KR101700806B1 - Manufacturing method of separator and separator for secondary battery accoring to the method - Google Patents

Abstract

The present invention relates to a separation membrane producing method and a separation membrane for a secondary battery produced by the method and a method for producing the same, which comprises sequentially coating a binder powder having conductivity by a plasma treatment and a ceramic powder And a separator for a secondary battery manufactured by such a method.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a separator for a secondary battery,

The present invention relates to a separation membrane production method having excellent thinning and thickness uniformity and a separation membrane for a secondary battery produced by such a method. Specifically, plasma treatment is performed to sequentially coat a binder powder and a ceramic powder having different conductivity from each other And a separation membrane for a secondary battery manufactured by such a method.

2. Description of the Related Art In recent years, with the rapid development of electronic and communication computer industries, portable electronic devices have been increasing in popularity, and research on secondary batteries having a long life and high energy density as a power source for portable electronic devices has been on the rise.

Among secondary batteries, lithium secondary batteries, which use an organic electrolyte solution and exhibit a discharge voltage and a high energy density two times higher than those of conventional batteries using an aqueous alkaline solution, are in the spotlight.

The lithium secondary battery can be classified according to the structure of the electrode assembly. Typical examples of the lithium secondary battery include a long-sheet type positive electrode and negative electrode, a jelly-roll (wound type) electrode assembly wound in a state in which a separator is interposed, A stacked (stacked) electrode assembly in which a plurality of cut out positive electrodes and negative electrodes are stacked with a separator interposed therebetween; a stacked (stacked) electrode assembly in which a predetermined number of positive and negative electrodes are stacked with a separator interposed therebetween; And a stack / folding type electrode assembly in which full cells are wound into a separator sheet.

On the other hand, in the electrode assembly component, the separation membrane prevents physical contact between the cathode and the anode, and at the same time passes lithium ions through the pores. As such, it does not participate in the electrochemical reaction during charging / discharging, The porosity, the hydrophilicity, the material, and the like, can significantly affect the cycle performance and safety of the battery.

Typical separator membranes include porous polyolefin separator membranes. However, due to the characteristics of the manufacturing process including material properties and elongation, the polyolefin separator may exhibit extreme heat shrinkage behavior at a high temperature of 100 ° C or higher, causing a short circuit between the cathode and the anode, thereby causing a battery accident. In addition, from the viewpoint of mechanical properties, physical breakdown characteristics of the separator are weak, which shortens the internal short circuit of the battery due to foreign substances in the battery.

Therefore, studies on a safety reinforced separator (hereinafter referred to as 'SRS membrane') that can fundamentally solve such thermal and mechanical strength and control the adhesion and thickness uniformity have been actively conducted have.

The present invention provides a separation membrane manufacturing method which is excellent in thinning and thickness uniformity.

Also, the present invention provides a secondary battery separator manufactured by the above method and a secondary battery comprising the same.

The present invention provides a separation membrane manufacturing method comprising a step of sequentially coating a binder powder and a ceramic powder having different conductivity by plasma treatment.

Specifically, in the present invention,

Preparing a binder powder and a ceramic powder;

Performing a plasma treatment on each of the powders;

Spraying the plasma-treated binder powder onto both surfaces of the separator substrate and coating the same; And

And adsorbing and coating the plasma-treated ceramic powder on both surfaces of the separation membrane coated with the binder powder.

In addition, in the present invention, it is possible to further include a step of secondarily spraying the plasma-treated binder powder after coating the ceramic powder.

In addition, the present invention provides a separation membrane for a secondary battery, which is produced by the separation membrane production method and is excellent in thickness and thickness uniformity.

The present invention also provides a secondary battery including a negative electrode, a positive electrode, an electrolyte, and a separator for a secondary battery of the present invention.

According to the present invention, it is possible to produce a separation membrane for a secondary battery which is thinned and has excellent thickness uniformity by sequentially coating a binder powder and a ceramic powder having different conductivity on the both surfaces of the separation membrane substrate. Furthermore, in the case of the secondary battery separator produced by this method, a synergistic effect of increasing the shrinkage ratio can be ensured, and a secondary battery having excellent stability can be produced.

1 is a process diagram of a separation membrane manufacturing method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The SRS separator used as a separator for a secondary battery is manufactured by coating a ceramic coating material containing ceramic particles and an ionic binder polymer on both sides of a polyolefin-based or polyester-based resin separator substrate (refer to Korean Patent Registration No. 1125013) Recently, a method of corona treatment of the surface of the separator substrate with plasma before coating the polymeric material or the like on the polyolefin-based separator substrate in order to further improve the adhesion of the separator (KOKAI Publication No. 2012-117221 (See Japanese Patent Application Laid-Open No. H06-33886). However, the SRS membrane produced by this method has a drawback in that it is thin and has a low thickness uniformity.

Thus, the present invention provides a separation membrane manufacturing method which is excellent in adhesion as well as thermal stability, mechanical strength and thickness uniformity.

Specifically, in one embodiment of the present invention

Preparing a binder powder and a ceramic powder;

Performing a plasma treatment on each of the powders;

Spraying the plasma-treated binder powder onto both surfaces of the separator substrate and coating the same; And

And adsorbing and coating the plasma-treated ceramic powder on both surfaces of the separation membrane coated with the binder powder.

In the method of the present invention, the binder powder is not particularly limited as long as it is a component that is excellent in the bonding force with the electrode stacked on the separation membrane and the bonding force with the ceramic powder, and is not easily dissolved by the electrolyte solution. Examples thereof include polyacrylic acid, poly Acrylic acid copolymer, butadiene-acrylic acid copolymer, butadiene-methacrylic acid copolymer, polyvinylsulfonate, chlorosulfonated polyethylene, perfluorinated sulfonated ionomer, , A sulfonated polystyrene, a styrene-acrylic acid copolymer, and a sulfonated butyl rubber. Specific examples of the polymer include polyvinylidene fluoride (PVdF), polyvinylidene Fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride Polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethylmethacrylate, polyvinyl acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile styrene butadiene copolymer, and poly And a polymer having one or two or more components selected from the group consisting of a polymer,

Further, if the ceramic powder does not cause oxidation and / or reduction reaction, that is, does not cause an electrochemical reaction with the positive electrode or the negative electrode current collector in the operating voltage range of the battery (for example, 0-5 V based on Li / Li + But not limited to, Al ₂ O ₃ , BaTiO ₃ , CaO, CeO ₂ , NiO, MgO, SiO ₂ , SnO ₂ , SrTiO ₃ , _{TiO 2, Y 2 O 3,} ZnO, ZrO 2, Pb (Zr, Ti) O 3 (PZT), Pb 1-x La x Zr 1-y TiyO 3 (PLZT), PB (Mg 1/3 Nb 2 / ₃ ) O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ).

The particle diameter of the binder powder and the ceramic powder is preferably in the range of 1 to 100 nm. If the particle diameters of the powders are more than 100 nm, the thickness of the separator may be increased to decrease the battery capacity. If the particle diameter is less than 1 nm, the dispersibility of the particles may deteriorate and the ion migration may be disturbed.

Meanwhile, in the plasma treatment, the gas is subjected to a large energy, and ionized particles other than the phase transition are almost the same in total and negative charge numbers, so that the plasma is changed into an electrically neutral state as a whole. Is used industrially to increase or increase the physical properties such as conductivity, adhesive force, and tensile strength. Such a plasma may be applied to MF (Medium Frequency) plasma using a low frequency AC signal of several to 60 KHz, RF (Radio Frequency) using 13.56 MHz belonging to Industrial and Scientific and Medical (ISM) frequency band, Radio Frequency Plasma, Microwave Plasma, which also belongs to the ISM band, uses 2.45GHz.

In the present invention, the plasma treatment of the binder powder and the ceramic powder can be carried out using MF or RF plasma.

The plasma treatment may be performed using oxygen, nitrogen, argon gas or the like, and is not limited to these gases.

At this time, in the method of the present invention, the binder powder and the ceramic powder may have opposite conductivity by the plasma treatment. For example, in the case of the binder powder, negative conductivity can be imparted to the surface by an atmospheric pressure plasma treatment using an Ar + O ₂ mixed gas. In addition, in the case of the ceramic powder, DC (direct current) discharge can be performed in the plasma generation method to impart positive conductivity to the surface. In other words, if the cathode is a nonconducting nonconductor, ions can not be supplied to the ion in the cathode, so the ions are accumulated on the surface of the cathode. When a lot of ions are accumulated, the cathode surface becomes a positive potential.

In addition, in the method of the present invention, the separation membrane substrate is not particularly limited as long as it is a conventional polyolefin-based polymer, and a known separation membrane having a thickness of about 10 to 15 탆 can be used as it is. Examples thereof include polyolefin- , A polyester-based resin, a polyacrylonitrile resin, and a cellulose-based material, and more specifically, a microporous film or nonwoven fabric made of polyethylene, polypropylene-based, polyvinyl And a microporous membrane or nonwoven fabric made of one or more components selected from the group consisting of polytetrafluoroethylene, polytetrafluoroethylene, polytetrafluoroethylene, polyethylene terephthalate, and polybutylene terephthalate.

Further, in the method of the present invention, spraying and coating the plasma-treated binder powder 11 may include the steps of: dissolving the plasma-treated binder powder 11 in a solvent to prepare a slurry; And a step of firstly spraying the slurry onto both surfaces of the membrane base material 21 by a spraying method (see step A of FIG. 1).

The solvent used to prepare the binder powder slurry should have good solubility characteristics for the polymer and non-solvent properties for the membrane substrate. Specific examples thereof include acetone, tetrahydrofuran, acetonitrile, dimethylformamide, dimethylsulfoxide, dimethylacetamide, N-methylpyrrole or water, or a mixture of two or more thereof.

Next, in the method of the present invention, the separation membrane base material 21 on which the binder powder 11 is coated is passed through the reaction tank 15 in which the plasma-treated ceramic powder 13 is dispersed. As a result, a ceramic powder having a positive conductivity is coated (adsorbed) on both sides of the separator substrate coated with the binder powder having negative conductivity (see step B of FIG. 1).

At this time, the adsorption thickness of the ceramic powder can be appropriately adjusted as needed by controlling the degree of conductivity imparting and the degree of exposure of the ceramic powder section. Specifically, the weight ratio of the binder powder: ceramic powder coated on both surfaces of the separator film is 1: 9, more specifically, the binder powder: the coating thickness ratio of the ceramic powder may be 2: 8. The total coating thickness of the binder powder and the ceramic powder is preferably 6 탆 to 8 탆. If the total thickness is 6 탆 or less, the desired mechanical strength and ion conductivity may not be improved. If the total thickness exceeds 8 탆, the mixed layer may act as a resistive layer to decrease the electric capacity.

The method of the present invention may further include the step of secondly spraying the plasma-treated binder powder to improve the adhesive force of the ceramic powder on both sides of the separation membrane coated with the ceramic powder (See step C of FIG. 1)

According to another embodiment of the present invention, a separation membrane for a secondary battery, which is manufactured by the method of the present invention and is excellent in thickness and thickness uniformity, can be provided.

According to another embodiment of the present invention, there is provided a secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte, wherein the separator is a lithium secondary battery manufactured by the separator manufacturing method of the present invention, Can be provided.

The anode may be prepared, for example, by applying a slurry prepared by mixing a positive electrode active material with a solvent such as NMP, onto a cathode current collector, followed by drying and rolling.

In addition to the positive electrode active material, the positive electrode material may optionally include a conductive material, a binder, a filler, and the like.

The positive electrode active material is _{LiCoO 2, LiNiO 2, LiMn 2} O 4, LiCoPO 4, LiFePO 4, LiNiMnCoO 2 and _{LiNi 1 -xy- z Co x M1 y} M2 z O 2 (M1 and M2 are independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo; x, y and z are, 0 < / = y < 0.5, 0 < / = z < 0.5, and x + y + z < 1) as the atomic fractions of the elements , But are not limited thereto.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing a chemical change in the battery, and includes, for example, 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 fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, 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 and the like can be used. Concrete examples of commercially available conductive materials include acetylene black series such as Chevron Chemical Company, Denka Singapore Private Limited, Gulf Oil Company, etc.), Ketjenblack, EC (Armak Company), Vulcan XC-72 (Cabot Company), and Super P (Timcal).

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The positive electrode collector is not particularly limited as long as it has electrical conductivity without causing chemical change in the battery. For example, the positive electrode collector may be formed of a metal such as carbon, stainless steel, aluminum, nickel, titanium, sintered carbon, , Nickel, titanium, silver, or the like may be used.

The negative electrode may be prepared, for example, by applying a negative electrode active material containing a negative active material on a negative electrode current collector, followed by drying. The negative electrode active material may further include a conductive material, a binder, And the like.

Examples of the negative electrode active material include natural graphite, artificial graphite, carbonaceous material; Lithium-containing titanium composite oxide (LTO), metals (Me) with Si, Sn, Li, Zn, Mg, Cd, Ce, Ni or Fe; An alloy composed of the metal (Me); An oxide of the metal (Me) (MeOx); And a composite of the metal (Me) and the carbon (C).

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel Surface-treated with carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The lithium salt-containing nonaqueous electrolyte solution is composed of an electrolyte solution and a lithium salt. As the electrolyte solution, a nonaqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte may be used.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane , Acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate Nonionic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyrophosphate, ethyl propionate and the like can be used.

The lithium salt is a material that is readily 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.

As described above, in the present invention, since the plasma-treated binder powder and the ceramic powder are sequentially coated by the spraying or adsorption method, it is not necessary to perform phase separation in the drying section unlike the conventional dip coating method, Can be imported. Further, the binder powder may be sprayed on both surfaces of the separation membrane substrate, and then the ceramic powder may be adsorbed through the separation membrane substrate into the reaction vessel in which the fine ceramic powder is distributed in the air, thereby thinning the separation membrane. Particularly, since particles having a large particle size at the stage of adsorption of ceramic powder are highly likely to be distributed at the bottom of the reaction vessel, a ceramic particle having a small particle size can be coated, thereby improving the thickness uniformity of the separation membrane and increasing the shrinkage ratio. Therefore, the capacity and stability of the secondary battery employing the SRS separator for a secondary battery of the present invention can be improved.

11: Plasma treated binder powder
13: Plasma-treated ceramic powder
15: Reactor
21: Membrane substrate
A: a step of first spraying the plasma-treated binder powder and coating
B: Step of adsorbing and coating the plasma-treated ceramic powder
C: Step of spraying secondarily sprayed plasma-treated binder powder

Claims (17)

Wherein the binder powder is selected from the group consisting of polyacrylic acid, polymethacrylic acid, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, a butadiene-acrylic acid copolymer, Butadiene-methacrylic acid copolymer, polyvinylsulfonate, chlorosulfonated polyethylene, perfluorinated sulfonate ionomer, sulfonated polystyrene, styrene-acrylic acid copolymer, sulfonated butyl rubber, polyvinylidene fluoride ( PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichlorethylene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE ), Polymethyl methacrylate, polyvinyl acetate, ethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetoacetate Cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile styrene butadiene aerials And one or more components selected from the group consisting of polyimides;
Subjecting each of the binder powders and the ceramic powder to a plasma treatment such that the binder powder has a negative conductivity and the ceramic powder has a positive conductivity;
Dissolving the plasma-treated binder powder in a solvent to prepare a binder powder slurry;
Spraying the plasma-treated binder powders on both sides of the separator substrate first and coating the same; And
A step of allowing the plasma-treated ceramic powder to be adsorbed on both surfaces of the separator coated with the binder powder by passing the plasma-treated binder powder through the separator coated with the ceramic powder;
The method of claim 1,
delete delete The method according to claim 1,
Wherein the ceramic is selected from the group consisting of Al ₂ O ₃ , BaTiO ₃ , CaO, CeO ₂ , NiO, MgO, SiO ₂ , SnO ₂ , SrTiO ₃ , _{TiO 2, Y 2 O 3,} ZnO, ZrO 2, Pb (Zr, Ti) O 3 (PZT), Pb 1-x La x Zr 1-y TiyO 3 (PLZT), PB (Mg 1/3 Nb 2 / ₃ ) a single substance selected from the group consisting of O ₃ -PbTiO ₃ (PMN-PT) and hafnia (HfO ₂ ) or a mixture of two or more thereof. delete delete delete The method according to claim 1,
Wherein the separation membrane substrate is a microporous membrane or nonwoven fabric comprising one or more components selected from the group consisting of a polyolefin resin, a fluororesin, a polyester resin, a polyacrylonitrile resin, and a cellulosic material. Way. The method according to claim 1,
The separator substrate may be a microporous membrane or a nonwoven fabric composed of one or more components selected from the group consisting of polyethylene, polypropylene-based, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate and polybutylene terephthalate ≪ / RTI > delete delete The method according to claim 1,
Wherein the weight ratio of the coated binder powder to the ceramic powder is 1: 9. The method of claim 12,
Wherein the weight ratio of the coated binder powder layer to the ceramic powder is 2: 8. The method according to claim 1,
Wherein the total coating thickness of the coated binder powder and the ceramic powder is from 6 탆 to 8 탆. The method according to claim 1,
Wherein the method further comprises the step of secondarily spraying the plasma-treated binder powder on both sides of the separator film substrate after the ceramic powder coating. The binder powder and the ceramic powder are sequentially coated on both sides of the separator base material, the binder powder and the ceramic powder are produced by the separation membrane separator manufacturing method according to claim 1,
The binder powder and the ceramic powder each have a particle diameter ranging from 1 to 100 nm,
The total coating thickness of the binder powder and the ceramic powder is 6 탆 to 8 탆,
The binder powder may be selected from the group consisting of polyacrylic acid, polymethacrylic acid, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, butadiene-acrylic acid copolymer, butadiene-methacrylic acid copolymer, polyvinylsulfonate, chlorosulfonated polyethylene, Polyvinylidene fluoride, hexafluoropropylene, polyvinylpyrrolidone, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, Polyvinylidene fluoride-trichlorethylene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-co-vinyl acetate Copolymers, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate pro One selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, onate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethyl sucrose, pullulan, carboxymethylcellulose, acrylonitrile styrenebutadiene copolymer and polyimide Or two or more components. A secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte,
Wherein the separation membrane comprises the separation membrane produced by the method according to claim 1.

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