KR20170023605A - A separator and an electrochemical battery comprising the separator - Google Patents

Abstract

The present invention relates to a separation membrane which includes a porous substrate and a porous adhesive layer which is formed on one side or both sides of the porous substrate, wherein the porous adhesive layer includes an acrylic copolymer containing three or more alkyl (meth)acrylate monomer-derived repeating units, (meth)acrylonitrile monomer-derived repeating units and monomer-derived repeating units with heterocyclic groups, and an electrochemical battery including the separation membrane. Accordingly, the present invention can provide the separation membrane with high ion conductivity and high adhesion even when being compressed at low temperatures.

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 base material, a negative electrode and an electrode even when compressed at a low temperature, 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 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 three or more alkyl (meth) acrylate monomer- ) A separator comprising an acrylic copolymer comprising a repeating unit derived from an acrylonitrile 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 having a glass transition temperature of 5 ° C to 20 ° C, wherein the compression thickness change ratio at 70 ° C according to the following formula is 70% or more.

 [Formula 1]

(%) = [(T ₀ - T ₁ ) / T ₀ ] × 100

In the formula 1, T ₀ is the thickness of the central portion measured after 1 hour from the pressing of the electrode assembly including the separation membrane at 20 ° C and a pressure of 9.3 kgf / cm ² for 3 seconds, T ₁ is 9 kgf / cm < ² > for 10 seconds and measured after 1 hour.

According to another embodiment of the present invention, there is provided a separation membrane comprising 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 a butylmethacrylate monomer, a repeating unit derived from a methylmethacrylate monomer , A repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group are provided.

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 cathode and an anode upon compression at a low temperature, so that deterioration of performance of the battery due to deterioration of the adhesion can be prevented. 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 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 three or more alkyl (meth) acrylate monomer- There is provided a separation membrane comprising an acrylic copolymer comprising a repeating unit derived from an acrylonitrile monomer and a repeating unit derived from a monomer 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. Examples of the porous substrate include, but are not limited to, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone , A polymer selected from the group consisting of polyetherimide, polyamideimide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide and polyethylene naphthalate, or 2 Or may be a polymer membrane formed of a mixture of two or more species. 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 at least three repeating units 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 separation membrane according to the present embodiment includes an acrylic copolymer containing repeating units derived from three or more alkyl (meth) acrylate monomers, repeating units derived from (meth) acrylonitrile monomers and repeating units derived from monomers having a heterocyclic group , Substrate adhesion, electrode adhesion, electrolyte impregnation, oxidation stability, and swelling properties can be improved. Particularly, the swelling property means the extent to which the separator 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. In addition, the above-mentioned separation film contains the repeating units derived from three or more alkyl (meth) acrylate monomers in the acrylic copolymer, so that the produced acrylic copolymer has a proper glass transition temperature and is excellent in processability and room temperature stability, Good jelly roll adhesion can be obtained.

Examples of the three or more alkyl (meth) acrylate monomers include n-butyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, (Meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, isooctyl (Meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, methyl (meth) acrylate, isobornyl (meth) acrylate and cyclohexyl Or more. Specifically, three or more alkyl (meth) acrylates having 1 to 5 carbon atoms in a straight chain or a branched chain, or alkyl (meth) acrylates having 1 to 4 carbon atoms in a straight chain or branched chain 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 Hydrofuran, and the like.

The acrylic copolymer may be prepared by polymerizing three or more kinds of alkyl (meth) acrylate monomers, (meth) acrylonitrile monomers and monomers 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, specifically, a peroxide system such as ammonium persulfate or benzoyl peroxide is added as an initiator to deionized water, A monomer having a (meth) 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 three or more alkyl (meth) acrylate monomers and a heterocyclic group is used in a weight ratio of 9: 1 to 4: 6, specifically 8: 2 to 4: 6, more specifically 7: 3 to 5: 5 < / RTI > 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 10 to 70 parts by weight, based on 100 parts by weight of the total of the three or more alkyl (meth) acrylate monomers and the monomer having a heterocyclic group Specifically 5 to 25 parts by weight. In the above range, the acrylic copolymer is easily dissolved in the solvent to facilitate the formation of the adhesive layer, but may not dissolve in the electrolytic solution.

In one embodiment, the acrylic copolymer may be prepared by polymerizing butyl methacrylate, methyl methacrylate, butyl acrylate, (meth) acrylonitrile and tetrahydrofurfuryl (meth) acrylate. Specifically, the acrylic copolymer is a copolymer of butyl methacrylate, methyl methacrylate, butyl acrylate, (meth) acrylonitrile, and tetrahydrofurfuryl (meth) acrylate in an amount of from 2.5 to 8.5: 0.5 to 1.5: 3: 1 to 3: 1 to 6, specifically 2.5 to 7.5: 0.5 to 1.5: 1 to 3: 1 to 3: 2 to 6, more specifically 3.5 to 6.5: 0.5 to 1.5: 3: 3 to 5 by weight. More specifically, they can be produced by polymerization in a weight ratio of 4: 1: 1: 1: 3. Also, for example, the butyl acrylate may be mixed with 5 to 25 parts by weight of the total monomer used in the production of the acrylic copolymer to be polymerized. The electrode adhesion force and the like can be improved within the above range.

The glass transition temperature of the acrylic copolymer may be in the range of 5 ° C to 20 ° C, specifically 5 ° C to 15 ° C, more specifically 10 ° C to 15 ° C. Within this range, the acrylic copolymer can form a good adhesion with the electrode or the porous substrate of the separator to ensure the morphological stability, and it is advantageous in view of the processability in the production of the acrylic copolymer, and the stability of the prepared acrylic copolymer is good at room temperature have. In particular, an acrylic copolymer having a glass transition temperature within the above range can exhibit excellent jelly roll adhesion even when pressed at a low temperature of 70 ° C or lower.

The method of measuring the glass transition temperature of the separation membrane is not particularly limited, and a commonly used method can be used. In one example, the glass transition temperature can be measured while raising the temperature from -40 ° C to 200 ° C at a rate of 10 ° C / min using a thermomechanical analyzer (TA).

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.

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 50 wt% to 95 wt%, specifically 75 wt% to 90 wt%, more specifically 80 wt% to 90 wt%, 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.

According to still another embodiment of the present invention, there is provided a separator comprising an acrylic copolymer having a glass transition temperature of 5 ° C to 20 ° C and having a crushing thickness change ratio of 70% or more at 70 ° C according to the following formula 1.

 [Formula 1]

(%) = [(T ₀ - T ₁ ) / T ₀ ] × 100

In Equation 1, T ₀ is the thickness of the central portion measured after 1 hour from the pressing of the electrode assembly including the separation membrane according to the embodiments of the present invention at a pressure of 9.3 kgf / cm ^{2 at} a pressure of 9.3 kgf / cm ² for 3 seconds, and T ₁ is the thickness of the central portion measured after 1 hour of pressing at 70 ° C for 10 seconds under a pressure of 9 kgf / cm ² .

The compression thickness change ratio may be 70% or more, specifically 73% or more. When the rate of change of the compression thickness is within the above range, compression bonding with the electrode can be sufficiently performed when the separation membrane is compressed even at a low temperature of 70 캜, and the adhesive force to the electrode can be excellent in the state of the electrode assembly.

The glass transition temperature of the acrylic copolymer may be in the range of 5 ° C to 20 ° C, specifically 5 ° C to 15 ° C, more specifically 10 ° C to 15 ° C. The glass transition temperature is as described above in the previous embodiment.

According to another embodiment of the present invention, there is provided a separation membrane comprising 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 a butylmethacrylate monomer, a repeating unit derived from a methylmethacrylate monomer , A repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group are provided. The separation membrane according to the present embodiment has an excellent swelling degree with respect to an electrolytic solution, has a good ion conductivity and has an excellent adhesion strength to a substrate, a positive electrode or a negative electrode even when compressed at a low temperature, and has an excellent shape stability.

For the butylmethacrylate monomer, methylmethacrylate monomer, butyl acrylate monomer, (meth) acrylonitrile monomer and monomer having a heterocyclic group, the same ones as described above in the foregoing examples can be used. The copolymer may be prepared by polymerizing the monomers in the same manner as in the previous examples. In one embodiment, the acrylic copolymer is selected from the group consisting of butyl methacrylate, methyl methacrylate, butyl acrylate, (meth) acrylonitrile and tetrahydrofurfuryl (meth) acrylate in a weight ratio of 2.5 to 8.5: 0.5 to 1.5 : 1 to 3: 1 to 3: 1 to 6.

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 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 surface or both surfaces of the porous substrate, and the thickness thereof may be in a range of 1 탆 to 10 탆, specifically, 1 탆 to 6 탆.

According to another 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. Specifically, it is possible to use at least one of cobalt, manganese, nickel, aluminum, iron or a composite oxide or composite phosphorus of metal and lithium in combination thereof. 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 and 2: Preparation of acrylic copolymer

Manufacturing example  One

To the DIW was added butyl methacrylate (BMA), methyl methacrylate (MMA), butyl acrylate (BA), acrylonitrile (AN) and tetrahydrofuran And sodium dodecyl sulfate (SDS, 85.0%) was added as an emulsifier, and ammonium persulfate was added as an emulsifying agent. The resulting mixture was dispersed in tetrahydrofurfuryl acrylate (THF-A) at a weight ratio of 4: 1: (APS, 98.0%) as a polymerization initiator 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 dried to prepare an acrylic copolymer (Tg: 12.1 ° C) having a weight average molecular weight of 640,000 ± 50,000.

Manufacturing example  2

(Tg: 5.4) was prepared in the same manner as in Preparation Example 1, except that BMA, MMA, BA, AN and THF-A were added in a weight ratio of 4: 1: 2: 1: Lt; 0 &gt; C).

Example  1 to 4 and Comparative Example  1: Preparation of membrane

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. PVdF binder (KF9300, Kureha, Mw: 1,000,000 to 1,200,000) was dissolved so as to be a solution of 45% by weight of acetone, 48% by weight of DMAc and 7% by weight of PVdF binder solid component and stirred at 40 DEG C for 4 hours using a stirrer to obtain PVdF To prepare a binder solution. Alumina (LS235, Japan light metal) was added to acetone in an amount of 25 wt%, followed by 3 hours of bead mill dispersion to prepare an alumina dispersion. The acrylic copolymer solution, the PVdF binder solution, and the alumina dispersion were mixed so that the weight ratio of the acrylic copolymer and PVdF binder to alumina was 1: 6, and the weight ratio of the acrylic copolymer to the PVdF binder was 8: 2. And acetone was added thereto so that the total solid content was 15% by weight to prepare a porous adhesive layer composition. On both sides of a polyethylene fabric (SK) having a thickness of 9 占 퐉, To prepare a separation membrane having a total thickness of 11 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

In Example 1, the separation membrane of Example 3 was produced in the same manner as in Example 1, except that the PVdF binder was not used.

Example  4

The procedure of Example 1 was repeated except that the alumina dispersion was not used and the porous adhesive layer composition was prepared so that the weight ratio of the acrylic copolymer to the PVdF binder was 8: .

Comparative Example  One

PVdF binder (KF9300, Kureha, Mw: 1,000,000 ~ 1,200,000) was dissolved so as to be a solution of 45% by weight of acetone, 48% by weight of DMAc and 7% by weight of solids of PVdF binder and stirred at 40 캜 for 4 hours using a stirrer to obtain PVdF To prepare a binder solution. The prepared PVdF binder solution was coated on both sides of a 9 占 퐉 thick polyethylene fabric (SK) with a thickness of 1 占 퐉 To prepare a separator of Comparative Example 1 having a total thickness of 11 탆.

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

Substrate / Thickness (탆) Binder composition Acrylic polymerization weight ratio Example 1 PE / 9 Acrylic / PVdF system, 8/2
(Acrylic: alumina = 1: 6) BMA + MMA + BA + AN + THF-A 4: 1: 1: 1: 3 Example 2 PE / 9 Acrylic / PVdF system, 8/2
(Acrylic: alumina = 1: 6) BMA + MMA + BA + AN + THF-A 4: 1: 2: 1: 2 Example 3 PE / 9 Acrylic, 100%
(Acrylic: alumina = 1: 6) BMA + MMA + BA + AN + THF-A 4: 1: 1: 1: 3 Example 4 PE / 9 Acrylic / PVdF system, 8/2 BMA + MMA + BA + AN + THF-A 4: 1: 1: 1: 3 Comparative Example 1 PE / 9 PVdF system, 100%
(PVdF system: alumina = 1: 6) - -

Experimental Example

With respect to the membranes prepared in Examples 1 to 4 and Comparative Example 1, the crushing thickness change ratio (%) and the charge / discharge retention ratio (%) after 100 cycles were measured by the measurement method described below, and the results are shown in Table 2 .

Crushing Thickness Change Rate ( % )

LCO (LiCoO ₂ ) was coated on an aluminum foil having a thickness of 20 μm as a cathode active material to a thickness of 94 μm, followed by drying and rolling to prepare a cathode having a total thickness of 114 μm. Natural graphite and artificial graphite (1: 1) were coated on a copper foil having a thickness of 10 탆 as a negative electrode active material to a thickness of 120 탆, followed by drying and rolling to prepare a negative electrode having a total thickness of 130 탆. The electrolytic solution was 1.5M LiPF ₆ (PANAX ETEC CO., LTD.) Mixed in an organic solvent of EC / EMC / DEC + 0.2% LiBF ₄ + 5.0% FEC + 1.0% VC + 3.00% SN + 1.0% PS + ) Was used.

The separator prepared in the above Examples and Comparative Examples was interposed between the positive electrode and the negative electrode and wound into a 7 cm * 6.5 cm jelly roll type electrode assembly.

The electrode assembly from the contact pressure between 20 ℃ at a pressure of 9.3kgf / cm ² 3 seconds and after 1 hour by using characters 15cm steel measuring the thickness of the central portion, and shows it to T _0. Thereafter, the electrode 50 ℃ the assembly, respectively, 70 ℃ or at 100 ℃ pressed for 10 seconds at a pressure of 9kgf / cm ² and after 1 hour by using characters 15cm steel measuring the thickness of the central portion, and shows it to T _1. Compression thickness of the electrode assembly at 20 ℃ (T ₀₎ and 50 ℃, 70 ℃, by using the thickness (T ₁₎ of each pressure bonded electrode assembly at 100 ℃ by the following equation: 1, 50 ℃, 70 ℃, 100 Lt; 0 &gt; C, respectively.

[Formula 1]

(%) = [(T ₀ - T ₁ ) / T ₀ ] × 100

After 100 cycles Charging and discharging  Retention rate % )

The lithium secondary battery was assembled using the separator prepared in the above Examples and Comparative Examples, and then charged with a constant current until the voltage reached 4.2 V by the constant current constant voltage charging method at 60 ° C and 1C. Thereafter, a charge / discharge cycle test was performed in which the lithium secondary battery was charged with a constant voltage and then discharged to 3.0 V at a constant current of 1C. The charge-discharge cycle test was performed up to 100 cycles. The ratio of the discharge capacity at the 100th cycle to the initial discharge capacity was defined as the capacity retention rate. The higher the retention rate value, the smaller the capacity decrease during charging and discharging. Which means that the deterioration is large.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Tg (占 폚) of the acrylic copolymer 12.1 5.4 12.1 12.1 - Crimp Thickness Change Rate (%) 50 ℃ 70 72 74 84 11 70 ℃ 71 72 74 85 12 100 ℃ 72 73 74 85 29 Charge / discharge retention ratio (%) after 100 cycles 96 94 83 71 98

With reference to Table 2 above, it was found that when an acrylic copolymer containing repeating units derived from three or more alkyl (meth) acrylate monomers, repeating units derived from (meth) acrylonitrile monomers and repeating units derived from monomers having a heterocyclic group In the case of the separation membranes of Examples 1 to 4 having an adhesive layer, the Tg of the acrylic copolymer was within the range of 5 占 폚 to 20 占 폚, and the compression thickness change rates at 100 占 폚, 70 占 폚 and 50 占 폚 were all 70% Compression at a low temperature of 70 ℃ or lower was observed, and charge / discharge retention was also good.

Claims (23)

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 at least three alkyl (meth) acrylate monomers, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group, . The composition according to claim 1, wherein the three or more alkyl (meth) acrylate monomers are 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, ethyl (meth) acrylate, ethyl (meth) acrylate, ethyl Lt; RTI ID = 0.0 &gt; 3 &lt; / RTI &gt; The composition of claim 1, wherein the monomer having a heterocyclic group is selected from the group consisting of acryloylmorpholine, vinylcaprolactam, tetrahydrofurfuryl (meth) acrylate, caprolactone-modified tetrahydrofurfuryl (meth) , And 5-dihydrofuran. The separation membrane according to claim 1, wherein the weight ratio of the three or more alkyl (meth) acrylate monomers and the monomer having a heterocyclic group in the acrylic copolymer is 9: 1 to 4: 6. 5. The separator according to claim 4, wherein the (meth) acrylonitrile monomer is contained in an amount of 5 to 80 parts by weight based on 100 parts by weight of the total of the three or more alkyl (meth) acrylate monomers and the monomer having the heterocyclic group, . The separation membrane according to any one of claims 1 to 5, wherein the acrylic copolymer has a glass transition temperature (Tg) of 5 占 폚 to 20 占 폚. The separation membrane according to any one of claims 1 to 5, wherein the acrylic copolymer has a weight average molecular weight of 100,000 to 1,000,000. The separation membrane according to any one of claims 1 to 5, further comprising a binder other than the acrylic copolymer. The method of claim 8, wherein the different kind of binder is selected from the group consisting of polyvinylidene fluoride (PVdF) polymer, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, but are not limited to, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and acrylonitrile Acrylonitrile-butadiene copolymer adiene 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 8, wherein the weight ratio of the acrylic copolymer to the binder of the other kind is from 9: 1 to 4: 6. The separation membrane according to any one of claims 1 to 5, wherein the porous adhesive layer further comprises inorganic particles. The separation membrane according to any one of claims 1 to 5, wherein the thickness of the porous adhesive layer is 1 占 퐉 to 10 占 퐉. Wherein the glass transition temperature is in the range of 5 to 20 DEG C, and the compression thickness change ratio at 70 DEG C according to the following formula (1) is 70% or more.
[Formula 1]
(%) = [(T ₀ - T ₁ ) / T ₀ ] × 100
In the formula 1, T ₀ is the thickness of the central portion measured after 1 hour from the pressing of the electrode assembly including the separation membrane at 20 ° C and a pressure of 9.3 kgf / cm ² for 3 seconds, T ₁ is 9 kgf / cm &lt; ² &gt; for 10 seconds and measured after 1 hour. 15. The separator according to claim 14, wherein the acrylic copolymer comprises a repeating unit derived from at least three alkyl (meth) acrylate monomers, a repeating unit derived from a (meth) acrylonitrile monomer, and a repeating unit derived from a monomer having a heterocyclic group . The method of claim 15, wherein the three or more alkyl (meth) acrylate monomers are 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, ethyl (meth) acrylate, ethyl (meth) acrylate, ethyl Lt; RTI ID = 0.0 &gt; 3 &lt; / RTI &gt; 16. The composition of claim 15, wherein the monomer having a heterocyclic group is selected from the group consisting of acryloylmorpholine, vinylcaprolactam, tetrahydrofurfuryl (meth) acrylate, caprolactone modified tetrahydrofurfuryl (meth) , And 5-dihydrofuran. The separation membrane according to any one of claims 14 to 17, wherein the separation membrane further comprises a binder other than the acrylic copolymer. 18. The separation membrane according to any one of claims 14 to 17, wherein the separation membrane further comprises inorganic particles. A porous substrate; And a porous adhesive layer formed on one or both sides of the porous substrate,
The porous adhesive layer is formed by repeating a repeating unit derived from a butyl methacrylate monomer, a repeating unit derived from a methyl methacrylate monomer, a repeating unit derived from a butyl acrylate monomer, a repeating unit derived from a (meth) acrylonitrile monomer and a monomer having a heterocyclic group Wherein the acrylic copolymer is an acrylic copolymer. The acrylic copolymer according to claim 20, wherein the acrylic copolymer is selected from the group consisting of butyl methacrylate, methyl methacrylate, butyl acrylate, (meth) acrylonitrile and tetrahydrofurfuryl (meth) acrylate in a weight ratio of 2.5 to 8.5: 1.5: 1 to 3: 1 to 3: 1 to 6. anode; cathode; A separation membrane according to any one of claims 1 to 5, 14 to 17, and 20 to 21; And an electrolytic solution. 23. The electrochemical cell of claim 22, wherein the electrochemical cell is a lithium secondary battery.

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