KR20000041210A - Porous polymer electrolyte - Google Patents

Abstract

PURPOSE: A porous polymer electrolyte is provided to improve the mechanical strength thereof, thereby enabling the electrolyte to be formed in the form of a film. The polymer electrolyte also has a high conductivity. CONSTITUTION: A polymer electrolyte comprises a polymer film and an ion conductive liquid electrolyte. The polymer film contains an absorbing material, and has a plurality of pores. The mixture of the absorbing material and the polymer engaging material is dissolved in a solvent of the polymer engaging material. The mixture is then cast in the form of a film. The polymer electrolyte for a secondary battery improves the mechanical strength thereof, and enables the electrolyte to be formed in the form of a film. The polymer electrolyte also has a high conductivity.

Description

Microporous polymer electrolyte containing absorbent and preparation method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polymer films for use in electrolytic cells, particularly secondary batteries. More specifically, the introduction of a liquid component and a lithium salt (hereinafter referred to as "liquid electrolyte") to the polymer membrane may provide a migration path of ions moving between the positive electrode and the negative electrode during the charge and discharge of the secondary battery. have.

The battery has three basic components: a positive electrode, a negative electrode, and an electrolyte. The material of the negative electrode is often a compound in which lithium metal or lithium ions can be intercalated. Polymeric materials can be used. Most materials for intercalation of lithium ions include lithium cobalt oxide (Li _x CoO ₂ ), lithium nickel oxide (Li _x NiO ₂ ), and lithium nickel cobalt oxide (Li _x (NiCo). Oxides or polymer materials such as O ₂ ), spinel type lithium manganese oxide (Li _x Mn ₂ O ₄ ), manganese dioxide (MnO ₂ ), and the like. By introducing a liquid electrolyte into the polymer membrane, an ion conductive matrix can be formed.

The battery using the polymer electrolyte has a lower risk of leakage and excellent electrochemical stability than the battery using the liquid electrolyte, and thus, various types of assembly are possible and automation of the manufacturing process is easy. Therefore, since the discovery that a polymer such as polyoxyethylene may have a metal ion conductivity when the polymer contains a polar heterogeneous element capable of electrical interaction with metal ions, research on ion conductive polymers, that is, polymer electrolytes, has been actively conducted. It has been going on.

However, the pure polymer of polyoxyethylene alone has a very low ionic conductivity of about 10 ^-8 S / cm at room temperature, so that a temperature of about 100 ° C is required to show a conductivity of 10 ^-3 S / cm applicable to a battery. Because of the problem of reaching, the main flow of polymer electrolyte research was to improve conductivity.

As it has been found that the conduction of ions in the polymer electrolyte requires the movement of the polymer chain, attempts to improve the conductivity of the ions have been made in the direction of increasing the flexibility of the polymer chain, Blonsky. Et al. Have introduced an phosphazene bond into the polymer backbone to produce an electrolyte with improved conductivity of 10 ⁻⁵ S / cm (J. Am. Chem. Soc., 106, 6854 (1984)), The electrolyte was poor in terms of conductivity and mechanical strength.

In addition, various attempts have been made to modify the structure of the polymer or to add an inorganic material to reduce the crystallinity of the polymer. However, a pure polymer electrolyte (not including a liquid electrolyte) composed of only a polymer and a metal salt does not show sufficient conductivity It is true.

In contrast, the gel-type electrolyte of US Pat. No. 5,219,679 contains a liquid electrolyte in the polymer backbone, and exhibits properties of the polymer in terms of mechanical properties and has conductivity close to that of the liquid electrolyte. It suggests practical possibilities. That is, there is no separate activation process for adding a liquid electrolyte, and a part of the liquid electrolyte is already contained in the process of preparing the polymer electrolyte (casting a mixture of the polymer solution and the liquid electrolyte). However, the electrolyte of US Pat. No. 5,219,679 includes a polymer such as polyacrylonitrile that is reactive toward lithium metal, so that reaction products accumulate between the electrolyte and the lithium electrode during storage and use of the battery. As a result, the interface resistance is continuously increased.

Meanwhile, Scrosati et al. Prepared a polyelectrolyte in the form of gel using polymethylmethacrylate, which is less reactive with lithium metal (Electrochim. Acta, 140, 991 (1995)). The electrolyte, which uses polymethyl methacrylate as a polymer component, has a low reactivity with the lithium surface and has a slight increase in resistance at the electrode surface during storage, but exhibits a weakness in mechanical strength and is sufficient to form a film. In order to obtain strength, the polymer content must be increased, and in this process, the conductivity drops to 10 ^-4 S / cm or less. In addition, since the gel-type electrolyte contains a large amount of liquid components, vaporization of the liquid components occurring on the surface of the electrolyte is inevitable, so that the change of composition and the decrease in conductivity due to the loss of the liquid components during the storage period are only concerned. In addition, the lithium salt contained in the liquid electrolyte is decomposed by reacting with moisture in the air, which has the disadvantage of requiring an extremely dehumidifying atmosphere with extremely low moisture.

U.S. Patent No. 5,296,318, U.S. Patent No. 5,418,091 and the like provide a hybrid polymer electrolyte system to supplement the above problems. Hybrid polymer electrolytes are liquid electrolytes that are sensitive to the effects of moisture while retaining the advantages of gel-type polymer electrolytes (containing a large amount of liquid electrolyte and having conductivity similar to liquid electrolyte because conduction of lithium ions proceeds through the liquid phase). By adding the battery just before packaging, it was possible to minimize the influence of moisture in the electrolyte manufacturing process. However, since the liquid electrolyte is added after the polymer membrane is prepared, a site for sucking the liquid component or a driving force for penetrating the liquid component into the polymer membrane is required in the polymer membrane. To this end, dibutyl phthalate was added as a plasticizer in the preparation of the polymer membrane, and after the assembly of the battery, the plasticizer was extracted with an organic solvent such as alcohol or ether to make a liquid inhalation spot. However, since the extraction process of dibutyl phthalate uses a chemical method, it has a fatal disadvantage of low reproducibility, low battery yield, and difficult automation for mass production.

In order to compensate for the above disadvantages, the inventors have invented a patent for a polymer electrolyte including an absorbent. The polymer membrane of the polymer electrolyte is composed of an absorbent and a polymer binder in a dried state. Since the polymer binder has a rather dense structure, in order to improve the absorbency of the liquid electrolyte and to have more excellent lithium ion conductivity, There is a need for an improved polymer electrolyte with altered conformation of the polymer membrane.

Therefore, in order to solve this problem, the present invention synthesizes the polymer membrane by adding an absorbent (absorbent) capable of absorbing the liquid electrolyte in the polymer matrix, and the liquid electrolyte is introduced into the activation process after the cell assembly is completed. In order to improve the lithium ion conductivity of the polymer electrolyte, the polymer matrix is induced to have a microporous structure while maintaining the mechanical strength of the polymer membrane, thereby facilitating absorption of the liquid electrolyte.

In the present specification, the polymer membrane means a polymer membrane in a dry state and does not contain a liquid electrolyte, and the polymer electrolyte means to include ionic conductivity by including a liquid electrolyte in the polymer membrane.

The battery assembly is a process of lamination, pressing, or the like, together with a positive electrode and a negative electrode separately prepared with a polymer film interposed therebetween. When the polymer membrane is prepared by the above method, since the liquid electrolyte is added after the assembly of the battery, the limitation of the dehumidification condition in the process can be minimized. In addition, the site that can absorb the liquid electrolyte is already made at the stage of manufacturing the polymer membrane, and since the extraction process of the plasticizer is not necessary, the process can be simplified, which lowers the manufacturing cost and facilitates automation and increases the yield. There are advantages to it. In addition, when the polymer membrane is manufactured by the above method, since the polymer matrix has a porous structure, the liquid electrolyte is easily moved, and thus the lithium ion conductivity of the polymer electrolyte may be improved with the same absorbent content.

1 is a schematic cross-sectional view of a battery using the polymer electrolyte of the present invention,

2 is a view showing the experimental results according to the linear potential scanning method to measure the electrochemical stability of the polymer electrolyte of the present invention.

Description of the main symbols in the drawings

1: polyelectrolyte 11: absorbent powder

2: anode 22: anode current collector

3: negative electrode 33: negative electrode current collector

The polymer electrolyte of the present invention includes a polymer membrane containing an absorbent and a porous structure and an ion conductive liquid electrolyte.

The polymer membrane may be preferably prepared by using a phase inversion method. More preferably, the wet method is prepared by dissolving a mixture of an absorbent and a polymer binder in a solvent of the polymer binder, casting it in the form of a membrane, and then exchanging the solvent with a nonsolvent of the polymer binder. in the form of a membrane by mixing a volatile solvent that dissolves the polymer binder and a nonvolatile nonsolvent, a pore former, and a wetting agent that do not dissolve the polymer binder in a wet process or a mixture of the absorbent and the polymer binder. Drying, which is produced by casting and drying completely, can be used.

The polymer electrolyte for a secondary battery may be made through an activation process of absorbing the ion conductive liquid electrolyte in the porous polymer membrane thus prepared.

Therefore, the polymer electrolyte of the present invention may be made by introducing an absorbent capable of absorbing the liquid electrolyte into the polymer membrane, making the polymer membrane matrix into a porous structure, and then injecting the liquid electrolyte. The lithium ion conductivity of the polymer electrolyte thus prepared is about 1 to 3 × 10 ⁻³ S / cm at room temperature.

A variety of absorbents that can absorb liquids are known, and they can be classified into those that can absorb water and oil (oil). The excellent water absorption is mainly used for disposable diapers, sanitary napkins, and the like, and the oil absorbent is mainly used to remove petroleum spilled out to sea or factories, or to remove organic solvents in laboratories. Absorbents for this purpose are mainly used porous polymers or inorganic materials. The porous polymer may be a mesh-like polymer having a bulky functional group introduced into a side chain, or a polypropylene or a polyethylene introduced by adjusting a variable of a manufacturing process, and a pulp, which is a natural polymer. ), Cellulose and cork can also be used.

As the absorbent of the present invention, any material in powder form may be used to improve the absorbency of the liquid electrolyte. Preferably, polymer particles, mineral particles, mesoporous molecular sieves, and commercially available absorbent particles may be used. More preferably, synthetic / natural polymer particles such as polyethylene particles, polypropylene particles, polystyrene particles, polyurethane particles, pulp, cellulose particles, cork particles, wood flour and the like; And mineral particles having a Phyllosilicates structure, such as Clay, Paragonite, Montmorillonite, Mica, etc .; And synthetic oxide particles such as zeolite, porous silica, porous alumina, etc .; And mesoporous molecular sieves such as MCM-41 (Mobil) or MCM-48 (Mobil) having a pore diameter of 2 to 30 nm in an oxide / polymer material such as silica; Or one or more mixtures selected from the group consisting of commercially available absorbers such as Absorbent W Product (Absorption Corp.), Oclansorb (Hi Point Industries), PP Spillow spill control (Aldrich), Leak-Sorb spill absorbent (Aldrich) Can be used.

The amount of the absorbent added is 30 to 95% by weight, more preferably 50 to 90% by weight based on the weight of the dry polymer membrane containing no liquid electrolyte. If the added amount is 95% by weight or more, the mechanical strength of the formed polymer membrane is lowered, and if it is 30% by weight or less, there is a problem that the ability to absorb the liquid electrolyte is lowered. In order not to reduce the mechanical strength and the uniformity of the polymer film to be formed, the absorbent agent is preferably 40 µm or less, more preferably 20 µm or less.

Almost all ordinary polymers can be used as the polymer binder, including polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, vinylidene fluoride and maleic anhydride. (maleic anhydride) copolymer, polyvinylchloride, polymethylmethacrylate, polymethacrylate, cellulose triacetate, polyurethane, polysulfone, poly Polyether, polyolefine such as polyethylene or polypropylene, polyethylene oxide, polyisobutylene, polybutyldiene, polyvinylalcohol, polyacrylonitrile, poly Polyimide, polyvinyl formal, acrylonitrilebutyldiene high Acrylonitrilebutyldiene rubber, ethylene-propylene-diene-monomer, tetra (ethylene glycol) diacrylate, polydimethylsiloxane, polycarbonate and polysilicone One or more mixtures or copolymers thereof selected from the group consisting of

By making the polymer membrane used as the matrix of the polymer electrolyte in a porous structure, the liquid electrolyte can be easily moved, and the lithium ion conductivity of the polymer electrolyte can be improved even with the same absorbent content.

Preferably, a wet method may be used in which a polymer membrane is microporous in a drying step after casting the polymer membrane, or a dry method including a pore former may be introduced before casting the polymer membrane.

The solvent of the polymer binder may be N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, cyclohexanone ), Chloroform, dichloromethane, hexamethylphosphoramide, dimethylsulfoxide, dimethylsulfoxide, acetone and dioxane selected from the group consisting of desirable.

The non-solvents of the polymer binder are water, ethanol, ethylene glycol, glycerol, acetone, dichloromethane, ethylacetate, butanol, pentanol, hexanol And one or more mixtures selected from the group consisting of ethers.

Pore formers are 2-propanol, resorcinol, trifluoroethanol, cyclohexanol, hexafluoroisopropanol, methanol, and maleic acid. one or two or more mixtures selected from the group consisting of hemiacetal obtained by the reaction of acid) with hexafluoroacetone.

Wetting agents are preferably nonionic surfactants, such as Triton X-100 (Aldrich), Igepal DM-710 (GAF Co.) and the like.

The liquid electrolyte to be absorbed in the porous polymer membrane containing the absorbent is prepared by dissolving lithium salt in an organic solvent. In this specification, the absorption of the liquid electrolyte into the porous polymer membrane is defined as activation.

The organic solvent is preferred to have high polarity and no reactivity with lithium metal in order to increase dissociation of ions by increasing the polarity of the electrolyte and to facilitate conduction of ions by lowering the local viscosity around the ions. Examples of organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, Dimethylsulfoxide, 1,3-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, N, N- Dimethylformamide (N, N-dimethylformamide), diglyme, triglyme, tetraglyme and the like. In particular, it is preferable to use two or more mixed solutions composed of a high viscosity solvent and a low viscosity solvent as the organic solvent.

It is preferable that lithium salt has small lattice energy and large dissociation degree. Examples of lithium salts include LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, LiC (CF ₃ SO ₂ ) ₃ , and optional mixtures thereof may also be used. Can be. The concentration of the lithium salt is preferably 0.5M to 2M.

The liquid electrolyte is added at 30 to 90% by weight, more preferably 40 to 85% by weight based on the total amount of the electrolyte including the liquid electrolyte.

The polymer electrolyte of the present invention is easier to manufacture than the conventional polymer electrolyte, and the ion conductivity is high because the conduction of lithium ions proceeds through the liquid phase, and is not affected by moisture or temperature until activation. It is characterized by not.

The invention also relates to a method of making such a polymer electrolyte.

The polymer electrolyte of the present invention comprises a wet method prepared through five steps of mixing an absorbent and a polymer binder, dissolving the mixture, casting, porosity and drying of the polymer matrix, and activation; Or it is prepared by the dry method which is prepared by mixing, absorbing and adding an additive (solvent, non-solvent, pore former, wetting agent), casting and drying, and activation. Details thereof are as follows.

1. Wet method

First, the powdery absorbent having a particle size of 40 µm or less and the polymer binder are dry mixed in an airtight container.

The mixture of such absorbent and polymeric binder is dissolved in the solvent of the polymeric binder. In order to facilitate the dissolution of the polymer binder and to prevent the absorbents from agglomerating with each other, a magnetic stirrer, a mechanical stirrer, a planetary mixer, or the like may be stirred. In this process, an ultrasonic stirrer may be used to prevent the absorbents from agglomerating with each other and to prevent bubbles from forming during mixing.

After the polymer binder is completely dissolved and uniformly mixed with the absorbent, it is poured into a flat plate, for example, a glass plate or a Teflon plate, and cast in a film form by adjusting to a constant thickness. At this time, the thickness of the film is preferably adjusted to 10 to 200㎛. If the thickness of the film is 10 µm or less, the mechanical strength is lowered, and if the thickness is 200 µm or more, the ion conductivity decreases, which is not preferable.

In order to introduce porosity into the polymer matrix after casting in the form of a membrane, the solvent of the polymer binder is extracted by dipping the cast membrane into a nonsolvent pool containing a nonsolvent of the polymer binder. The time for soaking in the nonsolvent is preferably about 1 minute to 1 hour depending on the type of solvent and nonsolvent. If the time is short enough porosity is not induced, on the contrary, if the time is long, productivity is not preferable because it is low. 10-90 degreeC is preferable and 20-80 degreeC of temperature at this time is more preferable. If the temperature is low enough porosity is not induced, if the temperature is too high is not preferable because the mechanical strength of the polymer membrane falls.

After the extraction of the solvent is completed, the resulting film is completely dried and a liquid electrolyte is introduced.

2. Dry Method

The powdery absorbent and polymer binder with a particle size of 40 μm or less are dry mixed in an airtight container. The mixture of such absorbent and polymeric binder is dissolved in the solvent of the polymeric binder. In order to facilitate dissolution of the polymer binder and to prevent the absorbents from agglomerating with each other, it may be stirred using a magnetic stirrer, a mechanical stirrer, a planetary stirrer, or the like. In this process, an ultrasonic stirrer may be used to prevent the absorbents from agglomerating with each other and to prevent bubbles from forming during mixing.

After the polymer binder is completely dissolved and uniformly mixed with the absorbent, a solvent which does not dissolve the polymer binder, that is, a non-solvent, is added within a range where precipitation of the polymer binder does not occur. It is preferable to add a pore former, a wetting agent, etc. in order to produce | generate a microporous structure smoothly. After these additives are uniformly mixed, they are poured into a flat plate, for example, a glass plate or a Teflon plate, and cast in a film form by adjusting to a constant thickness. At this time, the thickness of the film is preferably adjusted to 10 to 200㎛. If the thickness of the film is 10 µm or less, the mechanical strength is lowered, and if the thickness is 200 µm or more, the ion conductivity decreases, which is not preferable.

After casting in the form of a membrane, the polymer membrane is completely dried at 20 ° C. to 200 ° C., and then a liquid electrolyte is introduced.

The invention also relates to a secondary battery, in particular a lithium secondary battery, using the polymer electrolyte as an electrolyte.

After drying the porous polymer membrane of the dry solid state prepared by the above method without introducing the liquid electrolyte in the form of a battery together with the positive and negative electrodes prepared separately, the secondary battery through an activation step of absorbing the liquid electrolyte Manufacture. In order to be a polymer electrolyte having sufficient ion conductivity to be used, it is necessary to go through an activation step of absorbing a liquid electrolyte, which is in a state capable of operating as a battery. If the activation step is not performed, the room temperature ion conductivity is very low, and thus cannot be used as an electrolyte by itself.

A schematic cross-sectional view of a secondary battery using the polymer electrolyte of the present invention is shown in FIG. 1. The battery is constructed by bonding the positive electrode 2 and the negative electrode 3 to the center with the polymer electrolyte 1 obtained from the above process. The polymer electrolyte 1 contains the absorbent powder 11 and has a porous structure, so that the liquid electrolyte can be more easily contained. The positive electrode 2 is electrically connected with the positive electrode current collector 22 and the negative electrode 3 with the negative electrode current collector 33. The assembly thus constructed undergoes an activation step of absorbing the liquid electrolyte, thereby enabling the battery to operate.

Hereinafter, the embodiment will be described in detail a method for producing a polymer electrolyte according to the present invention. However, these examples do not limit the contents of the present invention, and modifications may be made without departing from the basic spirit of the present invention. For example, a battery may be fabricated through an activation process of absorbing a liquid electrolyte after assembling the battery with a separately manufactured positive electrode and a negative electrode, or may also investigate the characteristics of the polymer electrolyte and the performance of the battery in which the battery is applied. have. However, in the embodiment of the present invention, the production process of the actual battery was omitted in order to examine the characteristics of the polymer electrolyte only.

Example 1 (wet method)

The absorbent and the PVdF powder were put in a 20 mL vial, followed by dry mixing for about 5 minutes in a magnetic stirrer. 4 mL of NMP was added thereto and stirring continued until the binder was completely dissolved. Ultrasonic agitation was performed for 30 minutes during stirring to prevent the absorbent particles from agglomerating with each other. The liquid mixture produced by the above method was coated on a glass plate to have a thickness of about 100 μm. The coated film was directly immersed in non-solvent for about 10 minutes, and the film was taken out and dried at 40 ° C. for about 1 hour. The polymer membrane prepared by the above method was immersed in a liquid electrolyte solution for about 10 minutes, and then the weight change before and after the liquid electrolyte was completely absorbed was measured, and the conductivity was measured using an alternating current impedance method.

The characteristics and conductivity of the polymer electrolyte according to the type and content ratio of the absorbent and the binder are summarized in Table 1 below. In order to compare the ability of the polymer membrane to absorb the liquid electrolyte, the absorption capacity (Δ _ab ) was defined as follows.

Δ _ab = [amount of absorbed liquid electrolyte (mg)] / [weight of polymer membrane (mg)]

Example Absorbent PVdF Non-solvent Liquid electrolyte Δ _ab Ion Conductivity (mS / cm) Mechanical strength Kinds g g a Paragonite 0.13 0.28 H ₂ O EC / DMC 1M LiPF ₆ 7.0 2.1 Great b 〃 0.17 0.26 〃 〃 6.8 2.2 Great c 〃 0.72 0.24 〃 EC / PC 1M LiPF ₆ 6.9 1.9 Great d 〃 1.06 0.26 〃 〃 7.5 1.8 Great e 〃 1.51 0.26 〃 EC / DMC 1M LiPF ₆ 8.0 2.4 Great f 〃 2.00 0.26 〃 〃 8.5 2.5 Great g 〃 1.98 0.25 ethanol 〃 5.1 1.0 Great h Zeolite 1.37 0.60 H ₂ O 〃 7.2 1.9 Great i 〃 1.50 0.38 〃 〃 8.2 2.0 Great j 〃 1.65 0.29 〃 〃 8.0 2.4 Great k Montmorillonite 1.34 0.58 〃 〃 8.0 2.8 Great l 〃 1.50 0.38 〃 〃 8.2 2.9 Great m Porous silica 1.35 0.59 〃 〃 8.5 2.4 Great n Polypropylene 1.35 0.60 〃 〃 7.0 1.9 Great o Wood flour 1.35 0.60 〃 〃 7.4 2.0 Great

Example 2 (Wet method)

Paragonite powder and binder powder were placed in a 20 mL vial, followed by dry mixing for about 5 minutes in a magnetic stirrer. 4 mL of NMP was added thereto and stirring continued until the binder was completely dissolved. Ultrasonic agitation was performed for 30 minutes during stirring to prevent the absorbent particles from agglomerating with each other. The liquid mixture produced by the above method was coated on a glass plate to have a thickness of about 100 μm. The coated film was directly immersed in a water bath for about 10 minutes, and the film was taken out and dried at 40 ° C. for about 1 hour. The polymer membrane prepared by the above method was immersed in a liquid electrolyte solution for about 10 minutes, and then the weight change was measured before and after the liquid electrolyte was completely absorbed, and the conductivity was measured using an alternating current impedance method.

Example Paragonite Binder Liquid electrolyte Δ _ab Ion Conductivity (mS / cm) Mechanical strength g Kinds g p 1.98 PVdF 0.24 EC / DMC 1M LiPF ₆ 8.1 2.4 Great q 2.00 P (VdF-HFP) 0.26 〃 8.0 2.6 Great r 1.95 PAN 0.25 〃 7.8 2.2 Great s 2.00 PU 0.26 〃 8.9 2.9 Great t 1.98 PVC 0.25 〃 7.4 2.0 Great u 2.00 P (VdF-HFP) 0.26 〃 8.5 2.5 Great

Example 3 (dry method)

1.17 g of paragonite and 0.5 g of P (VdF-HFP) were added to a 20 mL vial, followed by dry mixing for about 5 minutes in a magnetic stirrer. 8 g of acetone was added thereto and stirring continued until the binder was completely dissolved. Ultrasonic agitation was performed for 30 minutes during stirring to prevent the absorbent particles from agglomerating with each other. 0.9 g of ethylene glycol, 0.1 g of Triton X-100, and 1.8 g of isopropanol were added to the mixed solution, and ultrasonic stirring was performed for about 10 minutes until they were uniformly mixed. The mixed solution prepared by the above method was coated on a glass plate so as to have a thickness of about 100 μm, and then dried at 40 ° C. for 2 hours, and then further dried at 50 ° C. in a vacuum dryer. The Δ _ab value calculated by measuring the weight change before and after the liquid electrolyte was completely absorbed after soaking the polymer membrane prepared by the above method for 10 minutes in an EC / DEC 1M LiPF ₆ solution was measured by AC impedance method. One room temperature ion conductivity was 2.0 × 10 ⁻³ S / cm.

Example 4 (comparative example)

2 g of paragonite and 0.26 g of PVdF were added to a 20 mL vial, followed by dry mixing for about 5 minutes in a magnetic stirrer. 4 mL of NMP was added thereto and stirring continued until the binder was completely dissolved. Ultrasonic agitation was performed for 30 minutes during stirring to prevent the absorbent particles from agglomerating with each other. The mixed solution prepared by the above method was coated on a glass plate to have a thickness of about 100 μm, and then dried at room temperature for about 2 hours and further dried by a vacuum dryer for 6 hours. At this time, the temperature of the vacuum dryer was adjusted to about 50 ℃. The polymer membrane prepared by the above method was immersed in a liquid electrolyte solution for about 10 minutes, and then the weight change before and after the liquid electrolyte was completely absorbed was measured, and the conductivity was measured using an alternating current impedance method. The lithium ion conductivity was 7.0 × 10 ⁻⁴ S / cm at room temperature.

Example 5

In order to measure the electrochemical stability of the polymer electrolyte, linear sweep voltammetry was performed using stainless steel (# 304) as a working electrode and lithium metal as a counter electrode and a reference electrode. The potential scan range was from the open circuit voltage to 5.4 V and the potential scan speed was 10 mV / sec. The results of the linear potential scanning analysis of the polymer electrolyte prepared by the method of Examples 1- (f), 1- (j), 1- (l) and Example 2- (s) are shown in FIGS. , Denoted D.

The polymer electrolyte of the present invention has excellent mechanical strength and can be formed into a thin film, and the porous structure and absorbent introduced into the polymer matrix smoothly contain the liquid electrolyte and correspond to the liquid electrolyte because there is no restriction in the movement of lithium ions. It has a high ionic conductivity and does not require a special dehumidification environment because lithium salts, which are decomposed by trace amounts of water, are not introduced in the process of preparing a polymer membrane, unlike general gel-type polymer electrolytes. It has a wide potential window and is characterized by easy automation for mass production because of a simple electrolyte manufacturing process. In addition, since the adhesion between the positive electrode and the negative electrode is excellent and the volume change due to the introduction of the liquid electrolyte is small, the interface resistance between the electrolyte and the electrode can be minimized, and thus it is suitable for use as an electrolyte for a lithium secondary battery.

Claims (6)

A polymer electrolyte for secondary batteries, comprising a polymer membrane containing an absorbent and having a porous structure and an ion conductive liquid electrolyte. The method of claim 1, wherein the polymer membrane has a thickness of 10 to 200 ㎛ in a dry state without a liquid electrolyte; Prepared by dissolving the mixture of absorbent and polymeric binder in a solvent of the polymeric binder, casting it in the form of a membrane, then exchanging the solvent with a non-solvent of the polymeric binder and drying; Dissolving the mixture of the absorbent and the polymeric binder in the solvent of the polymeric binder, adding the non-solvent, the pore former, and the wetting agent of the polymeric binder, casting the same in the form of a membrane, and drying the prepared product; Polymer electrolyte for secondary batteries characterized in that. The polymer electrolyte for secondary batteries of claim 2, wherein the polymer electrolyte is prepared through an activation process of absorbing an ion conductive liquid electrolyte into the prepared polymer membrane. The method of claim 1, wherein the absorbent has a particle diameter of 40 ㎛ or less; 30 to 95% by weight, based on the total weight of the dry polymer membrane containing no liquid electrolyte; Porous polymer particles such as polyethylene, polypropylene, polystyrene, polyurethane, pulp, cellulose, cork and wood flour; Mineral particles having a phyllosilicate structure such as clay, paragonite, montmorillonite and mica; Synthetic oxide particles such as zeolite, porous silica and porous alumina; Mesoporous molecular sieve having a pore diameter of 2 to 30 nm as an oxide or a polymer material; And one or two or more mixtures selected from the group consisting of commercially available absorbers; The ion conductive liquid electrolyte is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, 1,3-dioxene, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide In an organic solvent consisting of one or two or more mixtures selected from the group consisting of seed, sulfolane, N, N-dimethylformamide, diglyme, triglyme and tetraglyme, LiClO ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiBF ₄ Prepared by dissolving one or more lithium salts selected from the group consisting of LiN (CF ₃ SO ₂ ) ₂ , LiPF ₆ , LiSCN, and LiC (CF ₃ SO ₂ ) ₃ at a concentration of 0.5 to 2M; The ion conductive liquid electrolyte is 30 to 90% by weight based on the total weight of the total electrolyte including the liquid electrolyte; Polymer electrolyte for secondary batteries characterized in that. The method of claim 2, wherein the polymer binder is polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and maleic anhydride, polyvinyl chloride, polymethylmethacryl Latex, polymethacrylate, cellulose triacetate, polyurethane, polysulfone, polyether, polyethylene, polypropylene, polyethylene oxide, polyisobutylene, polybutyldiene, polyvinyl alcohol, polyacrylonitrile, polyimide, poly Vinyl formal, acrylonitrile butyl diene rubber, ethylene propylene diene monomer, tetraethylene glycol diacrylate, polydimethylsiloxane, polycarbonate, and a mixture of one or two or more selected from the group consisting of silicone polymers To; The solvent of the polymer binder is N-methylpyrrolidinone, dimethylformamide, dimethylacetamide, tetrahydrofuran, acetonitrile, cyclohexanone, chloroform, dichloromethane, hexamethylphosphoamide, dimethyl sulfoxide, acetone and di One or two or more mixtures selected from the group consisting of oxenes; The non-solvent of the polymer binder is one or two or more mixtures selected from the group consisting of water, ethanol, ethylene glycol, glycerol, acetone, dichloromethane, ethyl acetate, butanol, pentanol, hexanol and ether; The pore former is one selected from the group consisting of 2-propanol, resorcinol, trifluoroethanol, cyclohexanol, hexafluoroisopropanol, methanol, and hemiacetal obtained by reaction of maleic acid with hexafluoroacetone. Or a mixture of two or more; The wetting agent is a nonionic surfactant; Polymer electrolyte for secondary batteries characterized in that. After dissolving the mixture of the absorbent and the polymeric binder in the solvent of the polymeric binder, casting it in the form of a membrane, exchanging the solvent with the non-solvent of the polymeric binder, drying it to form a porous polymeric membrane containing the absorbent, , Lithium secondary battery prepared by absorbing the liquid electrolyte after assembling in the form of a battery with a positive electrode and a negative electrode produced separately from this.