KR102219691B1 - Ceramic coated separator having excellent thermal property and electro-chemical stability and the manufacturing method of it - Google Patents

Abstract

The present invention relates to a separator for a secondary battery, comprising a porous layer formed from a binder including inorganic particles surface-treated with a silane coupling agent and a monomer and/or oligomer curable by ultraviolet or electron beam, inorganic particles and a binder Heat resistance, chemical resistance, and water resistance of the secondary battery separator can be achieved through chemical crosslinking between the two.

Description

Ceramic coated separator having excellent thermal property and electro-chemical stability and the manufacturing method of it} with excellent heat resistance and electrochemical stability

The present invention relates to a separator for a secondary battery, and to a separator for a secondary battery prepared from a mixed coating liquid containing a monomer and oligomer capable of forming a crosslinkable structure through irradiation with ultraviolet rays or electron beams, and a method of manufacturing the same.

More specifically, heat resistance, chemical resistance, and water resistance through chemical crosslinking of inorganic particles, monomers, and oligomers by applying a mixed coating solution containing inorganic particles, monomers, and oligomers to a microporous membrane or electrode and then irradiating with ultraviolet rays or electron beams. It relates to a separator for a secondary battery that can be secured and a method of manufacturing the same.

Polyolefin-based microporous membrane (microporous polyolefin film) is widely used as a microporous membrane for various batteries (battery separator), separation filter and microfiltration membrane (membrane), etc. based on chemical stability and excellent properties. Among them, the microporous membrane for secondary batteries has a spatial blocking function of the positive electrode and the negative electrode, as well as a high ion transfer power through the internal pores. In recent years, as one of the methods for improving the electrical safety of the battery due to the high capacity and high output of the secondary battery, the demand for improving the characteristics of the microporous membrane is increasing. In the case of a lithium secondary battery, if the thermal stability of the polyolefin-based microporous membrane is deteriorated, a short circuit between the electrodes may occur along with damage or deformation of the microporous membrane due to an increase in temperature resulting from the abnormal behavior of the battery, and furthermore, overheating of the battery or There is a risk of ignition and explosion.

In conditions that require high power/high capacity of the battery, such as IT, electric vehicle (EDV), power tools, and ESS (Energy storage system), the possibility of ignition and explosion that occurs during abnormal behavior of the battery is several to tens of times higher than that of conventional batteries. Therefore, there is a desperate need for high-temperature thermal stability to prepare for the temperature increase of the battery.

In order to solve this safety problem, a method of forming a porous membrane using a polymer binder and inorganic particles that can impart high heat resistance to at least one side of a polyolefin-based microporous membrane was applied, thereby improving high temperature heat shrinkage. At the same time, research was conducted to improve battery stability.

However, in order to reinforce the stability and shape retention characteristics of the battery, a technique for inducing a thermal crosslinking reaction by introducing a crosslinking agent in a mixed coating solution of a polymer binder and inorganic material has been proposed. However, in this case, when the content of the crosslinking agent is too high, the solution The stability of the mixture was rapidly deteriorated and the mixed coating solution gelled, so that the application process could not be applied, or when the content of the crosslinking agent was small, sufficient crosslinking did not occur. In addition, the unreacted crosslinking agent may cause side reactions in the battery to cause a problem of deteriorating battery performance, and high temperature heat is applied to cause crosslinking. In this case, heat causes damage to the substrate, causing the substrate to shrink or damage the substrate. There may be secondary problems, such as being coated.

Bonding between polymeric binders through thermal crosslinking reaction, as described above, cannot sufficiently lead to physical bonding between polymeric binders even when a large amount of crosslinking agent is used. Not suitable

On the other hand, as an aspect for improving the heat resistance of the secondary battery separator, a process of forming a coating layer using a heat-resistant resin using an organic solvent is applied. At this time, a large amount of organic solvent is used to dissolve the heat-resistant resin. In the case of using an organic solvent, economic feasibility decreases due to the process of recovering or incineration of the solvent after application and drying, and there is a disadvantage that it is not environmentally friendly. In addition, the organic solvent has excellent affinity with the microporous membrane, and thus has a property of being absorbed into the pores of the microporous membrane in the coating process. Due to this characteristic, when the coating layer is formed with a solution in which the heat-resistant resin is dissolved, the inside of the pores of the microporous membrane is coated with the heat-resistant resin after the drying process. The microporous membrane coated with the heat-resistant resin reduces the pore size, resulting in a decrease in transmittance, and when the shutdown function of the microporous membrane is expressed at a high temperature, the shutdown is disturbed by the heat-resistant resin applied inside the pores. In this way, when the heat resistance is improved by using an organic solvent, there is a disadvantage of offsetting the advantage of applying the heat-resistant layer because it has a factor that hinders the basic function of the microporous membrane as well as environmental problems.

In order to secure the permeability, there are attempts to secure the permeability by adding a non-solvent or impregnating the coagulation tank of the poor solvent, but it is not easy to form a non-uniform pore structure or secure sufficient permeability by phase separation.

Accordingly, a method of manufacturing a separator for a secondary battery using environmentally friendly water as a solvent while securing heat resistance has been proposed by Japanese Patent Application Laid-Open No. 2004-227972 and Japanese Patent Application No. 2005-276503, but in the case of a water-soluble polymer binder While it is well soluble in water, it has a high moisture adsorption power, so the battery expands and deteriorates due to the generation of rare HF and gases in side reactions with lithium salt and electrolyte in the battery by moisture, or generation of additional moisture and cyclic side reactions through such side reactions. There is a problem that can cause it.

Japanese Patent Publication No. 2004-227972 Japanese Patent Publication No. 2005-276503

The present invention has been devised to solve the above problems, and by forming a chemical crosslink of a three-dimensional network structure between inorganic particles and a binder, it is possible to secure heat resistance and chemical resistance while improving the reliability and stability of the battery. It is possible to provide a secondary battery separator and a method for manufacturing the same.

In order to solve the above problems, the present invention includes a microporous membrane and a porous layer including inorganic particles and a binder, wherein the binder is formed from a monomer and/or oligomer curable by ultraviolet rays or electron beams. Can be

The present invention comprises the steps of preparing a mixed coating solution by mixing a binder including a silane coupling agent, inorganic particles, and monomers and/or oligomers curable with ultraviolet rays or electron beams; Applying the kneaded mixed coating liquid to the microporous membrane; Chemically crosslinking the inorganic particles and the binder surface-treated with a silane coupling agent by irradiation with ultraviolet rays or electron beams; and a mixed coating solution applied to the microporous membrane before and/or after irradiation with ultraviolet rays or electron beams. It may be a method of manufacturing a separator for a secondary battery including a step of drying.

In addition, the present invention comprises the steps of preparing a mixed coating solution by mixing a binder including a silane coupling agent, inorganic particles, and monomers and/or oligomers curable with ultraviolet rays or electron beams; Applying the mixed coating liquid to the electrode; Chemically crosslinking the inorganic particles and the binder surface-treated with a silane coupling agent by irradiation with ultraviolet rays or electron beams; and a mixed coating solution applied to the microporous membrane before and/or after irradiation with ultraviolet rays or electron beams. It may be a method of manufacturing a secondary battery including a step of drying.

The present invention overcomes the problem of lowering the transmittance in which the binder formed from the monomer and/or oligomer penetrates the microporous membrane, and provides a separator for a secondary battery having excellent heat resistance, chemical resistance, and water resistance, and a method of manufacturing the same.

In addition, the present invention can provide a secondary battery separator with improved battery stability and a method for manufacturing the same by chemical crosslinking formed through irradiation of ultraviolet rays or electron beams between inorganic particles and a binder polymer.

1 is an exemplary diagram for chemically crosslinking the inorganic particles and the binder according to the present invention.
2 is a view of the surface of a separator for a secondary battery manufactured according to an example of the present invention observed with a scanning microscope (SEM).

Hereinafter, the present invention will be described in more detail through examples and drawings, but they are only examples limited to the gist of the present invention. Meanwhile, it is obvious to those skilled in the art that the present invention is not limited to the process conditions presented in the following examples, and can be arbitrarily selected within the range of conditions necessary to achieve the object of the present invention.

In this case, unless there are other definitions in the technical terms and scientific terms used, they have the meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings A description of known functions and configurations that may unnecessarily obscure will be omitted.

The present invention relates to a separator for secondary batteries having excellent heat resistance, chemical resistance, and water resistance, and a method for manufacturing the same.In addition, inorganic particles surface-treated with a monomer and oligomer curable by ultraviolet or electron beam and a silane coupling agent It may relate to a secondary battery formed by applying a mixed coating liquid containing to the electrode.

That is, the present invention includes a microporous membrane and a porous layer including inorganic particles and a binder, and the binder may be a separator for a secondary battery that is formed from a monomer and/or oligomer curable by ultraviolet rays or electron beams.

The porous layer including inorganic particles and a binder of the separator for a secondary battery according to the present invention may be formed on one or both surfaces of the microporous membrane.

The microporous membrane according to the present invention is not limited and can be used as long as it is a polyolefin-based microporous membrane, and further, non-woven fabric, paper, and pores in the microporous membrane thereof or including inorganic particles on the surface thereof can be applied to a battery. It is not particularly limited if it is a porous membrane.

As an example, the polyolefin-based resin is preferably one or more polyolefin-based resins alone or as a mixture, and in particular, polyethylene, polyolefin using ethylene, propylene, α-olefin, 4-methyl-1-pentene, etc. as monomers and comonomers. It is effective to be at least one selected from propylene, poly-4-methyl-1-pentene, or copolymers thereof. Alternatively, the polyolefin-based resin may be composed of multiple layers, and inorganic particles and organic particles may be simultaneously included in the polyolefin resin composed of multi-layers.

More specifically, the polyolefin-based microporous membrane is preferably prepared as a sheet by melting/kneading/extruding a polyolefin-based resin and a diluent, and a polyolefin-based resin composition: diluent is 15 to 50: 85 to 50 weight ratio It is effective to use.

When the proportion of the polyolefin resin is less than 15 weight ratio, it is not easy to form a uniform sheet due to the diluent having an excessive viscosity, and it is difficult to secure mechanical strength due to insufficient orientation during the stretching process, and the mechanical properties of the sheet It is deteriorated, and problems such as fracture may occur during the stretching process. When the content of the polyolefin resin exceeds 50 weight ratio, the viscosity of the composition increases and the extrusion moldability decreases due to an increase in the load during kneading and extrusion, the permeability of the microporous polyolefin membrane is greatly reduced, and the sheet is hard, causing a problem of uneven stretching. .

The method for producing a polyolefin-based microporous membrane, which is an example of the microporous membrane according to the present invention, may use a method known in the art, but as an example, it may be produced including the steps of (a1) to (a5) below. .

(a1) A mixture containing 20 to 50% by weight of polyethylene having a weight average molecular weight of 2.0x10 ⁵ to 4.5x10 ⁵ and 80 to 50% by weight of diluent is melted/kneaded/extruded at a phase separation temperature above the phase separation temperature and subjected to thermodynamic stage in the extruder. Daily manufacturing steps;

(a2) forming a single-phase melt into a sheet form by causing phase separation to proceed;

(a3) stretching the sheet prepared in step (a2) to have a transverse and longitudinal draw ratio of 3.0 times or more, respectively;

(a4) extracting and drying the diluent while applying a certain tension from the stretched film; And

(a5) heat setting step of reducing the shrinkage rate of the film by removing residual stress of the dried film, etc.; may be prepared including a process of performing one or more times.

The inorganic particles included in the porous layer of the present invention have rigidity and are not deformed by external impacts and forces, so that short circuits caused by lithium dendrites and foreign substances can be prevented, and thermal deformation and side reactions do not occur even at high temperatures. It may be added to prevent shrinkage of the microporous membrane occurring at high temperature through bonding with.

In addition, since inorganic particles have a porosity of about 40 to 80% depending on the geometric structure and particle size distribution of the particles themselves, the porosity and transmittance of the final product can be controlled through an appropriate ratio with the heat-resistant resin.

It is effective that the inorganic particles have an average particle diameter of 0.01 to 20 μm, more preferably 0.1 to 10 μm, and most preferably 0.1 to 2.0 μm. If it is smaller than 0.1㎛, the specific surface area of the inorganic particles should be increased, so that the binder content to maintain the adhesive strength should be increased. Accordingly, if the transmittance is lowered or the binder content is lowered to increase the transmittance, a problem of lowering the adhesive strength occurs. There is a problem in that it is difficult to form a thin porous layer of 2 μm or less, and even when formed, a porous film in which inorganic particles are discontinuously present is formed, resulting in a stability problem such as deterioration of heat resistance, which does not meet the object of the present invention.

The volume of the inorganic particles is preferably contained in an amount of 30 to 99 volume% in the mixed coating liquid to be applied to the microporous membrane, and more preferably 60 to 95 volume%. When the volume of the inorganic particles is less than 30 volume%, impregnation of the liquid electrolyte decreases due to the decrease in porosity and permeability of the microporous membrane, the heat resistance of the microporous membrane decreases, and when the battery malfunctions, it becomes difficult to secure the space between electrodes, resulting in poor battery stability On the other hand, if it exceeds 99 volume%, the adhesion to the microporous membrane is lowered, resulting in detachment of the porous layer in the slitting and assembling process, resulting in a decrease in the assembling yield.

The kind of the inorganic particles may be used without limitation as long as they achieve the above purpose as inorganic particles, and as an example, alumina, aluminum hydroxide, silica, barium oxide, titanium oxide (alumina), aluminum hydroxide (AluminumHydroxide), silica (Silica), barium oxide (barium oxide), titanium oxide ( Titanium Oxide), magnesium oxide (Magnesium Oxide), magnesium hydroxide (Magnesium Hydroxide), clay (Clay), glass powder (Glass powder), boehmite (Boehmite), or a mixture thereof, may contain any one or more selected from the , More specifically, when alumina is used for inorganic particles, it has excellent rigidity and is effective in blocking short circuits caused by dendrite and foreign substances.

The binder contained in the porous layer according to the present invention may be used without limitation as long as it is formed in the microporous membrane by bonding with inorganic particles, so long as it can achieve thermal and chemical stability of the separator for a secondary battery.

As an example, the binder may be formed from a monomer and/or oligomer, and the monomer and oligomer may be curable by UV or electron beam.

Since general binders are physically bonded to inorganic particles, they are melted and dissolved by highly active substances generated by side reactions of electrolytes and lithium salts in the battery, resulting in a problem of weakening the binding strength between the binder and inorganic particles. Furthermore, the microporous membrane and the porous layer are separated, or the porous layer is locally lost, resulting in deterioration in the battery performance, and ultimately, the stability problem in the battery could be caused.

However, in the case of the separator for a secondary battery according to the present invention, by using a monomer and/or oligomer that can be cured by ultraviolet or electron beam, thermal and chemical stability are improved by chemical crosslinking including a three-dimensional network structure between inorganic particles and a binder. It is possible to provide a separator for a secondary battery that can dramatically improve the stability in the battery.

The three-dimensional network structure of chemical crosslinking can be formed by forming radicals by ultraviolet rays or electron beams, and by continuously crosslinking reactions by the formed radicals, and bonding them with a binder and a reactive group present in the inorganic particles.

The chemical crosslinking can be formed by irradiation with ultraviolet rays or electron beams. Unlike thermal curing, crosslinking reactions can occur only through ultraviolet or electron beam irradiation at a low temperature (room temperature), so even when a substrate weak to heat is used, the substrate is damaged. Without it, the crosslinking reaction can be completed.

In addition, in order to effectively conduct a crosslinking reaction for forming a chemical crosslinking of a three-dimensional network structure in the porous layer including inorganic particles and a binder, a crosslinking agent activated in a certain wavelength range may be added.

More specifically, in order to form a chemical crosslink between the inorganic particles and the binder, the inorganic particles may be surface-treated with a coupling agent, and the coupling agent is preferably a silane coupling agent. .

A silane coupling agent, which is an example of a coupling agent for surface treatment of inorganic particles according to the present invention, is methoxy (-OCH ₃ ) or ethylene which constitutes the silane coupling agent by moisture. Functional groups such as oxy (-OCH ₃ ) are hydrolyzed to form -OH groups, and the formed -OH groups undergo hydrogen bonding with a number of -OH groups present on the surface of inorganic particles, and are adsorbed on the surface of inorganic particles. Can be.

Primarily, the silane coupling agent adsorbed on the surface of inorganic particles has various functional groups such as acrylic, methacrylic, epoxy, methyl, vinyl, and amino mulcate at the ends. Uniform dispersion within it becomes possible. In addition, to increase the efficiency of surface treatment, it is possible to use equipment such as ultrasonic waves and beads mill, and finally, a dehydration condensation reaction occurs through a drying process, and a strong chemical bond between the inorganic particles and the silane coupling agent. (Chemical bonding) can be completed.

The silane coupling agent may be used without limitation as long as it is intended to achieve the above object, but a (meth)acrylate series is preferable, and as an example, 3-acryloxypropyl Trimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyldiethoxysilane, 3-methacryloxypropyldimethoxysilane, etc. However, it is not limited thereto.

The inorganic particles surface-treated with the silane coupling agent according to the present invention can form a chemical crosslink by irradiation with ultraviolet rays or electron beams with a binder formed from monomers and/or oligomers curable by ultraviolet rays or electron beams. .

That is, in the separator for a secondary battery according to the present invention, the inorganic particles are surface-treated with a silane coupling agent to form a chemical crosslink with a binder formed from a monomer and/or oligomer curable by ultraviolet rays or electron beams. I can.

Through chemical crosslinking by irradiation of ultraviolet rays or electron beams as described above, it is possible to overcome the disadvantages of the reduction of stability of the mixed coating solution and the physical bonding between the binder and the inorganic particles, which are limitations of conventional thermal crosslinking.

The monomer according to the present invention may be used without limitation as long as it can form chemical crosslinking by irradiation with ultraviolet or electron beam with inorganic particles surface-treated with a silane coupling agent. In forming the mixed coating solution, it can be adopted in consideration of the permeability aspect of the microporous membrane.

As a non-limiting example, the monomer is water-soluble, and may include at least one or more ethylene oxide (Ethylene Oxide) groups, (meth) acrylate groups, and urethane (Urethane) groups.

As a specific example, the water-soluble monomer is polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), ethoxylated trimethylolpropane triacylate (Ethoxylated Trimethylolpropane Triacylate). ;TMPTA), ethoxylated bisphenol A diacrylate (BPADA), ethoxylated bisphenol A dimethacylate (Ethoxylated bisphenol A dimethacylate; BPADMA) may be any one selected from.

The oligomer according to the present invention may be used without limitation as long as it can form a chemical crosslinking by irradiation with ultraviolet rays or electron beams with inorganic particles surface-treated with a silane coupling agent, and preferably urethane-based oligomers Can be

The urethane-based oligomer may be used without limitation as long as it has a photopolymerization characteristic having a urethane bond (~NH-COO~) as shown in the following formula (1), but preferably includes an acrylate group and/or a methacrylate group. It is better to be a urethane oligomer.

Formula (1)

Monomers and/or oligomers included in general binders have good affinity with the microporous membrane and penetrate into the pores, resulting in a problem of lowering the permeability.

However, the binder containing the water-soluble monomer and/or oligomer according to the present invention can prevent the penetration of the microporous membrane from being lowered by penetrating into the pores of the microporous membrane, thereby being excellent in terms of securing the performance of the battery.

In addition, a crosslinking agent may be used to more effectively combine the acrylate and/or methacrylate-based terminal functional groups formed on the surface of the inorganic particles according to the present invention with the acrylate and/or methacrylate present in the binder, It is preferable that the crosslinking agent can be activated by irradiation with ultraviolet rays or electron beams.

As a specific example of the crosslinking agent, it is preferable that it can be activated in a wavelength range of 200 to 500 nm, and benzophenone, alpha hydroxyketone (α-Hydroxyketone), alpha amino ketone (α-Aminoketone), phosphine oxide ( Phosphine oxide), phenylglyoxylate (Phenylglyoxylate), benzyldimethylketal (Benzildimethylketal), metallocene (Metallocene), it is effective to include at least one or more iodonium salt (Iodonium salt) groups, more preferably water 1173, 2959, 754, 819, 819DW among BASF's IRGACURE series products that can be dispersed in and form radicals in the long wavelength range of 300nm or more can be used.

The method of forming a porous layer containing inorganic particles and a binder according to the present invention on a microporous membrane is not particularly limited as it can be manufactured by a conventional method adopted in this field, and is as an example, bar coating. Method, rod coating method, die coating method, wire coating method, comma coating method, micro gravure/gravure method, dip coating method, spray method, inkjet (ink-jet) coating method or a method in which these are mixed and a method modified, and the like may be used.

In addition, a process of flattening or partially removing the porous coating layer on the surface using a doctor blade, air knife, bar, etc. may be additionally included, and during application, electrospinning and electrospray It may be formed in a fibrous form by a method and applied to have porosity.

For the binding of the binder and inorganic particles according to the present invention, ultraviolet rays or electron beams may be used, and when ultraviolet rays are used, ultraviolet lamps such as low pressure mercury lamps, fluorescent lamps, medium pressure mercury lamps, high pressure mercury lamps, metal halide lamps, and LED lamps can be used, Depending on the curing conditions, it may be cured while maintaining a nitrogen environment.

Before and/or after irradiation with ultraviolet rays or electron beams, in order to maintain the hydrogen bond formed between the inorganic particles and the silane coupling agent as a more robust chemical bonding, 40 to 120°C, preferably 40 to It may include a process of causing a dehydration condensation reaction through a process of drying at a temperature of 80 ℃. This is because a drying temperature of 40°C or less cannot sufficiently remove moisture and thus chemical bonding cannot be completed, and a drying temperature of 120°C or higher is not suitable because it damages the substrate.

The drying step for causing the dehydration condensation reaction may be performed before or after the ultraviolet irradiation step, and may be performed both before and after.

A mixed coating solution may be prepared in order to form a porous layer including inorganic particles and a binder according to the present invention, and a predetermined solvent may be included in the mixed coating solution.

The method of preparing the mixed coating solution may use any method known in the art, but first, an inorganic particle dispersion solution is prepared by dispersing the inorganic particles in a solvent, and the mixture is mixed with a monomer and/or oligomer curable with ultraviolet rays or electron beams. It can be prepared from

In addition, the method of preparing the mixed coating solution is to prepare an inorganic particle dispersion by dispersing the silane coupling agent in a solvent and then mixing and dispersing the inorganic particles, and mixing it with a monomer and/or oligomer curable with ultraviolet rays or electron beams. Can be manufactured from

The method of preparing the inorganic particle dispersion may be dispersed using a conventionally known method such as ultrasonic dispersion, bead mill, jet mill, basket mill, etc., but is not limited thereto.

In addition, the method of mixing the inorganic particle dispersion with a monomer and/or oligomer curable by ultraviolet or electron beam may be performed by various known methods such as a stirrer.

The solvent contained in the mixed coating solution according to the present invention may be used without limitation as long as it is capable of preparing an inorganic particle dispersion by dispersing the inorganic particles, but it is environmentally friendly and the monomer and oligomer penetrate into the pores of the microporous membrane. Considering the aspect to prevent the transmittance from being lowered, the solvent is preferably water.

That is, the binder containing monomers and/or oligomers has a disadvantage of penetrating into the pores due to good affinity with the microporous membrane, but the binder containing the water-soluble monomer and/or oligomer according to the present invention uses a solvent as water to obtain the permeability. The degradation problem can be overcome, and the battery performance can be increased.

The present invention may be a method of manufacturing a secondary battery separator having excellent heat resistance, chemical resistance, and water resistance as described above.

That is, the method of manufacturing a separator for a secondary battery according to the present invention prepares a mixed coating solution by kneading a binder including a silane coupling agent, inorganic particles, and a water-soluble monomer and/or oligomer curable with ultraviolet rays or electron beams. Step to do; Applying the mixed coating liquid to the microporous membrane; Chemically crosslinking the inorganic particles and the binder surface-treated with the silane coupling agent by irradiation with ultraviolet rays or electron beams; And coating on the microporous membrane before and/or after irradiation with the ultraviolet rays or electron beams It may be a method of manufacturing a separator for a secondary battery comprising; drying the mixed coating solution.

In the method of manufacturing a separator for a secondary battery according to the present invention, the mixed coating liquid may be prepared by a method commonly used in this technical field.

As an example, it may be prepared by first dispersing the inorganic particles in a solvent to prepare an inorganic particle dispersion, and mixing it with a monomer and/or oligomer curable by ultraviolet or electron beam.

In addition, the method of preparing the mixed coating solution is to prepare an inorganic particle dispersion by dispersing the silane coupling agent in a solvent and then mixing and dispersing the inorganic particles, and mixing it with a monomer and/or oligomer curable with ultraviolet rays or electron beams. Can be manufactured from

The solvent may be used without limitation as long as it can achieve the object of the present invention, but water is preferred, and the surface of the inorganic particles in the mixed coating solution is surface-treated with a silane coupling agent to form a chemical crosslinking bond. It can be distributed.

That is, the method of manufacturing a separator for a secondary battery according to the present invention may further include a step of surface treatment by adsorbing a silane coupling agent included in the mixed coating solution onto the inorganic particles.

According to the method using a bead mill, which is an example of the method for preparing the mixed coating solution according to the present invention, water as a solvent, inorganic particles, and a silane coupling agent are kneaded using a stirrer, etc. Then, the mixed solution may be added to a bead mill to prepare an inorganic particle dispersion, and then mixed with a monomer and/or oligomer to prepare a mixed coating solution.

A crosslinking agent for smoothness and surface adjustment in the step of preparing a mixed coating solution by kneading a binder containing the silane coupling agent, inorganic particles, and a water-soluble monomer and/or oligomer curable with ultraviolet rays or electron beams. , A defoamer, a wetting agent, a leveling agent, a slip agent, and the like may be added.

As a specific example of a crosslinking agent that can be added to the mixed coating solution according to the present invention, it is preferable that it can be activated in a wavelength range of 200 to 500 nm, and benzophenone, alpha hydroxy ketone (α-Hydroxyketone), alpha amino Ketone (α-Aminoketone), phosphine oxide (Phosphine oxide), phenylglyoxylate (Phenylglyoxylate), benzyldimethylketal (Benzildimethylketal), metallocene (Metallocene), at least one or more iodonium salt (Iodonium salt) group It is effective to include, more preferably, 1173, 2959, 754, 819, 819DW of BASF's IRGACURE series products that are dispersed in water and can form radicals in a long wavelength range of 300 nm or more can be used.

In addition, in order to control the viscosity of the mixed coating liquid, carboxylmethylcellulose-based, dextran-based, polyvinylpyrollidone-based, polyvinylalcohol-based, and polyacrylic acid ( Polyacrylic acid, polyacrylamide, polyimideamide, urethane, polyvinylacetamide, lignosulfonate, polyacrylonitrile One or more viscosity modifiers, such as (Polyacrylonitrile)-based, epoxy, and polyethyleneimine-based, may be used alone and/or in combination.

The method of applying the mixed coating liquid according to the present invention to the microporous membrane can use all methods known in the art without limitation, preferably bar coating method, rod coating method, die ( die) coating method, wire coating method, comma coating method, micro gravure/gravure method, dip coating method, spray method, ink-jet coating method, or a mixture of these A method and a modified method may be used.

The mixed coating solution according to the present invention may be applied to one side or both sides of the microporous membrane, and after passing through the coating step, a step of removing the solvent through a drying process under constant temperature and humidity conditions is performed.

The drying process for removing the solvent is not particularly limited, and methods such as air blowing and IR heater may be used alone or in combination.

In the method of manufacturing a separator for a secondary battery according to the present invention, the inorganic particles surface-treated with a silane coupling agent and a binder containing a water-soluble monomer and/or oligomer contained in the mixed coating solution after the drying step It may include the step of irradiating an electron beam or ultraviolet rays to form a chemical crosslinking therebetween.

However, prior to the electron beam or ultraviolet irradiation step, drying the mixed coating solution applied to the microporous membrane at 40 to 120° C. to remove moisture in the hydrogen bonds constituting the inorganic particles and the silane coupling agent. A drying temperature of 40°C or less cannot sufficiently remove moisture and thus chemical bonding cannot be completed, and a drying temperature of 120°C or more is not suitable because it damages the substrate.

The step of drying the mixed coating liquid applied to the microporous membrane may include both before or after the ultraviolet irradiation step, and before and after the ultraviolet irradiation step.

In the method for manufacturing a separator for a secondary battery according to the present invention, the water-soluble monomer and oligomer are those capable of forming chemical crosslinking by irradiation with ultraviolet rays or electron beams with inorganic particles surface-treated with a silane coupling agent. It may be used without limitation, but it can be considered that the solvent is water.

More specifically, the water-soluble monomer includes at least one of an ethylene oxide (Ethylene Oxide) group, a (meth) acrylate, and a urethane (Urethane) device, and includes polyethylene glycol diacrylate; PEGDA), Polyethylene Glycol Dimethacrylate (PEGDMA), Ethoxylated Trimethylolpropane (EO) Triacylate (TMPTA), Ethoxylated Bisphenol A Diacrylate (Ethoxylated) bisphenol A diacrylate; BPADMA), ethoxylated bisphenol A dimethacylate (Ethoxylated bisphenol A dimethacylate; BPADMA) is preferably any one selected from, and the oligomer includes an acrylate group and/or a methacrylate group. It is preferably a urethane oligomer.

In addition, in the manufacturing method of the separator for a secondary battery according to the present invention, the solvent contained in the mixed coating solution prevents the water-soluble monomer and oligomer according to the present invention from penetrating into the microporous membrane, thereby reducing the transmittance, and taking into account the environmentally friendly aspects. When viewed, it is preferable to be water.

According to the separator for a secondary battery according to the present invention and a method for manufacturing the same, a mixed coating comprising a binder formed from inorganic particles surface-treated with a silane coupling agent and a water-soluble monomer and/or oligomer curable by ultraviolet or electron beam The liquid is applied to a microporous polyolefin film and then irradiated with ultraviolet rays or electron beams to form chemical crosslinks, thereby providing a secondary battery separator having excellent heat resistance, chemical resistance, and water resistance.

Furthermore, the present invention may be a secondary battery manufactured by directly applying the mixed coating solution on an electrode.

That is, the present invention comprises the steps of preparing a mixed coating solution by mixing a binder including a silane coupling agent, inorganic particles, and monomers and/or oligomers curable with ultraviolet rays or electron beams; Applying the kneaded mixed coating liquid to an electrode; Chemically crosslinking the inorganic particles and the binder surface-treated with the silane coupling agent by irradiation with ultraviolet rays or electron beams; And coating on the microporous membrane before and/or after irradiation with the ultraviolet rays or electron beams Drying the mixed coating liquid; It may be a method of manufacturing a secondary battery including.

Here, the mixed coating liquid may include a solvent such as water, similar to the coating liquid prepared by the separator for a secondary battery and a method for manufacturing the same according to the present invention.

In addition, the water-soluble monomer is polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), ethoxylated trimethylolpropane (EO) triacrylate (Ethoxylated Trimethylolpropane). Triacylate; TMPTA), ethoxylated bisphenol A diacrylate (BPADA), ethoxylated bisphenol A dimethacylate (Ethoxylated bisphenol A dimethacylate; BPADMA) any one selected from, and the oligomer May be a method of manufacturing a secondary battery, which is a urethane-based oligomer containing an acrylate group and/or a methacrylate key.

Hereinafter, examples of a separator for a secondary battery and a method of manufacturing the same according to the present invention will be described, but the following examples are only examples of the present invention, and the technical idea of the present invention is not limited to those of ordinary skill in the art. Self-evident to those with knowledge.

The characteristics of the separator for secondary batteries of the present invention were evaluated by the following test method.

One) thickness

TESA-μHITE product was used as a contact method thickness gauge with a precision of 0.1㎛.

2) Of the applied layer thickness

When a porous layer was formed on the surface of the microporous membrane, the thickness of the microporous membrane before application and the thickness after application were measured, and the coating thickness after drying of the porous layer was calculated from the difference in thickness. In addition, micro-toming was performed to cut the cross section, and the cross section was observed using an electron microscope, and the thickness was measured.

3) particle size

Particle size using Microtrac's S3500 with laser particle size analysis area of 0.02 ~ 2,000㎛

Analysis was done. If necessary, it was measured from an electron micrograph of the film surface.

4) Gas permeability ( Gurley )

The gas permeability was measured from a porosity meter (Toyoseiki's Gurley densometer).

A certain volume (100ml) of gas fills a certain area (1in ² ) with a certain pressure (about 1-2 psig).

The time it takes to pass (second:sec) was used as a unit.

5) shrinkage rate

The separator for a secondary battery was measured by leaving it to freely shrink in an oven at 150° C. for 1 hour, and the shrinkage in the longitudinal and transverse directions was measured and the shrinkage rate was calculated as %.

[Equation]

Shrinkage (%) = (Initial length before heating-Deformed length after heating) x 100 / Initial length before heating

6) Electrolyte stability

Put the size of 5cm × 10cm into a vial containing electrolyte (EC/EMC/DEC = 3/1/6 1M LiPF _{6) and 120?} After leaving in an oven for 1 hour, it was determined whether or not the inorganic particles were peeled off when rubbing the coated surface with gauze.

7) Moisture content ( ppm )

a. Measurement sample: After drying and aging process is completed, leave the sample at 25?, 80% condition for more than 24 hours, and then leave it in a dry room with a dew point temperature of -30℃ or less for 30 minutes to remove moisture adsorbed on the surface, and then put it in a vial for measurement. 0.5g of sample was put.

b. Measurement method: Measurement sample was placed in a vial using Metrohm's 831 KFcoulometer provided in a dry room with a dew point temperature of -30℃ or less, and measured for 600 seconds using nitrogen dried in a compact oven at 150℃ at a flow rate of 60mL/min. . However, the measurement was continued until the rate of change of the water content dropped to 3 μg/min or less. Used at this time

The titration solution is HYDRANAL COULOMAT AG-OVEN from Fluka.

8) Weight average molecular weight

The molecular weight of the polymer was measured at 140°C using high-temperature GPC (Gel Permeation Chromatography) of Polymer Laboratory, and 1,2,4-trichlorobenzene (TCB) as a solvent. As a standard sample for molecular weight measurement, polystyrene ( Polystyrene) was used.

[ Example One]

One) Microporous Produce

35% by weight of high-density polyethylene with a weight average molecular weight of 3.8×10 ^{5 g/mole, and dibutyl}

Phthalate and paraffin oil having a kinematic viscosity of 160 cSt at 40° C. were mixed in a 1:1 weight ratio, and 68% by weight of Diluent was mixed. The composition was extruded at 245°C using a twin-screw compounder equipped with a T-die, passed through a section set at 180°C, causing phase separation between polyethylene and diluent existing as a single phase, and forming a sheet using a casting roll. Was prepared. The sheet prepared using the sequential biaxial stretching machine was stretched 7.0 times in the longitudinal and transverse directions at a stretching temperature of 126°C, respectively, and the heat setting temperature after stretching was 131°C. The resulting polyolefin-based microporous membrane had a final thickness of 12 μm and a gas permeability (Gurley) of 115 sec.

2) Preparation of mixed coating liquid

Adjust the pH to 4 using acetic acid in 1000 g of ion-exchanged water,

1.5 g of 3-acryloxypropyltrimethoxysilane (ShinEtsu, KBM-5103) was added and stirred for 1 hour so that the silane coupling agent was sufficiently dispersed. Then, 700g of boehmite having an average particle size of 1.5 μm was added, and milled for 10 minutes using a bead mill. Thereafter, 10 g of ethoxylated bisphenol A diacrylate, 10 g of ethoxylated trimethylolpropane triacrylate, 10 g of urethane oligomer containing a tetravalent acrylate group were added, and 1.5 g of a crosslinking agent Irgacure 819DW was added, followed by mixed coating. A solution was prepared.

3) For secondary battery Of the separator Produce

After plasma treatment of one surface of the microporous membrane, the mixed coating solution prepared by the above manufacturing method was applied by the die coating method, and then water was removed by applying a certain amount of air in an oven at 50°C. Thereafter, UV irradiation was performed in a nitrogen environment, and moisture was removed in an oven at 80° C. in a drying process to finally prepare a separator for a secondary battery having a dry coating thickness of 3 μm.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 1 below.

[ Example 2]

1) Preparation of mixed coating liquid

To 1000 g of ion-exchanged water, adjust the pH to 4 using acetic acid, and add 0.5 g of 3-methacryloxypropyltrimethoxysilane (ShinEtsu, KBM-503) to obtain a silane coupling agent. Stir for 1 hour so that it is sufficiently dispersed. Then, 650g of boehmite having an average particle size of 0.8 μm was added, and milled for 10 minutes using a bead mill. Thereafter, 10 g of ethoxylated trimethylolpropane triacrylate and 15 g of a urethane oligomer containing a tetravalent acrylate group were added, and 0.5 g of a crosslinking agent Irgacure 1173 was added to prepare a mixed coating solution.

2) For secondary battery Of the separator Produce

After plasma treatment of one surface of the microporous membrane, the mixed coating solution prepared by the above manufacturing method was applied by the die coating method, and then water was removed by applying a certain amount of air in an oven at 50°C. After that, after removing residual moisture in an 80℃ oven for 12 hours as a drying process, UV irradiation under a nitrogen environment and a secondary drying process for 12 hours in an 80℃ oven, and finally dry coating thickness of 3㎛ secondary A battery separator was prepared.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 1 below.

[ Example 3]

1) Preparation of mixed coating liquid

Adjust the pH to 4 using acetic acid to 1000 g of ion-exchanged water, and add 0.5 g of 3-acryloxypropyltrimethoxysilane (ShinEtsu, KBM-5103) to ensure sufficient silane coupling agent. Stir for 1 hour to disperse. Thereafter, 600 g of alumina hydroxide having an average particle size of 1.0 μm was added, and milled for 10 minutes using a bead mill. Thereafter, 15 g of ethoxylated trimethylolpropane triacrylate, 15 g of urethane oligomer containing a tetravalent acrylate group were added, 0.2 g of the crosslinking agent Irgacure 1173, 0.3 g of Irgacure 819DW were added, and sodiium carboxylmethyl as a viscosity modifier. A mixed coating solution was prepared by adding 0.5 g of cellulose (Sodium-carboxymethylcellulose, DAICEL 2200).

2) For secondary battery Of the separator Produce

After plasma treatment on one side of the microporous membrane, the mixed coating solution prepared by the above manufacturing method was applied by the Bar coating method, and then water was removed by applying a certain amount of air in an oven at 50°C. Thereafter, after removing residual moisture in an oven at 80° C. for 12 hours as a drying process, UV irradiation was performed in a nitrogen environment, and finally, a separator for a secondary battery having a dry coating thickness of 3 μm was manufactured.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 1 below.

Example 1 Example 2 Example 3 bookbinder
Kinds
Ethoxylated Bisphenol A Diacrylate Ethoxylated trimethylolpropane triacrylate Ethoxylated trimethylolpropane triacrylate Ethoxylated trimethylolpropane triacrylate Urethane oligomer Urethane oligomer menstruum Kinds water water water Crosslinking agent Kinds Irgacure 819DW Irgacure 1173 Irgacure 1173, 819DW Inorganic particles
Kinds AlOOH AlOOH Al(OH) ₃ Average particle diameter (㎛) 1.5 0.8 1.0 Coating method Kinds Die Die Bar Measure Thickness(㎛) 3 3 3 Gurley(s) 165 173 151 150 degree contraction MD 0.5 0.6 1.5 150 degree contraction TD 0.2 0.3 1.2 Electrolyte stability Good Good Good Moisture content (PPM/㎛) 102 93 125

[ Comparative example One]

1) Preparation of mixed coating liquid

Kureha's KF9300 3wt% was heated to 60 °C using a stirrer filled with nitrogen using 97wt% n-methyl-2-pyrrolidone (NMP), and stirred for 5 hours. Alumina having an average particle size of 0.8 μm was mixed in the prepared solution, and the bead mill was stirred for about 1 hour.

2) For secondary battery Of the separator Produce

After applying the mixed coating solution prepared by the above manufacturing method to the microporous membrane by the micro-gravure coating method, a constant air volume was added in an oven at 60° C. to remove NMP. Thereafter, the residual NMP was removed in an oven at 80° C. for 12 hours in a drying process to finally prepare a separator for a secondary battery having a dry coating thickness of 3 μm.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 2 below.

[ Comparative example 2]

1) Preparation of mixed coating liquid

To 1000g of ion-exchanged water, 3g of BYD's DISPERBYK-180 is added and stirred for 1 hour so that the dispersant is sufficiently dispersed. Then, 650g of boehmite having an average particle size of 0.8 μm was added, and milled for 10 minutes using a bead mill. Thereafter, 30g of Daicel's CMC1220 was added, and 20g of Xeon's BM900B was added to prepare a mixed coating solution.

2) For secondary battery Of the separator Produce

After applying the mixed coating solution prepared by the above manufacturing method to the microporous membrane by the die coating method, water was removed by applying a constant air volume in an oven at 50°C. Thereafter, residual moisture was removed in an oven at 80° C. for 12 hours in a drying process to finally prepare a separator for a secondary battery having a dry coating thickness of 3 μm.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 2 below.

[ Comparative example 3]

1) Preparation of mixed coating liquid

In 1000 g of ion-exchanged water, 4.5 g of CERASPERSE 5468CF, a dispersant from Sannovco, was used and stirred for 1 hour so that the dispersant was sufficiently dispersed. Thereafter, 580 g of alumina having an average particle size of 1.0 μm was added, and milled for 10 minutes using a bead mill. Thereafter, 20 g of ethoxylated trimethylolpropane triacrylate and 20 g of a urethane-based oligomer containing a tetravalent acrylate group were added, and 3 g of a crosslinking agent Irgacure 819DW was added to prepare a mixed coating solution.

2) For secondary battery Of the separator Produce

After applying the mixed coating solution prepared by the above manufacturing method to the microporous membrane by the die coating method, water was removed by applying a constant air volume in an oven at 50°C. Thereafter, residual moisture was removed in an oven at 80° C. for 12 hours in a drying process to finally prepare a separator for a secondary battery having a dry coating thickness of 3 μm.

The physical properties of the prepared composite microporous membrane were measured and shown in Table 2 below.

Comparative Example 1 Comparative Example 2 Comparative Example 3 bookbinder Kinds PVDF CMC 1220 Ethoxylated trimethylolpropane triacrylate - BM900B Urethane oligomer menstruum Kinds NMP water water Dispersant Kinds - DISPERBYK-180 5468CF Crosslinking agent Kinds - - Irgacure 819DW Inorganic particles Kinds Al ₂ O ₃ AlOOH Al ₂ O ₃ Average particle diameter (㎛) 0.8 0.8 1.0 Coating method Kinds Micro-gravure Die Die Measure Thickness(㎛) 3 3 3 Gurley(s) 232 156 163 150 degree contraction MD 23 0.8 18 150 degree contraction TD 26 0.3 19 Electrolyte stability Not good Not good Good Moisture content (PPM/㎛) 132 362 130

Only when the chemical crosslinking between the inorganic particles and the binder is maintained, both heat resistance and electrolyte stability are secured, and in the case of Comparative Example 1 using a non-aqueous binder, swelling is observed in the electrolyte, and heat resistance is significantly lowered. In the case of Comparative Example 2, when CMC, which is a water-soluble binder, is used, the moisture content due to the hygroscopicity of the binder is excessively high, and when applied to a battery, a large amount of by-products such as HF are generated, thereby reducing the reliability and safety of the battery. In the case of Comparative Example 3, since the silane coupling agent was not used, the binding force between the inorganic material and the binder was deteriorated, and thus heat resistance was eventually deteriorated.

Claims (16)

Microporous membrane; And
Including; a porous layer including inorganic particles and a binder,
The binder is formed from monomers and oligomers curable by ultraviolet rays or electron beams,
The inorganic particles are surface-treated with a silane coupling agent,
The monomer is a water-soluble monomer,
The oligomer is a urethane-based oligomer containing an acrylate group and/or a methacrylate group, and a three-dimensional network structure is formed by forming a chemical crosslink between the inorganic particles and a binder, a separator for a secondary battery. delete The method of claim 1,
The monomer is an ethylene oxide (Ethylene Oxide) group, a (meth) acrylate ((meth) acrylate) group, and a separator for a secondary battery containing at least one of a urethane (Urethane) group. The method of claim 3,
The monomers are polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), ethoxylated trimethylolpropane (EO) triacylate (Ethoxylated Trimethylolpropane Triacylate; TMPTA). ), ethoxylated bisphenol A diacrylate (BPADA), ethoxylated bisphenol A dimethacylate (Ethoxylated bisphenol A dimethacylate; BPADMA) is any one selected from a secondary battery separator. delete The method of claim 1,
The porous layer is a secondary battery separator formed from a mixed coating solution containing water as a solvent. The method of claim 6,
The inorganic particles include alumina, aluminum hydroxide, silica, barium titanium oxide, magnesium oxide, magnesium hydroxide, clay ( Clay), titanium oxide (Titanium Oxide), glass powder (Glass powder), the separator for a secondary battery comprising at least one selected from boehmite (Boehmite). Preparing a mixed coating solution by kneading a binder including a silane coupling agent, inorganic particles, and monomers and oligomers curable with ultraviolet rays or electron beams;
Applying the mixed coating solution to the microporous membrane;
Chemically crosslinking the inorganic particles and the binder surface-treated with the silane coupling agent by irradiating ultraviolet rays or electron beams; And
Drying the mixed coating solution applied to the microporous membrane before and/or after irradiation of the ultraviolet or electron beam;
The mixed coating liquid contains water as a solvent,
The monomer is a water-soluble monomer,
The oligomer is a urethane-based oligomer containing an acrylate group and/or a methacrylate group,
A method of manufacturing a separator for a secondary battery, comprising a three-dimensional network structure by forming a chemical crosslink between the inorganic particles and the binder. The method of claim 8,
The method of manufacturing a separator for a secondary battery further comprising a step of surface treatment by adsorbing a silane coupling agent included in the mixed coating solution to the inorganic particles. The method of claim 9,
The mixed coating liquid contains a crosslinking agent;
The crosslinking agent is a method of manufacturing a separator for a secondary battery to form a radical at a wavelength of 200 ~ 500nm. The method of claim 8,
The monomers are polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), ethoxylated trimethylolpropane (EO) triacylate (TMPTA). ), ethoxylated bisphenol A diacrylate (BPADA), ethoxylated bisphenol A dimethacylate (Ethoxylated bisphenol A dimethacylate; BPADMA) is any one selected from the method of manufacturing a secondary battery separator . delete delete delete delete delete

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