KR20220018348A - Composite Membrane and Method for Manufacturing of Composite Membrane - Google Patents

Abstract

The present invention relates to a composite separator including: a first coating film; a first ionic liquid film on the first coating film; a second ionic liquid film on the first ionic liquid film; and a second coating film on the second ionic liquid film, and a method for manufacturing a composite separator, including the steps of: i) forming a first coating body having the first coating film disposed on one surface of the first ionic liquid film; ii) forming a second coating body having the second coating film disposed on one surface of the second ionic liquid film; and iii) bonding the other surface of the first ionic liquid film in the first coating body to the other surface of the second ionic liquid film in the second coating body.

Description

Composite Membrane and Method for Manufacturing of Composite Membrane

The present invention relates to a composite separator and a method for manufacturing the composite separator.

A secondary battery is a battery that can be used repeatedly through discharge, in which chemical energy is converted into electrical energy, and charging in the reverse direction. The scope of its application is getting wider and wider. Currently, the most widely used secondary battery is a lithium secondary battery. A lithium secondary battery is composed of two solid electrodes (anode and cathode), a liquid non-aqueous electrolyte and a polymer porous separator. However, due to the high cost of lithium resources and transition metal (Co, Ni, etc.) resources used as positive electrode active materials for lithium secondary batteries, many efforts are being made to replace lithium secondary batteries with new low-cost secondary battery systems.

Among them, in particular, a redox flow battery (RFB) is receiving great attention as a next-generation secondary battery. Unlike conventional secondary batteries, redox flow batteries do not use a solid electrode active material, but use an electrolyte solution dissolved in an aqueous solution as an active material. Since the redox flow battery uses a liquid active material rather than a solid, the two electrolytes may be mixed, and in this case, self-discharge occurs. Therefore, an ion exchange resin-based separator is used to prevent physical mixing of these two electrolytes.

Nafion is the most widely applied ion exchange membrane for redox flow batteries to date. Nafion is a polymer membrane having a cation exchange functional group. It is a synthetic resin in which a strong acid sulfonic acid functional group is introduced into polytetrafluoroethylene (PTFE), which has excellent chemical resistance, and enables cation exchange reaction. Cation exchange takes place through the sulfonic acid functional groups present in tetrafluoroethylene, mainly transferring hydrogen cations. However, the Nafion separator is not effective in inhibiting the movement of vanadium cations, which are active materials, and thus self-discharge occurs and the charge balance between the two electrolytes is broken, thereby adversely affecting the lifespan of the battery system.

In order to solve the above-mentioned problems of Nafion membrane, Korean Patent Application Laid-Open No. 10-2016-0142821 uses an ionic liquid film, but over time, the ionic liquid impregnated in the support may leak out. have. Therefore, while allowing the movement of charge carriers, the crossover phenomenon in which the ions of the active material on both sides cross over is minimized, and the ionic liquid on the support is prevented from leaking, so that the battery characteristics and lifespan of the redox flow battery The development of a new separation membrane to improve properties is required.

Korean Patent Publication No. 10-2016-0142821

The present invention is to solve the above problems, and solves the self-discharge problem by improving the crossover problem of active material ions of the existing Nafion membrane, and ions after long-term operation in an ionic liquid film/ionic liquid film An object of the present invention is to provide a composite separator capable of improving the durability and/or lifespan characteristics of a battery by solving the problem of leakage of the liquid, and a method for manufacturing the same.

One embodiment of the present invention, the first coating film; a first ionic liquid film on the first coating film; a second ionic liquid film on the first ionic liquid film; and a second coating film on the second ionic liquid film.

Another embodiment of the present invention comprises the steps of: i) forming a first coating body in which a first coating film is disposed on one surface of a first ionic liquid film; ii) forming a second coating body having a second coating film disposed on one surface of the second ionic liquid film; and iii) bonding the other surface of the first ionic liquid membrane in the first coating body to the other surface of the second ionic liquid membrane in the second coating body; do.

Another embodiment of the present invention, a positive electrode; cathode; And it provides a secondary battery comprising the above-described composite separator.

The composite separator of the present invention can suppress the movement (crossover) of the active material by including an ionic liquid membrane including an ionic liquid impregnated on the porous support, and in addition, due to the coating film on the ionic liquid membrane, the porous support By preventing the ionic liquid impregnated with the ionic liquid from leaking to the outside, there is an effect of improving the durability, storage characteristics, capacity characteristics, lifespan characteristics and/or efficiency of the battery.

1 is a view schematically showing a method for manufacturing a composite separator according to an embodiment of the present invention.
2 is a view schematically showing a method for manufacturing a composite separator according to Comparative Example 1 of the present invention.
3 is a diagram schematically showing a diffusion cell according to Experimental Example 1 of the present invention.
4 is a view showing the result of measuring the concentration of vanadium ions (VO ²⁺ ) according to Experimental Example 1 of the present invention.
5 is a view showing the charge / discharge curve of the redox flow battery according to Experimental Example 2 of the present invention.
6 is a view showing the capacity retention rate of the redox flow battery according to Experimental Example 3 of the present invention.
7 is a view showing the efficiency characteristics of the redox flow battery according to Experimental Example 3 of the present invention.
8 is a view showing the capacity retention rate and efficiency characteristics of the redox flow battery according to Experimental Example 4 of the present invention.

When 'include', 'have', 'consist', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, the case in which the plural is included is included unless otherwise explicitly stated. In addition, in interpreting the components, it is interpreted as including an error range even if there is no separate explicit description.

In the present specification, the expression "on" may mean that the member and the member are directly bonded to each other, or may mean that the member and the member are positioned adjacent to each other.

Hereinafter, the present invention will be described in detail.

1. Composite Membrane

The present invention provides a composite separator.

'Secondary battery' as defined herein may mean a concept including all secondary batteries or energy storage devices capable of charging and discharging conventionally except for a fuel cell or a primary battery, and preferably a redox flow secondary battery or It can be understood as a concept including a redox flow battery.

The composite separator may include a first coating film; a first ionic liquid film on the first coating film; a second ionic liquid film on the first ionic liquid film; and a second coating film on the second ionic liquid film.

The composite separator may mean a separator in a battery, a membrane in a fuel cell, a membrane in water treatment, a membrane in an energy storage system (ESS), and the like, but is not limited thereto.

The first ionic liquid membrane may include a first porous support and a first ionic liquid impregnated in the first porous support, and the second ionic liquid membrane is a second porous support and the second porous support. It may include an impregnated second ionic liquid.

The ionic liquid membrane (Ionic Liquid Membrane) is also called a supported ionic liquid membrane (Supported Ionic Liquid Membrane), the ionic liquid is impregnated in the pores of the porous support, a separation membrane that exists in a fixed state by capillary force (capillary force) means This ionic liquid film has all the advantages of the absorption process and the membrane process, and as a liquid film is uniformly formed over the entire porous support, when used in a secondary battery, particularly a redox flow battery, mixing of active materials is prevented, Through the role of a charge carrier by the selective ion conductivity of the liquid, crossover of active material ions is prevented, but hydrogen ion exchange is selectively performed, thereby suppressing self-discharge and deterioration of the battery, thereby improving battery performance. have.

The first ionic liquid and the second ionic liquid may include a hydrophobic ionic liquid that does not mix with the electrolyte. For example, the first ionic liquid and the second ionic liquid are the same as or different from each other, and each independently comprises at least one cation selected from a nitrogen-containing aromatic ring cation and a quaternary ammonium and a fluorine-containing anion. it could be

The nitrogen-containing aromatic ring cation may include at least one selected from dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium, and dialkylpyrrolidinium.

The alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium may be the same or different from each other, and the alkyl group may have 1 to 10 carbon atoms.

Specific examples of the alkyl group include methyl group, ethyl group, propyl group, n-propyl group, isopropyl group, butyl group, n-butyl group, isobutyl group, tert-butyl group, sec-butyl group, 1-methylbutyl group, 1-ethylbutyl group, pentyl group, n-pentyl group, isopentyl group, neopentyl group, tert-pentyl group, hexyl group, n-hexyl group, 1-methylpentyl group, 2-methylpentyl group, 4-methyl group -2-pentyl group, 3,3-dimethyl butyl group, 2-ethylbutyl group, heptyl group, n-heptyl group, 1-methylhexyl group, cyclopentylmethyl group, cyclohexylmethyl group, octyl group, n-octyl group, tert-octyl group, 1-methylheptyl group, 2-ethylhexyl group, 2-propylpentyl group, n-nonyl group, 2,2-dimethylheptyl group, 1-ethylpropyl group, 1,1-dimethylpropyl group, an isohexyl group, a 4-methylhexyl group, a 5-methylhexyl group, or a benzyl group, but is not limited thereto.

In addition, the two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium may be the same as or different from each other.

The two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium are the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpi It may mean two alkyl groups (dialkyl) included in at least one compound selected from rollidinium.

At least one of the two alkyl groups (dialkyl) of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium, and dialkylpyrrolidinium may have 4 or more carbon atoms.

or the number of carbon atoms in one of the two alkyl groups (dialkyl) of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium is 3 or less, and the carbon number of the other alkyl group is It can be 4 or more. Specifically, one of the two alkyl groups (dialkyl) of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium has 1 to 3 carbon atoms, and the The number of carbon atoms may be 4 to 10.

In particular, when the number of carbon atoms in the two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium satisfies the above ranges, the hydrophobicity of the ionic liquid increases and ions As the liquid is stabilized, in the case of using the composite separator of the present invention including the same, the effect of suppressing the crossover phenomenon of electrode active material ions can be maximized.

The dialkylimidazolium is 1-butyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-heptyl-3-methylimidazolium , 1-octyl-3-methylimidazolium, 1-nonyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-hexyl-3-ethylimidazolium, 1-hexyl-3 -Propylimidazolium, 1-decyl-3-ethylimidazolium, or 1-decyl-3-propylimidazolium may include, but is not limited thereto.

The dialkylpyridinium is 1-butyl-1-methylpyridinium, 1-pentyl-1-methylpyridinium, 1-hexyl-1-methylpyridinium, 1-heptyl-1-methylpyridinium, 1-octyl- 1-methylpyridinium, 1-nonyl-1-methylpyridinium, 1-decyl-1-methylpyridinium, 1-hexyl-1-ethylpyridinium, 1-hexyl-1-propylpyridinium, 1-decyl- 1-ethylpyridinium, or 1-decyl-1-propylpyridinium, and the like, but are not limited thereto.

The dialkylpiperidinium is 1-butyl-1-methylpiperidinium, 1-pentyl-1-methylpiperidinium, 1-hexyl-1-methylpiperidinium, 1-heptyl-1-methylpiperidinium , 1-octyl-1-methylpiperidinium, 1-nonyl-1-methylpiperidinium, 1-decyl-1-methylpiperidinium, 1-hexyl-1-ethylpiperidinium, 1-hexyl-1 -Propylpiperidinium, 1-decyl-1-ethylpiperidinium, or 1-decyl-1-propylpiperidinium may be included, but is not limited thereto.

The dialkylpyrrolidinium is 1-butyl-1-methylpyrrolidinium, 1-pentyl-1-methylpyrrolidinium, 1-hexyl-1-methylpyrrolidinium, 1-heptyl-1-methylpyrrolidinium , 1-octyl-1-methylpyrrolidinium, 1-nonyl-1-methylpyrrolidinium, 1-decyl-1-methylpyrrolidinium, 1-hexyl-1-ethylpyrrolidinium, 1-hexyl-1 -Propylpyrrolidinium, 1-decyl-1-ethylpyrrolidinium, or 1-decyl-1-propylpyrrolidinium may be included, but is not limited thereto.

The quaternary ammonium may be represented by Formula 1 below.

[Formula 1]

In Formula 1, R1 to R4 may be the same as or different from each other, and may each independently be an alkyl group having 10 or less carbon atoms.

In Formula 1, at least one of R1 to R4 may be an alkyl group having 1 to 10 carbon atoms, specifically, an alkyl group having 4 to 10 carbon atoms.

The quaternary ammonium is tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, methyltripropylammonium, methyltributylammonium, ethyltripropylammonium, ethyltributylammonium, propyltriethylammonium , propyltributylammonium, butyltrimethylammonium, butyltriethylammonium, dibutyldimethylammonium, tributylmethylammonium, benzyltrimethylammonium, tetrabenzylammonium, and the like, but is not limited thereto.

The fluorine-containing anion is an anion containing at least one fluorine atom in the anion, and the fluorine-containing anion is at least selected from a fluorine-containing imide-based anion, a fluorine-containing phosphate-based anion, a fluorine-containing boron-based anion, and a fluorine-containing sulfone-based anion. may contain one.

The fluorine-containing imide-based anion may include an anion represented by the following formula (2).

[Formula 2]

In Formula 2, R5 and R6 are the same as or different from each other and each independently represent an alkyl group having 1 to 5 carbon atoms which is unsubstituted or substituted with at least one fluorine group.

The fluorine-containing imide-based anion may include at least one selected from anions represented by the following Chemical Formulas 2-1 to 2-5.

[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Formula 2-4]

[Formula 2-5]

The fluorine-containing phosphate-based anion may include hexafluorophosphate (PF ₆ ^- ) and the like.

The fluoro-containing boron-based anion may include tetrafluoroborate (BF ₄ ⁻ ) and the like.

The fluorine-containing sulfone-based anion may include nonaflate (CF ₃ (CF ₂ ) ₃ SO ₃ ⁻ ) and the like.

The fluorine-containing anion is an anion represented by Formula 2, hexafluorophosphate (PF ₆ ^- ), tetrafluoroborate (BF ₄ ^- ), and nonaflate (CF ₃ (CF ₂ ) ₃ SO ₃ ^- ) may include at least one selected from among.

The fluorine-containing anion is an anion represented by Formula 2-1, hexafluorophosphate (PF ₆ ^- ), tetrafluoroborate (BF ₄ ^- ), and nonaflate (CF ₃ (CF ₂ ) ₃ SO ₃ ^- ) may include at least one selected from among.

The porous support may include a hydrophobic polymer.

The porous support may be a single layer, or a plurality of layers may be formed by stacking them. The porous support may have a thickness of 20 μm to 1 mm. If the thickness of the porous support is less than 20 μm, crossover of the active material may occur, and if it is more than 1 mm, it is difficult to move the charge carrier, and thus the performance of the battery may be reduced. The thickness of the porous support may mean the thickness of the single layer when the porous support is a single layer, and when the porous support is a plurality of layers, it means the total thickness of the plurality of layers in which the porous support is laminated. can

The pores of the porous support may have a size of 1 nm to 1 μm, specifically 20 nm to 100 nm, and more specifically 20 nm to 50 nm. When the size of the pores of the porous support is less than 1 nm, the ionic liquid is not properly impregnated and the hydrophobicity is weakened, inhibiting the movement of ions for driving the secondary battery, and when it exceeds 1 μm, crossover of the active material is not prevented There may be problems that cannot be

The porosity of the porous support may be 10% to 90%, specifically 30% to 50%. When the porosity of the porous support is less than 10%, there is little impregnation of the ionic liquid, so a load may be applied to the movement of ions, and if it is more than 90%, a problem may occur in mechanical strength.

The size and porosity of the pores may be measured using a mercury adsorption method (porosimeter).

The hydrophobic polymer may include a polyolefin-based homopolymer or copolymer. The polyolefin-based resin is at least one selected from the group consisting of ultra-high molecular weight polyethylene, high molecular weight polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, high crystalline polypropylene, polyethylene-propylene copolymer, and mixtures thereof. may include

In addition, the polyolefin-based resin may include other resins in addition to the polyolefin resin. Examples of other resins include polyimide, polyester, polyamide, polyetherimide, polyamideimide, and polyacetal. In the case of including other resins as described above, the polyolefin-based resin may be prepared by blending the polyolefin-based resin and other resins in an appropriate solvent.

The first ionic liquid may be included in an amount of 20 to 90% by weight, specifically, in an amount of 40 to 80% by weight, based on the total weight of the first ionic liquid film. When the content of the first ionic liquid is less than 20% by weight, the charge carrier cannot move, and when it is more than 90% by weight, there may be a problem in the mechanical strength of the composite separator using the same.

The first porous support may be included in an amount of 10 to 80% by weight, specifically, in an amount of 20 to 60% by weight based on the total weight of the first ionic liquid membrane. If the content of the first porous support is less than 10% by weight, a problem may occur in the mechanical strength of the composite separator using the same, and if it is more than 80% by weight, the ion exchange property in the electrolyte is lowered, so that the performance of the battery may be reduced. have.

The thickness of the first ionic liquid film may be 20 μm to 1 mm. If the thickness of the first ionic liquid film is less than 20 μm, crossover of the active material may occur, and if it is more than 1 mm, it is difficult to move the charge carrier, so that the performance of the battery may be deteriorated.

The second ionic liquid may be included in an amount of 20 to 90% by weight, specifically, in an amount of 40 to 80% by weight, based on the total weight of the second ionic liquid film. When the content of the second ionic liquid is less than 20% by weight, the charge carrier cannot move, and when it is more than 90% by weight, there may be a problem in the mechanical strength of the composite separator using the same.

The second porous support may be included in an amount of 10 to 80% by weight, specifically, in an amount of 20 to 60% by weight based on the total weight of the second ionic liquid membrane. If the content of the second porous support is less than 10% by weight, a problem may occur in the mechanical strength of the composite separator using the same, and if it is more than 80% by weight, the ion exchange property in the electrolyte is lowered, and the performance of the battery may be reduced. have.

The thickness of the second ionic liquid film may be 20 μm to 1 mm. If the thickness of the second ionic liquid film is less than 20 μm, crossover of the active material may occur, and if it is more than 1 mm, it is difficult to move the charge carrier, and thus the performance of the battery may be deteriorated.

The first coating film and the second coating film may be the same as or different from each other, and may each independently include a fluorine-containing polymer.

The fluorine-containing polymer may include a homopolymer or a copolymer derived from a fluorine-containing monomer.

The fluorine-containing monomer may include, but is not limited to, tetrafluoroethylene, hexafluoropropylene, fluorovinylidene, chlorotrifluoroethylene, or trifluoroethylene.

When the fluorine-containing polymer is a copolymer derived from a fluorine-containing monomer, it may be a copolymer of different fluorine-containing monomers among the fluorine-containing monomers, or the fluorine-containing monomer is an ethylenically unsaturated monomer other than the fluorine-containing monomer, non-functional It may be formed by polymerization with monomers such as an acrylic monomer, a carboxyl group-containing monomer, or a hydroxyl group-containing monomer, but the types of monomers are not limited thereto.

The first coating film and the second coating film may be formed by spin coating on the first porous support and the second porous support, respectively.

The thickness of the first coating layer may be 10 nm to 10 μm, specifically, 100 nm to 1 μm. If the thickness of the first coating film is less than 10 nm, the ionic liquid may leak out of the ionic liquid film during long-term operation of the battery, and if it is more than 10 µm, it is difficult to move the charge carrier, so the performance of the battery is reduced. can be lowered

The thickness of the second coating layer may be 10 nm to 10 μm, specifically, 100 nm to 1 μm. If the thickness of the second coating film is less than 10 nm, the ionic liquid may leak out of the ionic liquid film during long-term operation of the battery, and if it is more than 1 µm, it is difficult to move the charge carrier, so the performance of the battery is poor. can be lowered

2. Manufacturing method of composite separator

The present invention provides a method for manufacturing a composite separator.

The method of manufacturing the composite separator includes: i) forming a first coating body having a first coating film disposed on one surface of a first ionic liquid film; ii) forming a second coating body having a second coating film disposed on one surface of the second ionic liquid film; and iii) bonding the other surface of the first ionic liquid film in the first coating body to the other surface of the second ionic liquid film in the second coating body.

First, the step i) comprises the steps of forming a first coating film on one surface of the first porous support; and impregnating the other surface of the first porous support with a first ionic liquid.

The step of forming the first coating film on one surface of the first porous support may include forming the first coating film by spin coating.

Specifically, forming the first coating film may include applying a first coating solution on the first porous support and rotating the first porous support to which the first coating solution is applied at high speed.

The step of applying the first coating solution on the first porous support may be performed by a commonly known coating method.

The step of rotating the first porous support coated with the first coating solution at high speed may include rotating at 100 rpm to 5,000 rpm. If the rotation speed is less than 100 rpm, the thickness of the coating film may be thick and non-uniformly coated, and if it exceeds 5,000 rpm, the thickness of the coating film may be too thin.

The step of rotating the first porous support coated with the first coating solution at high speed may include rotating for 30 seconds to 300 seconds. If the rotation time is less than 30 seconds, a non-uniform coating film may be formed, and if it exceeds 300 seconds, a problem in which the edge of the coating film is thickened may occur.

The first coating solution may be included in an amount of 5 parts by weight to 1,000 parts by weight based on 100 parts by weight of the first porous support. If the content of the first coating solution is less than 5 parts by weight based on 100 parts by weight of the first porous support, a problem may occur that the coating film is not uniformly formed, and if it exceeds 1,000 parts by weight, the coating film is thickly formed. can occur

Subsequently, the step of impregnating the first ionic liquid on the other surface of the first porous support on which the first coating film is formed may be performed.

The step of impregnating the first ionic liquid on the other surface of the first porous support on which the first coating film is formed may be performed at room temperature, and dropping the first ionic liquid on the other surface of the first porous support. may include steps.

Specifically, the step of impregnating the first ionic liquid on the other surface of the first porous support on which the first coating film is formed can be performed without a separate organic solvent, thereby simplifying the manufacturing process and minimizing waste remaining after the process. Therefore, it can be economical and eco-friendly.

In the case of impregnating the first ionic liquid after forming the first coating film on the first porous support as above, the first ionic liquid impregnated in the first porous support will not flow out even after time passes. can In particular, in the case of bonding the other surfaces (parts where the coating film is not formed) of the ionic liquid film in the first coating body and the second coating body to each other, as the first coating film and the second coating film are disposed on both sides of the composite separator, the first It is possible to prevent the ionic liquid and/or the second ionic liquid from leaking to the outside.

The first ionic liquid may be included in an amount of 20 to 90% by weight, specifically, in an amount of 40 to 80% by weight, based on the total weight of the first ionic liquid film. When the content of the first ionic liquid is less than 20% by weight, the charge carrier cannot move, and when it is more than 90% by weight, there may be a problem in the mechanical strength of the composite separator using the same.

The first porous support may be included in an amount of 10 to 80% by weight, specifically, in an amount of 20 to 60% by weight based on the total weight of the first ionic liquid membrane. If the content of the first porous support is less than 10% by weight, a problem may occur in the mechanical strength of the composite separator using the same, and if it is more than 80% by weight, the ion exchange property in the electrolyte is lowered, so that the performance of the battery may be reduced. have.

In addition, in the method for manufacturing the composite separator, after impregnating the other surface of the first porous support on which the first coating film is formed with a first ionic liquid, the first ionic liquid remaining on the surface of the first porous support It may further comprise the step of removing water.

The step of removing the first ionic liquid residue may include wiping the first ionic liquid residue remaining on the outside of the first porous support with a porous paper (eg, napkin, etc.) have.

Next, step ii) comprises the steps of forming a second coating film on one surface of the second porous support; and impregnating the other surface of the second porous support with a second ionic liquid.

The step of forming a second coating film on one surface of the second porous support may include forming a second coating film by spin coating.

Specifically, forming the second coating film may include applying a second coating solution on the second porous support and rotating the second porous support to which the second coating solution is applied at high speed.

The step of applying the second coating solution on the second porous support may be performed by a commonly known coating method.

The step of rotating the second porous support coated with the second coating solution at a high speed may include rotating at 100 rpm to 5,000 rpm. If the rotation speed is less than 100 rpm, the thickness of the coating film may be thick and non-uniformly coated, and if it exceeds 5,000 rpm, the thickness of the coating film may be too thin.

The step of rotating the second porous support coated with the second coating solution at high speed may include rotating for 30 seconds to 300 seconds. If the rotation time is less than 30 seconds, a non-uniform coating film may be formed, and if it exceeds 300 seconds, a problem in which the edge of the coating film is thickened may occur.

The second coating solution may be included in an amount of 5 parts by weight to 1,000 parts by weight based on 100 parts by weight of the second porous support. If the content of the second coating solution is less than 5 parts by weight based on 100 parts by weight of the second porous support, a problem may occur that the coating film is not uniformly formed, and if it exceeds 1,000 parts by weight, the coating film is thickly formed. can occur

Then, it may be to perform the step of impregnating the second ionic liquid on the other surface of the second porous support on which the second coating film is formed.

The step of impregnating the second ionic liquid on the other surface of the second porous support on which the second coating film is formed may be performed at room temperature, and dropping the second ionic liquid on the other surface of the second porous support. may include steps.

Specifically, the step of impregnating the second ionic liquid on the other surface of the second porous support on which the second coating film is formed can be performed without a separate organic solvent, thereby simplifying the manufacturing process and minimizing waste remaining after the process. Therefore, it can be economical and eco-friendly.

In the case of impregnating the second ionic liquid after first forming the second coating film on the second porous support as above, the second ionic liquid impregnated in the second porous support will not flow out even after time passes. can In particular, in the case of bonding the other surfaces (parts where the coating film is not formed) of the ionic liquid film in the first coating body and the second coating body to each other, as the first coating film and the second coating film are disposed on both sides of the composite separator, the first It is possible to prevent the ionic liquid and/or the second ionic liquid from leaking to the outside.

The second ionic liquid may be included in an amount of 20 to 90% by weight, specifically, in an amount of 40 to 80% by weight, based on the total weight of the second ionic liquid film. When the content of the second ionic liquid is less than 20% by weight, the charge carrier cannot move, and when it is more than 90% by weight, there may be a problem in the mechanical strength of the composite separator using the same.

The second porous support may be included in an amount of 10 to 80% by weight, specifically, in an amount of 20 to 60% by weight based on the total weight of the second ionic liquid membrane. If the content of the second porous support is less than 10% by weight, a problem may occur in the mechanical strength of the composite separator using the same, and if it is more than 80% by weight, the ion exchange property in the electrolyte is lowered, and the performance of the battery may be reduced. have.

In addition, in the method for manufacturing the composite separator, after impregnating the second ionic liquid on the other surface of the second porous support on which the second coating film is formed, the second ionic liquid remaining on the surface of the second porous support It may further comprise the step of removing water.

The step of removing the second ionic liquid residue may include wiping the second ionic liquid residue remaining on the outside of the second porous support with a porous paper (eg, napkin, etc.) have.

Subsequently, iii) bonding the other surface of the first ionic liquid film in the first coating body and the other surface of the second ionic liquid film in the second coating body; may be performed.

As described above, when the first coating body and the second coating body are laminated and bonded to each other so that the first coating membrane and the second coating membrane are disposed on both sides of the composite separator, the first ions impregnated in the first porous support It is possible to prevent the ionic liquid and the second ionic liquid impregnated in the second porous support from flowing out of the composite separator, and ultimately, the durability and lifespan characteristics of the battery are improved.

The first coating body and the second coating body may be the same as or different from each other.

The first porous support, the first coating film, the first ionic liquid, the first ionic liquid film, the second porous support, the second coating film, the second ionic liquid, the second ionic liquid film '1. Since the contents defined in 'composite separator' may be equally applied, it is omitted here.

3. Secondary battery

The present invention provides a secondary battery.

The secondary battery may include a positive electrode; cathode; and the composite separator described above.

The secondary battery may be meant to include any secondary battery or energy storage device capable of charging and discharging normally other than a fuel cell and/or a primary battery, and preferably includes a redox flow secondary battery or a redox flow battery can be understood as a concept that

In particular, the secondary battery may be a redox flow battery.

The redox flow battery consists of (1) two electrolytes in which active materials capable of oxidation and reduction are dissolved, (2) an external tank for storing them, (3) electrodes where oxidation and reduction reactions occur, and the above-described composite separator (ion exchange separator) ), and (4) a pump for continuous delivery of the electrolyte stored in the tank to the electrochemical cell. Since the composition of this redox flow battery, that is, the active material responsible for oxidation and reduction reactions is dissolved in an electrolyte rather than a solid electrode and stored in an external tank, simply increasing the volume of the electrolyte (that is, the size of the tank) capacity can be increased.

In the redox flow battery as described above, since the oxidation-reduction reaction of the active material occurs on the surface of the electrode, there is less degradation of the electrode compared to the conventional lithium secondary battery that undergoes a reaction in which ions are inserted/desorbed into the electrode, and accordingly semi-permanent recycling As this is possible, there is an advantage in that the lifespan characteristics are very excellent compared to other secondary batteries.

The positive electrode and the negative electrode can be used without limitation as long as they are materials that can be used in secondary batteries, and when the secondary battery is a redox flow battery, transition metals such as titanium, platinum, and ruthenium, alloys thereof, or transitions thereof A metal-ligand compound or the like may be used, but is not limited thereto.

Specifically, when the secondary battery includes a redox flow battery, vanadium, zinc/bromine, iron/chromium, or the like may be used as an active material. Among them, a vanadium redox flow battery (vanadium redox flow battery) using vanadium as an active material may be included.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. Next, the present invention will be described in more detail through specific examples.

Example 1

A porous polyolefin membrane (Celgard 2320, Celgard) was prepared as a porous support, and a Nafion (DuPont) solution (5 wt% Nafion in water and 1-propanol) was applied to one surface of the porous polyolefin membrane, followed by spin coating. A porous polyolefin membrane with a coating film was obtained.

Then, 60% by weight of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) as an ionic liquid was added to the coating layer. After impregnating the formed porous polyolefin membrane by dropping it on the other surface, the ionic liquid residue remaining on the surface of the support was wiped off to prepare a coated body.

The two coating bodies were prepared in the same manner, and the composite separator was manufactured by overlapping and bonding the two coating bodies so that the coating film faces outward.

Example 2

1-Butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl) instead of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid in Example 1 ) A composite separator was prepared in the same manner as in Example 1, except that imide (1-Butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide, BMPip TFSI) was used.

Comparative Example 1

A porous polyolefin membrane (Celgard 2320, Celgard Co.) was prepared as a porous support, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (1-Butyl-3-methylimidazolium) was prepared as an ionic liquid. After impregnating by dropping 60 wt% of bis(trifluoromethylsulfonyl)imide, BMIM TFSI) on the other surface of the porous polyolefin membrane, the ionic liquid residue remaining on the surface of the support was wiped off to prepare a coating body.

After the two coating bodies were prepared in the same manner, the two coating bodies were overlapped and bonded to each other to prepare a separation membrane.

Experimental Example 1 - Vanadium ion membrane permeation experiment

An experiment was conducted to measure the degree of permeation through the membrane by diffusion of vanadium ions. Vanadium (IV) cations exhibit dark blue light in aqueous solution, and therefore, penetration of vanadium ions through the separation membrane can be visually observed by changing the color of the electrode solution. Furthermore, since the color of the solution changes in proportion to the concentration, the change in the concentration of vanadium ions can be measured using UV/Visible spectroscopy.

First, a 1 M aqueous solution of sulfuric acid in which 0.5 M VOSO ₄ was dissolved and a 1 M aqueous solution of sulfuric acid in which 0.5 M MgSO ₄ was dissolved were prepared, and a total of two diffusions separated by the composite separation membrane of Example 1 and the separation membrane of Comparative Example 1, respectively. Cells were prepared. As shown in Figure 3, 0.5 M VOSO ₄ dissolved 1 M sulfuric acid aqueous solution was put in one side of both beakers of each diffusion cell, and 0.5 M MgSO ₄ 1 M sulfuric acid aqueous solution was dissolved in the same amount in the other side. Thereafter, the result of measuring the concentration of vanadium ions (VO ²⁺ ) over time in a 1 M aqueous solution of sulfuric acid in which 0.5 M MgSO ₄ was dissolved is shown in FIG. 4 .

According to FIG. 4 , when the separator of Comparative Example 1 was used, the transmittance of the composite separator of Example 1 and the vanadium ion (VO ²⁺ ) was similar at the initial stage (about 25 hours or less), but the permeability sharply increased over time. increase could be observed. In the separation membrane of Comparative 1, the ionic liquid impregnated therein leaks out over time, so that the permeation of vanadium ions cannot be properly suppressed, but in the case of the composite separation membrane of Example 1, the coating film formed on the surface is It was confirmed that the permeation of vanadium ions was effectively inhibited by blocking the outflow.

Experimental Example 2 - Redox flow battery charge/discharge experiment

Using the composite separator of Example 1 and the separator of Comparative Example 1, respectively, using 50 ml of 2M H ₂ SO ₄ electrolyte in which 1.6 M of V ^3.5+ was dissolved as an electrolyte, and 25 cm ² of graphite felt (carbon) felt) as an electrode to construct a redox flow battery. As a cell driving condition, a charge/discharge experiment was performed by a constant current scanning method in a voltage range of 0.8 V to 1.7 V with a current density of 40 mA/cm ² (1 A) at a flow rate of 40 ml/min, and the results are shown in FIG. 5 it was

Referring to FIG. 5 , when the composite separator of Example 1 was used, it was confirmed that the overvoltage during charging/discharging was much smaller than when the separator of Comparative Example 1 was used. This is that the separator of Comparative Example 1 was subjected to a large overvoltage as the ionic liquid impregnated therein rapidly leaked due to the flow of the electrolyte and the ionic conductivity decreased sharply, whereas the composite separator of Example 1 had ionic liquid due to the coating membrane It is confirmed that this is because the liquid remains without spillage and thus maintains good ionic conductivity.

Experimental Example 3 - Lifetime Characteristics and Efficiency Characteristics Experiment of Redox Flow Battery

Using the composite separator of Example 1 and the separator of Comparative Example 1, respectively, using 50 ml of 2M H ₂ SO ₄ electrolyte in which 1.6 M of V ^3.5+ was dissolved as an electrolyte, and 25 cm ² of graphite felt (carbon) felt) as an electrode to construct a redox flow battery. As a cell driving condition, a charge/discharge experiment was performed with a constant current scanning method in a voltage range of 0.8 V to 1.7 V with a current density of 40 mA/cm ² (1 A) at a flow rate of 40 ml/min to evaluate the lifespan characteristics and efficiency characteristics One result is shown in FIGS. 6 and 7 .

According to FIG. 6 , the composite separator of Example 1 was able to prevent the leakage of the ionic liquid by the coating membrane, so the permeability of the active material, vanadium, was low, and the capacity was maintained well even after 100 cycles. , on the other hand, in the separator of Comparative Example 1, it was confirmed that the capacity retention rate dropped to 60% or less from about 20 cycles.

According to FIG. 7 , it was confirmed that the composite separator of Example 1 was able to prevent the outflow of the ionic liquid by the coating membrane, so that both the Coulombic efficiency and the energy efficiency were superior to those of the separator of Comparative Example 1.

Experimental Example 4 - Lifetime Characteristics and Efficiency Characteristics Experiment of Redox Flow Battery

In Experimental Example 3, except that the composite separator of Example 2 was used instead of the composite separator of Example 1, a charge/discharge experiment was performed in the same manner as in Experimental Example 3 to evaluate the lifespan characteristics and efficiency characteristics. 8 shows.

According to FIG. 8 , it was confirmed that not only the composite separator of Example 1 but also the composite separator of Example 2 exhibited high lifespan characteristics and high efficiency characteristics.

Claims (20)

a first coating film;
a first ionic liquid film on the first coating film;
a second ionic liquid film on the first ionic liquid film; and
a second coating film on the second ionic liquid film;
A composite separation membrane comprising a. The method according to claim 1,
The first ionic liquid membrane is to include a first porous support and a first ionic liquid impregnated in the first porous support, the second ionic liquid membrane is impregnated in the second porous support and the second porous support and a second ionic liquid,
The first ionic liquid and the second ionic liquid are the same or different from each other, and each independently comprises at least one cation selected from a nitrogen-containing aromatic ring cation and a quaternary ammonium and a fluorine-containing anion. separator. 3. The method according to claim 2,
The nitrogen-containing aromatic ring cation includes at least one selected from dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium, and dialkylpyrrolidinium, and the quaternary ammonium is represented by the following formula (1) Which will be, the composite separator:
[Formula 1]

In Formula 1, R1 to R4 may be the same as or different from each other, and may each independently be an alkyl group having 10 or less carbon atoms. 4. The method according to claim 3,
Of the two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium, the carbon number of at least one alkyl group is 4 or more, the composite separation membrane. 4. The method according to claim 3,
One of the two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium has 3 or less carbon atoms, and the other alkyl group has 4 or more carbon atoms, composite separator. 3. The method according to claim 2,
The fluorine-containing anion is a composite separator comprising at least one selected from a fluorine-containing imide-based anion, a fluorine-containing phosphate-based anion, a fluorine-containing boron-based anion, and a fluorine-containing sulfone-based anion. 3. The method according to claim 2,
The fluorine-containing anion is an anion represented by the following Chemical Formula 2, hexafluorophosphate (PF ₆ ^- ), tetrafluoroborate (BF ₄ ^- ), and nonaflate (CF ₃ (CF ₂ ) ₃ SO ₃ ^- ), the composite separator comprising at least one selected from:
[Formula 2]

In Formula 2,
R5 and R6 are the same as or different from each other, and each independently represents an alkyl group having 1 to 5 carbon atoms which is unsubstituted or substituted with at least one fluorine group. The method according to claim 1,
The first coating film and the second coating film are the same as or different from each other, and each independently comprising a fluorine-containing polymer, a composite separator. The method according to claim 1,
The porous support is a composite separator comprising a hydrophobic polymer. i) forming a first coating body having a first coating film disposed on one surface of the first ionic liquid film;
ii) forming a second coating body having a second coating film disposed on one surface of the second ionic liquid film; and
iii) bonding the other surface of the first ionic liquid film in the first coating body to the other surface of the second ionic liquid film in the second coating body;
A method for manufacturing a composite separator comprising a. 11. The method of claim 10,
The step i) comprises: forming a first coating film on one surface of the first porous support; and impregnating the other surface of the first porous support with a first ionic liquid,
The step ii), forming a second coating film on one surface of the second porous support; and impregnating the other surface of the second porous support with a second ionic liquid. 12. The method of claim 11,
The first coating film and the second coating film are to be formed by spin coating, a method of manufacturing a composite separator. 11. The method of claim 10,
The first ionic liquid and the second ionic liquid are the same or different from each other, and each independently comprises at least one cation selected from a nitrogen-containing aromatic ring cation and a quaternary ammonium and a fluorine-containing anion. A method for manufacturing a separation membrane. 14. The method of claim 13,
The nitrogen-containing aromatic ring cation includes at least one selected from dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium, and dialkylpyrrolidinium, and the quaternary ammonium is represented by the following formula (1) The method of manufacturing a composite separator that will be:
[Formula 1]

In Formula 1, R1 to R4 may be the same as or different from each other, and may each independently be an alkyl group having 10 or less carbon atoms. 15. The method of claim 14,
One of the two alkyl groups of the dialkylimidazolium, dialkylpyridinium, dialkylpiperidinium and dialkylpyrrolidinium has 3 or less carbon atoms, and the other alkyl group has 4 or more carbon atoms, A method for manufacturing a composite separator. 14. The method of claim 13,
The fluorine-containing anion is an anion represented by the following Chemical Formula 2, hexafluorophosphate (PF ₆ ^- ), tetrafluoroborate (BF ₄ ^- ), and nonaflate (CF ₃ (CF ₂ ) ₃ SO ₃ ^- ), the method for producing a composite separator comprising at least one selected from:
[Formula 2]

In Formula 2,
R5 and R6 are the same as or different from each other, and each independently represents an alkyl group having 1 to 5 carbon atoms which is unsubstituted or substituted with at least one fluorine group. 11. The method of claim 10,
The first coating film and the second coating film are the same as or different from each other, and each independently comprises a fluorine-containing polymer, a method of manufacturing a composite separator. 11. The method of claim 10,
The porous support is a method for producing a composite separator comprising a hydrophobic polymer. anode;
cathode; and
A secondary battery comprising the composite separator according to any one of claims 1 to 9. 20. The method of claim 19,
A secondary battery that is a redox flow battery.

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