragraph 11, A method for manufacturing a positive electrode active material for a lithium secondary battery, wherein the above second heat treatment is performed in an oxygen atmosphere.

17. A positive electrode for a lithium secondary battery comprising the positive electrode active material of any one of claims 1 to 10.

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

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