WO2015076574A1

WO2015076574A1 - Separator and secondary battery using same

Info

Publication number: WO2015076574A1
Application number: PCT/KR2014/011179
Authority: WO
Inventors: 이경주; 김남효; 김양섭; 윤효상; 최종섭
Original assignee: 삼성에스디아이 주식회사
Priority date: 2013-11-21
Filing date: 2014-11-20
Publication date: 2015-05-28

Abstract

The present invention relates to a separator and a secondary battery comprising the separator, the separator comprising: a porous substrate; and an adhesive layer formed on one side or both sides of the porous substrate, the adhesive layer containing an acrylic copolymer comprising a (meth)acrylate-based monomer derived repeat unit, and a polyvinylidene fluoride-based polymer having a weight-average molecular weight of at least 1,000,000 g/mol.

Description

Separator and Secondary Battery Using the Same

The present invention relates to a separator and a secondary battery using the same.

BACKGROUND ART In general, portable electronic devices such as video cameras, mobile phones, and portable computers have been researched on secondary batteries used as driving power as light weights and high functionalities are advanced. As such a secondary battery, a nickel-cadnium battery, a nickel-hydrogen battery, a nickel-zinc battery, a lithium secondary battery, etc. are used, for example. Among these, lithium secondary batteries have been used in many fields because of their advantages such as small size and large size, high operating voltage, and high energy density per unit weight.

Due to the increase in the area and / or weight due to the size of the separator in the environment in the secondary battery, the separator wound between the electrode and the electrode is easily separated, so that the adhesion between the separator and the electrode is increased. In addition, it is required to have excellent shape stability of the secondary battery so as to prevent the shape from changing, such as distorting the battery due to continuous charging and discharging. In this regard, it is known to form an organic / inorganic mixed coating layer on one or both sides of the base film of the separator in order to improve the adhesion between the separator and the electrode and the heat resistance of the separator (Korean Patent No. 10-0775310). It cannot be sufficiently secured, so it is difficult to apply to batches of various sizes and shapes.

Therefore, it is necessary to develop a secondary battery including a separator having an adhesive force applicable to a large-area secondary battery and capable of maintaining morphological stability and adhesion of the battery even after charging and discharging, which is an environment in which an actual battery is used.

An object of the present invention is to provide a separator and an improved secondary battery using the same.

According to one embodiment of the present invention, an acrylic copolymer comprising a porous substrate and repeating units derived from (meth) acrylate monomers formed on one or both surfaces of the porous substrate, and a polyamide having a weight average molecular weight of 1,000,000 g / mol or more A separator is provided, comprising a vinylidene fluoride polymer containing adhesive layer.

According to another embodiment of the present invention, a separator comprising a porous substrate and a binder-containing adhesive layer formed on one or both sides of the porous substrate, the charge or discharge of the separator 1 after the charge and discharge of formula 1 to transfer the separator to the separator Separators are provided, the rates being at least 50% each.

[Equation 1]

Transfer rate (%) = (A ₁ / A ₀ ) X 100

In Formula 1,

A ₀ is the total area of the cathode or anode,

A ₁ forms an electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, and at the temperature of 20 ° C. to 110 ° C. for 1 second to 5 seconds, with a force of 1 kgf / cm ² to 30 kgf / cm ² . After pressing, the electrolyte solution is injected into the compressed electrode assembly, and the second electrode is pressed with a force of 1 kgf / cm ² to 30 kgf / cm ² for 60 ° C. to 110 ° C., 30 seconds to 180 seconds, and then charged, discharged and charged. When sequentially performed, the area of the positive electrode or negative electrode active material transferred to the separator.

According to another embodiment of the present invention, a secondary battery, particularly a lithium secondary battery, including the separator according to the above example is provided.

Separation membrane according to an embodiment of the present invention has the effect that the shape stability of the battery after the charge and discharge of the battery and the adhesion to the electrode is enhanced. In addition, the separator according to the present invention can maintain high efficiency charge and discharge characteristics due to improved shape stability.

1 is an exploded perspective view of a rechargeable battery according to an exemplary embodiment.

2 is an exploded perspective view of a secondary battery according to another embodiment.

3 is a photograph showing that the negative electrode active material is transferred to the separator (7cm × 7cm), it can be seen that the black active material is transferred to the white separator.

Hereinafter, the present invention will be described in more detail. The content not described in the present specification may be sufficiently recognized and inferred by those skilled in the art or similar fields of the present invention, and thus description thereof is omitted.

In one embodiment of the present invention, an acrylic copolymer comprising a porous substrate and repeating units derived from (meth) acrylate monomers formed on one or both surfaces of the porous substrate and polyvinylidene having a weight average molecular weight of 1,000,000 g / mol or more. A separator is provided that includes a fluoride-based polymer-containing adhesive layer.

The porous substrate may use a porous substrate having a plurality of pores and 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 , Polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, and any one polymer selected from the group consisting of polyethylene naphthalene or a polymer membrane formed of a mixture of two or more thereof Can be. In one example, the porous substrate may be a polyolefin-based substrate, the polyolefin-based substrate is excellent in the shutdown (shut down) function may contribute to the improvement of the safety of the battery. The polyolefin-based substrate may be selected from the group consisting of, for example, polyethylene monolayer, polypropylene monolayer, polyethylene / polypropylene double membrane, polypropylene / polyethylene / polypropylene triple membrane, and polyethylene / polypropylene / polyethylene triple membrane. In another example, the polyolefin resin may include a non-olefin resin in addition to the olefin resin, or may include a copolymer of an olefin and a non-olefin monomer. The porous substrate may have a thickness of 1 μm to 40 μm, more specifically 5 to 15 μm. When using the substrate within the thickness range, it is possible to produce a separator having a suitable thickness, 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 adhesive layer may be formed of an adhesive layer composition, and the adhesive layer composition may include an acrylic copolymer including a (meth) acrylate monomer-derived repeating unit, a polyvinylidene fluoride polymer and a solvent having a weight average molecular weight of 1,000,000 g / mol or more. It may include. In another example, the adhesive layer composition may further include inorganic particles. Although the adhesion between the electrode and the separator before the charge and discharge is good, the adhesion may be significantly reduced after the charge and discharge, but in the present application, an acrylic copolymer including a (meth) acrylate monomer-derived repeating unit as a binder of the adhesive layer and a weight average molecular weight By using the polyvinylidene fluoride-based polymer of 1,000,000 g / mol or more together, not only the adhesion to the electrode before charge and discharge, but also the adhesion to the electrode after charge and discharge, which is the environment in which the separator is actually used, can also be improved. After that, the shape stability of the battery can be improved. The acrylic copolymer may further include an acetate group-containing monomer-derived repeating unit in addition to the (meth) acrylate-based monomer-derived repeating unit.

The weight ratio of the acrylic copolymer and the polyvinylidene fluoride polymer may be 5: 5 to 8: 2, specifically 6: 4 to 8: 2, and more specifically 7: 3 to 8: 2. Within the weight ratio range, it may be advantageous in view of good adhesion and electrolyte impregnation with the positive electrode or the negative electrode even after charging and discharging. The higher the weight ratio of the acrylic copolymer tends to increase the adhesion between the negative electrode and the separator after charging and discharging, the higher the weight ratio of the acrylic copolymer is advantageous in terms of adhesive strength, but if the weight ratio is too high, the adhesive layer may be dissolved in the electrolyte. As the polyvinylidene fluoride polymer, for example, polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride-hexaxapropoxy (PVDF-HFP) copolymer, Or modified polymers thereof, and specifically, polyvinylidene fluoride-hexafluoropropylene copolymer or polyvinylidene fluoride homopolymer may be used. The weight average molecular weight (Mw) of the polyvinylidene fluoride polymer may be in the range of 1,000,000 g / mol to 1,700,000 g / mol. More specifically, the weight average molecular weight (Mw) may range from 1,000,000 g / mol to 1,500,000 g / mol. The use of the PVdF-based binder in the above molecular weight range has an advantage in that the adhesive force is enhanced after charge and discharge between the separator and the porous substrate, thereby producing a battery in which electrical output is efficiently generated. The glass transition temperature (Tg) of the acrylic copolymer may be 100 ° C. or less, for example, 20 ° C. to 60 ° C. Within this range, the separator may be positioned between the electrodes and formed to have good adhesion at a temperature at which the separator is pressed, thereby improving the shrinkage rate and improving heat resistance. The weight average molecular weight of the acrylic copolymer may be in the range of 100,000 g / mol to 1,000,000 g / mol, specifically 300,000 to 800,000 g / mol, or 400,000 to 700,000 g / mol. The acrylic copolymer including a (meth) acrylate-based monomer-derived repeat unit that can be used herein is not particularly limited as long as it can form a good adhesion between the positive electrode and the negative electrode as described above, for example, butyl (meth It may be a copolymer produced by polymerizing one or more (meth) acrylate monomers selected from the group consisting of) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate and methyl (meth) acrylate. Or the acrylic copolymer is a (meth) acrylate monomer such as butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate or methyl (meth) acrylate, and other monomers, for example, It may be a copolymer produced by polymerizing an acetate group-containing monomer such as vinyl acetate or allyl acetate.

The acetate group-containing monomer-derived repeating unit may be a repeating unit of Formula 1:

[Formula 1]

In Formula 1, R ₁ is a single bond, linear or branched alkyl having 1 to 6 carbon atoms, R ₂ is hydrogen or methyl, and l is an integer between 1 and 100, respectively. For example, the acetate group-containing monomer-derived repeating unit may be a repeating unit derived from an acetate group-containing monomer selected from at least one selected from the group consisting of vinyl acetate and allyl acetate. When the acryl-based copolymer is prepared by polymerizing a monomer other than the (meth) acrylate-based monomer and the (meth) acrylate-based monomer, for example, an acetate group-containing monomer, the (meth) acrylate-based monomer and the other monomer, specifically As such, the acetate group-containing monomer may be prepared by polymerization in a molar ratio of 3: 7 to 7: 3, specifically 4: 6 to 6: 4, and more specifically about 5: 5. For example, the acrylic copolymer may be a butyl (meth) acrylate monomer, a methyl (meth) acrylate monomer, and a vinyl acetate and / or allyl acetate monomer, in a weight ratio of 3 to 5: 0.5 to 1.5: 3 to 7, specifically, It may be prepared by a polymerization reaction of 4: 1: 5.

The inorganic particles used in the present invention are not particularly limited and may be inorganic particles commonly used in the art. 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 , SnO ₂ , and the like. These can be used individually or in mixture of 2 or more types. As the inorganic particles used in the present invention, for example, Al ₂ O ₃ (alumina) can be used. The size of the inorganic particles used in the present invention is not particularly limited, but the average particle diameter may be 1 nm to 2,000 nm, for example, 100 nm to 1,000 nm, or 400 nm to 600 nm. When using the inorganic particles in the size range, it is possible to prevent the dispersibility of the inorganic particles in the adhesive layer composition and the fairness of the formation of the adhesive layer can be prevented from being lowered, and the thickness of the adhesive layer is appropriately adjusted to decrease the mechanical properties and increase the electrical resistance. Can be prevented. In addition, the size of the pores generated in the separator is appropriately adjusted, there is an advantage that can lower the probability of the internal short circuit occurs during the charge and discharge of the battery. In preparing the adhesive layer composition, the inorganic particles may be used in the form of an inorganic dispersion in which it is dispersed in a suitable solvent. The appropriate solvent is not particularly limited and may be a solvent commonly used in the art. Acetone can be used as a suitable solvent for dispersing the inorganic particles, for example. The inorganic dispersion may be prepared by a conventional method without any particular limitation. For example, Al ₂ O ₃ may be added to acetone in an appropriate amount, and the inorganic dispersion may be milled and dispersed using a bead mill. Dispersions can be prepared. The inorganic particles in the adhesive layer may be included in 50 to 99% by weight, specifically 75 to 95% by weight, more specifically 80 to 95% by weight based on the total weight of the adhesive layer. When the inorganic particles are contained within the above range, the heat dissipation characteristics of the inorganic particles may be sufficiently exhibited, and when the adhesive layer is formed on the porous substrate using the inorganic particles, thermal contraction of the separator may be effectively suppressed.

Non-limiting examples of the solvent usable in the present invention include acetone, dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), dimethylacetamide (dimethyl acetamide, DMAc), dimethyl carbonate , DMC) or N-methylpyrrolidone (N-methylpyrrolydone, NMP) and the like. The content of the solvent may be 20 to 99% by weight, specifically 50 to 95% by weight, and more specifically 70 to 95% by weight based on the weight of the adhesive layer composition. When the solvent is contained in the above range, the preparation of the adhesive layer composition may be facilitated, and the drying process of the adhesive layer may be performed smoothly.

The adhesive layer or the adhesive layer composition according to another embodiment of the present invention may further include another binder in addition to the acrylic copolymer or the polyvinylidene fluoride polymer. Examples of binders that may be added include polymethylmethacrylate (PMMA), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), polyvinylacetate (PVAc), polyethylene Oxides (PEO), cellulose acetate (CA), cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), cyanoethylpullulan (CANO) CYEPL), cyanoethylpolyvinylalcohol (CR-V), cyanoethylcellulose (CEC), cyanoethylsucrose, pullulan, carboxyl methyl cellulose CMC), and the group consisting of acrylonitrilestyrene-butadiene copolymer Or a mixture thereof. In one example, polyvinylidene fluoride based polymers having a weight average molecular weight of less than 1,000,000 g / mol may further be used.

The separator according to another embodiment of the present invention is a separator including a porous substrate and a binder-containing adhesive layer formed on one or both surfaces of the porous substrate, and after the charge and discharge of Equation 1 of the separator to the separator of the positive electrode or negative electrode active material The transcription rates may each be at least 50%.

[Equation 1]

Transfer rate (%) = (A ₁ / A ₀ ) × 100

In Formula 1,

A ₀ is the total area of the cathode or anode, and A ₁ forms an electrode assembly in which the anode, separator and cathode are sequentially stacked, and at a temperature of 20 ° C. to 110 ° C., 1 kgf / cm ² , for 1 second to 5 seconds. 1 to 30 kgf / cm ² , the first crimp, the electrolyte is injected into the compressed electrode assembly and 60 ℃ to 110 ℃, 30 seconds to 180 seconds, with a force of 1 kgf / cm ² to 30 kgf / cm ² It is the area of the positive electrode or negative electrode active material transferred to the separator when the secondary pressing is carried out, and when charging, discharging, and charging are sequentially performed. The method of measuring the area of the positive electrode or the negative electrode active material is not limited as long as the area of the active material can be measured. For example, a known image analyzer (eg, a lumenera high resolution camera) is photographed and then a known image analyzer ( Example: Easy Measure converter 1.0.0.4) can be used to measure the transferred area of the positive or negative electrode active material.

Examples of the charging, discharging and charging conditions are shown in Table 1 below:

Table 1

Chung / Bang / Chung	4.35V, 0.2C, 50 mA cut-off	5 hrs
	0.2C, 3V cut-off	5 hrs
	0.5C, 4V cut-off	2 hrs

The transfer rate of the positive electrode or the negative electrode active material to the separator of 50% or more is related to the shape stability and adhesion of the battery after charge and discharge. The transcription rate may be specifically 55% or more, more specifically 60% or more, even more specifically 70% or more.

In the above example, as the binder in the adhesive layer, an acrylic copolymer as described above and a polyvinylidene fluoride polymer having a weight average molecular weight of 1,000,000 g / mol or more may be used, and other inorganic particles, solvents, etc. may be used as described above. And in content.

In the separator according to the above example, the thickness change rate of Equation 2 may be 7% or less. Specifically, the thickness change rate may be 5% or less, and more specifically 3% or less.

[Equation 2]

Thickness Change (%) = [(T ₁ -T ₂ ) / T ₁ ] × 100 × 100

In Equation 2, T ₁ is a separator between the positive electrode and the negative electrode, and the positive electrode, the separator and the negative electrode is laminated in sequence of 7 cm (length direction) × 6.5 cm (width direction) The thickness is measured by forming an electrode assembly, and T ₂ is the thickness measured after pressing the formed electrode assembly at a pressure of 1 kgf / cm ² to 30 kgf / cm ² at 20 ° C. to 110 ° C. for 1 to 5 seconds. . The shape stability of a battery is excellent in the said thickness change rate being the said range.

Separation membrane according to embodiments of the present invention may be less than 500 sec / 100cc, specifically 50 to 400 sec / 100cc, more specifically 50 to 300 sec / 100cc. Tensile strength in the MD direction of the separator according to embodiments of the present invention may be 1750 kg / cm ² or more, the tensile strength in the TD direction may be 1650 kg / cm ^{2 or} more. Specifically, the tensile strength in the MD direction of the separator may be 1750 kg / cm ² to 2550 kg / cm ^2, and the tensile strength in the TD direction may be 1700 kg / cm ² to 2500 kg / cm ² . The separator according to the examples of the present invention may not only have excellent shape stability and adhesion after charge and discharge, but also satisfy basic physical properties such as air permeability and mechanical strength required as the separator.

Hereinafter, a method of manufacturing a separator according to an embodiment of the present invention will be described. Method for producing a separator according to an embodiment of the present invention comprises an acrylic copolymer containing a (meth) acrylate monomer-derived repeating unit, and a polyvinylidene fluoride polymer having a weight average molecular weight of 1,000,000 g / mol or more bookbinder; And forming an adhesive layer composition comprising a solvent, and forming the adhesive layer with the adhesive layer composition on one or both surfaces of the porous substrate. The acrylic copolymer may further include a repeating unit derived from an acetate group-containing monomer such as vinyl acetate or allyl acetate monomer.

First, forming the adhesive layer composition is a binder comprising an acrylic copolymer and a polyvinylidene fluoride polymer having a weight average molecular weight of 1,000,000 g / mol or more, and a solvent and mixed at 10 to 40 ℃ for 30 minutes to 5 hours It may include stirring. When the inorganic particles are included, the stirred solution may include inorganic particles. At this time, the content of the solid content may be 10 to 20 parts by weight based on the adhesive layer composition, the weight ratio of the binder and the inorganic particles in the solid content may be 5: 5 to 0.1: 9.9.

Alternatively, the adhesive layer composition may be prepared by preparing an inorganic dispersion in which the inorganic particles are dispersed in a dispersion medium and mixing the mixture with a polymer solution containing a solvent and a binder including an acrylic copolymer and a polyvinylidene fluoride polymer. . When the inorganic dispersion is prepared separately as described above, the dispersibility and crude liquid stability of the inorganic particles and the binder may be improved. Therefore, in another embodiment, in preparing the adhesive layer composition of the present invention, the binder component and the inorganic particles may be prepared and mixed in a dissolved or dispersed state in a suitable solvent, respectively. For example, an adhesive layer composition may be prepared by preparing a solution in which each of an acrylic copolymer and a polyvinylidene fluoride binder are dissolved in a suitable solvent, and an inorganic dispersion in which inorganic particles are dispersed, and then mixing them with an appropriate solvent. It can manufacture. A ball mill, a beads mill, a screw mixer, or the like may be used for the mixing.

Subsequently, an adhesive layer is formed of the adhesive layer composition on one or both surfaces of the porous substrate. The method for forming the adhesive layer on the porous substrate is not particularly limited, and methods commonly used in the art, for example, a coating method, lamination, coextrusion, and the like may be used. Non-limiting examples of the coating method may include a dip coating method, a die coating method, a roll coating method, or a comma coating method. These may be applied alone or in combination of two or more methods. The adhesive layer of the separator of the present invention may be formed by, for example, a dip coating method.

The adhesive layer of the present invention may have a thickness of 0.01 to 20 μm, specifically 1 to 10 μm, and more specifically 1 to 5 μm. Within the thickness range, it is possible to form an adhesive layer having an appropriate thickness to obtain excellent thermal stability and adhesion, and to prevent the thickness of the entire separator from becoming too thick, thereby suppressing an increase in the internal resistance of the battery.

In the present invention, the adhesive layer may be dried by hot air, hot air, low humidity, vacuum drying or far infrared rays or electron beams. And the drying temperature is different depending on the type of the solvent, it can be dried at a temperature of approximately 60 to 120 ℃. The drying time also varies depending on the type of solvent, but may generally be dried for 1 minute to 1 hour. In embodiments, it may be dried for 1 minute to 30 minutes, or 1 minute to 10 minutes at a temperature of 70 to 120 ℃.

According to another embodiment of the present invention, an anode; cathode; A porous separator comprising an adhesive layer disclosed herein, positioned between the anode and the cathode; And it provides a secondary battery comprising an electrolyte.

The type of the secondary battery is not particularly limited and may be a battery of a kind known in the art.

Specifically, the secondary battery of the present invention may 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 of manufacturing the secondary battery of the present invention is not particularly limited, and a method commonly used in the technical field of the present invention may be used.

A non-limiting example of a method of manufacturing the secondary battery is as follows: A porous separator comprising the adhesive layer of the present invention is placed between the positive electrode and the negative electrode of the battery, and then the battery is prepared by filling an electrolyte therein. Can be.

1 and 2 are exploded perspective views of a secondary battery according to one or another embodiment. Although the secondary battery according to the embodiment is described as an example of a rectangular or cylindrical battery, the present invention is not limited thereto, and may be applied to various types of batteries such as pouch-type batteries and lithium polymer batteries.

1 and 2, the

secondary batteries

100 and 200 according to the exemplary embodiment may have a odor through the separators 30 and 30 'between the cathodes 10 and 10' and the anodes 20 and 20 '. The electrode assembly 40, and the

cases

50 and 50 ′ in which the electrode assembly 40 is embedded. The

positive electrode

10, 10 ′, the

negative electrode

20, 20 ′ and the

separator

30, 30 ′ are impregnated with an electrolyte (not shown).

The separators 30 and 30 'are as described above.

The

positive electrodes

10 and 10 ′ may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a binder, and optionally a conductive material.

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

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specifically, at least one of cobalt, manganese, nickel, aluminum, iron, or a combination of metal and lithium composite oxide or phosphoric acid 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 material particles well to each other, but also serves to adhere the positive electrode active material to the positive electrode current collector, and specific examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl chloride. , Carboxylated polyvinylchloride, polyvinylfluoride, ethylene oxide containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, Acrylated styrene-butadiene rubber, epoxy resin, nylon and the like, but is not limited thereto. These can be used individually or in mixture of 2 or more types.

The conductive material provides conductivity to the electrode, and examples thereof include natural graphite, artificial graphite, carbon black, carbon fiber, metal powder, and metal fiber, but are not limited thereto. These can be used individually or in mixture of 2 or more types. As the metal powder and the metal fiber, metals such as copper, nickel, aluminum, and silver may be used.

The

negative electrodes

20 and 20 ′ may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector.

The negative electrode current collector may include copper (Cu), gold (Au), nickel (Ni), a 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.

The negative electrode active material may be a material capable of reversibly intercalating and deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, a transition metal oxide, or a combination thereof. Can be used.

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

Kinds of the binder and the conductive material used in the negative electrode are the same as the binder and the conductive material used in the above-described positive electrode.

The positive electrode and the negative electrode may be prepared by mixing each active material, a binder, and optionally a conductive material in a solvent to prepare each active material composition, and applying the active material composition to each current collector. In this case, N-methylpyrrolidone may be used as the solvent, but is not limited thereto. Since such an electrode manufacturing method is well known in the art, detailed description thereof will be omitted.

The electrolyte solution contains 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 carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents and aprotic solvents.

Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene Carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Specifically, when a mixture of the chain carbonate compound and the cyclic carbonate compound is used, the dielectric constant may be increased, and the solvent may have a low viscosity. In this case, the cyclic carbonate compound and the chain carbonate compound may be mixed and used in a volume ratio of 1: 1 to 1: 9.

Examples of the ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, valerolactone, and meronate. Melononolactone, caprolactone, and the like. Examples of the ether solvent include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like. Cyclohexanone etc. are mentioned as said ketone solvent, Ethyl alcohol, isopropyl alcohol, etc. are mentioned as said alcohol solvent.

The organic solvents may be used alone or in combination of two or more thereof, and the mixing ratio in the case of mixing two or more kinds may be appropriately adjusted according to the desired battery performance.

The lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable operation of a basic secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode.

Examples of the lithium salt include 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 ) (x and y are natural numbers), LiCl, LiI, LiB (C ₂ O ₄ ) ₂ or a combination thereof Can be mentioned.

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, since the electrolyte has an appropriate conductivity and viscosity, it can exhibit excellent electrolyte performance, and lithium ions can move effectively.

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 being limited thereto.

실시예 Example

실시예 1: 분리막의 제조Example 1 Preparation of Membrane

Acetone is an acrylic copolymer binder in which butyl methacrylate (BMA), methyl methacrylate (MMA), and vinyl acetate (Vinyl Acetate, VAc) are polymerized at a 4/1/5 molar ratio. Dissolved in the first binder solution having a solid content of 5% by weight, and a PVdF-based polymer (Kurehasa KF9300, Mw: 1,200,000 g / mol) in acetone and DMAc mixed solvents to dissolve a second binder solution which is a 7% by weight solid solution. Prepared. Alumina dispersion was prepared by adding alumina (LS235, Nippon Light Metal) to acetone at 25% by weight and dispersing the beads for 3 hours. The first and second binder solutions and the alumina dispersion were mixed so that the weight ratio of the above-mentioned acrylic binder and the PVdF-based binder was 6: 4, so that the weight ratio of the binder solid and the alumina solid was 1/6, and the total solid was 12 wt. Acetone was added to make the coating solution. 7 µm thick polyethylene fabric (SK, Inc.) was coated on both sides of the coating solution with a thickness of 2 μm, respectively, to prepare a separator having a total thickness of about 11 μm.

실시예 2: 분리막의 제조Example 2: Preparation of Separator

The separation membrane of Example 2 was prepared in the same manner as in Example 1, except that the weight ratio of the acrylic binder and the PVdF binder was 7: 3 in Example 1.

실시예 3: 분리막의 제조Example 3: Preparation of Separator

The separator of Example 3 was prepared in the same manner as in Example 1, except that the weight ratio of the acrylic binder and the PVdF binder was 8: 2 in Example 1.

실시예 4: 분리막의 제조Example 4 Preparation of Membrane

A separator of Example 4 was prepared in the same manner as in Example 1, except that 5130 (Solva, Inc., weight average molecular weight: 1,000,000 to 1,200,000 g / mol) was used as the second binder in Example 1. .

실시예 5: 분리막의 제조Example 5: Preparation of Separator

The separation membrane of Example 5 was prepared in the same manner as in Example 4, except that the weight ratio of the acrylic binder and the 5130 binder was 7: 3 in Example 4.

실시예 6: 분리막의 제조Example 6: Preparation of Membrane

The separator of Example 6 was prepared in the same manner as in Example 4, except that the weight ratio of the acrylic binder and the 5130 binder was 8: 2.

비교예 1: 분리막의 제조Comparative Example 1: Preparation of Separator

Comparative Example 1 was carried out in the same manner as in Example 1 except that 21216 (Solva, Inc., weight average molecular weight: 570,000 to 700,000 g / mol, PVDF-HFP copolymer) was used instead of KF9300 in Example 1 A separator of 1 was prepared.

비교예 2: 분리막의 제조Comparative Example 2: Preparation of Separator

A separation membrane of Comparative Example 2 was prepared in the same manner as in Comparative Example 1 except that the weight ratio of the acrylic binder and the 21216 binder was 7: 3 in Comparative Example 1.

비교예 3: 분리막의 제조Comparative Example 3: Preparation of Separator

The separation membrane of Comparative Example 3 was prepared in the same manner as in Comparative Example 1, except that the weight ratio of the acrylic binder and the 21216 binder was 8: 2 in Comparative Example 1.

비교예 4: 분리막의 제조Comparative Example 4: Preparation of Separator

In Example 1, except that 6020 (Solva, Inc., weight average molecular weight: 670,000 to 700,000 g / mol, PVDF homopolymer) was used as the second binder in a weight ratio of 7: 3 in the same manner as in Example 1, except that KF9300 was used. The separation membrane of Comparative Example 4 was prepared.

The composition of each separator according to Examples 1 to 6 and Comparative Examples 1 to 4 is shown in Table 2 below.

TABLE 2

	Fabric / thickness (㎛)	Binder composition		Inorganic Particle Content (wt%)
	Fabric / thickness (㎛)	Acrylic / PVdF-based weight ratio	PVdF-based Mw (g / mol)	Inorganic Particle Content (wt%)
Example 1	PE / 7	6/4	1.2 million	86
Example 2	PE / 7	7/3	1.2 million	86
Example 3	PE / 7	8/2	1.2 million	86
Example 4	PE / 7	6/4	1 to 1.2 million	86
Example 5	PE / 7	7/3	1 to 1.2 million	86
Example 6	PE / 7	8/2	1 to 1.2 million	86
Comparative Example 1	PE / 7	6/4	570,000-700,000	86
Comparative Example 2	PE / 7	7/3	570,000-700,000	86
Comparative Example 3	PE / 7	8/2	570,000-700,000	86
Comparative Example 4	PE / 7	7/3	670,000-700,000	86

실험예 Experimental Example

Air permeability by the measurement method described below for the separator prepared in Examples 1 to 6 and Comparative Examples 1 to 4; The tensile strength; Transfer rate of the active material before and after charge and discharge; The rate of change of the thickness of the electrode assembly was measured and the results are shown in Table 3.

TABLE 3

		Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4
Breathability (sec / 100cc)		197	194	204	212	183	198	209	206	245	267
Tensile strength (kgf / cm ² )	MD	1799	1795	1796	1803	1751	1776	1807	1792	1765	1777
Tensile strength (kgf / cm ² )	TD	1714	1704	1699	1717	1682	1689	1709	1713	1680	1687
Thickness change rate (%)		Less than 3%	Less than 3%	Less than 3%	Less than 3%	Less than 3%	Less than 3%	3-7%	3-7%	3-7%	Greater than 7%
Transfer rate before charge and discharge (%)	cathode	95	90	95	70	70	70	93	93	95	-
Transfer rate before charge and discharge (%)	anode	99	99	99	99	99	99	99	99	99	-
Transfer rate after charge and discharge (%)	cathode	90	90	99	64	80	80	0	0	0	-
Transfer rate after charge and discharge (%)	anode	99	99	99	99	99	99	30	30	30	-

1. Breathability

Each of the separators prepared in the above Examples and Comparative Examples was prepared to cut 10 samples cut from 10 different points to a size of 1 inch (1 inch) in diameter, and then the air permeability measuring device (Asahi Seiko) G) was used to measure the time for passage of 100 cc of air in each sample. The time was measured five times each, and then the average value was calculated as air permeability.

2. Tensile Strength

Each of the separators prepared in Examples and Comparative Examples was cut into five pieces in a rectangular shape of 50 mm long by 150 mm long by 150 mm long by MD, and by 150 mm long by 50 mm wide by 50 mm long. Ten samples were prepared, and each sample was mounted on a UTM (tension tester) to be bitten to a measurement length of 20 mm, and then the sample was pulled to measure average tensile strength in the MD and TD directions.

3. Thickness change rate

The following method was performed to measure the thickness and rate of change of the electrode assembly having the separator prepared in Examples and Comparative Examples interposed between the positive electrode and the negative electrode.

LCO (LiCoO ₂ ) as an anode active material was coated on both sides of an aluminum foil having a thickness of 14 μm with a thickness of 94 μm, dried, and rolled to produce a cathode having a total thickness of 108 μm. Graphite) = 1: 1 was coated on both sides of copper foil having a thickness of 8 μm at 120 μm, dried, and rolled to prepare a negative electrode having a total thickness of 128 μm.

The anode and the cathode were cut in 100 cm (length direction) × 6.3 cm (width direction), respectively, and the separators prepared in Examples and Comparative Examples were cut in 100 cm (length direction) × 6.5 cm (width direction). Thereafter, the electrode assembly was wound up to 7 cm (length direction) x 6.5 cm (width direction) between the positive electrode and the negative electrode to form an electrode assembly, and the thickness of the electrode assembly was measured using a 30 cm steel ruler (T ₁ ).

Thereafter, the electrode assembly was pressed at 100 ° C. at a pressure of 5 kgf / cm ² for 3 seconds, and the thickness of the electrode assembly was measured using a 30 cm steel ruler (T ₂ ), and the thickness change rate was calculated by the following Equation 2.

[Equation 2]

Thickness Change (%) = [(T ₁ -T ₂ ) / T ₁ ] × 100

4. Transfer rate of active material before and after charge and discharge

As a positive electrode active material, LCO (LiCoO 2) was coated on both sides of an aluminum foil having a thickness of 14 μm with a thickness of 94 μm, dried, and rolled to prepare a positive electrode having a total thickness of 108 μm. As a negative electrode active material, natural graphite and artificial graphite (1: 1) were coated on both sides of a copper foil having a thickness of 8 μm at 120 μm, dried, and rolled to prepare a negative electrode having a total thickness of 128 μm. As electrolyte, 1.5M LiPF6 mixed with organic solvent of EC / EMC / DEC + 0.2% LiBF4 + 5.0% FEC + 1.0% VC + 3.00% SN + 1.0% PS + 1.0% SA (PANAX ETEC CO., LTD.) Was used.

The separators prepared in Examples and Comparative Examples were wound between the anode and the cathode with an electrode assembly of 7 cm × 6.5 cm. The electrode assembly was first pressed at 100 ° C. for 3 seconds under a pressure of 5 kgf / cm ² , placed in an aluminum coated pouch (8 cm × 12 cm), and the two adjacent corners were sealed at a temperature of 143 ° C., followed by 6.5 g of the electrolyte solution. Was added and sealed so that no air remained in the battery using a degassing machine for at least 3 minutes. The prepared battery was aged at 25 ° C. for 12 hours, and then pressed at 110 ° C. for 120 seconds under a pressure of 20 kgf / cm ² . Subsequently, the cell was dismantled to photograph an area where an active material of a negative electrode or a positive electrode was transferred to a separator (lumenera high resolution camera), and the image was transferred using an image analyzer (Easy Measure converter 1.0.0.4) to calculate the transferred area. It was set as the transcription rate. In addition, after the aging and the secondary pressing, the electrode assembly was continuously aged at 25 ° C. for 12 hours and pre-charged for 4.35V, 0.2C, and 1 hour to remove gas in the cell, and the following charging, After charging and discharging under the conditions of discharging and charging, the battery was dismantled, and the area transferred from the active material of the negative electrode or the positive electrode to the separator was measured by the same method as the transfer rate before charge and discharge, and the transfer rate after charge and discharge was determined.

As can be seen in Table 3, before the charge and discharge of the separator of Examples 1 to 6 in which the adhesive layer comprising the present acrylic copolymer and a polyvinylidene fluoride-based polymer having a weight average molecular weight of 1,000,000 g / mol or more is formed. The transfer rate after charge and discharge was good at all 50% or more, while the transfer rate before charge and discharge for Comparative Examples 1 to 3 using a polyvinylidene fluoride copolymer having a weight average molecular weight of less than 1,000,000 g / mol together with an acrylic copolymer Was more than 50%, but the charge rate was significantly lowered to less than 50% after charging and discharging. In addition, in the case of Comparative Example 4 using a polyvinylidene fluoride homopolymer having a weight average molecular weight of less than 1,000,000 g / mol with an acrylic copolymer, the thickness change rate was greater than 7%, and the separator was formed before and after charge and discharge. The transfer rate could not be measured because it was separated from the negative electrode or the positive electrode.

[Description of the code]

100, 200: secondary battery

10, 10 ': anode

20, 20 ': cathode

30, 30 ': separator

40: electrode assembly

50, 50 ': case

140: sealing member

Claims

Porous substrates; And

It includes an adhesive layer formed on one side or both sides of the porous substrate,

The adhesive layer comprises an acrylic copolymer comprising a repeating unit derived from a (meth) acrylate monomer, and a polyvinylidene fluoride polymer-containing adhesive layer having a weight average molecular weight of 1,000,000 g / mol or more.
The separation membrane according to claim 1, wherein the acrylic copolymer further comprises a repeating unit derived from an acetate group-containing monomer.
The separation membrane according to claim 2, wherein the acetate group-containing monomer-derived repeating unit is a single unit derived from one or more monomers of vinyl acetate and allyl acetate.
The repeating unit derived from the (meth) acrylate-based monomer according to claim 1, wherein the repeating unit derived from the (meth) acrylate monomer is selected from the group consisting of butyl (meth) acrylate, propyl (meth) acrylate, ethyl (meth) acrylate and methyl (meth) acrylate. A separator, which is a repeating unit derived from at least one monomer selected.
The separator according to claim 1, wherein the polyvinylidene fluoride polymer is at least one of polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, and modified polymer thereof.
Separation membrane according to any one of claims 1 to 5, wherein the adhesive layer further comprises inorganic particles.
The separation membrane according to any one of claims 1 to 6, wherein a weight ratio of the acrylic copolymer and the polyvinylidene fluoride polymer is 5: 5 to 8: 2.
The separator according to claim 1, wherein the polyvinylidene fluoride polymer has a weight average molecular weight in the range of 1,000,000 g / mol to 1,700,000 g / mol.
A porous substrate, and

Separation membrane comprising a binder-containing adhesive layer, formed on one or both sides of the porous substrate,

Separator, wherein the rate of transfer of the positive electrode or negative electrode active material to the separator after charging and discharging of the formula 1 is 50% or more, respectively.

[Equation 1]

Transfer rate (%) = (A 1 / A 0 ) X 100

In Formula 1,

A 0 is the total area of the cathode or anode,

A 1 forms an electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, and at the temperature of 20 ° C. to 110 ° C. for 1 second to 5 seconds, with a force of 1 kgf / cm 2 to 30 kgf / cm 2 . After pressing, the electrolyte solution is injected into the compressed electrode assembly, and the second electrode is pressed with a force of 1 kgf / cm 2 to 30 kgf / cm 2 for 60 ° C. to 110 ° C., 30 seconds to 180 seconds, and then charged, discharged and charged. When sequentially performed, the area of the positive electrode or negative electrode active material transferred to the separator.
The separator according to claim 9, wherein the thickness change rate of Equation 2 of the separator is 7% or less.

[Equation 2]

Thickness Change (%) = [(T 1 -T 2 ) / T 1 ] × 100

In Equation 2,

T 1 is interposed between the positive electrode and the negative electrode, and the positive electrode, the separator and the negative electrode is laminated to sequentially stacked to a size of 7 cm (length direction) × 6.5 cm (width direction) to form an electrode assembly Measured thickness,

T 2 is the thickness measured after pressing the formed electrode assembly at a pressure of 1 kgf / cm 2 to 30 kgf / cm 2 at 20 ° C. to 110 ° C. for 1 to 5 seconds.
The method of claim 9 or 10, wherein the adhesive layer comprises an acrylic copolymer containing a (meth) acrylate monomer-derived repeating unit and a polyvinylidene fluoride polymer having a weight average molecular weight of 1,000,000 g / mol or more, Separator.
The separation membrane according to claim 11, wherein the acrylic copolymer further comprises a repeating unit derived from an acetate group-containing monomer.
The separator according to claim 11 or 12, wherein a weight ratio of the acrylic copolymer and the polyvinylidene fluoride polymer is 5: 5 to 8: 2.
The separation membrane according to any one of claims 9 to 13, wherein the adhesive layer further includes inorganic particles.
A secondary battery comprising the separator according to any one of claims 1 to 14.
The secondary battery of claim 15, wherein the secondary battery is a lithium secondary battery.