WO2014112776A1 - Polymer electrolyte, lithium secondary battery using same, and method for manufacturing lithium secondary battery - Google Patents

Abstract

The present invention relates to a polymer electrolyte, a lithium secondary battery using the same, and a method for manufacturing the lithium secondary battery, wherein: an electrode assembly is formed by using a porous nanofiber web as an electrolyte matrix; an organic electrolyte having a mixture of a gel polymer-forming monomer and a polymerization initiator is injected, and a gel polymer electrolyte is formed by polymerization; and the porous nanofiber web is maintained in a web form such that stability can be increased by preventing a short circuit between a cathode and an anode. The polymer electrolyte, according to the present invention, comprises: the porous nanofiber web which is provided with a plurality of nanofibers; and a gel polymer portion which is impregnated into the porous nanofiber web, wherein the gel polymer portion is formed by polymerizing the gel polymer-forming monomer after a non-aqueous organic solvent, a solute of lithium salt, and the organic electrolyte having the gel polymer-forming monomer and the polymerization initiator have been impregnated into the porous nanofiber web.

Description

Polymer electrolyte, lithium secondary battery using same, and method for manufacturing same

The present invention relates to a polymer electrolyte, a lithium secondary battery using the same, and a method for manufacturing the same. Particularly, a gel polymer electrolyte is formed by polymerization of a gel polymer-forming monomer impregnated into a porous nanofiber web, and a porous nanofiber web is used. The present invention relates to a polymer electrolyte capable of preventing a short circuit between the positive electrode and the negative electrode, a lithium secondary battery using the same, and a method of manufacturing the same.

Conventionally, as an electrolyte of a lithium secondary battery, the electrolyte which impregnated the non-aqueous electrolyte solution into the film which has a pore called a separator generally was used. In recent years, attention has been paid to lithium secondary batteries (polymer batteries) using polymer electrolytes made of polymers rather than liquid electrolytes.

Such a polymer battery uses a gel electrolyte in which a liquid electrolyte is impregnated in a polymer. Since the electrolyte is retained in the polymer, the liquid is less likely to leak, and therefore, there is an advantage in that the safety of the battery is improved and the shape of the battery can be freed.

Since the polymer electrolyte has a lower conductivity of lithium ions than an electrolyte composed only of an electrolyte solution, a method of thinning the thickness of the polymer electrolyte is performed. However, when the polymer electrolyte is thinned in this manner, its mechanical strength is reduced, and the positive electrode and the negative electrode are short-circuited at the time of battery manufacturing, and thus the polymer electrolyte is easily destroyed.

Korean Laid-Open Patent Publication No. 10-2006-1743 discloses a lithium secondary battery comprising a positive electrode and a negative electrode capable of reversible intercalation / deintercalation of lithium, and an electrolyte, wherein the electrolyte includes a cyclic carbonate and an alkyl substituent. Eggplant has proposed a lithium secondary battery containing a non-aqueous organic solvent containing a lactone compound, a lithium salt and a gel forming compound.

However, since the secondary battery has a structure in which the positive electrode and the negative electrode are separated by a gel electrolyte, ionic conductivity is reduced when the electrolyte is formed into a thick film, and a short circuit occurs between the positive electrode and the negative electrode when formed as a thin film. There is.

Korean Laid-Open Patent Publication No. 10-2004-84117 is laminated in the order of an anode, a separator, and then a cathode, and inserted into an aluminum laminate film, and injected with a precursor mixed with a liquid electrolyte, a polymerized polymer, a reactive monomer or a macromonomer, and a polymerization initiator. Thereafter, a method of manufacturing a lithium ion polymer battery, in which a gel polymer electrolyte is prepared by vacuum encapsulation and holding and polymerization in a constant temperature chamber at 60 ° C. to 80 ° C. for up to 1 hour 30 minutes, has been proposed.

The manufacturing method of the lithium ion polymer battery is IPN (Interpenetrating Polymer Network), HDDA (Hexanedioldiacrylate) and triethylene glycol using one or two or more acrylate monomers capable of reacting with a polymer having an acrylate group polymerized in a precursor. The physical properties of the gel polymer electrolyte can be changed by adding a reactive modifier using at least one acrylate having two or more reactors such as diethyleneglycoldimehtacrylate and tetraethyleneglycoldiacrylate. It is characterized by changing the.

The method of manufacturing the lithium ion polymer battery has a low porosity by using a nonwoven fabric separator made of PE or PP, and has a problem in that ion conductivity is lowered due to a thick coating layer.

The inventors formed an electrode assembly using a porous nanofiber web made of nanofibers as an electrolyte matrix, and then injecting an organic electrolyte mixture of a gel polymer forming monomer and a polymerization initiator and inducing an addition polymerization reaction to form a gel polymer. The monomer was found to form a gel polymer electrolyte by rapid polymerization, but the porous nanofiber web was found to maintain the web shape. The present invention has been made based on this finding.

Therefore, the present invention has been proposed to solve the above problems of the prior art, the object of which is to form a gel polymer electrolyte by the polymerization reaction of the gel polymer forming monomer impregnated in the porous nanofiber web, and to the porous nanofiber web The present invention provides a polymer electrolyte, a lithium secondary battery using the same, and a method of manufacturing the same, which can prevent a short circuit between the positive electrode and the negative electrode.

Another object of the present invention is to provide a polymer electrolyte, a lithium secondary battery using the same, and a method of manufacturing the same, which can ensure fast and uniform impregnation of an organic electrolyte using a porous nanofiber web made of nanofibers as an electrolyte matrix.

It is still another object of the present invention to form a gel polymer electrolyte impregnated in a porous electrolyte matrix to form a gel polymer electrolyte by a polymerization reaction so that it is converted into a solid electrolyte having almost no liquid electrolyte, thereby preventing leakage. The present invention provides a polymer electrolyte, a lithium secondary battery using the same, and a method of manufacturing the same, capable of increasing ion conductivity along with thinning.

In order to achieve the above object, the polymer electrolyte of the present invention comprises a separator consisting of a first porous nanofiber web having a plurality of nanofibers; And a gel polymer part impregnated in the first porous nanofiber web, wherein the gel polymer part is impregnated in the first porous nanofiber web and includes an organic solvent, a solute of lithium salt, a gel polymer forming monomer and a polymerization initiator. It is formed by the polymerization reaction of the said monomer for gel polymer formation in the inside.

The lithium secondary battery according to the present invention includes a positive electrode and a negative electrode capable of occluding and releasing lithium, and a polymer electrolyte disposed between the positive electrode and the negative electrode, the polymer electrolyte comprising: a porous separator including a plurality of nanofibers; And a gel polymer part impregnated in the porous separator, wherein the gel polymer part is impregnated in the porous separator and contains the organic solvent, a solute of lithium salt, a monomer for forming a gel polymer and a monomer for forming the gel polymer in an electrolyte including a polymerization initiator. It is characterized by being formed by a polymerization reaction.

Method for producing a lithium secondary battery according to the present invention comprises the steps of dissolving a single or mixed polymer in a solvent to form a spinning solution; Spinning the spinning solution to form a porous separator having a plurality of nanofibers; Forming an electrode assembly by inserting the porous separator between an anode and a cathode each consisting of a plurality of unit electrode cells; Embedding the electrode assembly in a case and injecting an organic electrolyte including at least a monomer for forming a gel polymer and a polymerization initiator; And performing a gelling heat treatment to polymerize the gel polymer forming monomer to form a gel polymer electrolyte, wherein the porous separator maintains a web shape.

According to another feature of the present invention, a method of manufacturing a lithium secondary battery according to the present invention by using a pair of porous separators each having a plurality of nanofibers, while separating a plurality of unit cathode cells and a plurality of unit anode cells alternately Forming an electrode assembly by laminating; Taping the electrode assembly into a compression band; Embedding the electrode assembly in a case and injecting an organic electrolyte including at least a monomer for forming a gel polymer and a polymerization initiator; And performing a gelling heat treatment to polymerize the gel polymer forming monomer to form a gel polymer electrolyte.

According to another feature of the present invention, a lithium secondary battery according to the present invention is an electrode assembly alternately stacked while separating a plurality of unit cathode cells and a plurality of unit cathode cells using a pair of porous separator; A compression band taping the outer circumference of the electrode assembly; A case having an electrode assembly taped with the compression band; And a polymer electrolyte disposed between the unit anode cell and the unit cathode cell, wherein the polymer electrolyte includes a gel polymer part impregnated in the porous separator and the porous separator, and the gel polymer part is impregnated in the porous separator. It is formed by the polymerization reaction of the said monomer for gel polymer formation in the organic solvent, the solute of a lithium salt, the electrolyte for containing a gel polymer formation monomer, and a polymerization initiator.

As described above, in the present invention, a porous separator made of one of a porous nanofiber web, a laminate of a porous nanofiber web and an inorganic porous film, a laminate of a porous nanofiber web and a porous nonwoven fabric, and a laminate of a porous nonwoven fabric and an inorganic porous film. Is used as an electrolyte matrix to form an electrode assembly, and then an organic electrolyte solution containing a mixture of a gel polymer forming monomer and a polymerization initiator is injected and an addition polymerization reaction is performed to cause the gel polymer forming monomer to polymerize the gel polymer electrolyte by polymerization. However, as the porous nanofiber web maintains the shape of the web as it is, the short circuit between the anode and the cathode can be prevented and safety can be achieved.

In the present invention, the porous nanofiber web made of nanofibers is used as the electrolyte matrix, so that the porosity is high, thereby ensuring fast and uniform electrolyte impregnation of the organic electrolyte, and thinning the polymer electrolyte itself, thereby allowing ions between the anode and the cathode. The conductivity can be increased, and the mechanical properties are excellent.

In addition, in the present invention, by using a polymer electrolyte having excellent adhesion to the electrode, an increase in interfacial resistance can be suppressed by preventing a separation phenomenon between the electrolyte and the electrode, thereby reducing OCV (Open Circuit Voltage). The reduction can be minimized.

Furthermore, in the present invention, a part of the polymer electrolyte is filled in the positive electrode and the negative electrode so that the positive electrode and the negative electrode and the polymer electrolyte are adhered, thereby minimizing the reduction of OCV.

In the present invention, as the outside of the electrode assembly is wound with a non-swellable porous thin film sheet, the electrode assembly suppresses the shape of expansion and contraction during charging and discharging, thereby preventing the separation between the electrolyte and the electrode, thereby increasing the interfacial resistance. I can suppress it.

In the present invention, by using a porous separator in which a thin inorganic porous film or a porous nanofiber web is added to one side of the porous nonwoven fabric used as a support, a decrease in porosity (porosity) can be suppressed to decrease OCV.

1 is a cross-sectional view showing a lithium secondary battery according to a first embodiment of the present invention;

2 is a cross-sectional view showing a composite porous separator according to a second embodiment of the present invention;

3 is a cross-sectional view illustrating a process of manufacturing a porous separator used as a polymer electrolyte according to the present invention;

4 is a cross-sectional view illustrating a sealing process of a porous separator used as a positive electrode and a polymer electrolyte according to the present invention;

5 is a schematic cross-sectional view of an electrode assembly assembled according to the present invention;

6 is a schematic plan view of an electrode assembly assembled according to the present invention;

7 is a flowchart illustrating an assembly process of a lithium secondary battery according to the present invention;

8 is a cross-sectional view of a composite porous separator according to a third preferred embodiment of the present invention;

9 is a cross-sectional view of a composite porous separator according to a fourth preferred embodiment of the present invention;

10 is a manufacturing process diagram for manufacturing a composite porous separator according to the present invention,

11 is a modified manufacturing process chart for manufacturing a composite porous separator according to the present invention.

The above objects, features, and advantages will become more apparent from the following detailed description with reference to the accompanying drawings, and as such, those skilled in the art to which the present invention pertains may share the spirit of the present invention. It will be easy to implement.

In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, in the present specification, the polymer electrolyte is a porous nanofiber web (electrolyte matrix), which is a porous separator, is assembled into a case together with a positive electrode and a negative electrode, and an organic electrolyte solution in which a gel polymer forming monomer and a polymerization initiator are mixed is injected into a case. It refers to an inorganic pore type gel polymer electrolyte in which a gel polymer is synthesized by performing a gelation process in a state in which an organic electrolyte solution is embedded in a nanofiber web and then polymerizing a monomer.

1 is a cross-sectional view showing a lithium secondary battery according to a first preferred embodiment of the present invention, Figure 2 is a cross-sectional view showing a composite porous separator according to a second preferred embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery, that is, a lithium polymer battery according to a first preferred embodiment of the present invention may be, for example, a positive electrode 1 and a gel polymer electrolyte of an inorganic pore type when forming a full cell. (5) and the cathode (3).

The positive electrode 1 has a positive electrode active material layer 11b on one surface of the positive electrode current collector 11a, and the negative electrode 3 has a negative electrode active material layer 13b on one surface of the negative electrode current collector 13a. .

However, the positive electrode 1 may be disposed to face the negative electrode 3 and include a pair of positive electrode active material layers on both sides of the positive electrode current collector 11a to form a bicell.

The cathode active material layer 11b includes a cathode active material capable of reversibly intercalating and deintercalating lithium ions. Representative examples of the cathode active material include LiCoO ₂ , LiNiO ₂ , LiNiCoO ₂ , and LiMn ₂ O. _A substance capable of occluding and releasing lithium such as ₄ , LiFeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiS, MoS, or an organic disulfide compound or an organic polysulfide compound can be used. However, in the present invention, it is of course possible to use other types of positive electrode active materials in addition to the positive electrode active material.

The negative electrode active material layer 13b includes a negative electrode active material capable of intercalating and deintercalating lithium ions, and the negative electrode active material includes a carbon-based negative electrode active material of crystalline or amorphous carbon, carbon fiber, or carbon composite material. , Tin oxides, lithiated ones thereof, lithium, lithium alloys and mixtures thereof. However, the present invention is not limited to the type of the negative electrode active material.

The positive electrode 1 and the negative electrode 3 prepare a slurry by mixing an appropriate amount of an active material, a conductive agent, a binder, and an organic solvent, as in the method generally used in a conventional lithium ion battery, and then prepare a positive electrode and a negative electrode current collector ( 11a, 13a) can be obtained by casting, drying and rolling the prepared slurry on both sides of aluminum or copper foil or mesh.

For example, the positive electrode is used by casting a slurry composed of LiCoO ₂ , super-P carbon, PVdF as an active material, a conductive agent, a binder on an aluminum foil, and the negative electrode is MCMB (mesocarbon microbeads), super-P carbon, PVdF The constructed slurry can be cast and used on copper foil. In the positive electrode and the negative electrode, after the slurry is cast, it is preferable to perform roll pressing in order to increase the adhesion between the particles and the metal foil.

The polymer electrolyte 5 includes a porous nanofiber web 15 made of a plurality of nanofibers 150 and an organic electrolyte solution in which a monomer and a polymerization initiator for forming a gel polymer are mixed in the porous nanofiber web 15. The gel polymer unit 17 is composed of a gel polymer in which a gel polymer is synthesized by a polymerization reaction of monomers through a gelation heat treatment step.

In the first embodiment, a porous nanofiber web 15 composed of a single layer is used as the porous separator serving as an electrolyte matrix.

The porous nanofiber web 15 may be used as long as it is a polymer capable of dissolving in a solvent to form a spinning solution and then spinning by an electrospinning method to form the nanofibers 150. In this case, a single polymer or a mixed polymer can be used. The polymer may be a swellable polymer, a non-swellable polymer, a heat resistant polymer, a mixed polymer in which a swellable polymer and a non-swellable polymer are mixed, or a mixed polymer in which a swellable polymer and a high heat resistant polymer are mixed.

The porous nanofiber web 15 forms a spinning solution by dissolving a single or mixed polymer in a solvent to form a spinning solution, and then spins the spinning solution to form a porous nanofiber web made of ultra-fine fibers and calenders at a temperature below the melting point of the polymer. Ring is formed.

In this case, the porous nanofiber web 15 may include a predetermined amount of inorganic particles in the spinning solution to enhance heat resistance.

In addition, when using a mixed polymer of the swellable polymer and the non-swellable polymer, the swellable polymer and the non-swellable polymer are mixed in a weight ratio in the range of 6: 4 to 1: 9, preferably in a weight ratio in the range of 5: 5 to 3: 7. It is preferable. Non-swellable polymers have a relatively high melting point because of their high molecular weight compared to swellable polymers. In this case, the non-swellable polymer is preferably a resin having a melting point of 180 ° C. or higher, and the swellable polymer is preferably a resin having a melting point of 150 ° C. or lower, preferably in the range of 100 to 150 ° C.

The swellable polymers usable in the present invention are resins in which swelling occurs in the electrolyte, and can be formed into ultrafine nanofibers by electrospinning. For example, polyvinylidene fluoride (PVDF), poly (vinylidene fluoride-co-hexa) Fluoropropylene), perfuluropolymer, polyvinylchloride or polyvinylidene chloride and copolymers thereof and polyethylene glycol derivatives including polyethylene glycol dialkyl ether and polyethylene glycol dialkyl ester, poly (oxymethylene-oligo- Oxyethylene), polyoxides including polyethylene oxide and polypropylene oxide, polyvinylacetate, poly (vinylpyrrolidone-vinylacetate), polystyrene and polystyrene acrylonitrile copolymers, polyacrylonitrile methyl methacrylate copolymers Polyacrylonitrile containing Trill copolymers, polymethylmethacrylates, polymethylmethacrylate copolymers, and mixtures thereof.

In addition, the heat-resistant or non-swellable polymer that can be used in the present invention can be dissolved in an organic solvent for electrospinning, and swelling is slower or swelling than the swelling polymer by an organic solvent included in the organic electrolyte, and the melting point is 180 ° C. As the above resin, for example, polyacrylonitrile (PAN), polyamide, polyimide, polyamideimide, poly (meth-phenylene isophthalamide), polysulfone, polyetherketone, polyethylene terephthalate, poly Aromatic polyesters such as trimethylene telephthalate, polyethylene naphthalate and the like, polyphosphazenes such as polytetrafluoroethylene, polydiphenoxyphosphazene, poly {bis [2- (2-methoxyethoxy) phosphazene]} Copolymers, cellulose acetates, cellulose acetates, including polyurethanes and polyetherurethanes Sites butyrate, and the like can be used cellulose acetate propionate.

On the other hand, the porous nanofiber web 15 is obtained by spinning a spinning solution in which a swellable polymer alone or a mixed polymer in which a swellable polymer and a heat resistant or non-swellable polymer are mixed is dissolved, and the air electrospinning (AES) shown in FIG. It is desirable to radiate using air-electrospinning equipment.

The spinning methods usable in the present invention include, in addition to air electrospinning (AES), electrospinning, electrospray, electroblown spinning, centrifugal electrospinning, and flash electrospinning (flash). electrospinning).

For example, the porous nanofiber web 15 produced by air electrospinning (AES) has a thickness of 5 to 50 μm, preferably 10 to 25 μm, more preferably 10 to 15 μm. Do. When the thickness of the porous nanofiber web 15 is less than 5 μm, not only manufacturing is difficult but also the thickness becomes too thin, and a short may occur. When the thickness exceeds 50 μm, the thickness of the polymer electrolyte is also increased to increase the ions. The conductivity will drop.

The nanofibers 150 forming the porous nanofiber web 15 preferably have a diameter of 50 nm to 2 μm.

When the diameter of the nanofibers 150 is less than 50 nm, it is difficult to manufacture, and when the diameter of the nanofibers is greater than 2 μm, the thickness of the porous nanofiber web 15 also becomes a thick film.

The porosity of the porous nanofiber web 15 is set in the range of 60 to 80%, and the Gurley second is preferably 5 to 30 seconds.

The inorganic particles contained in the porous nanofiber web 15 in a small amount are Al ₂ O ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , SiO ₂ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O _{4, Sn 2 P 2 O 7} , Sn 2 B 2 O 5, Sn 2 BPO 6 and can be used at least one member selected from among those of the respective mixtures.

The content of the inorganic particles to be added is preferably contained in the range of 10 to 25% by weight when the size of the inorganic particles is between 10 to 100nm. More preferably, the inorganic particles are contained in the range of 10 to 20% by weight, and the size is in the range of 15 to 25 nm.

When the content of the inorganic particles is less than 10% by weight, the film does not maintain the shape, shrinkage occurs, the desired heat resistance characteristics are not obtained, and when it exceeds 25% by weight, the radiation trouble phenomenon that the tip of the spinning nozzle is contaminated occurs. The solvent volatilization is fast and the film strength is lowered.

In addition, when the size of the inorganic particles is less than 10nm, the volume is too large and difficult to handle, and when it exceeds 100nm, the phenomenon that the inorganic particles are agglomerated occurs a lot of exposed outside the fiber causes the strength of the fiber is lowered.

The gel polymer portion 17 of the polymer electrolyte 5 is polymerized with the gel polymer forming monomer in a state where the porous nanofiber web 15 is sandwiched between the positive electrode 1 and the negative electrode 3 and integrated into a case. After filling the organic electrolyte solution in which the initiator is mixed, the gel polymer in the gel state is synthesized by the polymerization reaction of the monomer through the gelation heat treatment step.

That is, the gel polymer electrolyte of the present invention is formed by polymerizing the above-mentioned monomer for gel polymer formation according to a conventional method. For example, the gel polymer electrolyte may be formed by in-situ polymerization of a monomer for forming a gel polymer in an electrochemical device.

In-situ polymerization in the electrochemical device is carried out through thermal polymerization, the polymerization time takes about 20 minutes to 12 hours, the thermal polymerization temperature may be 40 to 90 ℃.

To this end, the organic electrolyte contained in the porous nanofiber web 15 includes a non-aqueous organic solvent and a solute of lithium salt, a monomer for forming a gel polymer, and a polymerization initiator.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone may be used. The carbonate may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC) , Propylene carbonate (PC), butylene carbonate (BC) and the like can be used, the ester is butyrolactone (BL), decanolide (decanolide), valerolactone (valerolactone), mevalonolactone (mevalonolactone ), Caprolactone (caprolactone), n-methyl acetate, n-ethyl acetate, n-propyl acetate and the like can be used, the ether may be dibutyl ether and the like, the ketone is polymethyl vinyl ketone However, the present invention is not limited to the type of non-aqueous organic solvent, and may be used by mixing one or more kinds.

In addition, the lithium salt acts as a source of lithium ions in the battery to enable operation of the basic lithium battery, for example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiSbF ₆ , LiCl, LiI, LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2x + 1} SO ₂ ), wherein x and y are natural water and LiSO ₃ CF ₃ includes one or more or mixtures thereof.

As the monomer for forming the gel polymer, for example, a methyl methacrylate (MMA) monomer necessary for forming polymethyl methacrylate (PMMA) by a polymerization reaction may be used.

The gel polymer forming monomer may be any monomer as long as the polymer forms a gel polymer while the polymerization reaction is carried out by a polymerization initiator. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethacrylate (PMA), polymethyl methacrylate (PMMA) Or the polyacrylate which has two or more functional groups, such as a monomer with respect to the polymer, polyethyleneglycol dimethacrylate, and polyethyleneglycol acrylate, can be illustrated.

The gel polymer forming monomer is preferably used in an amount of 1 to 10% by weight based on the organic electrolyte. If the content of the monomer is less than 1, it is difficult to form a gel electrolyte, and if it exceeds 10% by weight, there is a problem of deterioration of life.

The polymerization initiator may be included in 0.01 to 5% by weight based on the monomer.

Examples of the polymerization initiator include organic peroxides and hydroperoxides such as Benzoyl peroxide (BPO), Acetyl peroxide, Dilauryl peroxide, Di-tertbutylperoxide, Cumyl hydroperoxide, and Hydrogen peroxide, and 2,2-Azobis (2-cyanobutane), 2 2-Azobis (Methylbutyronitrile), AIBN (Azobis (iso-butyronitrile), AMVN (Azobis)

azo compounds such as dimethyl-Valeronitrile). The polymerization initiator is decomposed by heat to form radicals, and reacts with the monomer by free radical polymerization to form a gel polymer electrolyte, that is, a gel polymer portion 17.

In the present invention, the gel polymer electrolyte forming the gel polymer part 17 is preferably made of a polymer having excellent conductivity so as to serve as a path for transporting lithium ions that are oxidized or reduced at the cathode and the anode during charging and discharging of the battery. Do.

In this case, since the gel polymer forming monomer proceeds rapidly to form a gel polymer, the porous nanofiber web 15 maintains the web shape.

The organic electrolyte according to the present invention may optionally contain other well-known additives and the like, in addition to the above components.

On the other hand, the present invention, as shown in the second embodiment shown in Figure 2, the inorganic porous polymer film 5a of the ultra-thin film laminated on one side or both sides of the inorganic polymer electrolyte type 5 of the first embodiment used as an adhesive layer ) May be included.

The structure of the second embodiment is first singulated or mixed by air electrospinning (AES) using, for example, a multi-hole spinning pack in which the spinning nozzles are spaced along the direction of travel of the collector. After forming the first porous nanofiber web 15 using the first spinning solution in which the polymer is dissolved, the second porous film of the thin film using the second spinning solution in which the single polymer is dissolved is first porous nano. It is laminated on top of the fibrous web 15 to form first and second porous nanofiber webs of two-layer structure.

The polymer used to prepare the second spinning solution is a polymer resin that swells in the electrolyte and is capable of conducting lithium ions and has excellent adhesion, and includes PVDF (polyvinylidene fluoride) and PEO (Poly-Ethylen Oxide) One of PMMA (polymethyl methacrylate) and TPU (Thermoplastic Poly Urethane) may be used, and a polymer having excellent swelling and excellent ion conductivity and adhesiveness, such as PVDF, is preferable.

Subsequently, in a subsequent step, the first and second porous nanofiber webs having a two-layer structure are heat-treated to face each other through an infrared lamp heater set at a temperature slightly lower than the melting point of the second porous nanofiber web. 2 The porous nanofiber web is converted to the inorganic porous polymer film 5a to obtain a laminated structure of the first porous nanofiber web 15 and the inorganic porous polymer film 5a.

The inorganic porous polymer film 5a is preferably formed into a thin film having a thickness of 2 to 5 μm, and when the thickness is less than 2 μm, the function of the adhesive layer is weak. The conductivity becomes low.

After forming the electrode assembly and filling the electrolyte using the composite porous separator in which the first porous nanofiber web 15 and the inorganic porous polymer film 5a are stacked, the gelation heat treatment process is performed. A polymer electrolyte is formed.

Hereinafter, a method of manufacturing a lithium polymer secondary battery according to the present invention will be described with reference to FIGS. 3 to 6.

3 is a cross-sectional view showing a manufacturing process of a porous separator used as a matrix of a polymer electrolyte according to the present invention, FIG. 4 is a cross-sectional view showing a sealing process of a positive electrode and a porous separator according to the present invention, and FIG. 5 is according to the present invention. Schematic cross-sectional view of an assembled electrode assembly, FIG. 6 is a schematic plan view of an electrode assembly assembled according to the present invention.

In the present invention, first, the nanofiber web 15 used as the porous separator as shown in FIG. 3 is manufactured by, for example, air electrospinning (AES).

That is, the collector is applied by applying a high voltage electrostatic force of 90 to 120 Kv between the spinning nozzle 24 and the collector 26 to which a single or mixed polymer spinning solution with sufficient viscosity is radiated using the air spray electrospinning device shown in FIG. 3. Ultrafine nanofibers 150 are spun on 26 to form a porous nanofiber web 15, in which case the spun nanofibers 150 are sprayed by injecting air 24a for each spinning nozzle 24. (26) will not be captured and catches flying.

In the present invention, the mixed polymer spinning solution is prepared by adding 40-90 wt% non-swellable polymer material and 10-60 wt% swellable polymer material to a two-component solvent or a one-component solvent. In this case, the solvent used for the mixed spinning solution is preferably a two-component solvent in which a boiling point (BP) is mixed with a high boiling point.

When using a mixed polymer, the air spray electrospinning apparatus used in the present invention uses the mixing motor 22a using pneumatic pressure as a driving source to prevent phase separation until the heat-resistant polymer material and the swellable polymer material are mixed with a solvent and spinning. Mixing tank (21) with a built-in stirrer 22, and a plurality of spinneret (24) connected to the high-voltage generator is a multi-hole nozzle pack (not shown) arranged in a matrix form. The mixed spinning liquid discharged from the mixing tank 21 to the plurality of spinning nozzles 24 connected through the metering pump and the transfer pipe 23 not shown is passed through the spinning nozzles 24 charged by the high voltage generator, and the nanofibers The nanofibers 150 are accumulated on a grounded collector 26 in the form of a conveyor which is discharged to 150 and moves at a constant speed to form a porous nanofiber web 15.

In this case, in the present invention, the transfer sheet 25a having a high tensile strength is transferred from the transfer roll 25 to the upper part of the collector 26 of the air spray electrospinning apparatus so as to improve the workability of the subsequent process and the positive electrode encapsulation process described later. The continuous nano fiber web 15 is formed by laminating the upper portion of the transfer sheet 25a.

The transfer sheet 25a may be, for example, a polyolefin-based film such as nonwoven fabric, PE, PP, or the like, which is made of paper or a polymer material that is not dissolved by a solvent contained therein when spinning a mixed spinning solution. . In the case of the porous nanofiber web 15 itself, the tensile strength is low, so that the drying process, the calendering process, and the winding process are difficult to be carried out at a high feed rate.

Moreover, after the porous nanofiber web 15 is produced, the subsequent encapsulation process with the positive or negative electrode is difficult to be carried out continuously with a high feed rate, but when the transfer sheet 25a described above is used, sufficient tensile strength is provided. The processing speed can be greatly increased.

In addition, when only the porous nanofiber web 15 is used, the phenomenon of sticking to other objects occurs due to static electricity, resulting in poor workability, but when the transfer sheet 25a is used, this problem can be solved.

The transfer sheet 25a is subjected to roll pressing with an electrode as shown in FIG. 4, and then peeled off and removed.

After preparing the spinning solution as described above using a multi-hole nozzle pack to proceed the spinning by air electrospinning (AES: Air-electrospinning) method of the ultra-fine nanofibers 150 of 0.3 ~ 1.5um diameter is made, Simultaneously with the generation of the nanofibers, porous nanofiber webs 15 fused and stacked in a three-dimensional network structure are formed on the transfer sheet 25a. Porous nanofiber web 15 made of ultrafine nanofibers is an ultra-thin, ultra-light, high surface area ratio to volume, and has a high porosity.

The porous nanofiber web 15 obtained as described above is then passed through a pre-air dry zone by the preheater 28 and the solvent and water remaining on the surface of the porous nanofiber web 15. After going through the process of adjusting the amount of calendering process using a heat compression roller 29 is made.

Pre-Air Dry Zone by the preheater 28 is a solvent remaining on the surface of the porous nanofiber web 15 by applying air of 20 ~ 40 ℃ to the web using a fan (fan) By controlling the amount of moisture and the porous nanofiber web 15 is to control the bulky (bulky) to increase the strength of the membrane and at the same time it is possible to control the porosity (Porosity).

In this case, if calendering is performed in a state in which the volatilization of the solvent is excessive, the porosity increases but the strength of the web decreases. On the contrary, when the volatilization of the solvent decreases, the web melts.

In the calendering process of the porous nanofiber web 15 subsequent to the above-described drying process, the heat compression roller 29 is used, and in this case, if the calendering temperature is too low, the web is too large. If it is bulky and has no rigidity and is too high, the web melts and the pores are blocked. In addition, thermocompression should be performed at a temperature that can completely volatilize the solvent remaining on the web, and if the volatilization is performed too little, the web will melt.

In the present invention, the heat compression roller 29 is set to a temperature of 170 to 210 ° C. and a pressure of 0 to 40 kgf / cm ² (excluding the self-weight pressure of the compression roller) to proceed with calendering of the porous nanofiber web 15. By performing the first line shrinkage, it is possible to maintain the stabilization of the porous nanofiber web 15 in actual use.

If the heat-resistant polymer and the swellable polymer are, for example, a combination of PAN and PVdF, respectively, the calendering temperature and pressure are as follows:

PAN and PVdF combination: 170 ~ 210 ℃, 20 ~ 30kgf / cm ²

When the calendering process of the nanofiber web is made, a porous nanofiber web 15 having a thickness of 5 to 50 μm is obtained.

In addition, in the present invention, the porous nanofiber web 15 obtained after the above-described calendering process, if necessary, preferably has a residual solvent or a secondary hot air dryer 30 having a temperature of 100 ° C. and a wind speed of 20 m / sec. After the process of removing water, the transfer sheet 25a is wound around the winder 31 as a winding roll of the porous nanofiber web 15 with the transfer sheet 25a disposed inside.

Hereinafter, an electrode encapsulation step and a battery assembling step will be described with reference to FIGS. 4 and 7.

Referring to FIG. 4, one of the positive electrode 1 and the negative electrode 3 may be encapsulated by an encapsulation process using two porous nanofiber webs 15 as a separator. In the description of the embodiment, the sealing of the positive electrode 1 will be described by way of example.

First, the positive electrode 1 double-sides the slurry including the positive electrode active materials 11b and 11c to form a bi-cell (or full cell) in the strip-shaped positive electrode current collector 11a and roll-presses the plurality of unit positive electrode cells. (1a-1d) forms the anode strip (1n) formed sequentially, and winding it to the reel using a winding machine (S11).

In addition, the negative electrode 3 is formed in a bi-cell (or full cell) structure in the same manner as the positive electrode (S11), and separated into individual unit negative electrode cells (S14), and the plurality of unit negative electrode cells 3a- as shown in FIG. Prepare 3c).

The anode strip 1n is blanked from the anode strip 1n by blanking (ie, punching) using a blanking equipment before winding to the reel or before the encapsulation process shown in FIG. 4 is started. The plurality of unit positive electrode cells 1a-1d are partially separated, leaving portions for forming the positive electrode terminal 11x (S12).

In addition, in the blanking process, the unit strip is transported by one unit process length according to the step-by-step method transfer of the anode strip 1n, and then blanking is performed for each unit process, and thus, between adjacent unit anode cells 1a-1d. By forming a plurality of perforations and forming a space between the unit anode cells 1a-1d and the masking tape attaching regions formed on both sides thereof, each unit anode cell 1a-1d has a constant area such as a rectangle or a square. It has a rectangular shape and punches to be interconnected.

Thereafter, as shown in FIG. 4, the pair of porous nanofiber webs 15a are disposed on the upper and lower portions of the positive electrode strip 1n and the pair of porous nanofiber webs 15a and 15b respectively stacked on the transfer sheets 15c and 15d. 15b) and the positive electrode strip 1n are subjected to roll pressing with heat and pressure while continuously passing the roll pressing apparatus 33 composed of a pair of hot pressing rolls 33a and 33b (S13).

In this case, the pair of porous nanofiber webs 15a and 15b have a strip shape having a width wider by a predetermined length than the width of the anode strip 1n, as shown in FIG. Preferably, the pair of porous nanofiber webs 15a and 15b are set equal to the width of the unit cathode cells 3a-3c. In Fig. 6, 11x indicates a positive terminal and 13x indicates a negative terminal.

Further, after the roll pressing for encapsulation of the unit anode cells 1a-1d, the transfer sheets 15c and 15d are peeled off and removed from the porous nanofiber webs 15a and 15b as shown in FIG.

As a result, the pair of porous nanofiber webs 15a and 15b sequentially encapsulate a plurality of unit anode cells 1a-1d of the anode strip 1n by a roll-to-roll method. The sealing can be made to have a high productivity.

In the above description of the embodiment, a plurality of unit anode cells 1a-1d are sequentially encapsulated using a pair of porous nanofiber webs 15a and 15b as separators, but may be encapsulated in another manner. .

Subsequently, for example, as shown in FIG. 5, the unit cathode cells 3a-3c are stacked between the plurality of unit anode cells 1a-1d encapsulated with the porous nanofiber web 15 to form the electrode assembly 100. ) Is formed (S15), and taped with a pressing band 101 made of a material having excellent tensile strength without swelling in the organic solvent to surround the outside of the electrode assembly 100 (S16).

In general, an electrode assembly 100 in which a plurality of unit cathode cells and a unit cathode cell are stacked in a lithium ion polymer battery has a problem that expansion and contraction occurs in the stacking direction of cells due to expansion inside thereof during charging and discharging. If this operation is repeated, the liquid electrolyte impregnated in the electrode is impregnated with the electrolyte and separation between the electrode and the electrolyte occurs. As a result, the interface resistance gradually increases, resulting in a decrease in the open circuit voltage (OCV). There is.

In the present invention, as described above, the outside of the electrode assembly 100 is taped with the thin film pressing band 101 made of a non-swellable material, so that the expansion and contraction of the electrode assembly 100 during charging and discharging proceeds. It is possible to reduce the OCV (open circuit voltage) by minimizing the increase in interfacial resistance by inducing the lateral direction instead of the vertical direction to prevent separation between the electrolyte and the electrode.

Furthermore, in the present invention, a part of the swellable polymer is filled in the positive electrode 1 and the negative electrode 3 in a continuous state with the polymer electrolyte 5 so that the positive electrode 1 and the negative electrode 3 and the Adhered to the polymer electrolyte 5, the reduction of the OCV (open circuit voltage) can be minimized.

The pressing band 101 may be, for example, an olefin-based film such as PP / PE or PE / PP / PE nonwoven fabric or PET film available from Celgard, and a thin ceramic.

In the exemplary embodiment illustrated in FIG. 5, a structure in which a large capacity electrode assembly 100 is formed by stacking unit cathode cells 3a-3c between a plurality of unit anode cells 1a-1d by a Z folding method is described. In addition, the present invention is not limited thereto. Alternatively, the electrode assembly 100 may be formed and taped to the compression band 101.

In this case, the pressure band 101 may be taped in a state in which at least one strength reinforcing plate is assembled to one side or both sides of the electrode assembly 100.

For example, instead of unit anode cells 1a-1d, a plurality of unit cathode cells 3a-3c are continuously encapsulated using a pair of porous nanofiber webs 15a, 15b, and then a plurality of unit cathodes are used. The unit anode cells 1a-1d may be stacked between the cells 3a-3c to form a large electrode assembly 100.

In addition, the porous nanofiber webs 15a and 15b may be sandwiched between the anode 1 and the cathode 3 and integrated by a heating lamination process, and then laminated or rolled to assemble into a case.

Furthermore, after bonding the porous nanofiber webs 15a and 15b to one surface of the anode 1 and the cathode 3, respectively, the anode 1 and the cathode 3 having the porous nanofiber webs 15a and 15b formed on one surface thereof. ) May be laminated and integrated by a heat lamination process, and then laminated or rolled to assemble into a case.

Subsequently, the electrode assembly 100 taped with the pressing band 101 is embedded in a case (not shown) (S17), and the heat treatment is performed to induce gelation by a polymerization reaction after injecting the above-described organic electrolyte solution and sealing. (S18, S19).

The gelation heat treatment process is injected into the organic electrolyte, and then heated to a condition of 20 minutes to 720 minutes at a temperature of 40 ℃ to 90 ℃ and then cooled.

In the present invention, since the porous nanofiber webs 15a and 15b disposed between the anode 1 and the cathode 3 are porous separators having a three-dimensional pore structure, impregnation is made very quickly when the organic electrolyte is injected.

In this case, the gel polymer forming monomer proceeds rapidly with the polymerization initiator to form a gel polymer, but the porous nanofiber web 15 maintains the web shape.

As a result, the polymer electrolyte 5 is gelated in a state where the gel polymer forming monomer is impregnated into the pores of the porous nanofiber web 15 to form the gel polymer portion 17, thereby forming a liquid organic solvent as a whole. The porous nanofiber web 15 maintains its shape as a matrix without swelling in the electrolyte while forming a gel electrolyte of an inorganic pore type that is substantially free of residual.

As a result, the gel polymer portion 17 in the gel state functions as a lithium ion conductor that carries lithium ions that are oxidized or reduced in the negative electrode 3 and the positive electrode 1 during charging and discharging of the battery, and the porous nano The fibrous web 15 serves as a separator that physically isolates the positive electrode 1 and the negative electrode 3, thereby preventing short circuits between the positive electrode and the negative electrode, thereby improving safety.

In this case, as part of the gel polymer penetrates into the positive electrode 1 and the negative electrode 3 through the gelation process, the interfacial resistance between the electrode and the polymer electrolyte 5 decreases and the polymer electrolyte ( 5) can be thinned.

Porous nanofiber web 15 of the present invention, by impregnating the injected organic electrolyte quickly and uniformly, the battery characteristics can be uniformly expressed over the entire electrolyte membrane.

In the above description of the embodiment, but using a single layer of the porous nanofiber web 15 made of nanofibers 150 to form a polymer electrolyte (5) as a separator, the present invention is not limited thereto, but the multilayer structure Composite porous separators can be used.

8 and 9 are cross-sectional views showing an example of the composite porous separator according to the present invention.

First, as shown in FIG. 8, the composite porous separator 210 according to the present invention is used as a matrix and has an adhesive layer on at least one side of the porous nonwoven fabric 211 and the porous nonwoven fabric 211 having micropores. And a porous nanofiber web 213 impregnated with an organic electrolyte solution.

The porous nonwoven fabric 211 which can be used as the substrate is a nonwoven fabric made of a double structured PP / PE fiber coated with PE on the outer circumference of the PP fiber as a core, or a PET nonwoven fabric made of polyethyleneterephthalate (PET) fiber and cellulose fiber. Any one of the nonwovens may be used.

The porous nonwoven fabric 211 has a porosity in the range of 70 to 80, the thickness of the porous nonwoven fabric is preferably set to 10 to 40um range.

The porous nanofiber web 213 stacked on one side of the porous nonwoven fabric 211 is inserted between the cathode and the anode (not shown) to serve as an adhesive layer that is easily bonded to the cathode when assembly is performed. To this end, the porous nanofiber web 213 may be a polymer obtained by electrospinning a polymer having excellent adhesion with a negative electrode active material, for example, PVDF (polyvinylidene fluoride).

In addition, since the porous nonwoven fabric 211 has too large pores, as shown in the separation membrane 210a of the embodiment shown in FIG. 9, the porous nanofiber web 213 is used instead of the porous nanofiber web 213 to lower the porosity. It is preferable to convert the inorganic porous polymer film to apply the ultra-thin inorganic porous film 213a.

The porous nanofiber web 213 and the inorganic porous film 213a are swollen in the electrolyte and are polymers capable of conducting electrolyte ions, for example, PVDF (polyvinylidene fluoride) and PEO (poly-ethylene oxide) , PMMA (polymethyl methacrylate), TPU (Thermoplastic Poly Urethane) can be used.

In particular, the PVDF is most preferred as a polymer having a swelling property to the electrolyte and capable of conducting electrolyte ions and excellent adhesion to the negative electrode active material.

The PVDF may be, for example, a CTFE-based PVDF copolymer containing 15-20 wt% of CT (Chlorotrifluoroethylene) in VF (vinylidene fluoride), or an HFP system containing 4-12 wt% of HFP (hexafluoropropylene) in VF (vinylidene fluoride) More preferred is a PVDF copolymer.

The CTFE-based PVDF copolymer cannot produce PVDF copolymer when it contains less than 15 wt% of CTFE comonomer, and the heat resistance of the PVDF copolymer becomes poor and too soft when it contains more than 20 wt% of CTFE comonomer. There is a problem that is difficult to use as a separation membrane because of too much absorption.

In addition, when the HFP-based PVDF copolymer contains less than 4wt% of HFP comonomer, it is impossible to manufacture the PVDF copolymer, and when the HFP comonomer exceeds 12wt%, the heat resistance of the PVDF copolymer is weakened and thus used as a separator. This is a difficult problem.

The above CTFE based PVDF copolymer can use Solef ^® 32008 in Solvay Solef ^® PVDF Fluoropolymer Resins supplied by Solvay Solexis, and the HFP based PVDF copolymer can be used in Solvay Solef ^® PVDF Fluoropolymer Resins in Solef ^® 21216 or ARKEMA KYNAR ^® PVDF Fluoropolymer You can use KYNAR FLEX LBG among the rests.

The CTFE-based PVDF copolymer and the HFP-based PVDF copolymer each contain CTFE or HFP when forming a copolymer, and thus, when the PVDF copolymer is used as a separator, ionic conductivity is higher than that of PVDF made of homopolymer of VF (vinylidene fluoride). There is an advantage that is improved.

In addition, the porous nanofiber web 213, for example, swelling in the electrolyte solution and dissolved the polymer capable of conducting the electrolyte ions in a solvent to form a spinning solution, as shown in Figure 10, multi-hole nozzle pack The ultra-fine nanofibers 215 are electrospun on one side of the porous nonwoven fabric 211 using the spinning solution 221 to collect the ultrafine fibers on the porous nonwoven fabric 211 to form a porous nanofiber web.

The porous nanofiber web 213 forms a porous nanofiber web made of ultrafine nanofibers 215, and is formed by calendering the obtained porous nanofiber web at a temperature below the melting point of the polymer in the calender device 226.

The inorganic porous film 213a may be formed by first forming a porous nanofiber web 213 on one side of the porous nonwoven fabric 211, and then, at a temperature lower than a melting point of the polymer (eg, PVDF) in a subsequent process. The porous nanofiber web 213 may be converted into the inorganic porous film 213a by heat-treating the surface using the heater 225.

In the heat treatment process, the heat treatment temperature may be performed at a temperature slightly lower than the melting point of the polymer because the solvent remains in the polymer nanofiber web.

The average diameter of the fibers constituting the porous nanofiber web 213 has a great influence on porosity and pore size distribution. The smaller the fiber diameter, the smaller the pore size and the smaller the pore size distribution. In addition, as the diameter of the fiber is smaller, the specific surface area of the fiber is increased, thereby increasing the electrolyte retention capacity, thereby reducing the possibility of electrolyte leakage.

The fiber diameter constituting the porous nanofiber web 213 is in the range of 0.3 ~ 1.5um. The thickness of the porous nanofiber web 213 used to form the inorganic porous film is preferably made of an ultra-thin film in the range of 1 to 10 μm, preferably 3 to 5 μm.

Porous nanofiber web made of ultra-fine fibers is ultra thin, ultra-light, has a high surface area to volume ratio and high porosity.

The inorganic porous film 213a applied to the above embodiment is capable of conducting lithium ions while being swelled by the electrolyte when impregnated with the organic electrolyte and is composed of an ultra-thin film, and thus does not act as a resistance, and the mobility of lithium ions is increased. Done.

When the electrode assembly film 213a is compressed to be in close contact with the surface of the negative electrode active material layer as described above, the electrode is swelled by the electrolyte and conducts lithium ions, but the space between the negative electrode and the separator 201a is performed. Blocking formation can prevent lithium ions from accumulating and depositing into lithium metal. As a result, dendrite formation can be suppressed on the surface of the cathode and stability can be improved.

The spinning solution prepared for forming the porous nanofiber web 213 by electrospinning may include a predetermined amount of inorganic particles to increase heat resistance and strength. The inorganic particles and the content are applied in the same manner as when forming the porous nanofiber web 15.

The composite porous separators 210 and 210a are applied to a lithium polymer battery including a positive electrode, a gel polymer electrolyte, and a negative electrode.

Using the composite porous membranes 210 and 210a as described above, as shown in FIG. 1 or 5, the electrode assembly is encapsulated, and an anode and a cathode are assembled. Then, the electrode assembly is cascaded and an organic electrolyte is injected, followed by gelation heat treatment. The gel polymer electrolyte is formed between the positive electrode and the negative electrode.

In this case, after assembling the electrode assembly, it is placed in an aluminum or aluminum alloy can or a similar container, and the opening is closed with a cap assembly, followed by injecting an organic electrolyte solution in which a gel polymer forming monomer and a polymerization initiator are mixed. The web 213 or the non-porous film 213a is swollen with the electrolyte and gelled.

A portion of the porous nanofiber web 213 or the inorganic porous film 213a in which the swelling is pushed into the large pores of the porous nonwoven fabric 211 blocks the pore inlet of one side of the porous nonwoven fabric 211 to lower porosity.

In particular, the thickness of the inorganic porous film 213a laminated on the porous nonwoven fabric 211 is made of an ultra-thin film of 1 to 10um range, preferably 3 to 5㎛ each, so that when the electrolyte is injected and impregnated, the micropores Is formed to allow the movement of lithium ions. As a result, OCV characteristics can be greatly improved without micro shorts occurring.

In addition, when the porous nanofiber web 213 laminated on the porous nonwoven fabric 211 is impregnated with an electrolyte solution, the nanofibers of the nanofiber webs swell about 500 times, and the pores are reduced in size to form a film. As a result, the movement of lithium ions through the micropores of the nanofiber web is possible, and the generation of micro shorts can be blocked to significantly improve the OCV characteristics.

Furthermore, in the present invention, since the porous nonwoven fabric 211 is used as a substrate, and one side of the nonwoven fabric is made of, for example, a PVDF inorganic porous film 213a, the inorganic porous film 213a having excellent adhesion has a surface of a negative electrode. Since it is in close contact with the assembly, it serves to suppress the formation of dendrite.

Hereinafter, a method of manufacturing the composite porous separator of the present invention will be described with reference to FIGS. 10 and 11.

In the composite porous membrane 210 according to the embodiment of the present invention, as shown in FIG. 10, first, a swelling is performed in an electrolyte and a spinning solution is prepared by dissolving a polymer capable of conducting electrolyte ions in a solvent.

Thereafter, the multi-hole nozzle pack 221 is used, for example, of the porous nonwoven fabric 11 to which the spinning solution is transported along the collector 223 on the lower side by air-electrospinning (AES). Ultrafine nanofibers 215 are electrospun on one side to form a porous nanofiber web 230 to form a laminate having a two-layer structure.

Air electrospinning (AES) method of the present invention is ultra-fine to the collector 223 by applying a high voltage electrostatic force of 90 ~ 120Kv between the spinneret and the collector 223 of the multi-hole nozzle pack 221 in which the polymer solution is radiated The nanofibers 215 are spun to form a porous nanofiber web 230, in this case is a spinning method that catches the flying fibers are not collected in the collector 223 by spraying air for each spinning nozzle.

When the laminate of the two-layer structure is calendered in the calender device 226 and the thickness of the laminate is controlled, the composite porous separator composed of the porous nonwoven fabric 211 and the porous polymer nanofiber web 213 as shown in FIG. 210 is obtained.

On the other hand, when manufacturing the composite porous membrane 210a according to another embodiment on one side of the porous nonwoven fabric 211, the porous nanofiber web 230 is laminated on one side of the porous nonwoven fabric 211, porous nano When the fibrous web 230 is transferred to the heater 225, the porous nanofiber web 230 is converted into the inorganic porous film 213a.

Subsequently, when the laminate of the two-layer structure is calendered in the calender device 226 and the thickness of the laminate is controlled, the composite porous separator composed of the porous nonwoven fabric 211 and the inorganic porous film 13a as shown in FIG. 210a is obtained.

However, in the manufacturing process of the composite porous membrane according to the present invention, as shown in Figure 11, the transfer sheet for transferring the spinning solution from the multi-hole nozzle pack 221 along the lower collector 223 using a transfer method The ultrafine nanofibers 215 are electrospun on one side of 211a to form a porous nanofiber web 230 made of ultrafine nanofibers.

The transfer sheet 211a may be, for example, a paper or a polyolefin-based film such as nonwoven fabric, PE, PP, or the like made of a polymer material which is not dissolved by a solvent contained therein during spinning of the spinning solution. In the case of the porous nanofiber web itself, it is difficult to carry out a drying process, a calendering process, and a winding process while being transferred at a high feed rate due to low tensile strength.

Moreover, it is difficult to carry out the encapsulation process with the positive or negative electrode subsequent to the fabrication of the porous nanofiber web continuously with a high feed rate, but in the case of using the transfer sheet 211a as described above, it provides sufficient tensile strength. Can greatly increase.

In addition, when only the porous nanofiber web is used, the phenomenon of sticking to other objects occurs due to static electricity, resulting in poor workability, but when the transfer sheet 211a is used, this problem can be solved.

Moreover, the electrospun nanofibers develop in the collector and are stacked along the pattern of the integrated part (ex. When the nanofibers are radiated onto the diamond pattern, the nanofibers begin to accumulate along the initial diamond pattern).

Therefore, in order to make a porous nanofiber web of nanofibers having good uniformity (pore size, air permeability, thickness, weight, etc.), spinning on paper is more suitable than nonwoven fabric.

In the case of calendaring by spinning directly on the nonwoven fabric, the melting point of the nonwoven fabric is limited by the control of the calendering temperature. The bonding temperature between PVdF fibers is about 150 degrees, but the melting point of nonwoven fabrics is 110 to 130 degrees. Therefore, the nanofibers are spun onto paper to form a porous nanofiber web, and the first calendering is performed at about 150 degrees, and the nonwoven fabric and the paper are formed by the second calendering at a temperature lower than the first calendering temperature. When made, it is possible to create a firm bond between fibers, creating a highly porous nanofiber web.

In addition, when forming a porous nanofiber web of nanofibers using a transfer sheet such as paper, the paper absorbs the residual solvent contained in the nanofiber web, thereby preventing the nanofibers from re-melting by the residual solvent. It can also serve to control the amount of residual solvent appropriately.

The porous nanofiber web 230 formed on the transfer sheet 211a is then laminated on one side of the porous nonwoven fabric 211 with the porous nanofiber web 230 obtained in a solvent remaining state, and the calender apparatus 226. It is also possible to form the composite porous separator 210 of the two-layer structure according to the embodiment by calendering in. The transfer sheet 211a is peeled off and removed after the lamination process as shown in FIG. 11.

In the present invention, when using a single solvent, considering that the solvent may not be volatilized well depending on the type of polymer, it passes through a pre-air dry zone by the pre-heater 225 after the spinning process. While controlling the amount of solvent and water remaining on the surface of the porous nanofiber web may be processed.

Since the membrane having a single layer or multilayer structure made of porous nanofiber web has low tensile strength, when the porous nonwoven fabric made of a nonwoven fabric having a relatively high tensile strength is used as a support, the tensile strength of the membrane can be increased.

In the above description, the composite porous separators 210 and 210a have a two-layer structure in which the porous nanofiber web 213 or the inorganic porous film 213a is laminated on one side of the porous nonwoven fabric 211. Accordingly, it is also possible to have a three-layer structure in which the porous nanofiber web 213 or the inorganic porous film 213a are laminated on both sides of the porous nonwoven fabric 211.

In this case, a part of the porous nanofiber web 213 or the inorganic porous film 213a laminated on both sides of the porous nonwoven fabric 211 may partially block the pores of the porous nonwoven fabric 211 so as to partially block the pores of the porous nonwoven fabric 211. It is embedded in the role of lowering the porosity of the porous nonwoven fabric 211, and serves as an adhesive layer to increase the adhesion between the composite porous separator (210,210a) and the cathode and anode.

When the composite porous separators 210 and 210a have a two-layer structure in which the porous nanofiber web 213 or the inorganic porous film 213a is laminated on one side of the porous nonwoven fabric 211, the porous nanofiber web 213 of the separator Alternatively, the inorganic porous film 213a is preferably assembled so that the negative electrode is adhered to the negative electrode. As a result, dendrite formation can be suppressed on the surface of the negative electrode, thereby improving stability.

In the above, the present invention has been illustrated and described with reference to specific preferred embodiments, but the present invention is not limited to the above-described embodiments, and the present invention is not limited to the spirit of the present invention. Various changes and modifications will be possible by those who have the same.

The present invention forms an electrode assembly using a porous nanofiber web as an electrolyte matrix, and then forms an gel polymer electrolyte by injecting an organic electrolyte mixture of a gel polymer forming monomer and a polymerization initiator and causing an addition polymerization reaction. Porous nanofiber web is a technology related to polymer electrolyte which can improve the safety and thinning at the same time by preventing the short circuit between anode and cathode by maintaining the web shape, and is flexible secondary like lithium polymer battery with polymer electrolyte. It can be applied to a battery.

Claims (20)

1. Separation membrane consisting of a first porous nanofiber web having a plurality of nanofibers; And

   It comprises a gel polymer portion impregnated in the first porous nanofiber web,

   The gel polymer portion is impregnated in the first porous nanofiber web and formed by a polymerization reaction of the monomer for gel polymer formation in an electrolyte containing an organic solvent, a solute of lithium salt, a monomer for gel polymer formation and a polymerization initiator. Polymer electrolyte.
2. The polymer electrolyte of Claim 1, wherein the gel polymer forming monomer is MMA (methyl methacrylate), and the gel polymer electrolyte is PMMA (polymethyl methacrylate).
3. The method of claim 1,

   Part of the gel polymer-forming monomer is a polymer electrolyte characterized in that the penetration into the inside of the positive electrode and the negative electrode disposed on both sides as the gelation by the polymerization reaction.
4. The polymer electrolyte of claim 1, wherein the first porous nanofiber web is obtained by spinning a single polymer or a mixed polymer spinning solution.
5. The polymer electrolyte according to claim 4, wherein the mixed polymer comprises a swellable polymer and a non-swellable polymer combination or a swellable polymer and a heat resistant polymer combination.
6. The polymer electrolyte of claim 1, wherein the first porous nanofiber web is made of a polymer that swells in an electrolyte and is capable of conducting electrolyte ions.
7. The polymer electrolyte of claim 6, wherein the polymer is a chlorofluorofluoro-based PVDF copolymer or a hexafluoropropylene-based PVDF copolymer.
8. According to claim 1, It is laminated on one side of the first porous nanofiber web, made of a polymer swelling in the electrolyte and excellent adhesion to the electrode, further comprising an inorganic porous polymer film layer without pores A polymer electrolyte, characterized in that.
9. The polymer electrolyte of claim 8, wherein a thickness of the first porous nanofiber web is set in a range of 5 to 50 μm, and a thickness of the inorganic porous polymer film layer is set in a range of 2 to 5 μm.
10. The method of claim 1, wherein the separation membrane

    A porous nonwoven fabric laminated on one side of the first porous nanofiber web, serving as a support, and having micropores; And

    Further comprising a second porous nanofiber web laminated on the back surface of the porous nonwoven fabric in which the first porous nanofiber web is laminated with the same structure as the first porous nanofiber web,

    A portion of the first and second porous nanofiber web is embedded in the surface layer of the porous nonwoven fabric to partially block the pores of the porous nonwoven fabric to lower the porosity of the porous nonwoven fabric.
11. A positive electrode and a negative electrode capable of occluding and releasing lithium, and a polymer electrolyte disposed between the positive electrode and the negative electrode,

    The polymer electrolyte,

    A porous separator having a plurality of nanofibers; And

    It includes a gel polymer portion impregnated in the porous separator,

    The gel polymer part is impregnated in the porous separator and formed by a polymerization reaction of the gel polymer forming monomer in an electrolyte solution containing an organic solvent, a solute of lithium salt, a monomer for forming a gel polymer and a polymerization initiator. .
12. The method of claim 11, wherein the porous separator,

    A porous nonwoven fabric serving as a support and having micropores; And

    A lithium secondary battery comprising a porous nanofiber web stacked on one side or both sides of the porous nonwoven fabric and having a plurality of electrospun nanofibers.
13. The lithium secondary battery according to claim 11, wherein the gel polymer forming monomer is MMA (methyl methacrylate), and the gel polymer electrolyte is PMMA (polymethyl methacrylate).
14. The lithium secondary battery of claim 13, wherein the diameter of the nanofibers is set in a range of 50 nm to 2 μm, and the thickness of the porous nanofiber web is set in a range of 5 to 50 μm.
15. An electrode assembly alternately stacked while separating a plurality of unit anode cells and a plurality of unit cathode cells using a pair of porous separators;

    A compression band taping the outer circumference of the electrode assembly;

    A case having an electrode assembly taped with the compression band; And

    It includes a polymer electrolyte disposed between the unit anode cell and the unit cathode cell,

    The polymer electrolyte may include a gel polymer part impregnated in the porous separator and the porous separator,

    The gel polymer part is impregnated in the porous separator and formed by a polymerization reaction of the gel polymer forming monomer in an electrolyte solution containing an organic solvent, a solute of lithium salt, a monomer for forming a gel polymer and a polymerization initiator. .
16. Dissolving a single or mixed polymer in a solvent to form a spinning solution;

    Spinning the spinning solution to form a porous separator having a plurality of nanofibers;

    Forming an electrode assembly by inserting the porous separator between an anode and a cathode each consisting of a plurality of unit electrode cells;

    Embedding the electrode assembly in a case and injecting an organic electrolyte including at least a monomer for forming a gel polymer and a polymerization initiator; And

    Performing a gelling heat treatment to polymerize the gel polymer forming monomer to form a gel polymer electrolyte,

    The porous separator is a method of manufacturing a lithium secondary battery, characterized in that to maintain the web shape.
17. The method of claim 16, wherein the gel polymer forming monomer is MMA (methyl methacrylate), and the gel polymer electrolyte is PMMA (polymethyl methacrylate).
18. The method of claim 16, wherein the gelling heat treatment is performed at a temperature in a range of 40 ° C. to 90 ° C. for 20 minutes to 720 minutes.
19. The method of claim 16, wherein forming the electrode assembly

    Forming an electrode strip by coating an electrode active material layer on at least one surface of the strip-shaped electrode current collector of any one of the positive electrode and the negative electrode;

    Performing sequential blanking while transferring the electrode strip in a step-by-step manner to partially form a plurality of first unit electrode cells from the electrode strip;

    Encapsulating the pair of porous separators on both sides while continuously transporting the plurality of first unit electrode cells; And

    And inserting and stacking a plurality of second unit electrode cells of one of the positive electrode and the negative electrode between the encapsulated plurality of first unit electrode cells, respectively.
20. Forming an electrode assembly by alternately stacking a plurality of unit anode cells and a plurality of unit cathode cells using a pair of porous separators each having a plurality of nanofibers;

    Taping the electrode assembly into a compression band;

    Embedding the electrode assembly in a case and injecting an organic electrolyte including at least a monomer for forming a gel polymer and a polymerization initiator; And

    And performing a gelation heat treatment to polymerize the gel polymer forming monomer to form a gel polymer electrolyte.

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