KR20220087656A - Binder composition for anode of secondary battery, method for manufacturing the same, anode and secondary battery including the same - Google Patents

Abstract

The present invention relates to a binder composition for a negative electrode of a secondary battery, a manufacturing method thereof, an anode comprising the same, and a secondary battery.
Specifically, in embodiments of the present invention, cyanoethylated polyvinyl alcohol; neutralized polyacrylic acid; and a styrene-butadiene-based copolymer; a binder composition for a negative electrode of a secondary battery comprising; its manufacturing method; a negative electrode including the same; and a secondary battery.

Description

Binder composition for negative electrode of secondary battery, manufacturing method thereof, negative electrode and secondary battery comprising same

The present invention relates to a binder composition for a negative electrode of a secondary battery, a manufacturing method thereof, an anode comprising the same, and a secondary battery.

BACKGROUND ART A secondary battery is in the spotlight as a power source for not only small electronic devices such as portable computers, portable telephones, and cameras, but also large electronic devices such as electric vehicles and power storage devices. Accordingly, interest in an anode active material having a theoretical capacity higher than 372 mAh/g, which is a theoretical capacity of graphite, is increasing.

In particular, silicon is a material having a theoretical capacity more than 10 times higher than that of graphite, and research for using a silicon-based anode active material as an anode active material is being actively conducted. Specifically, attempts have been made to use a silicon-based negative active material and a composite negative active material of the same and a graphite-based negative active material.

However, during the charging and discharging process of the secondary battery, an extreme volume change of the silicon-based negative active material occurs, which leads to problems such as a decrease in negative electrode adhesion and a decrease in battery capacity retention.

Accordingly, in order to suppress the deterioration of battery characteristics due to the volume change of the silicon-based negative active material, it is the key to apply an excellent binder system to the negative electrode of the secondary battery.

The present invention, in a secondary battery using a composite negative active material of a silicon-based negative active material and a graphite-based negative active material, suppresses deterioration of battery characteristics due to a change in the volume of the negative active material, and realizes excellent cycle characteristics.

In addition, the present invention is to realize excellent dispersibility and stability during the preparation of the negative electrode mixture slurry composition.

In embodiments of the present invention, cyanoethylated polyvinyl alcohol; neutralized polyacrylic acid; and a styrene-butadiene-based copolymer; a binder composition for a negative electrode of a secondary battery comprising; its manufacturing method; a negative electrode including the same; and a secondary battery.

The binder composition of the embodiment includes cyanoethylated polyvinyl alcohol having high adhesion and high dielectric properties and neutralized polyacrylic acid capable of overcoming the volume change of the negative electrode active material, and styrene having excellent adhesion properties with the graphite negative active material -It contains a butadiene-based copolymer.

Therefore, in a secondary battery using a composite negative active material of a silicon-based negative active material and a graphite-based negative active material, when the binder composition of one embodiment is applied to the negative electrode, the decrease in battery characteristics due to the volume change of the negative electrode active material is suppressed, and excellent cycle Characteristics may be implemented.

In addition, the negative electrode mixture slurry composition prepared using the binder composition of the embodiment may exhibit excellent dispersibility and stability.

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.

The terminology used herein is used to describe exemplary embodiments only, 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.

In this specification, when each layer or element is referred to as being formed "on" or "over" each layer or element, it means that each layer or element is formed directly on each layer or element, or another layer. or that elements may be additionally formed between each layer, on an object, on a substrate.

In the present specification, unless otherwise defined, "copolymerization" may mean block copolymerization, random copolymerization, graft copolymerization, or alternating copolymerization, and "copolymer" means block copolymer, random copolymer, graft copolymer, or alternating copolymers.

As used herein, "aqueous solution" and "aqueous dispersion" mean a composition in which an aqueous solvent is mixed, "polyvinyl alcohol", "cyanoethylated polyvinyl alcohol", "polyacrylic acid", "neutralized polyacrylic acid" , "styrene-butadiene-based copolymer", etc. may mean a solid content in which an aqueous solvent is not mixed.

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.

Binder for negative electrode of secondary battery

Limitations of commonly known binders for negative electrodes

Commonly known binders for negative electrodes of secondary batteries include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and the like.

Among them, PVDF has excellent interaction with a carbon-based negative active material such as graphite, and has an advantage of being electrochemically stable.

However, PVDF lacks interaction with the silicon-based anode active material, so the binding force is low and flexibility is insufficient. Accordingly, when PVDF is applied as a binder for a negative electrode of a secondary battery using a silicon-based negative active material and a composite negative active material of the graphite-based negative active material, the negative active material-binder bond is destroyed according to the contraction and expansion of the negative electrode active material during charging and discharging. , there is a problem in that the cycle characteristics of the secondary battery are deteriorated.

Moreover, PVDF has a problem of causing environmental pollution because it is necessary to prepare a non-aqueous negative electrode slurry using an organic solvent.

SBR is a particulate polymer produced by emulsion polymerization, and has the advantage of improving the capacity and initial charge/discharge efficiency of a secondary battery by being environmentally friendly and exhibiting excellent bonding strength even when used in a small amount.

However, the SBR has a narrow contact area to the anode active material. Therefore, when SBR is applied alone as a binder for a negative electrode of a secondary battery using a composite negative active material of a silicon-based negative active material and a graphite-based negative active material, SBR cannot suppress the volume change of the negative electrode active material, and it is difficult to maintain stable cycle characteristics. .

Cyanoethylated polyvinyl alcohol, neutralized polyacrylic acid and styrene-butadiene copolymer

In order to solve the problem of applying SBR alone, polyacrylic acid (PAA), which forms a strong hydrogen bond on the surface of the silicon-based negative active material, and shows high adhesion, and polyvinyl alcohol (PVA) with excellent mechanical properties, are mixed with styrene-butadiene (SBR). )-based copolymer and a blended binder may be considered.

However, polyacrylic acid and polyvinyl alcohol are polymers with strong polarity and hydrophilicity, and have poor compatibility with SBR and graphite-based anode active material particles, resulting in low dispersibility and stability in the preparation of anode slurry.

Accordingly, when polyacrylic acid, polyvinyl alcohol, and a styrene-butadiene-based copolymer are blended and applied to the negative electrode, battery cycle characteristics may be adversely affected.

In order to overcome the above limitations, in one embodiment of the present invention, polyacrylic acid was partially neutralized, polyvinyl alcohol was modified, and styrene-butadiene-based copolymer was blended.

In other words, in one embodiment of the present invention, cyanoethylated polyvinyl alcohol, neutralized polyacrylic acid, and a styrene-butadiene-based copolymer; provides a binder composition for a negative electrode of a secondary battery comprising.

The cyanoethylated polyvinyl alcohol is a polymer having a balance of hydrophilic functional groups and lipophilic functional groups due to the characteristics of functional groups in the molecule. Compared to non-cyanoethylated polyvinyl alcohol, styrene-butadiene copolymer and has excellent compatibility.

Furthermore, the cyanoethylated polyvinyl alcohol, as a high dielectric constant material with high adhesive properties, is advantageous for dissociation of lithium ions and movement of electrons.

Specifically, the cyanoethylated polyvinyl alcohol has a higher dielectric constant at high temperature compared to polyvinyl alcohol that is not cyanoethylated as well as generally known binders for negative electrodes (PVDF, SBR, etc.). holds

More specifically, the dielectric constants of cyanoethylated polyvinyl alcohol, non-cyanoethylated polyvinyl alcohol, PVDF, polyacrylic acid, and SBR with a cyanoethyl substitution rate of 80% are compared as follows.

Dielectric Constant (ε): Cyanoethylated polyvinyl alcohol with 80% cyanoethyl substitution (15) > polyvinyl alcohol (11) > PVDF (10) > polyacrylic acid (5) > SBR (3)

In particular, comparing the dielectric constants of polyvinyl alcohol cyanoethylated at 80% cyanoethyl substitution rate and polyvinyl alcohol that is not cyanoethylated at 25 °C, 50 °C and 75 °C, respectively, is as follows. same.

Dielectric Constant (ε) (cyanoethylated polyvinyl alcohol vs. polyvinyl alcohol: 15 vs. 11 (@ 25 °C) < 22 vs. 12 (@ 50 °C) < 31 vs. 14 (@ 75 °C)

Accordingly, the secondary battery to which the cyanoethylated polyvinyl alcohol is applied as a binder for the negative electrode can implement excellent cycle characteristics when driving the battery for a long period of time, and can be operated for a long time without deterioration in characteristics even in an environment exposed to high temperatures.

Moreover, the cyanoethylated polyvinyl alcohol is a polymer that overcomes the poor solubility of general cyano group-containing polymers, and has excellent solubility in low-boiling solvents, so an aqueous dispersion (water dispersion) manufacturing process using the evaporation method It is a material suitable for

On the other hand, when polyacrylic acid is partially neutralized, it may contain unneutralized acrylic acid and neutralized acrylic acid at the same time. In the present specification, those containing both unneutralized acrylic acid and neutralized acrylic acid are referred to as “neutralized acrylic acid”.

Here, 1) -COOH of non-neutralized acrylic acid (PAA-COOH) can cross-link (first ester bond) with OH in cyanoethylated polyvinyl alcohol through high-temperature heat treatment in the drying process during the manufacturing of the negative electrode. , can also cross-link (second ester bond) with OH on the silicone surface.

Accordingly, non-neutralized acrylic acid (PAA-COOH) forms a uniform interpenetrating polymer network (IPN)-like structure through the above two cross-linking reactions, thereby forming a binder binding structure that is stable even when the volume of the silicon-based negative active material changes. can keep

2) In the case of acrylic acid (PAA-COO ^- Na ⁺ ) neutralized by caustic soda (NaOH), etc., while stretching the polyacrylic acid polymer chain by the electrostatic repulsion between -COO ^- anions, the uniformity of the aqueous dispersion blending binder and It is possible to improve storage stability and overcome the volume change of the silicon-based negative active material.

Overall, in one embodiment of the present invention, cyanoethylated polyvinyl alcohol; neutralized polyacrylic acid; and a styrene-butadiene-based copolymer; provides a binder composition for a negative electrode of a secondary battery comprising.

In addition to cyanoethylated polyvinyl alcohol with high adhesion and high dielectric properties, and neutralized polyacrylic acid that can overcome the volume change of the negative electrode active material, a styrene-butadiene copolymer with excellent adhesion properties with the graphite negative active material. will include

Therefore, in a secondary battery using a composite negative active material of a silicon-based negative active material and a graphite-based negative active material, when the binder composition of one embodiment is applied to the negative electrode, the decrease in battery characteristics due to the volume change of the negative electrode active material is suppressed, and excellent cycle Characteristics may be implemented.

The binder composition of one embodiment may be a blending binder of a cyanoethylated polyvinyl alcohol aqueous dispersion, a neutralized polyacrylic acid aqueous solution, and a styrene-butadiene-based copolymer latex.

Hereinafter, the binder composition of the embodiment will be described in more detail.

Cyanoethylated polyvinyl alcohol

The cyanoethylated polyvinyl alcohol may be a polymer including a repeating unit represented by the following formula (1) and a repeating unit represented by the following formula (2):

[Formula 1]

[Formula 2]

Here, Formula 1 corresponds to a site that is not cyanoethylated, and Formula 2 represents a hydrogen atom of a hydroxy group (-OH) in polyvinyl alcohol to a cyanoethyl group (-CH ₂ CH ₂ CN). It corresponds to the substituted site.

Specifically, the polymer including the repeating unit represented by Chemical Formula 1 and the repeating unit represented by Chemical Formula 2 is subjected to Michael addition reaction of a hydroxyl group (-OH) of polyvinyl alcohol (PVA) and acrylonitrile (AN). can be manufactured by

In other words, the cyanoethylated polyvinyl alcohol may be a Michael addition reaction product of polyvinyl alcohol (PVA) and acrylonitrile (AN).

The cyanoethylation substitution rate refers to the mole fraction of a hydroxyl group (-OH) substituted with a cyanoethyl group (-CH ₂ CH ₂ CN) in 100 mol% of the hydroxyl group (-OH) in polyvinyl alcohol. This can be seen as the mol% content of the repeating unit represented by Formula 2 in 100 mol% of the cyanoethylated polyvinyl alcohol.

The cyanoethylation substitution rate may be measured through H-NMR. Specifically, in the repeating unit represented by Formula 2, a peak A by -CH ₂ CN is observed at 2.5 to 2.8 ppm, and a peak B by -CH ₂ - at 1.3 to 2.0 ppm is It is observed. Here, -CH ₂ - Since the peak is due to the main chain of the cyanoethylated polyvinyl alcohol, the cyanoethylation substitution rate can be obtained by substituting the H-NMR measurement result into Equation 1 below.

[Formula 1] Cyanoethylation substitution rate (%) = A/B

In Equation 1, A is a peak area of 2.5 to 2.8 ppm, and B is a peak area of 1.3 to 2.0 ppm.

The cyanoethylated polyvinyl alcohol may have a cyanoethyl substitution ratio of 50 to 99%.

As the cyanoethyl substitution ratio of the cyanoethylated polyvinyl alcohol increases, the dielectric constant increases, but the cyanoethylated polyvinyl alcohol (PVOH) that cross-reacts with non-neutralized acrylic acid (PAA-COOH) decreases, and The molecular weight of cyanoethylated polyvinyl alcohol is increased, and the crosslinking reaction is not relatively uniform, so battery efficiency tends to decrease. On the other hand, when the cyanoethyl substitution rate of the cyanoethylated polyvinyl alcohol is low, the effect derived from the cyanoethylated functional group is insignificant, and it is difficult to secure improved physical properties of the anode.

In consideration of this tendency, the cyanoethyl substitution rate of the cyanoethylated polyvinyl alcohol is 50% or more, 53% or more, 56% or more, or 60% or more, and 99% or less, 96% or less, 93% or more. It can be adjusted within the range of less than or equal to 90% or less.

The cyanoethylated polyvinyl alcohol may have a weight average molecular weight of 250,000 to 500,000 g/mol.

As described above, as the weight average molecular weight of the cyanoethylated polyvinyl alcohol increases, there is a disadvantage in that the crosslinking reaction becomes non-uniform.

In consideration of this tendency, the weight average molecular weight of the cyanoethylated polyvinyl alcohol is 250,000 g/mol or more, 260,000 g/mol or more, 270,000 g/mol or more, or 280,000 g/mol or more, and 500,000 g/mol or more. mol or less, 490,000 g/mol or less, 485,000 g/mol or less, or 480,000 g/mol or less.

neutralized polyacrylic acid

As mentioned above, the neutralized acrylic acid is partially neutralized polyacrylic acid, and may include unneutralized acrylic acid and neutralized acrylic acid at the same time.

The neutralization degree of the neutralized acrylic acid may be 1 to 20%. This can be measured according to common sense in the art using equipment such as IR.

As the degree of neutralization of the neutralized acrylic acid increases, the content of the aforementioned PAA-COO ^- Na ⁺ increases, improving the uniformity and storage stability of the aqueous dispersion blending binder, and it is advantageous to overcome the volume change of the silicon-based negative active material. . In addition, the polyacrylic acid polymer chain is stretched by the electrostatic repulsive force between the carboxylic acid anions, which can contribute to overcoming the volume change of the silicone negative active material.

However, as the degree of neutralization of the neutralized acrylic acid increases, the content of PAA-COOH is decreased, and the crosslinking reaction of cyanoethylated polyvinyl alcohol (PVOH) (first ester bond) and the crosslinking reaction of OH on the silicone surface Reaction sites are reduced for this, and the formation of a stable interpenetrating polymer network (IPN)-like structure may be insufficient.

In consideration of this tendency, the neutralization degree of the neutralized acrylic acid is 1% or more, 2% or more, 3% or more, or 4% or more, and 20% or less, 17% or less, 15% or less, or 12% or less. can be adjusted in

Styrene-butadiene-based copolymer

The styrene-butadiene-based copolymer may include a styrene-butadiene copolymer, a styrene-butadiene-acrylic acid copolymer, or a mixture thereof. Here, the copolymerization ratio is not particularly limited.

In addition, the styrene-butadiene-based copolymer may be prepared through emulsion polymerization, and may have a latex particle shape.

Blending binder composition of cyanoethylated polyvinyl alcohol, neutralized polyacrylic acid and styrene-butadiene copolymer

Among 100% by weight of the total solid content in the binder composition, 1 to 40% by weight of the neutralized polyacrylic acid, 1 to 30% by weight of the cyanoethylated polyvinyl alcohol, and the remainder of the styrene-butadiene-based copolymer.

As the content of the cyanoethylated polyvinyl alcohol increases, high adhesion and high dielectric properties can be realized, and when a high content styrene-butadiene copolymer is blended, compatibility with the styrene-butadiene copolymer is increased. Although excellent dispersibility and stability can be ensured during the preparation of the negative electrode mixture slurry composition, as the content of the neutralized polyacrylic acid is relatively decreased, the suppression force against the volume change of the negative electrode active material may be reduced.

Conversely, as the content of the neutralized polyacrylic acid increases, the suppression force against the volume change of the negative electrode active material may increase, but as the content of the cyanoethylated polyvinyl alcohol decreases, the dielectric properties decrease, or the negative electrode The excellent dispersibility and stability during the preparation of the mixture slurry composition may be reduced.

In consideration of this tendency, 1 to 40 wt% of the neutralized polyacrylic acid, specifically 5 to 37 wt%, such as 10 to 35 wt%, of the total amount of solid content in the binder composition of 100 wt%; 1 to 30% by weight of the cyanoethylated polyvinyl alcohol, specifically 5 to 27% by weight, such as 10 to 25% by weight; The remainder of the styrene-butadiene-based copolymer may be included.

Meanwhile, the binder composition of the embodiment may further include an aqueous solvent, that is, water.

The aqueous solvent, in terms of stability and viscosity control of the binder composition, in the total amount (100% by weight) of the binder composition of one embodiment, a total solid content (TSC) of about 10 to about 40% by weight, For example, it may be used so as to be adjusted to 10 to 30% by weight.

When the aqueous solvent is used too little, there may be a problem that the stability of the binder composition is lowered. Accordingly, there may be a problem in that the overall performance of the battery is deteriorated.

Method for manufacturing a binder for a negative electrode of a secondary battery

In another embodiment of the present invention, polyvinyl alcohol (PVA) and acrylonitrile (AN) are reacted to prepare cyanoethylated polyvinyl alcohol; preparing an aqueous dispersion of cyanoethylated polyvinyl alcohol by using an evaporation method; reacting polyacrylic acid (PAA) and caustic soda (NaOH) in an aqueous solvent to prepare a neutralized aqueous polyacrylic acid solution; mixing the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution; and mixing the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution with a styrene-butadiene-based copolymer latex; it provides a method for producing a binder composition for a negative electrode of a secondary battery, comprising a .

This corresponds to the method for preparing the binder composition of the above-described embodiment.

Hereinafter, a description overlapping with the above will be omitted, and the manufacturing method of the embodiment will be described in detail.

Manufacturing process of cyanoethylated polyvinyl alcohol

The cyanoethylated polyvinyl alcohol is prepared by Michael addition reaction of polyvinyl alcohol (PVA) and acrylonitrile (AN).

Here, 0.1 to 20 parts by weight of acrylonitrile (AN) may be reacted based on 1 part by weight of the polyvinyl alcohol (PVA).

The weight ratio of the polyvinyl alcohol (PVA) and the acrylonitrile (AN) may determine the cyanoethylation substitution rate of the reaction product (ie, cyanoethylated polyvinyl alcohol). In this regard, the weight ratio of the polyvinyl alcohol (PVA) and the acrylonitrile (AN) may be adjusted in consideration of the cyanoethylation substitution rate described above.

For example, based on 1 part by weight of the polyvinyl alcohol (PVA), 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 parts by weight or more, and 20 parts by weight or less, 16 parts by weight or less, 14 parts by weight or less, or 12 parts by weight or more Acrylonitrile (AN) in an amount of up to 1 part by weight may be reacted.

When preparing the cyanoethylated polyvinyl alcohol, 0.005 to 0.1 parts by weight of caustic soda (NaOH) may be added based on 1 part by weight of the polyvinyl alcohol (PVA).

For example, based on 1 part by weight of the polyvinyl alcohol (PVA), 0.005 parts by weight or more, 0.007 parts by weight or more, 0.009 parts by weight or more, or 0.01 parts by weight or more, and 0.1 parts by weight or less, 0.05 parts by weight or less, 0.03 parts by weight or more or less, or 0.02 parts by weight or less of caustic soda (NaOH) may be added.

Here, caustic soda (NaOH) may be added in an aqueous solution state dissolved in an aqueous solvent, that is, water. The content of caustic soda in the aqueous caustic soda solution may be 0.1 to 5 wt%, specifically 0.5 to 3 wt%, such as 0.7 wt% to 2 wt%.

More specifically, when preparing the cyanoethylated polyvinyl alcohol, the polyvinyl alcohol (PVA), the acrylonitrile (AN), and the caustic soda aqueous solution are added to a reactor equipped with a stirrer; at 30 to 70 °C, such as 40 to 60 °C; The reaction may be carried out for 80 to 120 minutes, such as 90 to 110 minutes.

Acetone and distilled water are added thereto and stirred for 20 to 60 minutes, such as 30 to 50 minutes; The reaction may be terminated by adding an aqueous acetic acid solution.

Thereafter, the reaction product is precipitated using distilled water and washed to obtain cyanoethylated polyvinyl alcohol.

Manufacturing process of cyanoethylated polyvinyl alcohol aqueous dispersion

After preparing cyanoethylated polyvinyl alcohol by the Michael addition reaction of polyvinyl alcohol (PVA) and acrylonitrile (AN), an aqueous dispersion of cyanoethylated polyvinyl alcohol can be prepared by distillation. have.

Specifically, when preparing the cyanoethylated polyvinyl alcohol aqueous dispersion, dissolving the cyanoethylated polyvinyl alcohol in acetone to prepare a cyanoethylated polyvinyl alcohol solution; and adding distilled water to the cyanoethylated polyvinyl alcohol solution and at the same time distilling acetone while dispersing the cyanoethylated polyvinyl alcohol in water.

More specifically, in a reactor equipped with a reflux condenser and a Dean-Stark device, the cyanoethylated polyvinyl alcohol and acetone are added, and the temperature is raised to 40 to 80 ℃, such as 50 to 70 ℃ to completely dissolve, and then distilled water While dripping for 1 hour, it can be dispersed in water while slowly distilling acetone through a Dean-Stark trap.

After completion of the aqueous dispersion, it is cooled to room temperature, and then filtered through 200 to 400 mesh to obtain an aqueous dispersion of cyanoethylated polyvinyl alcohol.

When preparing the aqueous dispersion of cyanoethylated polyvinyl alcohol, the solid content may be prepared to be 10 to 35% by weight, for example, 15 to 30% by weight.

Manufacturing process of neutralized polyacrylic acid aqueous solution

Meanwhile, the neutralized aqueous polyacrylic acid solution can be prepared by reacting polyacrylic acid (PAA) and caustic soda (NaOH) in an aqueous solvent.

Here, polyacrylic acid (PAA) having a weight average molecular weight of 10,000 to 1,000,000 g/mol, such as 100,000 to 700,000 g/mol, may be used.

Here, polyacrylic acid (PAA) may be used in a powder state or in an aqueous solution state dissolved in an aqueous solvent, that is, water. In the latter case, the content of polyacrylic acid in the aqueous polyacrylic acid solution may be 1 to 20 wt%, specifically 3 to 19 wt%, such as 6 wt% to 18.5 wt%.

Based on 1 part by weight of the polyacrylic acid (PAA), 0.01 to 0.1 parts by weight of the caustic soda (NaOH) may be reacted.

The weight ratio of the polyacrylic acid (PAA) and the caustic soda (NaOH) may determine the degree of neutralization of the reaction product (ie, neutralized polyacrylic acid). In this regard, the weight ratio of the polyacrylic acid (PAA) and the caustic soda (NaOH) may be adjusted in consideration of the degree of neutralization of the aforementioned neutralized polyacrylic acid.

For example, based on 1 part by weight of the polyacrylic acid (PAA), 0.01 parts by weight or more, 0.02 parts by weight or more, 0.03 parts by weight or more, or 0.04 parts by weight or more, and 0.1 parts by weight or less, 0.08 parts by weight or more, based on 1 part by weight of the caustic soda (NaOH) Hereinafter, 0.06 parts by weight or less, or 0.05 parts by weight or less may be reacted.

Here, caustic soda (NaOH) may be added in an aqueous solvent state, that is, an aqueous solution dissolved in water. The content of caustic soda in the aqueous caustic soda solution may be 0.1 to 5 wt%, specifically 0.5 to 3 wt%, such as 0.7 wt% to 2 wt%.

More specifically, distilled water is added to polyacrylic acid and stirred for 5 to 40 minutes, such as 10 to 30 minutes, to completely dissolve; An aqueous solution of caustic soda may be added to prepare a neutralized aqueous polyacrylic acid solution.

When preparing the neutralized aqueous polyacrylic acid solution, the solid content may be 1 to 20% by weight, for example, 5 to 15% by weight.

Mixing (blending) process of cyanoethylated polyvinyl alcohol aqueous dispersion and neutralized polyacrylic acid aqueous solution

Finally, when the aqueous dispersion of cyanoethylated polyvinyl alcohol and the aqueous neutralized polyacrylic acid solution are mixed (ie, blended), the binder composition of the above-described embodiment can be obtained.

Based on 1 part by weight of cyanoethylated polyvinyl alcohol in the cyanoethylated polyvinyl alcohol aqueous dispersion, 1/99 to 99 parts by weight of the neutralized polyacrylic acid in the neutralized polyacrylic acid aqueous solution may be mixed.

Specifically, the weight ratio of the cyanoethylated polyvinyl alcohol in the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid in the neutralized polyacrylic acid aqueous solution is 10:90 to 90:10, 25: It can be adjusted within the range of 75 to 75:25, specifically 40:60 to 60:40.

Here, an aqueous solvent, ie, water, may be further added so that the final obtained binder composition has a solid content of about 10 to about 40% by weight, such as 10 to 30% by weight.

The aqueous dispersion thus obtained can be used to implement an aqueous negative electrode. Here, the aqueous negative electrode does not include a non-aqueous solvent, but refers to a negative electrode manufactured using a negative electrode mixture slurry composition containing an aqueous solvent.

Such an aqueous negative electrode is environmentally friendly because there is no concern about the generation of harmful substances in the negative electrode manufacturing process, compared to a negative electrode (non-aqueous negative electrode) manufactured using a negative electrode mixture slurry composition containing a non-aqueous solvent.

Manufacturing process of styrene-butadiene-based copolymer latex

The styrene-butadiene-based copolymer latex may be prepared through emulsion polymerization.

Specifically, after preparing a uniform emulsion by mixing monomers and an emulsifier in consideration of the composition of the styrene-butadiene-based copolymer, then a polymerization initiator is added to perform polymerization for a certain period of time, and the styrene-butadiene-based copolymer latex composition is prepared can be obtained.

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.

The emulsion polymerization may be carried out in the presence of an emulsifier and a polymerization initiator in a solution containing an aqueous solvent.

The polymerization temperature and polymerization time of the emulsion polymerization 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.

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.

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

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 can be used alone or in mixture of two or more types, and it can be more effective when an anionic emulsifier and a nonionic emulsifier are mixed and used, but the present invention is 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, or about 0.05 to about 5 parts by weight may be used.

Mixing (blending) process of a mixed solution of cyanoethylated polyvinyl alcohol aqueous dispersion and neutralized polyacrylic acid aqueous solution and the styrene-butadiene-based copolymer latex

Finally, when the mixture of the aqueous dispersion of cyanoethylated polyvinyl alcohol and the aqueous solution of neutralized polyacrylic acid and the styrene-butadiene-based copolymer latex are mixed (that is, blended), the binder composition of the above-described embodiment can be obtained. have.

When mixing, 1 to 40% by weight of the neutralized polyacrylic acid, 1 to 30% by weight of the cyanoethylated polyvinyl alcohol, and the remainder of the styrene-butadiene-based copolymer among 100% by weight of the total solid content. can

This is the same as the blending ratio of the above-described embodiment, and detailed description thereof will be omitted.

An aqueous solvent, ie, water, may be further added so that the final obtained binder composition has a solid content of about 10 to about 40% by weight, such as 10 to 30% by weight.

The aqueous dispersion thus obtained can be used to implement an aqueous negative electrode. Here, the aqueous negative electrode does not include a non-aqueous solvent, but refers to a negative electrode manufactured using a negative electrode mixture slurry composition containing an aqueous solvent.

Such an aqueous negative electrode is environmentally friendly because there is no concern about the generation of harmful substances in the negative electrode manufacturing process, compared to a negative electrode (non-aqueous negative electrode) manufactured using a negative electrode mixture slurry composition containing a non-aqueous solvent.

cathode

In another embodiment of the present invention, a negative electrode current collector; and a negative electrode mixture layer positioned on the negative electrode current collector and including the binder composition and negative electrode active material of the embodiment described above.

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

The binder composition of one embodiment may be included in an amount of 1 wt% to 10 wt%, specifically 1 wt% to 5 wt%, based on the total weight (100 wt%) of the negative electrode mixture. When this is satisfied, the content of the negative 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 composition of one embodiment has excellent properties in binding force and mechanical properties, etc., when a graphite-based negative active material is used as the negative active material of the negative electrode mixture, as well as a negative active material having a higher capacity than that is used, the negative electrode active material It is possible to maintain the binding force between the negative active material and the negative electrode active material, between the negative electrode active material and the negative electrode current collector, and the expansion of the negative electrode active material can be suppressed by its mechanical properties.

The binder composition of one embodiment is suitable for application together with a composite negative active material of a graphite-based negative active material and a silicon-based negative active material,

Specifically, examples of the graphite-based negative active material include natural graphite, artificial graphite, carbon fiber, and non-graphitizable carbon. In addition, as the silicon-based compound, SiO _x (0 < x < 2), Si-C composite, Si-Q alloy (wherein Q is an alkali metal, alkaline earth metal, group 13 to 16 element, transition metal, rare earth element or It is a combination of these, and it is not Si) etc. are mentioned.

The negative electrode of one embodiment may use at least one of the above-listed graphite-based negative active materials and a composite composite negative active material of at least one of the above-listed silicon-based negative active materials.

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, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, the surface of 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 of which it is 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.

secondary battery

In another embodiment of the present invention, a secondary battery including the negative electrode of the embodiment described above is provided. Such a secondary battery, a positive electrode; electrolyte; and a negative electrode, and 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 negative electrode is the same as described above, and the remaining components will be described below.

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. 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.

A generally known binder may be used for the positive electrode. Representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, 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, and the like 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.

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, tetrahydroxyfuran, 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 derivative, sulfonate An aprotic organic solvent such as porane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, or ethyl propionate can be used.

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 may 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.

<Preparation of raw material of binder composition for negative electrode>

Synthesis Example 1-1: Cyanoethylated polyvinyl alcohol aqueous dispersion 1

(1) Synthesis of cyanoethylated polyvinyl alcohol

1 part by weight of polyvinyl alcohol (PVA), 6 parts by weight of acrylonitrile (AN), and 1.32 parts by weight of an aqueous solution of caustic soda in which 1% by weight of caustic soda is dissolved were put into a reactor equipped with a stirrer, and reacted at 50° C. for 100 minutes made it 10 parts by weight of acetone and 3 parts by weight of distilled water were added thereto and stirred for 40 minutes, and then 0.088 parts by weight of an acetic acid aqueous solution in which 25% by weight of acetic acid was dissolved was added to terminate the reaction. After the reaction product was precipitated and washed with distilled water, cyanoethylated polyvinyl alcohol was obtained.

The cyanoethylated polyvinyl alcohol has a cyanoethyl substitution rate of 79% by H-NMR measurement and the above-mentioned formula 1 calculation, and a weight average molecular weight (MW) obtained by gel permeation chromatography (GPC) This is 408,000 g/mol.

Specifically, the H-NMR measurement method and the GPC measurement method are as follows, respectively:

1) H-NMR: A solution containing 5 wt% of the cyanoethylated polyvinyl alcohol was prepared using a DMSO-d6 solvent. Using a heat block, the solution was heated enough to dissolve the cyanoethylated polyvinyl alcohol in the solution. Thereafter, the solution in which the cyanoethylated polyvinyl alcohol was dissolved was cooled to room temperature, and put into an NMR device (device name: 700MHz Avance Ⅲ HD NMR, BBO probe: 1H NMR, manufacturer: Bruker) to measure H-NMR spectrum. .

2) GPC: Using a GPC instrument (manufacturer: Waters, instrument name: Alliance e2695), the weight average molecular weight of the cyanoethylated polyvinyl alcohol was obtained under the following conditions.

-Column: PL mixed B x 2

-Solvent: DMF/0.05 M LiBr (0.45 ㎛ filtered)

-Flow rate: 1.0ml/min

-Sample concentration: 1.0 mg/ml

-Injection amount: 100 μl

-Column temperature: 65 ℃

-Detector: Waters 2414 RI detector

-Standard: PS (corrected by cubic function)

-Data processing: Empower 2

Specifically, 0.5 mg of the sample to obtain the weight average molecular weight (ie, the cyanoethylated polyvinyl alcohol) was placed in a vial, and diluted to a concentration of 1 mg/ml using DMF. Thereafter, a sample solution was obtained by filtering using a 0.45 μm syringe filter.

1ml or more of the sample solution was placed in a GPC-only vial. After putting the sample solution prepared in this way into the instrument, GPC measurement was started. Accordingly, a GPC chromatogram of the sample solution was obtained.

In the same manner as the sample solution, a GPC chromatogram for the standard solution was obtained.

A calibration curve and an equation were obtained from the GPC chromatogram of the standard solution, and the retention time of the sample solution was substituted into the equation to obtain the molecular weight of the sample.

(2) Preparation of cyanoethylated polyvinyl alcohol aqueous dispersion

In a reactor equipped with a reflux condenser and a Dean-Stark device, 1 part by weight of the cyanoethylated polyvinyl alcohol and 1.5 parts by weight of acetone were added, and the temperature was raised to 60° C. to completely dissolve it. Then, 3 parts by weight of distilled water was added dropwise for 1 hour, and while acetone was slowly distilled through a Dean-Stark trap, it was dispersed in water. After cooling to room temperature, it was filtered through 300 mesh to obtain an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight.

Synthesis Example 1-2: Cyanoethylated polyvinyl alcohol aqueous dispersion 2

When cyanoethylated polyvinyl alcohol was synthesized, 10 parts by weight of acrylonitrile was used. Other than that, in the same manner as in Synthesis Example 1-1, cyanoethylated polyvinyl alcohol was synthesized, and an aqueous dispersion (solid content of 25% by weight) was prepared.

The cyanoethylated polyvinyl alcohol has a cyanoethyl substitution rate of 89% by H-NMR measurement and the above-mentioned formula 1 calculation, and the weight obtained by gel permeation chromatography (GPC: Waters Alliance e2695) The average molecular weight (MW) is 475,000 g/mol. Here, H-NMR and GPC measurement methods are the same as in Synthesis Example 1-1.

Synthesis Example 1-3: Cyanoethylated polyvinyl alcohol aqueous dispersion 3

When synthesizing cyanoethylated polyvinyl alcohol, 3 parts by weight of acrylonitrile was used. Other than that, in the same manner as in Synthesis Example 1-1, cyanoethylated polyvinyl alcohol was synthesized, and an aqueous dispersion (solid content of 25% by weight) was prepared.

The cyanoethylated polyvinyl alcohol has a cyanoethyl substitution rate of 61% by H-NMR measurement and the above-mentioned formula 1 calculation, and the weight obtained by gel permeation chromatography (GPC: Waters Alliance e2695) The average molecular weight (MW) is 287,000 g/mol. Here, H-NMR and GPC measurement methods are the same as in Synthesis Example 1-1.

Synthesis Example 2: Polyvinyl alcohol aqueous solution

9 parts by weight of distilled water was added to 1 part by weight of polyvinyl alcohol (PVA: Aldrich, 341584: weight average molecular weight of 89,000 g/mol ) and stirred at 80° C. for 1 hour to prepare a polyvinyl alcohol aqueous solution having a solid content of 10% by weight.

Synthesis Example 3: Neutralized aqueous polyacrylic acid solution

4.5 parts by weight of distilled water was added to 1 part by weight of polyacrylic acid (PAA: Aldrich, 181285: weight average molecular weight of 450,000 g/mol), stirred for 20 minutes to completely dissolve, and then caustic soda aqueous solution in which 1% by weight of caustic soda was dissolved 4.5 By adding parts by weight, a neutralized aqueous polyacrylic acid solution having a solid content of 10% by weight was obtained.

The degree of neutralization of the neutralized polyacrylic acid in the neutralized polyacrylic acid aqueous solution is about 8%, and the degree of neutralization may be measured using equipment such as IR.

Synthesis Example 4: Preparation of styrene-butadiene-based copolymer

48 g of styrene (ST), 50 g of 1,3-butadiene (BD), and 2 g of acrylic acid (AA) were added to water containing 0.3 g of sodium lauryl sulfate and 0.1 g of potassium persulfate and mixed, followed by mixing at 70 ° C. Polymerization was carried out for 5 hours.

Thereafter, an aqueous solution of caustic soda was added to adjust the pH to 7 to 8, and a styrene-butadiene-based copolymer latex having a solid content of 40% was obtained.

<Preparation of negative electrode binder composition>

Preparation Example 1: Blending binder 1 of neutralized polyacrylic acid aqueous solution, cyanoethylated polyvinyl alcohol aqueous dispersion, and styrene-butadiene-based copolymer latex

After diluting 18 parts by weight of an aqueous solution of neutralized polyacrylic acid having a solid content of 10% by weight prepared in Synthesis Example 3 with 10 parts by weight of distilled water, 4.8 parts by weight of an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight prepared in Synthesis Example 1-1 Parts by weight were slowly added, and the mixture was stirred at room temperature for 1 hour.

Then, 17.5 parts by weight of the styrene-butadiene-based copolymer latex having a solid content of 40% by weight prepared in Synthesis Example 4 was slowly added, and stirred at room temperature for 1 hour to prepare a blending binder having a solid content of 20% by weight.

Preparation Example 2: Blending binder 2 of neutralized polyacrylic acid aqueous solution, cyanoethylated polyvinyl alcohol aqueous dispersion, and styrene-butadiene-based copolymer latex

30 parts by weight of a neutralized polyacrylic acid aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 3, 8 parts by weight of an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight prepared in Synthesis Example 1-1, and in Synthesis Example 4 An anode binder composition (solids content of 20 wt%) was prepared in the same manner as in Preparation Example 1, except that 12.5 parts by weight of the prepared styrene-butadiene-based copolymer latex having a solid content of 40 wt% was used.

Preparation Example 3: Blending binder 3 of neutralized polyacrylic acid aqueous solution, cyanoethylated polyvinyl alcohol aqueous dispersion, and styrene-butadiene-based copolymer latex

After diluting 12 parts by weight of the neutralized polyacrylic acid aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 3 with 14 parts by weight of distilled water, an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight prepared in Synthesis Example 1-1 7.2 Except for using 17.5 parts by weight of the styrene-butadiene-based copolymer latex having a solid content of 40 wt% prepared in Synthesis Example 4 and 17.5 parts by weight, the negative electrode binder composition (solid content 20 wt%) was prepared in the same manner as in Preparation Example 1 did

Preparation Example 4: Blending binder 4 of neutralized polyacrylic acid aqueous solution, cyanoethylated polyvinyl alcohol aqueous dispersion, and styrene-butadiene copolymer latex

After diluting 18 parts by weight of 10 parts by weight of a neutralized polyacrylic acid aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 3 with 10 parts by weight of distilled water, 4.8 parts by weight of an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight prepared in Synthesis Example 1-2 Except for using 17.5 parts by weight of the styrene-butadiene-based copolymer latex having a solid content of 40 wt% prepared in Synthesis Example 4 and 17.5 parts by weight, the negative electrode binder composition (solid content 20 wt%) was prepared in the same manner as in Preparation Example 1 did

Preparation Example 5: Blending binder of neutralized polyacrylic acid aqueous solution, cyanoethylated polyvinyl alcohol aqueous dispersion, and styrene-butadiene-based copolymer latex

After diluting 18 parts by weight of an aqueous solution of neutralized polyacrylic acid having a solid content of 10% by weight prepared in Synthesis Example 3 with 10 parts by weight of distilled water, 4.8 parts by weight of an aqueous dispersion of cyanoethylated polyvinyl alcohol having a solid content of 25% by weight prepared in Synthesis Example 1-3 Except for using 17.5 parts by weight of the styrene-butadiene-based copolymer latex having a solid content of 40 wt% prepared in Synthesis Example 4 and 17.5 parts by weight, the negative electrode binder composition (solid content 20 wt%) was prepared in the same manner as in Preparation Example 1 did

Preparation Example 6: Blending binder of neutralized polyacrylic acid aqueous solution, polyvinyl alcohol aqueous solution, and styrene-butadiene-based copolymer latex

After diluting 18 parts by weight of the neutralized polyacrylic acid aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 3 with 2 parts by weight of distilled water, 12 parts by weight of the polyvinyl alcohol aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 2, and Synthesis Example 4 Except for using 17.5 parts by weight of the styrene-butadiene-based copolymer latex having a solid content of 40% by weight prepared in Preparation Example 1, an anode binder composition (solids content of 20% by weight) was prepared in the same manner as in Preparation Example 1.

Preparation Example 7: Blending binder of neutralized polyacrylic acid aqueous solution and styrene-butadiene-based copolymer latex

30 parts by weight of the neutralized polyacrylic acid aqueous solution having a solid content of 10% by weight prepared in Synthesis Example 3 was diluted with 2 parts by weight of distilled water, and 17.5 parts by weight of a styrene-butadiene-based copolymer latex having a solid content of 40% by weight prepared in Synthesis Example 4 was used. Except that, an anode binder composition (solids content of 20% by weight) was prepared in the same manner as in Preparation Example 1.

<Manufacture of lithium ion battery>

Example 1

(1) Preparation of negative electrode mixture slurry composition

Artificial graphite 85.2 g, silicon oxide 9.5 g, acetylene black 1 g, 15 g of the blending binder of Preparation Example 1 (solid content 20% by weight). and 86.7 g of carboxymethyl cellulose as a thickener (solids content of about 1.5% by weight) were mixed, and then water was added as a dispersion medium so that the total solid content was 50% by weight, thereby obtaining a negative electrode mixture slurry composition.

(2) Preparation of negative electrode

Using a comma coater, the negative electrode mixture slurry composition was applied to a thickness of about 100 μm on a copper foil, dried in a dry oven at 80° C., and heat-treated in a vacuum oven at 120° C. for 1 hour.

The negative electrode of Example 1 was obtained by roll-pressing to a final thickness of 60 μm.

(3) Preparation of Lithium Ion Battery

LiNi _0.6 Mn _0.2 Co _0.2 O ₂ 90 g, acetylene black 5.0 g, and polyvinylidene fluoride (PVDF) 50 g (solids content 10% by weight) were used as the positive electrode active material, and the total solid content was 70% by weight. After adding NMP as a solvent as much as possible, the mixture was stirred for 1 hour to obtain a positive electrode mixture slurry composition.

Prepare an aluminum foil having a thickness of 20 μm and use it as a positive electrode current collector, and using a comma coater, apply the positive electrode mixture slurry composition to one surface of the positive electrode current collector at 15.6 mg/cm ² Loading (loading) After coating on both sides in a quantity, hot air dried in an oven at 80 ℃ for 10 minutes, and rolled to a total thickness of 190 ㎛

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

Example 2

An anode and a lithium ion battery were manufactured in the same manner as in Example 1, except that the blending binder of Preparation Example 2 was used instead of the blending binder composition of Preparation Example 1.

Example 3

An anode and a lithium ion battery were manufactured in the same manner as in Example 1, except that the blending binder of Preparation Example 3 was used instead of the blending binder composition of Preparation Example 1.

Example 4

An anode and a lithium ion battery were manufactured in the same manner as in Example 1, except that the blending binder of Preparation Example 4 was used instead of the blending binder composition of Preparation Example 1.

Example 5

An anode and a lithium ion battery were prepared in the same manner as in Example 1, except that the blending binder of Preparation Example 5 was used instead of the blending binder composition of Preparation Example 1.

Comparative Example 1

A negative electrode and a lithium ion battery were prepared in the same manner as in Example 1, except that 25 g (40 wt% of solid content) of the styrene-butadiene-based copolymer latex of Synthesis Example 4 was used instead of the blending binder composition of Preparation Example 1 .

Comparative Example 2

An anode and a lithium ion battery were prepared in the same manner as in Example 1, except that the blending binder of Preparation Example 6 was used instead of the blending binder composition of Preparation Example 1.

Comparative Example 3

An anode and a lithium ion battery were prepared in the same manner as in Example 1, except that the binder of Preparation Example 7 was used instead of the blending binder composition of Preparation Example 1.

<Experimental example>

(1) Measurement of the maximum particle size in the negative electrode mixture slurry composition

The maximum particle size in each of the negative electrode mixture slurry compositions of Examples 1 to 5 and Comparative Examples 1 to 3 was measured using a plate in which micropores having different sizes ranging from 1 μm to 100 μm were sequentially formed.

Specifically, 1 g of the negative electrode mixture slurry composition is taken and placed on the end of the large hole in the plate. The slurry was scraped off using a stick from the area in which micropores of 100 μm in size were formed to the area in which micropores in the size of 1 μm were formed. The pore size at the point where the slurry was no longer scratched was read and taken as the maximum particle size.

(2) Evaluation of negative electrode adhesion

Each negative electrode plate of Examples 1 to 5 and Comparative Examples 1 to 3 was cut to a predetermined size (specifically, 1 inch x 20 cm) and fixed to a slide glass, and an apparatus conforming to ASTM D903 (manufacturer: Texture Technologies, device name: Texture Analyzer), the current collector was peeled off at 25 °C at a speed of 0.3 m/min, and the 180 degree peel strength was measured.

This measurement was repeated 5 times, and the average value is shown in Table 1 below.

(3) Evaluation of capacity retention rate of lithium ion batteries

In a constant temperature chamber at 25° C., each lithium ion battery of Examples 1 to 5 and Comparative Examples 1 to 3 was charged at 36 A to 4.15 V in CC/CV mode and then CC to 3.0 V. Discharging in mode was one cycle, but a 20-minute rest period was placed between the charging and discharging, and a total of 30 and 100 cycles were performed.

According to Equation 2 and Equation 3 below, the ratio of each discharge capacity measured in 30 cycles and 100 cycles to the discharge capacity measured in the first cycle was calculated.

[Equation 2] 30 Cycle capacity retention rate (%) = 100x[Discharge capacity after 30 cycles / Discharge capacity after 1 cycle]

[Equation 3] 100 Cycle capacity retention rate (%) = 100×[discharge capacity after 100 cycles / discharge capacity after 1 cycle]

Maximum particle size in negative electrode mixture slurry composition (㎛) Cathode Adhesion (gf/cm) Capacity retention rate (%) 30 Cycles 100 Cycles Example 1 60 42 98 97 Example 2 54 35 97 91 Example 3 59 40 98 95 Example 4 77 38 94 91 Example 5 55 37 95 89 Comparative Example 1 88 25 96 82 Comparative Example 2 > 100 19 93 79 Comparative Example 3 > 100 18 91 71

In Table 1, compared to Comparative Examples 1 to 3, it can be seen that the maximum particle size in the negative electrode mixture slurry compositions of Examples 1 to 5 is small, and the negative electrode adhesion, 30 Cycle and 100 Cycle capacity retention rates are excellently exhibited. .

Specifically, in Examples 1 to 5 and Comparative Examples 1 to 3, silicon oxide as a silicon-based negative active material and artificial graphite as a graphite-based negative active material were mixed and applied in common.

In Comparative Example 1, the styrene-butadiene-based copolymer latex was applied to the negative electrode alone, and the capacity retention rate for 100 cycles was only 82%.

More specifically, in Comparative Example 1, the capacity retention rate of 100 cycles decreased by about 14.6% compared to the capacity retention rate of 30 cycles.

This means that the styrene-butadiene-based copolymer latex did not suppress the volume change of the silicone-based negative active material, and thus did not maintain stable cycle characteristics.

In Comparative Example 2, a neutralized polyacrylic acid aqueous solution, a non-cyanoethylated aqueous polyvinyl alcohol solution, and a styrene-butadiene-based copolymer latex blending binder (Preparation Example 6) were applied to the negative electrode, and the 100 cycle cycle capacity retention rate was Comparative Example It is lower than 1, only 79%.

More specifically, in Comparative Example 2, the maximum particle size in the negative electrode mixture slurry composition was very large, exceeding 100 μm, the negative electrode adhesion was only 19 gf/cm, and the 100 cycle capacity retention rate was reduced by about 15.1% compared to the 30 cycle capacity retention rate did

Polyvinyl alcohol, which is not cyanoethylated, has low compatibility with the styrene-butadiene-based copolymer and the graphite-based negative active material, resulting in low dispersibility and stability during preparation of the negative electrode slurry, which adversely affects battery cycle characteristics.

On the other hand, in Comparative Example 3, a neutralized polyacrylic acid aqueous solution and a blending binder of styrene-butadiene-based copolymer latex (Comparative Example 7) were applied to the negative electrode, and the 100 cycle capacity retention rate was lower than that of Comparative Examples 1 and 2, and to 71% it's just

More specifically, in Comparative Example 3, the maximum particle size in the negative electrode mixture slurry composition is very large, exceeding 100 μm, the negative electrode adhesion is only 18 gf/cm, and the 100 cycle capacity retention rate is reduced by about 22.0% compared to the 30 cycle capacity retention rate did

Although neutralized polyacrylic acid itself has excellent water dispersion properties, compatibility with the styrene-butadiene copolymer and graphite negative active material is low, resulting in low dispersibility and stability in the preparation of negative electrode slurry, and rather adversely affects battery cycle characteristics that would be crazy

On the other hand, in Examples 1 to 5, a neutralized polyacrylic acid aqueous solution, a cyanoethylated polyvinyl alcohol aqueous dispersion, and a styrene-butadiene-based copolymer latex blending binder (Preparation Examples 1 to 5) were applied to the negative electrode, and 100 Cycles A cycle capacity retention rate of 89% or more was ensured.

More specifically, in Examples 1 to 5, the maximum particle size in the negative electrode mixture slurry composition was as small as 77 μm or less, the negative electrode adhesion was as high as 35 gf/cm or more, and the degree of reduction of the 100 cycle capacity retention rate compared to the 30 cycle capacity retention rate was about 6.4% or less.

In addition to cyanoethylated polyvinyl alcohol with high adhesion and high dielectric properties, and neutralized polyacrylic acid that can overcome the volume change of the negative electrode active material, a styrene-butadiene copolymer with excellent adhesion properties with the graphite negative active material. Implementing a negative electrode mixture slurry composition having excellent dispersibility and stability through a binder system including; Furthermore, it means that excellent cycle characteristics of a secondary battery using a silicon-based negative active material and a composite negative active material of the silicon-based negative active material and the graphite-based negative active material can be realized.

Claims (21)

cyanoethylated polyvinyl alcohol;
neutralized polyacrylic acid; and
including; styrene-butadiene-based copolymer;
A binder composition for a negative electrode of a secondary battery. According to claim 1,
The cyanoethylated polyvinyl alcohol is
A polymer comprising a repeating unit represented by the following formula (1) and a repeating unit represented by the following formula (2),
Binder composition for negative electrode of secondary battery:
[Formula 1]

[Formula 2]

. According to claim 1,
The cyanoethylated polyvinyl alcohol is
A reaction product of polyvinyl alcohol (PVA) and acrylonitrile (AN),
A binder composition for a negative electrode of a secondary battery. According to claim 1,
The cyanoethylated polyvinyl alcohol is
Cyanoethyl substitution ratio of 50 to 99%,
A binder composition for a negative electrode of a secondary battery. According to claim 1,
The cyanoethylated polyvinyl alcohol is
The weight average molecular weight is 250,000 to 500,000 g / mol,
A binder composition for a negative electrode of a secondary battery. According to claim 1,
The styrene-butadiene-based copolymer,
styrene-butadiene copolymer, styrene-butadiene-acrylic acid copolymer, or mixtures thereof,
A binder composition for a negative electrode of a secondary battery. According to claim 1,
Among 100% by weight of the total amount of solids in the binder composition,
1 to 40% by weight of the neutralized polyacrylic acid, 1 to 30% by weight of the cyanoethylated polyvinyl alcohol, and the balance comprising the styrene-butadiene-based copolymer,
A binder composition for a negative electrode of a secondary battery. According to claim 1,
The binder composition,
further comprising an aqueous solvent;
A binder composition for a negative electrode of a secondary battery. 9. The method of claim 8,
The binder composition further comprising the aqueous solvent,
having a solids content of 1 to 40% by weight,
A binder composition for a negative electrode of a secondary battery. preparing cyanoethylated polyvinyl alcohol by reacting polyvinyl alcohol (PVA) and acrylonitrile (AN);
preparing an aqueous dispersion of cyanoethylated polyvinyl alcohol by using an evaporation method;
reacting polyacrylic acid (PAA) and caustic soda (NaOH) in an aqueous solvent to prepare a neutralized aqueous polyacrylic acid solution;
mixing the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution; and
Including; mixing a mixture of the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution, and a styrene-butadiene-based copolymer latex;
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
In the preparation of the cyanoethylated polyvinyl alcohol,
Based on 1 part by weight of the polyvinyl alcohol (PVA), 0.1 to 20 parts by weight of acrylonitrile (AN) is reacted,
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
In the preparation of the cyanoethylated polyvinyl alcohol,
Based on 1 part by weight of the polyvinyl alcohol (PVA), 0.005 to 0.1 parts by weight of caustic soda (NaOH) is added,
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
When preparing the cyanoethylated polyvinyl alcohol aqueous dispersion,
dissolving the cyanoethylated polyvinyl alcohol in acetone to prepare a cyanoethylated polyvinyl alcohol solution; and
A step of dispersing the cyanoethylated polyvinyl alcohol in water while adding distilled water to the cyanoethylated polyvinyl alcohol solution and at the same time distilling acetone.
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
When preparing the neutralized polyacrylic acid aqueous solution,
Using polyacrylic acid (PAA) having a weight average molecular weight of 10,000 to 1,000,000 g / mol,
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
Reacting 0.01 to 0.1 parts by weight of the caustic soda (NaOH) based on 1 part by weight of the polyacrylic acid (PAA),
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
When preparing the neutralized polyacrylic acid aqueous solution,
Prepared so as to have a solid content of 1 to 20% by weight,
A method of manufacturing a binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
When mixing the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution,
Mixing so as to be 1/99 to 99 parts by weight of neutralized polyacrylic acid in the neutralized polyacrylic acid aqueous solution based on 1 part by weight of cyanoethylated polyvinyl alcohol in the cyanoethylated polyvinyl alcohol aqueous dispersion,
A binder composition for a negative electrode of a secondary battery. 11. The method of claim 10,
When mixing the cyanoethylated polyvinyl alcohol aqueous dispersion and the neutralized polyacrylic acid aqueous solution, and styrene-butadiene-based copolymer latex,
Mixing to include 1 to 40% by weight of the neutralized polyacrylic acid, 1 to 30% by weight of the cyanoethylated polyvinyl alcohol, and the balance of the styrene-butadiene-based copolymer among 100% by weight of the total solid content,
A binder composition for a negative electrode of a secondary battery. negative electrode current collector; and
Located on the negative electrode current collector, the negative electrode mixture layer comprising the binder composition of claim 1 and the negative electrode active material; including,
negative electrode of the secondary battery. 20. The method of claim 19,
The negative active material is
Containing a composite negative active material of a silicon-based negative active material and a graphite-based negative active material,
negative electrode of the secondary battery. The negative electrode of claim 19; anode; And electrolyte; containing, a secondary battery.