KR20030019996A - Method of Manufacturing Polymer Electrolyte and Method of manufacturing Lithium Polymer Secondary Battery Utilizing Thereof - Google Patents

Abstract

PURPOSE: Provided are a process for producing a polymer electrolyte having improved mechanical properties and a process for producing a lithium polymer secondary battery having stable charge/discharge property by using the polymer electrolyte. CONSTITUTION: The process for producing the polymer electrolyte(4) comprises the steps of: mixing a polyvinylidene fluoride polymer and an electrolyte not containing electrolyte salts in the weight ratio of 1:2-10, wherein the electrolyte is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and gamma-butyrolactone; stirring and heating the mixture to prepare a homogeneous electrolyte slurry; and solidifying the electrolyte slurry. And the lithium polymer secondary battery is produced by laminating a cathode(6), the polymer electrolyte(4), and an anode(1).

Description

Method of manufacturing polymer electrolyte and method of manufacturing lithium polymer secondary battery using same {Method of Manufacturing Polymer Electrolyte and Method of manufacturing Lithium Polymer Secondary Battery Utilizing Thereof}

The present invention relates to a method for producing a gel polymer electrolyte having an improved manufacturing process and a method for producing a lithium polymer secondary battery using the same. More specifically, by forming using an electrolyte solution containing no electrolyte salt and a polyvinylidene fluoride-based polymer, the mechanical strength can be greatly improved, and a method for producing a polymer electrolyte having suitable properties for the process, and using the same and further The manufacturing method of the lithium polymer secondary battery which shows stable charging / discharging characteristic using the composition of the electrolyte solution to impregnate.

In general, a lithium polymer secondary battery is composed of a negative electrode, a positive electrode, and a polymer electrolyte, and these components must satisfy various conditions such as lifetime, capacity, temperature characteristics, and stability.

Lithium oxide compounds (LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ ) are exemplified as a cathode material constituting the lithium secondary battery, and have a laminate structure so that lithium ions can be inserted and escaped again. It is. As the negative electrode material, carbon such as graphite or coke may be used. The most widely used graphites are mesocarbon microbeads (MCMB) and mesophase carbon fibers (MPCF).

The polymer electrolyte constituting the lithium battery has the advantage that no leakage of electrolyte occurs and the battery can be easily manufactured, while exhibiting high ionic conductivity and high mechanical strength as well as thermal stability and electrochemical stability. Good adhesive properties with the electrode must be satisfied.

Polymer electrolytes currently in use or under development include polyvinyl fluoride and polyacrylates, polyethylene oxide and mixtures thereof, including main solvents such as ethylene carbonate (EC) and propylene carbonate (PC), and dimethyl carbonate (DMC). ), Co-solvents such as diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are also used. Together with these electrolytes, lithium salts such as LiPF ₆ , LiAsF ₆ , LiClO _4, and the like are mixed and used as an electrolyte. Polymers include polyvinylidene fluoride (PVdF), polyacrylates, polyethylene oxides, and mixtures thereof.

Many studies have been conducted using separators such as porous polyethylene, polypropylene, and glass fiber filter paper. In particular, a method of applying a binder resin solution to a separator in order to provide adhesion with an electrode (JP 1-089054), and a method of realizing adhesion to an electrode by filling a gel inside the separator by crosslinking a polymer component by UV irradiation (USP 5,691,005, 5,597,659), and also a method (USP 5,853,916, 5,716,421, 5,834,135, 5,681,357, 5,688,293), which has a function of coating a gelling layer on one or both sides of the separator to impart adhesion with the electrode, has been proposed. The present invention proposes a polymer electrolyte which is excellent in electrochemical and thermally stable polymer electrolyte, having excellent mechanical strength as the gel polymer electrolyte itself and maintaining porous properties.

PVdF-based polymer electrolytes exhibit excellent mechanical strength, and thus are widely used as separators for lithium secondary batteries, capacitors, sensors, and the like. However, the PVdF-based polymer itself has little adhesive force with the electrode. Therefore, many methods for compressing the electrode using heat after preparing the polymer electrolyte for application as a polymer electrolyte have been studied.

The method of bonding the electrode and the electrolyte by applying a high temperature heat will cause a problem in the impregnation of the liquid electrolyte, so to increase the porosity of the electrolyte and to mix the material such as dibutyl phthalate (DBP) in the electrolyte for smooth impregnation of the electrolyte A method of preparing a polymer electrolyte and then extracting it to secure pores in the electrolyte to achieve a smooth impregnation of the electrolyte solution has been proposed (USP 5,460,904, 5,456,000, 5,418,091). In this case, a plasticizer extraction process is required in order to increase the impregnation of the electrolyte, and it is difficult to completely remove the solvent and the plasticizer used in the extraction process and have a disadvantage in that the process is complicated.

The preparation of polymer cells with plasticizer extraction is also shown (USP 5,853,916, 5,688,293, 5,716,421, 5,834,135, 5,681,357, 5,688,293). According to this, the polymer membrane is uniformly coated on the porous separator having excellent mechanical strength and then thermally compressed with the electrode to immerse the bonded cell in the electrolyte, thereby expanding the electrolyte in the polymer layer. Since this method impregnates the electrolyte solution into the cell without the extraction process while maintaining excellent adhesion between the electrolyte and the electrode, the processability is excellent, but the electrolyte solution is absorbed by the dense polymer layer, which has a problem in that productivity is reduced.

In addition, conventional PVdF-based polymer electrolyte manufacturing techniques include a mixture of a highly volatile solvent such as THF or acetone, PVdF, and a weakly volatile electrolyte such as EC / PC (1/1) 1M LiPF ₆ at a temperature of about 60 ° C. After forming by the spin coating method, a method of drying a volatile solvent and molding it, or mixing PVdF and an electrolytic solution to form a film by pressing at a high temperature of about 100 to 130 ° C. (see USP 5,296,318) has been proposed.

There has also been proposed a method of using plasticizers and inorganic fillers. According to this method, a non-volatile solvent such as THF or acetone as a volatile solvent, propylene carbonate, dibutyl phthalate, ethylene carbonate, dimethyl carbonate, etc. as a volatile solvent, and alumina or silica as an inorganic filler are mixed and coated at about 50 ° C. To prepare a polymer electrolyte (USP 5,418,091). In the polymer electrolyte prepared as described above, the battery electrolyte is replaced with a plasticizer through a plasticizer extraction to produce a battery. The current mainstream of the polymer battery (USP 5,460,904, 5,587,257).

In addition, many methods for producing PVdF polymer electrolytes have been published. In the case of changing the amount of inorganic filler (USP 5,631,103) or coating using a volatile solvent which cannot be used as a battery solvent (USP 5,900,183) or the molecular weight change of PVdF (USP 5,962,168) There is research on this.

Such polymer electrolytes should have at least two times the electrolyte content based on the weight ratio in order to have sticky properties of the electrolyte itself or to have sufficient ionic conductivity properties. However, the sticky nature of the gel polymer electrolyte and the properties of maintaining the content of a large amount of electrolyte are emerging as a problem for the mass productivity of the gel polymer electrolyte. In particular, parts of the gel polymer electrolyte having a sticky property and the problem that the content of the electrolyte is continuously changed over time during the manufacturing of the cell, and also the physical properties of the polymer electrolyte due to the evaporation of the electrolyte Problems remain to be solved for mass production of gel polymer electrolyte.

An object of the present invention is to provide a method for producing a gel polymer electrolyte having a sufficient porosity by adjusting the composition and content of the electrolyte solution from which the electrolyte salt is removed.

Another object of the present invention is to provide a method for manufacturing a lithium polymer secondary battery that can be sufficiently impregnated with the electrode even if the thermocompression bonding at low temperatures by using the above-described polymer electrolyte, and the impregnation of the electrolyte solution without the need for extraction process will be.

1 is a schematic cross-sectional view of a stacked lithium secondary battery including a polymer electrolyte according to the method of the present invention.

2 is a view showing a charge and discharge voltage profile with time at a 0.2C rate of a lithium polymer battery prepared according to Example 1.

3 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 1.

4 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared in the same manner as in Example 1 and Comparative Example 1.

5 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared in the same manner as in Example 1 and Comparative Example 2.

6 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 2.

7 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 1 and Comparative Example 3.

8 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 3.

9 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 4, Comparative Example 4 and Comparative Example 5.

10 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 5.

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

1.cathode 4.polymer electrolyte

6 positive pole 8 positive collector

10 ... the negative collector

In the present invention to achieve the above object

Mixing the polyvinylidene fluoride polymer and the electrolyte solution in which the electrolyte salt is not dissolved in a weight ratio of 1: 2 to 10;

Heating the mixture with stirring to produce a substantially homogeneous electrolyte slurry; And

It provides a method for producing a polymer electrolyte comprising the step of solidifying the resulting electrolyte slurry.

Another object of the present invention described above

anode;

cathode; And

Stacking a polymer electrolyte which is positioned between the positive electrode and the negative electrode and is prepared by solidifying an electrolyte slurry obtained by mixing a polyvinylidene fluoride-based polymer and an electrolyte solution in which the electrolyte salt is not dissolved in a weight ratio of 1: 2 to 10. It is achieved by a method for producing a lithium polymer secondary battery comprising the step.

In particular, the polymer electrolyte and the electrode of any one of the positive electrode and the negative electrode are preferably bonded by any one of the method through the thermocompression bonding and the binder, the temperature during the thermocompression is to be in the range of 30 ~ 130 ℃. good.

In addition, it is also preferable to perform the step of aging the cell containing the positive electrode, the negative electrode and the polymer electrolyte in a temperature range of room temperature to 70 ℃.

In the present invention, a polymer electrolyte having sufficient porosity is prepared by adjusting the composition and content of the lithium salt-free electrolyte using PVdF-based polymer electrolyte, and sufficient adhesiveness to the electrode is obtained even when thermally compressed at an appropriately low temperature. The present invention proposes a polymer electrolyte that enables smooth impregnation of an electrolyte solution without the need for an extraction process.

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

The surface of the polymer electrolyte prepared in the present invention is solidified and does not have adhesion to the electrode. Therefore, the lithium secondary battery may be manufactured by imparting adhesive force between the electrode and the electrolyte through proper thermocompression bonding and the use of a binder. In particular, when the electrode and the polymer electrolyte are thermally compressed, the electrolyte solution, which is further impregnated before packing the battery, is thermocompressed so that the electrode and the electrolyte can be easily impregnated between the interface. The lithium polymer secondary battery manufactured by the above-mentioned method can provide stable charge and discharge characteristics and high capacity.

The solid polymer electrolyte prepared by using the polyvinylidene fluoride-based polymer and the electrolyte salt from which the electrolyte salt has been removed in the present invention has a large increase in resistance of the electrolyte since there is no electrolyte salt. However, electrolyte salts such as lithium salts contained in the electrolyte solution further impregnated before packing the battery can easily diffuse into the polymer electrolyte and control the composition of the impregnating electrolyte solution and the concentration of lithium salt, thereby greatly reducing the resistance of the electrolyte. In addition, the composition of the electrolyte solution to be further impregnated prior to packaging should be well controlled. In the present invention, it is possible to manufacture a lithium polymer secondary battery exhibiting high discharge capacity and stable charge and discharge characteristics using the composition of the electrolyte solution.

The molecular weight of the PVdF polymer used in the present invention is preferably 50,000 to 1,000,000, and is in the range of 1 to 4 of the poly disperse index. When the PVdF copolymer is used, the preferred proportion of hexafluoropropane (HFP) is preferably 2-30% per total weight of the copolymer. In addition, the molecular weight of the PVdF-HFP copolymer is preferably 50,000 to 1,000,000 and is in the range of 1 to 4 of the poly dispersion index.

If the molecular weight is lower than the above-mentioned molecular weight, the mechanical strength of the polymer electrolyte is so weak that it may not function well as a separator. If the molecular weight is too large, the viscosity of the electrolyte slurry may increase significantly to produce a polymer electrolyte film. A problem may arise that is not easy to do.

These PVdF-based polymers have attracted much attention as materials showing excellent mechanical properties and high ionic conductivity at room temperature. The gel polymer electrolyte should have at least two times the electrolyte content based on the weight ratio in order to have sticky properties of the electrolyte itself or to have sufficient ionic conductivity properties. However, the sticky nature of the gel polymer electrolyte and the properties of maintaining the content of many electrolytes are emerging as a problem for mass production of the gel polymer electrolyte.

In particular, parts of the gel polymer electrolyte having a sticky property and the problem that the content of the electrolyte is continuously changed over time during the manufacturing of the cell, and also the physical properties of the polymer electrolyte due to the evaporation of the electrolyte Problems still remain to be solved for mass production of gel polymer electrolytes.

In the present invention, in order to solve this problem, by forming a polymer electrolyte using an electrolyte solution containing no electrolyte salt and a polyvinylidene fluoride-based polymer, it is not sticky and hardly changes the physical properties of the electrolyte with time. It is to prepare a polymer electrolyte. This provides a polymer electrolyte more suitable for fairness.

Examples of the electrolyte used in the polymer electrolyte include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (ethyl). methyl carbonate (EMC) and gamma-butyrolactone ( -butyrolactone; At least one selected from the group consisting of -BL) can be preferably used. The ratio of the preferred polymer and the lithium salt mixed electrolyte is 1: 2-10. If the ratio of the polymer is increased, the mechanical strength of the polymer electrolyte increases, but the ion conductivity decreases because the proportion of the electrolyte is too low. The adhesion between the electrode and the electrolyte is also reduced.

In order to form an adhesive force between the electrode and the electrolyte, the amount of the electrolyte contained in the polymer electrolyte should be sufficient. However, if the content of the electrolyte is higher than the above ratio, although the ionic conductivity of the electrolyte is greatly increased, the mechanical strength of the electrolyte may be reduced, and a short cut may be formed when the cell is manufactured. More preferably, the ratio of the polymer and the electrolyte is in the range of 1: 4 to 8 by weight.

In order to exhibit ionic conductivity of 10 ⁻³ S / cm or more at room temperature, the ratio of EC is preferably 20% or more of the total weight of the solvent used. If the ratio of EC is lower than this, the electrolyte salt used is not sufficiently dissociated, and thus the ion conductivity of the electrolyte is greatly reduced. In addition, in order to exhibit high ionic conductivity at low temperature, the proportion of EC is preferably 80% or less of the total weight of the solvent. Therefore, the content of EC to be used based on the weight of the total solvent is preferably in the range of 20 to 80% by weight. A more preferable ratio is 30 to 60 weight% based on the total amount of electrolyte.

In the present invention, the polymer electrolyte is prepared using the electrolyte solution from which the electrolyte salt has been removed, and the electrolyte in the polymer electrolyte shows a stronger mechanical strength than the polymer electrolyte in which the electrolyte solution containing the electrolyte salt is prepared. As the electrolyte salt is removed, the affinity between the electrolyte and the polymer to be used is increased, thereby exhibiting a stronger mechanical strength than the polymer electrolyte prepared by using the electrolyte containing the electrolyte salt.

After the polymer mixture is formed, it is also possible to add about 2-50% of silicon oxide (SiO ₂ ), zeolite and aluminum oxide (Al ₂ O ₃ ) to the polymer mixture.

According to the method of the present invention, it is possible to prepare a gel polymer electrolyte using the composition of the electrolyte solution from which the electrolyte salt has been removed. In general, gel polymer electrolytes prepared using PVdF-based polymers or polyacrylate-based polymers have a high risk of short-circuit and have problems in cell stability. However, the polymer electrolyte prepared in the present invention can also be prepared as a very thin polymer electrolyte up to 15㎛ by adjusting the composition of the electrolyte solution to be used.

Using the polymer mixture, a polymer electrolyte is prepared as follows.

The electrolyte solution containing the electrolyte salt in the polymer is uniformly mixed at room temperature at room temperature in a ratio of about 1: 2 to 10. Then, the polymer slurry is heated to a temperature range of 60 to 150 ° C., which is a homogeneous solution of the polymer and the electrolyte solution. More preferable heating temperature is 80-130 degreeC. The viscosity increases as the polymer component is dissolved in the electrolyte during heating, and when the viscosity reaches about 1,000 to 100,000 cps, the homogeneous solution is solidified by casting or the like to prepare a polymer electrolyte.

The mixing process at room temperature is important for uniform mixing between the polymers and the solvents, and when the mixing time is short, since the polymers are often agglomerated, it becomes difficult to obtain a uniform mixture during the heating process. The electrolyte is also heterogeneous. Therefore, room temperature agitation is performed for a time sufficient to allow each component to be mixed sufficiently uniformly. Since the stirring time may vary depending on the amount, type, etc. of the components used, the stirring time is not particularly limited.

After mixing at room temperature, the mixture is heated to obtain an electrolyte slurry. As for heating temperature, the temperature range of 60-150 degreeC is preferable. In the temperature range below 60 ° C, the polymer may not melt and the electrolyte film may not be formed. Even though the electrolyte film is formed, there is a high local content of the polymer and this part acts as a barrier for ion transfer, thereby decreasing the ionic conductivity. can do. On the other hand, when the polymer electrolyte slurry is prepared at a temperature higher than 150 ° C., the decomposition reaction of the polymer occurs, which causes a problem that the mechanical strength of the polymer electrolyte film is reduced, which may cause an electrical short circuit due to contact between the positive electrode and the negative electrode during cell manufacture. Grows Therefore, it is important to stir at an appropriate temperature range for an appropriate time, but there is no need to specifically limit it, but it is preferable to make the above-mentioned temperature range.

The heating time of the polymer electrolyte is greatly influenced by each component for preparing the polymer electrolyte. For example, if the amount of EC in the electrolyte increases, the affinity between the PVdF polymer and the electrolyte decreases and the heating time for forming the gel increases somewhat. On the contrary, when the amount of EC decreases, the solubility of the electrolyte constituting the electrolyte becomes closer to PVdF and forms a polymer electrolyte in a shorter time. As a result of the repeated experiments of the present inventors, in view of the above factors, it is appropriate to stir for 5 minutes to 5 hours in the temperature range of 60 ~ 150 ℃.

The mechanical strength of the polymer electrolyte is superior to that of the polymer electrolyte prepared using an electrolyte solution containing an electrolyte salt and exhibits little physical change of the polymer electrolyte with time, and the battery is manufactured by assembling with an electrode after long time storage. Even if it shows high discharge capacity, it shows stable cycle characteristics.

The polymer electrolyte prepared as described above may be variously applied to lithium polymer secondary batteries, capacitors, and sensors.

The method for producing a lithium polymer secondary battery using the polymer electrolyte according to the present invention prepared as described above is as follows.

First, the prepared polymer electrolyte slurry is coated on a substrate to prepare a polymer electrolyte film. The substrate may be a release film in which the polymer electrolyte is easily separated and may be a non-reactive release film, or may be a positive electrode and a negative electrode. When the polymer electrolyte is formed on the release film, an electrode is attached between the polymer electrolyte films formed on the two release films, respectively, to obtain a structure in which the polymer electrolyte is adhered to both sides of the electrode.

In this case, the polymer electrolyte and the electrode may be adhered through proper thermocompression and the use of a binder. More preferably, the electrolyte solution further impregnated before the battery is packaged is thermocompressed because it can be easily impregnated between the interface between the electrode and the electrolyte. The preferable temperature at the time of thermocompression bonding is 30-130 degreeC. More preferable temperature is 35-100 degreeC. Of course, the electrolyte and the electrode can also be bonded using a binder. As the binder used, a polyacrylate-based polymer may be used.

In the structure of the prepared polymer electrolyte / cathode / polymer electrolyte, one single cell is prepared by adhering an anode on one polymer electrolyte surface (in this case, in the case of SPE film / anode / SPE film, the cathode is bonded). In this case, the single cell is composed of a polymer electrolyte / cathode / polymer electrolyte / anode, and when only a single cell is manufactured, the polymer electrolyte on the opposite side can be removed. The cell configuration at this time is the same as that of the negative electrode / polymer electrolyte / anode. In the case of the stacked cell, the single cell structure is laminated on the anode bonded to the outside to have a structure in which the anode / polymer electrolyte / cathode / polymer electrolyte is repeated. After the lamination cell is completed, the outermost polymer electrolyte may be removed later.

The heated electrolyte slurry may also be coated directly on the cathode or anode. In this case, the thickness of the polymer electrolyte is in the range of 20 to 100 µm. The procedure in the case of manufacturing a laminated cell is the same as that of using a release film. The polymer electrolyte is coated on both sides of the electrode to obtain the structure of the polymer electrolyte / cathode (or anode) / polymer electrolyte, and the counter electrode is adhered to one electrolyte surface to obtain a single cell, and the single cell is repeated to obtain a stacked cell. . A schematic diagram of the stacked cell is shown in FIG. 1.

1 is a schematic cross-sectional view of a stacked cell type lithium secondary battery including a polymer electrolyte according to an embodiment of the present invention. In the drawings, reference numeral 1 denotes a negative electrode, 4 denotes a polymer electrolyte, 6 denotes a positive electrode, 8 denotes a current collector of a positive electrode, and 10 denotes a current collector of a negative electrode.

According to the method described above, a single cell or a laminated cell is prepared and further impregnated with a liquid electrolyte containing an electrolyte salt such as lithium salt. The liquid electrolyte penetrates the electrode and the electrolyte, thereby improving the ion transfer between the electrode and the electrolyte. The process of adding a liquid electrolyte thus improves the high rate discharge and low temperature performance of the cell. Through this process, the electrolyte solution and the electrolyte salt are sufficiently impregnated in the polymer electrolyte prepared using the electrolyte solution from which the electrolyte salt has been removed.

As a result, a polymer electrolyte having good solidity can be obtained by removing the electrolyte salt when preparing the polymer electrolyte. However, since there is no electrolyte salt in the polymer electrolyte, the resistance of the electrolyte is greatly increased. However, by adjusting the electrolyte salt concentration of the electrolyte solution further impregnated before packing the battery, it is possible to greatly reduce the resistance of the polymer electrolyte, and the lithium polymer secondary battery manufactured in this manner will exhibit stable charge and discharge characteristics.

Further, electrolytes constituting the impregnated electrolyte include EC, PC, DEC, DMC, EMC, LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiPF ₆ , LiAsF _6, or the like may be used as -BL or a mixture of these solvents, an electrolyte salt, preferably a lithium salt, in a concentration of 1.0 to ₃ M. At this time, when the concentration of lithium salt is lower than 1.0M, the amount of lithium impregnated into the polymer electrolyte is insufficient, and the ion conductivity of the electrolyte is decreased. When the concentration of the lithium salt is higher than 3M, the viscosity of the electrolyte is increased so that the concentration overvoltage in the electrolyte is increased. Will increase. It also degrades the low temperature performance of lithium polymer batteries. Therefore, the concentration of the lithium salt is in the range of 1.0 to 3M concentration.

Thereafter, the case is sealed using a vacuum packaging machine and aged at a temperature of about 70 ° C. for a predetermined time at room temperature. In the present invention, the manufactured lithium polymer secondary battery may further have an aging process at high temperature for easier diffusion into the polymer electrolyte of the impregnated electrolyte solution and the electrolyte salt. The internal resistance of the battery may be reduced by aging the cell at high temperature for diffusion of electrolyte and electrolyte salt in a shorter time.

Aged cells are charged with a constant current at a rate of about 0.2C and maintain a constant voltage of 4.2V when the cell voltage reaches 4.2V while the current is about 1/5 to 1/20 of the current during constant current charging. It goes through a constant-voltage charging process that maintains a voltage of 4.2V until it reaches a degree. Subsequently, this process is repeated 2 to 5 times while discharging at a rate of 0.2C. At this time, when gas is generated inside the cell, degassing and resealing processes are added.

Hereinafter, the polymer electrolyte according to the present invention and a method of manufacturing a lithium secondary battery using the same will be described in detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

<Example 1>

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was hot pressed at 50 ° C. with the electrode to stack cells. Thereafter, 1.5 M LiPF ₆ dissolved in ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) solution was further impregnated and vacuum packed to complete the cell. The finished cell was aged at 50 ° C. for one day and then activated.

<Example 2>

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was stored for 5 days in a sealed state in an aluminum package at room temperature, and then laminated at high temperature at 50 ° C. with an electrode.

Thereafter, 1.5 M LiPF ₆ dissolved in ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) solution was further impregnated and vacuum packed to complete the cell. The finished cell was aged at 50 ° C. for one day and then activated.

<Example 3>

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was laminated while being assembled with an electrode using a binder showing adhesiveness including a polyacrylate polymer to prepare a cell. The binder used is 50 ℃ after uniformly stirring the polymer solution mixed with polyacrylate polymer and EC / DMC (1/1) 1M LiPF ₆ , tetrahydrofuran (THF) at a ratio of 1/2/6 at room temperature It was prepared by stirring for 10 minutes. Thereafter, 1.5 M LiPF ₆ dissolved in ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) solution was further impregnated and vacuum packed to complete the cell. The finished cell was aged at 50 ° C. for one day and then activated.

<Example 4>

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1 / 0.8 / 0.5 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was pressed at 50 ° C. with the electrode at high temperature to stack cells. Thereafter, a solution of ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 in weight ratio) in which 2M LiPF ₆ was dissolved was further impregnated and vacuum packed to complete the cell. The finished cell was aged at 50 ° C. for one day and then activated.

Example 5

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (0.3 / 0.8 / 0.5 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film is 15㎛ and can be made very thin, and the toughness was excellent. At this time, the cast polymer electrolyte was hot pressed at 50 ° C. with the electrode to stack cells. Thereafter, a solution of ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 in weight ratio) in which 2M LiPF ₆ was dissolved was further impregnated and vacuum packed to complete the cell. The finished cell was activated after aging in an oven at 50 ° C. for one day.

Comparative Example 1

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF, and 8 g of a mixed solution of 1 M LiPF ₆ in ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) are mixed together at room temperature. gave. After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 60 μm and the toughness was excellent. The obtained polymer electrolyte was cast with good mechanical strength and good adhesion to the electrode.

The cell of the laminated structure of the obtained polymer electrolyte, a positive electrode, and a negative electrode was produced. Thereafter, a solution of ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 in weight ratio) in which 1M LiPF ₆ was dissolved was further impregnated and vacuum packed to complete the cell.

Comparative Example 2

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) were mixed together at room temperature. . After stirring at 55 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was pressed at 50 ° C. with an electrode to stack cells. Thereafter, 1.5 M LiPF ₆ dissolved in ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) solution was further impregnated and vacuum packed to complete the cell. The finished cell was activated after aging in an oven at 50 ° C. for one day.

Comparative Example 3

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1/1 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was pressed at 150 ° C. with the electrode at high temperature to stack cells. Thereafter, 1.5 M LiPF ₆ dissolved in ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) solution was further impregnated and vacuum packed to complete the cell. The finished cell was activated after aging in an oven at 50 ° C. for one day.

<Comparative Example 4>

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1 / 0.8 / 0.5 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was hot pressed at 50 ° C. with the electrode to stack cells. Thereafter, an additional solution of ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 by weight) dissolved in 3.5M LiPF ₆ was further impregnated and vacuum packed to complete the cell. The finished cell was activated after aging in an oven at 50 ° C. for one day.

Comparative Example 5

1 g of Kynar 2801 (Atochem Inc.), a copolymer of PVdF-based polymer, and 8 g of a mixed solution without lithium salt of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (1 / 0.8 / 0.5 by weight) were mixed together at room temperature. . After stirring at 130 ℃ temperature for about 1 hour. The obtained polymer electrolyte slurry was cast on a substrate by a doctor blade method. The thickness of the cast polymer film was 40 μm and the toughness was excellent. At this time, the cast polymer electrolyte was hot pressed at 50 ° C. with the electrode to stack cells. Thereafter, a solution of ethylene carbonate / propylene carbonate / ethyl methyl carbonate (0.4 / 0.3 / 0.3 in weight ratio) dissolved in 0.8 M LiPF ₆ was further impregnated and vacuum packed to complete the cell. The finished cell was activated after aging in an oven at 50 ° C. for one day.

Performance tests were performed on the cells prepared according to the above-described examples and comparative examples as follows. The results will be described with reference to the accompanying drawings.

2 is a view showing the charge-discharge voltage profile with time when charging and discharging at a rate of 0.2C during the initial activation process of the lithium polymer battery prepared according to Example 1. 2 shows the potential characteristics of a typical lithium secondary battery and shows the same potential characteristics as a lithium polymer battery manufactured using an electrolyte including lithium salts.

3 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 1. 3 shows stable discharge capacity according to the cycle.

4 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared in the same manner as in Example 1 and Comparative Example 1. In the case of preparing the polymer electrolyte from which the lithium salt is removed and further impregnating the lithium salt, it can be seen that the discharge capacity and cycle characteristics similar to those of preparing the polymer electrolyte with the lithium salt-containing electrolyte are shown.

5 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared in the same manner as in Example 1 and Comparative Example 2.

The high rate discharge characteristics of the polymer electrolyte not containing lithium salt are greatly influenced by the heat treatment temperature for preparing the polymer electrolyte. Figure 5 shows the cycle characteristics at 1C rate according to the heat treatment temperature when forming such a polymer gel. 5 shows cycle characteristics of the lithium polymer battery including the polymer electrolyte prepared according to Example 1, and D shows cycle characteristics of the lithium polymer battery including the polymer electrolyte prepared according to Comparative Example 2. . In order to exhibit high high rate discharge characteristics, the heating temperature of the polymer electrolyte is preferably set to 60 ° C. or higher, and when the polymer electrolyte is prepared at a lower temperature, the high rate discharge characteristics are deteriorated.

6 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 2. After leaving the polymer electrolyte in which the lithium salt is removed in a sealed state in an aluminum package for 5 days, it can be seen that even in the case of a battery manufactured by using the same, the battery has stable cycle characteristics without a decrease in discharge capacity.

7 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 1 and Comparative Example 3. In the figure, E represents cycle characteristics at a 1C rate of the lithium polymer battery prepared in Example 1, and F represents cycle characteristics at a 1C rate of the lithium polymer battery prepared according to Comparative Example 3.

When the battery is manufactured by compressing the polymer electrolyte and the electrode at 150 ° C., it can be seen that the discharge capacity is also reduced and the cycle characteristics are much deteriorated compared to the case where the battery is compressed at 50 ° C. That is, when pressed at too high a temperature, the physical properties of the polymer electrolyte are greatly changed while the polymer electrolyte is melted, and when pressed with the electrode in such a state, impregnation of the electrolyte becomes difficult.

Adhesion between the polymer electrolyte and the electrode may be performed by using a binder prepared using a polyacrylate-based polymer in addition to the above-mentioned thermal compression. 8 shows the discharge capacity according to the cycle at 1C speed of the lithium polymer battery prepared in Example 3 by this method. It can be seen that during 400 cycles, the discharge capacity decreases by less than 10% compared to the initial cycle, and shows excellent cycle characteristics.

9 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 4, Comparative Example 4 and Comparative Example 5. In the figure, G represents cycle characteristics at 1C speed of the lithium polymer battery prepared according to Example 4, and H and I cycles at 1C speed of the lithium polymer battery prepared according to Comparative Example 4 and Comparative Example 5, respectively. It is characteristic.

If the concentration of the lithium salt contained in the electrolyte further impregnated after the production of the electrode and the polymer electrolyte assembly through the drawing is lower than 1M, the high rate discharge characteristics and the decrease in the discharge capacity is greatly increased, if the concentration of the lithium salt is higher than 3M Although the discharge capacity measured initially does not fall, it can be seen that the decreasing tendency of the capacity increases as the cycle progresses. This can be explained by the excessive increase in the concentration of lithium salt, the increase in the diffusion of lithium ions gradually increases as the cycle progresses.

10 is a view showing the discharge capacity according to the cycle at a 1C rate of the lithium polymer battery prepared according to Example 5. By preparing a polymer electrolyte using the lithium salt-free electrolyte, the mechanical strength of the electrolyte film could be greatly increased, and by reducing the content of ethylene carbonate, the affinity between the polymer and the electrolyte could be increased to produce a stronger polymer film. Could. It can be seen from the figure that the discharge characteristics gradually stabilized as the cycle progresses. That is, by using the polymer electrolyte prepared according to the method of the present invention, it is possible to prepare a very thin polymer electrolyte of about 15 μm that does not cause a short circuit.

As described above, in the present invention, the mechanical strength of the polymer electrolyte can be greatly improved by forming a polymer electrolyte using an electrolyte solution containing no electrolyte salt and a polyvinylidene fluoride-based polymer. It has more suitable properties for fairness. Since the electrolyte salt is removed, the polymer electrolyte has excellent mechanical strength, and thus can be manufactured very thinly.

The polymer electrolyte prepared according to the method of the present invention is a solid polymer electrolyte which is not sticky and hardly changes the physical properties of the polymer electrolyte with time. When the polymer electrolyte is prepared, an electrolyte salt such as lithium salt is removed, thereby facilitating evaporation of the electrolyte solution contained in the polymer electrolyte, and the surface of the polymer electrolyte is changed into a solid type having no sticky property in a short time.

In addition, the mechanical strength of the polymer electrolyte formed using the electrolyte solution containing no electrolyte salt and the polyvinylidene fluoride polymer was superior to the polymer electrolyte prepared using the electrolyte solution containing electrolyte salt, and the physical properties of the polymer electrolyte over time. It exhibits very little change, which makes handling easier in manufacturing.

In addition, in the present invention, a lithium polymer secondary battery capable of imparting adhesive force between the electrode and the electrolyte through appropriate thermocompression bonding and using a binder and maintaining stable charge / discharge characteristics using the composition of the impregnated electrolyte may be manufactured.

Although the present invention has been described above according to an embodiment of the present invention, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention.

Claims (14)

Mixing the polyvinylidene fluoride polymer and the electrolyte solution in which the electrolyte salt is not dissolved in a weight ratio of 1: 2 to 10; Heating the mixture with stirring to produce a substantially homogeneous electrolyte slurry; And A method for producing a polymer electrolyte comprising the step of solidifying the resulting electrolyte slurry. The method of claim 1, wherein the mixture is stirred at a temperature in the range of 60 to 150 ° C. for 5 minutes to 5 hours to prepare an electrolyte slurry. The method of claim 1, wherein the viscosity of the electrolyte slurry is in the range of 1,000 to 100,000 cps. The method of claim 1, wherein the polyvinylidene fluoride polymer has a molecular weight in the range of 50,000 to 1,000,000 and a poly disperse index in the range of 1 to 4. According to claim 1, wherein the polyvinylidene fluoride polymer is a copolymer of polyvinylidene fluoride and hexafluoropropane, the mixing ratio of the hexafluoropropane ranges from 2 to 30% of the total weight of the copolymer Wherein the copolymer has a molecular weight of 50,000 to 1,000,000 and a poly disperse index of 1 to 4; The method of claim 1, wherein the electrolyte is ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate ( ethyl methyl carbonate (EMC) and gamma-butyrolactone ( -butyrolactone; -BL) a method for producing a polymer electrolyte, characterized in that at least one selected from the group consisting of. The method of claim 6, wherein the amount of the ethylene carbonate used is in the range of 20 to 80% by weight of the total amount of the electrolyte. The method of claim 7, wherein the amount of the at least one electrolyte selected from the group consisting of diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate is in the range of 20 to 80 wt% of the total amount of the electrolyte. The method of claim 7, wherein the propylene carbonate or The amount of butyrolactone used is less than 60% by weight based on the amount of ethylene carbonate used. anode; cathode; And Stacking a polymer electrolyte which is positioned between the positive electrode and the negative electrode and is prepared by solidifying an electrolyte slurry obtained by mixing a polyvinylidene fluoride-based polymer and an electrolyte solution in which the electrolyte salt is not dissolved in a weight ratio of 1: 2 to 10. Method of manufacturing a lithium polymer secondary battery comprising the step. The method of claim 10, wherein the polymer electrolyte and the electrode of any one of the positive electrode and the negative electrode are bonded by any one of a method through thermocompression bonding and a binder. The method of claim 10, wherein the thermocompression temperature ranges from 30 ° C. to 130 ° C. 12. The method according to claim 10, wherein lithium perchlorate (LiClO ₄ ), lithium trifluoromethane sulfonate (LiCF ₃ SO ₃ ) at a concentration of 1.0 to 3 M in a cell including the positive electrode, the negative electrode and the polymer electrolyte. At least one lithium salt selected from the group consisting of lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium arsenic hexafluoride (LiAsF ₆ ). A method of manufacturing a lithium secondary battery, characterized by further impregnating an electrolyte solution comprising a. The method of claim 10, wherein the cell including the positive electrode, the negative electrode, and the polymer electrolyte is aged at a temperature ranging from room temperature to 70 ° C. 12.