KR100553737B1 - Electrode active material composition and separator composition for lithium ion polymer battery, and manufactring method of lithium ion polymer battery using the same - Google Patents

Abstract

The present invention discloses an electrode active material composition, a separator composition of a lithium ion polymer battery and a method of manufacturing a lithium ion polymer battery using the same. The electrode active material composition includes an active material, a conductive agent, a binder, a plasticizer and a solvent, and the solvent is a mixed solvent of N-methylpyrrolidone and acetone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone. do. According to the present invention, it is easier to control the viscosity compared to the case where acetone single solvent is used to prepare the electrode active material composition and the separator composition of the lithium ion polymer battery, thereby improving the coating property. In addition, the electrode active material composition may be directly coated on both sides of the current collector, and the separator composition may be directly coated on the electrode, thereby greatly reducing the number of manufacturing process steps. The adhesion between the current collector and the active material layer and the adhesion between the electrode and the separator are improved.

Description

Electrode active material composition and separator composition for lithium ion polymer battery, and manufactring method of lithium ion polymer battery using the same}

1 is a view showing an example of a conventional lithium ion polymer battery,

2 is a view illustrating a bicell structure of an electrode assembly in a typical lithium ion polymer battery.

<Explanation of symbols for the main parts of the drawings>

11 ... electrode assembly 12 ... case

13 ... electrode tab 13a ... connection tab

21 ... Anode 22, 22 '... Separator

23, 23 '... cathode

The present invention relates to an electrode active material composition, a separator composition of a lithium ion polymer battery and a method of manufacturing a lithium ion polymer battery using the same. More specifically, the active material layer on the electrode current collector and the separator on the electrode, respectively It relates to a method for producing a lithium ion polymer battery which can be formed by directly coating a composition for forming a.

Since the lithium ion polymer battery uses a solid electrolyte, there is little risk of leakage of the electrolyte solution, and excellent workability can be made into a battery pack. It is light in weight, low in volume, and has a very small self-discharge rate. Due to these characteristics, lithium ion polymer batteries are not only safer than lithium ion batteries, but also easy to manufacture in square and large sized batteries.

1 is a view showing an example of a conventional lithium ion polymer battery.

Referring to this, the lithium secondary battery includes an electrode assembly 11 formed by stacking a cathode, an anode, and a separator, and a case 12 enclosing and sealing the electrode assembly 11. The electrode tab 13 serving as an external electrical passage with the electrode assembly 11 is connected to a connection tab 13a provided at the cathode and the anode, and the electrode tab 13 is exposed to a predetermined length out of the case 12. do.

In the electrode assembly, the cathode and the anode are typically formed by laminating an active material layer of each electrode active material composition on top of each electrode current collector. At this time, the electrode active material composition contains an electrode active material, a binder, a conductive agent, a plasticizer and a solvent, and acetone is mainly used as the solvent. Then, the separator is laminated on the cathode and the separator is laminated on the anode to form the bicell structure of FIG. 2. Herein, the cathode, the anode, and the separator are impregnated with an electrolyte in the space where the plasticizer is taken out.

However, as described above, the lithium ion polymer battery has a problem in that the manufacturing cost is high due to the number of manufacturing processes due to the lamination process or the like when forming the active material and the separator.

Therefore, a lot of research has been started on the method of directly coating the respective active material composition and the separator composition on the electrode current collector and the upper electrode during electrode production. In order to directly coat the acetone used as a conventional solvent it is difficult to use any more. The reason is that acetone has a problem that the thickness of the active material layer and the separator becomes uneven because the acetone is too fast to dry the coating of the active material composition and the separator composition on the current collector and the electrode.

The technical problem to be achieved by the present invention is to provide a lithium ion polymer battery electrode active material composition that can be directly coated on the current collector to solve the above problems,

Another technical object of the present invention is to provide a separator composition for a lithium ion polymer battery that can be directly coated on an electrode,

Another object of the present invention is to provide a method of manufacturing a lithium ion polymer battery using the electrode active material composition and the separator composition.                         

In order to achieve the first technical problem, in the present invention, in the electrode active material composition for a lithium ion polymer battery comprising an active material, a conductive agent, a binder, a plasticizer and a solvent,

The solvent is a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone, to provide an electrode active material composition for a lithium ion polymer battery.

The second technical problem of the present invention is a separator composition for a lithium ion polymer battery comprising a polymer resin, a plasticizer and a solvent,

The solvent is a separator composition for a lithium ion polymer battery, characterized in that a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone.

The third technical problem of the present invention is to prepare an anode and a cathode by directly coating and drying an electrode active material composition including an active material, a conductive agent, a binder, a plasticizer and a solvent on the electrode current collector;

(b) directly coating and drying the separator composition including a polymer resin, a plasticizer, and a solvent on the anode to form a separator;

(c) forming a bi-cell structure by bringing the cathode in close contact with the upper part of the resultant obtained from step (b);

(d) removing plasticizer from the bicell structure and then drying;

(e) injecting an electrolyte into the dried bicell structure;

The solvent of the electrode active material composition and the separator composition is a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone. Is made by.

The cathode current collector of the electrode current collector is preferably an expanded metal or a punched metal, for the following reason.

The battery assembly of the lithium ion polymer battery according to the present invention preferably has a bicell structure of FIG. 2. 2, separators 22 and 22 'are positioned on both sides of the anode 21, and cathodes 23 and 23' are positioned on the upper and lower surfaces of the separator. have. In order to process the process of extracting the plasticizer from the battery assembly having such a structure in one step, there is a gap in the current collector of the cathode so that the plasticizer extraction solvent must reach the anode. Therefore, if the cathode current collector is expanded metal or punched metal, the plasticizer extraction process using an organic solvent such as ether or methanol can be processed only once, which has the advantage of reducing the number of manufacturing processes.

The present invention has a drying speed suitable for coating the electrode active material composition and the separator composition directly on the current collector of the electrode and the upper part of the electrode, respectively, and the adhesion of the active material layer to the current collector and the electrode current collector and the adhesion to the electrode. It is a feature of the present invention to provide a solvent system that can maintain a good adhesion of the peretta. In addition, the use of such a solvent has an advantage that it is easier to control the viscosity of the electrode active material composition and the separator composition.

The solvent system is a mixed solvent of N-methylpyrrolidone (NMP) and acetone or a mixed solvent of N-methylpyrrolidone (NMP) and methyl ethyl ketone (MEK). Here, it is preferable that the mixed weight ratio of the said acetone and N-methylpyrrolidone is 8: 2-6: 4, and the mixed weight ratio of methyl ethyl ketone and N-methylpyrrolidone is 7: 3-6: 4. . When the content of NMP to the acetone is less than the above range, the drying rate is fast, so that the distribution of the binder and the conductive agent is uneven, and when it exceeds the above range, the drying rate is not preferable, which is not preferable. If the content of NMP in the methyl ethyl ketone is less than the above range, the drying rate is high, and the distribution of the binder and the conductive agent is nonuniform, and if it exceeds the above range, the drying rate is low, which is not preferable.

The electrode active material composition and the composition for forming the separator according to the present invention will be described in more detail.

The electrode active material composition of the present invention contains an electrode active material, a conductive agent, a binder, a plasticizer and a solvent. Herein, the electrode active material, the conductive agent, the binder, and the plasticizer are materials commonly used in lithium ion polymer batteries, and their content is also at a normal level. Specific examples of the electrode active material include a cathode active material such as LiCoO ₂ , LiMn ₂ O ₃ , and the like, and an anode active material such as graphite and graphite. Examples of the conductive agent include carbon black and the like, and examples of the binder include vinylidene fluoride (VdF) -hexafluoropropylene (HFP) copolymer. Examples of the plasticizer include dibutyl phthalate.

And the separator composition comprises a polymer resin, a plasticizer and a solvent. Herein, the polymer resin and the plasticizer may be used as long as they are materials commonly used in lithium ion polymer batteries, and the amount of their use is also normal. Examples of the polymer resin include VdF-HFP copolymer, polyvinylidene fluoride, and the like, and examples of the plasticizer are the same as those of the electrode. In some cases, a filler may be further added to the separator composition in order to increase the mechanical strength of the separator. Examples of the filler here include silica, kaolin and the like.

As the solvent used in the constant electrode active material composition and the separator composition, a mixed solvent of N-methylpyrrolidone (NMP) and acetone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone, as mentioned above, is used. .

Meanwhile, a method of manufacturing a lithium ion polymer battery using the electrode active material composition and the separator composition will be described below.

First, the anode active material composition containing an anode active material, a plasticizer, a binder, a conductive agent, and a solvent is directly coated and dried on the anode current collector to form an anode active material layer on top of the anode current collector to manufacture an anode. At this time, the drying temperature is made from 50 to 100 ℃. If the drying temperature is less than 50 ° C, solvents such as N-methylpyrrolidone and the like are not sufficiently dried. If the temperature is above 100 ° C, organic substances such as plasticizers in the electrode active material composition change due to heat, which is not preferable. . The anode current collector may be a copper foil, an expanded metal, a punched metal, or the like, and is not particularly limited.

Separately, a cathode is prepared by directly coating and drying a cathode active material composition containing a cathode active material, a plasticizer, a binder, a conductive agent, and a solvent on the cathode current collector to form cathode active material layers on both sides of the cathode current collector. At this time, the drying temperature is made at 50 to 100 ℃ as in the case of the anode. And the cathode current collector is preferably aluminum expanded metal or aluminum punched metal, as already mentioned for the purpose of treating the plasticizer extraction process from subsequent electrode assemblies in one step.

Then, on both sides of the anode, the separator composition containing the polymer resin, the plasticizer, and the solvent is directly coated and dried. At this time, the drying temperature is preferably made at 50 to 100 ℃ as in the case of the electrode.

Thereafter, the cathode was brought into close contact with the upper portion of the resultant and then dried. Subsequently, the obtained electrode plate is cut to a predetermined size to form a bicell structure as shown in FIG. 2.

The plasticizer is completely removed from the bicell using an organic solvent such as methanol or ether as a plasticizer extraction solvent and then dried.

Thereafter, the obtained cell is dried under vacuum conditions and room temperature, and then placed in a plastic bag that can be sealed by heat. Thereafter, an electrolyte is injected into the resultant product under an argon gas atmosphere to complete a lithium ion polymer battery. Here, the electrolyte is composed of an organic solvent and a lithium salt. The organic solvent includes propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone, 1,3- Dioxolane (1,3-dioxolane), dimethoxyethane, dimethylcarbonate (DMC) and diethylcarbonate (DEC), methylethylcarbonate (MEC), tetrahydrofuran (tetrahydrofuran) THF), at least one solvent selected from dimethylsulfoxide and polyethyleneglycol dimethylether is used. And the content of the solvent is the usual level used in lithium ion polymer battery.

The lithium salt is not particularly limited as long as it is a lithium compound that dissociates in an organic solvent to give lithium ions. Specific examples thereof include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and hexafluoride. Group consisting of lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethansulfonate (LiCF ₃ SO ₃ ) and lithium bistrifluoromethansulfonylamide.LiN (CF ₃ SO ₂ ) ₂ ) At least one ionic lithium salt selected from is used and its content is at a typical level used in lithium ion polymer cells. When the organic electrolyte solution containing such an inorganic salt is introduced into the electrode structure, it acts as a path for moving lithium ions in the direction of the current.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

Example 1

The cathode active material composition was mixed with 200 g of LiCoO ₂ , 10 g of Superfine (SP) (MMM.carbon.Belglurn) and 10 g of graphite, followed by 24.6 g of Kynar Flex 2801 (Elf-Atochem). A mixture of 221.39 g of a mixed solvent of acetone and NMP in an 8: 2 weight ratio and 46.2 g of dibutyl phthalate was added to prepare a sufficiently mixed solution. It was directly spray-coated on both sides of the aluminum expanded metal, and then dried at room temperature, 50 ℃ or 90 ℃ to prepare a cathode. At this time, the drying time of the coated active material composition was measured, and the viscosity of the cathode active material composition and the adhesion state between the aluminum expanded metal and the cathode active material layer were investigated.

Example 2

The same procedure as in Example 1 was conducted except that the weight ratio of acetone and NMP was 7: 3 instead of 8: 2.

Example 3

The same procedure as in Example 1 was carried out except that the weight ratio of acetone and NMP was 6: 4 instead of 8: 2.

Example 4

The same procedure as in Example 1 was conducted except that NMP and MEK having a weight ratio of 3: 7 were used instead of acetone and NMP at an 8: 2 weight ratio.

Example 5

The same procedure as in Example 1 was carried out except that NMP and MEK having a weight ratio of 4: 6 were used instead of acetone and NMP at an 8: 2 weight ratio.

Example 6

The same procedure as in Example 1 was conducted except that acetone and NMP having a weight ratio of 8: 2 were used instead of acetone and NMP at an 8: 2 weight ratio.

Example 7

200 g of MCMB and 24.6 g of Kynar Flex 2801 were mixed with 221.39 g of a mixed solvent of acetone and NMP in an 8: 2 weight ratio and 46.2 g of dibutyl phthalate. 10 g of superpies and 10 g of graphite were added to the mixture, followed by sufficient mixing to prepare an anode active material composition.

The anode active material composition was spray coated on both sides of the copper expanded metal and dried at 60 ° C. to produce an anode.

24.6 g of Kynar Flex 2801 was mixed with 221.39 g of a mixed solvent of acetone and NMP in an 8: 2 weight ratio and 46.2 g of dibutyl phthalate. 10 g of SuperP, graphite 10, and 200 g of LiCoO ₂ were added to the mixture, followed by sufficient mixing to prepare a cathode active material composition.

The cathode active material composition was spray coated on both sides of aluminum expanded metal and dried at 60 ° C. to prepare a cathode.

Separately, 60 g of 88:12 VdF: HFP copolymer (Solvay 51216) was mixed with 394 g of a mixed solvent of acetone and NMP in an 8: 2 weight ratio and 80 g of dibutyl phthalate to prepare a separator composition.

The separator composition was coated and dried on both sides of the anode.

The separator composition was recoated on top of the resultant, the cathode was brought into close contact therewith, and dried. Subsequently, the obtained electrode plate was cut to a predetermined size to produce a bicell.

Dibutyl phthalate was completely removed from the bicell using ether as a plasticizer extraction solvent and then dried.

Thereafter, the obtained cell was dried for 1 hour at a temperature of 50 ° C. under vacuum, and then placed in a plastic bag that can be sealed by heat. Thereafter, an electrolyte solution (Merck, 1M LiPF ₆ in EC: DMC: DEC = 1: 1: 1) was injected into the resultant under argon gas atmosphere to complete a lithium ion polymer battery.

Example 8

In the cathode active material composition, the anode active material composition, and the separator composition, a lithium ion polymer battery was completed in the same manner as in Example 7, except that a mixed solvent of acetone and NMP in a 7: 3 weight ratio was used as the solvent. It was.

Example 9

In the cathode active material composition, the anode active material composition and the separator composition, a lithium ion polymer battery was carried out in the same manner as in Example 7 except that a mixed solvent of acetone and NMP in a 6: 4 weight ratio was used as the solvent. To complete.

Example 10

In the cathode active material composition, the anode active material composition and the separator composition, a lithium ion polymer was prepared in the same manner as in Example 7 except that a mixed solvent of NMP and MEK having a weight ratio of 3: 7 was used as the solvent. The cell was completed.

Example 11

In the cathode active material composition, the anode active material composition and the separator composition, a lithium ion polymer was prepared in the same manner as in Example 7 except that a mixed solvent of NMP and MEK having a weight ratio of 4: 6 was used as a solvent. The cell was completed.

Example 12

In the cathode active material composition, the anode active material composition, and the separator composition, a lithium ion polymer was prepared in the same manner as in Example 7 except that a mixed solvent of acetone and NMP having a weight ratio of 8: 2 was used as the solvent. The cell was completed.

Comparative Example 1

The same procedure as in Example 1 was carried out except that acetone single solvent was used instead of acetone in an 8: 2 weight ratio and NMP.

Comparative Example 2

The same procedure as in Example 1 was conducted except that 5: 5 weight ratio of acetone: MEK was used instead of 8: 2 weight ratio of acetone and NMP.

Comparative Example 3

The same procedure as in Example 1 was carried out except that 6: 4 weight ratio of NMP: MEK was used instead of 8: 2 weight ratio of acetone and NMP.

Comparative Example 4

The same procedure as in Example 1 was carried out except that an NMP single solvent was used instead of acetone and NMP in an 8: 2 weight ratio.

Comparative Example 5

The same procedure as in Example 1 was carried out except that a mixed solvent of acetone and MIBK in a 7: 3 weight ratio was used instead of the acetone and NMP in a 8: 2 weight ratio.

Comparative Example 6

The same procedure as in Example 1 was carried out except that a mixed solvent of acetone and NMP in a 3: 7 weight ratio was used instead of the acetone and NMP in a 8: 2 weight ratio.

In Examples 1-6 and Comparative Examples 1-6, the drying time of the coated cathode active material composition, the viscosity characteristics of the cathode active material composition, and the adhesion state of the cathode active material composition layer are shown in Table 1 below.

division Drying time Viscosity (cps) Adhesion Room temperature 50 ℃ 90 ℃ Example 1 3 minutes 50 seconds 1 minute 12 seconds 53 seconds 53000 Good Example 2 6 hours 21 minutes 4 minutes 30 seconds 56000 Very good Example 3 10 hours 1 hours 5 minutes 50 seconds 51000 〃 Example 4 Not dry 15 hours 10 minutes 20 seconds 49000 〃 Example 5 〃 1 hours 6 minutes 10 seconds 47000 〃 Example 6 4 minutes 30 seconds 1 minute 20 seconds 55 seconds 44000 Good Comparative Example 1 2 minutes 40 seconds 1 minute 10 seconds 50 seconds 34000 Poor Comparative Example 2 3 minutes 2 minutes 1 minute 50000 Poor Comparative Example 3 Not dry 57 minutes 7 minutes 50 seconds 56000 good Comparative Example 4 Not dry 3 hours 36 minutes 17 minutes 44000 Very good Comparative Example 5 4 minutes 10 seconds 2 minutes 50 seconds 1 minute 20 seconds 47000 Poor Comparative Example 6 17 hours 1 hour 38 minutes 14 minutes 44000 Good

From the results of Table 1, when only NMP is used (Comparative Example 5), the drying speed is slow, and the coating area on one side is dried while being dried, so that fine pores are formed on the surface of the electrode plate after coating, and only acetone is used. In the case (Comparative Example 1), the coating property was good, but after drying, a phenomenon in which the active material layer was peeled from the aluminum expanded metal occurred.

On the other hand, when the acetone and NMP mixed solvent is 6: 4 (Example 3), 7: 3 (Example 2) and 8: 2 (Example 6), both have good coating properties, but acetone and NMP When the weight ratio is 6: 4, the drying rate is slow, and when the weight ratio is 8: 2, the bonding strength is lower than when the weight ratio of the acetone and NMP mixed solvent is 7: 3. Therefore, the best ratio was obtained when the weight ratio of acetone and NMP was 7: 3.

In addition, the surface state of the active material layer prepared according to Example 1-6 and Comparative Example 1-6 was examined using a scanning electron microscope (SEM).

As a result, when acetone single solvent was used (Comparative Example 1), a mixed solvent of acetone and MEK in a 5: 5 weight ratio (Comparative Example 2), and acetone and MIBK in a 7: 3 weight ratio were used (Comparative Example 5 ), It was found that the binder is unevenly distributed. And when NMP single solvent was used (Comparative Example 4) and a mixed solvent of acetone and NMP in a 3: 7 weight ratio (Comparative Example 5), and a mixed solvent of NMP and MEK in a 6: 4 weight ratio (Comparative Example 3) ), The active material composition is uniformly coated on both sides of the aluminum expanded metal and the binder is evenly dispersed evenly, while the drying speed is too slow to produce mass.

On the other hand, when the weight ratio of acetone and NMP is 7: 3 (Example 2), it has a drying rate required for direct coating, it was confirmed that the binder is evenly distributed on both sides of the aluminum expanded metal.

On the other hand, in Example 8-12, the separator composition was coated on the electrode, and the drying time of the coated separator composition was measured. The results were almost similar to those of Example 1-7. And the viscosity of the separator composition and the adhesion between the electrode and the separator were measured, respectively, and the results also confirmed that the results were almost the same as when forming the electrode.

According to the present invention, it is easier to control the viscosity of the composition compared to the case where acetone single solvent is used to prepare the electrode active material composition and the separator composition of the lithium ion polymer battery, thereby improving coating property. In addition, the electrode active material composition may be directly coated on both sides of the current collector, and the separator composition may be directly coated on the electrode, thereby greatly reducing the number of manufacturing process steps. The adhesion between the current collector and the active material layer and the adhesion between the electrode and the separator are improved.

Claims (7)

In the electrode active material composition for lithium ion polymer batteries containing an active material, a conductive agent, a binder, a plasticizer and a solvent, An electrode active material composition for a lithium ion polymer battery, wherein the solvent is a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone. The mixed weight ratio of acetone and N-methylpyrrolidone is 8: 2 to 6: 4, and the mixed weight ratio of methyl ethyl ketone and N-methylpyrrolidone is 7: 3 to 6: 4. The electrode active material composition for lithium ion polymer batteries characterized by the above-mentioned. In the separator composition for lithium ion polymer batteries containing a polymer resin, a plasticizer and a solvent, Separator composition for a lithium ion polymer battery, characterized in that the solvent is a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone. The mixed weight ratio of acetone and N-methylpyrrolidone is 8: 2 to 6: 4, and the mixed weight ratio of methyl ethyl ketone and N-methylpyrrolidone is 7: 3 to 6: 4. Separator composition for lithium ion polymer batteries characterized by the above-mentioned. (a) directly coating and drying an electrode active material composition including an active material, a conductive agent, a binder, a plasticizer and a solvent on the electrode current collector to prepare an anode and a cathode, respectively; (b) directly coating and drying the separator composition including a polymer resin, a plasticizer, and a solvent on the anode to form a separator; (c) forming a bi-cell structure by bringing the cathode in close contact with the upper part of the resultant obtained from step (b); (d) removing plasticizer from the bicell structure and then drying; And (e) injecting an electrolyte into the dried bicell structure; The solvent of the electrode active material composition and the separator composition is a mixed solvent of acetone and N-methylpyrrolidone or a mixed solvent of N-methylpyrrolidone and methyl ethyl ketone. . The mixed weight ratio of acetone and N-methylpyrrolidone is 8: 2 to 6: 4, and the mixed weight ratio of methyl ethyl ketone and N-methylpyrrolidone is 7: 3 to 6: 4. A method for producing a lithium ion polymer battery, characterized in that. The method of claim 5, wherein the cathode current collector of the electrode current collector is an expanded metal or a punched metal.

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