KR20190137497A - Cathode active material for lithium secondary battery, method of manufacturing the same, cathode for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

A positive electrode active material for a lithium secondary battery comprises: lithium composite transition metal oxide core particles including nickel (Ni), cobalt (Co), and manganese (Mn); and a hydrophobic polymer coating layer formed on a lithium composite transition metal oxide core. The hydrophobic polymer coating layer comprises a hydrophobic polymer consisting of: a first repeating unit derived from a first crosslinking monomer having a trifunctional or higher (meth)acrylate group; and a second repeating unit derived from a second crosslinking monomer comprising at least one selected from the group consisting of a triazine group and a bifunctional or higher thiol group including at least two or more crosslinkable groups.

Description

Cathode active material for lithium secondary battery, manufacturing method thereof, positive electrode for lithium secondary battery and lithium secondary battery comprising same

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

Recently, the market demand for IT electronic devices such as smartphones, tablet PCs, and high-performance notebook PCs is increasing. In addition, as a measure against global warming and resource depletion, the demand for large-capacity power storage devices such as electric vehicles and smart grids has increased greatly, and the demand for secondary batteries is rapidly increasing.

Among them, lithium secondary batteries are the most attracting secondary batteries due to their excellent cycle life characteristics and high energy density. However, as the demand for high output, high capacity, and high stability increases, there is an urgent need for improvement measures for a lithium secondary battery that satisfies this.

Among the methods for implementing a high capacity and high output lithium secondary battery, increasing the operating voltage of the lithium secondary battery is the most efficient and easy method. However, there is a problem that the increase of the operating voltage causes the thermal stability of the battery and degradation of life characteristics. This problem is caused by the interfacial side reaction between the electrolyte and the positive electrode, and this phenomenon is more serious in a high capacity battery. Therefore, in order to develop high capacity and high output lithium secondary batteries, it is essential to develop individual materials such as a cathode, an anode, a separator, and an electrolyte, and to secure an interfacial reaction control and stabilization technology between the electrolyte and the electrode.

In order to solve this problem, the cathode active material is surface-modified with an inorganic oxide coating layer such as SiO ₂ , Al ₂ O ₃ , ZrO ₂ , or AlPO ₄ to control the surface reaction with the electrolyte and improve the performance under high voltage conditions. This has been proposed. However, since the surface modification of the positive electrode active material using the inorganic oxide coating layer has a form in which the coating layer is finely dispersed in the form of nano-sized particles rather than covering the entire surface of the positive electrode active material, the positive electrode active material surface modification effect by the inorganic oxide coating There is a limit that can only be limited.

In addition, in terms of battery performance, the inorganic oxide coating layer is a kind of ion insulating layer which is difficult to move lithium ions, which may cause a decrease in ionic conductivity, and in the manufacturing process such as surface reaction at a high temperature of several hundred degrees or more to form a coating layer. There is difficulty.

Korean Unexamined Patent Publication No. 10-2014-0029301 discloses a positive electrode active material for a nonaqueous electrolyte secondary battery, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery.

Korean Patent Publication No. 10-2014-0029301

One object of the present invention is to form a hydrophobic polymer coating layer on the lithium composite transition metal oxide core particles to suppress electrolyte swelling phenomenon, anode and electrolyte interface side reaction, improve the thermal stability of the active material, high capacity, high voltage, high It is to provide a cathode active material for a lithium secondary battery capable of implementing a lithium secondary battery having stability and high output characteristics, and a method of manufacturing the same.

In addition, another object of the present invention is to provide a lithium secondary battery positive electrode and a lithium secondary battery including the above-described positive electrode active material for lithium secondary batteries.

The present invention is lithium composite transition metal oxide core particles including nickel (Ni), cobalt (Co) and manganese (Mn); And a hydrophobic polymer coating layer formed on the lithium composite transition metal oxide core, wherein the hydrophobic polymer coating layer comprises a first repeating unit derived from a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, and at least two or more It provides a positive electrode active material for a lithium secondary battery comprising a hydrophobic polymer comprising a second repeating unit derived from a triazine group containing a crosslinkable group and a second crosslinking monomer comprising at least one member selected from the group consisting of bifunctional or higher thiol groups. do.

In addition, the present invention provides a second crosslinking comprising at least one member selected from the group consisting of a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, a triazine group containing at least two or more crosslinking groups, and a bifunctional or higher thiol group. Adding monomer and initiator to the solvent and mixing; Adding and mixing lithium composite transition metal oxide core particles to the solvent; And forming a hydrophobic polymer coating layer on the lithium composite transition metal oxide core by crosslinking the first crosslinking monomer and the second crosslinking monomer to provide a method of manufacturing a cathode active material for a lithium secondary battery.

In addition, the present invention provides a cathode for a lithium secondary battery including the cathode active material for a lithium secondary battery described above.

In addition, the present invention provides a lithium secondary battery comprising the positive electrode for a lithium secondary battery described above.

The positive electrode active material for a lithium secondary battery of the present invention includes a hydrophobic polymer coating layer formed on a surface of a lithium composite transition metal oxide core particle and including a hydrophobic polymer including a repeating unit derived from a specific first crosslinking monomer and a second crosslinking monomer. Since the hydrophobic polymer coating layer exhibits hydrophobicity, electrolyte swelling may be reduced on the surface of the active material, and thus side reactions with the electrolyte may be significantly prevented, and thermal stability of the positive electrode active material may be improved. Accordingly, the cathode active material for a lithium secondary battery may implement a lithium secondary battery having excellent life characteristics and thermal stability.

1 is a result of observing a cathode active material for a lithium secondary battery according to Example 1 with a scanning electron microscope.
2 is a result of observing a cathode active material for a lithium secondary battery according to Example 2 with a scanning electron microscope.
3 is a result of observing a cathode active material for a lithium secondary battery according to Comparative Example 1 with a scanning electron microscope.
4 is a result of observing a cathode active material for a lithium secondary battery according to Comparative Example 2 with a scanning electron microscope.
FIG. 5 is a graph illustrating evaluation results of thermal stability of positive electrode active materials for lithium secondary batteries of Example 1 and Comparative Example 1 using differential scanning calorimetry (DSC).

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. Based on the principle that the present invention should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

As used herein, the terms "comprise", "comprise" or "have" are intended to indicate that there is a feature, number, step, component, or combination thereof, that is, one or more other features, It should be understood that it does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

As used herein, "%" means weight percent unless otherwise indicated.

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

Cathode Active Material for Lithium Secondary Battery

The cathode active material for a lithium secondary battery of the present invention includes lithium composite transition metal oxide core particles including nickel (Ni), cobalt (Co), and manganese (Mn); And a hydrophobic polymer coating layer formed on the lithium composite transition metal oxide core, wherein the hydrophobic polymer coating layer comprises a first repeating unit derived from a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, and at least two or more And a hydrophobic polymer comprising a second repeating unit derived from a second crosslinking monomer comprising at least one member selected from the group consisting of a triazine group containing a crosslinkable group and a bifunctional or higher thiol group.

The positive electrode active material for a lithium secondary battery of the present invention is formed on a lithium composite transition metal oxide core particle and includes a hydrophobic polymer coating layer including repeating units derived from the first crosslinking monomer and the second crosslinking monomer. Since the hydrophobic polymer coating layer exhibits hydrophobicity, electrolyte swelling and side reaction with the electrolyte may be significantly prevented on the surface of the active material, and thermal stability of the cathode active material may be improved. Accordingly, the cathode active material for a lithium secondary battery may implement a lithium secondary battery having excellent life characteristics and thermal stability.

The lithium composite transition metal oxide core includes nickel (Ni), cobalt (Co) and manganese (Mn).

The lithium composite transition metal oxide core may have a content of nickel (Ni) of 60 mol% or more in the total transition metal elements contained therein. More preferably, the content of nickel (Ni) in the total metal elements may be 70 mol% or more. As described in the present invention, when a lithium composite transition metal oxide core having a high nickel content of nickel (Ni) of 60 mol% or more in the entire transition metal element is used, it may be possible to secure a higher capacity.

Specifically, the lithium composite transition metal oxide core may be a compound represented by Formula 1 below.

[Formula 1]

Li _{1 + p} [Ni _{1- (x + y + z)} Co _x Mn _y M _z ] O _{2 + q}

In Formula 1, M is at least one element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, Al, Cr, and Mo, -0.1≤p≤0.2, 0 <x≤0.4, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.1, −0.2 ≦ q ≦ 0.2, and 0 <x + y + z ≦ 0.4.

In the lithium composite transition metal oxide core of Chemical Formula 1, Li may be an amount corresponding to 1 + p. p is -0.1≤p≤0.2, specifically -0.05≤p≤0.1, and more specifically -0.05≤p≤0.05. In the above-described range, the output and capacity characteristics of the battery may be improved to a remarkable level.

In the lithium composite transition metal oxide core of Formula 1, Ni may be included as an amount corresponding to 1- (x + y + z), for example, 0.6 ≦ 1- (x + y + z) <1. . When the content of Ni in the lithium composite transition metal oxide core of Formula 1 is 0.6 or more, a sufficient amount of Ni may be secured to contribute to charging and discharging, thereby achieving high capacity. More preferably, Ni may be included as 0.7 ≦ 1- (x + y + z) ≦ 0.99.

In the lithium composite transition metal oxide core of Chemical Formula 1, Co may be included in an amount corresponding to x, that is, 0 <x≤0.4. If the content of Co in the lithium composite transition metal oxide core of Formula 1 exceeds 0.4, there is a fear of an increase in cost. Considering the remarkable effect of improving the capacity characteristics according to the inclusion of Co, Co may be included in a content of 0.05≤x≤0.2 more specifically.

In the lithium composite transition metal oxide core of Formula 1, Mn may improve the stability of the active material, and as a result, may improve the stability of the battery. In consideration of the improvement of lifespan characteristics, Mn may be included in an amount corresponding to y, that is, 0 <y≤0.4. When y in the lithium composite transition metal oxide core of Formula 1 exceeds 0.4, the output and capacity characteristics of the battery may be deteriorated, and Mn may be included in an amount of 0.05 ≦ y ≦ 0.2.

In the lithium composite transition metal oxide core of Chemical Formula 1, M may be a doping element included in the crystal structure of the lithium composite transition metal oxide core, and M may be included in an amount corresponding to z, that is, 0 ≦ z ≦ 0.1. have.

The average particle diameter (D ₅₀ ) of the lithium composite transition metal oxide core may be 1 μm to 30 μm, preferably 3 μm to 20 μm, and the output, capacity characteristics and thermal improvement of the battery described above when in the above range. Stability improvement effect can be implemented preferably.

The hydrophobic polymer coating layer includes a hydrophobic polymer.

The hydrophobic polymer is at least one member selected from the group consisting of a first repeating unit derived from a first crosslinking monomer containing a functional or more (meth) acrylate group, a triazine group including at least two or more crosslinking groups, and a bifunctional or higher thiol group. It includes a second repeating unit derived from a second crosslinking monomer comprising a.

The hydrophobic polymer coating layer includes a hydrophobic polymer including a first repeating unit in a net form serving as a matrix and a second repeating unit providing a hydrophobicity, and thus the hydrophobic polymer coating layer may be hydrophobic in its entirety. have. Accordingly, the hydrophobic polymer coating layer can reduce the swelling phenomenon caused by the electrolyte, and can effectively prevent the side reaction between the active material and the electrolyte. In addition, the hydrophobic polymer coating layer is formed on the lithium composite transition metal oxide core to protect the surface of the active material, thereby ensuring the structural stability and thermal stability of the active material.

In addition, the hydrophobic polymer may include a first crosslinking monomer containing a trifunctional or higher (meth) acrylate group as a crosslinking component, and thus, when crosslinking, the hydrophobic polymer coating layer may have a network. Accordingly, the hydrophobic polymer coating layer is sufficiently implemented in the above-described hydrophobicity, does not reduce the ion conductivity and electron mobility of the active material, and is excellent in the transfer capacity of lithium ions, it can maintain its form even in contact with the organic solvent. Accordingly, the cathode active material for a lithium secondary battery may have an effect of improving the life characteristics due to the above-described thermal stability improvement and prevention of side reactions of the electrolyte, and at the same time, it is possible to implement a cathode and a lithium secondary battery for a lithium secondary battery having a high output and a high capacity.

The first repeating unit may be derived from a first crosslinking monomer including a trifunctional or higher (meth) acrylate group, and specifically, a first crosslinking monomer having a trifunctional or higher (meth) acrylate group and having 10 to 60 carbon atoms. It may be derived from.

More specifically, the first repeating unit is dipentaerythritol hexa (meth) acrylate, pentaerythritol tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tree (meth) ) Acrylate, propoxylated glyceryl tri (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate trimethylolpropane It may be derived from a first crosslinking monomer comprising at least one member selected from the group consisting of tri (meth) acrylate, trimethylolpropane tris (3-mercaptopropionate) and dipentaerythritol penta (meth) acrylate. More specifically, propoxylated trimethylol propane tri (meth) acrylate and ethoxylated trimethyl Derived from a first crosslinking monomer comprising at least one member selected from the group consisting of propanetri (meth) acrylate, trimethylolpropanetri (meth) acrylate and trimethylolpropane tris (3-mercaptopropionate) And even more specifically, may be derived from propoxylated trimethylolpropane tri (meth) acrylate. By using the first repeating unit derived from the first crosslinking monomer, the hydrophobicity of the coating layer can be further improved without lowering the ion conductivity and electron mobility of the hydrophobic polymer coating layer.

The second repeating unit may be derived from a second crosslinking monomer including at least one selected from the group consisting of a triazine group and a bifunctional or higher thiol group including at least two or more crosslinkable groups. The second crosslinking monomer may include two or more crosslinkable groups or functional groups capable of crosslinking with other crosslinking monomers to form a network type hydrophobic polymer coating layer together with the first crosslinking monomer. In addition, when the hydrophobic polymer coating layer is formed by the crosslinking reaction of the second crosslinking monomer, the triazine group or thiol group included in these may preferably contribute to hydrophobicity improvement.

In the second crosslinking monomer comprising a triazine group including the two or more crosslinkable groups, the crosslinkable group may be, for example, an allyl group, an allyloxy group, a ketone group, a combination of two or more thereof, and preferably allyl Group, a ketone group, a combination of two or more thereof, and more preferably an allyl group.

The second crosslinking monomer including a bifunctional thiol group or more may specifically be an aliphatic thiol, an aromatic thiol, or a combination thereof, and preferably an aliphatic thiol in view of easily forming a hydrophobic polymer coating layer having a network. Can be. In addition, the aliphatic thiol and the aromatic thiol are preferably composed of a bifunctional or higher functional thiol group and a hydrocarbon in terms of improving hydrophobicity of the coating layer.

The aliphatic thiol may be an aliphatic thiol having 1 to 30 carbon atoms, specifically methanedithiol, 1,2-ethanedithiol, 1,2-propanedithiol, 1,3-propanedithiol, 1,4-butane Dithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,2-cyclohexanedithiol, 2-methylcyclohexane-2,3-dithiol, these It can be a combination of two or more of.

The aromatic thiol is 1,2-dimercaptobenzene, 1,3-dimercaptobenzene, 1,4-dimercaptobenzene, 1,2-bis (mercaptomethyl) benzene, 1,4-bis (mercaptomethyl) Benzene, 1,2-bis (mercaptoethyl) benzene, 1,4-bis (mercaptoethyl) benzene, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,4-naphthalenedithiol, 1,5-naphthalenedithiol, 2,6-naphthalenedithiol, 2,7-naphthalenedithiol, 2,2'-dimercaptobiphenyl, 4,4'-dimercaptobiphenyl, combinations of two or more thereof Can be.

Specifically, the second repeating unit is triallyl-1,3,5-triazine-2,4,6-trione, 2,4,6-triallyloxy-1,3,5-triazine, 1 An agent comprising at least one member selected from the group consisting of 3,5-triazine-2,4-dione, 1,5-pentanedithiol, 1,6-hexanedithiol, and 1,8-octanedithiol It may be derived from a crosslinking monomer, more specifically, triallyl-1,3,5-triazine-2,4,6-trione, 2,4,6-triallyloxy-1,3, May be derived from a second crosslinking monomer comprising at least one member selected from the group consisting of 5-triazine and 1,3,5-triazine-2,4-dione, and more specifically, triallyl- It may be derived from 1,3,5-triazine-2,4,6-trione. While the aforementioned second crosslinking monomer can be crosslinked to more preferably form a network of the coating layer, the hydrophobicity of the coating layer can be further improved, thereby not only effectively preventing the swelling phenomenon of the electrolyte, but also effectively It is preferable because the interface side reaction can be effectively controlled to improve the stability of the positive electrode active material.

The molar ratio of the first repeating unit and the second repeating unit is not particularly limited, and the molecular weight of the first and second crosslinking monomers forming the first repeating unit and the second repeating unit, the number of functional groups per molecule, and the coating layer In consideration of hydrophobic implementation, the molar ratio of the first repeating unit and the second repeating unit may be determined. For example, the molar ratio of the first and second repeating units may be determined so as to effectively implement the hydrophobicity of the coating layer while at the same time all or most of the functional groups in the first and second crosslinking monomers can be used for crosslinking. Specifically, the hydrophobic polymer coating layer has a molar ratio of 10:90 to 70:30, specifically 15:85 to 60:40, more specifically 20:80 to 50 The hydrophobic polymer may be included in a molar ratio of 50, and when included in the molar ratio described above, the hydrophobic polymer may have excellent lithium ion transfer ability without deterioration of charge mobility and ion conductivity while ensuring an excellent level of hydrophobicity of the coating layer.

The hydrophobic polymer coating layer may have a thickness of 0.001 μm to 0.1 μm, specifically 0.005 μm to 0.05 μm, preferably 0.01 μm to 0.03 μm. When having the above-described thickness range, it is possible to secure the hydrophobicity of the coating layer to an excellent level without excessively lowering the electron transfer resistance, effectively prevent the interfacial side reaction with the electrolyte solution, and can improve the thermal stability of the active material.

The hydrophobic polymer coating layer may be included in an amount of 0.01 parts by weight to 10.0 parts by weight, preferably 0.05 parts by weight to 5 parts by weight, based on 100 parts by weight of the positive electrode active material for a lithium secondary battery. When forming a hydrophobic polymer coating layer in the above-described range, the thermal stability of the active material and the effect of preventing the interfacial side reaction of the electrolyte may be maximized.

The average particle diameter (D ₅₀ ) of the positive electrode active material for the lithium secondary battery may be 1 μm to 35 μm, preferably 3 μm to 21 μm, while improving the capacity characteristics and output characteristics of the positive electrode active material in the above range, It is possible to implement the effect of improving the thermal stability of the above-described active material and preventing the electrolyte interface side reaction at an excellent level.

Manufacturing method of positive electrode active material for lithium secondary battery

In addition, the present invention provides a method for producing a cathode active material for a lithium secondary battery.

Specifically, the method for producing a cathode active material for a lithium secondary battery includes at least one selected from the group consisting of a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, a triazine group containing at least two or more crosslinking groups, and a bifunctional or higher thiol group Adding a second crosslinking monomer and an initiator comprising one kind to a solvent and mixing; Adding and mixing lithium composite transition metal oxide core particles to the solvent; And forming a hydrophobic polymer coating layer on the lithium composite transition metal oxide core by crosslinking the first crosslinking monomer and the second crosslinking monomer.

According to the above-described manufacturing method, it is possible to manufacture the above-described positive electrode active material for a lithium secondary battery, thereby the hydrophobic hydrophobic polymer coating layer having a hydrophobic effect can effectively prevent the interfacial side reaction with the electrolyte solution, and prevent the electrolyte swelling phenomenon, The thermal stability of the active material can be improved. Accordingly, the cathode active material manufactured may have improved lifetime characteristics and thermal stability, and may have high capacity and high output.

In addition, after the first crosslinking monomer and the second crosslinking monomer are mixed, the lithium composite transition metal oxide core particles are mixed together so that the first and second crosslinking monomers are coated or dispersed on the surface of the active material and then crosslinked. Since this is performed, it is possible to form a uniform hydrophobic polymer coating layer.

The type, content and content ratio of the first crosslinking monomer, the second crosslinking monomer and the lithium composite transition metal oxide core are as described above.

The hydrophobic polymer coating layer may have a molar ratio of 10:90 to 70:30, specifically a molar ratio of 15:85 to 60:40, and more specifically 20:80 to 50:50. Can be added. When added in the above-described molar ratio, it is possible to form a hydrophobic polymer coating layer which is excellent in hydrophobicity and effectively prevents an interfacial side reaction with the electrolyte solution without deteriorating charge mobility and ion conductivity.

The initiator may be a photoinitiator or a thermal initiator.

The photoinitiator may be a radical photoinitiator that generates radicals or a cationic photoinitiator that generates cations. Specific examples of the radical photoinitiator include dialkoxy acetophenone, benzilketal, hydroxyalkylphenyl ketone, benzoyl oxime ester or amino ketone. Although these etc. are mentioned, It is not limited to these. The cationic photoinitiator may include, but is not limited to, onium salts such as dialkyliodonium salts and triarylsulfonium salts. In addition, the thermal initiator is a material capable of generating radicals by heat, and specifically, a compound capable of generating radicals at a relatively low temperature of 200 ° C. or less may be used. More specifically, benzoyl peroxide, potassium persulfate, azobisisobutyronitrile, and the like, but are not limited thereto.

The initiator may be included in a catalytic amount in the hydrophobic polymer coating layer.

The solvent is alcohol, such as water (isopropyl alcohol), acetone (aceton), tetrahydrofuran (ttrahydrofuran), cyclohexane (cyclohexane), carbon chloride, chloroform (chloroform) , Methylene chloride, dimethyl formamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrlidone, and the like. Or mixtures of two or more may be used.

The solvent may further include a crosslinking accelerator and / or a coupling agent in addition to the above-described first crosslinking monomer, second crosslinking monomer, and the initiator.

In addition, the crosslinking accelerator is a material that promotes crosslinking of the first and second crosslinking monomers when forming a hydrophobic polymer coating layer, and specifically, diethylene triamine, triethylene tetramine, and diethylamino. Amines such as diethylamino propylamine, xylene diamine, isophorone diamine, or dodecyl succinic anhydride, phthalic anhydride Acid anhydrides, such as these, are mentioned.

The crosslinking accelerator may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total of the first and second crosslinking monomers.

In addition, the coupling agent is a material for increasing adhesion between the core particles and the coating layer, specifically, triethoxysilylpropyl tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl Triethoxysilane, chloropropyl triethoxysilane, vinyl triethoxysilane, methacryloxypropyl triethoxysilane, glycidoxypropyl trie It may be a silane coupling agent such as oxysilane (glycidoxypropyl triethoxysilane), isocyanatopropyl triethoxysilane, cyanatopropyl triethoxysilane and the like.

The coupling agent may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the total of the first and second crosslinking monomers.

The crosslinking reaction may be conventional thermal crosslinking or UV crosslinking, or a combination thereof may be performed. Preferably, the crosslinking reaction may be a thermal crosslinking reaction in that the process is simple and a uniform coating layer may be formed.

When the thermal crosslinking reaction is performed as the crosslinking reaction, it may be performed by heat treatment at 50 ° C to 400 ° C, specifically 60 ° C to 300 ° C, more specifically 80 ° C to 150 ° C. When the heat treatment temperature is in the above range, the hydrophobic polymer coating layer may be uniformly formed.

The time of the crosslinking reaction may be appropriately designed in consideration of the components to be mixed, the content, the manufacturing conditions, the half-life of the initiator, and the like, and 1 to 10 hours, specifically 1 to 7 hours in consideration of sufficient crosslinking reaction and formation of the coating layer. For example, it may be performed for 3 to 7 hours.

Anode for Lithium Secondary Battery

In addition, the present invention provides a lithium secondary battery positive electrode comprising the positive electrode active material for the lithium secondary battery.

Specifically, the positive electrode for a lithium secondary battery is formed on the positive electrode current collector and the positive electrode current collector, and includes a positive electrode active material layer containing the positive electrode active material for the lithium secondary battery.

In the positive electrode for a lithium secondary battery, the positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, and is, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. The surface-treated with carbon, nickel, titanium, silver, etc. can be used for the surface. In addition, the positive electrode current collector may have a thickness of about 3 to 500 μm, and may form fine irregularities on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material or the positive electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The cathode active material layer may include a conductive material and a binder together with the cathode active material for a lithium secondary battery described above.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any conductive material may be used as long as it has electronic conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal 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, or a mixture of two or more kinds thereof may be used. The conductive material may typically be included in an amount of 1 to 30% by weight based on the total weight of the positive electrode active material layer.

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

The positive electrode for a lithium secondary battery may be manufactured according to a conventional positive electrode manufacturing method except for using the positive electrode active material for a lithium secondary battery. Specifically, the composition for forming a cathode active material layer including the cathode active material and optionally, a binder and a conductive material may be coated on a cathode current collector, followed by drying and rolling. In this case, the type and content of the cathode active material, the binder, and the conductive material are as described above.

The solvent may be a solvent generally used in the art, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or acetone. Water, and the like, one of these alone or a mixture of two or more thereof may be used. The amount of the solvent is sufficient to dissolve or disperse the positive electrode active material, the conductive material, and the binder in consideration of the coating thickness of the slurry and the production yield, and to have a viscosity that can exhibit excellent thickness uniformity during application for the production of the positive electrode. Do.

In another method, the lithium secondary battery positive electrode may be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling from the support onto a positive electrode current collector.

Lithium secondary battery

In addition, the present invention provides an electrochemical device including the positive electrode for a lithium secondary battery. The electrochemical device may be specifically a battery or a capacitor, and more specifically, may be a lithium secondary battery.

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

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

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on a surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy and the like can be used. In addition, the negative electrode current collector may have a thickness of about 3 to 500 μm, and like the positive electrode current collector, fine concavities and convexities may be formed on the surface of the current collector to enhance the bonding force of the negative electrode active material. For example, it can be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven body.

The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer is coated with a negative electrode active material, and optionally a composition for forming a negative electrode including a binder and a conductive material on a negative electrode current collector and dried, or casting the negative electrode forming composition on a separate support It can also be produced by laminating a film obtained by peeling from this support onto a negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; Metallic compounds capable of alloying 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 thereof may be used. In addition, a metal lithium thin film may be used as the anode active material. As the carbon material, both low crystalline carbon and high crystalline carbon can be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is amorphous, plate, scaly, spherical or fibrous natural graphite or artificial graphite, Kish graphite (Kish) 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 typical.

In addition, the binder and the conductive material may be the same as described above in the positive electrode.

On the other hand, in the lithium secondary battery, the separator is to separate the negative electrode and the positive electrode and to provide a passage for the movement of lithium ions, if it is usually used as a separator in a lithium secondary battery can be used without particular limitation, in particular for ion transfer of the electrolyte It is desirable to have a low resistance against the electrolyte and excellent electrolytic solution-moisture capability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer, or the like Laminate structures of two or more layers may be used. In addition, conventional porous nonwoven fabrics such as nonwoven fabrics made of high melting point 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 optionally used as a single layer or a 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, a molten inorganic electrolyte, and the like, which can be used in manufacturing a lithium secondary battery. It doesn't happen.

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 may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, Carbonate solvents such as PC); Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or an ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolanes may be used. Of these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can improve the charge and discharge performance of a battery, and low viscosity linear carbonate compounds ( For example, a mixture of ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate and the like is more preferable. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of about 1: 1 to about 1: 9, so that 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 , LiAl0 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 and the like can 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 included in the above range, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, tri, etc. for the purpose of improving battery life characteristics, reducing battery capacity, and improving discharge capacity of the battery. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate 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 included. In this case, the additive may be included in 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 active material for a lithium secondary battery according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, laptop computers, digital cameras, and hybrids It is useful in the field of electric vehicles such as a hybrid electric vehicle (HEV).

Accordingly, the present invention provides a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack is a power tool (Power Tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Example 1

Propoxylatedtrimethylolpropanetri (meth) acrylate (TPPTA) as the first crosslinking monomer and triallyl-1,3,5-triazine-2,4,6-trione (TATATO) as the second crosslinking monomer and Benzoyl peroxide (BPO) as a thermal initiator was added to the isopropyl alcohol solvent and mixed. At this time, the first crosslinking monomer and the second crosslinking monomer were added in a 25:75 molar ratio.

A lithium composite transition metal oxide core Li [Ni _0.8 Co _0.09 Mn _0.09 Al _0.02 ] O ₂ (average particle diameter 15 μm) was added to the solvent and mixed. Thereafter, the solvent was removed using a filter paper to prepare a lithium composite transition metal oxide core and a mixture of the aforementioned crosslinking monomers.

Thereafter, the mixture was stored in an oven at 90 ° C. for 3 hours to thermally crosslink the first and second crosslinking monomers, and then to wash away the unreacted crosslinking monomers and thermal initiators that may remain with isopropyl alcohol. A cathode active material for a lithium secondary battery in which a hydrophobic polymer coating layer was formed on an oxide core was prepared.

At this time, the thickness of the hydrophobic polymer coating layer was 0.020㎛, the hydrophobic polymer coating layer was included in 0.5 parts by weight based on 100 parts by weight of the positive electrode active material for the lithium secondary battery.

Example 2

A positive active material for a lithium secondary battery was manufactured in the same manner as in Example 1 except that ethoxylated trimethylolpropane tri (meth) acrylate was used as the first crosslinking monomer.

Comparative Example 1

A positive active material for a lithium secondary battery of Comparative Example 1 was prepared using only the lithium composite transition metal oxide core of Example 1 without forming a hydrophobic polymer coating layer.

Comparative Example 2

A cathode active material for a lithium secondary battery was manufactured in the same manner as in Example 1 except that the polymer coating layer was formed on the lithium composite transition metal oxide core using acrylonitrile as the second crosslinking monomer.

Experimental Example

Experimental Example 1 Observation of Scanning Electron Microscopy

The results of observing the positive electrode active materials for lithium secondary batteries of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 with a scanning electron microscope are shown in FIGS. 1 to 4, respectively.

As a result, it can be seen that in Examples 1, 2 and Comparative Example 2, the first and second crosslinking monomers are crosslinked to form a polymer coating layer on the core.

Experimental Example 2: Evaluation of Thermal Stability

A cathode active material was prepared by mixing a cathode active material for a lithium secondary battery of Examples and Comparative Examples, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 97: 1: 2, thereby preparing an aluminum current collector. It coated on one surface, dried at 120 ° C. for 12 hours, and rolled to prepare a cathode for a lithium secondary battery.

Lithium metal was used as the negative electrode.

An electrode assembly is manufactured by interposing a separator of porous polyethylene between the anode and the cathode manufactured as described above, and the electrode assembly is placed in a case, and then an electrolyte is injected into the case to inject a coin-type half-cell. ) Was prepared. In this case, the electrolyte solution was prepared by dissolving LiPF ₆ in an organic solvent (ethyl carbonate (EC): diethyl carbonate (DEC) in a volume ratio of 1: 1) to a concentration of 1M.

Then, after the lithium secondary battery according to the Examples and Comparative Examples 0.2C charged and discharged once, 0.5C charged to 4.25V cut off, the battery was disassembled and the lithium secondary battery positive electrode 5mg in the DSC measurement cell, new 5 mg of electrolyte was added, and the thermal stability was evaluated by differential scanning calorimetry (DSC) at a temperature increase rate of 10 ° C./min in the range of 30 to 300 ° C., and the results are shown in FIG. 5 and Table 1 below. .

DSC Main peak (℃) Calorific value (J / g) Example 1 234.27 280.4 Example 2 232.31 320.3 Comparative Example 1 232.48 411.5 Comparative Example 2 232.56 390

Referring to Table 1, it can be seen that the positive electrode active material for lithium secondary batteries of the embodiments containing the hydrophobic polymer coating layer according to the present invention has a lower calorific value than the comparative examples, and the hydrophobic polymer coating layer has a side reaction between the active material and the electrolyte interface. It is thought to be due to improved thermal stability. Particularly, in Example 1, the calorific value is lower than that of Example 2, and the DSC main peak is slightly increased, which indicates that the hydrophobicity of the hydrophobic polymer coating layer of Example 1 is higher than that of Example 2, resulting in thermal stability. It is understandable because of the improvements.

Experimental Example 3: Evaluation of Cycle Characteristics

The cycle characteristics of the coin half cells of the examples and comparative examples prepared in Experimental Example 2 were evaluated.

The lithium secondary batteries of Examples and Comparative Examples were charged / discharged 80 times at a temperature of 45 ° C. under a condition of 0.33C within a range of 2.5 to 4.25V driving voltage. The cycle capacity retention, which is the ratio of the discharge capacity at the 80th cycle to the initial capacity after 80 charge / discharge cycles at room temperature, was measured and shown in Table 2 below.

80 cycle capacity retention at 45 ° C Example 1 75 Example 2 71 Comparative Example 1 5 Comparative Example 2 45

Referring to Table 2, the positive electrode active material for lithium secondary batteries of the embodiments containing the hydrophobic polymer coating layer according to the present invention can be judged to show an excellent capacity retention compared to the comparative examples, according to the embodiment of the positive electrode for lithium secondary batteries It can be seen that the hydrophobic polymer coating layer of the active material prevents side reaction with the electrolyte and improves the structural stability of the active material, thereby improving the life characteristics of the battery.

Claims (12)

Lithium composite transition metal oxide core particles including nickel (Ni), cobalt (Co) and manganese (Mn); And
It comprises a hydrophobic polymer coating layer formed on the lithium composite transition metal oxide core,
The hydrophobic polymer coating layer is at least selected from the group consisting of a first repeating unit derived from a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, and a triazine group and a bifunctional or higher thiol group including at least two or more crosslinking groups The positive electrode active material for lithium secondary batteries containing the hydrophobic polymer containing the 2nd repeating unit derived from the 2nd crosslinking monomer containing 1 type.
The method of claim 1, wherein the first crosslinking monomer is dipentaerythritol hexa (meth) acrylate, pentaerythritol tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tree ( Meth) acrylate, propoxylated glyceryl tri (meth) acrylate, ethoxylated pentaerythritol tetra (meth) acrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate trimethylol A positive active material for a lithium secondary battery, comprising at least one selected from the group consisting of propane tri (meth) acrylate, trimethylolpropane tris (3-mercaptopropionate), and dipentaerythritol penta (meth) acrylate.
The method of claim 1, wherein the second crosslinking monomer is triallyl-1,3,5-triazine-2,4,6-trione, 2,4,6-triallyloxy-1,3,5-triazine , At least one selected from the group consisting of 1,3,5-triazine-2,4-dione, 1,5-pentanedithiol, 1,6-hexanedithiol and 1,8-octanedithiol A positive electrode active material for lithium secondary batteries.
The method according to claim 1,
The hydrophobic polymer coating layer includes a hydrophobic polymer including the first repeating unit and the second repeating unit in a molar ratio of 10:90 to 70:30, the cathode active material for a lithium secondary battery.
The method according to claim 1,
The hydrophobic polymer coating layer is included in 0.01 parts by weight to 10.0 parts by weight based on 100 parts by weight of the positive electrode active material for lithium secondary batteries, positive electrode active material for lithium secondary batteries.
The method according to claim 1,
The hydrophobic polymer coating layer has a thickness of 0.001 μm to 0.1 μm.
The method according to claim 1,
The lithium composite transition metal oxide core is a compound represented by the following Chemical Formula 1, a lithium secondary battery positive electrode active material:
[Formula 1]
Li _{1 + p} [Ni _{1- (x + y + z)} Co _x Mn _y M _z ] O _{2 + q}
In Formula 1, M is at least one element selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, Al, Cr, and Mo, -0.1≤p≤0.2, 0 <x≤0.4, 0 <y ≦ 0.4, 0 ≦ z ≦ 0.1, −0.2 ≦ q ≦ 0.2, and 0 <x + y + z ≦ 0.4.
Solvent a second crosslinking monomer and an initiator comprising at least one member selected from the group consisting of a first crosslinking monomer comprising a trifunctional or higher (meth) acrylate group, a triazine group containing at least two or more crosslinking groups, and a bifunctional or higher thiol group Adding to and mixing;
Adding and mixing lithium composite transition metal oxide core particles to the solvent; And
And forming a hydrophobic polymer coating layer on the lithium composite transition metal oxide core by crosslinking the first crosslinking monomer and the second crosslinking monomer.
The method according to claim 8, wherein the first crosslinking monomer and the second crosslinking monomer are added in a molar ratio of 10:90 to 70:30.
The method of claim 8, wherein the crosslinking reaction is performed by a heat treatment at 50 ° C. to 400 ° C. 10.
A cathode for a lithium secondary battery comprising the cathode active material for lithium secondary battery according to claim 1.
Lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 11.

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