KR101578545B1 - Aqueous polyimide binder for secondary battery, Preparing method thereof, coating agent of electrodes for secondary battery and Electrodes for secondary battery - Google Patents

Abstract

The present invention relates to a water-soluble binder for a secondary battery, a preparing method thereof, a coating agent prepared by using the same, and a secondary battery electrode. The water-soluble binder for a secondary battery of the present invention is eco-friendly due to using water as a solvent, and can provides a binder for a secondary battery electrode of a water-soluble polyimide material having heat resistance, solvent resistance, oxidation resistance and high mechanical strength. In addition, the present invention can provides a flexible secondary battery electrode which has excellent flexibility as well as having excellent binding power between the electrode active material coating agent prepared by using the binder and an electrode current collector of a secondary battery.

Description

[0001] The present invention relates to a water-soluble binder for a secondary battery, a method for producing the same, an electrode active material coating agent for a secondary battery using the same, and an electrode for a secondary battery,

The present invention relates to a water-soluble binder for a secondary battery, and a coating agent using the binder of the present invention and a coating layer formed therefrom are excellent in flexibility, binding force and swelling property, and thus a flexible secondary battery electrode can be produced.

The secondary battery generally comprises a positive electrode having a positive electrode active material layer formed on at least one surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer formed on at least one surface of the negative electrode current collector and a separator interposed between the positive electrode and the negative electrode, Respectively. Examples of the method of forming the electrode active material layer on the current collector include a method in which the electrode active material slurry in which the electrode active material particles and the binder are dispersed in a solvent is directly applied and dried on the current collector or the electrode active material slurry is applied and dried on a separate support , And then the film peeled off from the support is laminated on the current collector. The binder plays a role of fixing and connecting between the electrode active material particles and the electrode current collector as well as between the electrode active material particles, and thus has a great influence on the performance of the electrode. That is, the binder should be excellent in adhesion so as to increase the content of the electrode active material particles, and should be electrochemically stable so that side reactions do not occur. In addition, a certain degree of flexibility is required to prevent breakage during the assembling process of the battery. The polyvinylidene fluoride polymer used as the binder of the lithium secondary battery has an advantage of being electrochemically stable. However, this binder is not only insufficient in adhesion, but also has environmental problems in that it must be dissolved in an organic solvent such as NMP (N-methyl-2-pyrrolidone) to prepare an electrode active material slurry. In recent years, flexible and portable devices have been made smaller and lighter with higher performance, and secondary batteries used in such portable devices are also required to be flexible.

As a binder, there has been developed a binder using an environmentally friendly solvent, not an organic solvent. A method of dispersing a synthetic rubber such as rubber (SBR) made of a styrene unit-butadiene unit into water to form an electrode is used (Japanese Patent Laid-Open Publication No. 3-53450, Japanese Patent Laid-Open No. 5-62668). Further, there has been proposed to use latex-based rubber particles suspended in water as a binder (for example, JP-A-5-21068 and JP-A-5-74461) There is not enough performance between the current collector and the active material. Such a synthetic rubber binder exhibits a point-sticking property, and therefore, there is a problem that the contact area is small and the adhesive force and / or the binding force are not sufficiently exhibited. Therefore, there is an inadequate problem to manufacture an electrode of a flexible secondary battery. Korean Patent No. 10-0767966 discloses a synthetic rubber binder containing an unsaturated carboxylic acid monomer unit such as acrylic acid or itaconic acid as an electrode binder having improved adhesion properties. However, the binder may cause gas to be generated by the remaining acid component.

Korean Patent No. 10-0767966 (Oct. 10, 2007)

An object of the present invention is to provide a water-soluble binder as a binder for a secondary battery, which has a molecular structure for improving solubility in water and satisfies a flexible bending structure and has improved binding force due to its high molecular weight.

Disclosure of the Invention In order to solve the above problems, the present invention relates to a water-soluble binder for a secondary battery, which comprises a polyamic acid aqueous solution in which 4 to 10 parts by weight of polyamic acid solid particles and 0.2 to 4 parts by weight of water- . ≪ / RTI >

In one preferred embodiment of the present invention, the polyamic acid solution may have a viscosity of 10 cps (25 ° C) to 1,000 cps (25 ° C).

In one preferred embodiment of the present invention, the polyamic acid solid particles may be prepared by adding a mixture of 100 parts by weight of a polyamic acid varnish and 4 to 10 parts by weight of a water-based reagent to a precipitant to dry the precipitated precipitate.

In one preferred embodiment of the present invention, the precipitant is contained in an amount of 400 to 600 parts by weight based on 100 parts by weight of the polyamic acid varnish.

In one preferred embodiment of the present invention, the hydration reagent is selected from the group consisting of DMZ (1,2-dimethylimidazole), DMEA (dimethylethanolamine), EMZ (2-Ethyl-4-methylimidazole), MDEA (Methyldiethanolamine) and TEOA And at least one selected from the group consisting of

In one preferred embodiment of the present invention, the polyamic acid varnish is a reactant obtained by reacting diamine with dihydride. The polyamic acid varnish may include 110 to 150 parts by weight of the dianhydride, based on 100 parts by weight of the diamine. .

In one preferred embodiment of the present invention, the polyamic acid varnish comprises 5 to 30% by weight of a solid component and has a viscosity of 800 cps (25 ° C) to 10,000 cps (25 ° C).

In one preferred embodiment of the present invention, the diamine is 3,5-diaminobenzoic acid, 1,4-bis (4-aminophenoxy) benzene (1,4-bis (4-aminophenoxy) benzene, 4,4 '- (1,3-phenylenedioxy) dianiline, 3,3'-dihydroxybenz Dihydroxybenzidine, p-phenylenediamine, 4,4 '- (4,4'-isopropylidenediphenyl-1,1'-dileoxy) di (4,4'- (4,4'-isopropylidenediphenyl-1,1'-diyldioxy) dianiline, Bis [4- (4-aminophenoxy) phenyl] sulfone, sulfone, 4,4'-Diaminodiphenylsulfone, 4,4'-Oxydianiline, 2,2-bis [4- (4- Aminophenoxyphenyl)] hexafluoropropane), 2,2'-bis (trifluoromethyl) benzazidine (2,2'-bis [ -Bis (trifluoromethyl) benzidine) and 2,2-bis (3-amino-4- Hydroxyphenyl) may be characterized in that it comprises at least one member selected from the group consisting of hexafluoro-propane (2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane).

In one preferred embodiment of the present invention, the diamine may include two or more diamines, and it is preferable that 1,4-bis (4-aminophenoxy ) Benzene, 4,4 '- (1,3-phenylene dioxy) thianiline, 3,3'-dihydroxybenzidine, p-phenylenediamine, 4,4' - (4-aminophenoxy) phenyl] sulfone, 4,4'-diaminodiphenylsulfone, 4,4'-oxy Dianiline, 2,2-bis [4- (4-aminophenoxyphenyl)] hexafluoropropane, 2,2'-bis (trifluoromethyl) benzidine and 2,2- Amino-4-hydroxyphenyl) hexafluoropropane in an amount of 700 to 1500 parts by weight.

In one preferred embodiment of the present invention, the dianhydride is selected from the group consisting of biphenyl-tetracarboxylic acid dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride ( 1,2,4,5-benzenetetracarboxylic dianhydride, 4,4 '- (hexafluoroisopropylidene) diphthalic dianhydride, 4,4'- (Hexafluoroisopropylidene) diphthalic dianhydride, 4,4'-Oxydiphthalic dianhydride, 1,2,4,5-cyclohexaneetetracarboxylic acid dianhydride and 3, 4, 5-cyclohexanetetracarboxylic acid dianhydride. , And 3 ', 4,4'-benzophenone tetracarboxylic acid dihydride (3,3', 4,4'-benzophenonetetracarboxylic acid dianhydride).

Another object of the present invention is to provide a method for producing the various types of water-soluble binders for secondary batteries as described above, which comprises a solid content of 5 to 30 wt% and a viscosity of 800 cps (25 캜) to 10,000 cps ) Of polyamic acid varnish; A second step of adding a mixed solution of a hydrating reagent to the polyamic acid varnish to a precipitant to obtain a precipitate; Drying the precipitate to prepare polyamic acid solid particles; And adding the polyamic acid solid particles to water and stirring and dissolving the polyamic acid solid particles in water to prepare a polyamic acid aqueous solution, thereby producing a water-soluble binder for a secondary battery.

As a preferred embodiment of the present invention, in the production method of the present invention, the first stage polyamic acid varnish can be prepared by adding dianhydride to a solution in which diamine is dissolved in a solvent and reacting.

In one preferred embodiment of the present invention, the precipitating agent in the second step is acetone.

In one preferred embodiment of the present invention, the polyamic acid solid particles in step 3 are prepared by drying the two-step precipitate under a vacuum of 30 ° C to 50 ° C.

In one preferred embodiment of the present invention, the aqueous polyamic acid solution in four stages has a viscosity of 10 cps (25 ° C) to 1,000 cps (25 ° C).

Another object of the present invention is to provide an electrode active material coating agent for a secondary battery, which is characterized by using an electrode material including the above-described various types of water-soluble binders for a secondary battery.

In one preferred embodiment of the present invention, the electrode active material coating material for a secondary battery of the present invention comprises 40 wt% to 50 wt% of an electrode material and 50 wt% to 60 wt% of water, ; Carboxymethyl cellulose (CMC); And an electrode lubricant.

It is still another object of the present invention to provide an electrode for a secondary battery, which comprises an electrode active material layer coated with the electrode active material coating material for the secondary battery.

In a preferred embodiment of the present invention, in the electrode for a secondary battery of the present invention, the electrode active material layer has an adhesion force of 0.8 gf / mm to 3.0 gf / mm 2 when measured according to a 180 ° peel test method .

The water-soluble binder for a secondary battery of the present invention can provide a water-soluble polyimide binder for a secondary battery which is eco-friendly and has heat resistance, solvent resistance, oxidation resistance and high mechanical strength by using water as a solvent.

Hereinafter, the present invention will be described in more detail.

The electrode assembly of the secondary battery includes electrodes (a cathode and an anode), and the electrode includes an electrode active material layer (a negative electrode active material layer and / or a positive electrode active material layer) and an electrode collector (a negative electrode collector and / In general, the electrode active material layer of the secondary battery is coated on one or both surfaces of the electrode current collector to form a coating layer.

The water-soluble binder for a secondary battery of the present invention is a material of an electrode active material coating material for a secondary battery, more specifically, a material of an electrode material constituting the electrode active material coating agent, and serves as a binder of an electrode active material.

The electrode active material coating material for a secondary battery of the present invention comprises 40 to 50 wt% of an electrode material and 50 to 60 wt% of water, preferably 42 to 48 wt% of an electrode material and 52 to 58 wt% of water, If the content of the electrode material is less than 40% by weight, the density of the electrode active material in the electrode active material layer formed of the electrode active material coating material may be low and the charging capacity of the secondary battery may be reduced. If the content of the electrode material is less than 60% , The water content of the electrode active material coating material may be relatively low and the viscosity of the electrode active material coating material may become too high, resulting in deterioration of coating properties.

In the electrode active material coating material of the present invention, the electrode material may be a water-soluble binder for the secondary battery; Carboxymethyl cellulose (CMC); Wherein the electrode material comprises 1 to 5% by weight of a water-soluble binder for a secondary battery, 0.5 to 3% by weight of the CMC, and 92 to 98% by weight of the electrode active material, 3 to 3 wt%, CMC 0.5 to 2 wt%, and 95 to 97 wt% of the electrode lubricant. If the content of the water-soluble binder for the secondary battery is less than 1% by weight, the amount of the water-soluble binder used for the secondary battery may be too small to cause a problem that the electrode-binder has a low binding force (and / If it is more than 5% by weight, the use amount thereof is too much, and the viscosity becomes high, and rather the electrode lubricant may be prevented from being appropriately dispersed and coated. If the CMC content is less than 0.5% by weight, the viscosity may not be sufficient and there may be a problem of dewetting due to coating, and even when the CMC content exceeds 2% by weight, It is economical. The content of the electrode lubricant is relatively determined depending on the water-soluble binder and the CMC content.

The electrode lubricant may be a commonly used electrode material used in the secondary battery electrode active material in the art, and preferably includes crystalline or amorphous carbon, carbon fiber, tin oxide, Lithium, a lithium alloy, and mixtures thereof. The crystalline or amorphous carbon may be a carbon nanotube, a carbon nanowire, a carbon nanofiber, a graphite, an activated carbon, a graphite, a graphite ), And the like.

In the electrode for a secondary battery according to the present invention comprising the electrode active material layer coated with the above-described electrode active material coating material for a secondary battery, when measured according to the 180 ° peel test method, Mm to 3.0 gf / mm, preferably 0.8 gf / mm 2 to 2.5 gf / mm 2, and more preferably 1.0 gf / mm 2 to 2.0 gf / mm 2 with respect to the negative electrode current collector gf / mm. As a result, it is possible to provide a flexible electrode.

In addition, the electrode active material layer may have swelling resistance of less than 150%, preferably 105% to 130%, more preferably 112% to 128%, and excellent expansion stability.

The water-soluble binder for a secondary battery of the present invention used for the above-described electrode active material coating agent for a secondary battery will be described.

The water-soluble binder for a secondary battery according to the present invention comprises an aqueous solution of polyamic acid in which water, polyamic acid solid particles and hydration reagent are dissolved, and the aqueous solution of polyamic acid has a viscosity of 10 cps (25 ° C) to 1,000 cps , Preferably from 10 cps (25 캜) to 200 cps (25 캜), and more preferably from 10 cps (25 캜) to 80 cps (25 캜).

Another object of the present invention is to provide a method for producing the various types of water-soluble binders for secondary batteries as described above, which comprises a solid content of 5 to 30 wt% and a viscosity of 800 cps (25 캜) to 10,000 cps ) Of polyamic acid varnish; A second step of adding a mixed solution of a hydrating reagent to the polyamic acid varnish to a precipitant to obtain a precipitate; Drying the precipitate to prepare polyamic acid solid particles; And adding the polyamic acid solid particles to water and stirring and dissolving the polyamic acid solid particles in water to prepare a polyamic acid aqueous solution, thereby producing a water-soluble binder for a secondary battery.

In the above step 1, the polyamic acid varnish can be prepared by adding dianhydride to a solution in which diamine is dissolved in a solvent and reacting.

The polyamic acid varnish is a reaction product of diamine and dianhydride, wherein 110 to 150 parts by weight of the dianhydride is reacted with 100 parts by weight of diamine. The polyamic acid varnish has a solid content of 5 to 30 wt% (25 ° C) to 10,000 cps (25 ° C), preferably a solid content of 5% by weight to 20% by weight, more preferably a solid content of 8% May have 920 cps (25 캜) to 7,500 cps (25 캜), and more preferably 1,000 cps (25 캜) to 6,000 cps (25 캜).

In the present invention, the diamine is preferably selected from the group consisting of 3,5-Diaminobenzoic acid, 1,4-bis (4-aminophenoxy) benzene ), 4,4 '- (1,3-phenylenedioxy) dianiline, 3,3'-dihydroxybenzidine (3,3 Dihydroxybenzidine, p-phenylenediamine, 4,4 '- (4,4'-isopropylidenediphenyl-1,1'-dyldioxy) - (4,4'-Isopropylidenediphenyl-1,1'-diyldioxy) dianiline, Bis [4- (4-aminophenoxy) phenyl] sulfone, Diaminodiphenylsulfone, 4,4'-oxydianiline, 2,2-bis [4- (4-aminophenoxyphenyl)] - Bis (trifluoromethyl) benzidine (2,2'-bis [4- (4-aminophenoxyphenyl)] hexafluoropropane, 2,2'- ) And 2,2-bis (3-amino-4-hydroxyphenyl) The oro propane (2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane) at least one selected from, may preferably include a combination of two or more. When the diamine is contained in an amount of 2 or more, 1,4-bis (4-aminophenoxy) benzene, 4,4 '- (1 , 3-phenylene dioxy) thianiline, 3,3'-dihydroxybenzidine, p-phenylenediamine, 4,4 '- (4,4'-isopropylidenediphenyl- Dianiline, bis [4- (aminophenoxy) phenyl] sulfone, 4,4'-diaminodiphenylsulfone, 4,4'-oxydianiline, 2,2-bis [4 - (4-aminophenoxyphenyl)] hexafluoropropane, 2,2'-bis (trifluoromethyl) benzidine and 2,2-bis It is advantageous to prepare an aqueous solution of polyamic acid having high solubility in water, in which 700 to 1,500 parts by weight, preferably 850 to 1,200 parts by weight, of at least one diamine selected from roprene is used.

In the present invention, the dianhydride is selected from the group consisting of biphenyl-tetracarboxylic acid dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride (1, 2,4,5-benzenetetracarboxylic dianhydride, 4,4 '- (hexafluoroisopropylidene) diphthalic dianhydride, 4,4' - (Hexafluoroisopropylidene) diphthalic dianhydride, 4,4'-Oxydiphthalic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, and 3,3'-cyclohexanetetracarboxylic acid dianhydride. ', 4,4'-benzophenone tetracarboxylic acid dihydride (3,3', 4,4'-benzophenonetetracarboxylic acid dianhydride), preferably biphenyl-tetracarboxylic acid liquid seed Dihydride, 4,4 ' - (hexafluoroisoprop < RTI ID = 0.0 > Phenylidene) dipyridic dihydride, 4,4'-oxydiphthalic dianhydride, and 3,3 ', 4,4'-benzophenone tetracarboxylic acid dihydride. And more preferably at least one selected from 4,4'-oxy diphthalic dianhydride and 3,3 ', 4,4'-benzophenone tetracarboxylic liquid sodium dihydride can be used .

The polyamic acid solid particles in the second step are prepared by mixing and stirring 4 to 10 parts by weight of an aqueous polymerization reagent and 4 to 7.5 parts by weight of an aqueous polymerization reagent with 100 parts by weight of a polyamic acid varnish as a precipitant And drying the precipitate thus precipitated. The hydration reagent is preferably at least one selected from DMZ (1,2-dimethylimidazole), DMEA (dimethylethanolamine), EMZ (2-ethyl-4-methylimidazole), MDEA (Methyldiethanolamine) and TEOA It is preferable to use at least one selected from DMZ, DMEA and EMZ.

The precipitant in the second step may be used in an amount of 400 to 600 parts by weight, preferably 450 to 570 parts by weight, based on 100 parts by weight of the polyamic acid varnish. The precipitant may be those generally used in the art , Preferably acetone, can be used.

The drying in three stages can be carried out under a vacuum of 30 ° C to 50 ° C, preferably 35 ° C to 45 ° C. If the drying temperature is lower than 30 ° C, there is a problem that the drying time becomes too long. , Drying may be accelerated, but there may be a problem that a part of the polyamic acid is imidized. Therefore, it is preferable to carry out drying under the above temperature.

Next, Step 4 is a step of dissolving the polyamic acid solid particles prepared in Step 3 in water to prepare an aqueous solution of polyamic acid, wherein the polyamic acid solid particles are dispersed in 4 to 10 parts by weight, If the content of the polyamic acid solid particles is less than 4 parts by weight, the viscosity of the polyamic acid aqueous solution may be too low to act as a binder for sufficient electrode lubricant. If the polyamic acid solid particle content is less than 4 parts by weight, If it exceeds 10 parts by weight, the polyamic acid solid particles may not be sufficiently dissolved.

The polyamic acid aqueous solution may contain 0.2 to 4 parts by weight, preferably 0.5 to 3 parts by weight, of water-base-forming reagent per 100 parts by weight of water. When the amount of the water-base-forming reagent is less than 0.2 parts by weight, There may be a problem that the solubility of the binder resin is lowered. If the binder resin is used in an amount exceeding 4 parts by weight, there may be a problem that the hydration reagent may act as an impurity in the binder action. The polyamic acid solid particles may have a solubility of 3 to 20, preferably 4.5 to 10, more preferably 4.7 to 9.0, in water at a temperature of 25 ° C.

In addition, the hydration reagent in Step 4 may be the same as the hydration reagent in Step 2, or may use another hydration reagent, and preferably the same hydration reagent may be used.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

[ Example ]

Example  1: Preparation of water-soluble binder for secondary battery

(1) Solids Containing Polyamic acid Varnish  Produce

To the reactor, 1,075 parts by weight of 1,4-bis (4-aminophenoxy) benzene and 5,000 parts by weight of NMP (N-methylpyrrolidone) as a solvent were added to 100 parts by weight of the 3,5- The solution was prepared by thoroughly dissolving the compounds in a solvent with a purge apparatus and stirring at room temperature.

Subsequently, 123.3 parts by weight of 4,4'-oxydiphthalic dianhydride was added to the inside of the reactor containing the solution as dianhydride, relative to 100 parts by weight of the diamine. At this time, the moisture was controlled so as not to penetrate into the reactor, and the temperature was maintained between 20 ° C and 25 ° C. It was possible to observe that the viscosity of the dihydride was increased by the small amount of the dihydride being fed into the reactor and the reaction was continued for about 5 hours with a small amount of NMP so as to match the viscosity for easy handling, A micamic varnish was prepared. The prepared polyamic acid varnish had a viscosity of 5,381 cps (25 캜) at a solid content of 10% by weight and a dark brown color.

(2) Numbering  Through conversion Polyamic acid  Preparation of aqueous solution

To 100 parts by weight of the polyamic acid varnish containing 10% by weight of the solid content, 6.5 parts by weight of DMZ as an aqueous solution reagent was added to the reactor and reacted at 25 DEG C for 1 hour to react to prepare a reaction product.

Next, for the washing and precipitation of the reactants, pure polyamic acid solid particles were obtained by slowly precipitating the reactants in acetone in small amounts. The acetone was used in an amount of 510 parts by weight based on 100 parts by weight of the polyamic acid varnish. Vacuum drying was performed at 40 占 폚 for 30 minutes in order to remove the solvent of the polyamic acid solid particles.

100 parts by weight of distilled water, 5.32 parts by weight of fully dried polyamic acid solid particles and 1.06 parts by weight of DMZ were added to the reactor and stirred at room temperature (about 25 ° C) for 12 hours or more to completely dissolve the solution to obtain a 5% by weight aqueous solution of polyamic acid , The viscosity of the aqueous solution of polyamic acid was 15 cps (25 캜), and it was brown.

The solubility of the polyamic acid solid particles in water is shown in Table 1 below.

Example  2

The same procedure as in Example 1 was carried out except that in the production of polyamic acid varnish As the dihydrides, 125 parts by weight of 3,3 ', 4,4'-benzophenone tetracarboxylic acid dihydride was used in place of 4,4'-oxydipthalic dianhydride to obtain a solid content of 10% by weight A polyamic acid varnish having a viscosity of 3,642 cps (25 캜) was prepared, and a polyamic acid aqueous solution having a viscosity of 8 cps (25 캜) was prepared in the same manner as in Example 1.

Example  3

The same procedure as in Example 1 was carried out except that in the production of polyamic acid varnish 125 parts by weight of 4,4 '- (hexafluoroisopropylidene) diphthalic dianhydride instead of 4,4'-oxydiphthalic dianhydride was used as dianhydride, and when the solid content was 10% by weight A polyamic acid varnish having a viscosity of 1,021 cps (25 캜) was prepared and a polyamic acid aqueous solution having a viscosity of 6 cps (25 캜) was prepared in the same manner as in Example 1.

Example  4

The same procedure as in Example 1 was carried out except that in the production of polyamic acid varnish As the diamine, 1,050 parts by weight of 4,4'-oxydianiline was used instead of 1,4-bis (4-aminophenoxy) benzene. When the solid content was 10% by weight, the viscosity was 4,150 cps A varnish was prepared and a polyamic acid aqueous solution having a viscosity of 11 cps (25 캜) was prepared in the same manner as in Example 1, using the varnish.

Example  5

The same procedure as in Example 1 was carried out except that in the production of polyamic acid varnish 1,100 parts by weight of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane was used as a diamine instead of 1,4-bis (4-aminophenoxy) , A polyamic acid varnish having a viscosity of 981 cps (25 캜) was prepared, and a polyamic acid aqueous solution having a viscosity of 5 cps (25 캜) was prepared in the same manner as in Example 1.

Example  6

The same procedure as in Example 1 was carried out except that in the production of polyamic acid varnish As the diamine, only 3,5-diaminobenzoquinone solution seed was used without using 1,4-bis (4-aminophenoxy) benzene, and the amount of 3,5- A polyamic acid varnish having a viscosity of 3,767 cps (25 캜) when the solid content was 10% by weight was prepared using 11 times of the amount of the 3,5-diaminobenzoquinone solution seed, and the same method as in Example 1 To prepare a polyamic acid aqueous solution having a viscosity of 10 cps (25 캜).

Example  7

8 parts by weight of the polyamic acid solid particles and 1.5 parts by weight of DMZ were added to the reactor in the same manner as in Example 1 except that 100 parts by weight of water was added to the reaction vessel for 13 hours at 25 ° C To obtain a polyamic acid aqueous solution having a concentration of 7% by weight. The viscosity of the polyamic acid aqueous solution was 15 cps (25 캜).

Comparative Example  One

2 parts by weight of the polyamic acid solid particles and 1.5 parts by weight of DMZ were added to the reactor in the same manner as in Example 1 except that 100 parts by weight of water was added to the reactor at a temperature of 25 ° C And completely dissolved to obtain a polyamic acid aqueous solution having a concentration of 2% by weight. The viscosity of the aqueous solution of polyamic acid was 4 cps (25 캜) and was brown.

Comparative Example  2

15 parts by weight of the polyamic acid solid particles and 2.5 parts by weight of DMZ were added to a reactor in the same manner as in Example 1 except that 100 parts by weight of water was added to the reactor at 25 ° C for 15 hours And completely dissolved to obtain an aqueous solution of polyamic acid having a concentration of 12.5% by weight. The viscosity of the aqueous solution of polyamic acid was 21 cps (25 캜) and was brown.

Experimental Example  1: Determination of solubility in water

The solubility of the polyamic acid solid particles in water (at 25 ° C) was measured in Examples 1 to 7, and the results are shown in Table 1 below.

division Solubility Example 1 5.1 Example 2 5.2 Example 3 4.7 Example 4 5.1 Example 5 4.7 Example 6 5.6 Example 7 7.1

From Table 1, it can be seen that the polyamic acid solid particles of Examples 1 to 7 of the present invention have high solubility in water, and thus it is possible to easily produce an aqueous solution of polyamic acid.

Manufacturing example  1: Manufacture of electrode for secondary battery

(1) For secondary battery electrode Electrode active material  Manufacture of coatings

97.5% by weight of graphite powder as an electrode lubricant, 1.5% by weight of the polyamic acid aqueous solution prepared in Example 1, and 1% by weight of CMC were mixed to prepare an electrode material.

Next, 45% by weight of the electrode material and 55% by weight of distilled water were mixed by a homogenizer mixer method to prepare an electrode active material coating material for a secondary battery electrode in the form of a slurry.

(2) Preparation of Secondary Battery Electrode

The electrode active material coating agent for the secondary battery electrode in the form of a slurry was cast on a copper foil (Cu) to a thickness of 104 to 106 탆 by doctor blade method. Next, the coated electrode was dried in an oven at 100 DEG C for about 2 hours, and then compressed through a roll press process. Next, the final compressed electrode was vacuum dried for 2 hours to prepare a secondary battery electrode.

Manufacturing example  2 ~ Manufacturing example  7 and Comparative Manufacturing Example  1 ~ Comparative Manufacturing Example  2

Except that the polyamic acid solution prepared in Examples 2 to 7 and Comparative Examples 1 to 2 was used instead of the aqueous solution of polyamic acid in Example 1, To prepare Secondary Battery Electrodes, Production Examples 2 to 7 and Comparative Production Examples 1 to 2 were respectively carried out.

Experimental Example  2: Evaluation test of physical properties of secondary electrode electrode

The properties of the secondary battery electrodes prepared in Preparation Examples 1 to 7 and Comparative Preparation Examples 1 to 2 were measured by the following methods, and the results are shown in Table 2 below.

(1) Flexibility evaluation

The electrode of the secondary battery was wound around a rod of 1.5Φ, 2Φ, 2.5Φ and 3Φ in size, and the surface of the electrode was examined for cracks by visual observation and microscopic evaluation.

(2) Binding force  evaluation

An adhesive tape was attached to the coated electrode and pressed with a roller for 10 times. The coated electrode with the adhesive tape was peel tested 180 degrees using a universal testing machine to measure the adhesive strength.

(3) Evaluation of swelling degree

The polymer film was fully immersed in the electrolyte, and after 72 hours at 72 ° C, the mass of the film was measured and the mass was calculated as the mass relative to the initial mass.

division Flexibility test Binding force
(gf / mm) Swelling degree
(%) Production Example 1 Crack generation x 1.7 gf / mm 118.3% Production Example 2 Crack generation x 1.5 gf / mm 120.6% Production Example 3 Crack generation x 0.9 gf / mm 112.6% Production Example 4 Crack generation x 1.4 gf / mm 119.3% Production Example 5 Crack generation x 0.8 gf / mm 114.2% Production Example 6 Crack generation x 1.6 gf / mm 125.1% Production Example 7 Crack generation x 1.7 gf / mm 118.5% Comparative Preparation Example 1 Cracking ○ 0.4 gf / mm 107.6% Comparative Production Example 2 Crack generation x 1.7 gf / mm 151.2%

As a result of the test results of Table 2, it was found that the adhesion strength of 0.6 gf / mm or more was observed in Production Examples 1 to 7 and Comparative Production Example 2, and cracks did not occur in the secondary battery. However, 4 weight parts of polyamic acid solid particles In Comparative Preparation Example 1, there was a problem that a low binding force and a crack were generated.

In Comparative Preparation Example 2 in which 15 parts by weight of polyamic acid solid particles were used in an amount of 10 parts by weight or more, there was a problem that the swelling degree of the electrode was too high as 130% or more as compared with Preparation Example 1.

It was confirmed through the above Examples and Experiments that a water-soluble polyimide water-soluble binder for a secondary battery, which is eco-friendly and has heat resistance, solvent resistance, oxidation resistance and high mechanical strength, can be provided by using water as a solvent .

Claims (17)

delete An aqueous solution of polyamic acid in which 4 to 10 parts by weight of polyamic acid solid particles and 0.2 to 4 parts by weight of water-based reagents are dissolved in 100 parts by weight of water,
The polyamic acid solid particles are prepared by adding a mixture of 100 parts by weight of a polyamic acid varnish and 4 to 10 parts by weight of a water-based reagent to a precipitant to dry the precipitated precipitate,
The polyamic acid varnish is a reactant obtained by reacting diamine with dihydride,
The diamine is added to 100 parts by weight of the 3,5-diaminobenzoquinone solution seed,
Examples of the above-mentioned 1,4-bis (4-aminophenoxy) benzene, 4,4 '- (1,3-phenylene dioxy) 4,4'- (4,4'-isopropylidene diphenyl-1,1'-dile dioxy) thianiline, bis [4-4 (aminophenoxy) phenyl] sulfone, (4-aminophenoxyphenyl)] hexafluoropropane, 2,2'-bis (trifluoromethyl) propane, and 2,2'- Benzazidine and 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane in an amount of 700 to 1500 parts by weight,
The dihydride may be selected from the group consisting of biphenyl-tetracarboxylic acid dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride, dianhydride, 4,4 '- (hexafluoroisopropylidene) 4,4' - (Hexafluoroisopropylidene) diphthalic dianhydride, 4,4'-oxydiphthalic dianhydride (4, 4'-Oxydiphthalic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, and 3,3 ', 4,4'- Benzophenone tetracarboxylic acid dihydride, and 3,3 ', 4,4'-benzophenonetetracarboxylic acid dianhydride.
Wherein the polyamic acid aqueous solution has a viscosity of 10 cps (25 캜) to 1,000 cps (25 캜).
3. The method of claim 2, wherein the hydrolyzing reagent is selected from the group consisting of DMZ (1,2-dimethylimidazole), DMEA (dimethylethanolamine), EMZ (2-Ethyl-4-methylimidazole), MDEA (Methyldiethanolamine) and TEOA Soluble binder for a secondary battery.
The water-soluble binder for a secondary battery according to claim 2, wherein the precipitant is contained in an amount of 400 to 600 parts by weight based on 100 parts by weight of the polyamic acid varnish.
delete The water-soluble binder for a secondary battery according to claim 2, wherein the binder comprises 110 to 150 parts by weight of the dianhydride with respect to 100 parts by weight of the diamine.
delete The water-soluble binder for a secondary battery according to claim 4, wherein the polyamic acid varnish comprises 5 to 30% by weight of a solid component and has a viscosity of 800 cps (25 캜) to 10,000 cps (25 캜).
40 wt% to 50 wt% of the electrode material and 50 wt% to 60 wt% of water,
Wherein the electrode material is a water-soluble binder for a secondary battery according to any one of claims 2 to 4, 6, and 8; Carboxymethyl cellulose (CMC); And an electrode lubricant. The electrode active material coating agent for a secondary battery according to claim 1,
An electrode for a secondary battery, comprising an electrode active material layer coated with the secondary battery electrode active material coating material of claim 9.
The electrode for a secondary battery according to claim 10, wherein the electrode active material layer has a binding force of 0.8 gf / mm to 3.0 gf / mm when measured according to a 180 ° peel test method.
A first step of preparing a polyamic acid varnish comprising a solid content of 5 wt% to 30 wt% and having a viscosity of 800 cps (25 캜) to 10,000 cps (25 캜);
A second step of adding a mixed solution of a hydrating reagent to the polyamic acid varnish to a precipitant to obtain a precipitate;
Drying the precipitate to prepare polyamic acid solid particles; And
Adding the polyamic acid solid particles to water, and stirring and dissolving the polyamic acid solution to prepare a polyamic acid aqueous solution;
The polyamic acid varnish in the first step is prepared by adding and reacting dihydride 3 to 5 times in a solution prepared by dissolving diamine in a solvent,
The diamine was added to 100 parts by weight of the 3,5-diaminobenzoquinone solution seed,
Examples of the above-mentioned 1,4-bis (4-aminophenoxy) benzene, 4,4 '- (1,3-phenylene dioxy) 4,4'- (4,4'-isopropylidene diphenyl-1,1'-dile dioxy) thianiline, bis [4-4 (aminophenoxy) phenyl] sulfone, (4-aminophenoxyphenyl)] hexafluoropropane, 2,2'-bis (trifluoromethyl) propane, and 2,2'- Benzamide and 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane in an amount of 700 to 1500 parts by weight based on 100 parts by weight of the water-soluble binder for a secondary battery Gt;
delete 13. The method of claim 12, wherein the dianhydride is selected from the group consisting of biphenyl-tetracarboxylic acid liquid dihydride, 1,2,4,5-benzenetetracarboxylic dianhydride, 4,4 '- (hexafluorois Propylidene) diphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic acid liquid dihydride and 3,3 ', 4, 4'-benzophenone tetracarboxylic liquid cidade dihydride. The method for producing a water-soluble binder for a secondary battery according to claim 1,
delete 13. The method for producing a water-soluble binder for a secondary battery according to claim 12, wherein the precipitating agent in the second step is acetone, and the drying in the third step is carried out in a vacuum state at a temperature of 30 ° C to 50 ° C.
13. The method for producing a water-soluble binder for a secondary battery according to claim 12, wherein the aqueous solution of the polyamic acid in the fourth step has a viscosity of 10 cps (25 캜) to 1,000 cps (25 캜).