KR102486285B1 - Redox flow battery - Google Patents

Abstract

The redox flow battery according to the present invention uses a zeolite-coated porous ceramic separator and an acid-acid/acid-base electrolyte system, and thus has excellent electrochemical performance such as current efficiency, voltage efficiency, and energy efficiency, and at the same time It prevents movement of active material ions and has an effect of minimizing capacitance fading.

Description

High energy density aqueous redox flow battery using ceramic membrane {Redox flow battery}

The present invention relates to a redox flow battery, and more particularly, to a redox flow battery capable of high energy density and minimizing crossover.

Redox flow batteries (RFBs) are becoming increasingly important because of their potential to improve power and energy storage in unique ways. In particular, the energy of a redox flow battery stored in chemical form in an external storage can be immediately recovered or further stored by an immediate oxidation-reduction reaction on the active surface of the electrode when the liquid electrolyte flows into the cell. Thus, redox flow battery systems can be expanded into the megawatt (MW/h) range by simply expanding the volume of the reservoir. Nevertheless, research into the development of redox flow batteries has been continued in order to improve or overcome items such as higher energy density, ion cross-separator problems, efficient electrodes, and capacitance fading.

As one way to increase the energy density, the electrolyte system can be designed by employing different metal ion combinations since each metal ion has a unique oxidation/reduction potential in an aqueous medium. Examples include Ce-V, Zn/Br ² , Zn/polyiodide, Li/polyiodide, iron chloride, and Zn/Fe metal ion combinations. On the other hand, since there is no H ₂ O, the potential can be broadened by selecting an appropriate electrolyte medium, for example a non-aqueous medium. For example, various types of redox active materials such as inorganic active materials (sulfur, iodine), redox active polymers and organometallic compounds have been used in non-aqueous redox flow batteries. However, when such a non-aqueous electrolyte is used, it is very sensitive to gases such as O 2 , N ₂ and CO ₂ in the atmosphere due to the use of lithium metal and the like, and ion mobility in a non-aqueous solution is much slower than that of water, an aqueous medium.

Therefore, another possibility to obtain a wider potential is to promote the production of electrocatalysts (redox active substances) in electrochemical cells by changing the pH using highly acidic or highly alkaline solutions in aqueous media. It is possible to expand the electrochemical potential by delaying the oxygen evolution reaction (OER) or the hydrogen evolution reaction (HER).

However, there is a chronic problem of causing capacitance fading in redox flow battery systems due to ion crossover through the conventional membrane. Over time, as the ions of the active material pass through the separator and move toward the opposite pole, the amount of the active material may be concentrated to either the anode or the cathode, which causes an imbalance in the capacity of the active material and lowers the utilization rate of the electrolyte. It acts as a cause of lowering the battery capacity. This phenomenon is called capacity fade due to cross-over of active materials.

In general, a Nafion-based polymer membrane is used as a separator used in a redox flow battery, but such an ion exchange membrane causes ion movement of an active material and thus a decrease in capacity.

Korean Registered Patent Publication No. 10-2130874 (2020.06.30)

An object of the present invention is to provide a redox flow battery with excellent electrochemical performance such as current efficiency, voltage efficiency, and energy efficiency.

Another object of the present invention is to provide a redox flow battery that prevents movement of active material ions through a separator and minimizes capacitance fading.

The redox flow battery according to the present invention includes an anode cell in which an anode electrolyte is introduced and an anode is provided, and a cathode cell in which a cathode electrolyte is introduced and a cathode is provided; and a separator disposed between the anode and the cathode to prevent mixing of the anode electrolyte and the cathode electrolyte, wherein the anode electrolyte is an acidic aqueous anode electrolyte, and the cathode electrolyte is a basic aqueous anode It is an electrolyte solution, and the separator is characterized in that it is a porous ceramic separator coated with zeolite.

In one example of the present invention, the separator may include an aluminum oxide-based porous ceramic film; and zeolite coated on the surface of the ceramic film.

In one example of the present invention, the separator may be manufactured by growing and coating zeolite on the surface of an aluminum oxide-based porous ceramic membrane by a hydrothermal synthesis method.

In one example of the present invention, the separator is a redox flow battery having a porosity of 10 to 50% and a pore size of 0.01 to 0.2 ㎛.

In one example of the present invention, the acidic aqueous anode electrolyte may have a pH of 2 to 6, and the basic aqueous cathode electrolyte may have a pH of 8 to 12.

In one example of the present invention, the acidic aqueous anode electrolyte may include vanadium ions and sulfur ions.

In one example of the present invention, the basic water-based cathode electrolyte may include sodium ions.

In one example of the present invention, the acidic aqueous anode electrolyte may be an aqueous solution containing VOSO ₄ and H ₂ SO ₄ , and the basic aqueous cathode electrolyte may be an aqueous solution containing Na ₂ S ₄ and NaOH.

In one example of the present invention, in the anode electrolyte, VOSO ₄ and H ₂ SO ₄ may be independently included in an aqueous solution at a molar concentration of 0.3 to 3M, and in the cathode electrolyte, Na ₂ S ₄ and NaOH are In the aqueous phase, each may be included independently of each other at a molar concentration of 0.3 to 3M.

A redox flow battery according to an example of the present invention includes an anode electrolyte supply unit for receiving the anode electrolyte and supplying it to the anode cell; and a cathode electrolyte supply unit for receiving the cathode electrolyte and supplying it to the cathode cell, wherein in the anode cell, the anode electrolyte may be accommodated between the anode and the separator, and in the cathode cell, The cathode electrolyte may be accommodated between the cathode and the separator.

A redox flow battery according to an example of the present invention may have an open circuit potential of 0.7 V or more.

A redox flow battery according to an example of the present invention may have an energy density of 200 Wh/L or more.

The redox flow battery according to the present invention has excellent electrochemical performance such as current efficiency, voltage efficiency, and energy efficiency.

The redox flow battery according to the present invention prevents movement of active material ions through a separator and has an effect of minimizing capacity fading.

1 is a schematic diagram showing a redox flow battery system according to Example 1 of the present invention.
2 is an actual image showing a cell module of a redox flow battery according to Example 1 of the present invention.
3 shows open circuit potential values according to electrolyte systems having different pH combinations in a redox flow battery.
4 is a cell resistance graph of redox flow batteries according to Comparative Example 1 and Example 1.
5 shows cyclic voltammetry (CV) values of V ⁴⁺ oxidation for acid-acid and acid-base electrolyte combinations in each cell in a redox flow battery according to Example 1 of the present invention.
6 is a UV-Visible spectrum of the redox flow battery according to Example 1 of the present invention, measuring the movement of vanadium ions and sulfur ions with respect to the separator.
Figure 7 shows the voltage potential due to charging and discharging in the redox flow battery according to Example 1 of the present invention.
8 is a measurement of voltage, voltage efficiency, current efficiency, energy efficiency, and capacity according to long-term charging and discharging in a 1-hour cycle in a redox flow battery according to Example 1 of the present invention.

Hereinafter, a high energy density aqueous redox flow battery using a ceramic membrane according to the present invention will be described in detail with reference to the accompanying drawings.

The drawings described in this specification are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art. Therefore, the present invention may be embodied in other forms without being limited to the drawings presented, and the drawings may be exaggerated to clarify the spirit of the present invention.

Unless otherwise defined, the technical and scientific terms used in this specification have meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may unnecessarily obscure are omitted.

Singular forms of terms used in this specification may be construed as including plural forms unless otherwise indicated.

s1, s2, s3, ... mentioned in this specification; a1, a2, a3, ...; b1, b2, b3, ...; a, b, c, ...; The term itself referring to each step of the etc. is only used to indicate a certain step, means, etc., and should not be interpreted as implying an order relationship of each object indicated by the terms.

In this specification, the unit of % used without particular notice means weight % unless otherwise defined.

In the conventional redox flow battery system, there is a limit in that the battery life is significantly reduced by causing degradation of battery performance, in particular, capacity fading, due to the problem of active material ions passing through the separator as the charge and discharge cycles are repeated.

On the other hand, in the redox flow battery system according to the present invention, since a porous ceramic separator coated with zeolite is used in an acid/base aqueous electrolysis system, electrochemical performance such as current efficiency, energy efficiency, and energy density is excellent, especially There is an effect of preventing the problem of active material ions passing through the separator and the problem of capacity reduction accordingly.

The redox flow battery according to the present invention includes an anode cell in which an anode electrolyte is introduced and an anode is provided, and a cathode cell in which a cathode electrolyte is introduced and a cathode is provided; and a separator disposed between the anode and the cathode to prevent mixing of the anode electrolyte and the cathode electrolyte, wherein the anode electrolyte is an acidic aqueous anode electrolyte, and the cathode electrolyte is a basic aqueous anode It is characterized in that the separator is a porous ceramic separator coated with zeolite.

Specifically, the separator according to the present invention includes a ceramic membrane; and zeolite coated on the surface of the ceramic film.

The separator, that is, the ceramic membrane may have a porosity of 10 to 50%, specifically, a porosity of 20 to 40%, and a pore size of 0.01 to 0.2 μm, specifically, a pore size of 0.05 to 0.15 μm. / It is preferable in terms of realizing excellent electrochemical performance while preventing the problem of active material ions passing through the separator in a base water-based electrolytic system.

The composition of the ceramic membrane is not particularly limited as long as it can stably support the structure as a separator in an acid/base aqueous electrolytic system and prevents active material ions from passing through the separator, but an aluminum oxide-based porous ceramic membrane may be preferable. there is.

The surface of the ceramic membrane referred to in this specification does not mean only the external surface, and includes the external surface as well as the surface of internal pores of the ceramic membrane. Therefore, the separator according to the present invention may be coated with zeolite on both the outer surface and the inner surface of the inner pores.

The zeolite coated on the surface of the ceramic film may be prepared by growing and coating by a hydrothermal synthesis method. That is, the separator according to a preferred embodiment may be manufactured by growing and coating zeolite on the surface of an aluminum oxide-based porous ceramic membrane by hydrothermal synthesis, and specifically, an aluminum oxide-based porous ceramic membrane; and zeolite grown and coated on the surface of the ceramic film by hydrothermal synthesis. If this is satisfied, there is an effect of implementing excellent electrochemical performance while preventing the problem of active material ions passing through the separator in the acid / base aqueous electrolysis system.

As a preferred example, as a method of coating the ceramic membrane with zeolite by hydrothermal synthesis, a separator may be prepared by depositing zeolite seeds on the surface of the ceramic membrane and performing secondary growth through hydrothermal synthesis. Various types of zeolite seeds may be used, but preferably, for example, MFI type zeolite seeds. In addition, the growth raw material is not particularly limited, and for example, a silicon-based compound such as tetraethyl orthosilicate (TEOS) may be used, and an alkalizing agent such as tetrapropylammoniumhydroxide (TPAOH) may be used. .

The hydrothermal synthesis conditions may be sufficient as long as the zeolite seed located on the surface of the ceramic membrane grows and the zeolite layer can be coated, for example, 1 to 12 hours at 100 to 300 ° C., specifically 2 to 8 It may be to react in the aqueous phase for a period of time. At this time, the pressure may be appropriately controlled according to the temperature.

As described above, the separator according to the present invention is characterized in that the surface of the ceramic membrane is coated with zeolite, and the separator must be used in an acid/base aqueous electrolytic system to prevent active material ions from passing through the separator. And there is an effect of realizing better electrochemical performance such as resistance reduction. When other separators such as Nafion-based polymer membranes are used in an acid/base aqueous electrolytic system instead of the separator according to the present invention in which the surface of the ceramic membrane is coated with zeolite, the above effect is not realized. That is, the separator according to the present invention coated with the above-described zeolite does not allow active material ions to pass through the separator in an acid-base aqueous electrolyte system, and can exhibit better electrochemical performance.

As described above, the redox flow battery according to the present invention uses an acid/base aqueous electrolyte system. Specifically, the pH of the acidic water-based anode electrolyte may be 2 to 6, and the pH of the basic water-based cathode electrolyte is It may be 8 to 12.

Preferably, the redox flow battery according to the present invention may be a vanadium redox flow battery in which the acidic aqueous anode electrolyte contains vanadium-based ions. More preferably, the acidic aqueous anode electrolyte may contain vanadium ions and sulfur ions.

The basic water-based cathode electrolyte is not particularly limited as long as it has a composition/composition ratio capable of increasing the potential difference with the acidic water-based anode electrolyte, but preferably contains sodium ions.

As a preferred example, the acidic aqueous anode electrolyte may be an aqueous solution containing VOSO ₄ and H ₂ SO ₄ , and the basic aqueous cathode electrolyte may be an aqueous solution containing Na ₂ S ₄ and NaOH.

The composition ratio in each electrolyte may be appropriately controlled according to the aforementioned pH range, type of ion, etc., and for example, when the acidic water-based anode electrolyte includes VOSO ₄ and H ₂ SO ₄ , each independently from each other in an aqueous solution. It may be included in a molar concentration of 0.3 to 3M, and when the basic water-based cathode electrolyte solution includes Na ₂ S ₄ and NaOH, it may be included in a molar concentration of 0.3 to 3M independently of each other in the aqueous solution.

For a more detailed structure of the redox flow battery according to an embodiment of the present invention, reference may be made to known redox flow batteries and related technical fields. Specifically, the redox flow battery according to an example of the present invention includes an anode electrolyte supply unit for receiving the anode electrolyte and supplying it to the anode cell; and a cathode electrolyte supply unit for accommodating the cathode electrolyte and supplying it to the cathode cell. In the anode cell, the anode electrolyte may be accommodated between the anode and the separator, and in the cathode cell, the cathode electrolyte may be accommodated between the cathode and the separator. The redox flow battery according to one embodiment of the present invention may further include a pump for introducing and discharging the electrolyte into and out of each cell. Electrodes such as the anode and the cathode may be made of various materials such as graphite, platinum, copper, etc., without reference to known literature. For more detailed structures and the like, refer to known literature.

The redox flow battery according to the present invention may have an open circuit potential (OCP) of 0.7 V or more by including the acid/base electrolysis system described above. The open circuit potential may vary depending on the composition/composition ratio of each electrolyte, and by using the above-described acid/base electrolysis system and separator, an open circuit potential of 0.7 V or more, specifically 0.8 V or more, while realizing high electrochemical performance At the same time, it is possible to minimize ion permeation of the active material of the separator and thus decrease in capacity, thereby minimizing the decrease in life due to charge/discharge.

In addition, the redox flow battery according to an example of the present invention may have an energy density of 200 Wh/ℓ or more, specifically 220 Wh/ℓ or more, by using the acid/base electrolysis system and the separator described above.

In addition, the redox flow battery according to an embodiment of the present invention may have a current efficiency of 90% or more, specifically 93% or more, based on 200 charge-discharge cycles by using the above-described acid/base electrolysis system and separator.

Hereinafter, the present invention will be described in detail through examples, but these are for explaining the present invention in more detail, and the scope of the present invention is not limited by the following examples.

<Manufacture of Separator>

A separator was prepared by depositing MFI-type zeolite seeds on the surface of a porous aluminum oxide (a-Al ₂ O ₃ ) support and performing secondary growth through hydrothermal synthesis.

Specifically, on the surface of a porous aluminum oxide (a-Al ₂ O ₃ ) tubular support (porosity: 32 vol%, outer diameter: 3.2 cm, inner diameter: 2.54 cm, length: 14.5 cm, average pore size: 0.11 μm) MFI-type zeolite seeds (ZSM-5, SiO ₂ /Al ₂ O ₃ =360) having a particle size of 1.8 μm were deposited and loaded into a Teflon-lined stainless steel autoclave. Subsequently, 2 ml of 1M tetrapropylammoniumhydroxide (TPAOH), 2 ml of tetraethyl orthosilicate (TEOS), and 36 ml of deionized water were added to the autoclave, and secondary growth was performed at 180 ° C. for 16 hours did After growth, it was washed with deionized water to remove ionic precipitates, and then calcined at 500° C. for 4 hours to prepare a porous aluminum oxide separator coated with MFI-type zeolite.

<Redox flow battery installation>

As shown in FIGS. 1 and 2 , a redox flow battery including a porous aluminum oxide separator coated with MFI-type zeolite was installed.

Specifically, a circular electric cell with a glass cell (electrolyte volume: 25 ml) containing an anode space and a cathode space partitioned by a separator, and a prototype plate and frame (made using Teflon, Viton, and SS end plate materials) A chemical cell was prepared. An anode electrode was disposed apart from the separator in the anode space, and a cathode electrode was disposed spaced apart from the separator in the cathode space. In addition, it is installed so that the anode electrolyte from the anode electrolyte tank (electrolyte volume: 200 ml) flows into the anode space by a peristaltic pump (Masterflex), and the cathode electrolyte from the cathode electrolyte tank (electrolyte volume: 200 ml) peristaltic pump (Masterflex) It was installed so as to flow into the cathode space by. At this time, graphite or nickel foam was used as a working electrode, platinum mesh was used as a counter electrode, and Ag/AgCl was used as a reference electrode. An aqueous solution containing 1M VOSO ₄ and 1M H ₂ SO ₄ was used as the anode electrolyte, and an aqueous solution containing 1M Na ₂ S ₄ and 1M NaOH was used as the cathode electrolyte.

[Comparative Example 1]

Example 1 was performed in the same manner as in Example 1, except that a Nafion separator (Nafion 324, DuPont, USA) was used instead of the porous aluminum oxide separator coated with MFI-type zeolite.

<Electrochemical properties>

Cyclic voltammetry (CV) and open circuit potential (OCP) according to the separators of Example 1 and Comparative Example 1 were measured using a PARC VersaSTAT 3 device at a scan rate of 20 mV/s. In addition, impedance measurement was performed using a PARC VersaSTAT 3 instrument for the effect of the acid-base electrolyte on each separator. Specifically, Galvanostatic mode with an applied current of 1 mA (vs. OCP) using a two-electrode configuration is performed using a Pt mesh as a counter and a working electrode (0.5 cm) with a frequency ranging from 200 kHz to 0.01 Hz. distance) was applied.

1. Open circuit potential

3 shows open circuit potential values for electrolyte systems with different pH combinations. In Figures 3a and b, the open circuit potential values for neutral-acidic and neutral-base pH were -0.04 V and 0.25 V, respectively, which is the open circuit potential value for neutral-neutral pH in Figure 3c - Deviated from 0.16 V. The open-circuit potential values for acid-base pH in FIG. 3f widened to a total of -1.2 V when the zeolite-coated porous aluminum oxide separator was used. In addition, in FIG. 2d and f, the open circuit potential value for acid-base pH increased to 0.8 V compared to acid-acid pH.

2. Cell Resistance

Apart from the potential enlargement by pH, the cell resistance can increase due to experimentally induced acid-base pH change as shown in Fig. 3.

4A is a cell resistance graph for Comparative Example 1, and FIG. 4B is a cell resistance graph for Example 1. In Comparative Example 1 in which the Nafion separator was used in FIG. 4A, the case of the acid-base electrolyte system (b) showed a relatively high internal resistance (Nyquist plot 4.72 Ω) compared to other electrolyte combinations, whereas in FIG. 4B, zeolite Example 1, in which the coated separator was used, showed a relatively low internal resistance compared to other electrolyte combinations in the acid-base electrolyte system (b). This is opposite to the case of Comparative Example 1, in which the resistance of the acid-acid electrolyte system is low. When the Nafion separator as in Comparative Example 1 is used, the acid-base and base-base electrolyte combinations may have little or no proton transfer due to the high base electrolyte medium. However, when a separator coated with zeolite is used, when the internal resistance decreases in the acid-base electrolyte combination, the size selectivity of protonated water molecules appears. As such, since the size-selective permeation of the zeolite-coated separator can act alone only in the acid-base electrolyte combination, Example 1, in which the zeolite-coated separator is used in the acid-base electrolyte system, has different resistance characteristics. It can be seen that it is excellent compared to the .

3. Cyclic voltammetry

5 shows the cyclic voltammetry (CV) response of V ⁴⁺ oxidation to acid-acid and acid-base electrolyte combinations in each half-cell. From the curve a of FIG. 5A, it can be seen that in the case of the acid-acid electrolyte combination, an oxidation peak at 1.15 V and a reduction peak at 1.0 V appear, resulting in a peak potential difference of 150 mV. In addition, from the curve b of FIG. 5A, it can be seen that the acid-base electrolyte combination has a lower oxidation peak of 0.83 V and a reduction peak of 0.76 V, resulting in a peak potential difference of 130 mV. Although the reversibility of the V ⁴⁺ /V ⁵⁺ system is maintained in the combination of the two electrolytes, the oxidation-reduction peak potential shifts less to a positive potential around 300 mV, indicating that the V ⁴⁺ oxidation is not dependent on the acid-base combination or base pH. means easier.

FIG. 5B is a case of base-base and base-acid electrolyte combinations in an anionic Ni-form electrode, and it can be seen from the curve b of FIG. 5B that a reduction plateau starting at -350 mV appears during forward scan. Similar oxidation regimes were seen at -250 mV during the reverse scan for S ₄ ^2- /2S ₂ ^2- oxidation-reduction in 1 M NaOH electrolyte in each half-cell. The plateau of the reduction and oxidation peaks can be attributed to the convection phenomenon caused by the fine channels of the Ni foam electrode. In Figure 5 B curve b, it can be seen that the base-acid electrolyte combination exhibits a 10 mV negative shifted oxidation-reduction potential, as a reduction plateau appeared at -360 mV and an oxidation plateau appeared at -42 mV. That is, a small change in potential change in pH change may be due to a decrease in electron emission from the electrode, and overall, the effect of pH change is more pronounced in the positive half-cell than in the negative half-cell.

<Ion Permeation Prevention Characteristics of Separator>

The movement of vanadium ions and sulfur ions through the membranes of Example 1 and Comparative Example 1 was measured through a separate electrolysis experiment for up to 50 hours or more.

Specifically, the transfer of vanadium ions (V ³⁺ ) from acids to bases and sulfur ions (S ₄ ^2- ) from bases to acids through each membrane was measured at an applied current density of 10 mA/cm ² as a separate electrolysis experiment. In order to examine the movement of vanadium ions (V ⁴⁺ ), the electrolyte solution of the cell containing the cathode space was sampled (5 ml) at each time interval and subjected to UV-visible spectrum analysis to confirm the presence or absence of vanadium ions did In the case of the movement of sulfur ions (S ₄ ^2- ), the electrolyte solution of the cell including the cathode space of the separator is sampled (5 ml) at each time interval, and ultraviolet rays are detected using a spectrophotometer (s-3100, Scinco). - Visible light spectrum analysis was performed to confirm the presence or absence of sulfur ions. At this time, the state of charge (SOC) was calculated through spectral analysis or titration with KMnO ₄ . For this purpose, a sample (5 ml) was extracted from the cell of the cathode electrode (charge) or anode electrode (discharge) at the required time interval and analyzed using a standard concentration plot.

6A is a measurement of whether vanadium ions migrate through the separator of Example 1, and is a UV-Visible spectrum of ions from the opposite half cell to the vanadium half cell for 1 hour. In FIG. 6A, curve a is the UV-Visible spectrum of vanadium ions (V ⁴⁺ ) of the anode cell, and it can be seen that the absorbance peak at 515 nm decreases after electrolyte sampling for 1 hour. In FIG. 6A, curve b is a UV-visible spectrum of vanadium ions (V ⁴⁺ ) of the cathode cell, and it can be seen that there is no peak for vanadium ions. Therefore, when using a separator coated with zeolite, vanadium ions do not cross from an acidic electrolyte (1M H ₂ SO ₄ ) to a basic electrolyte (1M NaOH), and it can be seen that the migration of vanadium ions through the zeolite-coated separator is completely prevented. there is.

6B is a measurement of whether or not sulfur ions migrate to the separator of Example 1, and is a UV-Visible spectrum of ions from the opposite half-cell to the sulfur half-cell for 1 hour. In FIG. 6B, curve a is the UV-visible spectrum of sulfur ions in the cathode cell, and shows the maximum absorbance at 300 nm. In FIG. 6B, curve b is the UV-Visible spectrum of sulfur ions in the anode cell, and it can be seen that the absorbance peak at 300 nm is completely reduced after electrolyte sampling for 1 hour. Therefore, it can be seen that when a zeolite-coated membrane is used, sulfur ions are not allowed to move through the zeolite-coated membrane.

<Charge-discharge cycle characteristics>

With respect to Example 1, using a current density of 5 mA/cm ² , charge/discharge performance was performed for a VS redox pair by a redox flow battery made of a zeolite-coated separator. In Example 1, graphite felt and Ni foam electrodes with a distance of 1 cm and a geometric working area of 4 cm ² were used. A peristaltic pump was used to circulate the electrolyte through the cell at a rate of 50 ml/min. All electrodes were cleaned by an electrochemical cycling method from 0 to -1.4 V in 0.1 M KNO ₃ aqueous solution, and finally washed with water and ethanol.

The results obtained for charging and discharging for 4 hours are shown in FIG. 7 . A charge potential of 2.15 V was found at 2 h charge and discharge potential of 0.81 V and reached 0.79 V in 2 h. The potential difference obtained is 1.34 V, which can lead to controlling the applied current density. The redox flow battery of the present invention had a voltage efficiency of 37.7%, an energy efficiency of 36.9%, and a current efficiency derived from a charged state (5%, 1 hour) of 94%.

8 is a measurement of voltage, voltage efficiency, current efficiency, energy efficiency, and capacity according to long-term charging and discharging in a cycle of 1 hour each. 8A, the charge and discharge potentials were 2.15 V and 0.81 V, respectively, and the potential difference maintained 1.34 V for at least 50 cycles. In addition, in FIG. 8B, the current efficiency was maintained at 94% for the entire 200 cycles, and the voltage efficiency and energy efficiency slightly increased from 43.3% to 47.6% and from 40.8% to 44.6%, respectively. In particular, since there is no movement of ions through the zeolite-coated membrane, capacity fading is completely minimized and maintained throughout all 200 cycles.

In addition, the redox flow battery according to the present invention had a volumetric energy density of 233.2 Wh/L for the acid-base electrolyte pH combination, which was very excellent compared to that of the acid-acid electrolyte pH combination.

Finally, as a result of cross-checking the acidity and alkalinity of each half-cell with appropriate indicators, no change in acidity and alkalinity concentration was found, indicating that the zeolite-coated separator effectively allows water molecules in the acid-base electrolyte system. Able to know.

As described above, in the redox flow battery according to the present invention, since the zeolite-coated separator is used in an acid-base electrolyte system, the movement of ions through the separator is completely restricted with high energy efficiency, so that repeated charge-discharge is performed. It can be seen that even if the cycle is performed, a remarkable effect of minimizing capacity fading is realized.

10: anode, 20: cathode,
30: separator, 40: anode electrolyte supply unit (anode electrolyte tank),
50: cathode electrolyte supply unit (cathode electrolyte tank), 60: power supply unit
70: pump

Claims (12)

An anode cell into which an anode electrolyte flows and having an anode, a cathode cell into which an electrolyte flows and having a cathode provided thereto; and
A redox flow battery comprising a separator disposed between the anode and the cathode to prevent mixing of the anode electrolyte and the cathode electrolyte,
In the redox flow battery, characterized in that the anode electrolyte is an acidic aqueous anode electrolyte, the cathode electrolyte is a basic aqueous cathode electrolyte, and the separator is a porous ceramic separator coated with zeolite,
The acidic aqueous anode electrolyte is a redox flow battery containing vanadium ions and sulfur ions.
According to claim 1,
The separator,
aluminum oxide-based porous ceramic film; and
Redox flow battery comprising a; zeolite coated on the surface of the ceramic membrane. According to claim 2,
The separator is a redox flow battery prepared by growing and coating zeolite on the surface of an aluminum oxide-based porous ceramic membrane by hydrothermal synthesis. According to claim 1,
The separator is a redox flow battery having a porosity of 10 to 50% and a pore size of 0.01 to 0.2 ㎛. According to claim 1,
The acidic aqueous anode electrolyte has a pH of 2 to 6,
The basic water-based cathode electrolyte solution has a pH of 8 to 12 redox flow battery. delete According to claim 1,
The basic water-based cathode electrolyte is a redox flow battery containing sodium ions. According to claim 1,
The acidic aqueous anode electrolyte is an aqueous solution containing VOSO ₄ and H ₂ SO ₄ ,
The basic water-based cathode electrolyte is a redox flow battery that is an aqueous solution containing Na ₂ S ₄ and NaOH. According to claim 8,
In the anode electrolyte, VOSO ₄ and H ₂ SO ₄ are each independently included in an aqueous solution at a molar concentration of 0.3 to 3M,
In the cathode electrolyte, Na ₂ S ₄ and NaOH are each independently contained in an aqueous solution at a molar concentration of 0.3 to 3M redox flow battery. According to claim 1,
The redox flow battery,
an anode electrolyte supply unit accommodating the anode electrolyte and supplying it to the anode cell; and
A cathode electrolyte supply unit for receiving the cathode electrolyte and supplying it to the cathode cell; includes,
In the anode cell, the anode electrolyte is accommodated between the anode and the separator,
In the cathode cell, the cathode electrolyte is accommodated between the cathode and the separator. According to claim 1,
A redox flow battery with an open circuit potential greater than 0.7 V. According to claim 1,
A redox flow battery having an energy density of 200 Wh/L or more.

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