KR20220039604A - Binder for anode of secondary battery, anode of secondary battery and secondary battery - Google Patents

Abstract

The present invention relates to a binder for a secondary battery negative electrode, a secondary battery negative electrode, and a secondary battery. Specifically, provided is a binder for a secondary battery negative electrode, which improves adhesion of the negative electrode and at the same time minimizes resistance in the secondary battery, and ultimately can improve the lifespan of the secondary battery.

Description

Binder for secondary battery negative electrode, secondary battery negative electrode, and secondary battery

The present invention relates to a binder for a secondary battery negative electrode, a secondary battery negative electrode, and a secondary battery.

Currently, a secondary battery having a high energy density and voltage is widely applied as a power source for small electronic devices such as portable computers, portable telephones, and cameras.

Recently, as large electronic devices (eg, electric vehicles, power storage devices, etc.) to which high-capacity secondary batteries are applied have also been commercialized, secondary batteries with high energy density and high output characteristics, low internal resistance, and long lifespan have been used. demand for it is increasing.

In order to meet this demand, various technologies for improving energy density through the positive active material and improving the output through the negative active material have been proposed. However, in each electrode to which a high-capacity positive active material and a high-output negative active material are applied, charging and discharging are repeated while a negative current collector and an active material; or different active materials; The bond between the two may be loosened, and the contact resistance between particles may increase, so that the resistance of the electrode itself may also be increased.

In particular, recently, research is underway to use silicon, tin, silicon-tin alloy, etc., which have a larger discharge capacity than natural graphite, as an anode active material. This causes a problem of increasing the internal resistance of the secondary battery and reducing the lifespan. However, such a problem is difficult to solve as long as the currently widely used binder for negative electrode (eg, PVDF) is used.

An object of the present invention is to provide a binder for a negative electrode of a secondary battery, which can improve the adhesion of the negative electrode and minimize the resistance in the secondary battery, and ultimately improve the lifespan of the secondary battery.

Specifically, in one embodiment of the present invention, among the total weight (100% by weight) of the repeating unit, a) 40 to 55% by weight of the first repeating unit derived from the aliphatic conjugated diene-based first monomer, b) the second aromatic vinyl-based unit 40 to 55 wt% of a second repeating unit derived from a monomer, c) 0.1 to 3 wt% of a third repeating unit derived from a third unsaturated carboxylic acid monomer, and d) 1 to 11 of a fourth repeating unit derived from polyethylene glycol mono(meth)acrylate A binder for a negative electrode of a secondary battery is provided, including; a copolymer comprising weight %.

In other embodiments of the present invention, the method for preparing the negative electrode binder of the embodiment, the secondary battery negative electrode mixture comprising the negative electrode binder and the negative electrode active material of the one embodiment, and the negative electrode binder of the embodiment negative electrode mixture layer There is provided a secondary battery negative electrode and a lithium secondary battery comprising the.

The binder for a negative electrode of a secondary battery according to one embodiment may improve adhesion to the negative electrode, minimize resistance in the secondary battery, and ultimately improve the lifespan of the secondary battery.

In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from other components.

In addition, the terminology used herein is used only to describe exemplary embodiments, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present specification, terms such as "comprise", "comprising" or "have" are intended to designate the existence of an embodied feature, number, step, element, or a combination thereof, but one or more other features or It should be understood that the existence or addition of numbers, steps, elements, or combinations thereof, is not precluded in advance.

Also in the present invention, when it is said that each layer or element is formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or other It means that a layer or element may additionally be formed between each layer, on the object, on the substrate.

Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

I. Binder for negative electrode of secondary battery

In one embodiment of the present invention, among the total weight (100% by weight) of the repeating unit,

a) 40 to 55 wt% of a first repeating unit derived from an aliphatic conjugated diene-based first monomer.

b) 40 to 55 wt% of a second repeating unit derived from an aromatic vinyl-based second monomer;

c) 0.1 to 3% by weight of a third repeating unit derived from an unsaturated carboxylic acid-based third monomer; and

d) 1 to 11% by weight of the fourth repeating unit derived from polyethylene glycol mono(meth)acrylate

A copolymer comprising;

A binder for a secondary battery negative electrode is provided.

The binder for the negative electrode of the embodiment includes a copolymer in which the type and content of the repeating unit are each controlled to a specific range. Such a copolymer may increase negative electrode adhesion and improve the lifespan of a secondary battery. At the same time, the resistance in the secondary battery can be lowered and the output thereof can be improved.

In particular, the fourth repeating unit derived from d) polyethylene glycol mono (meth) acrylate exhibits an effect of improving fluidity by a long ethylene oxide group of the structure, and increasing affinity with the current collector by a hydroxy group, , negative electrode current collector and active material; or different active materials; It is possible to increase the adhesion between the two, and to minimize the decrease in capacity of the secondary battery (ie, improve the lifespan characteristics).

In addition, the fourth repeating unit exhibits the effect of increasing ionic conductivity by increasing affinity with the electrolyte by the ethylene oxide group of the structure, facilitating the transfer of metal ions (eg, lithium ions), and of the secondary battery It is possible to improve the output characteristics by lowering the internal resistance.

However, the effect of the fourth repeating unit may be expressed only when the content of the fourth repeating unit is 1 to 11 wt% of the total weight (100 wt%) of the repeating unit.

This is because, when the content of the fourth repeating unit is less than 1% by weight, the effect is insignificant, and when the content of the fourth repeating unit is more than 11% by weight, there is a problem in that the strength of the binder itself is lowered, thereby lowering the adhesive force and reducing the lifespan.

On the other hand, even if the content of the fourth repeating unit satisfies 1 to 11% by weight, when any one of the first to third repeating units is replaced with another material, or the limited content range of the embodiment is not satisfied (lack of ), the negative electrode adhesion may be reduced or the capacity retention rate may be lowered.

The first repeating unit functions to improve the adhesion between the anode active material and the current collector while suppressing the swelling of the electrolyte at a high temperature, and the second repeating unit and the third repeating unit are the strength of the binder and the strength of the electrolyte. It enhances affinity.

When all of the repeating units satisfy the limited content ranges of the embodiment, the functions of the repeating units harmonize to improve negative electrode adhesion and minimize in the secondary battery, and ultimately improve the lifespan of the secondary battery there is.

In particular, the binder for a secondary battery negative electrode according to the exemplary embodiment may exhibit excellent effects in a secondary battery negative electrode mixture including a silicon compound as an anode active material. As an example, when a silicon compound is applied as a negative electrode active material, the hydrogen ion concentration index of the negative electrode mixture for a secondary battery containing the same is about pH 11, which may cause problems in that stability is reduced, viscosity is increased, and aggregates are generated when a binder is added. . The binder for a secondary battery negative electrode according to the embodiment contains a long hydrophilic functional group derived from polyethylene glycol mono (meth) acrylate, and thus excellent stability is expressed in a high pH secondary battery negative electrode mixture to which a silicon compound is applied as an anode active material. make it possible

Hereinafter, the binder for the negative electrode of the embodiment will be described in detail for each repeating unit.

weight ratio of repeating units

In the binder for the negative electrode of the embodiment, the type and content of each repeating unit satisfies the above-described range, and the weight ratio of the first repeating unit/the fourth repeating unit is 3.64 to 55, and the second repeating unit/the fourth repeating unit The weight ratio of the repeating unit may be 3.64 to 55, the weight ratio of the third repeating unit/the fourth repeating unit may be 0.01 to 3, and the weight ratio of the first repeating unit/the second repeating unit may be 0.73 to 1.38.

When all of these ranges are satisfied, a synergistic effect by the repeating units may be improved.

For example, the weight ratio of the first repeating unit/the fourth repeating unit is 4.4 to 48.5, the weight ratio of the second repeating unit/the fourth repeating unit is 4.4 to 48.5, and the third repeating unit/the fourth repeating unit by weight The ratio may be 0.2 to 2, and the weight ratio of the first repeating unit/the second repeating unit may be 1.

first repeat unit

The first repeating unit is derived from an aliphatic conjugated diene-based first monomer. Specifically, the first repeating unit corresponds to a structural unit of a copolymer formed by adding an aliphatic conjugated diene-based first monomer during polymerization.

When such a first repeating unit is included in the copolymer, the binder for the negative electrode of one embodiment can suppress the electrolyte swelling phenomenon at high temperature, and has elasticity due to the rubber component, thereby reducing the thickness of the negative electrode, In addition to reducing the gas generation phenomenon, it can also serve to improve the adhesive force so that the binding force between the negative electrode active material and the current collector can be maintained.

As the first monomer, which is the aliphatic conjugated diene-based monomer, an aliphatic conjugated diene-based compound having 2 to 20 carbon atoms may be used. As a non-limiting example, the aliphatic conjugated diene-based first monomer may include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,2-dimethyl-1, 3-butadiene, 1,4-dimethyl-1,3-butadiene, 1-ethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene, 1,3- Hexadiene, 1,4-hexadiene, 1,5-hexadiene, 2-methyl-1,5-hexadiene, 1,6-heptadiene, 6-methyl-1,5-heptadiene, 1,6- It may be at least one selected from the group consisting of octadiene, 1,7-octadiene, and 7-methyl-1,6-octadiene. For example, 1,3-butadiene may be used as the aliphatic conjugated diene-based first monomer.

The first repeating unit may be included in an amount of 40 to 55% by weight of the total weight (100% by weight) of the repeating unit. That is, when preparing the copolymer, the first monomer may be used in an amount of 40 to 55% by weight of the total weight (100% by weight) of the monomer.

For example, of the total weight (100 wt%) of the repeating unit, the first repeating unit is included in 40 wt% or more, 40.3 wt% or more, 40.6 wt% or more, or 41 wt% or more, or 55 wt% It may be included in an amount of 54.7 wt% or less, 54.4 wt% or less, or 54 wt% or less.

When the content of the first repeating unit is increased within the above range, the above-described effect with respect to the first repeating unit may be improved. However, when the content of the first repeating unit exceeds 55% by weight, the yield of the binder may be reduced or the strength of the obtained binder may be reduced.

second repeat unit

The second repeating unit is derived from an aromatic vinyl-based second monomer. Specifically, the second repeating unit corresponds to a structural unit of a copolymer formed by adding the above-described second monomer during polymerization.

When such a second repeating unit is included in the copolymer, the binder for the negative electrode of the embodiment may have improved strength and affinity with the electrolyte.

The aromatic vinyl-based second monomer is styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, chlorostyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, and divinylbenzene. It may be one or more selected from the group consisting of, for example, may be styrene.

The second repeating unit may be included in an amount of 40 to 55 wt% based on the total weight (100 wt%) of the repeating unit. That is, in the preparation of the copolymer, the second monomer may be used in an amount of 40 to 55% by weight based on the total weight (100% by weight) of the monomer.

For example, of the total weight (100 wt%) of the repeating unit, the second repeating unit is included in 40 wt% or more, 40.3 wt% or more, 40.6 wt% or more, or 41 wt% or more, or 55 wt% It may be included in an amount of 54.7 wt% or less, 54.4 wt% or less, or 54 wt% or less.

When the content of the second repeating unit is increased within the above range, the above-described effect with respect to the second repeating unit may be improved. However, when the amount of the second repeating unit in the copolymer exceeds 55% by weight, fluidity of the binder may be reduced or adhesive strength may be deteriorated.

third repeat unit

The third repeating unit is derived from an unsaturated carboxylic acid-based third monomer. Specifically, the third repeating unit corresponds to a structural unit of the copolymer formed by adding the above-described third monomer during polymerization.

When the third repeating unit is included in the copolymer, the binder for the negative electrode of the embodiment may have improved strength, polymerization, and storage stability.

The unsaturated carboxylic acid-based third monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid. there is. For example, it may be acrylic acid.

The third repeating unit may be included in an amount of 0.1 to 3% by weight of the total weight (100% by weight) of the repeating unit. That is, when preparing the copolymer, the second monomer may be used in an amount of 0.1 to 3% by weight based on the total weight (100% by weight) of the monomer.

For example, of the total weight (100 wt%) of the repeating unit, the third repeating unit is included in 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, or 1.5 wt% or more, or 3 wt% It may be included in an amount of 2.8 wt% or less, 2.5 wt% or less, or 2.3 wt% or less.

When the content of the third repeating unit is increased within the above range, the above-described effect with respect to the third repeating unit may be improved. However, when the third repeating unit is included in an amount of more than 3% by weight in the copolymer, there may be problems in that the fluidity of the binder is lowered or the affinity with the electrolyte is lowered.

4th repeat unit

The fourth repeating unit is derived from a polyethylene glycol mono(meth)acrylate-based fourth monomer. Specifically, the fourth repeating unit corresponds to a structural unit of a copolymer formed by adding the fourth monomer during polymerization.

When the fourth repeating unit is included in the copolymer, the binder for the negative electrode of one embodiment includes a negative electrode current collector and an active material; or different active materials; It is possible to facilitate the transfer of metal ions (eg, lithium ions) while increasing the adhesion between them. Accordingly, it is possible to minimize the decrease in capacity of the lithium secondary battery (ie, improve the lifespan characteristics), lower the internal resistance, and improve the output characteristics.

The polyethylene glycol mono(meth)acrylate-based fourth monomer may be polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, or a mixture thereof.

The fourth repeating unit may be included in an amount of 1 to 11 wt% based on the total weight (100 wt%) of the repeating unit. That is, when preparing the copolymer, the second monomer may be used in an amount of 1 to 11% by weight of the total weight (100% by weight) of the monomer.

For example, of the total weight (100 wt%) of the repeating unit, the fourth repeating unit is included in 1 wt% or more, 11 wt% or less, 10.6 wt% or less, 10.3 wt% or less, or 10 wt% may be included below.

When the content of the fourth repeating unit increases within the above range, the above-described effect with respect to the fourth repeating unit may be improved. However, when the amount of the fourth repeating unit in the copolymer exceeds 11 wt %, the adhesive strength of the binder may decrease or battery life may be reduced.

Average particle diameter of polymer (latex particles)

On the other hand, in the binder for the negative electrode of the embodiment, the copolymer may have a form of latex particles prepared through emulsion polymerization.

Specifically, the copolymer may be a latex particle having an average particle diameter of 50 to 500 nm.

The average particle diameter of the latex particles may be measured using a particle size analyzer (NICOMP AW380, manufactured by PSS) using dynamic light scattering.

Specifically, in the present specification, the 'average particle diameter' means an arithmetic average particle diameter in a particle size distribution measured by dynamic light scattering, wherein the arithmetic average particle diameter is the scattering intensity average particle diameter, It can be measured by the average particle diameter of volume distribution or the average particle diameter of number distribution, and it is preferable to measure the average particle diameter of scattering intensity among them.

For example, the copolymer may be a latex particle having an average particle diameter of 50 nm or more, or 70 nm or more, or 100 nm or more, and 500 nm or less, or 400 nm or less, or 300 nm or less, or 200 nm or less. there is. If the average particle diameter of the latex particles is too small, the viscosity may increase and the adhesion of the mixture layer including the same to the current collector may be weakened. Conversely, if the average particle diameter of the latex particles is too large, the stability of the particles may be reduced.

Gel content in binder

On the other hand, the binder for the negative electrode of the embodiment may have a gel content calculated by Equation 1 below 95% or more:

[Equation 1]

Gel content (%) = M _b /M _a * 100

In Equation 1 above,

Ma _is the weight measured after drying the binder for the negative electrode at 80 degrees for 24 hours,

M _b is after immersing the weighed negative electrode binder in 50 g of THF (Tetrahydrofuran) for 24 hours or more, filtering it through 200 mesh, and then drying the mesh and the negative electrode binder remaining in the mesh at 80 degrees for 24 hours. It is the weight of the copolymer remaining in the mesh.

The gel content refers to the degree of crosslinking of the copolymer, and is calculated as in Equation 1 and is expressed as an insoluble fraction in the electrolyte. Preferably, the gel content in the binder for the negative electrode of one embodiment is 95% to 99%, or 95% to 98%, or 96% to 97.5%, and when the gel content is less than 95%, swelling to the electrolyte ( swelling) may increase and the lifespan of the battery may be reduced.

Stability of the binder (peel strength)

In addition, 100 g of the binder for the negative electrode of one embodiment is put in a container, shear is applied at 3000 rpm for 10 minutes, and then the amount of coagulation (Coagulum) measured through 200 mesh is 200 ppm or less, or 150 ppm or less, or 130 ppm or less At the same time, the 180-degree peel strength between the negative electrode mixture and the current collector prepared using the negative electrode binder of the embodiment is 25 g/in or more, or 28 g/in or more, or 30 g/in or more, and 50 g/in inches or less, or 48 g/in or less, or 45 g/in or less.

aqueous solvent

In addition, an aqueous solvent, ie, water, may be added to the binder for the negative electrode of the embodiment in addition to the above-described copolymer, ie, latex particles.

The aqueous solvent may be used in an amount of about 50 to about 1,000 parts by weight, specifically about 100 to about 400 parts by weight, based on 100 parts by weight of the copolymer, in terms of stability and viscosity control of the latex particles. For example, in the total amount (100% by weight) of the binder for the negative electrode of the embodiment, it may be used so that the total solid content (TSC) is adjusted to about 10 to about 65%.

When the aqueous solvent is used too little, there may be a problem that the stability of the latex particles is lowered. Performance degradation may occur.

II. Manufacturing method of binder for secondary battery negative electrode

In another embodiment of the present invention, in the presence of an emulsifier and a polymerization initiator, emulsion polymerization of a monomer mixture to prepare a copolymer; provides a method for producing a binder for a secondary battery negative electrode comprising a.

Of the total weight (100% by weight) of the monomer mixture, a) 40 to 55% by weight of an aliphatic conjugated diene-based first monomer, b) 40 to 55% by weight of an aromatic vinyl-based second monomer, c) an unsaturated carboxylic acid-based agent 3 to contain 0.1 to 3% by weight of the monomer and d) 1 to 11% by weight of the polyethylene glycol mono (meth)acrylate monomer.

The method of manufacturing the binder for the negative electrode of the embodiment may be the method of manufacturing the binder for the negative electrode of the embodiment described above.

In this regard, a description overlapping with the above description will be omitted.

emulsion polymerization

In addition, the emulsion polymerization may be performed by single polymerization or multi-stage polymerization. Here, single polymerization refers to a method in which used monomers are put into a single reactor and polymerized at the same time, and multistage polymerization refers to a method in which used monomers are sequentially polymerized in two or more stages.

In addition, the emulsion polymerization may be carried out in the presence of an emulsifier and a polymerization initiator in a solution containing the above-described aqueous solvent.

The polymerization temperature and polymerization time of the emulsion polymerization for the preparation of the copolymer may be appropriately determined depending on the case. For example, the polymerization temperature may be from about 50 °C to about 200 °C, and the polymerization time may be from about 0.5 hours to about 20 hours.

polymerization initiator

As the polymerization initiator usable during the emulsion polymerization, an inorganic or organic peroxide may be used, for example, a water-soluble initiator containing potassium persulfate, sodium persulfate, ammonium persulfate, etc., cumene hydroperoxide, benzoyl peroxide Oil-soluble initiators including oxides and the like can be used.

activator

In addition, an activator may be further included to promote the initiation of the reaction of the peroxide together with the polymerization initiator, and such activators include sodium formaldehyde sulfoxylate, sodium ethylenediaminetetraacetate, ferrous sulfate, and dextrose. At least one selected from the group consisting of may be used.

emulsifier

And, as the emulsifier for the emulsion polymerization, an anionic emulsifier such as sodium dodecyl diphenyl iser disulfonate, sodium lauryl sulfate, sodium dodecyl benzene sulfonate, dioctyl sodium sulfosuccinate, or polyoxyethylene Nonionic emulsifiers such as polyethylene oxide alkyl ethers such as lauryl ether, polyethylene oxide alkyl aryl ethers, polyethylene oxide alkyl amines, and polyethylene oxide alkyl esters may be used. Such an emulsifier is a material having a hydrophilic group and a hydrophobic group at the same time, and during the emulsion polymerization process, a micelle structure is formed, and polymerization of each monomer can occur inside the micellar structure. Preferably, the anionic emulsifier and the nonionic emulsifier may be used alone or in a mixture of two or more, and it may be more effective when a mixture of an anionic emulsifier and a nonionic emulsifier is used, but the present invention is not necessarily such an emulsifier is not limited to the type of

And, the emulsifier, for example, based on 100 parts by weight of the total monomer components used in the preparation of the copolymer, about 0.01 to about 10 parts by weight, about 1 to about 10 parts by weight, or about 3 to about 5 parts by weight can be used as wealth.

III. negative electrode mixture and negative electrode

In another embodiment of the present invention, there is provided a secondary battery negative electrode mixture including the binder for the secondary battery negative electrode and negative electrode active material of the above-described embodiment, and a negative electrode mixture layer and negative electrode current collector comprising the secondary battery negative electrode mixture It provides a secondary battery negative electrode comprising.

Except for the binder for the negative electrode of the embodiment, the negative electrode active material used for the negative electrode mixture and the negative electrode, the negative electrode current collector, and the like, may each include generally known components.

cathode

The binder for the negative electrode of the embodiment may be included in an amount of 1% to 10% by weight, specifically, 1% to 5% by weight of the total weight (100% by weight) of the negative electrode mixture. When this is satisfied, the content of the negative electrode active material may be relatively increased, and the discharge capacity of the negative electrode may be further improved.

On the other hand, since the binder for a negative electrode of one embodiment has excellent properties in binding force and mechanical properties, etc., when a graphite-based negative electrode active material is used as the negative electrode active material of the negative electrode mixture, as well as a negative electrode active material having a higher capacity than that is used, the negative electrode The binding force between the active material and the negative electrode active material, between the negative electrode active material and the negative electrode current collector, etc. can be maintained, and expansion of the negative electrode active material can be suppressed by its own mechanical properties.

Since the binder for the negative electrode of one embodiment is suitable to be applied not only with the graphite-based negative active material but also with the negative active material having a higher capacity than that, in one embodiment of the present invention, the type of the negative electrode active material is not particularly limited.

Specifically, as the negative active material, carbon such as non-graphitizable carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen; 0<x≤1;1≤y≤3;1≤z≤8); lithium metal; lithium alloy; silicon-based alloys; tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , metal oxides such as Bi ₂ O ₅ ; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; Lithium titanium oxide and the like can be used.

According to one embodiment, the negative active material is a material capable of reversibly intercalation and deintercalation of lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium , and a transition metal oxide.

Examples of the material capable of reversibly intercalating and deintercalating the lithium ions include crystalline carbon, amorphous carbon, or a mixture thereof as a carbonaceous material. Specifically, the carbonaceous material is natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch-based carbon fiber (mesophase pitch based carbon fiber), carbon microbeads, petroleum or coal tar pitch derived cokes, soft carbon, hard carbon, and the like.

The lithium metal alloy includes Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd. It may be an alloy of a metal selected from the group consisting of and lithium.

The material capable of doping and dedoping lithium is Si, Si-C composite, SiOx (0<x<2), Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 an element selected from the group consisting of an element, a group 16 element, a transition metal, a rare earth element, and a combination thereof; except for Si), Sn, SnO ₂ , a Sn-R alloy (wherein R is an alkali metal, an alkali It is an element selected from the group consisting of an earth metal, a Group 13 element, a Group 14 element, a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and a combination thereof; however, Sn is excluded.) and the like. In addition, as the material capable of doping and dedoping lithium, at least one of the above examples and SiO ₂ may be mixed and used. Wherein Q and R are Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe , Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S , Se, Te, Po, or the like.

In addition, the transition metal oxide may be vanadium oxide, lithium vanadium oxide, lithium titanium oxide, or the like.

Preferably, the negative electrode may include at least one negative electrode active material selected from the group consisting of a carbonaceous material and a silicon compound. Here, the carbonaceous material is, as exemplified above, natural graphite, artificial graphite, quiche graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fiber, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon It is one or more substances selected from the group consisting of. In addition, the silicon compound is a compound containing Si exemplified above, that is, Si, a Si-C composite, SiOx (0<x<2), the Si-Q alloy, a mixture thereof, or at least one of these and SiO It may be a mixture of ₂ .

The negative electrode current collector is generally made to have a thickness of 3 μm to 500 μm. Such a negative current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, the surface of copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated, aluminum-cadmium alloy, etc. may be used. In addition, the bonding strength of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwovens.

The negative electrode is manufactured by coating the negative electrode mixture including the negative electrode active material and the binder on the negative electrode current collector, drying and rolling, and, if necessary, may be prepared by further adding a conductive material, a filler, and the like.

The conductive material is used to impart conductivity to the negative electrode, and any electronically conductive material can be used as long as it does not cause chemical change in the battery configured, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black , carbon-based materials such as carbon fibers; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or a metal fiber; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

The filler is optionally used as a component for suppressing the expansion of the negative electrode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. A fibrous material such as glass fiber or carbon fiber may be used.

anode

The positive electrode includes a positive active material, and the positive active material is a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Formula Li _1+x Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, lithium manganese composite oxide represented by Ni, Cu or Zn; LiNi _x Mn _2-x O ₄ A lithium manganese composite oxide having a spinel structure; LiMn ₂ O ₄ in which a part of Li in the formula is substituted with an alkaline earth metal ion; disulfide compounds; Although Fe2 _{(MoO4)3 etc. are} mentioned, It is not limited only to these.

The positive electrode current collector is generally made to have a thickness of 3 μm to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver, etc. may be used on the surface of the surface-treated. The current collector may increase the adhesion of the positive electrode active material by forming fine irregularities on the surface thereof, and various forms such as a film, sheet, foil, net, porous body, foam body, and non-woven body are possible.

The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or 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 fibers and metal fibers; 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 may be used.

Among the negative electrode and the positive electrode, a generally known binder may be used for the electrode in which the above-described binder is not used. Representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, Polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like may be used, but is not limited thereto.

The negative electrode and the positive electrode may be prepared by mixing an active material and a binder, in some cases, a conductive material, a filler, etc. in a solvent to prepare a slurry-like electrode mixture, and applying the electrode mixture to each electrode current collector. Since such an electrode manufacturing method is widely known in the art, a detailed description thereof will be omitted herein.

IV. secondary battery

In another embodiment of the present invention, a secondary battery including the secondary battery negative electrode of the embodiment described above is provided. Such a battery, specifically, a positive electrode; electrolyte; and a negative electrode.

The secondary battery may be implemented as a lithium secondary battery.

The lithium secondary battery may be manufactured by impregnating an electrode assembly including a positive electrode, a separator, and a negative electrode with a non-aqueous electrolyte.

The positive electrode and the negative electrode are the same as described above.

In the case of the separator, any one commonly used in lithium batteries may be used as it separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. That is, a low-resistance to ion movement of the electrolyte and excellent electrolyte moisture content may be used. For example, it may be selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for lithium ion batteries, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and optionally single-layer or multi-layer structure can be used.

In some cases, a gel polymer electrolyte may be coated on the separator to increase battery stability. Representative examples of such a gel polymer include polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, and the like.

However, when a solid electrolyte other than the non-aqueous electrolyte is used, the solid electrolyte may also serve as a separator.

The non-aqueous electrolyte may be a liquid electrolyte including a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, and the like are used.

Examples of the non-aqueous electrolyte include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate , gamma-butylolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane Aprotic organic solvents such as derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used. can

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ions A polymer containing a sexually dissociating group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates, etc. of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like may be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiSCN, LiC(CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic lithium carboxylate, 4 phenyl lithium borate, and the like can be used.

In addition, for the purpose of improving charge/discharge characteristics, flame retardancy, etc. in the electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart incombustibility, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (fluoro-ethylene) carbonate), propene sultone (PRS), and fluoro-propylene carbonate (FPC) can be further included.

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

Hereinafter, preferred embodiments are presented to help the understanding of the invention. However, the following examples are only for illustrating the invention, and do not limit the invention thereto.

<Example>

Example 1

(1) Preparation of binder for negative electrode

(a) 1,3-butadiene (47.5 parts by weight), (b) styrene (47.5 parts by weight), (c) acrylic acid (2 parts by weight), and (d1) polyethylene glycol monoacrylate (3 parts by weight) a monomer mixture; sodium lauryl sulfate (0.3 parts by weight) as an emulsifier; And potassium persulfate (0.1 parts by weight) as a polymerization initiator was added to water (150 parts by weight) as a solvent.

After raising the temperature of the mixture to 75° C., the polymerization reaction was carried out at 75° C. for about 5 hours to obtain a binder including a copolymer in the form of latex particles and water.

The pH of the polymerization-completed binder was adjusted to a pH of 7 to 8 using sodium hydroxide, and the binder of Example 1 was obtained.

The binder of Example 1 thus obtained had a total solid content of 40%, and the average particle diameter of the latex particles measured using a particle size analyzer (NICOMP AW380, manufactured by PSS) was 155 nm.

(2) Preparation of negative electrode mixture

Artificial graphite (95 parts by weight) as an anode active material, acetylene black (1.5 parts by weight) as a conductive material, the binder of Example 1 (2.0 parts by weight), and carboxymethyl cellulose (1.5 parts by weight) as a thickener were used. , these were mixed by stirring for 1 hour in water as a dispersion medium. At this time, the slurry phase was adjusted so that the total solid content was 45 wt%, to obtain the negative electrode mixture of Example 1.

(3) Preparation of negative electrode

A copper foil having a thickness of 10 μm was prepared and this was used as a negative electrode current collector. Using a comma coater, the negative electrode mixture of Example 1 was applied at a loading amount of 8.0 mg/cm ² per side of the negative electrode current collector on both sides, and an oven at 80 ° C. After drying with hot air for 10 minutes in a , roll-pressed to a total thickness of 190 ㎛. Thus, the negative electrode of Example 1 was obtained.

(4) Preparation of secondary battery

Using 90 parts by weight of Li _1.03 Ni _0.6 Co _0.6 Mn _0.2 O ₂ as a positive electrode active material, 5.0 parts by weight of acetylene black as a conductive material, and 50 parts by weight (10% solids) of polyvinylidene fluoride (PVdF) as a binder, These were mixed by stirring for 1 hour in NMP which is a solvent. At this time, the slurry phase was adjusted so that the total solid content was 70% by weight, and a positive electrode mixture of Example 1 was obtained.

An aluminum foil having a thickness of 20 μm was prepared and this was used as a positive electrode current collector. Using a comma coater, the positive electrode mixture of Example 1 was applied on both sides at a loading amount of 15.6 mg/cm ² per one side of the negative electrode current collector, and an oven at 80 ° C. After drying with hot air for 10 minutes in a , roll-pressed to a total thickness of 190 ㎛. Thus, the positive electrode of Example 1 was obtained.

After assembling by inserting a separator between the negative electrode and the positive electrode of Example 1, the electrolyte was injected, and a lithium ion battery was completed according to a method commonly known in the art.

As the electrolyte, a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) (EC:PC:DEC=3:2:5 weight ratio) was dissolved in LiPF ₆ so as to have a concentration of 1.3M, and fluoroethylene carbonate (FEC) was added to account for 10% by weight of the total weight of the electrolyte.

Examples 2 to 7 and Comparative Examples 1 to 9

(1) Preparation of binder for negative electrode

Binders of Examples 2 to 7 and Comparative Examples 1 to 9 were respectively prepared by polymerization in the same manner as in Example 1, except that the monomer composition was changed according to Table 1 below.

The binders of Examples 2 to 7 and Comparative Examples 1 to 9 commonly include a copolymer in the form of latex particles, and have a total solid content of 40%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

Examples 2 to 7 and Comparative Examples 1 to 9 using the same method as in Example 1, except that the binders of Examples 2 to 7 and Comparative Examples 1 to 9 were used instead of the binder of Example 1, respectively. of each negative electrode mixture, negative electrode, and lithium secondary battery were prepared.

In Table 1, the first monomer is (a) 1,3-butadiene (BD), the second monomer is (b) styrene (SM), the third monomer is (c) acrylic acid (AA), and the fourth monomer is ( d1) polyethylene glycol monoacrylate (PEGA) or (d2) polyethylene glycol monomethacrylate (PEGMA), respectively.

In addition, the monomer content is based on the content (% by weight) in the total weight (100% by weight) of the monomer, and the content ratio of the monomer is based on the weight ratio. However, if there is a number with three decimal places or less, it is rounded off from the third decimal place and displayed to the second decimal place.

Monomer content (wt%) Monomer content ratio M1 M2 M3 M4 M1/M4 M2/M4 M3/M4 M1/M2 Example 1 47.5 47.5 2 3 15.83 15.83 0.67 One Example 2 47.5 47.5 2 3 15.83 15.83 0.67 One Example 3 47.5 47.5 2 3 15.83 15.83 0.67 One Example 4 48.5 48.5 2 One 48.5 48.5 2 One Example 5 44 44 2 10 4.4 4.4 0.2 One Example 6 48.5 48.5 2 One 48.5 48.5 2 One Example 7 44 44 2 10 4.4 4.4 0.2 One Comparative Example 1 49 49 2 0 - - - One Comparative Example 2 48.6 48.6 2 0.8 60.75 60.75 2.5 One Comparative Example 3 43 43 2 12 3.58 3.58 0.17 One Comparative Example 4 48.6 48.6 2 0.8 60.75 60.75 2.5 One Comparative Example 5 43 43 2 12 3.58 3.58 0.17 One Comparative Example 6 39 56 2 3 13 18.67 0.67 0.70 Comparative Example 7 56 39 2 3 18.67 13 0.67 1.44 Comparative Example 8 48.5 48.5 0 3 16.17 16.17 0 One Comparative Example 9 46.5 46.5 4 3 15.5 15.5 1.33 One

*M1: first monomer *M2: second monomer

*M3: third monomer *M4: fourth monomer

In Table 1, each of the monomer mixtures of Examples 1 to 7 satisfies all of the monomer types and contents limited in the embodiment.

Specifically, the monomer mixtures of Examples 1 to 7, respectively, of the total weight (100% by weight) of the monomer mixture, a) 40 to 55% by weight of the aliphatic conjugated diene-based first monomer. b) 40 to 55% by weight of aromatic vinyl-based second monomer, c) 0.1 to 3% by weight of unsaturated carboxylic acid-based third monomer, and d) 1 to 11% by weight of polyethylene glycol mono (meth)acrylate derived A binder was prepared by emulsion polymerization of a monomer mixture.

On the other hand, Comparative Example 1 does not include the fourth monomer, and Comparative Examples 2 to 5 include the fourth monomer, but less than or exceeding the content range limited to the one embodiment (Comparative Examples 2 and 4) (Comparative Examples 2 and 4) Examples 3 and 5). Comparative Examples 6 and 7 relate to a case in which the fourth monomer is included, but the content ranges of the first and second monomers are out of the preferred range. Comparative Examples 8 and 9 relate to a case in which the fourth monomer is included but the third monomer is not included or is outside the preferred range.

Further, in the monomer mixtures of Examples 1 to 7, the weight ratio of the first monomer/the fourth monomer (ie, the weight ratio of the first repeating unit/the fourth repeating unit) is in the range of 3.64 to 55, and the second the weight ratio of the monomer/fourth monomer (ie, the weight ratio of the second repeating unit/the fourth repeating unit) is in the range of 3.64 to 55, and the weight ratio of the third monomer/the fourth monomer (ie, the third repeating unit/ The weight ratio of the fourth repeating unit) is in the range of 0.01 to 3, while the weight ratio of the first monomer/second monomer (ie, the weight ratio of the first repeating unit/the second repeating unit) is in the range of 0.73 to 1.38.

On the other hand, in the monomer mixtures of Comparative Examples 1 to 5, respectively, the weight ratio of the third monomer/fourth monomer is in the range of 0.01 to 3 and the weight ratio of the first monomer/the second monomer is in the range of 0.73 to 1.38, but The weight ratio of the first monomer/the fourth monomer and the weight ratio of the second monomer/the fourth monomer do not satisfy the above-described ranges. In the monomer mixtures of Comparative Examples 6 and 7, the weight ratio of the first monomer/second monomer is outside the preferred range. In the monomer mixture of Comparative Example 8, the weight ratio of the third monomer/fourth monomer was outside the preferred range.

Comparative Example 10

(1) Preparation of binder for negative electrode

Methyl methacrylate (45 parts by weight), polyethylene glycol monoacrylate (45 parts by weight), acrylic acid (1.3 parts by weight), methacrylic acid (3.7 parts by weight), and trimethylolpropane triacrylate (5 parts by weight) A binder of Comparative Example 10 was prepared by polymerization in the same manner as in Example 1, except that the monomer mixture and water (500 parts by weight) as a solvent were used.

The binder of Comparative Example 10 includes a copolymer in the form of latex particles, and has a total solid content of 17%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

A negative electrode mixture, a negative electrode, and a lithium secondary battery of Comparative Example 10 were prepared in the same manner as in Example 1, except that the binder of Comparative Example 10 was used instead of the binder of Example 1.

Comparative Example 11

(1) Preparation of binder for negative electrode

The same method as in Example 1, except that a monomer mixture containing polyethylene glycol monoacrylate (86.4 parts by weight) and trimethylolpropane triacrylate (13.6 parts by weight) and water (500 parts by weight) as a solvent were used. By polymerization, the binder of Comparative Example 11 was prepared.

The binder of Comparative Example 11 includes a copolymer in the form of latex particles, and has a total solid content of 17%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

A negative electrode mixture, a negative electrode, and a lithium secondary battery of Comparative Example 11 were prepared in the same manner as in Example 1, except that the binder of Comparative Example 11 was used instead of the binder of Example 1.

Comparative Example 12

(1) Preparation of binder for negative electrode

Polyethylene glycol monoacrylate (30 parts by weight), vinyl acetate (15 parts by weight), acrylic acid (1.3 parts by weight), methacrylic acid (3.7 parts by weight), methyl methacrylate (45 parts by weight), and trimethylolpropanetri A binder of Comparative Example 12 was prepared by polymerization in the same manner as in Example 1, except that a monomer mixture containing acrylate (5 parts by weight) and water (500 parts by weight) as a solvent were used.

The binder of Comparative Example 12 includes a copolymer in the form of latex particles, and has a total solid content of 17%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

A negative electrode mixture, a negative electrode, and a lithium secondary battery of Comparative Example 12 were prepared in the same manner as in Example 1, except that the binder of Comparative Example 12 was used instead of the binder of Example 1.

Comparative Example 13

(1) Preparation of binder for negative electrode

A monomer mixture containing polyethylene glycol monoacrylate (30 parts by weight), vinyl acetate (55 parts by weight), acrylic acid (2 parts by weight), and trimethylolpropane triacrylate (13 parts by weight) and water as a solvent (500 parts by weight) Part) was polymerized in the same manner as in Example 1, except that the binder of Comparative Example 13 was prepared.

The binder of Comparative Example 13 includes a copolymer in the form of latex particles, and has a total solid content of 17%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

A negative electrode mixture, a negative electrode, and a lithium secondary battery of Comparative Example 13 were prepared in the same manner as in Example 1, except that the binder of Comparative Example 13 was used instead of the binder of Example 1.

Comparative Example 14

(1) Preparation of binder for negative electrode

Polyethylene glycol dimethacrylate (5 parts by weight), cyclohexyl methacrylate (30 parts by weight), methacrylic acid (1 part by weight), acrylic acid (1 part by weight), acrylamide (0.1 parts by weight), methacrylic acid 2-hydroxyethyl (5 parts by weight), 2-ethylhexyl acrylate (55 parts by weight), methyl methacrylate (1 part by weight), butyl methacrylate (0.4 parts by weight), butyl acrylate (1 part by weight) ), and by polymerization in the same manner as in Example 1, except that a monomer mixture containing trimethylolpropane triacrylate (0.5 parts by weight) was used, to prepare a binder of Comparative Example 14.

The binder of Comparative Example 14 includes a copolymer in the form of latex particles, and has a total solid content of 40%.

(2) Preparation of negative electrode mixture, negative electrode, and secondary battery

A negative electrode mixture, a negative electrode, and a lithium secondary battery of Comparative Example 14 were prepared in the same manner as in Example 1, except that the binder of Comparative Example 14 was used instead of the binder of Example 1.

Experimental Example 1: Evaluation of binder for negative electrode

For Examples 1 to 7 and Comparative Examples 1 to 14, binders were evaluated under the following conditions, respectively, and the results are recorded in Table 2 below.

(1) Average particle diameter of latex particles: Using a particle size analyzer (NICOMP AW380, manufactured by PSS), the arithmetic average particle diameter of the latex particles in the binder, specifically, the average particle diameter of scattering intensity (Intensity distribution) was obtained.

(2) Gel content in binder: Calculated using Equation 1. Specifically, after drying a predetermined binder at 80° C. for 24 hours, about 0.5 g was taken and the exact weight was measured, and this was defined as _Ma in Equation 1.

Thereafter, the weighed binder was immersed in 50 g of THF (Tetrahydrofuran) for 24 hours. After that, the binder contained in THF was filtered through 200 Mesh of known weight, and the mesh and the copolymer remaining in the mesh were dried together at 80 degrees for 24 hours, and the weight of the copolymer remaining in the mesh and the mesh was measured. , where the weight of 200 mesh was deducted, M _b was the weight of the copolymer remaining in the mesh.

[Equation 1] Gel content (%) = M _b /M _a * 100

For each binder, the average value of three or more samples was obtained, and the results are shown in Table 2 below.

(3) Stability of binder: 100 g of binder was put into a container using a homogenizer, the head was fixed immersed in latex, shear was applied at 3000 rpm for 10 minutes, and the amount of coagulation (Coagulum) was measured by filtering through 200 mesh.

Average particle diameter (㎛) of polymer (latex particles) Gel content in binder
(%) Binder Stability Test
(aggregation amount, ppm) Example 1 155 98.9 150 Example 2 151 98.8 210 Example 3 150 98.7 170 Example 4 152 98.7 180 Example 5 153 98.2 220 Example 6 150 98.8 190 Example 7 155 98.1 220 Comparative Example 1 153 98.5 180 Comparative Example 2 155 98.7 180 Comparative Example 3 160 97.8 230 Comparative Example 4 153 98.8 190 Comparative Example 5 161 97.7 250 Comparative Example 6 153 98.8 170 Comparative Example 7 155 98.7 210 Comparative Example 8 237 99.1 7,980 Comparative Example 9 150 99.0 190 Comparative Example 10 109 93.7 350 Comparative Example 11 121 99.2 1,250 Comparative Example 12 102 95.2 550 Comparative Example 13 210 98.2 980 Comparative Example 14 165 90.3 390

In Table 2, the binders of Examples 1 to 7 each contained a copolymer (latex particles) having an average particle diameter of 50 to 500 nm, and had a gel content of 95% or more, and 250 ppm or less in a stability test. It can be seen that the cohesive force appears.

On the other hand, in the binders of Comparative Examples 10 to 14, the polyethylene glycol mono (meth) acrylate-based fourth monomer was used, respectively, but the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer were not used and were used as other monomers. Replaced, it is found that at least one of gel content and stability is inferior.

On the other hand, in the binders of Comparative Examples 1 to 5, respectively, the polyethylene glycol mono (meth) acrylate-based fourth monomer was not used or the amount used did not satisfy the limited range in the embodiment, but the aliphatic conjugated diene-based first As long as the monomer and the aromatic vinyl-based second monomer are used, it is confirmed that the gel content and stability are secured at the same level as in Examples 1 to 7 above. The binders of Comparative Examples 6 and 7 do not satisfy the limited range of the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer, but as long as they are used, the gel content and stability are secured at the same level as those of Examples 1 to 7 confirmed to have been It is confirmed that the binder of Comparative Example 8 did not use the third monomer, and thus stability was lowered. The binder of Comparative Example 9 did not satisfy the limited range of the third monomer, but as long as the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer were used, the gel content and stability were equivalent to those of Examples 1 to 7 confirmed to be secured with

However, with respect to the binders of Comparative Examples 1 to 9, it is necessary to additionally check the effect when the battery is applied.

Experimental Example 2: Evaluation of negative electrode and secondary battery

For Examples 1 to 7 and Comparative Examples 1 to 14, the negative electrode and the lithium secondary battery were evaluated under the following conditions, respectively, and the results are recorded in Table 3 below.

(1) Negative electrode adhesion: For each negative electrode of Examples and Comparative Examples, the peel strength was measured 5 times or more, and the average value was obtained, and the average value is shown in Table 3 below. Here, the peeling strength is measured by attaching the negative electrode to an adhesive tape having a width of 10 mm using a tension measuring instrument (Stable Micro System, TA-XT), and then removing the tape from the negative electrode at a peeling angle of 180˚. The force (N) is measured.

(2) Initial discharge resistance of secondary battery: In a constant temperature chamber at 25 ° C, each lithium ion battery is discharged from a state of 50% SOC (state of charge) to a current of 150 A for 10 seconds. The voltage drop was recorded and the DC-resistance value was calculated using R=V/I (Ohm's Law).

(3) Capacity retention rate after 100 cycles of secondary battery: in a constant temperature chamber at 25° C., each lithium secondary battery is charged in CC/CV mode up to 4.15 V at 36 A, and then reaches 3.0 V Discharging in the CC mode was defined as one cycle, and a 20-minute rest period was placed between the charging and the discharging, and a total of 100 cycles were performed. The ratio of the discharge capacity measured in the first cycle to the discharge capacity measured in the 100th cycle was calculated.

cathodic adhesion
(gf/cm) Secondary battery initial discharge resistance
(mΩ) Capacity retention rate of secondary battery after 100 cycles (%) Example 1 29.1 1.15 92.5 Example 2 28.9 1.14 92.7 Example 3 29.3 1.15 92.5 Example 4 27.2 1.25 92.1 Example 5 25.8 1.05 91.5 Example 6 27.1 1.25 92.0 Example 7 25.7 1.07 91.4 Comparative Example 1 21.1 1.29 88.3 Comparative Example 2 25.5 1.27 89.1 Comparative Example 3 22.7 1.05 88.5 Comparative Example 4 25.7 1.25 89.0 Comparative Example 5 22.5 1.07 88.7 Comparative Example 6 18.2 1.15 89.3 Comparative Example 7 23.7 1.20 89.0 Comparative Example 8 19.1 1.18 87.5 Comparative Example 9 21.1 1.15 88.9 Comparative Example 10 19.2 1.11 89.5 Comparative Example 11 15.8 1.10 81.5 Comparative Example 12 17.3 1.15 85.7 Comparative Example 13 14.1 1.19 85.5 Comparative Example 14 22.3 1.23 87.5

From Table 3, it can be seen that Examples 1 to 7 showed excellent negative electrode adhesion, initial discharge resistance and lifespan of the secondary battery.

This is a result of emulsion polymerization of a monomer mixture that satisfies all the types and contents of the monomers (derived repeating units) limited in the embodiment, and as a result, the binder including the polymer has excellent adhesion to the negative electrode, minimizes the resistance of the secondary battery, and ultimately This means that it contributes to improving the lifespan of the secondary battery.

However, when the binder containing the fourth monomer is applied (Comparative Example 1), the negative electrode adhesive force is only 21.1 gf / cm, the initial discharge resistance of the secondary battery is high as 1.29 mΩ, and above all, the secondary battery after 100 cycles It appears that the capacity retention rate is only 88.3%.

In the case of including the fourth monomer, but less than the content range limited in the embodiment (Comparative Examples 2 and 4), the negative electrode adhesion strength than in Comparative Example 1 due to the presence of the polyethylene glycol mono (meth)acrylate-based fourth monomer increases, and the initial discharge resistance of the secondary battery partially decreased to a level of 1.25 to 1.27 mΩ, but the capacity retention rate of the secondary battery after 100 cycles remained at 89.0 to 89.1%.

In Comparative Examples 2 and 4, each weight ratio of the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer to the polyethylene glycol mono (meth)acrylate-based fourth monomer (ie, the first monomer/the fourth monomer) The weight ratio of the monomer and the weight ratio of the second monomer/the fourth monomer) exceed the above-mentioned ranges.

On the contrary, when it includes the fourth monomer but exceeds the content range limited to the one embodiment (Comparative Examples 3 and 5), by the presence of the fourth polyethylene glycol mono (meth) acrylate-based monomer than in Comparative Example 1 As the negative electrode adhesion increased, the initial discharge resistance of the secondary battery was partially decreased. However, as the content of the first and second monomers relatively decreased, the negative electrode adhesion was lower than in Comparative Examples 2 and 4, and the initial discharge resistance of the secondary battery was partially increased. Above all, it appears that the capacity retention rate of the secondary battery after 100 cycles was maintained at 88.5 to 88.7%.

In Comparative Examples 3 and 5, each weight ratio of the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer to the polyethylene glycol mono(meth)acrylate-based fourth monomer (ie, the first monomer/the fourth monomer) The weight ratio of the monomer and the weight ratio of the second monomer/the fourth monomer) are also less than the above-mentioned ranges.

When the fourth monomer is included, but the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer do not satisfy the limited range (Comparative Examples 6 and 7), the negative electrode adhesion is low or the resistance is high and the secondary battery after 100 cycles It appears that the capacity retention rate of

When the fourth monomer is included but the unsaturated carboxylic acid-based third monomer does not satisfy the limited range (Comparative Examples 8 and 9), the negative electrode adhesion is low and the capacity retention rate of the secondary battery after 100 cycles is 87.5 to 88.9%. appear.

In addition, when the polyethylene glycol mono (meth) acrylate-based fourth monomer is included, but the aliphatic conjugated diene-based first monomer and the aromatic vinyl-based second monomer are not included and are replaced with other monomers (Comparative Examples 10 to 14) , it can be seen that the adhesive strength and lifespan are inferior to those of Examples 1 to 7.

On the other hand, in Examples 1 to 7, by controlling the content of each monomer and the content ratio of two kinds of monomers, it is confirmed that the negative electrode adhesion, the initial resistance and the lifespan of the secondary battery can be adjusted.

This is, in addition to the description of the embodiment, by controlling the content of each monomer and the content ratio of two types of monomers with reference to the examples of Examples 1 to 7, negative electrode adhesion, initial resistance and lifespan of the secondary battery. It means that it is also possible to adjust the range.

Claims (20)

of the total weight (100% by weight) of the repeating units,
a) 40 to 55 wt% of a first repeating unit derived from an aliphatic conjugated diene-based first monomer;
b) 40 to 55 wt% of a second repeating unit derived from an aromatic vinyl-based second monomer;
c) 0.1 to 3% by weight of a third repeating unit derived from an unsaturated carboxylic acid-based third monomer; and
d) 1 to 11% by weight of the fourth repeating unit derived from polyethylene glycol mono(meth)acrylate
A copolymer comprising;
Binder for secondary battery negative electrode.
The method of claim 1,
The weight ratio of the first repeating unit to the fourth repeating unit is,
3.64 to 55 (first repeating unit / fourth repeating unit),
Binder for secondary battery negative electrode.
The method of claim 1,
The weight ratio of the second repeating unit to the fourth repeating unit is,
3.64 to 55 (second repeating unit / fourth repeating unit),
Binder for secondary battery negative electrode.
The method of claim 1,
The weight ratio of the third repeating unit to the fourth repeating unit is,
0.01 to 3 (third repeating unit / fourth repeating unit),
Binder for secondary battery negative electrode.
The method of claim 1,
The weight ratio of the first repeating unit to the second repeating unit is,
0.73 to 1.38 (first repeating unit/second repeating unit),
Binder for secondary battery negative electrode.
The method of claim 1,
of the total weight (100% by weight) of the repeating units,
The first repeating unit derived from the aliphatic conjugated diene-based first monomer is included in an amount of 41 to 54 wt%,
Binder for secondary battery negative electrode.
The method of claim 1,
of the total weight (100% by weight) of the repeating units,
The second repeating unit derived from the aromatic vinyl-based second monomer is included in an amount of 41 to 54 wt%,
Binder for secondary battery negative electrode.
The method of claim 1,
of the total weight (100% by weight) of the repeating units,
The third repeating unit derived from the unsaturated carboxylic acid-based third monomer is included in an amount of 1.5 to 2.3% by weight,
Binder for secondary battery negative electrode.
The method of claim 1,
of the total weight (100% by weight) of the repeating units,
The fourth repeating unit derived from polyethylene glycol mono (meth) acrylate is included in an amount of 1 to 10% by weight,
Binder for secondary battery negative electrode.
The method of claim 1,
The first monomer is
1,3-Butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,2-dimethyl-1,3-butadiene, 1,4-dimethyl-1,3- Butadiene, 1-ethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 3-methyl-1,3-pentadiene, 4-methyl -1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene, 3-ethyl-1,3-pentadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5- Hexadiene, 2-methyl-1,5-hexadiene, 1,6-heptadiene, 6-methyl-1,5-heptadiene, 1,6-octadiene, 1,7-octadiene and 7-methyl- At least one selected from the group consisting of 1,6-octadiene,
Binder for secondary battery negative electrode.
The method of claim 1,
The second monomer is
At least one selected from the group consisting of styrene, α-methylstyrene, β-methylstyrene, pt-butylstyrene, chlorostyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, and divinylbenzene ,
Binder for secondary battery negative electrode.
The method of claim 1,
The third monomer is
At least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, glutaric acid, itaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, and nadic acid,
Binder for secondary battery negative electrode.
The method of claim 1,
The copolymer is a latex particle having an average particle diameter of 50 nm to 500 nm,
Binder for secondary battery negative electrode.
The method of claim 1,
further comprising an aqueous solvent;
Binder for secondary battery negative electrode.
15. The method of claim 14,
The aqueous solvent is
Based on 100 parts by weight of the copolymer, 50 to 1,000 parts by weight included,
Binder for secondary battery negative electrode.
In the presence of an emulsifier and a polymerization initiator, emulsion polymerization of a monomer mixture to prepare a copolymer;
Of the total weight (100% by weight) of the monomer mixture, a) 40 to 55% by weight of an aliphatic conjugated diene-based first monomer, b) 40 to 55% by weight of an aromatic vinyl-based second monomer, c) a third unsaturated carboxylic acid 0.1 to 3% by weight of a monomer and d) 1 to 11% by weight of a polyethylene glycol mono (meth)acrylate monomer,
A method of manufacturing a binder for a negative electrode of a secondary battery.
A secondary battery negative electrode comprising the binder and the negative electrode active material of claim 1,
Secondary battery negative mix.
18. The method of claim 17,
further comprising a conductive material,
Secondary battery negative mix.
A negative electrode mixture layer comprising the secondary battery negative mixture of claim 17; and
including a negative electrode current collector;
secondary battery negative electrode.
Including the negative electrode of the secondary battery of claim 19,
secondary battery.