KR101829748B1 - Separators comprising bonding layer and secondary battery using the separator - Google Patents

Abstract

A porous substrate; And an adhesive layer formed on one side or both sides of the substrate, wherein the adhesive layer comprises a polyvinylidene fluoride (PVdF) system having a unit derived from vinylidene fluoride and having a unit content derived from hexafluoropropylene (HFP) of 5% (PVDF) having a unit derived from hexafluoropropylene (HFP) in an amount of 10 to 30% by weight, the unit comprising a first binder, a unit derived from a vinylidene fluoride and a unit derived from hexafluoropropylene (HFP), and a polyvinylidene fluoride Wherein the weight ratio of the polyvinylidene fluoride (PVdF) first binder to the polyvinylidene fluoride (PVdF) second binder is 0.5: 9.5 to 2: 8, and the second binder includes the second binder. To a secondary battery.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator comprising an adhesive layer and a secondary battery using the separator.

The present invention relates to a separation membrane including an adhesive layer and a secondary battery using the separation membrane.

2. Description of the Related Art [0002] Portable electronic devices such as video cameras, cellular phones, and portable computers are generally made lighter and more sophisticated, and a lot of research has been conducted on secondary batteries used as driving power sources. Examples of such a secondary battery include a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, and a lithium secondary battery. 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.

It is required to improve the shape stability of the secondary battery by increasing the adhesive force between the separator and the electrode so as to prevent the shape of the secondary battery from being changed due to continuous charge and discharge in the secondary battery.

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 separation membrane in order to improve the adhesion between the separation membrane and the electrode and the heat resistance of the separation membrane (Korean Patent Registration No. 10-0775310) Can not be sufficiently ensured, and thus it is difficult to be applied to a separator having various sizes and shapes.

Accordingly, there is a need to develop a secondary battery which includes a separator having sufficient physical properties applicable to a secondary battery, and which can maintain the shape stability and adhesion of the battery even after charging / discharging, which is an environment in which an actual battery is used.

Korean Patent No. 10-0775310 (Announcement of November 11, 2007)

 none

Disclosed is a separator which has good heat resistance and is excellent in adhesion between a separator and an electrode, so that the shape of the cell can be maintained even after charging and discharging.

In one embodiment of the invention, a porous substrate; And an adhesive layer formed on one side or both sides of the substrate, wherein the adhesive layer comprises a polyvinylidene fluoride (PVdF) system having a unit derived from vinylidene fluoride and having a unit content derived from hexafluoropropylene (HFP) of 5% (PVDF) having a unit derived from hexafluoropropylene (HFP) in an amount of 10 to 30% by weight, the unit comprising a first binder, a unit derived from a vinylidene fluoride and a unit derived from hexafluoropropylene (HFP), and a polyvinylidene fluoride Wherein the weight ratio of the polyvinylidene fluoride (PVdF) first binder to the polyvinylidene fluoride (PVdF) second binder is 0.5: 9.5 to 2: 8 .

In another embodiment of the present invention, there is provided a secondary battery comprising a positive electrode, a negative electrode, a separator disclosed herein between the positive electrode and the negative electrode, and an electrolyte.

The separator according to one embodiment of the present invention is advantageous in that it has good heat resistance and air permeability and is excellent in adhesion between the separator and the electrode after charging and discharging, so that the shape of the battery is not deformed.

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

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.

As used herein, 'homopolymer' refers to a polymer comprising repeating units derived from one type of monomer, and 'copolymer' refers to a repeating unit derived from two or more types of monomers .

An embodiment of the present invention is a porous substrate comprising: a porous substrate; And an adhesive layer formed on one side or both sides of the substrate, wherein the adhesive layer comprises a polyvinylidene fluoride (PVdF) system having a unit derived from vinylidene fluoride and having a unit content derived from hexafluoropropylene (HFP) of 5% (PVDF) having a unit derived from hexafluoropropylene (HFP) in an amount of 10 to 30% by weight, the unit comprising a first binder, a unit derived from a vinylidene fluoride and a unit derived from hexafluoropropylene (HFP), and a polyvinylidene fluoride Wherein the weight ratio of the first binder of the polyvinylidene fluoride (PVdF) system to the second binder of the polyvinylidene fluoride (PVdF) system is from 0.5: 9.5 to 2: 8 .

The porous substrate may have a plurality of pores and may be a porous substrate that can be used in an electrochemical device. Porous substrates include but are not limited to polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide , A polyimide imide, a polybenzimidazole, a polyether sulfone, a polyphenylene oxide, a cyclic olefin copolymer, a polyphenylene sulfide, and a polyethylene naphthalene, or a mixture of two or more thereof Lt; / RTI > In one embodiment, the porous substrate may be a polyolefin-based substrate, and the polyolefin-based substrate may have an excellent shut down function, thereby contributing to improvement of the safety of the battery. 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 embodiment, 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 between 1 μm and 40 μm, more specifically between 1 μm and 20 μm, more specifically between 1 μm and 15 μm. When a porous substrate within the above-mentioned thickness range is used, it is possible to manufacture a separator having a suitable thickness, which is thick enough to prevent shorting of the positive and negative electrodes of the battery but not thick enough to increase the internal resistance of the battery.

The adhesive layer may include a polyvinylidene fluoride (PVdF) first binder and a second polyvinylidene fluoride (PVDF) binder.

The first polyvinylidene fluoride (PVdF) binder may be a polymer comprising vinylidene fluoride derived units.

In one embodiment, the first binder based on polyvinylidene fluoride (PVdF) may be a homopolymer containing only the vinylidene fluoride derived unit. In another embodiment, the polyvinylidene fluoride (PVdF) based first binder may be a copolymer of units different from the vinylidene fluoride derived units. The other unit may be at least one of units derived from chlorotrifluoroethylene (CTFE), trifluoroethylene (TFE), hexafluoropropylene (HFP), ethylene tetrafluoride, and ethylene, but is not limited thereto .

The copolymer of the other unit and the vinylidene fluoride derived unit is electrochemically stable and can have a sufficient potential window between the electrode potential of the lithium ion secondary battery.

When the first binder of the polyvinylidene fluoride (PVdF) system contains hexafluoropropylene (HFP) derived units, the content of units derived from hexafluoropropylene (HFP) may be 5% by weight or less. Specifically, it may be 3% by weight or less, more specifically 1% by weight or less. When a hexafluoropropylene (HFP) -derived unit is included in the above content range, when the separator containing the unit is included in the battery, the electrolytic solution in the separator and sufficient heat resistance can be exhibited.

In the case of containing chlorotrifluoroethylene (CTFE), trifluoroethylene (TFE), ethylene tetrafluoride or ethylene derived units, the content of the units may be 3 wt% or less, Can be improved.

The second polyvinylidene fluoride (PVdF) binder may be a copolymer comprising units derived from vinylidene fluoride and units derived from hexafluoropropylene (HFP).

The content of the hexafluoropropylene (HFP) -derived unit of the second binder may be 10 to 30% by weight. Specifically 10 to 25% by weight, and more specifically 10 to 20% by weight. When the hexafluoropropylene (HFP) -derived unit is contained in the above content range, it is possible to have excellent solubility in an organic solvent and excellent adhesion to an electrode.

In one embodiment, the second binder based on polyvinylidene fluoride (PVdF) may be a copolymer containing units other than units derived from vinylidene fluoride, units derived from hexafluoropropylene (HFP). The other unit may be at least one of units derived from chlorotrifluoroethylene (CTFE), trifluoroethylene (TFE), ethylene tetrafluoride, and ethylene.

The content of the other units may be specifically 3 wt% or less, more specifically 1 wt% or less, and the stability of the separator may be improved within the above range.

By using the above two types of polyvinylidene fluoride (PVdF) binder together, it is possible to obtain a separator which is excellent in solubility in an organic solvent and is not dissolved in an electrolyte solution but also has an adhesive force with an electrode and an adhesive force with a substrate have.

The weight ratio of the polyvinylidene fluoride (PVdF) first binder to the polyvinylidene fluoride (PVdF) second binder may be specifically 0.5: 9.5 to 2: 8. More specifically, it may be 0.5: 9.5 to 1: 9. In this range, solubility in an organic solvent is excellent, residual organic solvent content after the production of an adhesive layer is low, air permeability of the separator is good, and an adhesive strength to an electrode is excellent, so that deformation of the battery can be prevented. Further, it is possible to retain an excellent electrode adhesion force even after charging / discharging.

In the first binder of the polyvinylidene fluoride (PVdF) system and the second binder of the polyvinylidene fluoride (PVdF) system, the total amount of hexafluoropropylene (HFP) may be 10 to 35 wt%. Within this range, sufficient solubility in an organic solvent can be obtained.

The first polyvinylidene fluoride (PVdF) binder may have a weight average molecular weight of 900,000 to 2,000,000, more specifically 1,000,000 to 1,900,000, and still more specifically 1,100,000 to 1,800,000.

The weight average molecular weight of the second polyvinylidene fluoride (PVdF) binder may be specifically from 500,000 to 800,000. More specifically 500,000 to 700,000.

It is possible to obtain a sufficiently strong adhesive force between the adhesive layer and the porous substrate within the molecular weight range of the first binder and the second binder and effectively prevent the short circuit between the positive electrode and the negative electrode. It can be easily dissolved in a solvent, and the electrolytic impregnability can be excellent.

The total content of the polyvinylidene fluoride (PVdF) first binder and the polyvinylidene fluoride (PVdF) second binder may be specifically from 10 to 100% by weight based on the total weight of the dried adhesive layer , More specifically 20 to 90 wt%, and more particularly 20 to 60 wt%.

The adhesive layer in the present invention may further include a binder other than the polyvinylidene fluoride (PVdF) first binder and the polyvinylidene fluoride (PVdF) second binder. Examples of the binder that may be added include polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose (also referred to as " cyanoethyl cellulose, cyanoethyl cellulose, cyanoethyl cellulose, cyanoethyl cellulose, cyanoethyl cellulose, cyanoethyl cellulose, cyanoethyl cellulose, pullulan, carboxyl methyl cellulose, and acrylonitrile styrene butadiene copolymer. Mixture. .

Another embodiment of the present invention may further comprise inorganic particles in the adhesive layer. This embodiment differs from the embodiment of the present invention only in that it additionally includes inorganic particles, and the other structures are substantially the same, and therefore, the inorganic particles will be mainly described below.

The inorganic particles usable in the present invention are not particularly limited and inorganic particles commonly used in this technical field can be used. Specific 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. 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, and 300 nm to 500 nm. When the inorganic particles having the above-mentioned size range are used, the dispersibility of the inorganic particles in the adhesive layer composition and the processability of the adhesive layer can be prevented from being lowered, and the thickness of the adhesive layer can be controlled appropriately, Can be prevented. In addition, the size of the pores generated in the separation membrane is appropriately controlled, thereby reducing the probability of an internal short circuit occurring during charging and discharging of the battery.

In the adhesive layer, the inorganic particles may be contained in an amount of not more than 95% by weight, specifically not more than 75% by weight, more specifically not more than 55% by weight, based on the total weight of the dried adhesive layer, Specifically from 20% by weight to 55% by weight. When the inorganic particles are contained within the above range, the heat radiation characteristics of the inorganic particles can be sufficiently exhibited and the heat shrinkage of the separator can be effectively suppressed.

The total thickness of the adhesive layer may be specifically in the range of 1 to 15 mu m. More specifically from 1 to 6 mu m. In the above range, shrinkage and breakage do not occur and heat resistance can be excellent.

In order to manufacture the separation membrane according to the embodiments of the present invention, the first binder of the polyvinylidene fluoride (PVdF) system and the second binder of the polyvinylidene fluoride (PVdF) system are respectively dissolved in an appropriate solvent to form the adhesive layer composition Can be prepared.

The first polyvinylidene fluoride (PVdF) binder may be selected from the group consisting of dimethylacetamide, dimethyl formamide, dimethyl sulfoxide, dimethyl carbonate, (N-methylpyrrolidone) or the like in a high-boiling solvent to prepare a polymer solution.

Since the second binder of the polyvinylidene fluoride (PVdF) system has a relatively high solubility in an organic solvent, it is preferable to use acetone, tetrahydrofuran, methylene chloride, chloroform, cyclohexane cyclohexane) or the like to form a polymer solution state. In case of a high boiling point solvent, there is a high possibility of remaining in the adhesive layer after the drying process. If the solvent remains, the electrode adhesion after charging and discharging may be lowered. However, the second binder has excellent solubility in a low boiling point solvent, There is an advantage that it can be reduced. Herein, the term "low boiling point solvent" may be a solvent having a boiling point of 90 ° C. or lower, and a "high boiling point solvent" may be a solvent having a boiling point of 90 ° C. or higher. Examples of the low boiling point solvent include alcohols such as methanol, ethanol and isopropyl alcohol; And ketones such as acetone. Examples of the high-boiling solvent include N-methylpyrrolidone (NMP) and dimethylacetamide (DMAc). However, the solvent is not limited thereto.

When it further contains inorganic particles, it can be produced, for example, in the form of an inorganic dispersion dissolved in acetone. Thereafter, the polymer solution and the inorganic dispersion may be mixed with an appropriate solvent to prepare an adhesive layer composition.

Solvents usable in the present invention may be organic solvents. Specific examples thereof include ketones such as acetone, alcohols such as methanol, ethanol and isopropyl alcohol, dimethylacetamide (DMAc), tetrahydrofuran, methylene chloride, chloroform, dimethylform Dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane. These may be used alone or in combination of two or more.

The adhesive layer composition may be prepared in the form of a mixture through a process of sufficiently stirring the polymer solution and the solvent using a ball mill, a beads mill, a screw mixer or the like.

A pretreatment such as a sulfonation treatment, a graft treatment, a corona discharge treatment, an ultraviolet ray irradiation treatment, a plasma treatment or a sputter etching treatment may be arbitrarily performed to improve the adhesion with the adhesive layer before the adhesive layer is formed on one surface or both surfaces of the separator substrate have.

The method of forming the adhesive layer on the porous substrate is not particularly limited, and a method commonly used in the technical field of the present invention, for example, a coating method, a lamination method, a coextrusion method and the like can be used. Non-limiting examples of the coating method include a roll coating, a spin coating, a dip coating, a flow coating, a spray coating, and the like. The adhesive layer of the separator of the present invention may be formed by, for example, dip coating or spin coating.

The step of forming an adhesive layer on the porous substrate using the adhesive layer composition and then drying the porous substrate is not particularly limited and a method commonly used in the technical field of the present invention can be used.

The drying step may be performed by, for example, a hot air drying method.

The drying process can be performed preferably at a temperature ranging from 70 to 120 ° C. When the drying process is performed within the above temperature range, the drying process can be completed within a proper time. That is, there is an advantage that a smooth surface can be formed with a smooth surface while avoiding the occurrence of surface irregularities due to excessively rapid drying, while avoiding a long time in the drying step.

In another embodiment of the present invention, a separation membrane is provided, which can have an air permeability of 100 to 300 sec / 100cc. More specifically, it may be 100 to 280 sec / 100 cc.

The method of measuring the air permeability of the separation membrane is not particularly limited. As a method for measuring the air permeability, a method commonly used in the technical field of the present invention can be used. Non-limiting examples of the method of measuring the permeability are as follows: Ten specimens cut at 10 different points are made Then, the average time taken for the permeation of 100 cc of air through the separator having a circular area of 1 inch in diameter was measured five times each using the EG01-55-1 MR (Asahi Seiko) model The average value is calculated to measure the air permeability.

In addition, the separator may have a heat shrinkage ratio in the longitudinal direction (MD direction) and transverse direction (TD direction) at 130 ° C for 5 minutes of 20% or less. Specifically, the heat shrinkage rate may be 10% or less.

The method of measuring the heat shrinkage ratio is not particularly limited. As a method for measuring the shrinkage ratio, a method commonly used in the technical field of the present invention can be used. Non-limiting examples of the method of measuring the shrinkage ratio are as follows: MD 60 mm x TD 60 mm , 10 pieces of separation membrane specimens cut at 10 different points were prepared and 25 mm in length and width were marked. The marked specimens were allowed to stand in an oven at 130 to 200 ° C for 5 minutes, The degree of shrinkage is measured to calculate the average heat shrinkage.

The separation membrane having the heat shrinkage rate and air permeability has an advantage of not only facilitating movement between ions in the cathode and the anode, but also having excellent heat resistance, thereby effectively preventing short-circuiting of the electrode and improving safety of the battery.

The separation membrane may have a residual amount of the solvent in the adhesive layer of 100 ppm or less. Specifically, the residual amount of the high boiling point solvent of the polyvinylidene fluoride (PVdF) first binder may be 100 ppm or less. Specifically, it may be 80 ppm or less, more specifically 50 ppm or less. The high boiling point solvent is as described above.

When the residual amount of the solvent in the adhesive layer of the separator exceeds 100 ppm, there is a problem that the binder component is difficult to exhibit sufficient adhesive property by an excessive amount of solvent, and the adhesive strength of the adhesive layer is lowered to effectively suppress the heat shrinkage of the porous substrate In addition, when the battery is charged and discharged, it participates in an electrochemical reaction and acts as an obstacle to the performance of the battery. In addition, there is a problem that an electrode is short-circuited when the battery is overheated.

The method for measuring the remaining amount of the solvent is not particularly limited, and a method commonly used in the technical field of the present invention can be used.

A method for measuring the residual amount of the solvent is as follows. The dried separation membrane is immersed in methanol, and after 4 hours, the methanol (containing residual solvent extracted) is subjected to gas chromatography Gas-Chromatography), and the remaining amount of the solvent in the dried separator adhesive layer is measured.

The separation membrane may have a transfer ratio of 60% or more to the separation membrane of the anode or the anode active material after charging / discharging of Equation (1).

[Formula 1]

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

In Equation (1)

A ₀ is the total area of the separation membrane,

A ₁ is a method in which a separator is placed between an anode and a cathode and primary compression is performed at 95 to 105 ° C for 1 to 5 seconds under a force of 1 to 5 kgf / cm ² , and an electrolyte is injected into the pressed anode / Followed by secondary compression with a force of 95 to 105 DEG C for 25 to 40 seconds at a pressure of 10 to 200 kgf / cm < ² >, and then charging, discharging, and charging are sequentially performed to measure the area of the positive electrode or negative electrode active material transferred to the separator . The area of the positive electrode or negative electrode active material can be measured by a known image analyzer.

The charging, discharging and charging conditions are shown in Table 1 below.

Char / Room / Charge (Charge) 4.35V, 0.2C, 50 mA cut-off 5 hrs (Room) 0.2C, 3V cut-off 5 hrs (Charge) 0.5C, 4V cut-off 2 hrs

The transfer rate of the positive electrode or the negative electrode active material to the separator is 60% or more because the charge and discharge are repeated so as to minimize changes in battery shape in an environment where battery expansion and contraction are repeated, Or deterioration of battery performance due to this can be minimized. The transfer ratio may be specifically 70% or more, more specifically 80% or more.

Another embodiment of the present invention relates to a positive electrode, a negative electrode, a separator disclosed herein between the positive electrode and the negative electrode, and a secondary battery comprising the electrolyte.

The type of the secondary battery is not particularly limited and may be a battery of a kind known in the technical field of the present invention. 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 for producing the secondary battery of the present invention is not particularly limited, and a method commonly used in the technical field of the present invention can be used.

In detail, a method of manufacturing a secondary battery according to an embodiment of the present invention is as follows. A separator of the present invention is placed between an anode and a cathode of a battery, and then an electrolytic solution is filled in the separator. A battery can be manufactured.

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

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

The separation membrane 30 is as described above.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The secondary battery according to another example of the present invention may have a 100 cycle charge / discharge retention rate in the range of 70% to 100%, specifically 80% to 100%.

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Example  And Comparative Example

Example  One

1. Preparation of adhesive layer composition

(PVdF) first binder (HSV 500, Arkema) having a weight average molecular weight of about 1,600,000 and a hexafluoropropylene (HFP) content of 1% by weight or less was mixed with an acetone / DMAc mixed solution (acetone: DMAc weight ratio = 50: 50), and the mixture was stirred at 25 占 폚 for 4 hours using a stirrer to prepare a first polymer solution.

A second binder (Solef21216, Solvay, Korea) having a weight average molecular weight of about 600,000 and a hexafluoropropylene (HFP) content of 12% by weight was mixed with acetone ), And the mixture was stirred at 25 캜 for 4 hours using a stirrer to prepare a second polymer solution.

The first polymer solution and the second polymer solution were mixed so that the weight ratio of the first binder and the second binder was 1: 9, and the mixture was stirred at 25 ° C for 2 hours using a power mixer to prepare an adhesive layer composition.

2. Preparation of Membrane

The adhesive layer composition prepared above was coated on both sides of a 12 占 퐉 thick polyethylene single film base film by dip coating method and then dried for 0.03 hours at a drying temperature of 120 占 폚 and an air velocity of 15 m / Was prepared.

Example  2

An adhesive layer composition and a separator were prepared in the same manner as in Example 1, except that the weight ratio of the first binder to the second binder was 2: 8.

Example  3

An adhesive layer composition and a separation membrane were prepared in the same manner as in Example 1, except that the weight ratio of the first binder to the second binder was 0.5: 9.5.

Example  4

In Example 1, the first polymer solution and the second polymer solution were mixed so as to have a weight ratio of 1: 9 in the first binder and the second binder in preparing the adhesive layer composition, and alumina (Al ₂ O ₃ , Except that the inorganic dispersion liquid prepared by adding 25% by weight to acetone and milling at 25 캜 for 3 hours using a ball mill was mixed so that the weight ratio of the binder to the alumina was 6: 4 An adhesive layer composition and a separation membrane were prepared in the same manner as in Example 1.

Comparative Example  One

An adhesive layer composition and a separator were prepared in the same manner as in Example 1, except that the first polymer solution was not used but only the second polymer solution was used.

Comparative Example  2

An adhesive layer composition and a separator were prepared in the same manner as in Example 1, except that the weight ratio of the first binder to the second binder was 3: 7.

Comparative Example  3

An adhesive layer composition and a separation membrane were prepared in the same manner as in Example 1, except that the weight ratio of the first binder to the second binder was 5: 5.

Comparative Example  4

An adhesive layer composition and a separator were prepared in the same manner as in Example 4 except that the first binder and the second binder were mixed so as to have a weight ratio of 8: 2.

Experimental Example

The properties of the prepared Examples 1 to 4 and Comparative Examples 1 to 4 were measured by the following methods, and the results are shown in Table 2.

Experimental Example  1: Measurement of air permeability of membrane

The following experiments were performed to measure the air permeability of the membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 4.

Each of the membranes prepared in the above Examples and Comparative Examples was cut into 10 specimens cut in 10 different sizes so that a circle having a diameter of 1 inch or more could be inserted. Then, the air permeability measuring device EG01-55 -1MR (Asahi Seiko Co., Ltd., Japan) was used to measure the passage time of 100 cc of air in each of the above specimens. The time was measured five times in each case, and the average value was measured to measure the air permeability (sec / 100cc).

Experimental Example  2: High point  Measurement of residual solvent amount

Each of the membranes prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was sampled and immersed in methanol.

After 4 hours, the methanol (containing extracted and contained DMAc) was analyzed by gas-chromatography and the amount of DMAc remaining in the dried separator adhesive layer was measured (ppm).

The results of the measurements according to Experimental Examples 1 and 2 are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Air permeability (sec / 100cc) 260 270 245 220 220 290 550 > 1000 Remaining amount of solvent (DMAc) (ppm) 20 30 <10 <10 0 100 150 300

Experimental Example  3: Charging and discharging  Transfer rate of active material

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 was first pressed at 100 ° C. for 3 seconds under a pressure of 3 kgf / cm ² , sealed in an aluminum coated pouch (8 cm × 12 cm), sealed at a temperature of 143 ° C., And the battery was sealed using a degassing machine for 3 minutes or more so that no air remained in the battery. The prepared battery was aged at 25 캜 for 12 hours and subjected to secondary compression at 100 캜 for 30 seconds under a pressure of 30 kgf / cm ² . After pre-charge at 4.35V, 0.2C for 1 hour, the gas in the cell was removed and the battery was charged / discharged under the conditions of charging, discharging and charging below, and the battery was disassembled and the area of the anode or anode active material transferred to the separator A ₁ ) was measured using an image analyzer (product name: Easy Measure converter 1.0.0.4).

(Charge) 4.35V, 0.2C, 50 mA cut-off, 5 hours

(Discharge) 0.2C, 3V cut-off, 5 hours

(Charge) 0.5C, 4V cut-off, 2 hours

The area (A ₁ ) was divided by the total area (A ₀ ) of the separator and multiplied by 100 to calculate the transfer ratio (%) of the positive electrode or negative electrode active material to the separator.

In the case of the transfer ratio of 60% or more, the image is expressed as 'phase', the case where the transfer ratio is 40% or more and less than 60% is indicated as 'middle' and the case where the transfer rate is less than 40%

The results of the measurement according to Experimental Example 3 are shown in Table 3 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Transfer rate (%, anode) Prize Prize Prize Prize Ha medium Ha Ha Transfer rate (%, cathode) Prize Prize Prize Prize Ha medium Ha Ha

As shown in Tables 2 and 3, in Comparative Example 1 using only the second binder of the polyvinylidene fluoride (PVdF) system, the adhesive strength was lowered, and the first binder of polyvinylidene fluoride (PVdF) Comparative Examples 2 to 4, which were contained at relatively high ratios, showed lowered air permeability and electrode adhesive properties after charge and discharge. On the other hand, Examples 1 to 4 showed improved adhesion to the anode or anode while satisfying basic properties such as air permeability.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (14)

A porous substrate; And
And an adhesive layer formed on one side or both sides of the substrate,
Wherein the adhesive layer comprises a first polyvinylidene fluoride (PVdF) binder containing units derived from vinylidene fluoride and having a unit content of hexafluoropropylene (HFP) of 5% by weight or less and a first binder comprising a vinylidene fluoride derived unit and a hexafluoro And a second polyvinylidene fluoride (PVDF) based binder containing units derived from propylene (HFP) and having a hexafluoropropylene (HFP) unit content of 10 to 30% by weight,
The weight ratio of the polyvinylidene fluoride (PVdF) first binder to the polyvinylidene fluoride (PVdF) second binder is 0.5: 9.5 to 1: 9,
Wherein the inorganic particles are contained in an amount of not more than 75% by weight based on the total weight of the dried adhesive layer. The polyvinylidene fluoride (PVdF) binder according to claim 1, wherein the total content of the polyvinylidene fluoride (PVdF) first binder and the hexafluoropropylene (HFP) in the polyvinylidene fluoride (PVdF) %, Separator. The separation membrane according to claim 1, wherein the weight average molecular weight of the polyvinylidene fluoride (PVdF) first binder is 900,000 to 2,000,000. The separation membrane according to claim 1, wherein the second polyvinylidene fluoride (PVdF) binder has a weight average molecular weight of 500,000 to 800,000. delete The separation membrane according to claim 1, wherein the inorganic particles are at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO ₂ and SnO ₂ . The separation membrane according to any one of claims 1 to 4, wherein the total thickness of the adhesive layer is 1 to 15 占 퐉. The separation membrane according to claim 7, wherein the total thickness of the adhesive layer is 1 to 6 占 퐉. The separation membrane according to any one of claims 1 to 4, wherein the separation membrane has an air permeability of 100 to 300 sec / 100 cc 占 퐉 16 占 퐉. The separator according to any one of claims 1 to 4, wherein the separator has a heat shrinkage ratio of 20% or less in the longitudinal direction (MD direction) and the transverse direction (TD direction) at 130 캜 for 5 minutes. The separation membrane according to any one of claims 1 to 4, wherein the remaining amount of the solvent in the adhesive layer is 100 ppm or less. The separation membrane according to any one of claims 1 to 4, wherein the transfer ratio of the positive electrode or the negative electrode active material to the separation membrane after charging and discharging is 60% or more, respectively.
[Formula 1]
Transfer rate (%) = (A ₁ / A ₀ ) × 100
In Equation (1)
A ₀ is the total area of the separation membrane,
A ₁ is a method in which a separator is placed between an anode and a cathode and primary compression is performed at 95 to 105 ° C for 1 to 5 seconds under a force of 1 to 5 kgf / cm ² , and an electrolyte is injected into the pressed anode / separator / Followed by secondary compression at 95 to 105 DEG C for 25 to 40 seconds under a force of 10 to 200 kgf / cm &lt; ² &gt;, and then charging, discharging and charging are sequentially performed under the following conditions: the positive electrode or the negative electrode active material .
(Charge) 4.35V, 0.2C, 50 mA cut-off, 5 hours
(Discharge) 0.2C, 3V cut-off, 5 hours
(Charge) 0.5C, 4V cut-off, 2 hours anode; cathode; A separation membrane according to any one of claims 1 to 4, which is located between the anode and the cathode; And an electrolyte. 14. The secondary battery according to claim 13, wherein the secondary battery is a lithium secondary battery.

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