KR102368234B1 - Binder for secondary battery, composite separator and secondary battery prepared by using the same - Google Patents

Abstract

One aspect of the present invention relates to a binder for a secondary battery comprising water-soluble polyvinyl alcohol and an acid-treated water-soluble chitosan modifier, a composite separator using the same, and a secondary battery.

Description

Binder for secondary battery, composite separator and secondary battery using same {Binder for secondary battery, composite separator and secondary battery prepared by using the same}

The present invention relates to a binder for a secondary battery, a composite separator using the same, and a secondary battery.

Recently, the range of secondary batteries has been expanded from batteries for small IT electronic devices to medium and large batteries such as electric vehicles.

In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator, and the safety of each of the constituent units is very important. For example, a composite separator having an inorganic particle layer is recently introduced in the separator, and the heat resistance, adhesiveness, and chemical stability of the inorganic particle layer play an important role in securing the safety of the battery. Therefore, in order to secure the safety according to the high capacity and high output of the secondary battery, research on a new material with excellent thermal stability is in progress.

As an example, as a method for improving the safety of a separator, in the case of a composite separator in which an inorganic particle layer including heat-resistant inorganic particles and an adhesive binder is formed on at least one surface of a porous substrate, it is effective in improving heat resistance, but battery safety, lifespan, capacity and output There is a problem of deterioration of properties, and in order to solve this problem, the role of the binder is very important. Specifically, since the conventional binder does not have sufficient adhesion to both the porous substrate and the inorganic particles, the inorganic particle layer is easily detached, thereby reducing the safety of the battery. In addition, if the adhesive strength of the separator is to be improved, the air permeability is deteriorated and the interfacial resistance is increased, so that the battery performance is limited.

In addition, in the case of an electrode, a new electrode active material capable of providing high capacity and high output is being applied in order to provide a battery with high energy density that can be applied to medium and large-sized batteries such as electric vehicles. However, the conventional binder cannot be used in various ways for a new active material because of its low adhesive strength, and the stability and lifespan of the electrode or battery may be deteriorated.

Accordingly, it is necessary to develop a new binder that can simultaneously secure battery safety, long life, high energy density, and high output characteristics.

KR 10-2022603 B1

One aspect of the present invention aims to provide a binder for a secondary battery that can simultaneously secure high safety, long life, high energy density, and high output characteristics of the battery.

In addition, one aspect of the present invention provides a composite separator capable of simultaneously implementing excellent adhesion and air permeability by using the binder.

In addition, one aspect of the present invention provides a secondary battery having improved both thermal stability and device characteristics by using the composite separator.

For the above purpose, the present invention provides a binder for a secondary battery comprising a water-soluble polyvinyl alcohol and an acid-treated water-soluble chitosan modifier.

The saponification degree of the water-soluble polyvinyl alcohol according to an aspect of the present invention may be 75 mol% or more, and a weight average molecular weight may be 3,000 to 500,000 g/mol.

The chitosan modifier according to an aspect of the present invention may be treated with an aqueous inorganic acid solution at a temperature of 10 to 100° C. for 5 to 20 hours.

The modified chitosan according to an aspect of the present invention may be decomposed by acid to contain 60 mol% or more of glucosamine.

The acid-treated water-soluble chitosan modifier may be included in an amount of 0.1 to 200 parts by weight based on 100 parts by weight of the water-soluble polyvinyl alcohol according to an embodiment of the present invention.

The binder for a secondary battery according to an aspect of the present invention is polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyacrylonitrile, polyvinylmethyl ether, polypropylene glycol, cellulose, poly-isopropylmethacrylamide and polyethylene It may further include one or two or more water-based polymers selected from oxides.

The binder according to an aspect of the present invention may be an aqueous binder for a secondary battery separator.

In addition, the present invention is the binder for the secondary battery; inorganic particles; and a solvent; provides a slurry composition comprising.

The binder according to an aspect of the present invention may be included in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the inorganic particles.

In addition, the present invention provides a porous substrate; and an inorganic particle layer coated on one side or both sides of the substrate, wherein the inorganic particle layer is connected and fixed by the binder for a secondary battery according to an aspect of the present invention to form pores between the inorganic particles, a composite A separator is provided.

According to an aspect of the present invention, the pore size may be 0.001 to 10 μm, and the porosity may be 10 to 80%.

In addition, the present invention provides a secondary battery comprising the composite separator.

The binder for a secondary battery according to an aspect of the present invention can not only have excellent adhesion performance, but also realize high ionic conductivity by itself. Accordingly, the composite separator manufactured using the binder according to an aspect of the present invention can simultaneously implement excellent adhesion and ion mobility. Specifically, the composite separator according to an aspect of the present invention can effectively improve the adhesion between the inorganic particles and between the inorganic particles and the substrate while there is no or minimal reduction in the pore size and porosity of the porous substrate. In addition, the excellent air permeability may improve the ionic conductivity properties as well as reduce the interfacial resistance.

That is, the composite separator according to an aspect of the present invention can improve the thermal stability problem of the conventional polyolefin-based separator, and at the same time satisfy all of the electrical characteristics and lifespan characteristics of an electrochemical device employing the same.

Hereinafter, the present invention will be described in more detail. If there is no other definition in the technical and scientific terms used at this time, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and may unnecessarily obscure the subject matter of the present invention in the following description. A description of possible known functions and configurations will be omitted.

Throughout the specification describing the present invention, when a part "includes" a certain element does not exclude other elements unless otherwise stated, it means that other elements may be further included. can

Unless otherwise defined herein, when a part of a layer, film, thin film, region, plate, etc. is "on" or "on" another part, it is not only in the case of being "on" another part, but also in the middle It may include a case where there is another part in .

Unless otherwise specified herein, "polymer" includes oligomers and may include homopolymers and copolymers. The copolymer is an alternating polymer, a block copolymer, a random copolymer, a branched copolymer, a crosslinked copolymer. It may be a coalescence or one including all of them.

Hereinafter, the present invention will be described in detail.

The binder for a secondary battery according to an aspect of the present invention may be applied to a positive electrode, a negative electrode, or a separator of a battery. As an example, a composite separator that can be applied with a binder is one in which an inorganic particle layer is formed on one or both sides of a porous substrate such as polyolefin, and the inorganic particle layer is an inorganic particle layer in which the inorganic particles are connected and fixed by a binder to form pores. , the inorganic particle layer is similarly adhered to the porous substrate layer by the binder.

However, the composite separator is effective in improving heat resistance to some extent, but there is a problem in that the safety, lifespan, capacity and output characteristics of the battery are deteriorated, and the role of the binder is very important to solve this problem.

Conventional binders do not have sufficient adhesion to both the polyolefin-based porous substrate and the inorganic particles, and the inorganic particle layer is easily detached from the substrate, thereby causing a decrease in battery stability. In order to solve this problem, a method for improving the mechanical properties of the separator has been proposed by using a binder having excellent adhesion, forming a thick inorganic particle layer, or increasing the packing density of the inorganic particle layer. However, the mechanical properties of the separator and the battery characteristics are in a trade-off relationship with each other, and these attempts, even if the adhesion and mechanical properties of the separator are improved, deteriorate the air permeability and ion permeability of the separator, and increase the interface resistance. Limitations exist.

In addition, in the case of the electrode, a new electrode active material capable of providing high capacity and high output is being applied in order to provide a battery of high energy density that can be applied to a medium or large battery such as an electric vehicle. However, the conventional binder has a low adhesive strength, so it cannot be used in various ways for a new active material, and there is a problem in that the stability and lifespan of the electrode or battery are deteriorated.

Accordingly, the development of a new binder capable of simultaneously securing battery safety, long life, high energy density, and high output characteristics is also required.

As a result of many studies conducted by the inventors of the present invention to solve the above problems, a binder for a secondary battery comprising a water-soluble polyvinyl alcohol and an acid-treated water-soluble chitosan modifier is used as a binder for fixing the inorganic particle layer of the separator, or Alternatively, it has been found that when the positive and negative active materials are used as binders for fixing the current collector to the current collector, it is possible to provide a battery satisfying all of safety, lifespan, energy density, and output characteristics. Specifically, when the binder for a secondary battery having the above configuration is applied to a composite separator, the adhesion to both the porous substrate and the inorganic particles can be remarkably improved without deterioration of the air permeability and ion permeability of the separator.

Hereinafter, each configuration of the present invention will be described in more detail. However, this is merely exemplary and the present invention is not limited to the specific embodiments described by way of example.

bookbinder

The binder for a secondary battery according to an aspect of the present invention may be applied to a positive electrode, a negative electrode, or a separator of a battery. it is not going to be

The binder for a secondary battery according to an aspect of the present invention may include a water-soluble polyvinyl alcohol and an acid-treated water-soluble chitosan modifier.

The modified chitosan according to an aspect of the present invention may include chitosan and glucosamine formed by decomposition of chitosan by acid. For example, when only chitosan or a chitosan derivative that does not contain glucosamine is used, the adhesive performance is not sufficient to be applied as a binder for a secondary battery, and the water solubility is significantly lowered, so that it is difficult to apply it as an aqueous binder. On the other hand, the modified chitosan according to an aspect of the present invention can be evenly dispersed in water, and can impart better battery characteristics by expressing the ion conductive properties of the binder itself. In addition, by improving the applicability of the binder, a uniform inorganic particle layer can be formed, and the adhesion between the porous substrate and the inorganic particle layer can be further improved.

As the binder for a secondary battery according to an aspect of the present invention includes a combination of an acid-treated water-soluble chitosan modifier and water-soluble polyvinyl alcohol, when applied to a composite separator, the adhesion between the inorganic particles or between the inorganic particles and the substrate is very excellent. can not only improve the performance of the battery, but also improve the battery performance and stability at the same time. Specifically, it is possible to more effectively improve the adhesion and coatability between the inorganic particles and between the inorganic particles and the substrate while there is no or minimal reduction in the pore size and porosity of the porous substrate. In addition, the composite separator to which the binder is applied has excellent adhesion performance, excellent ion permeability and mobility, and excellent wettability to an electrolyte, so that the performance and electrochemical stability of a battery including the same can be improved.

Specifically, the chitosan modifier according to an aspect of the present invention may include glucosamine in 60 mol% or more, for example, 70 mol% or more, or 80 mol% or more, or 80 mol% to 95 mol%. . As the glucosamine content in the above range is satisfied, the effect of simultaneously improving the adhesion performance and ion permeability of the composite separator can be more effectively implemented.

The chitosan modifier according to an aspect of the present invention may be one that has been treated with an aqueous inorganic acid solution, specifically, it may be one that has been treated for 5 to 20 hours at a temperature condition of 10 to 100 ℃, more specifically, a temperature of 50 to 90 ℃ It may be treated under the conditions for 10 to 20 hours.

The inorganic acid may include, for example, hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, perchloric acid and carbonic acid, specifically hydrochloric acid. For example, when chitosan is treated with an organic acid such as acetic acid or formic acid, it cannot be decomposed into a sufficient amount of glucosamine and it may be difficult to achieve satisfactory adhesion performance and water solubility, but it is not preferred, but as long as the object of the present invention is achieved, it is not limited thereto does not

The degree of saponification of the water-soluble polyvinyl alcohol according to an aspect of the present invention is not particularly limited when it has water solubility, but may be, for example, 75 mol% or more, for example, 80 mol% or more, or 85 mol% to 100 mol%. When the saponification degree of the above range is satisfied, it is more preferred because the adhesion performance between the inorganic particles or between the inorganic particles and the substrate can be further improved by just adding a small amount of polyvinyl alcohol. In addition, polyvinyl alcohol satisfying the saponification degree of the above range may be more preferred because it can impart a synergistic effect in the simultaneous improvement of the adhesive strength and ionic conductivity of the binder by combining with the chitosan modifier as described above.

In addition, the water-soluble polyvinyl alcohol may have a weight average molecular weight of 3,000 to 500,000 g/mol, for example, 10,000 to 300,000 g/mol, or 10,000 to 100,000 g/mol, or 10,000 to 50,000 g/mol. . By using polyvinyl alcohol satisfying the weight average molecular weight in the above range, it is preferred because the adhesive performance of the binder and the stability to the electrolyte can be more appropriately adjusted.

The binder for a secondary battery according to an aspect of the present invention contains 0.01 to 100 parts by weight, or 0.05 to 50 parts by weight, or 0.1 to 20 parts by weight of the acid-treated water-soluble chitosan modifier based on 100 parts by weight of the water-soluble polyvinyl alcohol. can In the above range, the desired effect in the present invention without compromising the stability of the formulation, that is, it is preferable to show remarkable in the effect of simultaneously improving the adhesion of the binder and the battery performance, but is not necessarily limited thereto.

In addition, the binder for secondary transfer according to an aspect of the present invention may further include a water-based polymer if necessary, and the water-based polymer is, for example, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyacrylonitrile. , polyvinylmethyl ether, polypropylene glycol, cellulose, poly- may be one or two or more selected from isopropylmethacrylamide and polyethylene oxide, but is not necessarily limited thereto.

For example, the binder according to an aspect of the present invention may be an aqueous binder for a secondary battery separator.

Inorganic Particles and Slurry Compositions

One aspect of the present invention provides a slurry composition comprising the above-described binder for a secondary battery, inorganic particles and a solvent.

The inorganic particles according to an aspect of the present invention are not particularly limited as long as they are electrochemically stable, but as a non-limiting example, the particles are aluminum oxide, boehmite, barium titanium oxide (Barium Titanium Oxide), titanium oxide, magnesium oxide , clay, glass powder, boron nitride and aluminum nitride may be one or two or more selected from the group consisting of, but it may be more preferable to use boehmite without limitation. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and/or reduction reactions do not occur in the operating voltage range of the applied battery (eg, 0 to 5V based on Li/Li +), but ion transfer ability Inorganic particles having this may be more preferable because it is possible to improve the performance by increasing the ionic conductivity in the electrochemical device.

In addition, the diameter of the inorganic particles is not particularly limited, but may be 0.01 to 10 μm, preferably 0.1 to 5 μm, in terms of forming an inorganic particle layer of a uniform thickness and implementing appropriate porosity.

The slurry composition according to an embodiment of the present invention may have a solid content of 20 to 80% by weight, preferably 25 to 60% by weight, more preferably 30 to 50% by weight, but is not limited thereto.

In the slurry composition according to an aspect of the present invention, the binder may be included in an amount of, for example, 0.01 to 20 parts by weight, 0.01 to 10 parts by weight, 0.01 to 5 parts by weight, based on the solid content based on 100 parts by weight of the inorganic particles, but this It is not limiting. In the above range, the pore size and porosity of the composite separator can be more effectively controlled, and adhesion between the inorganic particles and/or between the inorganic particles and the substrate can be more effectively improved.

Porous substrate and composite separator

One aspect of the present invention is a porous substrate; and an inorganic particle layer prepared by coating the above-described slurry composition on one or both surfaces of a substrate; it provides a composite separator comprising a. Specifically, the composite separator may include a porous substrate; and an inorganic particle layer coated on one or both surfaces of the substrate, wherein the inorganic particle layer is connected and fixed by the binder according to an embodiment of the present invention to form pores between the inorganic particles can

The porous substrate according to an aspect of the present invention may be a polyolefin-based porous substrate. A non-limiting example of the polyolefin-based component may be one or two or more selected from high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, or derivatives thereof, but is not limited thereto.

In addition, the pore size of the porous substrate may be 0.001 to 10 μm, or 0.005 to 2 μm. In addition, the porosity of the porous substrate may be 5 to 80%, or 10 to 70%, or 20 to 60%. In the above range, it may have better mechanical strength and air permeability, and by further improving the wettability to the electrolyte, excellent ionic conductivity may be realized, and thus, it is preferred, but not necessarily limited thereto.

The thickness of the inorganic particle layer according to an aspect of the present invention is not particularly limited, but may be 0.1 to 10 μm, preferably 0.5 to 5 μm. In the above range, more excellent mechanical strength and air permeability can be implemented at the same time, which is preferred, but is not limited thereto.

In addition, the size of the pores formed between the inorganic particles in the inorganic particle layer according to an embodiment of the present invention may be 0.001 to 10 μm, or 0.005 to 2 μm. In addition, the porosity may be 5 to 80%, or 10 to 70%, or 20 to 60%. That is, the binder according to an embodiment of the present invention can effectively improve adhesion and coating properties between inorganic particles and between inorganic particles and a substrate while there is no or minimal reduction in the pore size and porosity of the porous substrate. Accordingly, the composite separator to which the binder is applied has excellent adhesion as well as ion permeability and mobility, so that the performance and electrochemical stability of a battery including the same can be improved.

The composite separator according to an aspect of the present invention may be manufactured according to a conventional method known in the art. As a non-limiting example thereof, the method for manufacturing the composite separator may include (a) preparing a slurry composition by adding and mixing the binder for the secondary battery and the inorganic particles to water; and (b) applying the slurry composition of step (a) on one or both sides of the porous substrate and drying to form an inorganic particle layer.

The water in step (a) according to an aspect of the present invention is preferably water alone, but may further include an organic solvent if necessary. Non-limiting examples of the organic solvent include ethanol, isopropylalcohol, acetone, tetrahydrofuran, chloroform, dimethylformamide, N-methyl- It may be selected from 2-pyrrolidone (N-methyl-2-pyrrolidone, NMP), cyclohexane, or a combination thereof.

The method for applying the slurry composition in step (b) is not particularly limited as long as it is a conventional coating method known in the art, but as a non-limiting example, a bar coating method, a rod coating method, a die ) coating method, wire coating method, comma coating method, micro gravure/gravure method, dip coating method, spray method, ink-jet coating method, or a mixture thereof and modified methods may be used.

In addition, the drying temperature in step (b) is not particularly limited, but may be 45°C or more and 150°C or less, more specifically 45°C or more and 120°C or less. When drying at the above drying temperature, coating defects can be prevented by uniformly drying the inorganic particle layer without affecting the physical properties of the porous substrate.

In addition, the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and the composite separator of the present invention.

The electrochemical device may include any device that undergoes an electrochemical reaction, and specific examples thereof may be selected from all kinds of secondary cells, fuel cells, solar cells, or capacitors. In particular, a lithium secondary battery is preferable among secondary batteries, and non-limiting examples thereof include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Hereinafter, a lithium secondary battery according to an embodiment will be described, but the present invention is not limited thereto.

A lithium secondary battery including a composite separator according to an aspect of the present invention may be manufactured including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and negative electrode are prepared by mixing and stirring a solvent, a binder, a conductive material, a dispersing material, etc., to the positive electrode active material and the negative electrode active material, if necessary, and then applying (coating) it to the current collector of a metal material, drying it, and pressing ( Press) can be prepared. In addition, it is of course that using this, using a commonly used electrolyte solution used in this field, it can be prepared by a possible method within a range that can be recognized by those skilled in the art.

Hereinafter, the present invention will be described in detail by way of Examples. However, the following examples are only for illustrating the present invention, and the content of the present invention is not limited by the following examples. At this time, if there is no other definition in the technical terms and scientific terms used, those of ordinary skill in the art to which this invention belongs have the meanings commonly understood. In addition, repeated description of the same technical configuration and operation as in the prior art will be omitted.

The physical properties of the present invention were measured as follows.

(1) thickness

The thickness was measured with TESA-Mhite with a contact-type thickness measuring device with a precision of 0.1 μm.

(2) interfacial adhesion

The interfacial adhesion between the porous substrate and the coating layer was measured using TEST0NE's TO-102 universal tester. The coated separator was attached to the slide using double-sided tape and measured using the 180° Peel test method.

(3) air permeability

A composite membrane sample having a size of 60 mm horizontally and vertically was prepared, and the time (seconds) required to pass 100 ml of air was measured using 4110N of Thwing-Alber (manufactured in the United States).

(4) ionic conductivity

The composite separator was impregnated with an ethylene carbonate/propylene carbonate/diethyl carbonate-based electrolyte solution (EC/PC/DEC=3:2:5 volume ratio, 1M LiPF ₆ ). Thereafter, the ionic conductivity of the membrane impregnated with the electrolyte was measured using a Metrohm712 instrument. At this time, the measurement temperature was 25 degreeC.

(5) heat shrinkage

After cutting the composite separator to a size of 40mm*40mm, it was left in a drying oven at 140° C. for 30 minutes for chitosan lc analysis, and the shrinkage size was measured and calculated.

(6) Capacity retention rate

The lithium secondary battery was charged at a constant current/constant voltage (CC/CV) condition at 25° C. at a C-rate of 1.0 to 4.4V, and then cut-off at a C-rate of 0.1. Thereafter, it was discharged (CC condition) at a C-rate of 1.0 to 3.0V. 200 cycles were implemented by making the said charging/discharging cycle 1 cycle. After 200 cycles, the capacity retention rate was evaluated.

(7) Glucosamine content

The glucosamine content of the chitosan modified form was analyzed using HPLC (High-performance liquid chromatography). The column used for HPLC analysis was Bondclone 10 NH ₂ (300x3.9mm, 10 micron, phenomenex), the mobile phase was CH ₃ CN:H ₂ O=65:35 (v/v), and the detector was RI (Refractive). Index Detector), and the flow rate was 0.8 mL/min.

[Preparation Example 1] Preparation of acid-treated water-soluble chitosan modifier

100 g of chitosan was placed in 1 L of distilled water, and stirred at room temperature for 10 minutes to prepare a 10 wt% chitosan suspension. A 0.2 M aqueous hydrochloric acid solution was added until the pH of the chitosan suspension reached 2.5, and from the moment the pH reached 5, the mixture was stirred at 65° C. for 16 hours. Thereafter, the resulting solid was removed by centrifugation, and the solution from which the solid was removed was neutralized to pH 7.8 using 1.0M NaOH, and an aqueous layer was obtained by centrifugation again. Thereafter, the aqueous layer was washed several times with distilled water and lyophilized to prepare a modified chitosan having a glucosamine content of 85 mol%.

[Production Example 2]

A chitosan modified form having a glucosamine content of 46 mol% was prepared in the same manner as in Preparation Example 1, except that the pH of the chitosan suspension was adjusted to 5.0.

[Example 1]

manufacture of binders

With respect to 100 parts by weight of polyvinyl alcohol having a saponification degree of 88 mol% and a weight average molecular weight of 22,000 g/mol, 10 parts by weight of the chitosan modified product of Preparation Example 1 and the remaining amount of purified water were mixed, and 5 hours at room temperature (25° C.) A uniform solution of the binder was prepared by stirring for a while.

Preparation of the slurry composition

The binder is dissolved and/or dispersed in water to be 1 wt% based on the solid content, and alumina particles (Al ₂ O ₃ ) having an average diameter of 0.5 μm in the water in which the binder is dissolved and/or dispersed are 40 wt% was added to prepare a slurry composition.

Manufacture of Composite Separator

After coating the slurry composition on one side of a polyethylene substrate having a thickness of 20 μm and a porosity of 45% using a slot coating die, drying in a vacuum oven at 60° C. for 6 hours, an inorganic material having a thickness of 3 μm on one side of the substrate A composite separator with a particle layer was prepared, and its physical properties are shown in Table 1 below.

Manufacturing of Lithium Secondary Battery

1) Preparation of anode

94% by weight of LiCoO ₂ as a positive electrode active material, 3% by weight of carbon black as a conductive agent, and 3% by weight of PVdF as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent and stirred to obtain a uniform positive electrode A mixture slurry was prepared. The slurry was coated on an aluminum foil having a thickness of 30 μm, dried at a temperature of 120° C., and then compressed to prepare a positive electrode plate having a thickness of 150 μm.

2) Preparation of cathode

96 wt% of artificial graphite as an anode active material, 1 wt% of carbon black as a conductive material, and 3 wt% of PVdF as a binder were added to NMP, a solvent, and stirred to prepare a uniform anode mixture slurry. The slurry was coated on a copper foil having a thickness of 20 μm, dried at a temperature of 120° C., and compressed to prepare a negative plate having a thickness of 150 μm.

3) Manufacturing of battery

A pouch-type battery was assembled in a stacking method using the positive electrode, the negative electrode, and the composite separator prepared above. Lithium secondary battery by injecting 1M lithium hexafluorophosphate (LiPF ₆ ) dissolved ethylene carbonate/propylene carbonate/diethyl carbonate (EC/PC/DEC=3:2:5 volume ratio) electrolyte into each of the assembled batteries paper was prepared, and its physical properties are shown in Table 1 below.

[Example 2]

Except for using water-soluble polyvinyl alcohol having a saponification degree of 60 mol%, it was carried out in the same manner as in Example 1, and its physical properties are shown in Table 1 below.

[Example 3]

Except for using the modified chitosan of Preparation Example 2 instead of the modified chitosan of Preparation Example 1, it was carried out in the same manner as in Example 1, and its physical properties are shown in Table 1 below.

[Comparative Example 1]

It was carried out in the same manner as in Example 1 except that a commercially available water-based acrylic binder (Sumitomo seika, AQC binder) was used instead of the binder prepared in Example 1, and its physical properties are shown in Table 1 below.

[Comparative Example 2]

It was carried out in the same manner as in Example 1, except that chitosan without acid treatment was used as it is instead of the chitosan modified form of Preparation Example 1, and its physical properties are shown in Table 1 below.

[Comparative Example 3]

Example 1 was carried out in the same manner as in Example 1 except that the chitosan modifier was not used, and its physical properties are shown in Table 1 below.

Thickness (㎛) interface resistance
(Ohm) ionic conductivity
(mS/cm) breathability
(sec/100ml) interfacial adhesion
(gf) heat shrinkage
(%) Capacity retention rate
(%) Example 1 23 1.268 0.919 272.8 137 2.0 97 Example 2 23 1.332 0.838 270.2 112 4.0 95 Example 3 23 1.155 0.866 278.3 126 4.0 95 Comparative Example 1 23 1.391 0.819 289.7 110 3.0 96 Comparative Example 2 23 1.402 0.807 249.6 95 9.0 93 Comparative Example 3 23 1.348 0.714 278.1 80 18.0 90 Separator before coating 20 1.224 0.813 240.6 - 71.0 97

Referring to Table 1, it can be seen that the composite separator prepared from the binder according to an embodiment of the present invention has excellent adhesion and air permeability, thereby improving ionic conductivity properties. In addition, it was confirmed that the composite separator according to the present invention has improved ionic conductivity and improved interfacial resistance, so that the capacity retention rate of the battery employing the same is significantly improved. That is, the binder according to the present invention can secure battery safety, long life, high energy density, and high output characteristics at the same time.

On the other hand, the separator of Comparative Example 1 using a commercially available aqueous acrylic binder had limitations in that air permeability and ionic conductivity were deteriorated even though interfacial adhesion was somewhat improved. In addition, it was confirmed that in the case of the composite separator using the binders of Comparative Examples 2 and 3 that did not contain a chitosan modifier or used unacid-treated chitosan as it is, interfacial adhesion was significantly reduced.

As described above, the present invention has been described with reference to the limited embodiments, but these are provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and common knowledge in the field to which the present invention pertains is provided. Various modifications and variations are possible from such a base material.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (12)

As a binder for a secondary battery comprising a water-soluble polyvinyl alcohol and acid-treated water-soluble chitosan modifier,
The chitosan modifier is decomposed by acid to contain 60 mol% or more of glucosamine, a binder for a secondary battery. The method of claim 1,
The saponification degree of the water-soluble polyvinyl alcohol is 75 mol% or more, and the weight average molecular weight is 3,000 to 500,000 g/mol, a binder for a secondary battery. The method of claim 1,
The chitosan modifier is a binder for a secondary battery that is treated with an aqueous inorganic acid solution at a temperature of 10 to 100 °C for 5 to 20 hours. delete The method of claim 1,
The water-soluble chitosan modifier acid-treated with respect to 100 parts by weight of the water-soluble polyvinyl alcohol is included in an amount of 0.1 to 200 parts by weight, a binder for a secondary battery. The method of claim 1,
One or more water-based polymers selected from polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, polyacrylonitrile, polyvinylmethyl ether, polypropylene glycol, cellulose, poly-isopropylmethacrylamide and polyethylene oxide are further added Including, a binder for a secondary battery. The method of claim 1,
The binder is an aqueous binder for a secondary battery separator, a binder for a secondary battery. The binder for a secondary battery of any one of claims 1 to 3, 5 to 7 selected from; inorganic particles; And a solvent; Containing, the slurry composition. 9. The method of claim 8,
The binder is contained in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the inorganic particles, the slurry composition. porous substrate; and an inorganic particle layer coated on one or both surfaces of the substrate; as a composite separator comprising:
In the inorganic particle layer, the inorganic particles are connected and fixed by the binder of any one of claims 1 to 3 and 5 to 7 to form pores between the inorganic particles. 11. The method of claim 10,
The pore size is 0.001 to 10 μm, and the porosity is 10 to 80%, the composite separator. A secondary battery comprising the composite separator of claim 10 .