KR20200047409A - Separator Comprising Binders with Different Solvation Temperature and Method for Preparing the Same - Google Patents

Abstract

The present invention relates to a separation membrane which comprises: a separation membrane basic material made of a polyolefin-based polymer resin; and a coating layer including an inorganic material formed on one surface or both surfaces of the separation membrane basic material, wherein the coating layer includes a first binder having a melting temperature of 55°C or less for an electrolyte solution, and a second binder having the melting temperature of 55°C or greater for the electrolyte solution.

Description

Separator Comprising Binders with Different Solvation Temperature and Method for Preparing the Same}

This application claims the benefit of priority based on Korean Patent Application No. 2018-01277359 filed on October 24, 2018, and all contents disclosed in the literature of the Korean patent application are incorporated as part of this specification.

The present invention relates to a separation membrane containing a binder having a different dissolution temperature and a method for manufacturing the same, specifically, by preventing two or more binders having different temperatures from being dissolved in an electrolyte solution from being prevented from being deteriorated in adhesion with an electrode and having high ions. It relates to a separation membrane capable of ensuring conductivity and a method for manufacturing the same.

2. Description of the Related Art With the reduction in weight and high functionality of portable wireless devices such as mobile phones, tablets, and wearable devices, the demand for secondary batteries as their energy source is rapidly increasing. In particular, research on lithium secondary batteries with high energy density and discharge voltage has been actively conducted. have.

In addition, the secondary battery is also attracting attention as a power source for electric vehicles, hybrid electric vehicles, and the like, which are proposed as solutions for air pollution, such as existing gasoline vehicles and diesel vehicles using fossil fuels.

The secondary battery unit is a mono cell composed of an anode / separator / cathode or a bicell composed of an anode / separator / cathode / separator / anode or composed of a cathode / separator / anode / separator / cathode. As a cell, a lamination / stack electrode assembly in which the unit cells are stacked may be manufactured, or a stack / folding electrode assembly wound in a state where the unit cell is placed on a long sheet-shaped separator may be manufactured.

As described above, a lamination process in which an anode and a cathode are adhered to a separator is required for manufacturing an electrode assembly, and for this purpose, a separator coated with an inorganic material and an adhesive binder is used.

However, when the content of the adhesive binder is too small or is easily dissolved in the electrolyte, there is a problem of separation from each other due to low adhesion between the electrode and the separator, and when the content of the adhesive binder is increased in order to increase the adhesion of the separator, ion conductivity May cause a problem that deteriorates.

In this regard, Patent Document 1 discloses a separator coated with a slurry in which two types of binders composed of a first binder polymer and a second binder polymer are dissolved, and the first binder polymer and the second binder polymer are solvents and non-solvents, respectively. As a binder having a different solubility index for, the present invention relates to a technique in which a second binder is more present on a separator substrate, so that the binding property to the electrode is good and inorganic particles are detached during assembly of the battery.

Patent document 1 discloses a method of improving adhesion to an electrode by using a separator comprising binders having different solubility indexes for a solvent or non-solvent.

Patent Document 2 relates to a separation membrane manufacturing method comprising sequentially coating a slurry solution containing a first binder polymer and a binder solution containing a second binder polymer on a separator substrate, the second solvent being formed while drying A porous polymer outer layer including pores is formed, and as the inorganic particles are connected and fixed by the first binder polymer, pores are formed between the inorganic particles.

The separation membrane of Patent Document 2 has a porous polymer outer layer formed on the surface to improve binding to an electrode and facilitate lamination, and the outer layer serves to prevent inorganic particles in the inner layer from being detached to the outside.

Patent document 3 relates to a separator having a structure in which a first coating layer including a first binder, a second coating layer including a second binder, and a non-solvent layer are sequentially formed on a separator substrate.

The separation membrane of Patent Document 3 has a feature of having excellent adhesion to an electrode and lowering of resistance by having a coating layer formed of a layered structure.

Patent Document 4 is a first polyvinylidene fluoride-based copolymer having a solubility of 25% by weight or more with respect to acetone at 35 ° C, a second polyvinylidene fluoride-based system having a solubility of 10% by weight or less with respect to acetone at 35 ° C It relates to a separator having a porous coating layer comprising a copolymer and a polymer having a cyano group.

That is, Patent Document 4 improves the initial output of the battery by using PVdF having a difference in solubility at the same temperature.

Although many techniques have been proposed, the adhesive strength between the electrode and the separator is prevented from deteriorating while maintaining the strength of the separator, and the demand for a separator having a high impregnation rate and high ionic conductivity for the electrolyte has not been solved.

Korean Patent Publication No. 2011-0097715 (2011.08.31.) Korea Patent Publication No. 2011-0035847 (2011.04.06.) Korea Patent Publication No. 2013-0045601 (2013.05.06.) Korea Patent Publication No. 2010-0108997 (2010.10.08.)

The present invention is to solve the above problems, in the lamination process for manufacturing an electrode assembly, the adhesion between the electrode and the separator is maintained, and by impregnating the electrode assembly with an electrolyte, partially pores are formed in the separator coating layer to improve ion conductivity. An object of the present invention is to provide a separation membrane and a method for manufacturing the same.

The separation membrane according to the present invention for achieving this object includes a separation membrane substrate made of a polyolefin-based polymer resin, and a coating layer comprising an inorganic substance formed on one or both surfaces of the separation membrane substrate, wherein the coating layer has a dissolution temperature for the electrolyte. It may include a first binder having a temperature of 55 ° C. or less, and a second binder having a dissolution temperature for an electrolyte of more than 55 ° C.

The electrolyte is a cyclic carbonate series such as ethylene carbonate and propylene carbonate, and a linear carbonate such as ethyl methyl carbonate and dimethyl carbonate. , Ester-based electrolyte such as methyl propionate, or a mixture thereof.

The weight ratio of the first binder and the second binder may be configured in the range of 1:99 to 20:80.

The dissolution temperature of the first binder in the electrolyte may be 20 ° C to 55 ° C, and the dissolution temperature of the second binder in the electrolyte may be 60 ° C to 150 ° C.

The first binder contains a PVdF-HFP copolymer having a molecular weight of 420 ㎏ / mol, and in the PVdf-HFP copolymer included in the first binder, HFP has a content of 15 mol% (63 kg / mol) or more, The second binder includes a PVdF-HFP copolymer having a molecular weight of 390 kg / mol, and the HFP content in the PVdf-HFP copolymer contained in the second binder may be 8 mol% (31 kg / mol) or less. .

The coating layer may have a single layer structure.

The inorganic material may be at least one selected from the group consisting of (a) an inorganic material having a dielectric constant of 5 or more, (b) an inorganic material having piezoelectricity, and (c) an inorganic material having lithium ion transfer ability.

Another aspect of the present invention may be an electrode assembly prepared by stacking the separator to be positioned between the positive electrode and the negative electrode, and pressurizing the stacked body on which the positive electrode, the separator and the negative electrode are stacked.

Another aspect of the invention of the present invention is a method of manufacturing a secondary battery including the electrode assembly, (a) an inorganic material, a first binder having a melting temperature of 55 ° C. or less for an electrolyte, and a melting temperature of an electrolyte solution of more than 55 ° C. A step of preparing a separator by coating a slurry in which two binders are mixed on at least one surface of a separator substrate, (b) combining the separator with an anode or a cathode, and then laminating to prepare an electrode assembly, and (c) heating the electrode assembly at a high temperature. Laminating by pressing, and (d) storing the electrode assembly and the electrolyte in a battery case, and then performing an activation process to form pores in the coating layer.

The activation process of step (d) may be performed at a temperature higher than the dissolution temperature for the electrolyte of the first binder and lower than the dissolution temperature for the electrolyte of the second binder.

In the step (c), the shapes of the first binder and the second binder may be maintained.

In addition, after the step (d), it may further include a step (e) of additionally injecting the electrolyte or replacing the existing electrolyte.

As described above, the separation membrane according to the present invention and a method for manufacturing the same, because it contains a binder having a low melting temperature for the electrolytic solution, it is dissolved in the activation process, pores are formed, and a separation membrane including a coating layer can be provided. have.

Therefore, in the process of manufacturing the electrode assembly, it is possible to prevent the binding force between the electrode and the separator from being lowered, and after the electrolyte is injected, the impregnation property of the electrode assembly with the electrolyte can be improved by the pores, and the mobility and ion conductivity of lithium ions are improved. Can increase

In addition, it is possible to provide a lithium secondary battery with improved life characteristics and cycle characteristics by increasing the ionic conductivity.

1 is a result of a comparative experiment of the adhesive strength using the separator of a comparative example and the separator of an embodiment according to the present invention.
2 is a photograph of the surface of the anode transferred after the comparative experiment results of the adhesion using the separation membrane of the comparative example and the separation membrane of the embodiment according to the present invention.

The separation membrane according to the present invention includes a separation membrane substrate made of a polyolefin-based polymer resin, and a coating layer comprising an inorganic material formed on one or both surfaces of the separation membrane substrate, wherein the coating layer is a first binder having a melting temperature for an electrolyte of 55 ° C. or less, And it may be made of a structure comprising a second binder having a dissolution temperature for the electrolyte is greater than 55 ℃.

The separator substrate is mainly made of polyethylene (polyethylene, PE) or polypropylene (polypropylene, PP) material. The method of making a microporous structure is divided into a wet process based on an extraction process and a dry process based on a stretching process. In the wet method, a polymer material and a low molecular weight wax are mixed and extruded into a film at a high temperature, and then a wax is extracted using a solvent to form a microporous structure.

At this time, biaxial stretching and heat treatment are appropriately performed to secure the mechanical properties required in the assembly process of the lithium secondary battery. On the other hand, the dry method does not use wax, makes pores only by stretching and heat treatment processes, and controls mechanical properties.

The separator must also secure the tensile strength required in the assembly process of the lithium secondary battery and the perforation strength characteristics that can withstand the internal pressure formed during the battery charging and discharging process. However, even a separation membrane that satisfies these physical properties cannot achieve desired electrochemical properties without ensuring sufficient wettability with the electrolyte. In particular, while the polyolefin material used as a separator is hydrophobic, the electrolyte solution using a carbonate-based organic solvent is hydrophilic, and thus there is a problem that it is difficult to secure wettability. Moreover, considering that the level of ionic conductivity of the separator is about 10% of that of the liquid electrolyte, improving the wettability of the separator is as important as improving physical properties.

The coating layer includes an inorganic material for securing the physical properties of the separator, and also includes a binder for fixing the inorganic material, bonding the coating layer with the separator substrate, and securing adhesion between the separator and the electrode.

The binder includes a first binder having a relatively low melting temperature for the electrolyte, and a second binder having a relatively high melting temperature for the electrolyte, wherein the melting temperature of the first binder is 55 ° C or less, and the second binder The dissolution temperature of may be greater than 55 ° C.

Specifically, the dissolution temperature of the first binder in the electrolytic solution is 20 ° C to 55 ° C, and the dissolution temperature of the second binder in the electrolyte solution may be 60 ° C to 150 ° C.

That is, since the melting temperatures of the first binder and the second binder do not overlap, if the activation proceeds to a temperature higher than the melting temperature of the first binder and lower than the melting temperature of the second binder, only the first binder is dissolved. Therefore, pores may be formed in the portion of the coating layer in which the first binder is dissolved. Therefore, the wettability of the separator may be improved, and the conductivity of lithium ions may also be increased. Thus, a secondary battery with improved life characteristics may be provided using a secondary battery to which the separator is applied.

The first binder contains a PVdF-HFP copolymer having a molecular weight of 410 kg / mol to 450 kg / mol, and in the PVdf-HFP copolymer included in the first binder, HFP has a content of 15 mol% or more, and the The second binder includes a PVdF-HFP copolymer having a molecular weight of 380 kg / mol to 400 kg / mol, and in the PVdf-HFP copolymer contained in the second binder, the HFP content may be 8 mol% or less.

The weight ratio of the first binder and the second binder may be included in the range of 1:99 to 20:80, specifically 5:95 to 15:85, and more specifically, in a weight ratio of 10:90 Can be included.

When the content of the first binder is less than 1% by weight based on the total weight of the first binder and the second binder, it is difficult to achieve an effect of improving ion conductivity, and when more than 20% by weight is included, the separator after the activation step It is not preferable because it may cause a problem of lowering the adhesion between the electrode and the electrode.

In addition, when only the first binder is included as a binder included in the coating layer, the adhesive force between the electrode and the separator is significantly lowered because the first binder is dissolved during the activation process, resulting in a problem that the electrode is separated from the separator. You can.

When only the second binder is included as the binder included in the coating layer, it is the same as that of the conventional binder, and a low wettability problem of the separator including only the conventional binder remains.

The electrolyte solution may be formed of a lithium salt and a non-aqueous organic solvent, and additionally, an organic solid electrolyte, an inorganic solid electrolyte, and the like may be included, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and gamma. -Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxorun, formamide, dimethylformamide, dioxol , Acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxon derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbohydrate Aprotic organic solvents such as nate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, Polymers including ionic dissociative groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ nitrides such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

The lithium salt is a material soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, non-aqueous electrolytes are provided for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide , Nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. can be added It might be. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) carbonate), PRS (Propene sulfone), and the like.

The inorganic material may be at least one selected from the group consisting of (a) an inorganic material having a dielectric constant of 5 or more, (b) an inorganic material having piezoelectricity, and (c) an inorganic material having lithium ion transfer ability.

The inorganic constant (a) having a dielectric constant of 5 or more may be SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ or SiC.

The inorganic material having a piezoelectric property (b) is a potential difference is formed due to the positive charge and negative charge generated between both sides of the particles when a certain pressure is applied, BaTiO ₃ , Pb (Zr, Ti) O ₃ (PZT), Pb _{1- x} La _x Zr _1-y Ti _y O ₃ (PLZT), Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiC, or a mixture thereof.

The inorganic material (c) having the lithium ion transfer ability contains a lithium element, but moves lithium ions without storing lithium, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3 ), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3), lithium germanium thiophosphate such as Li _3.25 Ge _0.25 P _0.75 S ₄ (Li _x Ge _y P _z S _w , 0 <x <4, 0 Lithium nitride such as <y <1, 0 <z <1, 0 <w <5), Li ₃ N (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO _4- SiS ₂ series glass such as Li ₂ S-SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), P such as LiI-Li ₂ SP ₂ S _{5 2} S ₅ series glass (Li _x P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7) or a mixture thereof.

The present invention also provides an electrode assembly including the separator, and the separator is stacked so as to be positioned between the positive electrode and the negative electrode, and the positive electrode, the separator, and the negative electrode can be manufactured by hot pressing the laminated body.

The positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, followed by drying, and if necessary, a filler is further added.

The positive electrode current collector is generally made to a thickness of 3 micrometers or more and 500 micrometers or less. The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver or the like may be used. The current collector may also increase the adhesion of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, sheet, foil, net, porous body, foam, and nonwoven fabric are possible.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as the formula Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; A Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The conductive material is usually added in 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that assists in bonding the active material and the conductive material and the like to the current collector, and is usually added at 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene styrene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component that inhibits the expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes in the battery, and includes, for example, an olefinic polymer such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode is manufactured by applying and drying a negative electrode material on a negative electrode current collector, and if necessary, components as described above may be optionally further included.

The negative electrode current collector is generally made to a thickness of 3 micrometers or more and 500 micrometers or less. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. In addition, like the positive electrode current collector, it is also possible to form a fine unevenness on the surface to enhance the bonding force of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

Examples of the negative electrode active material include carbons such as non-graphitized carbon and graphite-based carbon; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, group 1, group 2, group 3 elements of the periodic table, halogen; metal composite oxides such as 0 <x≤1;1≤y≤3;1≤z≤8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , and Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni based materials and the like can be used.

The present invention may also provide a battery pack including the secondary battery.

Specifically, the battery pack may be used as a power source for devices requiring high temperature safety, long cycle characteristics, high rate characteristics, and the like, and detailed examples of such devices include mobile devices and wearable devices. ), A power tool that is moved by power by an all-electric motor (power tool); Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf carts; An electric power storage device (Energy Storage System) may be mentioned, but is not limited thereto.

In addition, the present invention provides a method for manufacturing a secondary battery including the electrode assembly, specifically,

(a) preparing a separator by coating a slurry obtained by mixing an inorganic material, a first binder having a melting temperature of 55 ° C. or less, and a second binder having a melting temperature of 55 ° C. or higher of the electrolyte solution on at least one surface of a separator substrate ;

(b) combining the separator with an anode or a cathode and then laminating to prepare an electrode assembly;

(c) laminating the electrode assembly by hot pressing; And

(d) forming pores in the coating layer by storing the electrode assembly and the electrolyte solution in a battery case and then performing an activation process;

It may include.

The coating process of the step (a) may use deposition methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), and sputtering. The use of this method does not require the use of a separate binder and solvent, and has the advantage of forming a coating layer at the nanometer level.

The method of coating using a slurry is a method of uniformly dispersing a slurry using a doctor blade or the like after applying the slurry to a separator substrate, die casting, comma coating, screen printing ( Screen printing). In addition, after forming the slurry on a separate substrate (Substrate), a method of bonding with a separator substrate by pressing or lamination may also be considered. The thickness of the electrode slurry solution or the number of coatings, etc., may be adjusted to control the coating thickness of the final coating.

The coating layer formed on at least one surface of the separator substrate may be formed of a single layer structure formed by coating a slurry including an inorganic material, a first binder, and a second binder, and the thickness of the coating layer is relatively higher than that of the coating layer formed of a plurality of layered structures. As it can be formed thin, the process for forming a coating layer is simple, and has the advantage of having low resistance.

The activation process of step (d) may be performed at a temperature higher than the dissolution temperature of the first binder in the electrolyte and lower than the dissolution temperature of the second binder in the electrolyte.

Therefore, in the activation process, the first binder is dissolved in the electrolyte, and pores are formed in the coating layer where the first binder was. The wettability of the separator to the electrolyte may be improved by the formation of the pores, and the ion conductivity may be improved by being used as a migration path for lithium ions.

That is, in the lamination step of step (c) of the present application, even if pressure is applied under high temperature, the first binder cannot be dissolved because the electrolyte is not impregnated. Therefore, in the lamination step, the lamination process proceeds in a state in which the first binder as well as the second binder is not liberated or melted and the original shape is maintained.

However, as the electrolyte formed in the pores formed through the step (d) is filled with the electrolyte impregnation rate of the separator is increased, to prevent the electrolyte from being exhausted and deteriorating the life characteristics of the battery, after the step (d) The method may further include a step (e) of additionally injecting an electrolyte or replacing an existing electrolyte. Replacing the electrolyte solution is to replace the existing electrolyte solution with a new electrolyte solution to minimize the influence of the first binder dissolved in the electrolyte solution.

(Example, Example)

PVDF-HFP copolymer having a molecular weight of 410 to 450 kg / mol as a first binder (HFP content of 15 mol% or more, Tm is 140 ° C or less) and a PVDF-CTFE copolymer having a molecular weight of 250 to 300 kg / mol (Tm is A mixture of 160 ° C or higher) was used.

As the second binder, PVDF-HFP copolymer having a molecular weight of 380 to 400 kg / mol (HFP content is 8 mol% or less, Tm is 150 ° C or higher) and PVDF-CTFE copolymer having a molecular weight of 250 to 300 kg / mol (Tm Silver 160 ° C or more) was used.

A binder according to an embodiment was prepared by mixing the same weight of the first binder and the second binder.

As a mineral, Al ₂ O ₃ and the binder were mixed with acetone to make a slurry, which was coated on both sides of a polypropylene porous substrate and dried to prepare a separator.

(Comparative Example 1, Comp. Ex. 1)

A separator was prepared in the same manner as in Example 1, except that only the first binder was used.

(Comparative Example 2, Comp. Ex 2)

A separator was prepared in the same manner as in Example 1, except that only the second binder was used.

(Experimental example)

Anode production: A cathode material in which Ni, Co, and Mn were mixed at a constant ratio was used as an active material, and a PVdF polymer and a carbon-based conductive material were mixed at a constant ratio as a binder, and then a cathode slurry was prepared using acetone as a solvent. Then, it was applied to an aluminum foil as a current collector and dried.

After laminating the prepared positive electrode and the separators prepared in Example 1 and Comparative Example 1 and Comparative Example 2, they were laminated at a pressure of 5 kg / cm 2 in a temperature range of 25 ° C to 75 ° C.

After measuring the peel strength of the laminate of the prepared positive electrode and the separator, the positive electrode surface was transferred and photographed.

In order to measure the adhesive strength, a double-sided tape was attached to the glass plate, and the positive electrode and the separator laminated to the specimen were fixed.

After attaching the separator part of the specimen to UTM equipment (manufactured by TA), a force required to peel the separator was measured by applying a force of 180 degrees at a measurement speed of 300 mm / min.

The results of the adhesion test and the results of the transfer of the anode surface after the adhesion test are shown in FIGS. 1 and 2, respectively.

1 is a comparative experiment result of the adhesive strength using the separation membrane of the comparative example and the embodiment according to the present invention. When the adhesive strength was measured using the separation membrane using only the first binder (Comparative Example 1), it can be seen that the adhesive strength was decreased based on 55 ° C. This is because the first binder is dissolved in the electrolyte at 55 ° C.

When the adhesive force was measured using the separation membrane (Comparative Example 2) using only the second binder, it can be seen that the adhesive strength was decreased based on 70 ° C. This is because the second binder is dissolved in the electrolyte at 70 ° C.

In the embodiment according to the present invention, the first binder and the second binder are mixed at 50:50, and it can be seen that the adhesive strength decreases at 65 ° C or higher. When the separator according to the present invention is used, it can be seen that the first binder has an effect of maintaining adhesion even at a relatively high temperature, although it can be formed by dissolving at a low temperature.

2 is a photograph of the surface of the positive electrode transferred after the comparative experiment results of the adhesive strength using the separation membrane of the comparative example and the embodiment according to the present invention.

Similar to the results of FIG. 1, Comparative Example 1 and Comparative Example 2 show that the surface of the anode was changed after 45 ° C and 70 ° C, respectively, but it can be seen that the embodiment according to the present invention was changed after 65 ° C.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above.

Claims (11)

Separator substrate made of polyolefin-based polymer resin, and
It includes a coating layer comprising an inorganic material formed on one or both sides of the separator substrate,
The coating layer is a separator comprising a first binder having a dissolution temperature for the electrolyte of 55 ° C or less, and a second binder having a dissolution temperature for the electrolyte of greater than 55 ° C. According to claim 1,
The electrolyte is a cyclic carbonate series such as ethylene carbonate and propylene carbonate, and a linear carbonate such as ethyl methyl carbonate and dimethyl carbonate. , Methyl propionate (methyl propionate), such as one of the ester-based electrolyte, or a mixture of these separators. According to claim 1,
The weight ratio of the first binder and the second binder is a separator composed of a range of 1:99 to 20:80. According to claim 1,
The melting temperature of the first binder in the electrolyte is 20 ° C to 55 ° C,
The separation temperature of the second binder in the electrolyte is 60 ° C to 150 ° C. According to claim 1,
The coating layer is a separator made of a single layer structure. According to claim 1,
The inorganic material is at least one separator selected from the group consisting of (a) an inorganic material having a dielectric constant of 5 or more, (b) an inorganic material having piezoelectricity, and (c) an inorganic material having lithium ion transfer ability. The separation membrane according to any one of claims 1 to 6 is stacked to be positioned between the anode and the cathode,
An electrode assembly prepared by hot-pressing the laminate in which the positive electrode, the separator, and the negative electrode are stacked. A method for manufacturing a secondary battery comprising the electrode assembly according to claim 7,
(a) preparing a separator by coating a slurry obtained by mixing a inorganic material, a first binder having a melting temperature of 55 ° C. or less, and a second binder having a melting temperature of 55 ° C. or higher of the electrolyte solution on at least one surface of the separator substrate ;
(b) combining the separator with an anode or a cathode and then laminating to prepare an electrode assembly;
(c) laminating the electrode assembly by hot pressing; And
(d) forming pores in the coating layer by storing the electrode assembly and the electrolyte solution in a battery case and then performing an activation process;
Method of manufacturing a secondary battery comprising a. The method of claim 8,
The activation process of step (d) is a method of manufacturing a secondary battery that is performed at a temperature higher than the dissolution temperature for the electrolyte of the first binder and lower than the dissolution temperature for the electrolyte of the second binder. The method of claim 8,
The method of manufacturing a secondary battery in which the shapes of the first binder and the second binder are maintained in the step (c). The method of claim 8,
A method of manufacturing a secondary battery further comprising the step (e) of additionally injecting an electrolyte after the step (d).

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