WO2016032223A1 - Surface-coated positive electrode active material, method for preparing same, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a surface-coated positive electrode active material, a method for preparing the same, and a lithium secondary battery comprising the same. More specifically, the present invention relates to a positive electrode active material which is surface-coated with a nanofilm containing polyimide (PI) and carbon black, to a method for preparing the same, and to a lithium secondary battery comprising the same. The positive electrode active material which is surface-coated with the nanofilm can prevent a direct contact between a positive electrode active material and an electrolyte, and thus can suppress a side reaction between the positive electrode active material and the electrolyte, can significantly improve lifespan characteristics of a lithium secondary battery using a positive electrode containing the positive electrode active material, and especially can improve lifespan characteristics and conductivity in high-temperature and high-voltage conditions.

Description

Surface-coated positive electrode active material, preparation method thereof, and lithium secondary battery comprising same

Citation with Related Applications

This application claims the benefit of priority based on Korean Patent Application No. 10-2014-0111504 dated August 26, 2014 and Korean Patent Application No. 10-2015-0117752 dated August 21, 2015. All content disclosed in the literature is included as part of this specification.

Technical Field

The present invention relates to a surface-coated positive electrode active material, a method of manufacturing the same, and a lithium secondary battery including the same. More specifically, the present invention relates to a cathode active material surface-coated with a nano-film including polyimide (PI) and carbon black, a method of manufacturing the same, and a lithium secondary battery including the same.

Lithium secondary batteries have been widely used as power sources for portable devices since they emerged in 1991 as small, light and large capacity batteries. Recently, with the rapid development of electronics, telecommunications, and computer industry, camcorders, mobile phones, notebook PCs, etc. have emerged, and they are developing remarkably, and the demand for lithium secondary battery as a power source to drive these portable electronic information communication devices increases day by day. Doing.

Lithium secondary batteries have a problem in that their lifespan drops rapidly as they are repeatedly charged and discharged.

This degradation of life characteristics is due to the side reaction between the positive electrode and the electrolyte, and this phenomenon may become more severe at high voltage and high temperature.

Therefore, it is necessary to develop a secondary battery for high voltage, and for this purpose, a technology for controlling side reactions or electrode interface reactions between the positive electrode active material and the electrolyte is very important.

In order to solve this problem, a technology for coating a metal oxide including Mg, Al, Co, K, Na, or Ca on the surface of the positive electrode active material has been developed.

In particular, the surfaces of these cathode active materials are Al ₂ O ₃ , ZrO ₂ , and AlPO _4. It is generally known that oxides such as these can be coated on the surface of the positive electrode active material. It is also established that the coating layer improves the safety characteristics of the positive electrode active material.

However, in the case of the surface coating using the oxide coating layer, the oxide coating layer is finely dispersed in the form of nano-sized particles rather than entirely covering the surface of the positive electrode active material.

For this reason, the surface modification effect of the positive electrode active material by the oxide coating layer was limited to be limited. In addition, the oxide coating layer is a kind of ion insulating layer that is difficult to move lithium ions, and may cause a decrease in ion conductivity.

Under the above background, while the present inventors are studying a positive electrode active material which is excellent in safety and can exhibit excellent life characteristics even under high voltage conditions, the present inventors include polyimide and carbon black having a specific iodine number and oil absorption number on the surface of the positive electrode active material. The surface-coated positive electrode active material prepared by forming a nano-film can effectively suppress side reactions between the positive electrode active material and the electrolyte due to the nano-film, thereby providing excellent safety and excellent life characteristics and conductivity even under high voltage conditions. The present invention was completed by confirming.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) KR2009-0018981 A

The present invention has been made to solve the above problems, an object of the present invention by coating the entire surface of the positive electrode active material with a nano-film capable of lithium ion migration, it effectively suppresses side reactions between the positive electrode active material and the electrolyte solution and excellent safety. At the same time, to provide a surface-coated positive electrode active material having excellent lifespan characteristics under high temperature and high voltage conditions as well as excellent conductivity.

Another object of the present invention to provide a method for producing the surface-coated positive electrode active material.

Still another object of the present invention is to provide a positive electrode including the surface-coated positive electrode active material.

In addition, another object of the present invention is to provide a lithium secondary battery including a separator interposed between the positive electrode, the negative electrode and the positive electrode and the negative electrode.

In order to solve the above problems, the present invention is a positive electrode active material; And a nano coating including polyimide (PI) and carbon black coated on the surface of the positive electrode active material, wherein the nano coating includes the polyimide and carbon black in a weight ratio of 0.5 to 5 by weight. Provided is a coated cathode active material.

In addition, the present invention comprises the steps of preparing a mixed solution in which carbon black is mixed and dispersed in an organic solvent in which a polyamic acid is diluted; Dispersing a positive electrode active material in the mixed solution to form a film including polyamic acid and carbon black on the surface of the positive electrode active material; And imidizing the positive electrode active material having the coating formed thereon, wherein the carbon black is used in an amount of 0.05 wt% to 5 wt% based on 100 wt% of the positive electrode active material. It provides a method of manufacturing.

In addition, the present invention provides a positive electrode including the surface-coated positive electrode active material.

Furthermore, the present invention provides a lithium secondary battery including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The positive electrode active material according to the present invention has a polyimide and carbon black, especially an iodine number of 200 mg / g to 400 mg / g, and an oil absorption number of 0.1 cc / g to 0.2 cc / g. Since the surface is coated with a nano-film including phosphorous carbon black, direct contact between the positive electrode active material and the electrolyte may be prevented, thereby preventing side reactions between the positive electrode active material and the electrolyte.

Thus, the life characteristics of the lithium secondary battery using the positive electrode including the positive electrode active material surface-coated with the nano-film according to the present invention can be significantly improved, in particular, the life characteristics and conductivity at high temperature and high voltage conditions can be improved.

The following drawings, which are attached to this specification, illustrate preferred embodiments of the present invention, and together with the contents of the present invention serve to further understand the technical spirit of the present invention, the present invention is limited to the matters described in such drawings. It should not be construed as limited.

1 is an electron microscope (FE-SEM) photograph of the surface of a cathode active material surface-coated with a nano-film including polyimide and carbon black prepared in Example 1 of the present invention.

FIG. 2 is an electron microscope (FE-SEM) photograph of the surface of the uncoated positive electrode active material prepared in Comparative Example 1. FIG.

3 is an electron microscope (FE-SEM) photograph of the surface of the positive electrode active material surface-coated with the polyimide prepared in Comparative Example 2.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention.

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The present invention provides a surface-coated positive electrode active material having excellent safety and excellent life characteristics and conductivity at high temperature and high voltage conditions.

The surface-coated positive electrode active material according to an embodiment of the present invention is a positive electrode active material; And a nano coating comprising polyimide (PI) and carbon black coated on the surface of the positive electrode active material, wherein the nano coating includes the polyimide and carbon black in a weight ratio of 0.5 to 5 by weight.

The nano-film according to the present invention is a lithium ion transfer is not an ion insulating layer, such as inorganic oxide surface coating layer generally known in the art, the nano-film as described above may include polyimide (PI) and carbon black Can be. The nano-film may include a lithium ion migration by including polyimide (PI), and the electronic conductivity may be improved by including carbon black.

In addition, the nanofilm may surround the entire surface of the positive electrode active material, and the nanofilm surrounding the surface of the positive electrode active material may prevent direct contact between the positive electrode active material and the electrolyte, thereby causing side reactions between the positive electrode active material and the electrolyte. It can be suppressed. As a result, it is possible to improve the safety and lifespan characteristics of the lithium secondary battery using the positive electrode including the positive electrode active material coated with the nano-film, and in particular, not only general voltage conditions, but also high temperature and high voltage conditions The conductivity may be excellent.

Specifically, the polyimide included in the nano-film may serve as a protective film to prevent the positive electrode active material from directly contacting the electrolyte.

The polyimide is a generic term for a polymer having an acid imide structure, and can be obtained by synthesizing using an aromatic anhydride and an aromatic diamine. In the present invention, the polyimide can be obtained by imidization reaction using a polyamic acid as described below.

In addition, the carbon black included in the nano-film is very excellent in electrical conductivity and lithium ion conductivity may serve to provide a path (path) to react with lithium ions in the electrode, the nano-film is coated on the surface During the charge and discharge cycle of the lithium secondary battery including the positive electrode active material, the current and voltage distribution in the electrode may be maintained uniformly, thereby greatly improving the life characteristics.

The carbon black according to the present invention may have a value in which the iodine value and the oil absorption number are selected within a specific numerical range.

The term "iodine number" used in the present invention refers to the amount of halogen absorbed in the case of reacting halogen or fat to fatty acids or fatty acids using a reaction in which halogen is added to a double bond to 100 g of a sample. The amount of iodine to be absorbed is expressed in g, which is used as a numerical value representing the number of double bonds of unsaturated fatty acids in the sample. The higher the iodine number, the higher the number of double bonds.

In the case of the carbon black used in the present invention, the iodine number may be a value measured based on ASTM D-1510 of 200 mg / g to 400 mg / g, the iodine number of the carbon black If it is less than 200 mg / g it may be difficult to sufficiently disperse the carbon black in the nano-film, if it exceeds 400 mg / g may cause a problem that the conductivity is lowered.

That is, when the iodine number is in the above range, the number of unsaturated bonds (double bonds) present in the carbon black may be appropriate. Specifically, the bonding force between the carbon black particles, the bonding strength with the solvent when dispersing in the solvent, and other mixtures The bonding strength of the resin can be controlled appropriately, and the carbon black can be uniformly dispersed when the carbon black is dispersed in the solvent, and the agglomeration can be appropriately performed to ensure the conductive network.

The term "Oil Absorption number (OAN)" used in the present invention is a measure of the property of absorbing liquid (oil) can be used as a numerical value that can indicate the structural characteristics of the sample, in particular the degree of dispersibility. .

In the case of the carbon black used in the present invention, the oil absorption number (oil absorption number) may be a value measured based on ASTM D-2414 is 100 cc / 100 g to 200 cc / 100 g.

As such, when the number of oil absorption is in the above range, it may mean that the secondary structure formed by agglomeration of the primary particles of carbon black partially has an appropriate shape, and the shape of the secondary structure is appropriate. This may mean that the carbon black can be smoothly dispersed in a solvent and can secure various routes in securing a conductive network.

Since the carbon black according to the present invention has the iodine value and the oil absorption number, dispersibility in a solvent can be better than that of carbon black generally used, and the shape of the secondary structure is excellent to secure a conductive network. Can be fairly easy.

The positive electrode active material according to the present invention is a nano-coating formed on the surface, and when the carbon black is uniformly distributed with the polyimide on the nano-coating, it has better dispersibility and proper 2 It is required to have a car structure. Therefore, it may be difficult to uniformly disperse the carbon black on the nanofilm by the numerical values of the iodine value and the oil absorption number of the carbon black generally used in preparing the electrode slurry.

However, as described above, in the case of the carbon black having the iodine value and the oil absorption number value, the iodine can be distributed fairly uniformly due to its excellent dispersibility when it is distributed on the nanofilm, and because of the uniform and excellent secondary structure As a result, the challenge network can be secured.

In addition, the carbon black may be a mixture of primary particles, secondary particles or primary particles and secondary particles, when the carbon black is the primary particles, the average particle diameter of the carbon black is 10 nm to 100 When the carbon black is secondary particles, the average particle diameter of the carbon black may be less than 1000 nm. In addition, when the carbon black is secondary particles, the secondary particles may be pulverized to have an average particle diameter similar to that of the primary particles.

In addition, it may be preferable that the surface of the carbon black is hydrophobized. At this time, the surface hydrophobization treatment is not particularly limited and may be carried out by methods commonly known in the art, for example, carbon black is heat-treated in an air or nitrogen atmosphere at a temperature in the range of 450 to 550 ° C. and acid solution or alkali. It may be carried out by dispersing in a perfluorinated compound after supporting the solution by pretreatment.

As described above, the nano-film according to the present invention may include the polyimide and carbon black in a ratio of 1: 0.5 to 5 by weight. If the weight ratio of the polyimide and the carbon black is less than 1: 0.5, it may be difficult to obtain sufficient electrical conductivity. If the weight ratio is greater than 1: 5, the carbon black may be detached from the nano-film.

In addition, the carbon black may be included in an amount of 0.05 wt% to 5 wt% with respect to 100 wt% of the total surface coated positive active material, and preferably 0.2 wt% to 2 wt%.

The nanofilm thickness may be 1 nm to 200 nm, preferably 5 nm to 50 nm. When the thickness of the nanofilm is less than 1 nm, the side reaction effect of the positive electrode active material and the electrolyte due to the nanofilm and the synergistic effect of the electrical conductivity may be insignificant. In addition, when the thickness of the nano-film exceeds 200 nm, the thickness of the nano-film is excessively increased, the mobility of the lithium ions is hindered, the resistance may increase.

The cathode active material according to the present invention may be applied to a general voltage and a high voltage, and may be used without particular limitation as long as it is a compound capable of reversibly inserting / desorbing lithium.

Specifically, the positive electrode active material according to an embodiment of the present invention is a spinel lithium transition metal oxide having a hexagonal layered rock salt structure, olivine structure, cubic structure having a high capacity characteristics, in addition to V ₂ O ₅ , TiS, MoS It may include any one selected from the group consisting of two or more of these complex oxides.

More specifically, the cathode active material may include any one selected from the group consisting of oxides of Formulas 1 to 3, and V ₂ O ₅ , TiS, and MoS, or a mixture of two or more thereof:

<Formula 1>

Li _{1 + x} [Ni _a Co _b Mn _c ] O ₂ (−0.5 ≦ x ≦ 0.6, 0 ≦ a, b, c ≦ 1, x + a + b + c = 1);

<Formula 2>

LiMn _{2 - x} M _x O ₄ (M = Ni, Co, Fe, P, S, Zr, Ti and Al, at least one element selected from the group consisting of 0 ≦ x ≦ 2);

<Formula 3>

Li _{1 + a} Fe _{1 - x} M _x (PO _4-b ) X _b (M = Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y At least one element selected from the group consisting of X, at least one element selected from the group consisting of F, S, and N, wherein -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, and 0 ≤ b ≤ 0.1)

More specifically, the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li [Ni _a Co _b Mn _c ] O ₂ (0 <a, b, c ≤ 1, a + b + c = 1) and LiFePO ₄ and any one or a mixture of two or more thereof selected from the group consisting of.

In addition, the present invention provides a method for producing the surface-coated positive electrode active material.

Method for producing a surface-coated positive electrode active material according to an embodiment of the present invention comprises the steps of preparing a mixed solution in which carbon black is mixed and dispersed in an organic solvent in which polyamic acid is diluted (step 1); Dispersing a cathode active material in the mixed solution to form a film including polyamic acid and carbon black on the surface of the cathode active material (step 2); And imidating the positive electrode active material on which the coating is formed (step 3), wherein the carbon black is used in an amount of 0.05 wt% to 5 wt% based on 100 wt% of the positive electrode active material.

Step 1 is a step for preparing a mixed solution in which the material forming the nano-film is uniformly dispersed, and may be performed by adding and mixing carbon black to the organic solvent in which the polyamic acid is diluted.

At the time of mixing and dispersing the organic solvent in which carbon black and the polyamic acid are diluted in step 1, the dispersing agent may be further included. The dispersant is not particularly limited as long as it is mixed with the organic solvent in which the carbon black and the polyamic acid are diluted, and may serve to help the carbon black to be uniformly dispersed in the organic solvent. Block polymers such as styrene-butadiene-styrene block polymer or styrene-butadiene-ethylene-styrene block polymer may be applied as a dispersant.

Mixing and dispersing the organic solvent in which carbon black and the polyamic acid are diluted in step 1 may be performed using a mixer that can be driven at a rotational speed of 10,000 rpm or more at normal temperature (about 15 to 30 ° C.). The temperature range and the rotational speed range may be a condition in which the fibrous carbon material may be smoothly dispersed in the organic solvent in which the polyamic acid is diluted. If the temperature is excessively high, the polyimide reaction converts the polyamic acid to polyimide. There is a risk of this happening early.

On the other hand, when carbon black is coated on the positive electrode active material first, or when each is coated separately, such as when polyimide is coated first, a conductive network can be secured by coating carbon black, and by coating polyimide, However, when carbon black is coated inside, the conductive network may not be secured well. When polyimide is coated inside, the conductive nanoparticles may not be prevented from contacting the electrolyte. There exists a possibility that the role of carbon black and a polyimide may collide with each other.

However, according to the method of manufacturing a positive electrode active material according to an embodiment of the present invention, by performing step 1, a nano film in which carbon black and polyimide are uniformly dispersed in the positive electrode active material may be formed, thereby facilitating a conductive network. It can be ensured, and the side reaction can be effectively prevented by playing an excellent role in preventing contact with the electrolyte.

The polyamic acid according to the present invention is a precursor material for forming the polyimide included in the above-described nanofilm, and may include a four-component polyamic acid.

The four-component polyamic acid may be a polyamic acid including pyromellitic dianhydride, biphenyl dianhydride, phenylenediamine, and oxydianiline. Can be.

In addition, the polyamic acid is not particularly limited and may be prepared and used by a method commonly known in the art, or may be used by purchasing a commercially available material. When the polyamic acid is prepared and used, the polyamic acid may be used as an aromatic anhydride. Aromatic diamines can be obtained by reacting in polar aromatic solvents. At this time, the aromatic anhydride and the aromatic diamine can be reacted with the same equivalent weight.

Specifically, the aromatic anhydride is not particularly limited, for example, phthalic anhydride, pyromellitic dihydride, 3,3'4,4'-biphenyltetracarboxylic dianhydride, 4'4-oxy Diphthalic anhydride, 3,3'4,4'-benzophenonetetracarboxylic dianhydride, trimellitic ethylene glycol, 4,4 '-(4'4-isopropylbiphenoxy) biphthalic It may be any one selected from the group consisting of an anhydride and a trimellitic anhydride, or a mixture of two or more thereof.

In addition, the aromatic diamine is not particularly limited, for example, 4,4'-oxydianiline, p-phenyl diamine, 2,2-bis (4- (4-aminophenoxy ) -Phenyl) propane, p-methylenedianiline, propyltetramethyldisiloxane, polyaromatic amine, 4,4'-diaminodiphenyl sulfone, 2,2'-bis (trifluoromethyl) -4,4 It may be any one selected from the group consisting of '-diaminobiphenyl and 3,5-diamino-1,2,4-triazole, or a mixture of two or more thereof.

The polyamic acid may be used in an amount of 0.1 wt% to 1 wt% based on 100 wt% of the organic solvent.

The organic solvent is not particularly limited as long as it is a solvent capable of dissolving the polyamic acid, but is selected from the group consisting of cyclohexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide and N-methylpyrrolidone. It may be any one or a mixture of two or more thereof.

In addition, the carbon black according to the present invention may be used in the amount of 0.05% to 5% by weight with respect to 100% by weight of the positive electrode active material, preferably 0.2% to 2% by weight.

In the step 2, in order to form a film on the surface of the positive electrode active material, the positive electrode active material is dispersed in the mixed solution prepared in step 1 to form a film containing polyamic acid and carbon black on the surface of the positive electrode active material, the mixing The positive electrode active material may be added to the solution, uniformly dispersed, and heated and concentrated to remove the solvent.

Dispersion of the positive electrode active material is not particularly limited, but for example, the positive electrode active material may be added to the mixed solution, followed by stirring for 1 hour or more using a high speed stirrer.

Step 3 is a step of imidizing the cathode active material including the film prepared in step 2 to produce a cathode active material having a nano-film formed on the surface.

In the imidization reaction, the positive electrode active material including the film obtained in step 2 is heated to a rate of 3 ° C./minute at intervals of 50 ° C. to 100 ° C. to about 300 ° C. to 400 ° C., and 10 minutes to 300 ° C. in a range of 300 ° C. to 400 ° C. By holding for 120 minutes. In addition, after the temperature is raised at intervals of 50 to 100 ° C., for example, it may be maintained for 10 minutes to 120 minutes, and then heated again. More specifically, the positive electrode active material including the coating is heated at a rate of 3 ° C./minute at 60 ° C., 120 ° C., 200 ° C., 300 ° C., and 400 ° C., respectively, at 60 ° C. for 30 minutes, at 120 ° C. for 30 minutes, The imidation reaction may be advanced by maintaining at 200 ° C. for 60 minutes, at 300 ° C. for 60 minutes, and at 400 ° C. for 10 minutes.

In addition, the present invention provides a positive electrode including the surface-coated positive electrode active material.

The positive electrode can be prepared by conventional methods known in the art. For example, a solvent, a binder, a conductive agent, a filler, and a dispersant may be mixed and stirred in the surface-coated positive electrode active material to prepare a positive electrode active material slurry, which is then coated (coated) on a positive electrode current collector, compressed, and then dried to obtain a positive electrode. Can be prepared.

The positive electrode current collector may be generally used having a thickness of 3 ㎛ to 500 ㎛, any of the positive electrode active material slurry is a metal that can easily adhere as long as it has a high conductivity without causing chemical changes in the battery. Can also be used. Non-limiting examples of the positive electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon or a surface treated with carbon, nickel, titanium, or silver on the surface of aluminum or stainless steel, and an aluminum-cadmium alloy. Can be used. In addition, in order to bond with the positive electrode active material, fine concavo-convex is formed on the surface, or may be used in various forms such as film, sheet, foil, net, porous body, foam, nonwoven fabric.

The solvent for forming the positive electrode includes an organic solvent such as NMP (N-methyl pyrrolidone), DMF (dimethyl formamide), acetone, dimethyl acetamide or water, and these solvents alone or in combination of two or more. Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder, and the conductive agent in consideration of the coating thickness of the slurry and the production yield.

The binder is a component that assists the bonding between the positive electrode active material and the conductive agent and the positive electrode current collector, for example, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene Fluoride (polyvinylidenefluoride), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, Tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid and hydrogens thereof , Polymers substituted with Na or Ca, or Various kinds of binder polymers such as various copolymers can be used.

The conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The filler is a component that suppresses the expansion of the positive electrode and can be used or not as necessary, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. For example, an olefin polymer such as polyethylene or polypropylene may be used. ; It may be a fibrous material such as glass fiber, carbon fiber.

The dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The coating may be performed by a method commonly known in the art, but for example, the positive electrode active material slurry may be distributed on the upper surface of the positive electrode current collector and then uniformly dispersed using a doctor blade or the like. Can be. In addition, the method may be performed by a die casting method, a comma coating method, a screen printing method, or the like.

The drying is not particularly limited, but may be performed within one day in a vacuum oven at 50 to 200 ℃.

Furthermore, the present invention provides a lithium secondary battery including the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode.

The lithium secondary battery according to an embodiment of the present invention comprises a separator and an electrolyte interposed between the positive electrode and the negative electrode, the positive electrode and the negative electrode including a positive electrode active material coated on the surface of the nano-film including polyimide and carbon black It is characterized by including.

In addition, the lithium secondary battery according to an embodiment of the present invention may exhibit excellent life characteristics in both the normal voltage and the high voltage region, and may be particularly excellent in the high temperature and high voltage region. Specifically, the charging voltage of the lithium secondary battery is characterized in that the 4.2V to 5.0V.

The term "general voltage" as used herein refers to the case where the charging voltage of the lithium secondary battery is in the range of 3.0V to less than 4.2V, the term "high voltage" is the region of the charge voltage is 4.2V to 5.0V range It may mean a case, the term "high temperature" may mean a range of 45 to 65 ℃.

The negative electrode is not particularly limited, but may be prepared by applying a negative electrode active material slurry on the upper surface of one side of the negative electrode current collector and then drying the negative electrode active material slurry, in addition to the negative electrode active material, such as a binder, a conductive agent, a filler, and a dispersant as necessary. It may include an additive.

As the negative electrode active material used for the negative electrode according to an embodiment of the present invention, a carbon material, lithium metal, silicon, tin, or the like, in which lithium ions may be occluded and released, may be used. Preferably, a carbon material may be used, and as the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes.

The negative electrode current collector may be the same as or included with the aforementioned positive electrode current collector, and additives such as binders, conductive agents, fillers, and dispersants used in the negative electrode may be the same as those used in the aforementioned positive electrode manufacture. It may be included.

In addition, the separator may be an insulating thin film having high ion permeability and mechanical strength, and may generally have a pore diameter of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm. Such separators include porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers. These may be used alone or in combination thereof, or a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like may be used, but is not limited thereto.

The electrolyte used in the present invention may include a lithium salt commonly used in the electrolyte, and is not particularly limited.

The lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ^{_{(CF 3) 3 PF 3 -}} , (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF ^{_{3 SO 2) 2 N -,}} (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO _{^{2) 3 C -, CF 3}} (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N It may be abnormal.

Examples of the electrolyte used in the present invention include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. no.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be cylindrical, square, pouch type, or coin type using a can.

The lithium secondary battery according to the present invention may not only be used in a battery cell used as a power source for a small device, but also preferably used as a unit battery in a medium-large battery module including a plurality of battery cells.

Preferred examples of the medium-to-large device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Production Example  One

To 20 g of a solution diluted to a concentration of 0.5% by weight of polyamic acid in dimethylacetamide, 0.1 g of carbon black having an iodine value of 200 mg / g, an oil absorption of 150 cc / 100 g, and an average particle diameter of 200 nm was added. The mixture was uniformly dispersed to prepare a mixed solution of polyamic acid and carbon black.

LiNi ₀ as a positive electrode active material in the prepared mixed solution _{. 6} Mn _{0 . 2} Co _{0 .} 20 g of ₂ O ₂ particles were added thereto, followed by stirring using a high speed stirrer for 1 hour. The positive electrode active material coated on the surface of the film containing polyamic acid and carbon black was prepared by increasing the temperature to the boiling point of the solvent while evaporating the solvent while evaporating the solvent.

The cathode active material coated on the surface of the film containing the polyamic acid and carbon black prepared above was heated to 60 ° C., 120 ° C., 200 ° C., 300 ° C., and 400 ° C. at a rate of 3 ° C./min, respectively, at 60 ° C. for 30 minutes. , 30 minutes at 120 ° C, 60 minutes at 200 ° C, 60 minutes at 300 ° C, and 10 minutes at 400 ° C to proceed with the imidization reaction. LiNi ₀ coated on the surface of the nano-film including the polyimide and carbon black as the imidization reaction is completed _{. 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared. At this time, the polyimide and carbon black in the prepared nano-film showed a weight ratio of 1: 0.5.

Production Example  2

LiNi ₀ coated on the surface of the nano-film including polyimide and carbon black by the same method as in Preparation Example 1, except that the carbon black with iodine value of 400 mg / 100 g instead of 200 mg / g _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ A positive electrode active material was prepared.

Production Example  3

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 300 mg / g and an oil absorption number of 100 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

Production Example  4

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 300 mg / g and an oil absorption number of 200 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

Production Example  5

Including the polyimide and carbon black through the same method as in Preparation Example 1, except that the amount of polyamic acid and carbon black added so that the polyimide and carbon black have a weight ratio of 1: 5 in the final nano-film prepared. LiNi ₀ coated on the surface _{. 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  One

LiNi ₀ without surface coating _{. 6} Mn _{0 . 2} Co _{0 . 2} 0 ₂ was used.

compare Production Example  2

Except that carbon black was not added in Preparation Example 1, LiNi _{0. The} surface coating of the polyimide was carried out in the same manner as in Preparation Example 1 _{. 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  3

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 150 mg / g and an oil absorption number of 150 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  4

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 450 mg / g and an oil absorption number of 150 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  5

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 300 mg / g and an oil absorption number of 50 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  6

LiNi coated on the surface of the nano-film including polyimide and carbon black by the same method as Preparation Example 1 except that carbon black having an iodine value of 300 mg / g and an oil absorption number of 250 cc / 100 g was used. _{0 . 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  7

Including the polyimide and carbon black through the same method as in Preparation Example 1, except that the amount of polyamic acid and carbon black added so that the polyimide and carbon black have a weight ratio of 1: 0.1 in the final nano-film prepared LiNi ₀ coated on the surface _{. 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

compare Production Example  8

Polyimide and carbon black were included in the same manner as in Preparation Example 1, except that the amount of polyamic acid and carbon black added so that the polyimide and carbon black had a weight ratio of 1:15 in the finally prepared nanofilm. LiNi ₀ coated on the surface _{. 6} Mn _{0 . 2} Co _{0 . A 2} 0 ₂ positive electrode active material was prepared.

Example  One

Anode manufacturing

Surface-coated LiNi ₀ prepared in Preparation Example 1 _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ positive electrode active material, carbon black as a conductive agent, polyvinylidene fluoride (PVdF) as a binder is mixed in a weight ratio of 95: 3: 2, and N-methyl-2-pyrrolidone (NMP) solvent It was added to to prepare a positive electrode active material slurry. The positive electrode active material slurry is applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and dried at 130 ° C. for 2 hours to prepare a positive electrode, followed by roll press to prepare a positive electrode. It was.

Cathode manufacturing

Lithium metal foil was used as the negative electrode.

Manufacture of electrolyte

1 M LiPF ₆ non-aqueous electrolyte was prepared by adding LiPF ₆ to a non-aqueous electrolyte solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1: 2 as an electrolyte.

Lithium Secondary Battery Manufacturing

The prepared positive electrode and the negative electrode were made of polyethylene separator (Donensa, F2OBHE, thickness = 20 μm), and a mixed separator of an electrolyte solution and a polypropylene was interposed, and then a polymer battery was manufactured by a conventional method. Injecting a lithium secondary battery of the coin cell type was prepared.

Example  2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Preparation Example 2 was used instead of the cathode active material prepared in Preparation Example 1.

Example  3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Preparation Example 3 was used instead of the cathode active material prepared in Preparation Example 1.

Example  4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Preparation Example 4 was used instead of the cathode active material prepared in Preparation Example 1.

Example  5

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Preparation Example 5 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 1 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 2 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 3 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  4

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 4 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  5

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 5 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  6

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 6 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  7

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 7 was used instead of the cathode active material prepared in Preparation Example 1.

Comparative example  8

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the cathode active material prepared in Comparative Preparation Example 8 was used instead of the cathode active material prepared in Preparation Example 1.

Experimental Example  One: SEM  Micrograph

Morphology of the positive electrode active materials prepared in Preparation Example 1 and Comparative Preparation Examples 1 and 2 were analyzed using an electron microscope (FE-SEM). The results are shown in FIGS. 1 to 3, respectively.

Specifically, Figure 1 is LiNi ₀ coated on the surface of the nano-film including the polyimide and carbon black prepared in Example 1 of the present invention _{. 6} Mn _{0 . 2} Co _{0 .} As a result of observing the surface of the ₂ O ₂ particles, the coated LiNi _{0 . 6} Mn _{0 . 2} Co _{0 .} It can be seen that a nanofilm having a thickness of several nanometers in which polyimide and carbon black are well dispersed is formed on the surface of the ₂ O ₂ particles.

2 is LiNi ₀ of Comparative Preparation Example 1 _{. 6} Mn _{0 . 2} Co _{0 .} Pure LiNi _{0 with 2} O ₂ particles and uncoated on the surface _{. 6} Mn _{0 . 2} Co _{0 . 2} O ₂ particles, FIG. 3 shows LiNi _0. Surface coated with polyimide prepared in Comparative Preparation Example 2 _{. 6} Mn _{0 . 2} Co _{0 . As 2} O ₂ particles, no carbon black was observed.

Experimental Example  2: Charging and discharging  Capacity and Efficiency Characterization

In order to evaluate the charging and discharging capacity and the efficiency characteristic of each lithium secondary battery prepared in Examples 1 to 5 and Comparative Examples 1 to 8, the respective lithium secondary batteries (4.3mAh battery capacity) were 3 to 4.4V at 45 ° C. Charge and discharge (0.5C charge / 1C discharge) was performed in the voltage range of. C-rate is the ratio of the capacity when the battery charged at 0.5C charged at 0.1C and the capacity when discharged at 2C as shown in Equation 1 below.

[Equation 1]

division	First charge capacity (mAh / g)	1st discharge capacity (mAh / g)	First efficiency (%)	C-rate (%)	50th capacity retention rate (%)
Example 1	219	198	90.4	91.3	97
Example 2	220	199	90.5	91.8	97
Example 3	220	199	90.5	91.5	97
Example 4	219	198	90.4	91.4	97
Example 5	220	199	90.5	91.8	97
Comparative Example 1	218	200	91.6	91.2	85
Comparative Example 2	218	196	90.0	88.5	95
Comparative Example 3	219	195	89.0	88.5	85
Comparative Example 4	218	194	89.0	88.7	88
Comparative Example 5	220	195	88.6	90.0	90
Comparative Example 6	219	194	88.6	90.0	90
Comparative Example 7	219	195	89.0	88.7	85
Comparative Example 8	220	190	86.4	88.0	80

As can be seen in Table 1, the lithium secondary batteries of Examples 1 to 5 were similar in the initial charge and discharge capacity compared to the lithium secondary batteries of Comparative Examples 1 to 8, but the rate-rate characteristics (C-rate) and 50 It can be seen that the capacity retention rate is remarkably excellent.

Specifically, when comparing the lithium secondary battery of Example 1 to Example 5, the lithium secondary battery of Example 1 to Example 5 and the lithium secondary battery according to the present invention, which had a surface-coated positive electrode active material is similar but significantly superior 50 times It was confirmed that the capacity retention ratio was compared with Comparative Example 2, which is a lithium secondary battery including a cathode active material coated only with polyimide, and the capacity retention ratio of the 50th time was slightly higher, but the rate-rate characteristic was remarkably excellent.

In addition, the positive electrode active material according to the present invention is compared with the lithium secondary batteries of Comparative Examples 3 to 8, which are coated with polyimide and carbon black, but which are not carbon black according to the present invention or include a positive electrode active material which is out of the mixing ratio. It was confirmed that the lithium secondary batteries of Examples 1 to 5, including the rate-rate characteristics and the 50th capacity retention rate were excellent, in particular, the 50th capacity retention rate was significantly increased.

Therefore, it was confirmed that the lithium secondary batteries of Examples 1 to 5 generally improved the performance of the lithium secondary batteries as compared to Comparative Examples 1 to 8.

Claims (25)

1. Positive electrode active material; And a nano coating comprising polyimide (PI) and carbon black coated on the surface of the positive electrode active material,

   The nano coating is a surface-coated positive electrode active material, characterized in that containing the polyimide and carbon black in a weight ratio of 1: 0.5 to 5.
2. The method according to claim 1,

   The carbon black has a surface coated positive active material, characterized in that the iodine number (iodine number) measured in accordance with ASTM D-1510 is 200 mg / g to 400 mg / g.
3. The method according to claim 1,

   The carbon black has a surface absorption positive electrode active material, characterized in that the oil absorption number (oil absorption number) measured in accordance with ASTM D-2414 is 100 cc / 100 g to 200 cc / 100 g.
4. The method according to claim 1,

   The carbon black is a surface-coated positive electrode active material, characterized in that the surface is hydrophobized.
5. The method according to claim 1,

   The carbon black has a surface-coated positive electrode active material, characterized in that the average particle diameter is less than 1000 nm.
6. The method according to claim 1,

   The thickness of the nano-film is a surface-coated positive electrode active material, characterized in that in the range of 1 nm to 200 nm.
7. The method according to claim 1,

   The content of the carbon black is a surface-coated positive electrode active material, characterized in that 0.05% to 5% by weight relative to the total 100% by weight of the surface-coated positive electrode active material.
8. The method according to claim 1,

   The cathode active material is a surface-coated cathode active material, characterized in that the oxide of Formula 1 to Formula 3, and any one or a mixture of two or more selected from the group consisting of V ₂ O ₅ , TiS, MoS:

   <Formula 1>

   Li _{1 + x} [Ni _a Co _b Mn _c ] O ₂ (−0.5 ≦ x ≦ 0.6, 0 ≦ a, b, c ≦ 1, x + a + b + c = 1);

   <Formula 2>

   LiMn _{2 - x} M _x O ₄ (M = Ni, Co, Fe, P, S, Zr, Ti and Al, at least one element selected from the group consisting of 0 ≦ x ≦ 2);

   <Formula 3>

   Li _{1 + a} Fe _{1 - x} M _x (PO _4-b ) X _b (M = Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y At least one element selected from the group consisting of: X is at least one element selected from the group consisting of F, S, and N, and -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)
9. The method according to claim 8,

   The positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li [Ni _a Co _b Mn _c ] O ₂ (0 <a, b, c ≤ 1, a + b + c = 1) and Surface-coated positive electrode active material, characterized in that any one selected from the group consisting of LiFePO ₄ or a mixture of two or more thereof.
10. Preparing a mixed solution in which carbon black is mixed and dispersed in an organic solvent in which a polyamic acid is diluted;

    Dispersing a positive electrode active material in the mixed solution to form a film including polyamic acid and carbon black on the surface of the positive electrode active material; And

    Imidating the positive electrode active material having the coating formed thereon;

    Method for producing a surface-coated positive electrode active material, characterized in that using the carbon black in an amount of 0.05% to 5% by weight based on 100% by weight of the positive electrode active material.
11. The method according to claim 10,

    The imidation reaction is a method of producing a surface-coated positive electrode active material, characterized in that performed at a rate of 3 ℃ / min at a temperature of 50 to 100 ℃ interval to 300 to 400 ℃.
12. The method according to claim 11,

    The imidation reaction is a method of producing a surface-coated positive electrode active material, characterized in that it further comprises the step of maintaining for 10 to 120 minutes in the range of 300 to 400 ℃ after the elevated temperature.
13. The method according to claim 10,

    The carbon black is a method of producing a surface-coated positive electrode active material, characterized in that the iodine number (iodine number) measured according to ASTM D-1510 is 200 mg / g to 400 mg / g.
14. The method according to claim 10,

    The carbon black is a method of producing a surface-coated positive electrode active material, characterized in that the oil absorption number (oil absorption number) measured in accordance with ASTM D-2414 is 100 cc / 100g to 200 cc / 100 g.
15. The method according to claim 10,

    The carbon black is a method of producing a surface-coated positive electrode active material, characterized in that the surface is hydrophobized.
16. The method according to claim 10,

    Wherein the polyamic acid is used in an amount of 0.1 wt% to 1 wt% based on 100 wt% of the organic solvent.
17. The method according to claim 10,

    The polyamic acid is a method of producing a surface-coated positive electrode active material, characterized in that prepared by reacting the aromatic anhydride and diamine in the same equivalent.
18. The method according to claim 17,

    The aromatic anhydrides are phthalic anhydride, pyromellitic dihydride, 3,3'4,4'-biphenyltetracarboxylic dionhydride, 4'4-oxydiphthalic anhydride, 3,3 ' 4,4'-benzophenonetetracarboxylic dianhydride, trimellitic ethylene glycol, 4,4 '-(4'4-isopropylbiphenoxy) biphthalic unhydride and trimellitic unhydride Method of producing a surface-coated positive electrode active material, characterized in that any one selected from the group consisting of, or a mixture of two or more thereof.
19. The method according to claim 17,

    The diamine is 4,4'-oxydianiline, p-phenyl diamine, 2,2-bis (4- (4-aminophenoxy) -phenyl) propane, p-methylene Dianiline, propyltetramethyldisiloxane, polyaromatic amine, 4,4'-diaminodiphenyl sulfone, 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl and 3, Method for producing a surface-coated positive electrode active material, characterized in that any one selected from the group consisting of 5-diamino-1,2,4-triazole, or a mixture of two or more thereof.
20. The method according to claim 10,

    The polyamic acid is a method of producing a surface-coated positive electrode active material, characterized in that it comprises a four-component polyamic acid.
21. The method of claim 20,

    The four-component polyamic acid is a polyamic acid including pyromellitic dianhydride, biphenyl dianhydride, phenylenediamine and oxydianiline. Method for producing a surface-coated positive electrode active material.
22. The method according to claim 10,

    The organic solvent includes any one selected from the group consisting of cyclohexane, carbon tetrachloride, chloroform, methylene chloride, dimethylformamide, dimethylacetamide and N-methylpyrrolidone or a mixture of two or more thereof. Method for producing a coated positive electrode active material.
23. A positive electrode comprising the surface-coated positive electrode active material according to claim 1.
24. A lithium secondary battery comprising the positive electrode, the negative electrode and the separator interposed between the positive electrode and the negative electrode of claim 23.
25. The method of claim 24,

    The charge voltage of the lithium secondary battery is a lithium secondary battery, characterized in that 4.2V to 5.0V.

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