KR20150088076A - Electrolyte composition comprising organic acids and redox flow battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte composition comprising an active ingredient and an organic acid having one or more carboxylic groups and to a redox flow battery using the same, wherein due to the electrolyte composition comprising an organic acid having carboxylic groups, the corrosion of the cell can be reduced, thereby decreasing a risk of the battery and providing a redox flow battery having excellent charge/discharge capacity and the level of the corrosion of an ion exchange membrane and a current collector can be reduced, thereby providing a redox flow battery which can extend a period until replacement of the device.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte composition containing an organic acid and a redox flow battery containing the electrolyte composition,

The present invention relates to an electrolyte composition and a redox flow battery using the electrolyte composition.

In recent years, as a countermeasure against global warming, introduction of new energy such as solar power generation and wind power generation has been promoted worldwide. Since these power generation outputs are influenced by weather, problems in operation of the power system in which it becomes difficult to maintain the frequency and the voltage when a large amount of the power is supplied is predicted.

The most important issue in the current power system is precisely forecast demand and running the generator at the right time. But energy is not easy to control. Accordingly, the introduction of power storage devices that will act as a buffer between generation capacity and consumption and demand will be needed.

Redox flow batteries (RFBs) are attracting attention as a countermeasure to such problems. A redox flow battery (RFB) is a very efficient technology for storing power by increasing the amount of power stored through a simple method of increasing the amount of electrolyte.

A redox flow battery (RFB) is charged and discharged by supplying a positive electrode electrolytic solution and a negative electrode electrolytic solution to a battery cell having a diaphragm interposed between the positive electrode and the negative electrode. The electrolytic solution is typically an aqueous solution containing water-soluble metal ions whose valence is changed by redox reaction, and these metal ions are used for the active material.

These redox flow batteries (RFBs) are classified according to redox couples such as Cr / Cr, V / Sn, V / Fe, and V / V.

The redox flow battery has the same ability to store intermittent energy supply and demand as the other batteries, but also has the advantage of less electricity changeable capacity over time and can produce electricity by reacting immediately when needed. Until now, redox flow batteries have been disadvantageous in that they are large, expensive and difficult to control at suitable temperatures. However, through the use of an all-vanadium redox flow battery (VRB) We are trying to solve the efficiency problem.

However, as disclosed in Patent Documents 1 and 2, the conventional vanadium redox flow battery (VRB) uses sulfuric acid or hydrochloric acid as a solvent of the electrolytic solution, and sulfuric acid Or hydrochloric acid is apt to corrode the cell, thereby deteriorating the performance of the cell. Secondary damage may occur due to a high acidity of the electrolytic solution, such as an outflow, have.

Patent Document 1: Japanese Patent No. 3143568 Patent Document 2: Korean Patent Publication No. 2013-0038234

It is an object of the present invention to provide an electrolyte composition comprising an organic acid having at least one carboxyl group, thereby providing a redox flow battery capable of improving cell corrosion and filling capacity.

The present invention relates to a process for the preparation of And an organic acid having at least one carboxyl group.

The present invention also relates to a positive electrode comprising a positive electrode; A cathode cell including a cathode electrode; A separation membrane for separating the anode cell and the cathode cell; And a positive electrode electrolyte composition and a negative electrode electrolyte composition supplied to the positive electrode cell and the negative electrode cell, respectively, wherein the positive electrode electrolyte solution or negative electrode electrolyte solution comprises a redox flow cell according to the present invention.

The present invention can reduce the corrosion of the cell and reduce the risk of the resulting battery by including the organic acid in place of the solvent having high acidity such as sulfuric acid or hydrochloric acid as the electrolytic solution of the redox flow battery, In addition, it is possible to provide an excellent redox flow battery and reduce the degree of corrosion of the ion exchange membrane and the current collector, thereby increasing the replacement period of the device.

1 is a structural view showing the structure of a redox flow battery according to an embodiment of the present invention.
FIGS. 2 and 3 are cyclic voltammetric curves (CV) graphs of a redox flow cell using an electrolyte according to an embodiment of the present invention and a comparative example.
4 is a graph showing changes in battery voltage with charge / discharge time of a redox flow battery using an electrolyte according to an embodiment of the present invention and a comparative example
5 is a graph showing charge / discharge capacities of a redox flow battery using an electrolyte according to an embodiment of the present invention and a comparative example.
6 is a graph showing coulon efficiency and energy efficiency of a redox flow battery using an electrolyte according to an embodiment of the present invention and a comparative example.
7 is a graph showing a battery voltage (V) according to a cycle time (h) of charge and discharge of a redox flow battery using an electrolyte according to an embodiment of the present invention.
8 and 9 are cyclic voltammetric curves (CV) graphs of a redox flow battery using an electrolyte according to another embodiment of the present invention.

The present invention relates to a process for the preparation of And an organic acid having at least one carboxyl group.

The term " electrolytic solution containing organic acid " or " organic acid electrolytic solution " used in the present invention means an electrolytic solution containing an acid as an acid component and containing an organic acid as a main component. In the case of an electrolytic solution containing an inorganic acid such as sulfuric acid or hydrochloric acid .

Here, the expression " includes as a main component " means that the content of the corresponding organic acid with respect to the total acid component is 95% or more, 99% or more, or 99.9% or more.

The active material may be any conventional metal compound used in redox flow batteries. For example, as the active material, vanadium compounds of +2 to +5 can be used.

In one embodiment, the cathode active material may be a +5 to +4 -valent vanadium-based compound. Examples of the cathode active material include (VO ₂ ) ₂ SO ₄ , VO (SO ₄ ), or a combination thereof.

The concentration of the cathode active material solution may be 1M to 10M. When the concentration of the cathode active material solution is within the above range, there may be advantages of high energy density and high power density. When the concentration of the cathode active material solution is lower than 1M, the amount of the active material per unit volume is low to lower the energy density, whereas when the concentration of the cathode active material solution is higher than 10M, the viscosity of the active material solution increases sharply and the oxidation / .

In another embodiment, the negative electrode active material may be a vanadium compound of +2 to +3 valence, and examples of the negative electrode active material include VSO ₄ , V ₂ (SO ₄ ) _3, or a combination thereof.

The concentration of the negative electrode active material solution may be 1M to 10M. When the concentration of the negative electrode active material solution is within the above range, there may be advantages of high energy density and high power density. When the concentration of the negative active material solution is lower than 1M, the amount of active material per unit volume is low to lower the energy density. When the concentration of the active material solution is higher than 10M, the viscosity of the active material solution increases sharply and the rate of oxidation / .

In the present invention, the organic acid electrolytic solution composition may further include metal ions other than the vanadium metal component to improve the utilization ratio of vanadium ions.

The organic acid which can be used in the present invention is not particularly limited and includes formic, acetic, propionic, butyric, valeric, hexanoic, heptanoic, caprylic, nonanoic, decanoic, Straight chain saturated carboxylic acids having one carboxyl group such as decyl acid, myristic acid, pentadecanoic acid, and also palmitic acid; Saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, or sebacic acid; Unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, glutaconic acid, traumatic acid, or muconic acid; Aromatic dicarboxylic acids such as phthalic acid, isophthalic acid or terephthalic acid; And carboxylic acids having three or more carboxyl groups such as citric acid, isocitric acid, aconic acid, carbalic acid, tribeic acid, and mellitic acid.

In an embodiment, the organic acid is an unsaturated aliphatic dicarboxylic acid such as maleic acid, fumaric acid, glutaconic acid, traumatic acid, or muconic acid; Carboxylic acids having three or more carboxyl groups such as citric acid, isocitric acid, aconic acid, carbalic acid, tribeic acid, or mellitic acid; Or a saturated aliphatic dicarboxylic acid such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid or sebacic acid, and more specifically, maleic acid, citric acid , And oxalic acid may be used. More specifically, oxalic acid may be used.

The organic acid electrolyte composition according to the present invention is expected to form a chelate structure in the organic acid solution, and the chelate structure is considered to affect the charge-discharge capacity of the battery. Further, the organic acid electrolytic solution of the present invention can improve the stability and reactivity of vanadium ions, suppress side reactions, and reduce internal resistance.

In the present invention, the form of the organic acid is not particularly limited, but may be a solution using an organic solvent or water as a solvent.

At this time, for example, acetone, ethanol, and methanol may be used as the organic solvent.

In embodiments, isopropyl alcohol (IPA) may be used as the organic solvent.

When the concentration of the organic acid in the electrolytic solution is too high, the solubility is lowered. Therefore, the molar content of the organic acid in the electrolytic solution may be 1 to 5M, 1 to 3M or 1 to 2M, It is possible to lower the solubility and increase the efficiency of the battery.

On the other hand, the pH of the electrolytic solution may be in the range of 2 to 5, for example. In the present invention, when the pH of the organic acid is in the above range, the corrosion resistance is low and the cell stability is excellent and the efficiency of the battery such as charge / discharge capacity is not hindered.

The present invention also relates to a positive electrode comprising a positive electrode; A cathode cell including a cathode electrode; A separation membrane for separating the anode cell and the cathode cell; And a positive electrode electrolyte composition and a negative electrode electrolyte composition supplied to the positive electrode cell and the negative electrode cell, respectively, wherein the positive electrode electrolyte solution or the negative electrode electrolyte solution comprises a redox flow comprising the electrolyte composition according to any one of claims 1 to 10 Thereby providing a battery.

At this time, the negative electrode electrolytic solution has a vanadium ion having an oxidation number of +3 to +4, and the positive electrode electrolytic solution has a vanadium ion having an oxidation number of +4 to +5, so that a redox flow cell Can be provided.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

The redox flow battery 100 typically includes a power generator (e.g., a solar generator, a wind turbine, a general power generator, etc.) through an AC / DC converter ), And a load of a power system or a consumer, the power generation unit is used as a power supply source to perform charging, and the load is subjected to electric discharge as a power supply target. In order to carry out the charging / discharging, the following battery system is constructed, which includes a redox flow battery 100 and a circulation mechanism (tank, piping, pump) for circulating the electrolyte in the battery 100.

The redox flow battery 100 includes a positive electrode cell 20 in which a positive electrode 21 is embedded, a negative electrode cell 30 in which a negative electrode 31 is embedded, a separator 30 for separating the two cells 20, For example, an ion exchange membrane 40 for selectively transmitting ions. A tank (50) for a cathode electrolyte is connected to the anode cell (20) through a pipe (51). In the cathode cell 30, a tank 60 for a cathode electrolyte is connected via a pipe 61. The piping (50, 60) is provided with a pump (52, 62) for circulating the electrolytic solution of each pole. The redox flow cell 100 is constructed by connecting the positive electrode 20 (positive electrode 21), the negative electrode 30 (negative electrode 31), and the positive electrode 20 And the negative electrode electrolytic solution of the tank 60 are circulated and supplied to perform charging and discharging in accordance with the change reaction of the metal ions acting as the active material in the electrolytic solution of each electrode.

At this time, the ion exchange membrane 40 of the redox flow secondary battery 100 may be formed of nafion. The cathode electrode 31 and the anode electrode 21 may be coated with a carbon layer uniformly on a porous metal surface. For example, a carbon felt may be used. As a counter electrode, platinum Can be used.

 [Example 1]

- Organic acid electrolytic solution composition using oxalic acid as a basic solvent -

9 g of oxalic acid powder was dissolved in 100 ml of ultrapure water to prepare an organic acid solution of 1 M, and an electrolytic solution was prepared by dissolving the organic acid solution thus prepared in a concentration of 1 M of vanadium sulfate. At this time, the pH of the electrolytic solution in Example 1 was 3.7.

[Example 2]

An electrolytic solution was prepared in the same manner as in Example 1, except that 12 g of maleic acid powder was used instead of oxalic acid powder. At this time, the pH of the electrolytic solution prepared in Example 2 was 3.7.

[Example 3]

An electrolytic solution was prepared in the same manner as in Example 1, except that 19.2 g of citric acid powder was used instead of oxalic acid powder. At this time, the pH of the electrolytic solution prepared in Example 2 was 3.6.

[Comparative Example 1]

An electrolytic solution was prepared in the same manner as in Example 1, except that an aqueous sulfuric acid solution was used instead of the organic acid solution. At this time, the pH of the electrolytic solution prepared in Comparative Example 1 was 0.5.

[Test Example 1]

- Cyclic Voltammetry (CV) -

Using the electrolytic solutions obtained in Example 1 and Comparative Example 1, the change in current value according to the potential change was measured at a scan rate of 100 mV / s and a potential range of 0 to 1.65 V, respectively. A reference electrode (Ag / AgCl) was used as a reference electrode, a graphite electrode was used as a working electrode, and an anion exchange membrane was used as an ion exchange membrane. .

The cyclic voltammetric curves (CV) for the cells under the above conditions are shown in Fig.

The cyclic voltammetric curves (CV) measured under the same conditions as those of the above-described [Test Example 1] were measured, except that the carbon felt was used as a working electrode and the potential scanning range was changed from 0 to 1.3 V 3.

As shown in FIG. 2 and FIG. 3, it was confirmed that the electrolyte according to Example 1 of the present invention had excellent redox characteristics of the electrolyte regardless of the type of the electrode, as compared with Comparative Example 1 using sulfuric acid as a solvent of the electrolyte have.

[Test Example 2]

Each of the electrolytic solutions prepared in Example 1 and Comparative Example 1 was charged into both of the storage tanks in an amount of 10 mL and purged with nitrogen to shut off the contact with the outside air and seal it.

The flow rate of the electrolytic solution, which was cut off from contact with the outside air, was adjusted so as to flow into a 3 cm * 3 cm carbon felt (the reaction area of the electrode was 9 cm 2) at a constant rate of 3 to 4 mL / The current scanning rate, which regulates the charging / discharging rate, was constantly controlled to about 250 mA.

As shown in Fig. 4, charging is terminated at a point where the switching voltage has reached 1.60 V so that the filling depth of the positive electrode electrolyte at the end of charging is 90% or less, The change of the battery voltage V is shown in Fig.

[Test Example 3]

Each of the electrolytes prepared in Example 1 and Comparative Example 1 was charged and discharged in both storage tanks using a low current scanning rate of 50 mA / cm 2 or less. In order to prepare a high purity filling solution, 10 ml was added to a 20 ml positive electrode, and an electrolyte solution approximately twice as much as the positive electrode was charged into the negative electrode. At this time, carbon felt was used for each electrode, and the area of each electrode was 9 cm 2.

The charging capacity density (A × h (hour) / L (battery volume (liter)) and the discharge capacity density (A × h (hour) / L (battery volume (liter))) And the coulomb efficiency (%) and the energy efficiency (%) were measured by the method of the following equation, which is shown in FIG.

[expression]

Voltage efficiency (%) = (average voltage at discharge / average voltage at charging) X 100

Coulomb efficiency (%) = (discharge capacity / charge capacity) X 100

Energy efficiency (%) = (Voltage efficiency / 100) X (Coulomb efficiency / 100) X 100

As a result of Test Examples 2 and 3, it was found that the use of the electrolyte of Example 1 using the organic acid oxalic acid as a solvent was faster than the case of using the electrolyte of Comparative Example 1 using sulfuric acid as a solvent, The discharge capacity can be increased, and the efficiency of the battery is also high.

[Test Example 4]

The relationship between the cycle time (h) of charging and discharging and the cell voltage (V) is shown in FIG. 7 by repeating the charging and discharging in the same manner as in Experimental Example 2 using the electrolyte prepared in Example 1 Respectively.

As shown in Fig. 7, there is almost no difference in charging / discharging voltage between batteries for repetitive charging / discharging. Thus, when the electrolyte according to the present invention is used, the long-term stability of the redox flow battery is also high It is expected.

[Test Example 5]

- Cyclic Voltammetry (CV) -

8 and 9 show the cyclic voltammetric curves (CV) for the cells under the same conditions as those of the above-mentioned Test Example 1, using the electrolytes obtained in Examples 2 and 3, respectively.

As shown in FIGS. 8 and 9, when the scanning speed of 100 mV is compared, it can be seen that the reversibility and the reaction rate are similar to those of Comparative Example 1 using conventional sulfuric acid.

All of the above Test Examples 1 to 5 were carried out at room temperature.

Claims (12)

Active material; And
And an organic acid having at least one carboxyl group.
The method according to claim 1,
Wherein the active material is a vanadium-based compound of +2 to +5.
3. The method of claim 2,
Wherein the active material is at least one cathode active material selected from the group consisting of (VO ₂ ) SO ₄ and VO (SO ₄ ).
The method of claim 3,
And the concentration of the cathode active material is 1 to 10 M.
3. The method of claim 2,
Wherein the active material is at least one negative electrode active material selected from the group consisting of VSO ₄ and VO ₂ (SO ₄ ) ₃ .
6. The method of claim 5,
And the concentration of the negative electrode active material is 1 to 10 M.
The method according to claim 1,
The organic acid is a straight chain saturated carboxylic acid having one carboxyl group; Saturated aliphatic dicarboxylic acids; Unsaturated aliphatic dicarboxylic acids; Aromatic dicarboxylic acids; And a carboxylic acid having three or more carboxyl groups.
8. The method of claim 7,
Wherein the saturated aliphatic dicarboxylic acid is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.
9. The method of claim 8,
Wherein the saturated aliphatic dicarboxylic acid is oxalic acid.
The method according to claim 1,
Wherein the concentration of the organic acid is 1 to 5 M.
The method according to claim 1,
Wherein the pH of the electrolytic solution is 2 to 5.
A positive electrode including a positive electrode;
A cathode cell including a cathode electrode;
A separation membrane for separating the anode cell and the cathode cell; And
A cathode electrolyte composition and a cathode electrolyte composition supplied to the anode cell and the cathode cell, respectively,
Wherein the positive electrode electrolyte solution or negative electrode electrolyte solution comprises the electrolyte composition according to any one of claims 1 to 11.

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