KR102236115B1 - Separator for Secondary Battery and The Method for Manufacturing of The Same - Google Patents

Abstract

The present invention relates to a separator for a secondary battery comprising: a porous hydrophobic polymer membrane support; and a liquid membrane of an ionic liquid including an imidazolium-based cation and an imide-based anion represented by chemical formula 1, and to a manufacturing method of the separator for a secondary battery, comprising a step of impregnating the porous hydrophobic polymer membrane support with an ionic liquid including the imidazolium-based cation and the imide-based anion represented by chemical formula 1, thereby providing the secondary battery having excellent capacity properties, lifespan properties, and/or efficiency.

Description

Separator for Secondary Battery and The Method for Manufacturing of The Same}

The present invention relates to a separator for a secondary battery and a method of manufacturing the same.

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. Portable (small) electronic products such as mobile phones and notebook computers, electric vehicles and energy storage devices (ESS), etc. The range of applications such as large-sized devices is gradually expanding. Currently, the most widely used secondary battery is a lithium secondary battery. The lithium secondary battery is composed of two solid electrodes (anode and negative electrode), a liquid non-aqueous electrolyte and a polymer porous separator. However, due to the problem of high cost of transition metal (Co, Ni, etc.) resources and lithium resources used as positive electrode active materials of lithium secondary batteries, many efforts to replace lithium secondary batteries with new low-cost secondary battery systems are being made.

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

To date, Nafion is the most widely applied ion exchange membrane for redox flow batteries. Nafion is a polymer membrane having a cation exchange functional group, and is a synthetic resin in which a sulfonic acid functional group of a strong acid is introduced into polytetrafluoroethylene (PTFE) having excellent chemical resistance, and enables a cation exchange reaction. Cation exchange takes place through the sulfonic acid functional group present in tetrafluoroethylene, and mainly carries hydrogen cations. However, since Nafion membranes cannot completely suppress the crossover phenomenon in which ions of both electrode active materials cross over, it is not possible to completely control the mixing of aqueous solutions of two electrode active materials. Accordingly, when using Nafion membranes, oxidation-reduction Self-discharge and deterioration of the flow battery occur. Korean Patent Publication No. 2017-0029235 discloses a technique for improving ion exchange properties by modifying a fluorine-based polymer resin with ionic inorganic particles, but there is a problem in that crossover of the electrode active material ions may still occur. .

Therefore, development of a new separator for preventing the crossover phenomenon of electrode active material ions in such a redox flow battery is required.

Korean Patent Application Publication No. 2017-0029235

The present invention is to solve the above problems, by improving the crossover problem of the electrode active material ions of the existing Nafion separator, preventing mixing between the two electrode active material aqueous solution in a secondary battery, especially a redox flow battery. , To solve the self-discharge problem of a secondary battery by preventing a crossover phenomenon of electrode active material ions by using an ionic liquid having an immiscibility characteristic with an aqueous electrode active material solution.

The present invention is a porous hydrophobic polymer membrane support; And a liquid film of an ionic liquid containing an imidazolium-based cation and an imide-based anion represented by Formula 1 below:

[Formula 1]

In Formula 1,

R ₁ and R ₂ are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group, _{and at least one of R 1} and R ₂ is a substituted or unsubstituted alkyl group having 5 to 10 carbon atoms.

In addition, the present invention provides a method for producing a separator for a secondary battery comprising the step of impregnating an ionic liquid containing an imidazolium-based cation and an imide-based anion represented by Formula 1 in a porous hydrophobic polymer membrane support. do.

In addition, the present invention is a positive electrode; cathode; And it provides a secondary battery including the above-described secondary battery separator.

The separator for a secondary battery of the present invention uses a separator of an immobilized liquid membrane formed by impregnating a hydrophobic ionic liquid into a porous hydrophobic polymer membrane support, so that the anode active material aqueous solution and the anode active material aqueous solution are completely separated with the separator as above. In particular, when the separator of such a hydrophobic immobilized liquid membrane is used for a redox flow battery, it is possible to improve the effect of inhibiting the crossover of the electrode active material ions compared to the conventional Nafion-based separator, so that the redox flow battery By suppressing the self-discharge and deterioration phenomenon, ultimately, there is an effect of providing a secondary battery having excellent storage characteristics, capacity characteristics, life characteristics, and/or efficiency despite several times of charging and discharging.

1 is a view showing the color change result _{of the MgSO 4} aqueous solution according to Experimental Example 1 of the present invention.
2 is a view showing the result of measuring the color change _{of the MgSO 4} solution according to Experimental Example 1 of the present invention by UV/Visible spectroscopy.
3 is a view showing the results of measuring the ionic conductivity of the separators of Example 1 and Comparative Example 3 according to Experimental Example 2 of the present invention.
4 is a diagram showing the results of an open circuit voltage experiment of the redox flow battery according to Experimental Example 3 of the present invention.
5 is a diagram showing a charge/discharge curve of a redox flow battery using the separator of Example 1 according to Experimental Example 4 of the present invention.
6 is a view showing the capacity retention rate and efficiency change according to the cycle of the redox flow battery using the separator of Example 1 according to Experimental Example 4 of the present invention.
7 is a diagram showing a charge/discharge curve of a redox flow battery using the separator of Comparative Example 4 according to Experimental Example 4 of the present invention.
8 is a view showing the charge and discharge capacity of the redox flow battery using the separators of Example 1 and Comparative Example 5 according to Experimental Example 5 of the present invention.

When'include','have', and'consist of' mentioned in the present specification are used, other parts may be added unless'only' is used. In the case of expressing the constituent elements in the singular, it includes the case of including the plural unless specifically stated otherwise.

In interpreting the constituent elements, it is interpreted as including an error range even if there is no explicit description.

Hereinafter, the present invention will be described in detail.

Separator for secondary battery

The present invention provides a separator for a secondary battery.

The'secondary cell' as defined in the present specification may mean a concept including all secondary cells or energy storage devices that are normally chargeable and discharged except for a fuel cell or a primary cell, and is preferably a redox flow secondary cell or It can be understood as a concept involving a redox flow cell.

The separator for a secondary battery may include a porous hydrophobic polymer membrane support; And a liquid film of an ionic liquid including an imidazolium-based cation and an imide-based anion represented by Formula 1 below.

[Formula 1]

In Formula 1,

R ₁ and R ₂ are the same as or different from each other, and each independently a substituted or unsubstituted alkyl group, _{and at least one of R 1} and R ₂ is a substituted or unsubstituted alkyl group having 5 to 10 carbon atoms.

The R ₁ and R ₂ may be the same as or different from each other, and may each independently be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms.

In addition, R ₁ and R ₂ may be different from each other. Specifically, R ₁ may be a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ₂ may be a substituted or unsubstituted alkyl group having 5 to 10 carbon atoms.

In particular, when the two alkyl substituents of the imidazolium-based cation are asymmetric and the number of carbon atoms of any one of the substituents is 5 to 10, as the hydrophobicity increases and the ionic liquid is stabilized, the separator for a secondary battery of the present invention including the same When used, the effect of suppressing the crossover phenomenon of the electrode active material ions is maximized.

The R ₁ may be a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group, but if it is an alkyl group having 1 to 4 carbon atoms, it is not limited thereto, and R ₂ is a pentyl group, a neopentyl group, a hexyl group, and isohex It may be a sil group, a heptyl group, an octyl group, a nonyl group, or a decyl group, but the alkyl group having 5 to 10 carbon atoms is not limited thereto.

Specifically, the imidazolium-based cation is 1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-heptyl-3-methylimidazolium, and 1-octyl-3-methylimida Zolium, 1-nonyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-hexyl-3-ethylimidazolium, 1-hexyl-3-propylimidazolium, 1-hexyl- 3-butylimidazolium, 1-decyl-3-ethylimidazolium, 1-decyl-3-propylimidazolium, or 1-decyl-3-butylimidazolium, etc., but are limited thereto. It is not.

The imide-based anion may include a sulfonylimide-based anion.

In addition, the imide-based anion may include a halogenated sulfonylimide-based anion.

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

[Formula 2]

In Formula 2,

R ₃ and R ₄ are the same as or different from each other, and each independently represents an alkyl group having 1 to 5 carbon atoms substituted or unsubstituted with at least one fluorine group.

The imide-based anion may include at least one selected from anions represented by Formulas 2-1 to 2-5 below.

[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Formula 2-4]

[Formula 2-5]

For a liquid film of an ionic liquid having improved hydrophobicity and stability by binding with the imidazolium-based cation, it is preferable that the imide-based anion includes bis(trifluoromethylsulfonyl)imide.

The ionic liquid may be hydrophobic.

The hydrophobic polymer membrane support may be a single layer, or may be a plurality of layers in which several are stacked. The thickness of the hydrophobic polymer membrane support may be 20 µm to 1 mm, and specifically 100 µm to 300 µm. When the thickness of the hydrophobic polymer membrane support is less than 20 µm, crossover of the positive electrode active material may occur, and when the thickness of the hydrophobic polymer membrane support is more than 1 mm, it is difficult to move the charge carrier and thus the performance of the battery may be deteriorated. The thickness of the hydrophobic polymer membrane support may mean the thickness of the single layer when the hydrophobic polymer membrane support is a single layer, and when the hydrophobic polymer membrane support is a plurality of layers, the hydrophobic polymer membrane support is laminated. It can mean the total thickness of multiple layers.

The pore size of the hydrophobic polymer membrane support may be 1 nm to 1 μm, specifically 20 nm to 100 nm, and more specifically 20 nm to 50 nm. When the pore size of the hydrophobic polymer membrane support is less than 1 nm, the ionic liquid is not properly impregnated and the hydrophobicity is weakened, thereby inhibiting the movement of ions for driving the secondary battery, and when it exceeds 1 μm, crossover of the positive electrode active material There may be a problem that does not prevent it.

The porosity of the hydrophobic polymer membrane support may be 10% to 90%, and specifically 30% to 50%. When the porosity of the hydrophobic polymer membrane support is less than 10%, impregnation of the ionic liquid is small, so that a load may be applied to the movement of ions, and when the porosity is greater than 90%, a problem may occur in mechanical strength.

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

The hydrophobic polymer may include a polyolefin-based homopolymer or copolymer.

The polyolefin 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. Can include.

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

The ionic liquid may be included in an amount of 20 to 90% by weight based on the total weight of the separator for the secondary battery, and specifically, may be included in an amount of 40 to 80% by weight. When the content of the ionic liquid is less than 20% by weight, it is impossible to move the charge carrier, and when it is more than 90% by weight, a problem may occur in the mechanical strength of a separator for a secondary battery using the same.

The hydrophobic polymer membrane support may be included in an amount of 10 to 80% by weight based on the total weight of the separator for a secondary battery, and specifically, may be included in an amount of 20 to 60% by weight. When the content of the hydrophobic polymer membrane support is less than 10% by weight, a problem may occur in the mechanical strength of the separator for a secondary battery using the same, and when the content of the hydrophobic polymer membrane support is more than 80% by weight, the ion exchange property in the electrolyte solution decreases, resulting in a decrease in battery performance. I can.

The thickness of the hydrophobic polymer membrane support impregnated with the ionic liquid may be 20 µm to 1 mm, and specifically 100 µm to 300 µm. If the thickness of the hydrophobic polymer membrane support impregnated with the ionic liquid is less than 20 μm, crossover of the positive electrode active material may occur, and if it exceeds 1 mm, it is difficult to move the charge carrier and thus the performance of the battery may be degraded.

The hydrophobic polymer membrane support impregnated with the ionic liquid may be a single layer or may be a plurality of layers in which several are stacked. The thickness of the hydrophobic polymer membrane support impregnated with the ionic liquid may mean the thickness of the single layer when the hydrophobic polymer membrane support impregnated with the ionic liquid is a single layer. When the hydrophobic polymer membrane support has a plurality of layers, it may mean the total thickness of the plurality of layers in which the hydrophobic polymer membrane support impregnated with the ionic liquid is stacked.

The separator for secondary batteries may be configured in the form of a supported ionic liquid membrane (SILM) by impregnating (supporting) a hydrophobic ionic liquid on a porous hydrophobic polymer membrane support and immobilizing it. This immobilized liquid film has the advantages of an absorption process and a film process, and as the liquid film is uniformly formed over the entire porous hydrophobic polymer membrane support, it is used for secondary batteries, especially redox flow batteries, to prevent mixing of electrode active materials. , Through the role of a charge carrier by selective ion conductivity of the ionic liquid, the crossover of the electrode active material ions is prevented, but the exchange of hydrogen ions is selectively performed, thereby suppressing the self-discharge and deterioration of the secondary battery. It can improve performance.

Method of manufacturing separator for secondary battery

The present invention provides a method of manufacturing a separator for a secondary battery.

The method of manufacturing a separator for a secondary battery may include impregnating an ionic liquid containing an imidazolium-based cation and an imide-based anion represented by Formula 1 into a porous hydrophobic polymer membrane support.

The above-described contents may be equally applied to the secondary battery, imidazolium-based cation, imide-based anion, ionic liquid, and hydrophobic polymer membrane support.

Impregnating the ionic liquid into the porous hydrophobic polymer membrane support may include dropping the ionic liquid onto the surface of the hydrophobic polymer membrane at room temperature.

Specifically, the impregnation step may be performed without a separate organic solvent, etc., thereby simplifying the manufacturing process and minimizing waste remaining after the process, thereby making it economical and eco-friendly.

The method of manufacturing a separator for a secondary battery may include removing an ionic liquid residue remaining on the surface of the hydrophobic polymer membrane support after the impregnation step.

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

In addition, after the step of removing the ionic liquid residue, a step of drying the manufactured separator for a secondary battery may be further included. In this case, the drying may include putting the separator for a secondary battery from which the ionic liquid residue has been removed using a vacuum oven, and drying it in a vacuum of 120° C. or higher.

The method of manufacturing a separator for a secondary battery may further include forming a hydrophilic glass fiber filter (glass filter or glass fiber filter) on both surfaces of the separator for a secondary battery after removing the ionic liquid residue. have.

The forming of the hydrophilic glass fiber filter on both sides of the secondary battery separator includes laminating the secondary battery separator containing the ionic liquid on the hydrophilic glass fiber filter at room temperature, and then laminating the hydrophilic glass fiber filter on the secondary battery separator again. It may include.

When the hydrophilic glass fiber filter is formed on both sides of the separator for secondary batteries, the interface between the electrolyte and the separator for secondary batteries is stabilized, thereby reducing the charge transfer resistance at the interface. In addition, when the secondary battery is charged/discharged, the aqueous electrolyte solution is physically flowing from the surface of the separator, so the ionic liquid may be physically lost.If the hydrophilic glass fiber filter is present, the aqueous electrolyte solution on the surface of the separator for a hydrophobic secondary battery Since the flow of the ionic liquid is suppressed, the physical loss of the ionic liquid can be reduced, thereby improving durability.

Secondary battery

The present invention provides a secondary battery.

The secondary battery includes a positive electrode; cathode; And a separator for a secondary battery described above.

The secondary battery may mean not a fuel cell or a primary cell, but includes all secondary cells or energy storage devices that are generally capable of charging and discharging, and preferably, a concept including a redox flow secondary battery or a redox flow battery. Can be understood as

The redox flow battery includes (1) an aqueous solution of two electrode active materials in which an active material capable of oxidation and reduction is dissolved, (2) an external tank storing the same, (3) an electrode in which oxidation and reduction reactions occur, and an ion exchange membrane. It may consist of an electrochemical cell, and (4) a pump for continuous transport of the aqueous electrode active material solution stored in the tank to the electrochemical cell. Since the configuration of the redox flow battery, that is, the electrode active material responsible for oxidation and reduction reactions, is dissolved in an electrolyte rather than a solid electrode and stored in an external tank, the volume of the electrode active material aqueous solution (that is, the size of the tank) is increased. It is only possible to increase the capacity of the secondary battery.

In the above redox flow battery, since the redox reaction of the electrode active material occurs on the surfaces of the positive electrode and the negative electrode, compared to conventional batteries (for example, lithium secondary batteries) that undergo a reaction in which ions are inserted/desorbed into the electrode active material. As the electrode is less deteriorated and thus semi-permanent recycling 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 may be used without limitation as long as the material can be used for a secondary battery, and when the secondary battery is a redox flow battery, a transition metal such as titanium, platinum, ruthenium, an alloy thereof, or a transition 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 implement the present invention. However, the present invention may be implemented in various 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

1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide as an ionic liquid in a hydrophobic porous polyolefin separator (Celgard 2320, Celgard) as a support. )imide, HMIM TFSI) was impregnated by dropping, and then the ionic liquid residue remaining on the surface of the support was wiped off to form a liquid film of the ionic liquid.

Seven layers of the support impregnated with the ionic liquid prepared as described above were stacked to prepare a support impregnated with a plurality of layers of ionic liquid having a thickness of 140 μm.

Subsequently, a hydrophilic glass fiber filter (Qualitative filter paper, Advantec Co., Ltd.) was laminated with a support impregnated with a plurality of layers of ionic liquid prepared above, and the same hydrophilic glass fiber filter was laminated on the separator to form a total of three layers. Was prepared.

Example 2

1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl) in place of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid in Example 1 above. ) A separator was prepared in the same manner as in Example 1, except that imide (1-Decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, DMIM TFSI) was impregnated.

Comparative Example 1

1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) in place of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid in Example 1 above. ) A separator was prepared in the same manner as in Example 1, except that imide (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EMIM TFSI) was impregnated.

Comparative Example 2

1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) in place of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid in Example 1 above. ) A separation membrane was prepared in the same manner as in Example 1, except that imide (1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, BMIM TFSI) was impregnated.

Comparative Example 3

After impregnating the Nafion membrane (Nafion 115) with pure water, the membrane was prepared by drying at room temperature to remove the pure residue remaining on the surface of the Nafion membrane.

Comparative Example 4

In Example 1, a hydrophobic porous polyolefin separator that did not undergo the step of impregnating an ionic liquid was prepared as a separator.

Comparative Example 5

As an anion exchange membrane, a Selemion ^TM AAV membrane was impregnated with 1 wt% sulfuric acid solution, and then dried at room temperature to remove pure residues remaining on the surface to prepare a separation membrane.

Experimental Example 1-Separation membrane permeation experiment of vanadium ions

An experiment was conducted to measure the degree of permeation of the separator due to diffusion of vanadium ions. The vanadium (IV) cation exhibits a deep blue light in the aqueous solution, so the penetration of vanadium ions into the separator can be observed with the naked eye through a change in 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 sulfuric acid aqueous solution in which 0.5 M VOSO ₄ was dissolved and a 1 M sulfuric acid aqueous solution in which 0.5 M MgSO ₄ was dissolved were prepared, and a total of 5 H separated by the separation membranes of Examples 1 and 2 and Comparative Examples 1 to 3 -The cell was prepared. A 1 M sulfuric acid aqueous solution in which _{0.5 M VOSO 4} was dissolved was added to one side of each beaker of each H-cell, and an equal amount of 1 M sulfuric acid aqueous solution in which _{0.5 M MgSO 4 was dissolved was added to the other side.}

Then, the color change of the MgSO ₄ aqueous solution over time is shown in FIG. 1.

In addition, _{by measuring the color change of the MgSO 4} solution over time by UV/Visible spectroscopy, the change in the concentration of vanadium ions in the solution over time is shown in FIG. 2. For the _{change in the concentration of vanadium ions in the MgSO 4} aqueous solution, a standard curve related to the correlation between the absorbance and the vanadium ion concentration was used. When measuring a sample using a UV/Visible spectrometer, the absorbance at a specific wavelength of light can be known, so _{after preparing a sample in which various concentrations of VOSO 4} are dissolved, use the absorbance measured in each of the above samples to be used as a standard curve. Prepared.

As shown in FIG. 1, when the Nafion membrane of Comparative Example 3 was applied, it was observed that the color _{of the MgSO 4 aqueous solution changed to blue after 43 hours.} This means _{that vanadium ions in the VOSO 4} aqueous solution penetrated the Nafion membrane and _{diffused into the MgSO 4} aqueous solution. In addition, in the case of using the EMIM-TFSI-based separator of Comparative Example 1 and the BMIM-TFSI-based separator of Comparative Example 2, it can be seen that the color _{of the MgSO 4 aqueous solution changes to blue in 43 hours.}

However, in the case of using the separator to which the HMIM-TFSI of Example 1 was applied and the separator to which the DMIM-TFSI of Example 2 was applied, it can be seen that there is no color change of the _{MgSO 4 aqueous solution even after 159 hours.} This shows that the SILM-based separator according to the present invention does not permeate vanadium ions.

In addition, according to FIG. 2, in the case of the separators of Examples 1 and 2, it can be confirmed that no vanadium ions were detected even after 140 hours. In particular, in the case of the separator of Example 1, it can be confirmed that no vanadium ions were detected even after 1,500 hours. This shows that the separators of Examples 1 and 2 do not permeate vanadium ions at all. However, in the case of using the separators of Comparative Examples 1 to 3, it can be seen that the concentration of vanadium ions increases in proportion with time from the beginning of the experiment. That is, the separation membranes of Comparative Examples 1 to 3 show the result that vanadium ions permeate and diffuse.

Experimental Example 2-Measurement of the ion conductivity of the separator

In order to confirm the degree of indicating the degree of ion exchange of the charge carrier of the separation membrane, an experiment was performed to measure the ion conductivity of the separation membrane. Three H-cells not including Example 1 and Comparative Example 3 and the separator were prepared. After installing a platinum electrode with a diameter of 1 cm with a distance of 2 cm on both sides of the H-cell, a 2.4 M sulfuric acid electrolyte in which 1.6 M of vanadium ions with an oxidation number of 3.5 is dissolved is filled. Put the prepared H-cell in a beaker with water circulating at a specific temperature and maintain it at 283 K, 288 K, 293 K, 298 K, and 303 K during the experiment. After that, the impedance of the electrolyte is obtained by measuring the impedance in the frequency range of 100 to 50,000 Hz using the SP-150 potentiometer of Bio-logic Science Instrument.

The resistance value of the separator was calculated by subtracting the resistance value measured in Example 1 and Comparative Example 3 by the resistance value of the H-cell not including the separator, and using the separator thickness and diameter of 140 um and 1.9 cm, respectively. The ionic conductivity was calculated.

The results of measuring the ionic conductivity of the separator of Example 1 and the separator of Comparative Example 3 are shown in FIG. 3. The temperature according to the ionic conductivity was plotted, and in particular, in order to use the Arrhenius relational equation, the ionic conductivity was plotted as a logarithm of base 10, and the reciprocal value divided by 1000 by the temperature of the system. At room temperature, the ionic conductivity was 7.98 mS/cm and 37.95 mS/cm in Example 1 and Comparative Example 3, respectively, and the activation energy determined through the slope was 32.28 kJ/mol and 14.31 kJ/mol in Example 1 and Comparative Example 3, respectively. appear. At this time, the charge carrier may be a hydrogen ion or a counter anion.

Experimental Example 3-Open circuit voltage experiment of redox flow battery

After configuring the redox flow battery in a charged state, the open circuit voltage of the redox flow battery was measured over time. The open circuit voltage of a redox flow cell follows the Nernst equation. In other words, the open circuit voltage of the redox flow battery is determined by the concentration of vanadium ions, which is an active material dissolved in the electrode solution. However, in the charged state, when the active material ions pass through the separation membrane and move to the counter electrode solution, self-discharge occurs by reacting with the active material ions in the counter electrode solution. When self-discharge occurs, active material ions in a charged state are consumed and their concentration decreases, resulting in a change in which the open circuit voltage decreases. In other words, since the degree to which the open circuit voltage of the redox flow battery decreases with time is proportional to the degree of penetration of the active material ions of the redox flow battery through the separation membrane, vanadium ions penetrate the separation membrane from the change in the open circuit voltage of the redox flow battery. The degree can be predicted.

Using the separator of Example 1 and the separator of Comparative Example 3, respectively, 50 ml of a vanadium electrolyte having an oxidation number of 3.5 as an anolyte and a catholyte, and a redox flow battery using a graphite felt having a size of ^{25 cm 2 as an electrode.} Configured. As a cell driving condition, a charge/discharge experiment was performed at a current density of ^{40 mA/cm 2} (1 A) at a flow rate of 40 ml/min. After performing the initial formation phase, after charging to 80% of the charge depth (SOC), the results of measuring the open circuit voltage over time are shown in FIG. 4.

As shown in FIG. 4, when the separator of Example 1 is applied, the open circuit voltage drop is insignificant even after 2,500 hours, whereas when the separator of Comparative Example 3 is applied, self-discharge rapidly proceeds even though 200 hours have not elapsed. It can be confirmed that the voltage is completely discharged to near 0 V. Therefore, from this, the conventional membrane using the Nafion membrane does not inhibit the permeation of vanadium ions, whereas the membrane using the SILM membrane based on the ionic liquid of the present invention exhibits very excellent ion selective permeation properties that inhibit the permeation of vanadium ions. You can check the show.

Experimental Example 4-Charging/discharging experiment of redox flow battery

Using the separator of Example 1 and the separator of Comparative Example 4, respectively, 50 ml of vanadium electrolyte having an oxidation number of 3.5 as an anolyte and a catholyte, and a redox flow battery using a graphite felt having a size of ^{25 cm 2 as an electrode.} Configured. As a cell driving condition, a charge/discharge experiment was performed at a current density of ^{40 mA/cm 2} (1 A) at a flow rate of 40 ml/min.

The charge/discharge curve of the redox flow battery using the separator of Example 1 is shown in FIG. 5, and the capacity retention rate and efficiency change according to the cycle are shown in FIG. 6.

The charge/discharge curves of the redox flow battery using the separator of Comparative Example 4 are shown in FIG. 7.

As can be seen from the charge/discharge curve shown in FIG. 5 and the life and efficiency characteristics shown in FIG. 6, the redox flow battery using the separator of Example 1 of the present invention shows small polarization characteristics, stable life characteristics, and high efficiency characteristics. I can confirm. However, as shown in FIG. 7, in the case of using the separator of Comparative Example 4 without impregnation of an ionic liquid, it can be seen that the redox flow battery does not charge and discharge at all. This means that since the polyolefin separator is hydrophobic, the electrolyte was not impregnated with the polyolefin separator at all, and thus, the transfer of charge carriers did not occur, and the redox flow battery was not operated. Therefore, this is to disprove that the ionic liquid acts as a charge transfer medium in the polyolefin separation membrane impregnated with the ionic liquid of Example 1.

Experimental Example 5-Charging/discharging capacity experiment of redox flow battery

Using the separator of Example 1 and the separator of Comparative Example 5, respectively, _{50 ml of VOSO 4} electrolyte was used as an ^{anolyte and a catholyte, and a redox flow battery using 25 cm 2} of graphite felt as an electrode was constructed. As the cell driving condition, the charging/discharging behavior was confirmed at a flow rate of 40 ml/min and at various current densities. The electrode width is 9 cm ² , 90 mA, 180 mA, 360 mA, 720 mA, 990 mA (current density 10 mA/cm ² , 20 mA/cm ² , 40 mA/cm ² , 80 mA/cm ² , respectively, 110 mA/cm ² ) was confirmed by three cycles, respectively. The results are shown in FIG. 8.

According to FIG. 8, the redox flow battery using the separator of Example 1 performs well even in a range of various current densities, whereas the battery using the separator of Comparative Example 5 operates at a current density ^{of 20 mA/cm 2 or higher.} You can see what you can't do. In particular, Comparative Example 5 is an anion exchange membrane in which counter ions _{are replaced with SO 4} ^2- It is known that it can be used in a vanadium redox flow battery using a sulfuric acid-based electrolyte. When the current density of is exceeded, operation as a battery is impossible, whereas in the case of the separator of Example 1, it can be confirmed that the capacity expression is excellent even when a high current is applied, so that the separator for a secondary battery of the present invention is compared to other separators. It can be seen that it has better performance.

Claims (20)

Porous hydrophobic polymer membrane support; And
A liquid film of an ionic liquid comprising an imidazolium-based cation represented by the following formula (1) and an imide-based anion represented by the following formula (2);
A separator for a secondary battery comprising:
[Formula 1]

In Formula 1,
R ₁ is a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ₂ is a substituted or unsubstituted alkyl group having 5 to 10 carbon atoms.
[Formula 2]

In Formula 2,
R ₃ and R ₄ are the same as or different from each other, and each independently represents an alkyl group having 1 to 5 carbon atoms unsubstituted or substituted with at least one fluorine group. delete delete The method according to claim 1,
R ₁ is a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group,
The R ₂ is a pentyl group, a neopentyl group, a hexyl group, an isohexyl group, a heptyl group, an octyl group, a nonyl group, or a decyl group. delete delete delete The method according to claim 1,
The imide-based anion is a separator for a secondary battery comprising at least one selected from anions represented by the following Formulas 2-1 to 2-5:
[Formula 2-1]

[Formula 2-2]

[Formula 2-3]

[Formula 2-4]

[Formula 2-5]

. The method according to claim 1,
The hydrophobic polymer is a separator for a secondary battery comprising a polyolefin-based homopolymer or a copolymer. A method for producing a separator for a secondary battery comprising impregnating an ionic liquid containing an imidazolium-based cation represented by the following formula (1) and an imide-based anion represented by the following formula (2) into a porous hydrophobic polymer membrane support:
[Formula 1]

In Formula 1,
R ₁ is a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, and R ₂ is a substituted or unsubstituted alkyl group having 5 to 10 carbon atoms.
[Formula 2]

In Formula 2,
R ₃ and R ₄ are the same as or different from each other, and each independently represents an alkyl group having 1 to 5 carbon atoms substituted or unsubstituted with at least one fluorine group. The method of claim 10,
And removing the ionic liquid residue remaining on the surface of the hydrophobic polymer membrane support after the impregnation step. The method of claim 10,
The method of manufacturing a separator for a secondary battery further comprising the step of forming a hydrophilic glass fiber filter on both sides of the separator for a secondary battery. delete The method of claim 10,
R ₁ is a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group,
The R ₂ is a pentyl group, a neopentyl group, a hexyl group, an isohexyl group, a heptyl group, an octyl group, a nonyl group, or a decyl group. delete delete delete The method of claim 10,
The method of manufacturing a separator for a secondary battery, wherein the hydrophobic polymer comprises a polyolefin-based homopolymer or a copolymer. anode;
cathode; And
A secondary battery comprising the separator for a secondary battery according to any one of claims 1, 4, and 8 to 9. The method of claim 19,
A secondary battery that is a redox flow battery.

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