KR20240094576A - Binder for secondary battery and secondary battery comprising the same - Google Patents

Abstract

The binder for a secondary battery according to exemplary embodiments may include an acrylic resin polymerized with a (meth)acrylate monomer of a specific structure. Accordingly, a lithium secondary battery with improved adhesion between the electrode active material and the electrode current collector and improved initial charge/discharge efficiency and capacity maintenance rate can be provided.

Description

Binder for secondary batteries and secondary batteries containing the same {BINDER FOR SECONDARY BATTERY AND SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a binder for secondary batteries and a secondary battery containing the same. More specifically, it relates to a binder for secondary batteries containing a polymer compound and a secondary battery containing the same.

Secondary batteries are batteries that can be repeatedly charged and discharged, and have been widely applied to portable electronic communication devices such as camcorders, mobile phones, and laptop PCs with the development of the information and communication and display industries. Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction. It has been actively developed and applied in this regard.

A lithium secondary battery may include, for example, an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an exterior material in the form of, for example, a pouch that accommodates the electrode assembly and the electrolyte.

Generally, electrodes for lithium secondary batteries are manufactured by applying an electrode mixture containing an electrode active material, a binder, and a conductive material to an electrode current collector. A binder is used to secure adhesion or cohesion between electrode active materials and between electrode active materials and electrode current collectors.

Conventionally, materials used as binders have poor binding properties to current collectors or active materials, making it difficult to demonstrate their effectiveness as binders unless used in large quantities. For this reason, there is a problem in that the content of the electrode active material and conductive material in the electrode cannot be increased, thereby lowering the capacity and electronic conductivity of the electrode.

For example, binders such as styrene-butadiene-based polymers and styrene-acrylate-based polymers lack high-temperature stability and adhesive strength and may cause side reactions with the electrolyte solution. For example, Korean Patent No. 10-1320381 discloses a secondary battery comprising CMC and SBR that satisfy certain physical property conditions as a negative water-based binder, but fails to overcome the above-mentioned limitations.

Korean Patent No. 10-1320381

One object of the present invention is to provide a binder for secondary batteries with excellent stability and adhesion.

One object of the present invention is to provide a secondary battery electrode and a lithium secondary battery including a secondary battery binder with excellent stability and adhesion.

The binder for secondary batteries according to exemplary embodiments may include an acrylic resin polymerized with a (meth)acrylate monomer represented by Structural Formula 1 below.

[Structural Formula 1]

In Structural Formula 1, R ₁ may be a hydrogen atom or a methyl group, R ₂ may be a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and L may be an alkylene group having 1 to 10 carbon atoms.

In some embodiments, in Structural Formula 1, R ₁ and R ₂ are each independently a hydrogen atom or a methyl group, and L may be an alkylene group having 1 to 4 carbon atoms.

In some embodiments, the acrylic resin is i) 30 to 90% by weight of a (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms, ii) 1 selected from the group consisting of an unsaturated carboxylic acid and an unsaturated monomer containing a hydroxyl group. It may be polymerized including 0.5 to 10% by weight of one or more monomers, and iii) 1 to 20% by weight of a (meth)acrylate monomer represented by Structural Formula 1 above.

In some embodiments, the monomer of i) is methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isopropyl (meth)acrylate, and isopropyl (meth)acrylate. Butyl acrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl acrylate, isooctyl acrylate, octyl methacrylate, 2-ethylhexyl (meth)acrylate, isodecyl acrylate , decyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, and lauryl (meth)acrylate.

In some embodiments, the monomer of ii) is acrylic acid, itaconic acid, maleic anhydride, fumaric acid, crotanic methacrylic acid, ethyl methacrylic acid, hydroxymethyl (meth)acrylate, and hydroxyethyl (meth)acrylic. Latex, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxylauryl (meth)acrylate and hydroxyl. It may include one or more selected from the group consisting of propylene glycol (meth)acrylate.

In some embodiments, the acrylic resin may be polymerized by further including iv) one or more monomers selected from the group consisting of styrene, unsaturated acetate, and unsaturated nitrile.

In some embodiments, the monomer of iv) is selected from the group consisting of vinyl acetate, styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, divinylbenzene, acrylonitrile, and methacrylonitrile. It may contain one or more things.

In some embodiments, the acrylic resin may be polymerized by further including an epoxy group-containing unsaturated monomer.

In some embodiments, the binder may further include one or more compounds selected from the group consisting of melamine, isocyanate, aldehyde, amine, and diazonium salt.

In some embodiments, the compound may be included in an amount of 0.1 mol or less relative to 1 mole of the (meth)acrylate monomer represented by Structural Formula 1.

According to exemplary embodiments, the electrode mixture for a secondary battery may include the binder and electrode active material for a secondary battery described above.

In some embodiments, the binder may be included in an amount of 1 to 10% by weight based on the total weight of the electrode mixture.

According to exemplary embodiments, an electrode for a secondary battery may include a current collector and a layer including the above-described electrode mixture formed on at least one surface of the current collector.

According to example embodiments, a lithium secondary battery may include the electrode described above.

According to exemplary embodiments, the binder for a secondary battery may include an acrylic resin in which a (meth)acrylate monomer represented by Structural Formula 1 is polymerized with other monomers. Accordingly, a lithium secondary battery with improved adhesion between the electrode active material and the electrode current collector and improved lifespan and capacity characteristics can be provided.

1 is a schematic plan view showing a secondary battery according to example embodiments.
Figure 2 is a schematic cross-sectional view showing a secondary battery according to example embodiments.

According to embodiments of the present invention, a binder for a secondary battery containing an acrylic resin polymerized with a (meth)acrylate monomer represented by a specific structural formula can be provided.

In addition, a secondary battery electrode and a lithium secondary battery containing the binder for a secondary battery, improved adhesion between the electrode active material and the electrode current collector, and improved initial charge/discharge capacity and cycle characteristics may be provided.

In some embodiments, the binder for secondary batteries can be used in a process for manufacturing electrodes by a dry method in addition to a slurry-based wet method, so a heat treatment process is not required and an organic solvent may not be used. Therefore, the process in manufacturing electrodes can be shortened, costs can be reduced, and the occurrence of environmental pollution can be reduced.

In this specification, the term “(meth)acrylate” may be a general term for acrylate and methacrylate.

Hereinafter, the present invention will be described in detail.

<Binder for secondary batteries>

A binder for secondary batteries (hereinafter abbreviated as binder) according to exemplary embodiments may include an acrylic resin polymerized with a (meth)acrylate monomer represented by Structural Formula 1 below.

[Structural Formula 1]

In Structural Formula 1, R ₁ may be a hydrogen atom or a methyl group, R ₂ may be a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and L may be an alkylene group having 1 to 10 carbon atoms.

For example, R ₂ may be a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, a hydrogen atom, a methyl group or an ethyl group, or a hydrogen atom or a methyl group.

For example, L is an alkylene group with 1 to 10 carbon atoms, an alkylene group with 1 to 8 carbon atoms, an alkylene group with 1 to 7 carbon atoms, an alkylene group with 1 to 5 carbon atoms, an alkylene group with 1 to 4 carbon atoms, or an alkylene group with 1 to 4 carbon atoms. It may be an alkylene group of 3. Here, the alkylene group may be straight chain or branched, and may be substituted or unsubstituted.

In some embodiments, in Structural Formula 1, R ₁ and R ₂ are each independently a hydrogen atom or a methyl group, and L may be an alkylene group having 1 to 4 carbon atoms.

For example, L may be an ethylene group or a branched-chain butylene group.

In some embodiments, the (meth)acrylate monomer represented by Structural Formula 1 may include at least one of the compounds represented by Formulas 1-1 to 1-4 below.

[Formula 1-1]

[Formula 1-2]

[Formula 1-3]

[Formula 1-4]

The (meth)acrylate monomer represented by Structural Formula 1 has a cyano acetate functional group and is an ion conductive monomer capable of moving ions from one side to the other, so it may have high ionic conductivity. Therefore, the binder formed from the binder has high ionic conductivity, and the lithium secondary battery manufactured using the binder can improve the efficiency and lifespan of the battery because lithium ions can move smoothly.

In some embodiments, the (meth)acrylate monomer represented by Structural Formula 1 may be included in an amount of 1 to 20% by weight based on the total weight of the acrylic resin. Within the above range, the ionic conductivity of the binder is high, and the efficiency and lifespan characteristics of the lithium secondary battery can be improved.

In some embodiments, the acrylic resin is i) 30 to 90% by weight of a (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms, ii) 1 selected from the group consisting of an unsaturated carboxylic acid and an unsaturated monomer containing a hydroxyl group. It may be polymerized including 0.5 to 10% by weight of one or more monomers, and iii) 1 to 20% by weight of a (meth)acrylate monomer represented by Structural Formula 1 above.

The monomers may be added and polymerized in a mixed state, or may be added sequentially and polymerized.

In some embodiments, the (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms is methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and isopropyl (meth)acrylate. Latex, butyl (meth)acrylate, isobutyl acrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl acrylate, isooctyl acrylate, octyl methacrylate, 2-ethylhexyl It may include one or more selected from the group consisting of (meth)acrylate, isodecyl acrylate, decyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, and lauryl (meth)acrylate. .

For example, the alkyl group of the (meth)acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms may have 1 to 14 carbon atoms, and preferably 2 to 14 carbon atoms. Within the above range, polymerization stability and binding properties of the acrylic resin can be improved.

For example, the (meth)acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms may be included in an amount of 30 to 90% by weight based on the total weight of the acrylic resin. Within the above range, the flexibility of the electrode active material to the electrode current collector can be improved, and the stability of the acrylic resin can be improved.

In some embodiments, the monomer of ii) is acrylic acid, itaconic acid, maleic anhydride, fumaric acid, crotanic methacrylic acid, ethyl methacrylic acid, hydroxymethyl (meth)acrylate, and hydroxyethyl (meth)acrylic. Latex, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxylauryl (meth)acrylate and hydroxyl. It may include one or more selected from the group consisting of propylene glycol (meth)acrylate.

For example, the monomer of ii) may be included in an amount of 0.5 to 10% by weight based on the total weight of the acrylic resin. Within the above range, the binding property of the electrode active material to the electrode current collector may be improved, and the stability of the acrylic resin may be improved.

In some embodiments, the acrylic resin may be polymerized by further including iv) one or more monomers selected from the group consisting of styrene, unsaturated acetate, and unsaturated nitrile.

In some embodiments, the monomer of iv) is selected from the group consisting of vinyl acetate, styrene, α-methylstyrene, β-methylstyrene, p-t-butylstyrene, divinylbenzene, acrylonitrile, and methacrylonitrile. It may contain one or more things.

For example, the monomer of iv) may be included in an amount of 5 to 55% by weight, preferably 7 to 45% by weight, based on the total weight of the acrylic resin. Within the above range, the binding property of the electrode active material to the electrode current collector may be improved, and the stability of the acrylic resin may be improved.

In some embodiments, the acrylic resin may be polymerized by further including an epoxy group-containing unsaturated monomer. For example, the epoxy group-containing unsaturated monomers include glycidyl (meth)acrylate, alphamethylglycidyl (meth)acrylate, allyl glycidyl ether, oxocyclohexyl (meth)acrylate, and 3,4-epoxy. It may include one or more selected from the group consisting of cyclohexylmethyl (meth)acrylate.

For example, the epoxy group-containing unsaturated monomer may be included in an amount of 0.1 to 3% by weight based on the total weight of the acrylic resin, and within this range, the polymerization stability of the acrylic resin may be improved.

In some embodiments, the binder may further include one or more compounds selected from the group consisting of melamine, isocyanate, aldehyde, amine, and diazonium salt.

For example, the (meth)acrylate monomer represented by Structural Formula 1 can be crosslinked alone, so a separate crosslinking agent is not needed for polymerization of acrylic resin. However, by including the above compound, battery swelling can be reduced by securing electrolyte resistance through a post-crosslinking reaction after polymerization of the acrylic resin.

In some embodiments, the compound may be included in an amount of 0.1 mol or less relative to 1 mole of the (meth)acrylate monomer represented by Structural Formula 1. Within the above range, the degree of crosslinking can be made appropriate and the adhesion between the electrode active material and the electrode current collector can be improved.

For example, the isocyanate compound may include one or more selected from the group consisting of aromatic polyisocyanate, aliphatic polyisocyanate, araliphatic polyisocyanate, and cycloaliphatic polyisocyanate.

Examples of the aromatic polyisocyanate include 1,3-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and 2,4-tolylene. Diisocyanate, 2,6-tolylene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-triisocyanate toluene, 1,3,5-triisocyanate benzene, dianisidine diisocyanate, 4,4' -Diphenyl ether diisocyanate, 4,4',4"-triphenylmethane triisocyanate, xylylene diisocyanate, etc. are mentioned.

Examples of the aliphatic polyisocyanate include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3- Butylene diisocyanate, dodecamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, etc. are mentioned.

Examples of the aromatic aliphatic polyisocyanate include ω, ω'-diisocyanate-1,3-dimethylbenzene, ω, ω'-diisocyanate-1,4-dimethylbenzene, ω, ω'-diisocyanate-1,4- Diethylbenzene, 1,4-tetramethylxylylene diisocyanate, 1,3-tetramethylxylylene diisocyanate, etc. are mentioned.

Examples of the cycloaliphatic polyisocyanate include 3-isocyanate methyl-3,5,5-trimethylcyclohexylisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, and 1,4-cyclohexane diisocyanate. , methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexylisocyanate), 1,4-bis(isocyanatemethyl)cyclohexane, etc. You can.

For example, the aldehyde may be at least one of formalin and paraformaldehyde.

For example, the amine may be one or more selected from the group consisting of aliphatic amines, araliphatic amines, and cycloaliphatic amines.

In some embodiments, the binder for secondary batteries is styrene-butadiene rubber (SBR), polyvinyl alcohol (poly vinyl alcohol), poly acrylic acid (PAA), carboxymethyl cellulose, It may further include at least one selected from the group consisting of CMC), hydroxypropylcellulose, and diacetylcellulose. Preferably, it may contain styrene-butadiene rubber or polyacrylic acid for compatibility with graphite-based active materials.

Accordingly, the mixing properties of the binder for secondary batteries can be improved, and the dispersibility and coating properties within the electrode mixture can be improved. Accordingly, the initial efficiency, charge/discharge capacity, and high temperature stability of the secondary battery electrode containing the binder can be improved.

In some embodiments, the polymerization reaction of the monomers to produce the acrylic resin may be emulsion polymerization in which the heat of reaction can be easily controlled.

For example, after adding water, electrolyte, and surfactant to the reactor, the temperature is raised to 80°C to remove oxygen and dissolve the initiator to prepare a solution. Separately, an emulsion can be prepared by adding water, electrolyte, and surfactant to the mixture of the above monomers.

An acrylic resin can be prepared by continuously adding the emulsion and initiator to the solution, raising the temperature to 80°C, and then cooling to room temperature. The pH of the acrylic resin can be adjusted to 6 to 9, preferably 7 to 8.

For example, the initiator may include a water-soluble polymerization initiator such as ammonium or alkali metal persulfate, hydrogen peroxide, peroxide, and hydroperoxide.

For example, one or more reducing agents may be used together to perform an emulsion polymerization reaction at low temperature. Examples of the reducing agent include sodium bisulfite, sodium metabisulfite, sodium hydrosulfite, sodium thiosulfate, sodium formaldehyde sulfoxylate, ascorbic acid, etc.

For example, the temperature of the polymerization reaction may be 0 to 100°C, preferably 40 to 90°C.

For example, the electrolyte can adjust pH and provide stability to the acrylic resin being polymerized. The electrolyte may include one or more selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium phosphate, sodium sulfate, and sodium chloride.

For example, the surfactant may be used to generate initial particles during the polymerization reaction, control the size of the generated particles, and stabilize the particles. The surfactant consists of a hydrophilic group and a lipophilic group, and may include at least one of an anionic surfactant, a cationic surfactant, and a nonionic surfactant.

For example, the acidity (pH) of the acrylic resin can be adjusted by an alkaline substance. Examples of the alkaline substance include inorganic substances such as hydroxides, chlorides, and carbonates of monovalent or divalent metals, ammonia, or organic amines.

<Electrode for secondary battery>

The electrode mixture for secondary batteries according to exemplary embodiments may include the binder and electrode active material for secondary batteries described above.

In some embodiments, the binder may be included in an amount of 1 to 10% by weight, preferably 1.5 to 8% by weight, based on the total weight of the electrode mixture. Within the above range, the adhesion, flexibility, and binding properties of the electrode active material to the electrode current collector can be improved, and the ionic conductivity of the binder increases, preventing the movement of electrons but allowing lithium ions to move smoothly, increasing resistance within the electrode. This can be prevented, and high energy density can be provided. Therefore, the electrical characteristics of the lithium secondary battery can be improved.

In some embodiments, the electrode mixture may further include at least one of a conductive material and a filler.

For example, examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives, etc. can be mentioned.

The filler may be optionally used as a component to suppress expansion of the cathode. Examples of fillers include olipine polymerizers such as polyethylene and polypropylene; Examples include fibrous materials such as glass fiber and carbon fiber.

In electrodes for secondary batteries according to exemplary embodiments, the electrode mixture may be applied to an electrode current collector.

Electrodes for secondary batteries according to example embodiments may include a current collector and a layer containing the above-described electrode mixture formed on at least one surface of the current collector.

Electrodes for secondary batteries can be manufactured by a dry method as well as a slurry-based wet method. When manufactured using a dry method, a heat treatment process is not required, which can shorten the process and reduce costs. Since organic solvents are not used, a drying process is not required, which shortens the process, reduces costs, and reduces environmental pollution. occurrence can be reduced.

For example, an electrode for a secondary battery can be manufactured by mixing an electrode active material and the binder in a dry manner without a solvent to prepare an electrode mixture, attaching the electrode mixture to the surface of an electrode current collector, and rolling it.

The electrode may be an anode or a cathode.

The thickness of the positive electrode current collector may be 3 to 500㎛. For example, the positive electrode current collector may include stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc.

The thickness of the negative electrode current collector may be 3 to 500 μm. For example, the negative electrode current collector may include gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes copper or a copper alloy.

The positive electrode active materials include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide, lithium copper oxide (Li ₂ CuO ₂ ), vanadium oxide, lithium manganese complex oxide disulfide compounds; It may include Fe ₂ (MoO ₄ ) ₃ and the like.

The negative electrode active material may include a carbon-based active material and/or a silicon-based active material.

The silicon-based active material may include silicon ( _Si ), silicon oxide (SiO These may be used alone or in combination of two or more.

The carbon-based active material may include amorphous carbon such as hard carbon, soft carbon, calcined coke, and mesophase pitch carbide, and/or crystalline carbon such as natural graphite and artificial graphite. These may be used alone or in combination of two or more.

<Lithium secondary battery>

Hereinafter, secondary batteries according to embodiments of the present invention will be described in detail with reference to the attached drawings. However, this is only illustrative and the present invention is not limited to the specific embodiments described as examples.

1 and 2 are schematic plan views and cross-sectional views, respectively, showing secondary batteries according to example embodiments. For example, FIG. 2 is a cross-sectional view cut in the thickness direction of a lithium secondary battery along line II' shown in FIG. 1.

1 and 2, two directions that intersect each other perpendicularly on a plane are defined as a first direction and a second direction. For example, the first direction may be the longitudinal direction of the lithium secondary battery, and the second direction may be the width direction of the lithium secondary battery.

Meanwhile, for convenience of explanation, the anode and cathode are omitted in FIG. 2 .

Referring to Figures 1 and 2, the secondary battery may be provided as a lithium secondary battery. According to example embodiments, the secondary battery may include an electrode assembly 150 and a case 160 that accommodates the electrode assembly 150. The electrode assembly 150 may include an anode 100, a cathode 130, and a separator 140.

The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one surface of the positive electrode current collector 105. According to example embodiments, the positive electrode active material layer 110 may be formed on both surfaces (eg, the upper and lower surfaces) of the positive electrode current collector 105. For example, the positive electrode active material layer 110 may be coated on the top and bottom surfaces of the positive electrode current collector 105, respectively, or may be directly coated on the surface of the positive electrode current collector 105.

The positive electrode current collector 105 according to the exemplary embodiment is as described above.

The positive electrode active material layer 110 may include lithium metal oxide as a positive electrode active material, and according to exemplary embodiments, may include lithium (Li)-nickel (Ni)-based oxide.

In some embodiments, the lithium metal oxide included in the positive electrode active material layer 110 may be represented by Chemical Formula A below.

[Formula A]

Li _1+a Ni _1-(x+y) Co _x M _y O ₂

In the formula A, -0.05≤α≤0.15, 0.01≤x≤0.2, 0≤y≤0.2, and M is selected from the group consisting of Mg, Sr, Ba, B, Al, Si, Mn, Ti, Zr, and W. It may be one or more types of elements. In one embodiment, 0.01≤x≤0.20, 0.01≤y≤0.15.

Preferably, in Formula A, M may be manganese (Mn). In this case, nickel-cobalt-manganese (NCM)-based lithium oxide may be used as the positive electrode active material.

For example, nickel (Ni) may be provided as a metal associated with the capacity of a lithium secondary battery. The higher the nickel content, the better the capacity and output of the lithium secondary battery. However, if the nickel content is excessively increased, the lifespan may decrease and it may be disadvantageous in terms of mechanical and electrical stability. For example, cobalt (Co) may be a metal associated with the conductivity or resistance of lithium secondary batteries. In one embodiment, M includes manganese (Mn), and Mn may be provided as a metal related to the mechanical and electrical stability of lithium secondary batteries.

Capacity, output, low resistance, and lifetime stability can be improved from the positive electrode active material layer 110 through the interaction of nickel, cobalt, and manganese described above.

For example, a positive electrode mixture can be prepared by mixing and stirring the positive electrode active material and the above-described binder, and additional conductive materials and fillers can be added as needed. After the positive electrode mixture is coated on the positive electrode current collector 105, the positive electrode active material layer 110 can be formed by compression and drying.

For example, a positive electrode mixture can be prepared by mixing and stirring the positive electrode active material with the dry binder described above without a solvent, and additional conductive materials and fillers can be added as needed. After the positive electrode mixture is coated on the positive electrode current collector 105, it can be compressed and dried to form the positive electrode active material layer 110 (the layer containing the positive electrode mixture is not shown). Additionally, the positive electrode mixture may be attached to the surface of the positive electrode current collector 105 and then rolled to produce the positive electrode 100.

For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, carbon nanofibers, and carbon nanotubes, and/or metal-based conductive materials such as tin, tin oxide, zinc oxide, titanium oxide, and metal fiber. You can.

In some embodiments, the electrode density of the anode 100 may be 3.0 to 3.9 g/cc, and preferably 3.2 to 3.8 g/cc.

The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one surface of the negative electrode current collector 125. According to example embodiments, the negative electrode active material layer 120 may be formed on both surfaces (eg, the top and bottom surfaces) of the negative electrode current collector 125. The negative electrode active material layer 120 may be coated on the top and bottom surfaces of the negative electrode current collector 125, respectively. For example, the negative electrode active material layer 120 may directly contact the surface of the negative electrode current collector 125.

The negative electrode current collector 125 according to the exemplary embodiment is as described above, and the negative electrode active material layer 120 may include the negative electrode active material described above.

For example, a negative electrode mixture can be prepared by mixing and stirring the negative electrode active material and the above-described binder, and additional conductive materials and fillers can be added as needed. After the negative electrode mixture is coated on the negative electrode current collector 125, the negative electrode active material layer 120 can be formed by compression and drying.

For example, a negative electrode mixture can be prepared by mixing and stirring the negative electrode active material with the dry binder described above without a solvent, and additional conductive materials and fillers can be added as needed. After coating the negative electrode mixture on the negative electrode current collector 125, it can be compressed and dried to form the negative electrode active material layer 120 (the layer containing the negative electrode mixture is not shown). Additionally, the negative electrode mixture can be attached to the surface of the negative electrode current collector 125 and then rolled to produce the negative electrode 130.

Materials that are substantially the same as or similar to those used to form the anode 100 may be used as the conductive material.

According to example embodiments, the charge density of the anode active material layer 120 may be 1.4 to 1.9 g/cc.

In some embodiments, the area (eg, contact area with the separator 140) and/or volume of the cathode 130 may be larger than that of the anode 100. Accordingly, for example, lithium ions generated from the anode 100 can be smoothly moved to the cathode 130 without precipitating in the middle, thereby further improving output and capacity characteristics.

A separator 140 may be interposed between the anode 100 and the cathode 130. The separator 140 may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The separator may include a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc.

The separator 140 extends in the second direction between the positive electrode 100 and the negative electrode 130, and may be folded and wound along the thickness direction of the lithium secondary battery. Accordingly, a plurality of anodes 100 and cathodes 130 may be stacked in the thickness direction through the separator 140.

According to exemplary embodiments, an electrode cell is defined by an anode 100, a cathode 130, and a separator 140, and a plurality of electrode cells are stacked, for example, an electrode in the form of a jelly roll. Assembly 150 may be formed. For example, the electrode assembly 150 can be formed through winding, lamination, folding, etc. of the separator 140.

The electrode assembly 150 is accommodated in the case 160, and the electrolyte may be injected into the case 160 together. Case 160 may include, for example, a pouch, a can, etc.

According to exemplary embodiments, a non-aqueous electrolyte solution may be used as the electrolyte.

The non ^- aqueous electrolyte solution ^{contains a} lithium salt as an electrolyte and ^an organic solvent. The lithium salt is expressed, for example ^{, as} Li ⁺ 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 ^- , Examples include SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylmethyl carbonate (EMC). ), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran can be used. . These may be used alone or in combination of two or more.

As shown in FIG. 2, electrode tabs (positive electrode tab and negative electrode tab) protrude from the positive electrode current collector 105 and negative electrode current collector 125 belonging to each electrode cell, respectively, and extend to one side of the exterior case 160. It can be. The electrode tabs may be fused together with the one side of the exterior case 160 and connected to electrode leads (positive lead 107 and negative lead 127) extended or exposed to the outside of the exterior case 160.

In FIG. 1, the positive electrode lead 107 and the negative electrode lead 127 are shown as being formed on the same side of the lithium secondary battery or exterior case 160, but they may be formed on opposite sides of the lithium secondary battery or exterior case 160.

For example, the positive lead 107 may be formed on one side of the external case 160, and the negative lead 127 may be formed on the other side of the external case 160.

Lithium secondary batteries can be manufactured, for example, in a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

Hereinafter, experimental examples including specific examples and comparative examples are presented to aid understanding of the present invention, but this is only illustrative of the present invention and does not limit the scope of the appended claims, and does not limit the scope and technical idea of the present invention. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

<Synthesis example>

Synthesis Example 1 (Synthesis of Formula 1-1)

[Formula 1-1]

Dissolve 13.014 g (0.1 mol) of 2-hydroxyethyl methacrylate and 8.506 g (0.1 mol) of cyanoacetic acid in 200 mL of dichloromethane, then use dicyclohexylcarbodiimide as a reagent and react in a nitrogen atmosphere for 24 hours. The reaction was carried out at room temperature for an hour. Afterwards, the solvent was removed using a PVDF membrane filter, and Chemical Formula 1-1 (15.719 g) was obtained.

Synthesis Example 2 (Synthesis of Formula 1-2)

[Formula 1-2]

Proceed in the same manner as in Synthesis Example 1, except that 15.820 g (0.1 mol) of 2-hydroxybutyl methacrylate was used instead of 13.014 g (0.1 mol) of 2-hydroxyethyl methacrylate, and Formula 1-2 (18.523 g) was obtained.

Synthesis Example 3 (Synthesis of Formula 1-3)

[Formula 1-3]

Proceed in the same manner as Synthesis Example 1, except that 11.612 g (0.1 mol) of 2-hydroxyethyl acrylate was used instead of 13.014 g (0.1 mol) of 2-hydroxyethyl methacrylate, and Formula 1-3 ( 16.219 g) was obtained.

Synthesis Example 4 (Synthesis of Formula 1-4)

[Formula 1-4]

Instead of 13.014 g (0.1 mol) 2-hydroxyethyl methacrylate and 8.506 g (0.1 mol) cyanoacetic acid, replace 11.612 g (0.1 mol) 2-hydroxyethyl acrylate and 9.909 g (0.1 mol) 2-cyanopropanoic acid. By proceeding in the same manner as Synthesis Example 1, except that mol) was used, Chemical Formula 1-4 (18.883 g) was obtained.

Synthesis Example 5 (Synthesis of Formula 2-1)

[Formula 2-1]

11.612 g (0.1 mol) 2-hydroxyethyl acrylate and 9.909 g (0.1 mol) 3-cyanopropanoic acid instead of 13.014 g (0.1 mol) 2-hydroxyethyl methacrylate and 8.506 g (0.1 mol) cyanoacetic acid. Mol) was used in the same manner as in Synthesis Example 1, and Chemical Formula 2-1 (18.883 g) was obtained.

<Examples and Comparative Examples>

Example 1

Manufacturing of binders for secondary batteries

Ethylhexyl acrylate (70 g) as a monomer, and (meth)acrylate monomer (30 g) represented by the following formula 1-1 obtained in Synthesis Example 1, and azobisisobutyronitrile-containing methyl ethyl ketone as a polymerization initiator. were added, mixed, and polymerized at 70°C for about 6 hours. Afterwards, vacuum drying was performed at 70°C to remove the solvent, and vacuum drying was performed at 120°C to remove residual monomers. A binder for a secondary battery containing an acrylic resin in which monomers were polymerized through the above polymerization was manufactured.

[Formula 1-1]

Manufacturing of cathodes for secondary batteries

A negative electrode mixture was prepared by mixing 0.2 g of the binder for secondary batteries with 1 g of silicon-based active material, 8.7 g of natural graphite, and 0.1 g of carbon black conductive material. Here, water was added so that the total solid content was 55% by weight. The negative electrode mixture was coated on copper foil to a thickness of 150㎛ using a doctor blade, placed in a dry oven at 80°C, dried for 30 minutes, and then rolled to an appropriate thickness to prepare a negative electrode.

Manufacturing of lithium secondary batteries

The cathode was drilled into a circular shape with a surface area of 1.54 cm ² to serve as a working electrode, and a coin-type half-cell was manufactured using lithium metal drilled into a circular shape with a surface area of 1.77 cm ² as a jackpot. A separator made of polyolefin microporous film was interposed between the working electrode and the counter electrode, and then a mixed solvent of EC (ethyl carbonate):EMC (ethylmethyl carbonate) = 3:7 (weight ratio) was used and LiPF ₆ electrolyte was added at a concentration of 1M. A lithium secondary battery was manufactured by adding the dissolved electrolyte solution.

Example 2

Example 1 and A binder for a secondary battery, a negative electrode for a secondary battery, and a lithium secondary battery were manufactured using the same method.

[Formula 1-2]

Example 3

Example 1 and A binder for a secondary battery, a negative electrode for a secondary battery, and a lithium secondary battery were manufactured using the same method.

[Formula 1-3]

Example 4

Example 1 and A binder for a secondary battery, a negative electrode for a secondary battery, and a lithium secondary battery were manufactured using the same method.

[Formula 1-4]

Comparative Example 1

A binder for a secondary battery, a negative electrode for a secondary battery, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the (meth)acrylate monomer (30 g) represented by Chemical Formula 1-1 was not used.

Comparative Example 2

Example 1 and A binder for a secondary battery, a negative electrode for a secondary battery, and a lithium secondary battery were manufactured using the same method.

[Formula 2-1]

Comparative Example 3

A negative electrode for a secondary battery and a lithium secondary battery were manufactured in the same manner as in Example 1, except that polyvinylidene fluoride (PVDF) was used instead of the binder for a secondary battery in Example 1.

<Experimental example>

1. Evaluation of adhesion of cathode

For the negative electrodes of Examples and Comparative Examples, an experiment was performed to measure the adhesion between the layer containing the negative electrode mixture and the negative electrode current collector.

The negative electrode plates of Examples and Comparative Examples were cut to a certain size and fixed on a glass slide, and then the current collector was peeled off and the 180° peel strength was measured. The results were determined as the average value of five or more peeling strengths.

2. Evaluation of charge/discharge characteristics and lifespan characteristics of lithium secondary batteries

Charge and discharge experiments were performed on the lithium secondary batteries of Examples and Comparative Examples. A charge/discharge test was performed twice with a charge/discharge current density of 0.1C, a charge end voltage of 1.5V (Li/Li+), and a discharge end voltage of 7mV (Li/Li+). Next, charge/discharge tests were performed 20 times with a charge/discharge current density of 0.5C, a charge end voltage of 1.5V (Li/Li+), and a discharge end voltage of 5mV (Li/Li+).

All discharges were performed at constant current/constant voltage, and the end current of constant voltage charging was 0.02C. After completing a total of 53 cycles of testing, the charge/discharge efficiency (discharge capacity/charge capacity, initial efficiency) of the first cycle was obtained. Then, the capacity ratio (53th/3rd) was calculated by dividing the charging capacity of the 53rd cycle by the charging capacity of the third cycle and was considered as the capacity maintenance rate.

The evaluation results are shown in Table 1 below.

cathodic adhesion
(gf/cm) initial efficiency
(%) Capacity maintenance rate
(%) Example 1 0.63 85.12 94.21 Example 2 0.61 84.38 93.71 Example 3 0.58 83.44 93.54 Example 4 0.58 84.21 94.01 Comparative Example 1 0.51 82.61 91.73 Comparative Example 2 0.49 81.60 90.18 Comparative Example 3 0.55 83.16 92.14

Referring to Table 1, the examples had high cathode adhesion, initial efficiency, and cycle capacity maintenance rate. Therefore, when an acrylic resin polymerized including the (meth)acrylate monomer contained in the above-mentioned structural formula 1 is used, the adhesion between the electrode active material and the electrode current collector is improved, the cohesion of the binder is improved, and the lifespan of the lithium secondary battery is improved. And it can be seen that the capacity characteristics are improved.

However, in the case of comparative examples, as an acrylic resin polymerized without containing the (meth)acrylate monomer included in Structural Formula 1 was used or polyvinylidene fluoride was used as a binder, the negative electrode adhesion, initial efficiency, and cycle Capacity maintenance rate deteriorated.

100: positive electrode 105: positive electrode current collector
110: positive electrode active material layer 120: negative active material layer
125: negative electrode current collector 130: negative electrode
140: Separator 150: Electrode assembly
160: case

Claims (13)

A binder for a secondary battery comprising an acrylic resin polymerized with a (meth)acrylate monomer represented by the following structural formula 1:
[Structural Formula 1]

(In structural formula 1, R ₁ is a hydrogen atom or a methyl group, R ₂ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and L is an alkylene group having 1 to 10 carbon atoms).
The binder for a secondary battery according to claim 1, wherein in structural formula 1, R ₁ and R ₂ are each independently a hydrogen atom or a methyl group, and L is an alkylene group having 1 to 4 carbon atoms.
The method according to claim 1, wherein the acrylic resin is i) 30 to 90% by weight of a (meth)acrylate monomer having an alkyl group having 1 to 14 carbon atoms, ii) at least one selected from the group consisting of an unsaturated carboxylic acid and an unsaturated monomer containing a hydroxyl group. A binder for a secondary battery that is polymerized including 0.5 to 10% by weight of monomer, and iii) 1 to 20% by weight of (meth)acrylate monomer represented by Structural Formula 1.
The method of claim 3, wherein the monomer of i) is methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, and isobutyl acrylate. Latex, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl acrylate, isooctyl acrylate, octyl methacrylate, 2-ethylhexyl (meth)acrylate, isodecyl acrylate, decyl A binder for a secondary battery, comprising at least one selected from the group consisting of methacrylate, dodecyl methacrylate, isobornyl methacrylate, and lauryl (meth)acrylate.
The method of claim 3, wherein the monomer of ii) is acrylic acid, itaconic acid, maleic anhydride, fumaric acid, crotanic methacrylic acid, ethyl methacrylic acid, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, Hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxylauryl (meth)acrylate and hydroxypropylene glycol. A binder for a secondary battery comprising at least one selected from the group consisting of (meth)acrylates.
The binder for a secondary battery according to claim 1, wherein the acrylic resin is polymerized by further comprising iv) one or more monomers selected from the group consisting of styrene, unsaturated acetate, and unsaturated nitrile.
The method of claim 6, wherein the monomer of iv) is one selected from the group consisting of vinyl acetate, styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, divinylbenzene, acrylonitrile, and methacrylonitrile. A binder for secondary batteries containing the above.
The binder for a secondary battery according to claim 1, wherein the acrylic resin is polymerized by further including an epoxy group-containing unsaturated monomer.
The binder for a secondary battery according to claim 1, wherein the binder further includes one or more compounds selected from the group consisting of melamine, isocyanate, aldehyde, amine, and diazonium salt.
The binder for a secondary battery according to claim 9, wherein the compound is contained in an amount of 0.1 mol or less based on 1 mole of the (meth)acrylate monomer represented by Structural Formula 1.
An electrode mixture for a secondary battery comprising the binder for a secondary battery and an electrode active material according to claim 1.
An electrode for a secondary battery, comprising a current collector and a layer containing the electrode mixture according to claim 11 formed on at least one surface of the current collector.
A lithium secondary battery comprising the electrode according to claim 12.