KR102520065B1 - Positive electrode material for secondary battery, method for preparing the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention mixes a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a lithium raw material and over-fires at a temperature of 980 ° C. or higher to form a single particle. The first lithium composite transition metal Forming a mixture comprising an oxide and a second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles; And by pressing the mixture, the second lithium composite transition metal oxide in the form of secondary particles in which the primary particles are aggregated is pulverized, so that the first positive electrode active material of small particles and the second positive electrode active material of large particles are bimodal. Forming a cathode material having a particle size distribution of (bimodal); provides a method for manufacturing a cathode material for a secondary battery, including.

Description

Cathode material for secondary battery, method for manufacturing the same, and lithium secondary battery including the same

The present invention relates to a cathode material for a secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same.

Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries is rapidly increasing. In particular, lithium secondary batteries are in the limelight as a driving power source for portable devices because they are lightweight and have high energy density. Accordingly, research and development efforts to improve the performance of lithium secondary batteries are being actively conducted.

A lithium secondary battery is an oxidation state when lithium ions are intercalated/deintercalated from the positive electrode and the negative electrode in a state in which an organic electrolyte or polymer electrolyte is charged between a positive electrode and a negative electrode made of an active material capable of intercalation and deintercalation of lithium ions. and electrical energy is produced by a reduction reaction.

Cathode active materials of lithium secondary batteries include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMnO ₂ or LiMn ₂ O ₄ etc.), a lithium iron phosphate compound (LiFePO ₄ ), and the like were used. Among them, lithium cobalt oxide (LiCoO ₂ ) has the advantage of high operating voltage and excellent capacity characteristics, and is widely used and applied as a positive electrode active material for high voltage. However, due to the price increase and unstable supply of cobalt (Co), there is a limit to mass use as a power source in fields such as electric vehicles, and the need to develop a cathode active material that can replace it has emerged.

Accordingly, a nickel-cobalt-manganese-based lithium composite transition metal oxide (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxide') in which a part of cobalt (Co) is substituted with nickel (Ni) and manganese (Mn) has been developed. However, conventionally developed NCM-based lithium composite transition metal oxides are generally in the form of secondary particles in which primary particles are aggregated, and have low particle strength and high lithium by-product content, resulting in a large amount of gas generated during cell operation and poor stability. Had a falling problem. As described above, the conventionally developed NCM-based lithium composite transition metal oxide has limitations in application to high-voltage batteries, in particular, because stability is not secured. In addition, in order to increase the capacity per unit volume of the electrode, it is necessary to increase the rolling density, and the conventionally developed NCM-based lithium composite transition metal oxide has a low rolling density due to material characteristics compared to lithium cobalt oxide (LiCoO ₂ ).

Therefore, it is still necessary to develop a cathode material of NCM-based lithium composite transition metal oxide capable of realizing high capacity by improving particle strength and stability and improving rolling density.

Korean Patent Publication No. 10-2016-0075196

The present invention is to provide a positive electrode material of NCM-based lithium composite transition metal oxide with improved particle strength and improved stability. It is intended to provide an alternative cathode material for lithium cobalt oxide (LiCoO ₂ ) applicable to high-voltage lithium secondary batteries by improving the stability of NCM-based lithium composite transition metal oxide. In addition, it is intended to provide a cathode material for a secondary battery with improved energy density and improved capacity by increasing the rolling density of NCM-based lithium composite transition metal oxide.

The present invention mixes a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a lithium raw material and over-fires at a temperature of 980 ° C. or higher to form a single particle. The first lithium composite transition metal Forming a mixture comprising an oxide and a second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles; And by pressing the mixture, the second lithium composite transition metal oxide in the form of secondary particles in which the primary particles are aggregated is pulverized, so that the first positive electrode active material of small particles and the second positive electrode active material of large particles are bimodal. Forming a cathode material having a particle size distribution of (bimodal); provides a method for manufacturing a cathode material for a secondary battery, including.

In addition, the present invention is a bimodal positive electrode material comprising a first positive electrode active material of small particles and a second positive electrode active material of opposites, wherein the first and second positive electrode active materials are made of nickel (Ni), cobalt (Co) and Provided is a lithium composite transition metal oxide containing manganese (Mn), made of a single particle, and having a crystal size of 180 nm or more for a secondary battery.

In addition, the present invention provides a positive electrode and a lithium secondary battery including the positive electrode material.

According to the present invention, it is possible to improve the particle strength and stability of the NCM-based positive electrode material. The positive electrode material of the NCM-based lithium composite transition metal oxide of the present invention can secure excellent stability and can be applied to a high-voltage lithium secondary battery. In addition, according to the present invention, by increasing the rolling density of the NCM-based positive electrode material, it is possible to improve energy density and improve capacity.

1 is a graph showing the particle size distribution of cathode materials prepared in Examples 1 and 2 and Comparative Example 1.
2a and 2b are enlarged pictures of the positive electrode material prepared in Comparative Example 1 with a scanning electron microscope (SEM).
3 is a photograph of the positive electrode material prepared in Example 1 enlarged and observed with a scanning electron microscope (SEM).
4 is a graph showing the rolling density of cathode materials prepared in Example 1 and Comparative Example 1.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention. At this time, the terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor appropriately defines the concept of terms in order to explain his/her invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

< of cathode material Manufacturing method>

The positive electrode material for a secondary battery of the present invention mixes a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a lithium raw material and over-fires at a temperature of 980 ° C. or higher to form a single particle. Forming a mixture including a lithium composite transition metal oxide and a second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles; And by pressing the mixture, the second lithium composite transition metal oxide in the form of secondary particles in which the primary particles are aggregated is pulverized, so that the first positive electrode active material of small particles and the second positive electrode active material of large particles are bimodal. Forming a positive electrode material having a (bimodal) particle size distribution; includes.

The manufacturing method of the positive electrode material will be described step by step in detail.

First, a lithium raw material is mixed with a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) and overfired at a temperature of 980 ° C. or higher to form a single particle. First lithium composite transition metal oxide and a second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles.

The precursor may be purchased and used as a commercially available cathode active material precursor, or may be prepared according to a method for preparing a cathode active material precursor well known in the art.

For example, the precursor may be prepared by adding an ammonium cation-containing complex forming agent and a basic compound to a transition metal solution containing a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material, followed by a coprecipitation reaction.

The nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, etc., specifically, Ni(OH) ₂ , NiO, NiOOH, NiCO ₃ ㆍ 2Ni(OH) ₂ 4H ₂ O, NiC ₂ O ₂ 2H ₂ O, Ni(NO ₃ ) ₂ 6H ₂ O, NiSO ₄ , NiSO ₄ 6H ₂ O, fatty acid nickel salts, nickel halides or any of these It may be a combination, but is not limited thereto.

The cobalt-containing raw material may be cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide or oxyhydroxide, and specifically, Co(OH) ₂ , CoOOH, Co(OCOCH ₃ ) ₂ 4H ₂ O , Co(NO ₃ ) ₂ 6H ₂ O, CoSO ₄ , Co(SO ₄ ) ₂ 7H ₂ O, or a combination thereof, but is not limited thereto.

The manganese-containing raw material may be, for example, manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, specifically Mn ₂ O ₃ , MnO ₂ , Mn ₃ manganese oxides such as O ₄ ; manganese salts such as MnCO ₃ , Mn(NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylic acids, manganese citrate, and manganese fatty acids; It may be manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

The transition metal solution is a mixture of nickel-containing raw materials, cobalt-containing raw materials, and manganese-containing raw materials in a solvent, specifically, water or an organic solvent (eg, alcohol, etc.) capable of being uniformly mixed with water. It may be prepared by adding or mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and a manganese-containing raw material.

The ammonium cation-containing complexing agent is, for example, NH ₄ OH, (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , NH ₄ Cl, CH ₃ COONH ₄ , NH ₄ CO ₃ Or it may be a combination thereof, but is not limited thereto. Meanwhile, the ammonium cation-containing complex forming agent may be used in the form of an aqueous solution, and in this case, water or a mixture of an organic solvent (specifically, alcohol, etc.) and water that can be uniformly mixed with water may be used as the solvent.

The basic compound may be 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. The basic compound may also be used in the form of an aqueous solution, and in this case, water or a mixture of an organic solvent (specifically, alcohol, etc.) and water that can be uniformly mixed with water may be used as the solvent.

The basic compound is added to adjust the pH of the reaction solution, and may be added in an amount such that the pH of the metal solution is 11 to 13.

Meanwhile, the co-precipitation reaction may be performed at a temperature of 40° C. to 70° C. under an inert atmosphere such as nitrogen or argon.

By the above process, particles of nickel-cobalt-manganese hydroxide are produced and precipitated in the reaction solution. The precipitated nickel-cobalt-manganese hydroxide particles can be separated according to a conventional method and dried to obtain a nickel-cobalt-manganese precursor. The precursor is secondary particles formed by aggregation of primary particles, and the average particle diameter (D ₅₀ ) of the precursor secondary particles may be 4 to 8 μm, more preferably 4 to 7.5 μm, and still more preferably 4 μm. to 7 μm.

Next, the precursor and the lithium raw material are mixed and overfired at a temperature of 980 ° C. or higher to obtain single particles of the first lithium composite transition metal oxide and secondary particles in which the primary particles are aggregated without being single particles A mixture comprising the second lithium composite transition metal oxide in the form of

As the lithium raw material, a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and is not particularly limited as long as it is soluble in water. Specifically, the lithium source is Li ₂ CO ₃ , LiNO ₃ , LiNO ₂ , LiOH, LiOHㆍH ₂ O, LiH, LiF, LiCl, LiBr, LiI, CH ₃ COOLi, Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, or Li ₃ C ₆ H ₅ O ₇ and the like, and any one or a mixture of two or more of them may be used.

The lithium source material may be mixed so that the molar ratio (Li/M) of lithium (Li) of the lithium source material to all metal elements (M) of the precursor is 1 to 1.5. More preferably, the lithium source material may be mixed so that Li/M is 1 to 1.5, more preferably 1 to 1.1.

In order to form the single particle first lithium composite transition metal oxide, the underfiring temperature is preferably 980 ° C or higher, more preferably 990 to 1100 ° C, and even more preferably 1000 to 1050 ° C. can The over-baking may be performed for 10 to 30 hours, more preferably for 20 to 26 hours. The over-firing may be performed in an oxygen atmosphere or an air atmosphere, more preferably in an oxygen atmosphere. By overfiring in this way, it is possible to form a single particle first lithium composite transition metal oxide, and the single particle first lithium composite transition metal oxide has improved particle strength and is less likely to break during rolling. suppressed, it is possible to reduce side reactions with the electrolyte, it is possible to reduce the amount of gas generated during cell operation, and it is possible to secure excellent stability. When the underfiring temperature is less than 980 ° C, the first lithium composite transition metal oxide in single particle form cannot be formed, and only lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated exists, resulting in particle strength and Stability may deteriorate.

The first lithium composite transition metal oxide of the present invention is composed of single particles, that is, primary particles, not in the form of agglomerated secondary particles. In the present invention, 'primary particle' means a primary structure of a single particle, and 'secondary particle' refers to the physical physical properties between primary particles without intentional aggregation or assembly process for the primary particles constituting the secondary particles. Alternatively, it means an aggregate in which primary particles are aggregated by chemical bonding, that is, a secondary structure.

An average particle diameter (D ₅₀ ) of the first lithium composite transition metal oxide formed into single particles may be 4 μm to 8 μm. It may be more preferably 5 to 7.5 μm, more preferably 5.5 to 7.5 μm.

In the present invention, the average particle diameter (D ₅₀ ) may be defined as a particle diameter corresponding to 50% of the cumulative volume in the particle diameter distribution curve. The average particle diameter (D ₅₀ ) may be measured using, for example, a laser diffraction method. For example, the method for measuring the average particle diameter (D ₅₀ ) of the positive electrode active material is to disperse the particles of the positive electrode active material in a dispersion medium, and then introduce it into a commercially available laser diffraction particle size measuring device (eg, Microtrac MT 3000) to approximately After irradiating 28 kHz ultrasonic waves with an output of 60 W, the average particle diameter (D ₅₀ ) corresponding to 50% of the cumulative volume in the measuring device can be calculated.

When overfiring is performed at a firing temperature of 980° C. or higher to form the single particle first lithium composite transition metal oxide, not all particles are formed into single particles. That is, a mixture including the single particle first lithium composite transition metal oxide and the second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles is formed. . In the second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles, the primary particles may have a size of 1.5 to 2.5 μm and the secondary particles may have a size of 6 to 10 μm. More preferably, the second lithium composite transition metal oxide may have primary particles of 1.8 to 2.5 μm and secondary particles of 6.5 to 10 μm.

Next, by pressing the mixture, the second lithium composite transition metal oxide in the form of secondary particles in which the primary particles are aggregated is pulverized, comprising a first positive electrode active material of small particles and a second positive electrode active material of large particles A positive electrode material having a bimodal particle size distribution is formed.

The press may be performed at 100 to 300 MPa. More preferably, it may be performed at 200 to 290 MPa, more preferably at 200 to 260 MPa. By pressing with a strength within the above range, the agglomerated second lithium composite transition metal oxide in the form of secondary particles can be pulverized into small primary particles, and a positive electrode material having a bimodal particle size distribution can be formed. there is. When the press strength is less than 100 MPa, the second lithium composite transition metal oxide may not be pulverized into small primary particles and may not form a bimodal particle size distribution, and when it exceeds 300 MPa, 1 There is a problem that the tea particles are not pulverized apart from each other, but the particles themselves are broken. In this case, the D _min value decreases and the D _max value increases.

According to an embodiment of the present invention, the first lithium composite transition metal oxide formed by overfiring into single particles and the second lithium composite transition metal in the form of secondary particles in which primary particles are aggregated without being single particles By forming a positive electrode material having a bimodal particle size distribution by pressing a mixture including an oxide, the rolling density may be remarkably increased to improve energy density and increase capacity.

The positive electrode material having a bimodal particle size distribution formed as described above includes a first positive electrode active material of small particles and a second positive electrode active material of large particles.

The first cathode active material of the small particles may have an average particle diameter (D ₅₀ ) of 1.5 to 2.5 μm, more preferably 1.8 to 2.5 μm, and still more preferably 1.8 to 2.4 μm. According to the present invention, the first positive electrode active material of small particles satisfying the above range may be formed by manufacturing the underfired mixture by pressing.

The average particle diameter (D ₅₀ ) of the opposite second positive active material may be 4 to 8 μm, more preferably 4.5 to 7.5 μm, and still more preferably 5 to 7.5 μm.

Since both the first cathode active material and the second cathode active material are overfired, the crystallite size may be greater than or equal to 180 nm. More preferably, the crystal size of the first and second cathode active materials may be 180 nm to 300 nm, more preferably 185 nm to 270 nm.

In the present invention, 'particles' refer to grains in micro units, and when observed under magnification, they can be classified as 'grains' having a crystal form of several tens of nanometers. If this is further enlarged, it is possible to identify a distinct region in which atoms form a lattice structure in a certain direction, which is called a 'crystallite', and the size of the particle observed in XRD is defined by the size of the crystallite. . A method of measuring the crystallite size can estimate the crystallite size using peak broadening of XRD data, and can be quantitatively calculated through the Scherrer equation.

When the crystal size of the first and second cathode active materials according to an embodiment of the present invention satisfies 180 nm or more, particle breakage due to rolling may be suppressed, and life characteristics and stability may be improved.

The positive electrode material having a bimodal particle size distribution formed as described above may include the first positive electrode active material and the second positive electrode active material in a weight ratio of 1:3 to 1:4.5. More preferably, it may be included in a weight ratio of 1:3.5 to 1:4.5, and more preferably, it may be included in a weight ratio of 1:3.8 to 1:4.2. When the first and second cathode active materials are included in a mixing ratio within the above range, the rolling density may be remarkably increased to improve energy density and increase capacity.

< cathode material >

The positive electrode material for a secondary battery of the present invention is a bimodal positive electrode material comprising a first positive electrode active material of small particles and a second positive electrode active material of opposite particles, wherein the first and second positive electrode active materials are nickel (Ni) and cobalt (Co). ) and manganese (Mn), is composed of a single particle, and has a crystallite size of 180 nm or more.

The positive electrode material according to the present invention, as in the manufacturing method according to one embodiment of the present invention described above, the first lithium composite transition metal oxide which is single particle by over-firing at a temperature of 980 ° C. or higher, and is not single particle A mixture including the second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated is formed, and the second lithium composite transition metal oxide is pulverized by pressing the mixture to form a bimodal product. It can be prepared to have a particle size distribution of. In the case of a bimodal positive electrode material in which small particles and large positive electrode active materials are mixed as in the present invention, empty spaces between particles of opposite positive electrode active materials can be filled with small particle positive electrode active materials, so more dense filling is possible. , can increase the energy density of the anode. According to the present invention, the first lithium composite transition metal oxide in the form of single particles is formed in the underfiring process, and the second lithium composite transition metal oxide in the form of secondary particles is formed in the press process. Since they are pulverized into particles, the first and second positive electrode active materials are made of single particles. Since the first and second cathode active materials are composed of single particles, particle strength is improved, particle breakage is suppressed during rolling, side reactions with the electrolyte can be reduced, and gas generation during cell operation can be reduced. and excellent stability can be secured.

Since both the first cathode active material and the second cathode active material are overfired, the crystallite size satisfies 180 nm or more. More preferably, the crystal size of the first and second cathode active materials may be 180 nm to 300 nm, more preferably 185 nm to 270 nm. When the crystal sizes of the first and second cathode active materials are greater than or equal to 180 nm, cracking of particles due to rolling may be suppressed, and life characteristics and stability may be improved.

The first cathode active material of the small particles may have an average particle diameter (D ₅₀ ) of 1.5 to 2.5 μm, more preferably 1.8 to 2.5 μm, and still more preferably 1.8 to 2.4 μm. According to the present invention, the first cathode active material of small particles may satisfy the above range by preparing the underfired mixture by pressing.

The average particle diameter (D ₅₀ ) of the opposite second positive active material may be 4 to 8 μm, more preferably 4.5 to 7.5 μm, and still more preferably 5 to 7.5 μm.

A positive electrode material having a bimodal particle size distribution according to an embodiment of the present invention may include the first positive electrode active material and the second positive electrode active material in a weight ratio of 1:3 to 1:4.5. More preferably, it may be included in a weight ratio of 1:3.5 to 1:4.5, and more preferably, it may be included in a weight ratio of 1:3.8 to 1:4.2. When the first and second cathode active materials are included in a mixing ratio within the above range, the rolling density may be remarkably increased to improve energy density and increase capacity.

The first positive electrode active material and the second positive electrode active material of the present invention are lithium composite transition metal oxides containing nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium composite transition metal oxide is a total metal element (M ) The molar ratio of lithium (Li) to (Li/M) may be 1 to 1.3, more preferably 1 to 1.1, and more preferably 1 to 1.05.

More specifically, the first cathode active material and the second cathode active material according to an embodiment of the present invention may be a lithium composite transition metal oxide represented by Chemical Formula 1 below.

[Formula 1]

Li _p Ni _1-(x1+y1+z1) Co _x1 Mn _y1 M ^a _z1 O _2+δ

In the above formula, M ^a is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, Cr, Ba, Sr and Ca, 1≤p≤1.3, 0<x1≤0.5, 0<y1≤0.5, 0≤z1≤0.1, -0.1≤δ ≤1.

In the lithium composite transition metal oxide of Formula 1, Li may be included in an amount corresponding to p, that is, 1≤p≤1.3. If p is less than 1, there is a possibility of a decrease in capacity, and if it exceeds 1.3, the strength of the fired cathode active material increases, making it difficult to pulverize, and there may be an increase in gas generation due to an increase in Li by-products. Considering the effect of improving the capacity characteristics of the cathode active material according to the control of the Li content and the sinterability balance during the preparation of the active material, the Li may be included in an amount of 1.0≤p≤1.1.

In the lithium composite transition metal oxide of Chemical Formula 1, Ni may be included in an amount corresponding to 1-(x1+y1+z1), for example, 0<1-(x1+y1+z1)≤0.9. More preferably, Ni may be included as 0.4≤1-(x1+y1+z1)≤0.9.

In the lithium composite transition metal oxide of Chemical Formula 1, Co may be included in an amount corresponding to x1, that is, 0<x1≤0.5. When the content of Co in the lithium composite transition metal oxide of Chemical Formula 1 exceeds 0.5, there is a concern about cost increase. Considering the remarkable effect of improving capacity characteristics due to the inclusion of Co, the Co may be more specifically included in an amount of 0.2≤x1≤0.4.

In the lithium composite transition metal oxide of Chemical Formula 1, Mn may be included in an amount corresponding to y1, that is, 0<y1≤0.5. Mn can improve the stability of the positive electrode active material and, as a result, the stability of the battery. More specifically, Mn may be included in an amount of 0.05≤y1≤0.2.

In the lithium composite transition metal oxide of Formula 1, M ^a may be a doping element included in the crystal structure of the lithium composite transition metal oxide, and M ^a may be included in a content corresponding to z1, that is, 0≤z1≤0.1. there is.

The positive electrode material according to an embodiment of the present invention may have a particle strength of 180 MPa or more. More preferably, it may be 200 MPa or more, and more preferably, it may be 230 MPa or more. The positive electrode material according to an embodiment of the present invention may suppress particle breakage during rolling, improve rolling density, and improve stability when particle strength satisfies the above range.

In addition, the positive electrode material according to an embodiment of the present invention may have a rolling density of 3.08 g/cc or more, more preferably 3.14 g/cc or more, and even more preferably 3.16 g/cc or more. This may be the rolling density when pressed to 63.694 MPa. The positive electrode material according to an embodiment of the present invention may increase energy density and improve capacity when the rolling density satisfies the above range.

<Cathode and secondary battery>

According to another embodiment of the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery including the positive electrode material are provided.

Specifically, the positive electrode includes a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector and including the positive electrode material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , those surface-treated with nickel, titanium, silver, etc. may be used. In addition, the cathode current collector may have a thickness of typically 3 to 500 μm, and adhesion of the cathode active material may be increased by forming fine irregularities on the surface of the cathode current collector. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In addition, the positive electrode material layer may include a conductive material and a binder together with the positive electrode material described above.

At this time, the conductive material is used to impart conductivity to the electrode, and in the battery, any material that does not cause chemical change and has electronic conductivity can be used without particular limitation. 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode material layer.

In addition, the binder serves to improve the adhesion between the particles of the positive active material and the adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC) ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and the like may be used alone or in a mixture of two or more of them. The binder may be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode material layer.

The positive electrode may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode material described above. Specifically, the composition for forming a cathode material layer including the cathode material and, optionally, a binder and a conductive material may be coated on a cathode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode material, the binder, and the conductive material are as described above.

The solvent may be a solvent commonly used in the art, and dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water and the like, and one type alone or a mixture of two or more types of these may be used. The amount of the solvent used is enough to dissolve or disperse the positive electrode material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity capable of exhibiting excellent thickness uniformity during subsequent coating for manufacturing the positive electrode. do.

Alternatively, the positive electrode may be manufactured by casting the composition for forming the positive electrode material layer on a separate support and then laminating a film obtained by peeling the support from the support on a positive electrode current collector.

According to another embodiment of the present invention, an electrochemical device including the anode is provided. The electrochemical device may be a battery or a capacitor, and more specifically, a lithium secondary battery.

The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the positive electrode is as described above. In addition, the lithium secondary battery may optionally further include a battery container accommodating the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member sealing the battery container.

In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode material layer positioned on the negative electrode current collector.

The anode current collector is not particularly limited as long as it does not cause chemical change in the battery and has high conductivity. For example, it is formed on the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. A surface treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector may have a thickness of typically 3 to 500 μm, and, like the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to enhance bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

The negative electrode material layer optionally includes a binder and a conductive material along with the negative electrode active material. For example, the negative electrode material layer is formed by applying a composition for forming a negative electrode including a negative electrode active material, and optionally a binder and a conductive material on a negative electrode current collector and drying it, or by casting the composition for forming a negative electrode on a separate support, and then , It may be produced by laminating a film obtained by peeling from the support on a negative electrode current collector.

A compound capable of reversible intercalation and deintercalation of lithium may be used as the anode active material. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of being alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides capable of doping and undoping lithium, such as SiO _β (0 < β < 2), SnO ₂ , vanadium oxide, and lithium vanadium oxide; or a composite including the metallic compound and the carbonaceous material, such as a Si—C composite or a Sn—C composite, and any one or a mixture of two or more of these may be used. In addition, a metal lithium thin film may be used as the anode active material. In addition, as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft carbon and hard carbon are typical examples of low crystalline carbon, and high crystalline carbon includes amorphous, platy, scaly, spherical or fibrous natural graphite, artificial graphite, or kish graphite. graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch High-temperature calcined carbon such as derived cokes is representative.

Also, the binder and the conductive material may be the same as those described in the foregoing positive electrode.

On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ion movement, and any separator used as a separator in a lithium secondary battery can be used without particular limitation, especially for the movement of ions in the electrolyte. It is preferable to have low resistance to the electrolyte and excellent ability to absorb the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these A laminated structure of two or more layers of may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single layer or multilayer structure.

In addition, the electrolyte used in the present invention includes an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery, and is limited to these. it is not going to be

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without 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 includes 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-based solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, PC) and other carbonate-based solvents; alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Alternatively, sulfolane or the like may be used. Among them, carbonate-based solvents are preferred, and cyclic carbonates (eg, ethylene carbonate or propylene carbonate, etc.) having high ion conductivity and high dielectric constant capable of increasing the charge and discharge performance of batteries, and low-viscosity linear carbonate-based compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.

The lithium salt may be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlO _{4 , LiAlCl 4 ,} LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ . LiCl, LiI, or LiB(C ₂ O ₄ ) ₂ or the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

In addition to the above electrolyte components, the electrolyte may include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and triglycerides for the purpose of improving battery life characteristics, suppressing battery capacity decrease, and improving battery discharge capacity. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

As described above, since the lithium secondary battery including the cathode material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles ( It is useful for electric vehicles such as hybrid electric vehicles (HEVs).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack may include a power tool; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Alternatively, it may be used as a power source for one or more medium or large-sized devices among power storage systems.

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

Example One

In a batch type batch 40L reactor set at 50°C, NiSO ₄ , CoSO ₄ , and MnSO ₄ were mixed in water in an amount such that the molar ratio of nickel:cobalt:manganese was 50:30:20 to obtain a concentration of 2.4M. A precursor formation solution was prepared.

After putting 13 liters of deionized water into the co-precipitation reactor (capacity: 40 L), nitrogen gas was purged through the reactor at a rate of 25 liters/min to remove dissolved oxygen in the water and create a non-oxidizing atmosphere in the reactor. Thereafter, 83 g of a 25% NaOH aqueous solution was added, stirred at a stirring speed of 700 rpm at a temperature of 50 ° C, and maintained at pH 11.5.

Thereafter, the precursor forming solution was added at a rate of 1.9 L/hr, and the aqueous solution of NaOH and the aqueous solution of NH ₄ OH were added together for _a co-precipitation reaction for 48 hours to _{obtain a} nickel-cobalt-manganese- _containing hydroxide (Ni _0.5 Co _0.3 Mn Particles _{of 0.2 (} OH) ₂ ) were _formed . The hydroxide particles were separated, washed, and then dried in an oven at 120° C. to prepare a precursor of a cathode active material (D ₅₀ =4.8 μm). The positive electrode active material precursor thus prepared was in the form of secondary particles in which primary particles were aggregated.

The cathode active material precursor and lithium source LiOH thus prepared were put into a Henschel mixer (20L) so that the Li/M (Ni, Co, Mn) molar ratio was 1.02, and mixed at the center at 300 rpm for 20 minutes. The mixed powder was put into an alumina crucible with a size of 330mmx330mm and calcined at 1010 to 1030°C for 15 hours in an oxygen atmosphere to form single particles of the first lithium composite transition metal oxide (D ₅₀ =6㎛, Li/M = 1.0 to 1.02 ) and the second lithium complex transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles (secondary particle D ₅₀ =7㎛, primary particle 1.5 ~ 2㎛, Li / M = 1.0 ~ 1.02 ) was prepared.

Thereafter, the mixture was pressed with a carver at 220 MPa to pulverize the second lithium composite transition metal oxide, and a cathode material including a first cathode active material of small particles and a second cathode active material of large size was prepared.

Example 2

The first lithium composite transition metal oxide (D ₅₀ =5.5 μm, Li/M = 1.0 to 1.02), which was calcined at 990 ° C. for 15 hours in an oxygen atmosphere to become single particles, and 2 in which primary particles were aggregated without being single particles Examples except for preparing a mixture containing the second lithium composite transition metal oxide in the form of secondary particles (secondary particle D ₅₀ =7 μm, primary particle 1.5 to 1.8 μm, Li / M = 1.0 to 1.02) A positive electrode material was prepared in the same manner as in 1.

comparative example One

A positive electrode material was prepared in the same manner as in Example 1, except that the mixture of Example 1 was not pressed.

comparative example 2

As an allele, it is in the form of secondary particles in which primary particles are aggregated, and LiNi _0.5 Co _0.3 Mn _0.2 O ₂ with D ₅₀ = 7㎛ of secondary particles is used, and as small particles, it is in the form of secondary particles in which primary particles are aggregated. , LiNi ₀ with D ₅₀ = 2 μm of secondary particles _{. 5} Co _{0 . 3Mn0 . _ 2} O ₂ was used, and a cathode material was prepared by mixing the large particles and small particles in a weight ratio of 7:3.

[ Experimental example One: of cathode material particle size distribution]

The particle size distribution of the positive electrode materials prepared in Examples 1 and 2 and Comparative Example 1 was measured using PSD (Particle Size Distribution), and the results are shown in FIG. 1 below.

Referring to FIG. 1, the positive electrode materials prepared in Examples 1 and 2 exhibited a bimodal particle size distribution including small particles and large particles, and Comparative Example 1 showed a monomodal particle size distribution. You can check.

[ Experimental example 2: of cathode material observe]

The cathode materials of Example 1 (FIG. 3) and Comparative Example 1 (FIGS. 2a and 2b) were observed using SEM images.

Referring to Figures 2a, 2b and 3, it can be seen that in the case of Comparative Example 1 that is not pressed (FIGS. 2a, 2b), some are single particles, and some are in the form of secondary particles in which primary particles are agglomerated. On the other hand, in the case of the pressed Example 1 (FIG. 3), it can be confirmed that the secondary particles in which the primary particles are aggregated are pulverized into small primary particles.

[ Experimental example 3: particle shape and crystal size of cathode active material]

The particle shape of the positive electrode materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 was observed, and the crystal size was measured. The particle shape was observed using SEM pictures, and the crystal size (Crystalite size) was measured by XRD and the average value was calculated.

single particle crystal size (nm) 1st Cathode Active Material Second Cathode Active Material Example 1 O O 200 Example 2 O O 220 Comparative Example 1 monomodal 200 Comparative Example 2 X X 150

Referring to Table 1, in the positive electrode materials prepared in Examples 1 and 2, both the first positive electrode active material of small particles and the second positive electrode active material of large particles were in the form of single particles, and the crystal size was 180 nm or more. On the other hand, Comparative Example 1 showed a monomodal particle size distribution, some of which were single particles, and some were in the form of secondary particles in which primary particles were aggregated. In Comparative Example 2, both the first positive electrode active material of small particles and the second positive electrode active material of large particles were in the form of secondary particles in which primary particles were aggregated, and the crystal size was less than 180 nm.

[ Experimental example 4: grain strength and rolling density]

Particle strength and rolling density of the positive electrode materials prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. Particle strength was measured using a particle strength meter (MCTW500E). The rolling density was measured using HPRM-1000. Specifically, 5 g of the positive electrode materials of Examples 1 and 2 and Comparative Examples 1 and 2 were respectively put into a cylindrical mold, and then the mold containing the positive electrode material was pressed at 63.694 MPa. Thereafter, the height of the pressed mold was measured with a vernier caliper, and the rolling density was obtained. The results are shown in Table 2 and Figure 4 (rolling density).

Grain strength (MPa) Rolling density (g/cc) Example 1 264.7 3.27 Example 2 264.7 3.2 Comparative Example 1 264.7 3.02 Comparative Example 2 121.6 3.02

Referring to Table 2, it can be seen that the positive electrode materials prepared in Examples 1 and 2 have significantly improved particle strength compared to Comparative Examples 1 and 2. In addition, referring to Table 3 and FIG. 4, it can be confirmed that the rolling density of the positive electrode materials prepared in Examples 1 and 2 is significantly increased compared to Comparative Examples 1 and 2.

[ Experimental example 5: Evaluation of capacity and life characteristics]

Each of the positive electrode materials, carbon black conductive material, and PVdF binder prepared in Examples 1 and 2 and Comparative Example 2 were mixed in a weight ratio of 96: 2: 2 in an N-methylpyrrolidone solvent to prepare a positive electrode composite, , After applying this to one surface of an aluminum current collector, drying at 100 ℃, and then rolling to prepare a positive electrode.

Lithium metal was used as the negative electrode.

An electrode assembly was prepared by interposing a porous polyethylene separator between the positive electrode and the negative electrode prepared as described above, the electrode assembly was placed inside a case, and an electrolyte solution was injected into the case to prepare a lithium secondary battery. At this time, the electrolyte is ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (mixed volume ratio of EC / EMC / DEC = 3/4/3) in an organic solvent consisting of 1.0M concentration of lithium hexafluorophosphate (LiPF ₆ ) is dissolved It was prepared by

For each half cell of the lithium secondary battery manufactured as described above, it is charged in CCCV mode at 25°C until it becomes 0.2C and 4.4V (end current 1/20C), and 3.0V with a constant current of 0.2C. The initial charge and initial discharge capacities were measured by discharging until The CFC cell was charged until it reached 4.4V at 0.7C in CCCV mode and discharged at 0.5C constant current to 3.0V, and the capacity retention rate was measured when the charge/discharge experiment was conducted 100 times to evaluate the life characteristics. . The results are shown in Table 3.

Initial discharge capacity (mAh/g) Capacity retention rate (%) (@100 cycles) Example 1 176 91 Example 2 174 90 Comparative Example 2 178 88

Referring to Table 3, in the case of using the cathodes prepared in Examples 1 and 2, it can be confirmed that the lifespan characteristics are increased compared to Comparative Example 2.

[ Experimental example 6: evaluation of high temperature storage characteristics]

For the lithium secondary battery half cell prepared as in Experimental Example 6 using each cathode material prepared in Examples 1 and 2 and Comparative Example 2, when 0.5C and 4.4V in CCCV mode. (end current 1/20C). Two sheets of the positive electrode and two sheets of the polyethylene separator thus charged were alternately stacked on the lower plate of the coin cell. Then, after injecting the electrolyte solution, the laminated electrode plate was fixed by covering it with a gasket. Thereafter, the mixture was stored at 60° C. for 2 weeks and the generated gas was measured using a gas chromatograph-mass spectrometer (GC-MS). The results are shown in Table 4 below.

High-temperature storage gas generation (μL/g) Example 1 750 Example 2 800 Comparative Example 2 2,000

Referring to Table 4, when the positive electrode material prepared in Examples 1 and 2 was used, the amount of high-temperature storage gas generated was significantly reduced compared to the case where the positive electrode material prepared in Comparative Example 2 was used.

Claims (17)

By mixing a precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) with a lithium raw material and over-firing at a temperature of 980 ° C. or higher, the first lithium composite transition metal oxide formed into single particles and a single Forming a mixture including a second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being granulated; and
By pressing the mixture, the second lithium composite transition metal oxide in the form of secondary particles in which the primary particles are aggregated is pulverized, and the bimodal including the first positive electrode active material of small particles and the second positive electrode active material of large particles ( forming a positive electrode material having a particle size distribution of bimodal);
The press is performed at 100 MPa to 300 MPa,
The first positive electrode active material and the second positive electrode active material are made of single particles and are lithium composite transition metal oxides represented by Formula 1 below, a method for producing a positive electrode material for a secondary battery:
[Formula 1]
Li _p Ni _1-(x1+y1+z1) Co _x1 Mn _y1 M ^a _z1 O _2+δ
In the above formula, M ^a is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, Cr, Ba, Sr and Ca, 1≤p≤1.3, 0<x1<0.5, 0<y1<0.5, 0≤z1≤0.1, -0.1≤δ ≤1.
According to claim 1,
The overfiring temperature is a method for producing a cathode material for a secondary battery of 990 to 1100 ° C.
delete According to claim 1,
The single particle (single particle) first lithium composite transition metal oxide is a method for producing a secondary battery cathode material having an average particle diameter (D ₅₀ ) of 4 to 8 μm.
According to claim 1,
In the second lithium composite transition metal oxide in the form of secondary particles in which primary particles are aggregated without being single particles, the primary particles are 1.5 to 2.5 μm and the secondary particles are 6 to 10 μm. Ash manufacturing method.
According to claim 1,
The method of manufacturing a cathode material for a secondary battery wherein the first cathode active material has an average particle diameter (D ₅₀ ) of 1.5 to 2.5 μm.
According to claim 1,
Wherein the second cathode active material has an average particle diameter (D ₅₀ ) of 4 to 8 μm.
According to claim 1,
Wherein the first cathode active material and the second cathode active material have a crystal size of 180 nm or more.
According to claim 1,
Wherein the first positive electrode active material and the second positive electrode active material are included in a weight ratio of 1:3 to 1:4.5.
A bimodal positive electrode material comprising a first positive electrode active material of small particles and a second positive electrode active material of opposites,
The first and second cathode active materials include nickel (Ni), cobalt (Co), and manganese (Mn), and are lithium composite transition metal oxides represented by Formula 1 below, made of single particles, and crystals. Cathode material for secondary batteries with a size (Crystalite size) of 180 nm or more:
[Formula 1]
Li _p Ni _1-(x1+y1+z1) Co _x1 Mn _y1 M ^a _z1 O _2+δ
In the above formula, M ^a is at least one element selected from the group consisting of Al, Zr, Ti, Mg, Ta, Nb, Mo, Cr, Ba, Sr and Ca, 1≤p≤1.3, 0<x1<0.5, 0<y1<0.5, 0≤z1≤0.1, -0.1≤δ ≤1.
According to claim 10,
The first cathode active material has an average particle diameter (D ₅₀ ) of 1.5 to 2.5 μm, a cathode material for a secondary battery.
According to claim 10,
The second cathode active material has an average particle diameter (D ₅₀ ) of 4 to 8 μm.
According to claim 10,
The first cathode active material and the second cathode active material are included in a weight ratio of 1:3 to 1:4.5.
According to claim 10,
The cathode material is a cathode material for a secondary battery having a particle strength of 180 MPa or more.
According to claim 10,
The cathode material is a cathode material for a secondary battery having a rolling density of 3.08 g / cc or more.
A cathode for a secondary battery comprising the cathode active material according to any one of claims 10 to 15.
A lithium secondary battery comprising the cathode according to claim 16.

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