KR102191617B1 - Silicone Electrode Binder - Google Patents

Abstract

This application relates to a binder. In the present application, a binder that is applied to the manufacture of a silicon-based negative electrode and can respond well to contraction and expansion due to repeated charging and recharging, and has excellent binding strength between active materials and adhesion to the current collector, active material composition including the same, electrode and secondary battery Can provide.

Description

Silicon electrode binder {Silicone Electrode Binder}

This application relates to a silicon electrode binder.

Secondary batteries such as lithium-ion secondary batteries can be manufactured in a small size and light weight, have high energy density, and are capable of repetitive charging and discharging, so they are used in various ways, and research is also being conducted to improve the performance of secondary batteries.

For example, there is an attempt to increase the capacity by employing a silicon negative active material as a negative electrode active material.

Although the silicon-based active material has a high theoretical capacity, it greatly expands and contracts during charging and discharging, thereby deteriorating the active material over time, destroying the electrode plate structure, and damaging the conductive path within the electrode. There is a problem.

This application relates to a silicon negative electrode binder. In the present application, since it is applied to the manufacture of a silicon-based negative electrode, it is possible to provide a binder that can respond well to shrinkage and expansion due to repeated charging and discharging, and has excellent binding strength between active materials and adhesion to a current collector.

The present application relates to a silicon negative electrode binder. The term silicon anode binder refers to a binder used to manufacture a silicon-based anode.

The binder of the present application includes a gradient polymer. The gradient copolymer contains two or more types of monomer units, and a gradation from a monomer unit composition in which one monomer species predominates along the chain of the copolymer to a monomer unit composition superior in another monomer species. It means a copolymer showing gradual change. The gradient copolymer is distinguished from a block copolymer in which a change in the composition of the monomer unit occurs abruptly or a random copolymer in which the composition of a continuous monomer unit does not change.

In the present specification, the term unit refers to a state in which a certain monomer forms a main chain or side chain of a polymer through a polymerization reaction.

In the present application, by configuring the gradient copolymer having the above characteristics using predetermined monomers, it effectively responds to repeated contraction and expansion due to charging and discharging of the secondary battery, and secures the binding force between active materials and excellent adhesion to the current collector. It can provide a binder that can be.

The gradient copolymer as described above may form a micelle structure by an appropriate treatment, thereby exhibiting the above-mentioned effects.

The gradient copolymer may include at least a first monomer unit having a water solubility of 20% or more of a single polymer and a second monomer unit having a water solubility of 15% or less of the single polymer.

In the present application, the term water solubility of a single polymer means the water solubility of a homopolymer prepared using a certain monomer, which is measured in the manner presented in Examples.

In addition, in describing certain physical properties in the present specification, when the measurement temperature affects the corresponding physical properties, the corresponding physical properties are those measured at room temperature unless otherwise specified. The term room temperature is a natural temperature that is not heated or reduced, for example, any one temperature within the range of 10°C to 30°C, about 23°C or about 25°C.

The gradient copolymer of the present application includes two kinds of monomer units having different water solubility as described above, and one of the two kinds of monomer units along the chain of the copolymer is different in the monomer unit composition. The unit represents a gradual change to the composition of a superior monomer unit.

By employing such a form, a copolymer having a structure suitable for the purpose of the present application can be formed.

In one example, the water solubility of the single polymer of the first monomer unit is about 50% or more, about 55% or more, about 60% or more, about 65% or more, about 70% or more, about 75% or more, about It may be about 80% or more, about 85% or more, about 90% or more, or about 95% or more. The water solubility of the single polymer of the first monomer unit may be about 100% in another example.

In addition, the water solubility of the single polymer of the second monomer unit may be about 40% or less, about 35% or less, about 30% or less, about 25% or less, about 20% or less, or about 15% or less. In another example, the water solubility of the single polymer of the second monomer is about 0.5% or more, about 1% or more, about 1.5% or more, about 2% or more, about 2.5% or more, about 3% or more, about 3.5% or more, about 4% or more, about 4.5% or more, about 5% or more, about 5.5% or more, about 6% or more, about 6.5% or more, about 7% or more, about 7.5% or more, about 8% or more, about 8.5% or more, about It may be about 9% or more or about 9.5% or more.

The water solubility is measured by the method disclosed in Examples to be described later.

In the present application, in order to form a gradient copolymer, the relationship between the first monomer or precursor forming the first monomer unit and the second monomer forming the second monomer unit or the precursor is controlled. Can be. In the above, the precursor of the monomer is a monomer having a protecting group when a monomer having a protecting group is applied in addition to the case of using the first and/or second monomer as it is to form the first and/or second monomer unit. it means.

In addition, the reactivity ratio controlled to form the gradient polymer in the above is a value determined by the Mayo-Lewis equation (May-Lewis Equation), and the first monomer forming the first monomer unit or its The reactivity ratio of the precursor is a reactivity ratio determined in relation to the first monomer or the second monomer or the precursor thereof, and the reactivity ratio of the second monomer or the precursor forming the second monomer unit is, It is a reactivity ratio determined in the relationship between the second monomer or its precursor and the first monomer or its precursor.

In order to form a gradient polymer, a reactivity ratio (r1) of the first monomer or a precursor thereof and a reactivity ratio (r2) of the second monomer or a precursor thereof may satisfy a relationship of r1> 1> r2.

It is known that the monomers or their precursors satisfying the relationship of the reactivity ratio as described above form a gradient polymer due to the consumption rate and kinetics of the monomer during polymerization.

The specific value of the reactivity ratio is not particularly limited as long as the relationship is satisfied, and for example, the ratio of the reactivity ratio (r1/r2) is about 1.5 or more, about 2 or more, about 2.5 or more, about 3 or more, or about It may be about 3.5 or more, and the ratio (r1/r2) may be, for example, about 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, or 5 or less.

In the present specification, the "glass transition temperature" of the single polymer may be measured as a polymer made of only a corresponding monomer, or may be a glass transition temperature calculated based on the monomer composition. The glass transition temperature of the single polymer of the first monomer may be, for example, 85°C or higher, 90°C or higher, 95°C or higher, or 100°C or higher. The upper limit of the glass transition temperature of the single polymer of the first monomer is not particularly limited, for example, the glass transition temperature is 200°C or less, 190°C or less, 180°C or less, 170°C or less, 160°C or less, 150°C or less. , 140°C or less, 130°C or less, 120°C or less, or 110°C or less. The glass transition temperature of the single polymer of the second monomer is, for example, 75℃ or less, 70℃ or less, 65℃ or less, 60℃ or less, 55℃ or less, 50℃ or less, 45℃ or less, 40℃ or less, 35℃ Or less, 30°C or less, 25°C or less, 20°C or less, 15°C or less, 10°C or less, 5°C or less, 0°C or less, -5°C or less, -10°C or less, -15°C or less, -20°C or less, It may be -25°C or less, -30°C or less, -35°C or less, -40°C or less, -45°C or less, -50°C or less, or -55°C or less. The lower limit of the glass transition temperature of the single polymer of the second monomer is not particularly limited, for example, the glass transition temperature is about -200°C or higher, -190°C or higher, -180°C or higher, -170°C or higher, -160°C It may be at least -150°C, -140°C or more, -130°C or more, -120°C or more, -110°C or more, -100°C or more, -90°C or more, -80°C or more, or -70°C or more.

The gradient copolymer including the first and second monomer units having a glass transition temperature within the above range may form an appropriate micelle structure that simultaneously realizes appropriate rigidity and elasticity.

If necessary, the molecular weight characteristics of the gradient copolymer or the ratio of the first and/or second monomer units may be adjusted.

For example, the gradient copolymer may have a Number Average Molecular Weight (Mn) of 50,000 to 500,000. The number average molecular weight mentioned in the present specification can be measured using, for example, GPC (Gel Permeation Chromatograph), and unless otherwise specified in the present specification, the molecular weight of the copolymer refers to the number average molecular weight.

The gradient copolymer may have a molecular weight distribution (PDI; Mw/Mn), that is, a ratio (Mw/Mn) of a weight average molecular weight (Mw) and a number average molecular weight (Mn) in a range of about 1.5 to 2.5.

The total ratio of the first monomer unit in the gradient copolymer may be selected in consideration of the rigidity of the desired binder. For example, the ratio of the first monomer unit may be about 10 to 50% by weight based on the total weight of the gradient copolymer. In another example, the ratio may be in the range of about 15% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more.

The ratio of the second monomer unit may be included in a ratio of 100 to 900 parts by weight based on 100 parts by weight of the first monomer unit. In another example, the ratio of the second monomer unit is 110 parts by weight or more, 850 parts by weight or less, 800 parts by weight or less, 750 parts by weight or less, 700 parts by weight or less, 650 parts by weight or less with respect to 100 parts by weight of the first monomer unit. , 600 parts by weight or less, 550 parts by weight or less, 500 parts by weight or less, 450 parts by weight or less, 400 parts by weight or less, 350 parts by weight or less, 300 parts by weight or less, 250 parts by weight or less, or 200 parts by weight or less. .

Under this ratio, the gradient copolymer can form a micelle structure having appropriate stiffness and elasticity.

The gradient copolymer may include only the first and second monomer units, or, if necessary, further include units of other monomers in addition to the units. In addition, the shape may be in various shapes such as linear, branched, or constellation.

The gradient copolymer may be an acrylic copolymer. The term acrylic copolymer is a copolymer containing an acrylic monomer unit as a main component. In the present specification, it means that a component is included as a main component, wherein the weight ratio of the component is about 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80 This is the case in which it is at least 85% by weight, or at least 90% by weight. In the above, the upper limit of the proportion of the main component is not particularly limited, and may be about 100% by weight.

The term acrylic monomer means acrylic acid, methacrylic acid or derivatives thereof, for example acrylic acid esters or methacrylic acid esters.

In one example, the first monomer unit may be a monomer unit having a carboxyl group. As described above, the unit may be included in a proportion of about 10 to 50% by weight in the gradient copolymer.

As the monomer having a carboxyl group, a known component may be used without particular limitation, and for example, (meth)acrylic acid, 2-(meth)acryloyloxy acetic acid, 3-(meth)acryloyloxy propyl acid , 4-(meth)acryloyloxy butyric acid, acrylic acid duplex, itaconic acid, maleic acid and maleic anhydride, etc. may be used. It is not limited thereto. In one example, acrylic acid may be applied.

In one example, the second monomer unit may be a monomer unit having a hydroxy group, a heterocyclic moiety, or a ureido group. Examples of the heterocyclic moiety in the above may include a tetrahydrofurfuryl group.

As the monomer, a known component may be used without particular limitation, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth) Hydroxyalkyl (meth)acrylate, such as acrylate, 6-hydroxyhexyl (meth)acrylate or 8-hydroxyoctyl (meth)acrylate, or 2-hydroxypolyethylene glycol (meth)acrylate or 2- Hydroxy group-containing monomers such as hydroxypolyalkylene glycol (meth)acrylate such as hydroxypolypropylene glycol (meth)acrylate, and monomers having heterocyclic residues such as tetrahydrofurfuryl (meth)acrylate; Alternatively, a ureido group-containing monomer such as ureido (meth)acrylate may be used. It is not limited thereto. In one example, 2-hydroxyethyl acrylate may be applied.

The gradient copolymer may include other monomer units when necessary in addition to the first and second monomer units. At this time, the monomer that can be applied is not particularly limited.

For example, the gradient copolymer is an alkyl (meth)acrylate unit, for example, an alkyl group having 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Branches are alkyl (meth)acrylate units, etc., or (meth)acrylonitrile, (meth)acrylamide, N-methyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-vinyl pyrrolidone Or nitrogen-containing monomer units such as N-vinyl caprolactam; Styrene-based monomer units such as styrene or methyl styrene; Glycidyl group-containing monomer units such as glycidyl (meth)acrylate; Alternatively, a carboxylic acid vinyl ester unit such as vinyl acetate may be exemplified, but is not limited thereto.

When a unit of a monomer that may be additionally included as described above is included, the monomers are 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight based on 100 parts by weight of the total of the first and second monomer units. It can be included in the following ratio. The lower limit of the ratio of the other monomer units is not particularly limited. For example, when the monomer unit is not included, the ratio is 0 parts by weight, and when included, it is more than 0 parts by weight.

The method for preparing the gradient copolymer as described above is not particularly limited, and may be prepared in a conventional manner. The gradient copolymer is, for example, polymerized by the LRP (Living Radical Polymerization) method, for example, an organic rare earth metal composite is used as a polymerization initiator, or an organic alkali metal compound is used as a polymerization initiator to form an alkali metal or an alkaline earth metal. Anionic polymerization synthesized in the presence of inorganic acid salts such as salts, anionic polymerization methods synthesized in the presence of organoaluminum compounds using an organic alkali metal compound as a polymerization initiator, atom transfer radical polymerization using an atom transfer radical polymerization agent as a polymerization control agent ARGET (Activators Regenerated by Electron Transfer) ARGET (Activators Regenerated by Electron Transfer) method (ATRP), ICAR (Initiators), which uses an atom transfer radical polymerization agent as a polymerization control agent but performs polymerization under an organic or inorganic reducing agent that generates electrons. for continuous activator regeneration) atomic transfer radical polymerization (ATRP), reversible addition-cleavage chain transfer using an inorganic reducing agent reversible addition-cleavage chain transfer polymerization method (RAFT), or a method using an organic tellurium compound as an initiator. In this case, an appropriate method can be selected and applied among these methods.

This application also relates to a silicone electrode binder composition. The composition may include at least the above-described gradient copolymer or a binder having the same, and may further include other components. For example, the binder composition may include a crosslinking component capable of crosslinking the gradient copolymer. Such a crosslinking component may be selected so that, for example, the gradient copolymer can crosslink the shell portion when the micelle is formed.

The type of the crosslinking component applied above is not particularly limited, and may be selected according to a known method.

For example, when the gradient polymer includes a crosslinkable functional group such as a hydroxy group, a urethane crosslinking method in which a crosslinking agent such as an isocyanate crosslinking agent is applied may be applied. In this case, as the crosslinking agent, diisocyanate compounds such as tolyene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoboro diisocyanate, tetramethylxylene diisocyanate or naphthalene diisocyanate, or the diisocyanate. A compound obtained by reacting the compound with a polyol (ex. trimethylol propane) may be exemplified. In another way, a material such as isocyanatoalkyl (meth)acrylate is applied to convert some or all of the hydroxy groups into radical reactive groups such as (meth)acryloyl groups, and then a crosslinked structure is implemented through a radical reaction. Method, etc. can be used.

Such a crosslinked structure may be provided so that an appropriate degree of crosslinking is ensured to impart appropriate elasticity to the binder. For example, the degree of crosslinking may be imparted such that the gel fraction calculated by the distilled water extraction residue is in the range of 10 to 30%. This degree of crosslinking (gel fraction) can be achieved through adjustment of the type or ratio of the crosslinking agent to be applied, the type or ratio of the crosslinking functional group, or the conditions for crosslinking.

The gel fraction may be specifically determined according to Equation 1 below.

[Equation 1]

Gel fraction (%) = B/A × 100

In Equation 1, A is the mass of the block copolymer, and B is the insoluble, collected after 72 hours immersion in distilled water at room temperature with the block copolymer having the mass A in a 200 mesh size net. Shows the dry mass of sea meal.

By maintaining the gel fraction in the above range, a binder suitable for the purpose of the present application may be implemented.

In the above, room temperature is a natural temperature that is heated or not reduced, and is any one temperature in the range of about 10°C to 30°C, about 23°C or about 25°C.

In addition, in the above, the dry mass means a state in which a suitable drying process is performed on the collected insoluble matter so that the insoluble matter does not substantially contain a solvent (etal acetate, etc.), for example, The amount is about 1% by weight or less, 0.5% by weight or less, 0.1% by weight or less, or 0.05% by weight or less. Drying conditions applied for this purpose are not particularly limited, and may be adjusted so that the amount of solvent as described above can be achieved.

The silicone electrode binder composition may be the gradient copolymer itself, or may include the gradient copolymer and other known additives or binders.

As the additive that can be applied in the above, an aqueous solvent such as water, a solvent such as an organic solvent or a mixed solvent of two or more types, a thickener, a conductive material, a reinforcing material, a leveling agent, or an electrolyte solution additive may be exemplified.

The present application also relates to a silicon electrode active material composition. The active material composition may be, for example, a silicon negative active material composition.

The active material composition may include an electrode (eg, negative electrode) active material and the binder, wherein the active material may include a silicon negative electrode active material. By using such an active material composition, the productivity of the electrode can be improved, and the secondary battery can exhibit excellent cycle characteristics and storage stability. The proportion of the binder in the composition may be about 0.05 to 10% by weight based on the solid content. In addition, the solid content in the above is a state that does not contain a solvent such as an organic or aqueous solvent, for example, the ratio of the solvent is 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight Hereinafter, 1% by weight or less, 0.5% by weight or less, or 0% by weight.

The composition basically includes the binder and the active material, and if necessary, may include a solvent or other components (thickener, etc.).

The electrode active material, for example, the negative electrode active material, is a material capable of transferring electrons from the negative electrode of a secondary battery, for example, a lithium secondary battery. For example, as a negative active material for a lithium ion secondary battery, a material capable of storing and releasing lithium is generally used. The composition of the present application includes at least a silicon negative active material as an active material.

Examples of the silicon negative electrode active material include silicon (Si), an alloy containing silicon, SiO, SiO2, SiOx, and a composite product of a Si-containing material and conductive carbon formed by coating or complexing a Si-containing material with conductive carbon. . These silicon negative active materials may be used singly or in combination of two types.

In the above, as the alloy containing silicon, an alloy composition including at least one element selected from the group consisting of silicon and titanium, iron, cobalt, nickel, and copper may be exemplified. Further, as an alloy containing silicon, for example, an alloy composition containing silicon, a transition metal such as aluminum and iron, and a rare earth element such as tin and yttrium can also be used.

SiOx is SiO and SiO ₂ It may be a compound containing at least one of and Si, wherein x is generally 0.01 or more and less than 2 in the range. SiOx can be formed using, for example, a disproportionation reaction of SiO. Specifically, SiOx can be prepared by optionally heat-treating SiO in the presence of a polymer such as polyvinyl alcohol to produce silicon and silicon dioxide. The heat treatment may be performed at a temperature of, for example, 900°C or higher or 1000°C or higher in an atmosphere containing an organic gas and/or steam after pulverizing and mixing SiO and the polymer.

Examples of the composite of Si-containing material and conductive carbon include compounds obtained by heat-treating a pulverized mixture of SiO and a polymer such as polyvinyl alcohol and optionally a carbon material in an atmosphere containing organic gas and/or steam. . In addition, the composite product is a method of coating the surface of SiO particles by chemical vapor deposition using organic gas, etc., a method of forming (assembly) SiO particles with graphite or artificial graphite by a mechanochemical method. It can also be obtained by a known method.

From the viewpoint of increasing the capacity, the silicon-containing alloy and SiOx described above may be used as the silicon negative active material.

The active material may be typically included in a ratio of 90 to 97 parts by weight based on 100 parts by weight of the binder.

In addition, in the composition, as an active material, the silicone material and other known carbon-based negative active materials and/or metal-based negative active materials may be used in combination.

Other components that may be included in the active material composition may include, but are not limited to, a solvent, a thickener, a conductive material, a reinforcing material, a leveling agent, or an electrolyte solution additive.

The active material composition may be prepared by mixing the components in a known manner without any particular limitation.

For example, the composition can be prepared by adding and mixing an appropriate dispersion medium as necessary to each of the above components. For example, a ball mill, sand mill, bead mill, pigment disperser, ultrasonic disperser, homogenizer, rotation It can be prepared by mixing each of the above components using a mixer such as a revolutionary mixer or a fill mix.

The present application also relates to a silicon electrode for a secondary battery, for example, a silicon negative electrode for a secondary battery. The electrode may be used, for example, in a lithium secondary battery.

For example, the silicon electrode includes a current collector and an electroactive layer formed on the current collector, and the electrode active layer contains at least a silicon electrode active material and the binder. Each component included in the electroactive layer was included in the active material composition, and specific examples and ratios thereof are in accordance with the above-mentioned contents. 1 shows a case where the electrode active layer 200 is inclined on the current collector 100.

The electrode may be manufactured according to a known method of, for example, applying and drying the above-described active material composition on a current collector, and rolling if necessary.

In the above, the method of applying the composition onto the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. Such coating may be performed only on one side of the current collector, or may be performed on both sides, and a known thickness may be applied to the thickness of such coating.

In the above, as the current collector, a material having electrical conductivity and electrochemically durable is used. In general, as the current collector, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, copper foil or platinum are used, and these materials are used alone or in combination of two or more. It could be.

The present application also relates to a secondary battery including the electrode, for example, a lithium ion secondary battery having the silicon electrode as a negative electrode.

The configuration of such a secondary battery is not particularly limited, and may have a known configuration as long as it includes the electrode.

For example, the lithium ion secondary battery may include the silicon electrode as the negative electrode in a general configuration including a positive electrode, a negative electrode, an electrolyte, and a separator.

Each component included in the secondary battery, for example, a specific type of a positive electrode, an electrolyte, a separator, or the like, or a method of forming a secondary battery using the same, is not particularly limited, and a known method may be applied.

In the present application, a binder that is applied to the manufacture of a silicon-based negative electrode and can respond well to contraction and expansion due to repeated charging and recharging, and has excellent binding strength between active materials and adhesion to the current collector, active material composition including the same, electrode and secondary battery Can provide.

1 is an exemplary schematic diagram of an electrode of the present application.

Hereinafter, the apparatus and method will be described in detail through Examples and Comparative Examples, but the scope of the apparatus and method is not limited by the following Examples.

1. Molecular weight evaluation

The weight average molecular weight (Mw) and molecular weight distribution (PDI) were measured under the following conditions using GPC (Gel Permeation Chromatograph), and the measurement results were converted using standard polystyrene of Agilent system to prepare a calibration curve.

<Measurement conditions>

Measuring instrument: Agilent GPC (Agilent 1200 series, U.S.)

Column: PLGel-M, PLGel-L series connection

Column temperature: 35°C

Eluent: THF (Tetrahydrofuran)

Flow rate: 1.0 mL/min

Concentration: ~ 1 mg/mL (100 μL injection)

2. Polymer conversion and NMR evaluation

Conversion rate was calculated according to Equation 1 below by applying the integral value of the signal by the monomer and the signal by the polymer in the spectrum obtained by NMR analysis.

NMR analysis was performed at room temperature using Agilent's 500 MHz instrument, and the analyte (polymerization reactant, etc.) was diluted to a concentration of about 10 mg/ml in a measurement solvent (CDCl3 and D2O). Expressed in ppm.

[Equation 1]

Conversion rate (%) = 100 × polymer signal integral value/(polymer signal integral value + monomer signal integral value)

3. Solubility measurement method

Solubility was evaluated by collecting 1 g of a solubility measurement object (polymer or monomer), putting it in 5 g of water, stirring at room temperature (25° C.) for 30 minutes, and removing undissolved residual solute. The amount of the removed residual solute was measured, the amount of the solute left in the solvent was measured, and the measured amount was converted into a value for 100 g of the solvent to evaluate the solubility. In the above, the residual solute was removed by holding the solution while the pore size was about 0.45 μm.

The water solubility was calculated as a percentage based on the weight of the amount of solute dissolved in the solvent (water solubility = 100 × B (B + A), where B is the weight of the solute (unit: g), and A is the solvent Is the weight (unit g).).

In addition, the polymer solubility shown in Table 1 was measured in the above manner for the polymer itself prepared in each Example or Comparative Example, and the water solubility of the single polymer of the monomer was prepared by the method disclosed in the following Examples, Only the above monomer was measured for a homopolymer itself by applying the method disclosed in the following examples. For example, the water solubility of acrylic acid (AA) was measured for a polymer obtained by removing tert-butyl group as a protecting group after preparing tert-butyl acrylate (t-BA) according to the method presented below.

4. Adhesion measurement

The prepared negative electrode was punched so that the horizontal length was about 1.5 cm and the vertical length was about 12 cm to prepare a specimen. Next, a double-sided tape was applied on a glass slide glass, the back side of the 3M's adhesive tape was affixed on the double-sided tape, and the slurry side of the punched negative electrode was stuck on the adhesive tape to obtain a measurement sample. After that, tear off one end of the negative electrode attached to the glass about 0.5 cm, fix it to the lower clamp of the Texture Analyzer, fix the other sagging part of the negative electrode with the upper clamp, and pull the negative electrode slurry with a force of about 2 gf. Measure the force at the time of falling.

5. Maximum particle size measurement

The maximum particle size was measured using a plate having fine pores having different sizes from 1 μm to 100 μm. Take 1 g of the prepared slurry and place it on the end of the large hole. The slurry was scraped down from the 100 μm portion to the side where the small hole was cut with a plate stick, and the size of the hole at the place where the slurry was no longer scratched was read to determine the maximum particle size.

Preparation Example 1. Preparation of gradient polymer (A1)

To a 100 mL round bottom flask, add 14.2 g of 2-hydroxyethyl methacrylate (2-HEMA, water solubility: about 12%), 7.3 g of tert-butyl acrylate (t-BA) and 40 g of ethanol, It was sealed. In the above, tert-butyl acrylate is a precursor for finally forming an acrylic acid (AA, water solubility: 99% or more) unit through a process described later. Oxygen was removed by bubbling with nitrogen for 30 minutes, and after placing the reaction flask in an oil bath heated to 65°C, 2 mg of CuBr2, 6 mg of tris(2-pyridylmethyl)amine ( The reaction was initiated by administering tris(2-pyridylmethyl)amine) and 7 mg of initiator (VA-65, Wako Chem). For the monomers applied above, the reactivity ratio obtained by the Mayo-Lewis integral equation was about 2 for 2-HEMA and about 0.5 for t-BA. The reaction was performed for about 10 hours and then terminated to prepare a gradient polymer. The conversion rate calculated for the sum of the monomers HEMA and t-BA applied in the reaction was about 90%.

As described above, since the reactivity ratio (r1) of 2-HEMA is about 2 and the reactivity ratio (r2) of t-BA is about 0.5 satisfies the relationship of r1> 1> r2, the consumption rate and kinetics of monomers during polymerization It can be seen that the gradient polymer is formed by considering.

After dispersing 5 g of the gradient polymer in 20 g of distilled water, 5 g of trifluoroacetic acid was added and refluxed at 80°C to remove the tert-butyl group as a protecting group from the t-BA polymerization unit, and a hydroxy group (2-HEMA Derived) and a gradient polymer having a carboxyl group (from t-BA) was formed. In the gradient polymer, the weight ratio of the 2-HEMA unit and the AA unit (AA: acrylic acid, water solubility: 99% or more) (from t-BA) was about 65:35 (2-HEMA:AA).

The NMR analysis results of the prepared gradient polymer are as follows.

<NMR measurement result>

<1>H NMR(D2O): [delta] 3.44-3.58 (br, 2.7H); ? 2.01-2.40 (br, 0.7H); δ 1.25~1.97 (br, 6H)

Preparation Example 2. Preparation of gradient polymer (A2)

The gradient polymer was prepared in the same manner as in Preparation Example 1, except that 3-hydroxypropyl methacrylate (3-HPMA, water solubility: about 10%) was applied instead of 2-hydroxyethyl methacrylate (2-HEMA). Formed. For the monomers applied above, the reactivity ratio obtained by the Mayo-Lewis integral equation was about 1.9 for 3-HPMA and about 0.5 for t-BA.

Considering the relationship between the reactivity ratio, the consumption rate of the monomer, and kinetics as described above, it can be seen that the gradient polymer was formed.

In the same manner as in Preparation Example 1, 5 g of the gradient polymer was dispersed in 20 g of distilled water, and then 5 g of trifluoroacetic acid was added, followed by refluxing at 80°C to remove the tert-butyl group, a protecting group, from the t-BA polymerization unit. Thus, a gradient polymer having a hydroxy group (from 3-HPMA) and a carboxyl group (from t-BA) was formed. In the gradient polymer, the weight ratio of the 2-HPMA unit and the AA unit (from t-BA) was about 65:35 (2-HPMA:AA).

The NMR analysis results of the prepared gradient polymer are as follows.

<NMR measurement result>

<1>H NMR(D2O): [delta] 3.20~3.58 (br, 3.7H); ? 2.01-2.40 (br, 0.7H); δ 1.25~1.97 (br, 6H)

Preparation Example 3. Preparation of gradient polymer (A3)

A gradient polymer was prepared in the same manner as in Preparation Example 1, but the weight of the monomer was adjusted so that the weight ratio of the 2-HEMA unit and the AA unit (from t-BA) in the gradient polymer was about 55:45 (2-HEMA:AA). Controlled to prepare a gradient polymer (2-HEMA: 14 g, t-BA: 11.5 g).

Considering the relationship between the reactivity ratio, the consumption rate of the monomer, and kinetics as described above, it can be seen that the gradient polymer was formed.

The NMR analysis results of the prepared gradient polymer are as follows.

<NMR measurement result>

<1>H NMR(D2O): [delta] 3.44-3.58 (br, 2.3H); ? 2.01-2.40 (br, 0.8H); δ 1.25~1.97 (br, 5.9H)

Preparation Example 4. Preparation of block polymer (B1)

To a 100 mL round-bottom flask, 5 g of 2-hydroxyethyl methacrylate (2-HEMA) protected by trimethylsilyl group and 16 g of ethyl acetate were added, and the inlet was sealed. Oxygen was removed by bubbling with nitrogen for 30 minutes, and after placing the reaction flask in an oil bath heated to 65°C, 1 mg of CuBr2, 4 mg of tris(2-pyridylmethyl)amine ( tris(2-pyridylmethyl)amine) and 3 mg of initiator (VA-65, Wako Chem) were administered to initiate the reaction. The reaction was terminated after the reaction for about 8 hours (synthesis of the first segment, conversion of monomer (2-HEMA) about 89%).

The obtained first segment was dissolved in 20 g of ethyl acetate, 2.4 g of tert-butyl acrylate was added, and the inlet was sealed. Oxygen was removed by bubbling with nitrogen for 30 minutes, and 0.5 mg of CuBr2, 2 mg of tris(2-pyridylmethyl)amine after placing the reaction flask in an oil bath heated to 65°C (tris(2-pyridylmethyl)amine) and 1.5 mg of initiator (VA-65, Wako Chem) were administered to initiate the reaction. The reaction was terminated after the reaction for about 9 hours (synthesis of block copolymer, conversion of monomer (t-BA) about 99%).

After dispersing 5 g of the block copolymer in 20 g of distilled water, 5 g of trifluoroacetic acid was added and refluxed at 80°C to remove the tert-butyl group as a protecting group from the t-BA polymerization unit, and The trimethylsilyl group was removed.

Preparation Example 5. Preparation of binder (B2)

A binder was prepared by mixing styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) obtained from Sigma-Aldrich at a weight ratio of 7:3 (SBR:CMC).

Example 1.

After mixing the polymer (A1) (binder), active material mixture, and conductive material (Super C) prepared in Preparation Example 1 at a weight ratio of 4:95:1 (binder: active material mixture: conductive material), water was added as a solvent Thus, a negative electrode slurry composition was prepared. In the above, the active material mixture is a known silicone-based mixture, and a mixture in which a carbon active material and a silicone-based active material are mixed in a weight ratio of about 90:10 (carbon active material: silicon-based active material) was used. Thereafter, the slurry was coated on a copper foil current collector having a thickness of about 20 μm so that the thickness after drying was about 100 μm, and vacuum-dried for about 10 hours at about 100 to about 1.5 mAh/cm2 A phosphorus negative electrode was prepared.

Example 2.

A negative electrode was prepared in the same manner as in Example 1, except that the polymer (A2) prepared in Preparation Example 2 was used.

Example 3.

A negative electrode was prepared in the same manner as in Example 1, except that the polymer (A3) prepared in Preparation Example 3 was used.

Comparative Example 1.

A negative electrode was prepared in the same manner as in Example 1, except that the polymer (B1) prepared in Preparation Example 4 was used.

Comparative Example 2.

A negative electrode was prepared in the same manner as in Example 1, except that the binder (B2) prepared in Preparation Example 5 was used.

The physical properties measured above are summarized and described in Table 1 below.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Polymer solubility More than 80% More than 80% More than 90% Less than 20% Less than 5% Maximum particle size of slurry (㎛) 60 72 58 100 90 Adhesion (gf/cm) 58 55 60 47 53

From Table 1, in the case of the Example, it can be seen that aggregation of the binder or the active material is small when preparing the slurry, which is expected to be due to the structural characteristics of the gradient polymer. That is, it is expected that this is because the first monomer unit having high solubility exists in a form in which the ratio gradually increases throughout the polymer, thereby increasing the overall solubility of the formed micelles. In addition, in the case of the example, the adhesive properties were also excellent.

Through this, it can be seen that when the binder of the present application is applied, there is an effect of increasing the dispersibility of the active material while maintaining the adhesive strength in the silicon-based negative electrode material, and thus, excellent cycle characteristics can be secured.

100: current collector
200: electroactive layer

Claims (16)

A gradient polymer having a first monomer unit having a water solubility of 20% or more of a single polymer and a second monomer unit having a water solubility of 15% or less of the single polymer,
The first monomer is a carboxyl group-containing monomer, the second monomer is a hydroxy group-containing monomer, a heterocyclic moiety-containing monomer, or a ureido group-containing monomer,
The ratio of the second monomer unit in the gradient polymer is in the range of 100 to 900 parts by weight based on 100 parts by weight of the first monomer unit. A silicone electrode binder comprising a linear or branched gradient polymer having a first monomer unit having a water solubility of a single polymer of 20% or more and a second monomer unit having a water solubility of a single polymer of 15% or less. The reactivity ratio (r1) determined in the relationship with the first monomer or the second monomer of the precursor or the precursor and the first monomer or the precursor of the second monomer or the precursor according to claim 1 or 2 A silicon electrode binder containing a gradient polymer in which the relationship of the reactivity ratio (r2) determined in the relationship with r1> 1> r2 is satisfied. The silicone electrode binder according to claim 1 or 2, wherein the single polymer of the first monomer has a glass transition temperature of 80°C or higher. The monomer according to claim 1 or 2, wherein the carboxyl group-containing monomer is (meth)acrylic acid, 2-(meth)acryloyloxy acetic acid, 3-(meth)acryloyloxy propyl acid, and 4-(meth)acrylic. A silicone electrode binder which is royloxy butyric acid, acrylic acid duplex, itaconic acid, maleic acid or maleic anhydride. The silicone electrode binder according to claim 1 or 2, wherein the weight ratio of the first monomer unit in the gradient polymer is in the range of 10 to 50% by weight. The silicon electrode binder according to claim 1 or 2, wherein the glass transition temperature of the single polymer of the second monomer is less than 80°C. delete The method according to claim 1 or 2, wherein the second monomer is hydroxyalkyl (meth)acrylate, hydroxy polyalkylene glycol (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, or ureido (meth)acrylate. ) A silicon electrode binder that is an acrylate. delete A silicone electrode binder composition comprising the binder of claim 1 or 2. An active material composition comprising the silicon electrode binder of claim 1 or 2 and an electrode active material. The active material composition of claim 12, wherein the electrode active material is a silicone active material. A current collector and an electrode formed on one surface of the current collector and including the silicon electrode binder of claim 1 or 2 and an electrode active material. The electrode according to claim 14, wherein the electrode active material is a silicon active material. A secondary battery comprising the electrode of claim 15 as a negative electrode.

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