Cathode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present invention relates to a cathode active material for a lithium secondary battery, the cathode active material comprising: a lithium metal oxide containing at least 80 mol% of nickel on the basis of the total number of moles of metals other than lithium; and a coating layer disposed on the surface of the lithium metal oxide, wherein the increase in moisture content of the cathode active material over 7 days immediately following synthesis does not exceed 3000 ppm.

Description

Cathode active material for lithium secondary batteries and lithium secondary batteries containing the same

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

[0002]

[0003] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0004] Among various cathode materials, the use of NCM cathode active materials, which are three-component cathode active materials of nickel, cobalt, and manganese, is expected to increase significantly, and in particular, high-nickel NCM cathode active materials with a nickel content of 80% or more can achieve high capacity.

[0005] However, although high-nickel NCM-based cathode active materials have the advantage of high capacity, since nickel ions have similar ionic radii to lithium ions, nickel ions occupy the lithium ion lattice sites within the lithium layer, which causes a phenomenon called cation mixing. This causes problems such as a decrease in capacity characteristics due to the formation of a rock salt structure, gas generation due to side reactions between a large amount of residual lithium and the electrolyte, and a decrease in life characteristics. In particular, high-nickel NCM-based cathode active materials absorb moisture well, so the moisture content is high immediately after the cathode active material is synthesized, and the moisture content increases rapidly over time. Excessive moisture in the cathode active material has the problem of changing the surface structure of the cathode material, causing an overall decrease in the capacity and life characteristics of the cathode active material.

[0006]

[0007] Accordingly, one object of the present invention is to provide a cathode active material for a lithium secondary battery containing a high nickel content with improved capacity and lifespan characteristics by controlling the rate of increase in the moisture content of the cathode active material over time, and a lithium secondary battery including the same.

[0008]

[0009] One embodiment of the present invention provides a cathode active material for a lithium secondary battery, which comprises a lithium metal oxide containing nickel of 80 mol% or more based on the total mole number of metals excluding lithium, and a coating layer disposed on the surface of the lithium metal oxide, wherein the cathode active material has a moisture content increase of 3000 ppm or less for 7 days immediately after synthesis.

[0010] The above-mentioned positive electrode active material for a lithium secondary battery may have a moisture content increase of 1500 to 2600 ppm for 7 days immediately after synthesis.

[0011] The above-mentioned positive electrode active material for a lithium secondary battery may have a moisture content of 3200 ppm or less immediately after 7 days from the time of synthesis.

[0012] The above-mentioned positive electrode active material for a lithium secondary battery may have a moisture content of 1700 to 2900 ppm immediately after 7 days from the time of synthesis.

[0013] The above-mentioned positive electrode active material for a lithium secondary battery may have a moisture content of 280 ppm or less immediately after synthesis.

[0014] The above-mentioned positive electrode active material for a lithium secondary battery may have a moisture content of 175 to 250 ppm immediately after synthesis.

[0015] The above coating layer may include boron (B).

[0016] The content of boron in the above coating layer may be 100 ppm or more based on the total weight of the lithium metal oxide.

[0017] The content of boron in the above coating layer may be 300 to 700 ppm based on the total weight of the lithium metal oxide.

[0018] The above lithium metal oxide may contain 4 to 10 mol% of cobalt (Co) based on the total molar number of metals excluding lithium.

[0019] The above lithium metal oxide may contain 1 to 5 mol% of manganese (Mn) based on the total mole number of metals excluding lithium.

[0020] The above lithium metal oxide may further include zirconium (Zr), aluminum (Al), or a combination thereof as a doping element.

[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 z M1 w1 M2 w2 ]O2

[0024] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0.04≤y≤0.1, 0.01≤z≤0.05, 0≤w1≤0.1, 0≤w2≤0.1, and x+y+z+w1+w2=1, M1 is Zr, Al, or a combination thereof, and M2 is B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0025]

[0026] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0027] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for the lithium secondary battery.

[0028]

[0029] A cathode active material for a lithium secondary battery according to one embodiment of the present invention contains a high content of nickel, and the rate of increase in moisture content over time is appropriately controlled, thereby improving capacity and life characteristics.

[0030]

[0031] Figure 1 is a graph of the moisture content as time elapses from immediately after synthesis of positive electrode active materials manufactured according to examples and comparative examples.

[0032] Figure 2 is a graph showing the increase in moisture content over time from immediately after synthesis of positive electrode active materials manufactured according to examples and comparative examples.

[0033]

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0039] 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.

[0040] 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.

[0041]

[0042] 1. Positive active material

[0043] According to one embodiment of the present invention, a cathode active material for a lithium secondary battery comprises a lithium metal oxide containing nickel in an amount of at least 80 mol% based on the total molar number of metals excluding lithium. Since the lithium metal oxide contains such a high nickel content, high-capacity characteristics can be achieved. More specifically, the nickel content may be at least 85 mol% based on the total molar number of metals excluding lithium.

[0044] Additionally, the lithium metal oxide may have a layered crystal structure.

[0045] In addition, the lithium metal oxide may be a secondary particle formed by agglomeration of multiple primary particles. In the present specification, the term "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 formed of a single crystal grain or multiple crystal grains.

[0046] However, since the nickel ions in lithium metal oxides with a high nickel content have similar ionic radii to those of lithium ions, nickel ions in the transition metal layer may migrate to the lithium layer and occupy lithium ion lattice sites in the lithium layer, which may cause a phenomenon called cation mixing. As a result, an electrochemically inactive rock salt structure may be formed on the surface of the lithium metal oxide, which may result in a decrease in capacity and lifespan characteristics. In addition, a large amount of residual lithium may be formed, which may cause a side reaction with the electrolyte, resulting in a decrease in lifespan due to gas generation. In particular, lithium metal oxides with a high nickel content absorb moisture well, so that the moisture content is high immediately after synthesis, and the moisture content increases rapidly over time. Excessive moisture in the positive electrode active material may change the surface structure of the positive electrode material, which may overall reduce the capacity and lifespan characteristics.

[0047] Accordingly, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention further includes a coating layer disposed on the surface of a lithium metal oxide. The coating layer can appropriately control the moisture content within the positive electrode active material, thereby improving capacity and lifespan characteristics.

[0048] Accordingly, the positive electrode active material may have a moisture content increase of 3000 ppm or less for 7 days immediately after synthesis, and more specifically, 1300 to 2600 ppm or 1500 to 2600 ppm. If the moisture content increase in the positive electrode active material is too high, there may be a decrease in capacity and life characteristics due to excessive moisture. If the moisture content increase in the positive electrode active material is too low, there may be a decrease in capacity characteristics.

[0049] Meanwhile, in this specification, the “moisture content” of the positive electrode active material can be measured by leaving it in an atmosphere of 25°C and 50% humidity.

[0050] In addition, the positive electrode active material for the lithium secondary battery may have a moisture content of 3200 ppm or less immediately after 7 days from the time of synthesis, and more specifically, may have a moisture content of 1300 to 2900 ppm or 1700 to 2900 ppm.

[0051] In addition, the positive electrode active material for the lithium secondary battery may have a moisture content of 280 ppm or less immediately after synthesis, and more specifically, may have a moisture content of 150 to 250 ppm or 175 to 250 ppm.

[0052] The technical significance of controlling the moisture content immediately after the synthesis of the above-mentioned positive electrode active material or immediately after 7 days from the synthesis is the same as the technical significance of controlling the amount of increase in moisture content, and therefore is omitted.

[0053] Additionally, the coating layer may include boron (B). Boron may form a compound on the surface of the positive electrode material, thereby reducing the moisture content or the amount of moisture content increase of the positive electrode active material.

[0054] At this time, the content of boron in the coating layer may be 100 ppm or more based on the total weight of the lithium metal oxide, and more specifically, may be 300 to 900 ppm or 300 to 700 ppm. If the content of boron in the coating layer is too high, the moisture content or the increase in moisture content of the positive electrode active material may become too low. If the content of boron in the coating layer is too low, the moisture content or the increase in moisture content of the positive electrode active material may become too high.

[0055] Additionally, the lithium metal oxide may contain 4 to 10 mol% of cobalt (Co) based on the total molar number of metals excluding lithium.

[0056] The above lithium metal oxide may contain 1 to 5 mol% of manganese (Mn) based on the total mole number of metals excluding lithium.

[0057] The above lithium metal oxide may further include zirconium (Zr), aluminum (Al), or a combination thereof as a doping element. Accordingly, there may be advantages of improved capacity and lifespan.

[0058] The content of zirconium in the lithium metal oxide may be, more specifically, 0.15 to 0.5 mol% based on the total mole number of metals excluding lithium, and more specifically, 0.3 to 0.4 mol%. When the content of zirconium satisfies the above range, the aforementioned doping effect may be more preferably implemented.

[0059] The content of aluminum in the lithium metal oxide may be, more specifically, 0.5 to 3 mol% based on the total mole number of metals excluding lithium, and more specifically, 0.5 to 2 mol% or 0.5 to 1.5 mol%. When the content of aluminum satisfies the above range, the aforementioned doping effect may be more preferably implemented.

[0060] The above lithium metal oxide can be represented by the following chemical formula 1.

[0061] [Chemical Formula 1]

[0062] Li a [Ni x Co y Mn z M1 w1 M2 w2 ]O2

[0063] In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0.04≤y≤0.1, 0.01≤z≤0.05, 0≤w1≤0.1, 0≤w2≤0.1, and x+y+z+w1+w2=1, M1 is Zr, Al, or a combination thereof, and M2 is B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

[0064] 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≤1.2. 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 an amount of 0.9≤a≤1.1 more preferably.

[0065] In the lithium metal oxide of the above chemical formula 1, nickel may be included in an amount corresponding to x, that is, 0.8≤x<1, 0.8≤x≤0.97, or 0.85≤x≤0.95. 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.

[0066] In the lithium metal oxide of the above chemical formula 1, cobalt may be included in an amount corresponding to y, i.e., 0.04≤y≤0.1 or 0.05≤y≤0.09. The technical significance of controlling the cobalt amount is the same as described above and is therefore omitted.

[0067] In the lithium metal oxide of the above chemical formula 1, manganese may be included in a content corresponding to z, i.e., 0.01≤z≤0.05 or 0.02≤z≤0.04. The technical significance of controlling the manganese content is the same as described above and is therefore omitted.

[0068] In the lithium metal oxide of the above chemical formula 1, M1 may be included in a content corresponding to w1, that is, 0≤w1≤0.1. M1 may be further included as a doping element, such as Zr, Al, or a combination thereof, in an appropriate content within a range that implements the aforementioned doping effect.

[0069] In the lithium metal oxide of the above chemical formula 1, M2 may be included in a content corresponding to w2, that is, 0≤w2≤0.1. M2 may be another doping element, such as B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof, and may be further included in an appropriate content to implement a doping effect within a range that does not deteriorate electrochemical performance.

[0070] Meanwhile, the average particle diameter (D50) of the positive electrode active material for a lithium secondary battery according to one embodiment of the present invention may be 8 to 16 μm. In the present specification, the average particle diameter (D50) may be defined as a particle diameter corresponding to 50% of the volume accumulation amount in the particle diameter distribution curve. The average particle diameter (D50) may be measured using, for example, a laser diffraction method.

[0071]

[0072] The increase in moisture content of a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention, the moisture content immediately after synthesis, or the moisture content immediately after 7 days may vary sharply not only depending on the type and content of the elements contained in the coating layer mentioned above, but also on the conditions of the positive electrode active material manufacturing process. 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.

[0073]

[0074] First, prepare a metal precursor.

[0075] The above metal precursor may more specifically be a metal hydroxide.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086]

[0087] Next, the metal precursor and lithium raw material are mixed and then calcined to form lithium metal oxide.

[0088] At this time, 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 Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a combination thereof, but is not limited thereto.

[0089] At this time, the lithium raw material may be added so that the molar ratio of lithium (Li / Me) to the total metal in the metal precursor is 1.04 to 1.08 or 1.05 to 1.07. If the amount of lithium raw material added is too small, there may be a problem of reduced capacity characteristics. If the amount of lithium raw material added is too large, there may be a problem of reduced life characteristics.

[0090] Additionally, the firing may be performed at a temperature of 700 to 770°C. If the firing temperature is too low, there may be a problem of reduced capacity characteristics. If the firing temperature is too high, there may be a problem of reduced life characteristics.

[0091] Additionally, the firing can be performed for 5 to 15 hours. If the firing time is too short, there may be a problem of reduced capacity characteristics. If the firing time is too long, there may be a problem of reduced life characteristics.

[0092] Additionally, the above firing can be performed in an oxygen atmosphere. By performing the firing in an oxygen atmosphere, there may be advantages in terms of improved capacity and life characteristics compared to firing in an air atmosphere.

[0093] At this time, in addition to the metal precursor and lithium raw material, a doping raw material may be further mixed, and the doping raw material may include a Zr raw material, an Al raw material, or a combination thereof.

[0094] The above Zr raw materials are ZrO2, Zr(SO4)2, ZrS2, Zr(NO3) 4, It may be ZrC or a combination thereof, but is not necessarily limited thereto.

[0095] The above Al raw material may be Al(OH)3, Al2O-3, AlF3 or a combination thereof, but is not necessarily limited thereto.

[0096] The above Zr raw material may be added so that the content of Zr is 0.15 to 0.5 mol% or 0.2 to 0.4 mol% based on the total mole number of metals excluding lithium in the lithium metal oxide. In addition, the above Al raw material may be added so that the content of Al is 0.5 to 3 mol%, 0.5 to 2 mol% or 0.5 to 1.5 mol% based on the total mole number of metals excluding lithium in the lithium metal oxide.

[0097] The technical significance of introducing Zr and Al as doping elements and controlling their content is the same as described above, so it is omitted.

[0098]

[0099] Next, the lithium metal oxide is crushed.

[0100] The above disintegration can be performed using equipment commonly used in the art. For example, the disintegration can be performed using a rotar mill, but is not necessarily limited thereto.

[0101]

[0102] Next, the above-mentioned disintegrated lithium metal oxide is washed.

[0103] Through the above washing, residual lithium remaining on the surface of the lithium metal oxide after calcination can be removed.

[0104] The above washing can be performed more specifically by adding lithium metal oxide to distilled water, which is a washing liquid, and stirring the mixture.

[0105]

[0106] Next, the washed lithium metal oxide is dried.

[0107] The above drying can be performed, for example, by a vacuum drying method.

[0108] At this time, the drying can be performed at a temperature of 100 to 140°C, and more specifically, at a temperature of 110 to 130°C. If the temperature during drying is too low, there may be a problem that the moisture content increases too much, and if the temperature during drying is too high, the moisture content decreases too much, and there may be a problem that the capacity characteristics deteriorate.

[0109]

[0110] Next, the dried lithium metal oxide and the coating raw material are mixed and then heat-treated to form a coating layer.

[0111] The above coating raw material may be a boron raw material, for example, B(OH)3, B2O3, Li3BO3, WB, WB2, (NH4)3BO3, or a combination thereof. From the perspective of controlling the moisture content, B(OH)3 may be more preferable as the boron raw material.

[0112] At this time, the coating heat treatment can be performed at a temperature of 250 to 300°C. If the coating heat treatment temperature is too low, the coating layer may not form properly, resulting in a minimal effect on reducing the moisture content. If the coating heat treatment temperature is too high, there may be problems with reduced capacity and life characteristics.

[0113] Additionally, the coating heat treatment may be performed for 3 to 9 hours, and more specifically, for 4 to 8 hours. If the coating heat treatment time is too short, the coating layer may not form properly, resulting in a minimal effect on reducing the moisture content. If the coating heat treatment time is too long, there may be problems with reduced capacity and life characteristics.

[0114] Additionally, the above coating heat treatment can be performed in an air atmosphere.

[0115] In addition, the coating raw material may be added so that the content of the coating element is 100 ppm or more, more specifically 300 to 900 ppm, based on the total weight of the lithium metal oxide. The technical significance of adjusting the content of the coating raw material is the same as the technical significance of adjusting the content of the coating element described above, and therefore, is omitted.

[0116] Through the above series of processes, a positive electrode active material for a lithium secondary battery according to one embodiment of the present invention can be formed, and at this time, physical properties such as an increase in moisture content can be appropriately obtained within the range according to the present invention.

[0117]

[0118] 2. Cathode and lithium secondary battery

[0119] Another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129]

[0130] Another embodiment of the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery as described above.

[0131] The above lithium secondary battery may more specifically include a positive electrode; a negative electrode; a separator; and an electrolyte.

[0132] The above lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] The above binder and conductive material may be the same as those described above for the positive electrode.

[0138]

[0139] 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.

[0140]

[0141] 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.

[0142] Specifically, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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).

[0147] 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.

[0148] 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.

[0149]

[0150] 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.

[0151]

[0152] Example 1

[0153] (1) Manufacturing of positive electrode active material

[0154] (Co-precipitation) Ni through co-precipitation reaction 0.9 Co 0.07 Mn 0.03 A metal precursor with the composition (OH)2 was prepared.

[0155] (After firing), LiOH·H2O was added to the metal precursor so that the molar ratio of lithium to the entire metal in the metal precursor (Li / Me) was 1.06, ZrO2 was added so that the content of Zr to the entire metal excluding lithium in the lithium metal oxide was about 0.1 to 0.5 mol%, and Al(OH)3 was added so that the content of Al to the entire metal excluding lithium in the lithium metal oxide was about 0.5 to 3.0 mol%, and the mixture was mechanically mixed in a mixer to form a mixture. Thereafter, the mixture was fired at a temperature of 735°C for 10 hours in an oxygen atmosphere to form a lithium metal oxide.

[0156] (Crushing and classification) After that, the lithium metal oxide was crushed and classified using a rotar mill.

[0157] (After washing), the above-mentioned crushed and classified lithium metal oxide was placed in distilled water at 9°C and stirred for 10 minutes to wash.

[0158] (After drying), the washed lithium metal oxide was vacuum dried at a temperature of 120°C for more than 6 hours.

[0159] (Coating) After that, the dried lithium metal oxide and B(OH)3 were mixed, and a coating heat treatment was performed at a temperature of 280℃ for 6 hours in an air atmosphere to form a coating layer. At this time, the amount of B(OH)3 added was such that the B content was 600 ppm based on the total weight of the lithium metal oxide.

[0160] Thus, a positive electrode active material was obtained, and the average particle diameter (D50) of the obtained positive electrode active material was 13.5 μm.

[0161] (2) Lithium secondary battery manufacturing

[0162] The slurry for manufacturing the electrode plate was mixed with the above-mentioned positive electrode active material: conductive material (Super-C): binder (PVDF, KF1120) = 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 an 8.48 μm thick Al foil using a doctor blade, and then dried and rolled. The electrode loading amount was 15 to 17 mg / cm 2 and the rolling density (25℃, 20kN) was 3.4 to 3.7 g / cm 3 It was.

[0163] The electrolyte used was an electrolyte containing lithium salt, and a coin cell was manufactured using a PP separator and a lithium negative electrode (200 μm).

[0164]

[0165] Comparative Example 1

[0166] 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 heat treatment was performed without adding B(OH)3.

[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 amount of B(OH)3 added was such that the content of B was 200 ppm based on the total weight of lithium metal oxide.

[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 amount of B(OH)3 added was such that the content of B was 400 ppm based on the total weight of lithium metal oxide.

[0173]

[0174] Example 4

[0175]

[0176] 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 amount of B(OH)3 added was set so that the content of B was 800 ppm based on the total weight of lithium metal oxide.

[0177]

[0178] Example 5

[0179]

[0180] 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 amount of B(OH)3 added was such that the content of B based on the total weight of lithium metal oxide was 1000 ppm.

[0181]

[0182] Experimental Example 1: Evaluation of the Moisture Content of Positive Electrode Active Material

[0183] For the positive electrode active materials manufactured according to the examples and comparative examples, the moisture content immediately after synthesis and the moisture content immediately after 1 to 7 days were evaluated by leaving them in an atmosphere of 25°C and 50% humidity, and the results are shown in Table 1 and Figures 1 and 2 below.

[0184] Figure 1 is a graph of the moisture content as time elapses from immediately after synthesis of positive electrode active materials manufactured according to examples and comparative examples.

[0185] Figure 2 is a graph showing the increase in moisture content over time from immediately after synthesis of positive electrode active materials manufactured according to examples and comparative examples.

[0186] The function rate measurement was performed using MX-50 equipment.

[0187] Category B Content (ppm) Immediately after synthesis +1 day +3 day +5 day +7 day Moisture content (ppm) Moisture content (ppm) Moisture content increase (ppm) Moisture content (ppm) Moisture content increase (ppm) Moisture content increase (ppm) Moisture content increase (ppm) Moisture content (ppm) Comparative example 102421558131625302288320229603884Example 22002621350108820761814258523232968Example 34002321621138920771845241821862792Example 1600186105687015241338167914931972Example 48001667265601057891132211561579 Example 51000142582440757615866724996

[0188] Referring to Table 1, it was confirmed that the increase in the functional ratio over time in the comparative example was much greater than in the example.

[0189] Experimental Example 2: Evaluation of Electrochemical Characteristics of Lithium Secondary Battery

[0190] The electrochemical characteristics of lithium secondary batteries manufactured according to the examples and comparative examples were evaluated and are shown in Table 2 below.

[0191] (1) Initial capacity and initial efficiency evaluation

[0192]

[0193] After fabricating a lithium secondary battery half-cell, it was aged at 25°C for 10 hours and then subjected to a charge-discharge test at 25°C. To evaluate the initial capacity, the battery was charged to 4.3 V at a constant current of 0.1 C with a reference capacity of 200 mAh / g, then 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 3.0 V at a constant current of 0.1 C with a reference capacity of 200 mAh / g.

[0194] (2) Evaluation of high temperature life characteristics (45℃, 30 cycles)

[0195] After fabricating a lithium secondary battery half-cell, it was charged to 4.3 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 3.0 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.

[0196] ClassificationInitial charge capacity (mAh / g)Initial discharge capacity (mAh / g)Initial efficiency (%)High temperature life characteristics (%)Comparative example 1237.8215.790.786.2Example 2239.3218.691.387.3Example 3243226.193.186.3Example 1241.4224.49386.7Example 4239.0221.892.888.6Example 5240.1221.892.488.7

[0197] Referring to Table 2, in the case of the examples in which the moisture content-related properties, including the moisture content increase amount, satisfied the range according to the present invention, it was confirmed that the initial discharge capacity, initial efficiency, and high-temperature life characteristics were generally very superior to those of the comparative examples. On the other hand, in the case of comparative example 1, it was confirmed that the moisture content-related properties, including the moisture content increase amount, were too high, resulting in the initial discharge capacity, initial efficiency, and high-temperature life characteristics being inferior to those of the examples. In addition, in the case of examples 1 and 3 in which the moisture content increase amount and other properties were more appropriately controlled, it was confirmed that the initial discharge capacity, initial efficiency, and high-temperature life characteristics were more desirably implemented than those of the other examples.

[0198]

[0199] 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.

[0200] 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 lithium metal oxide containing nickel of 80 mol% or more based on the total molar number of metals excluding lithium, and a coating layer disposed on the surface of the lithium metal oxide, The above cathode active material is a cathode active material for a lithium secondary battery, the increase in moisture content of which is 3000 ppm or less for 7 days immediately after synthesis.

2. In paragraph 1, The above-mentioned cathode active material for a lithium secondary battery is a cathode active material for a lithium secondary battery having a moisture content increase of 1500 to 2600 ppm for 7 days immediately after synthesis.

3. In paragraph 1, The above-mentioned cathode active material for a lithium secondary battery is a cathode active material for a lithium secondary battery having a moisture content of 3200 ppm or less immediately after 7 days from the time of synthesis.

4. In paragraph 1, The above-mentioned cathode active material for a lithium secondary battery is a cathode active material for a lithium secondary battery having a moisture content of 1700 to 2900 ppm immediately after 7 days from synthesis.

5. In paragraph 1, The above-mentioned cathode active material for a lithium secondary battery is a cathode active material for a lithium secondary battery having a moisture content of 280 ppm or less immediately after synthesis.

6. In paragraph 1, The above-mentioned cathode active material for a lithium secondary battery is a cathode active material for a lithium secondary battery having a moisture content of 175 to 250 ppm immediately after synthesis.

7. In paragraph 1, The above coating layer is a positive electrode active material for a lithium secondary battery containing boron (B).

8. In paragraph 7, A positive electrode active material for a lithium secondary battery, wherein the content of boron in the coating layer is 100 ppm or more based on the total weight of the lithium metal oxide.

9. In paragraph 7, A positive electrode active material for a lithium secondary battery, wherein the content of boron in the coating layer is 300 to 700 ppm based on the total weight of the lithium metal oxide.

10. In paragraph 1, The above lithium metal oxide is a positive electrode active material for a lithium secondary battery containing 4 to 10 mol% of cobalt (Co) based on the total molar number of metals excluding lithium.

11. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery containing 1 to 5 mol% of manganese (Mn) based on the total mole number of metals excluding lithium.

12. In paragraph 1, The above lithium metal oxide is a cathode active material for a lithium secondary battery, further comprising zirconium (Zr), aluminum (Al) or a combination thereof as a doping element.

13. In paragraph 1, The above lithium metal oxide is a positive electrode active material for a lithium secondary battery represented by the following chemical formula 1: [Chemical Formula 1] Li a [Ni x Co y Mr z M1 w1 M2 w2 ]O2 In the above chemical formula 1, 0.8≤a≤1.2, 0.8≤x<1, 0.04≤y≤0.1, 0.01≤z≤0.05, 0≤w1≤0.1, 0≤w2≤0.1, and x+y+z+w1+w2=1, M1 is Zr, Al, or a combination thereof, and M2 is B, Y, Mg, Ti, Nb, W, Sc, Si, V, Fe, Y, Mo, Ce, Hf, Ta, La, Sr, or a combination thereof.

14. A positive electrode for a lithium secondary battery comprising the positive electrode active material of Article 13.

15. A lithium secondary battery comprising the positive electrode for a lithium secondary battery of Article 14.

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