KR101812577B1 - A separator and an electrochemical battery comprising the separator - Google Patents

Abstract

The porous adhesive layer includes a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a (meth) acrylonitrile monomer, and a porous adhesive layer formed on one or both surfaces of the porous substrate. And an acrylic copolymer containing a monomer-derived repeating unit having a heterocyclic group, and an electrochemical cell including the separator.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator and an electrochemical cell including the separator.

The present invention relates to a separation membrane excellent in adhesion to a substrate or an electrode, and an electrochemical cell including the separation membrane.

[0002] Portable electronic devices such as video cameras, mobile phones, and portable computers are generally made lighter and more sophisticated, and thus much research has been conducted on electrochemical cells used as driving power sources. Such electrochemical cells include, for example, nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries and the like. Of these, lithium secondary batteries are used in many fields because of their small size and large size, high operating voltage, and high energy density per unit weight.

A separator for an electrochemical cell means an interlayer capable of charging and discharging the battery by keeping the ion conductivity constant while isolating the positive electrode and the negative electrode from each other in the battery.

Due to the increase of the area and / or the weight of the separator due to the enlargement of the separator in the environment in the electrochemical cell or the use of the exterior material having a weak shape preservation such as a pouch type, the separation membrane wound between the electrode and the electrode may be detached, The adhesion force of the adhesive layer tends to be weakened, and an increase in the adhesion between the separation membrane and the electrode and between the separation membrane substrate and the separation membrane adhesion layer is required.

In this connection, it has been known to form an organic / inorganic mixed coating layer on one side or both sides of a base film of a separator (Korean Patent Registration No. 10-0775310) in order to improve the adhesion between the separator and the electrode, By including the inorganic particles, the adhesive force between the separation membrane coating material and the separation membrane substrate is weakened, and the coated materials are easily peeled off from the substrate.

Therefore, it has an adhesive force applicable to a secondary battery using an external material such as a large-sized electrochemical cell or a pouch-type external appearance material, And to develop an electrochemical cell using the separator.

Korean Registered Patent No. 10-0775310 (published on November 11, 2007)

An object of the present invention is to provide a separator having an excellent ion conductivity and an excellent adhesion to a substrate, a positive electrode or a negative electrode and having excellent shape stability, and an electrochemical cell using the separator.

According to an embodiment of the present invention, there is provided a separation membrane including a porous substrate and a porous adhesive layer formed on one or both sides of the porous substrate, wherein the porous adhesive layer comprises a repeating unit derived from an alkyl (meth) acrylate monomer, There is provided a separation membrane comprising an acrylic copolymer comprising a repeating unit derived from a nitrile monomer and a repeating unit derived from a monomer having a heterocyclic group.

According to another embodiment of the present invention, there is provided a separator comprising an acrylic copolymer comprising a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer and a repeating unit derived from a monomer having a heterocyclic group , A separator having a separator having an anode adhesive strength of 350 mN / 25 mm or more and a cathode adhesive strength of 250 mN / 25 mm or more.

According to another embodiment of the present invention, there is provided an electrochemical cell, particularly a lithium secondary battery, including the separation membrane according to the above embodiments.

The separator according to an embodiment of the present invention is excellent in adhesion to a porous substrate or a negative electrode and a positive electrode, thereby preventing deterioration of the performance of the battery due to a decrease in adhesion. In addition, the electrolytic solution impregnation rate of the separator is improved, and the electrolytic solution is retained in the porous adhesive layer to have a high electrolyte ion conduction ability, thereby improving the cell performance.

1 is an exploded perspective view of an electrochemical cell according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail. Those skilled in the art will appreciate that those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

According to an embodiment of the present invention, there is provided a separation membrane including a porous substrate and a porous adhesive layer formed on one or both surfaces of the porous substrate, wherein the porous adhesive layer comprises a repeating unit derived from an alkyl (meth) acrylate monomer, There is provided a separation membrane comprising an acrylic copolymer comprising a monomer-derived repeating unit and a monomer-derived repeating unit having a heterocyclic group.

The porous substrate may have a plurality of pores and may be a porous substrate that can be used in an electrochemical device. Porous substrates include but are not limited to polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide , A polymer selected from the group consisting of polyamideimide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide and polyethylene naphthalene, or a mixture of two or more thereof It may be a polymer membrane. In one example, the porous substrate may be a polyolefin-based substrate, and the polyolefin-based substrate is excellent in shut down function, thereby contributing to safety improvement of the cell. The polyolefin-based substrate may be selected from the group consisting of, for example, a polyethylene single film, a polypropylene single film, a polyethylene / polypropylene double film, a polypropylene / polyethylene / polypropylene triple film and a polyethylene / polypropylene / polyethylene triple film. In another example, the polyolefin-based resin may include, in addition to the olefin resin, a non-olefin resin or a copolymer of an olefin and a non-olefin monomer. The thickness of the porous substrate may be from 1 탆 to 40 탆, specifically from 5 탆 to 20 탆, more specifically from 5 탆 to 16 탆. When a base film within the above-mentioned thickness range is used, it is possible to produce a separator having an appropriate thickness which is thick enough to prevent a short circuit between the positive and negative electrodes of the battery, but not thick enough to increase the internal resistance of the battery. The porosity of the porous substrate may range from 30% to 80%, specifically from 40% to 60%, and the air permeability may be 250 sec / 100cc or less, specifically 200 sec / 100cc or less, more specifically 150 sec / 100cc or less.

The porous adhesive layer may include an acrylic copolymer containing a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group. Examples of the alkyl (meth) acrylate monomers include n-butyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, (Meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, isooctyl (meth) acrylate, octyl (Meth) acrylate, lauryl (meth) acrylate, methyl (meth) acrylate, isobonyl (meth) acrylate and cyclohexyl But is not limited thereto. Specifically, straight or branched alkyl (meth) acrylates having 1 to 5 carbon atoms or alkyl (meth) acrylates having 1 to 4 straight or branched carbon atoms can be used.

The (meth) acrylonitrile monomer may be an acrylonitrile monomer or a methacrylonitrile monomer. The acrylic copolymer may contain only a repeating unit derived from an acrylonitrile monomer as the repeating unit derived from a (meth) acrylonitrile monomer, or may contain only a repeating unit derived from a methacrylonitrile monomer, or a repeating unit derived from a methacrylonitrile monomer And repeating units derived from an acrylonitrile monomer may be contained together at an arbitrary ratio.

Examples of the monomer having a heterocyclic group include acryloylmorpholine, vinylcaprolactam, tetrahydrofurfuryl (meth) acrylate, caprolactone modified tetrahydrofurfuryl (meth) acrylate, or 2,5-di And the like, but is not limited thereto.

The separator includes an acrylic copolymer containing a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group, Electrolyte impregnation property, oxidation stability, and swelling property can be improved. In particular, the swelling property means the degree to which the binder absorbs and swells the electrolyte. Although not wishing to be bound by any particular theory, it is believed that the heteroatom of the heterocyclic group has high electronegativity and therefore affinity to lithium ions in the electrolytic solution improves the electrolyte-impregnating property or swelling property of the porous adhesive layer. When the electrolyte impregnating property or the swelling property is increased, the electrolyte can be retained in the porous adhesive layer, and the electrolyte may have a high electrolyte ion conduction capability, thereby improving battery performance. Therefore, the separation membrane disclosed herein can improve the electrolyte ion conduction ability due to the high electrolyte impregnation property of the porous adhesive layer.

The acrylic copolymer may be prepared by polymerizing an alkyl (meth) acrylate monomer, a (meth) acrylonitrile monomer and a monomer having a heterocyclic group. The polymerization method is not particularly limited and a method known to a person skilled in the art can be used. For example, a method of adding a peroxide system such as ammonium persulfate or benzoyl peroxide as an initiator to deionized water, A monomer having an acrylate monomer and a heterocyclic group, a (meth) acrylonitrile monomer, and an emulsifier are charged into the reactor at an appropriate weight ratio. The temperature of the reactor may be between 65 ° C and 85 ° C and the polymerization may be carried out for 2 hours to 12 hours after the temperature is raised. In this case, the monomer having an alkyl (meth) acrylate monomer and a heterocyclic group is polymerized in a weight ratio of 9: 1 to 4: 6, specifically 8: 2 to 4: 6, more specifically 7: 3 to 5: . The weight ratio in the above range may be advantageous in terms of electrolyte impregnability, adhesion to electrodes and porous substrate.

The (meth) acrylonitrile monomer is used in an amount of 5 to 80 parts by weight, specifically 10 to 70 parts by weight, more preferably 20 to 70 parts by weight, based on 100 parts by weight of the total of the alkyl (meth) acrylate monomer and the monomer having the heterocyclic group To 60 parts by weight. If it is contained in an amount exceeding the above range, it is difficult to form an adhesive layer because it is insoluble in a solvent, and if it is contained in the above range, it may be dissolved in an electrolytic solution.

The acrylic copolymer which can be used in one embodiment of the present invention is at least one selected from the group consisting of butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate and methyl (meth) Alkyl (meth) acrylates; (Meth) acrylonitrile; A monomer having at least one heterocyclic group selected from the group consisting of tetrahydrofurfuryl (meth) acrylate and caprolactone modified tetrahydrofurfuryl (meth) acrylate. In one embodiment, the acrylic copolymer is a copolymer of butyl (meth) acrylate, methyl (meth) acrylate, (meth) acrylonitrile and tetrahydrofurfuryl (meth) acrylate in an amount of from 2.5 to 8.5: 0.5 to 1.5: 1 to 3: 1 to 6, specifically 2.5 to 7.5: 0.5 to 1.5: 1 to 3: 2 to 6, more specifically 3.5 to 6.5: 0.5 to 1.5: 1 to 3: 3 to 5 . In another embodiment, the acrylic copolymer may be prepared by polymerizing butyl methacrylate, methyl methacrylate, (meth) acrylonitrile, and tetrahydrofurfuryl (meth) acrylate, in which case 3.5 to 6 : 0.5 to 1.5: 1 to 3: 0.5 to 6, specifically 4: 1: 2: 3.

The glass transition temperature of the acrylic copolymer may be in the range of 0 ° C to 50 ° C, specifically 0 ° C to 40 ° C, more specifically 0 ° C to 15 ° C, for example, 10 ° C to 20 ° C. Within this range, the acrylic copolymer forms good adhesion with the electrode of the separation membrane or with the porous base material, thereby securing the form stability. The weight average molecular weight (Mw) of the acrylic copolymer may be 100,000 to 1,000,000. Specifically, it may be 500,000 to 1,000,000. When the acrylic copolymer within the above molecular weight range is used, the adhesion between the porous adhesive layer and the porous substrate is strengthened, and the shape stability of the separation membrane can be improved. Also, it is possible to produce a separator having a sufficiently improved impregnation property of an electrolytic solution, and it is advantageous to produce a cell in which an electric output is efficiently generated.

The separation membrane according to another embodiment of the present invention may further contain other kinds of organic binders in addition to the acrylic copolymer according to the above embodiment in the porous adhesive layer. Is substantially the same as the separator according to the embodiments of the present invention described above, except that it further includes an organic binder in the porous adhesive layer. Therefore, in the following, other binders included in addition to the acrylic copolymer will be mainly described. In the present embodiment, the adhesive strength and heat resistance of the separator can be further improved by further including another binder. Examples of the binder that can be added in addition to the acrylic copolymer include polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), etc. Of PVdF based polymer, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate (polyvinylpyrrolidone), polyvinylpyrrolidone, Cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, hydroxypropylcellulose, Cyanoethyl sucrose ( cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and acrylonitrile styrene-butadiene copolymer, or a mixture thereof. More specifically, a polyvinylidene fluoride (PVdF) homopolymer or a polyvinylidene fluoride-based copolymer may be used. The polyvinylidene fluoride copolymer may include polyvinylidene fluoride-hexafluoro Propylene (polyvinylidene fluoride-Hexafluoropropylene copolymer, PVdF-HFP). In the present invention, the polyvinylidene fluoride homopolymer refers to a polymer containing only repeating units derived from vinylidene fluoride (VdF) as a repeating unit, and the polyvinylidene fluoride copolymer includes, in addition to the repeating units derived from vinylidene fluoride (VdF) Means a polymer containing at least two or more repeating units including other types of repeating units. The PVdF binder may have a weight average molecular weight (Mw) ranging from 500,000 to 1,700,000.

The weight ratio of the acrylic copolymer to the additional binder may be 9: 1 to 4: 6. Specifically 8: 2 to 5: 5, more specifically 8: 2 to 6: 4. When used within this range, it is possible to produce an electrochemical cell having excellent shape stability while maintaining sufficient adhesion of the separator. As a result, deterioration in the performance of the produced battery can be prevented, and the battery can have charge / discharge characteristics of high efficiency.

Hereinafter, a method of manufacturing a separation membrane according to an embodiment of the present invention will be described.

First, the acrylic copolymer or the acrylic copolymer and another binder are dissolved or mixed in a solvent to prepare a porous adhesive layer composition solution. The solvent used for preparing the porous adhesive layer composition solution is not particularly limited as long as it is a solvent capable of dissolving the acrylic copolymer and other binders. Non-limiting examples of the solvent usable in the present invention include acetone, dimethyl formamide, dimethyl sulfoxide, dimethylacetamide, dimethyl carbonate or N-methylpiperazine. N-methylpyrrolidone, cyclohexane, and the like. The content of the solvent based on the weight of the porous adhesive layer composition may be 20 wt% to 99 wt%, specifically 50 wt% to 95 wt%, and more specifically 70 wt% to 95 wt%. When the solvent is contained in the above range, the production of the porous adhesive layer composition is facilitated and the drying process of the adhesive layer can be performed smoothly.

The separation membrane according to another embodiment of the present invention may further include inorganic particles in the porous adhesive layer. Is substantially the same as the separator according to the embodiments of the present invention described above, except that it further includes inorganic particles in the porous adhesive layer. Therefore, the following description will focus on the inorganic particles further included. The inorganic particles used in the present invention are not particularly limited and inorganic particles commonly used in the art can be used. Non-limiting examples of the inorganic particles usable in the present invention include Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO _2, and SnO ₂ . These may be used alone or in combination of two or more. Specifically, Al ₂ O ₃ (alumina) can be used. The size of the inorganic particles is not particularly limited, but may be an average particle diameter of 1 nm to 2,000 nm, for example, 100 nm to 1,000 nm. It is possible to prevent degradation of the dispersibility of the inorganic particles in the porous adhesive layer and the processability of forming the porous adhesive layer and to appropriately control the thickness of the porous adhesive layer, An increase in resistance can be prevented. In addition, the size of the pores generated in the porous adhesive layer is appropriately controlled, thereby reducing the probability of an internal short circuit occurring during charging and discharging of the battery.

In the porous adhesive layer, the inorganic particles may be contained in an amount of 60% by weight to 95% by weight, specifically 75% by weight to 90% by weight, more specifically 80% by weight to 90% by weight, based on the total weight of the porous adhesive layer. When inorganic particles are contained within the above range, the heat radiation characteristics of the inorganic particles can be sufficiently exhibited.

The method of forming the porous adhesive layer on the porous substrate is not particularly limited, and a method commonly used in the technical field of the present invention such as a coating method, a lamination method, and a coextrusion method can be used. Non-limiting examples of the coating method include a dip coating method, a die coating method, a roll coating method, and a comma coating method. These may be applied alone or in combination of two or more methods. The porous adhesive layer of the separator of the present invention may be formed by, for example, a dip coating method. The porous adhesive layer may be formed on one side or both sides of the porous substrate, and the thickness thereof may be in the range of 1 탆 to 10 탆, specifically 1 탆 to 6 탆.

The porous adhesive layer may have an adhesive strength to the porous substrate of 800 mN / 25 mm or more, specifically 800 mN / 25 mm to 1500 mN / 25 mm. More specifically, it may be 850 mN / 25 mm to 1500 mN / 25 mm, or 1000 mN / 25 mm to 1400 mN / 25 mm, and the adhesive force may be measured by a known method. For example, it can be measured by the following method, but is not limited thereto: It is tested according to 8 of Korean Industrial Standard KS-A-01107 (Test Method of Adhesive Tape and Adhesive Sheet). The separator film was used as a test piece having a width of 25 mm and a length of 250 mm, and a tape (nitto 31B) was attached to each side of the separating film to complete the evaluation test piece, and the test piece was reciprocated once at a speed of 300 mm / And the specimen is squeezed. After a lapse of 30 minutes from the pressing, one side of the specimen was turned 180 ° to remove about 25 mm. The tape 31B attached to one side of the separator and separator was fixed to the upper clip of the tensile strength device, The tape 31B was fixed to the lower clip and pulled at a pulling rate of 60 mm / min to measure the pressure when the porous adhesive layer was peeled from the porous substrate. The tensile strength tester uses, for example, Instron Series IX / s Automated materials Tester-3343.

According to still another embodiment of the present invention, there is provided an acrylic copolymer comprising an acrylic copolymer comprising a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer, and a monomer derived repeating unit having a heterocyclic group As the separation membrane, a separation membrane having an anode bonding strength of 350 mN / 25 mm or more and a cathode bonding strength of 250 mN / 25 mm or more is provided.

Since the acrylic copolymer is substantially the same as that described above in the previous embodiment, the explanation will be made below regarding the anode adhesive force and the anode adhesive force of the separator.

The positive electrode or negative electrode adhesion force means an adhesion force between the separator and the anode or the cathode. Specifically, the anode adhesive force may be 350 mN / 25 mm to 500 mN / 25 mm and the anode adhesive force may be 250 mN / 25 mm to 400 mN / 25 mm. More specifically, the anode adhesive force may be 350 mN / 25 mm to 450 mN / 25 mm, May be between 250 mN / 25 mm and 300 mN / 25 mm. Within the above range, the separator and the anode or the cathode can be sufficiently bonded. Further, as the charging and discharging of the battery including the separator is repeated in the range of the adhesive force, the change of the battery shape can be minimized in the environment where the expansion and contraction of the battery are repeated, Can be improved. The anodic or cathodic adhesive strength can be measured by a known method, and in one example, it can be measured by the following method, but it is not limited thereto. The test shall be carried out in accordance with Clause 8 of Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tape and Adhesive Sheet). The separator film is used as a test piece with a width of 25 mm and a length of 250 mm, and a tape (nitto 31B) is attached to one surface of the separator to complete the test piece. On the other side of the separator, a cathode film (LCO (lithium cobalt oxide) cathode active material / binder styrene butadiene rubber (SBR) + carboxymethyl cellulose (CMC) / carbon black = 95 / 2.5 / 2.5) A film (natural graphite anode active material / binder (styrene butadiene rubber (SBR) + carboxymethyl cellulose (CMC) 5% / conductive black 98/1/1) / Min. ≪ / RTI > After a lapse of 30 minutes from the pressing, one side of the test piece was turned 180 ° to peel off about 25 mm, and a tape 31B attached to one side of the separating film and the separating film was attached to the upper clip of the tensile strength device, The film is fixed to the lower clip and pulled at a pulling rate of 60 mm / min to measure the pressure when the anode or cathode film is peeled off from the separator. The tensile strength tester uses, for example, Instron Series IX / s Automated materials Tester-3343.

According to an embodiment of the present invention, cathode; A separator disclosed herein between the anode and the cathode; And an electrolyte.

The type of the electrochemical cell is not particularly limited and may be a battery of a kind known in the technical field of the present invention.

The electrochemical cell of the present invention may specifically be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The method for producing the electrochemical cell of the present invention is not particularly limited and a method commonly used in the technical field of the present invention can be used.

A method of manufacturing the electrochemical cell is as follows: A separator comprising the porous adhesive layer of the present invention is placed between the positive electrode and the negative electrode of the battery, and then the battery is manufactured in such a manner that the electrolyte is filled in the separator. can do.

1 is an exploded perspective view of an electrochemical cell according to one embodiment. The electrochemical cell according to one embodiment is a secondary battery, and the present invention is not limited thereto, but may be applied to various types of batteries such as a pouch type battery, a lithium polymer battery, and a cylindrical battery.

Referring to FIG. 1, a secondary battery 100 according to an embodiment includes an electrode assembly 40 wound around a separator 30 between an anode 10 and a cathode 20, And a case 50 in which the case 50 is embedded. The anode 10, the cathode 20 and the separator 30 are impregnated with an electrolyte (not shown).

The separation membrane 30 is as described above.

The anode 10 may include a cathode current collector and a cathode active material layer formed on the cathode current collector. The cathode active material layer may include a cathode active material, a binder, and optionally a conductive material.

The cathode current collector may be aluminum (Al), nickel (Ni) or the like, but is not limited thereto.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Concretely, at least one of cobalt, manganese, nickel, aluminum, iron or a composite oxide or composite phosphorus of a metal and lithium in combination thereof may be used. More specifically, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate or a combination thereof may be used.

The binder not only adheres the positive electrode active materials to each other well but also adheres the positive electrode active material to the positive electrode current collector. Specific examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride , Carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like. These may be used alone or in combination of two or more.

The conductive material imparts conductivity to the electrode. Examples of the conductive material include, but are not limited to, natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, and metal fiber. These may be used alone or in combination of two or more. The metal powder and the metal fiber may be made of metals such as copper, nickel, aluminum, and silver.

The cathode 20 may include a negative electrode collector and a negative electrode active material layer formed on the negative collector.

The negative electrode current collector may be copper (Cu), gold (Au), nickel (Ni), copper alloy, or the like, but is not limited thereto.

The negative electrode active material layer may include a negative electrode active material, a binder, and optionally a conductive material.

Examples of the negative electrode active material include a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, a transition metal oxide, Can be used.

Examples of the material capable of reversibly intercalating and deintercalating lithium ions include carbonaceous materials, and examples thereof include crystalline carbon, amorphous carbon, and combinations thereof. Examples of the crystalline carbon include amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, and the like. As the lithium metal alloy, a lithium-metal alloy may be selected from the group consisting of lithium, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, An alloy of a selected metal may be used. As the material capable of doping and dedoping lithium, Si, SiO _x (0 <x <2), Si-C composite, Si-Y alloy, Sn, SnO ₂ , Sn-C composite, Sn- And at least one of them may be mixed with SiO ₂ . The element Y may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Se, Te, Po, and combinations thereof. Examples of the transition metal oxide include vanadium oxide, lithium vanadium oxide, and the like.

The kinds of the binder and the conductive material used for the cathode are the same as those used for the anode and the conductive material.

The positive electrode and the negative electrode may be prepared by mixing each active material and a binder with a conductive material in a solvent to prepare each active material composition and applying the active material composition to each current collector. The solvent may be N-methyl pyrrolidone or the like, but is not limited thereto. The method of manufacturing the electrode is well known in the art, and therefore, a detailed description thereof will be omitted herein.

The electrolytic solution includes an organic solvent and a lithium salt.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples thereof may be selected from a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent and an aprotic solvent.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate Carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Specifically, when a mixture of a chain carbonate compound and a cyclic carbonate compound is used, it can be prepared from a solvent having a high viscosity and a high dielectric constant. Here, the cyclic carbonate compound and the chain carbonate compound may be mixed in a volume ratio of 1: 1 to 1: 9.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone, decanolide, valerolactone, Mevalonolactone, caprolactone, and the like. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. Examples of the ketone-based solvent include cyclohexanone, and examples of the alcohol-based solvent include ethyl alcohol, isopropyl alcohol, and the like.

The organic solvents may be used alone or in combination of two or more. When two or more of them are used in combination, the mixing ratio may be appropriately adjusted according to the performance of the desired cell.

The lithium salt is dissolved in an organic solvent to act as a source of lithium ions in the cell to enable operation of a basic secondary cell and accelerate the movement of lithium ions between the positive electrode and the negative electrode.

For example the lithium salt _{is, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiN (SO 3 C 2 F 5) 2, LiN (CF 3 SO 2) 2, LiC 4 F 9 SO 3, LiClO 4, LiAlO 2 , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) where x and y are natural numbers, LiCl, LiI, LiB (C ₂ O ₄ ) _2, .

The concentration of the lithium salt can be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolytic solution has an appropriate conductivity and viscosity, and thus can exhibit excellent electrolytic solution performance, and lithium ions can effectively move.

Hereinafter, the present invention will be described in more detail by describing Examples, Comparative Examples and Experimental Examples. However, the following examples, comparative examples and experimental examples are merely examples of the present invention and should not be construed as limiting the scope of the present invention.

Example

Manufacturing example  1 to 4: Preparation of acrylic copolymer

Manufacturing example  One

A mixture of butyl methacrylate (BMA), methyl methacrylate (MMA), and acrylonitrile (AN) tetrahydrofurfuryl acrylate (THF-A) was added to deionized water (DIW) (APS, 98.0%) was emulsified with an emulsifying agent and sodium dodecyl sulfate sodium salt (SDS, 85.0%) was added thereto at a weight ratio of 4: 1: 4: And 0.8% by weight and 0.3% by weight based on the total weight of the monomers, respectively. Then, the mixed solution was put into a thermostatic chamber, stirred, heated to 75 캜 and reacted for 3 hours to synthesize an acrylic copolymer. The resulting emulsion was cooled to room temperature, and then added with stirring into an aqueous 2 wt% ammonium sulfate solution to obtain a precipitated polymer resin. The obtained polymer was separated from the solvent, washed with distilled water several times, and then dried to prepare an acrylic copolymer having a weight average molecular weight of 640,000 ± 50,000.

Manufacturing example  2

An acrylic copolymer was prepared in the same manner as in Preparation Example 1, except that BMA, MMA, AN, and THF-A were added at a ratio of 4: 1: 3: 2.

Manufacturing example  3

An acrylic copolymer was prepared in the same manner as in Preparation Example 1, except that BMA, MMA, AN and THF-A were added at a ratio of 4: 1: 2: 3.

Manufacturing example  4

In Production Example 1, an acrylic copolymer was prepared in the same manner as in Production Example 1, except that BMA, MMA and AN were added at a weight ratio of 4: 1: 5 without adding THF-A.

Example  1 to 4 and Comparative Example  1 to 2: Preparation of separator

Example  One

The acrylic copolymer prepared in Preparation Example 1 was dissolved in acetone to prepare an acrylic copolymer solution having a solid content of 10% by weight. The acrylic copolymer solution and the PVdF binder solution were mixed so that the weight ratio of the acrylic copolymer to the PVdF binder (KF9300, Kureha, Mw: 1,200,000) was 8: 2. Acetone was added so that the total solid content was 15% To prepare a porous adhesive layer composition. On both sides of a polyethylene fabric (SK) having a thickness of 7 占 퐉, To prepare a separation membrane having a total thickness of 9 탆.

Example  2

The separation membrane of Example 2 was prepared in the same manner as in Example 1 except that the acrylic copolymer prepared in Preparation Example 2 was used instead of the acrylic copolymer prepared in Preparation Example 1. [

Example  3

The separation membrane of Example 3 was prepared in the same manner as in Example 1, except that the acrylic copolymer prepared in Preparation Example 3 was used instead of the acrylic copolymer prepared in Production Example 1.

Example  4

In Example 3, the separation membrane of Example 4 was produced in the same manner as in Example 3, except that the PVdF binder was not used.

Comparative Example  One

A separator of Comparative Example 1 was prepared in the same manner as in Example 1, except that the acrylic copolymer prepared in Preparation Example 4 was used instead of the acrylic copolymer prepared in Preparation Example 1.

Comparative Example  2

In Example 1, a PVdF binder was dissolved in a mixed solvent of acetone and DMAc without an acrylic copolymer to prepare a binder solution having a solid content of 7 wt%, and the same procedure as in Example 1 was carried out except that the binder solution was used A separator of Comparative Example 2 was prepared.

The composition of each separator according to Examples 1 to 4 and Comparative Examples 1 and 2 is shown in Table 1 below.

Substrate / Thickness (탆) Binder composition Acrylic polymerization weight ratio Example 1 PE / 7 Acrylic / PVdF system, 8/2 BMA + MMA + AN + THF-A 4: 1: 4: 1 Example 2 PE / 7 Acrylic / PVdF system, 8/2 BMA + MMA + AN + THF-A 4: 1: 3: 2 Example 3 PE / 7 Acrylic / PVdF system, 8/2 BMA + MMA + AN + THF-A 4: 1: 2: 3 Example 4 PE / 7 Acrylic, 100% BMA + MMA + AN + THF-A 4: 1: 2: 3 Comparative Example 1 PE / 7 Acrylic / PVdF system, 8/2 BMA + MMA + AN 4: 1: 5 Comparative Example 2 PE / 7 PVdF system, 100% - -

Experimental Example

The separating films prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were measured for substrate adhesion, anodic bonding strength, anodic bonding strength and LSV by the measurement method described below. The results are shown in Table 2.

Substrate adhesion

The test was carried out in accordance with Clause 8 of Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tape and Adhesive Sheet). The separator film prepared in the above examples and comparative examples was used as a test piece having a width of 25 mm and a length of 250 mm, and a tape (nitto 31B) was attached to each side of the separation film to complete an evaluation test piece. And the test piece was pressed by using a pressing roller having a load of 2 kg once and reciprocating at a speed of 300 mm / min. After a lapse of 30 minutes from the pressing, one side of the specimen was turned 180 ° to remove about 25 mm. The tape 31B attached to one side of the separator and separator was fixed to the upper clip of the tensile strength device, The tape 31B was fixed to the lower clip and pulled at a pulling rate of 60 mm / min to measure the pressure when the porous adhesive layer was peeled from the porous substrate. The tensile strength machine used was Instron Series IX / s Automated materials Tester-3343.

Anode adhesive force

The test was carried out in accordance with Clause 8 of Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tape and Adhesive Sheet). The separator film prepared in the above Examples and Comparative Examples was used as a test piece having a width of 25 mm and a length of 250 mm and a tape (nitto 31B) was attached to one surface of the separator to complete the test piece. 2 kg of a cathode film (lithium cobalt oxide cathode active material / binder styrene butadiene rubber (SBR) + carboxymethyl cellulose (CMC) / carbon black = 95 / 2.5 / 2.5) And was reciprocated once at a speed of 300 mm / min using a pressing roller. After a lapse of 30 minutes from the pressing, one side of the test piece was turned 180 ° to peel off about 25 mm. The tape 31B attached to one side of the separating film and the separating film was attached to the upper clip of the tensile strength device, And then pulled at a pulling rate of 60 mm / min to measure the pressure when the anode film was peeled off from the separator. The tensile strength machine used was Instron Series IX / s Automated materials Tester-3343.

Cathode adhesion

The test was carried out in accordance with Clause 8 of Korean Industrial Standard KS-A-01107 (Test Method for Adhesive Tape and Adhesive Sheet). The separator film prepared in the above Examples and Comparative Examples was used as a test piece having a width of 25 mm and a length of 250 mm and a tape (nitto 31B) was attached to one surface of the separator to complete the test piece. A negative electrode film (natural graphite anode active material / binder (styrene butadiene rubber (SBR) + carboxymethyl cellulose (CMC) 5%) / conductive material (carbon black) = 98/1/1) And was reciprocated once at a speed of 300 mm / min. After a lapse of 30 minutes after the pressing, one side of the test piece was turned 180 ° to peel off about 25 mm. The tape 31B attached to one side of the separating film and the separating film was attached to the upper clip of the tensile strength device, And then pulled at a pulling rate of 60 mm / min to measure the pressure when the negative electrode film was peeled off from the separator. The tensile strength machine used was Instron Series IX / s Automated materials Tester-3343.

LSV ( Linear Sweep Voltammetry )

For the LSV evaluation, a three electrode cell was fabricated using a platinum disk electrode (d = 1 mm) as a working electrode and a lithium foil as a reference electrode (quasireference) and a counter electrode. In addition, all cells were fabricated in a dry room and measured after blocking with parafilm (NEENAH, WI 54956).

1M lithium hexafluorophosphate (LiPF ₆ ) was added to a solvent in which EC (Ethylene carbonate), EMC (Ethyl methyl carbonate) and DEC (Diethyl carbonate) were mixed in a volume ratio of 3: 5: Was used. Further, PMA, PVDF, PHFP, and PAM were added to the electrolytic solution at a weight ratio of 1%, respectively, in order to examine the change of the oxidative decomposition potential according to each polymer.

To measure the oxidative decomposition voltage of the polymer electrochemically, 1 mL of the polymer solution dissolved in the solvent is dropped on the platinum disk and the preparation is carried out at 60 ° C for 4 hours. After the preparatory work, the electrolyte was placed in a cell and connected to a potentiostat (Solatron 1470E) to reach an electrochemical equilibrium for 1 hour at the beginning. The cut-off voltage was set at 3V to 7V, The scan rate was measured at 1 mV / sec.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Base Adhesion (mN / 25mm) 1170 1180 1285 1325 790 735 Anode adhesive force (mN / 25 mm) 360 360 365 385 340 280 Cathode Adhesion (mN / 25mm) 255 256 260 272 240 120 LSV 4.7 4.6 4.5 4.4 4.8 4.9

With reference to Table 2 above, it can be seen that, with a porous adhesive layer using an acrylic copolymer containing repeating units derived from alkyl (meth) acrylate monomers, repeating units derived from (meth) acrylonitrile monomers and repeating units derived from monomers having heterocyclic groups In the case of the separation membranes of Examples 1 to 4, the substrate adhesion, the positive electrode and the negative electrode adhesion, and the LSV were all good.

Claims (22)

1. A separation membrane comprising a porous substrate and a porous adhesive layer formed on one or both sides of the porous substrate,
Wherein the porous adhesive layer comprises an acrylic copolymer comprising a repeating unit derived from an alkyl (meth) acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group,
The weight ratio of the repeating unit derived from the alkyl (meth) acrylate monomer to the repeating unit derived from the monomer having a heterocyclic group in the acrylic copolymer is 9: 1 to 4: 6, and the repeating unit derived from the (meth) acrylonitrile monomer Is contained in an amount of 5 to 80 parts by weight based on 100 parts by weight of the repeating unit derived from the alkyl (meth) acrylate monomer and the repeating unit derived from the monomer having the heterocyclic group,
The monomer-derived repeating unit having a heterocyclic group may be at least one selected from the group consisting of acryloylmorpholine, vinylcaprolactam, tetrahydrofurfuryl (meth) acrylate, caprolactone-modified tetrahydrofurfuryl (meth) Wherein the repeating unit is at least one monomer-derived recurring unit selected from the group consisting of hydrofluorocarbons and hydrofuran. The method of claim 1, wherein the repeating unit derived from the alkyl (meth) acrylate monomer is selected from the group consisting of n-butyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, (Meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (Meth) acrylate, lauryl (meth) acrylate, methyl (meth) acrylate, isobonyl (meth) acrylate and cyclohexyl (meth) Wherein the repeating unit is a repeating unit derived from a monomer. delete delete delete The separation membrane according to claim 1 or 2, wherein the weight average molecular weight of the acrylic copolymer is 100,000 to 1,000,000. The method according to claim 1 or 2, wherein the repeating unit derived from the alkyl (meth) acrylate monomer is at least one selected from the group consisting of butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) And at least one monomer-derived recurring unit selected from the group consisting of The acrylic copolymer according to claim 1 or 2, wherein the acrylic copolymer is a copolymer of butyl (meth) acrylate, methyl (meth) acrylate, (meth) acrylonitrile and tetrahydrofurfuryl (meth) 8.5: 0.5 to 1.5: 1 to 3: 1 to 6. The separation membrane according to claim 1 or 2, wherein the porous adhesive layer further comprises a binder other than the acrylic copolymer. The method of claim 9, wherein the different kind of binder is selected from the group consisting of polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride (PVdF) based copolymer, polymethylmethacrylate, Polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate, cellulose acetate, But are not limited to, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, , Carboxyl methyl cellulose e), and acrylonitrile styrene-butadiene copolymer, or a mixture thereof. The separation membrane according to claim 9, wherein the other kind of binder is selected from the group consisting of polyvinylidene fluoride (PVdF) homopolymer and polyvinylidene fluoride-based copolymer, or a mixture thereof. The separation membrane according to claim 9, wherein the weight ratio of the acrylic copolymer to the other kind of binder in the porous adhesive layer is from 9: 1 to 4: 6. The separation membrane according to claim 1 or 2, wherein the porous adhesive layer further comprises inorganic particles. The separation membrane according to claim 1 or 2, wherein the porous adhesive layer has a thickness of 1 占 퐉 to 10 占 퐉. The separator according to claim 1 or 2, wherein the adhesive strength of the porous adhesive layer to the porous substrate is 800 mN / 25 mm or more. 3. The method according to claim 1 or 2,
Wherein the separator has an anode adhesive strength of 350 mN / 25 mm or more and a cathode adhesive strength of 250 mN / 25 mm or more. delete delete The separation membrane according to claim 16, wherein the separation membrane further comprises a binder other than the acrylic copolymer. 17. The separation membrane according to claim 16, wherein the separation membrane further comprises inorganic particles. An electrochemical cell comprising an anode, a cathode, a separator according to claim 1 or 2, and an electrolyte. The electrochemical cell according to claim 21, wherein the electrochemical cell is a lithium secondary battery.

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