KR20240156838A - Preparation method of cathode electrolyte for vanadium aqueous redox flow battery - Google Patents

Abstract

The present invention relates to a method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery. According to one embodiment of the present invention, a method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery includes the step of adding an organic reducing agent to a vanadium electrolyte having a pentavalent oxidation state to produce a vanadium electrolyte having a tetravalent oxidation state.

Description

{PREPARATION METHOD OF CATHODE ELECTROLYTE FOR VANADIUM AQUEOUS REDOX FLOW BATTERY}

The present invention relates to a method for producing a cathode electrolyte for a vanadium aqueous redox flow battery.

The importance of Energy Storage Systems (ESS) is increasing to solve the problems of renewable energy, such as intermittency of power generation and uneven power quality. Among the various types of ESS, the characteristics required for ESS used in conjunction with renewable energy are the ability to store large amounts of energy and high safety against fire and explosion accidents. Redox Flow Battery (RFB) is a secondary battery developed as a large-capacity ESS. It has the characteristic that the part responsible for energy output and the energy storage tank that determines the capacity can be designed independently, allowing for large-capacity batteries. In addition, since the risk of ignition and explosion can be eliminated if the electrolyte is composed of an aqueous system, it is attracting attention as an ESS linked to renewable energy.

The characteristics of a redox flow battery are determined by the type of active material. Among various redox flow batteries, the vanadium redox flow battery (VRFB), which uses vanadium as the electrolyte for both poles, is a secondary battery that charges and discharges by utilizing the characteristic that vanadium can exist in four types depending on its oxidation state. When VRFB is in a discharged state, the negative electrode exists in a V ³⁺ (trivalent) state and the positive electrode exists in a VO ²⁺ (tetravalent) state, but when charged, the negative electrode changes to a V ²⁺ (bivalent) state and the positive electrode changes to a VO ²⁺ (pentavalent) state, and the opposite reaction occurs when discharging. The mechanism is as follows.

In order for VRFB to be able to charge and discharge in this way, the initial cathode and anode must exist in trivalent and tetravalent states, respectively. However, among the commercially available vanadium precursors, inexpensive V ₂ O ₅ (pentavalent) or VOSO ₄ (tetravalent) are used due to price issues. Therefore, a process is required to manufacture the electrolyte in trivalent and tetravalent forms for the cathode and anode, respectively, which enable the initial charge and discharge of vanadium.

A representative method is one that uses an organic reducing agent.

Figure 1 is a drawing for explaining the process of manufacturing a vanadium electrolyte in the form of a conventional negative electrode V ³⁺ (trivalent) and positive electrode V ⁴⁺ (tetravalent) and the charging process.

As shown in Figure 1, when a battery is configured with a tetravalent electrolyte on both sides and energy is charged, the oxidation number of the negative electrode changes from tetravalent to trivalent and that of the positive electrode changes from tetravalent to pentavalent. At this time, when oxalic acid, an organic reducing agent, is added to the pentavalent electrolyte, the pentavalent electrolyte changes to tetravalent.

However, in this method, an additional heating process of several tens of hours is required after extracting the solution through an external reactor to reduce the positive pentavalent to tetravalent.

The present invention is to solve the above-described problems, and an object of the present invention is to provide a method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery capable of reducing vanadium having a pentavalent oxidation state to tetravalent in a short period of time without a heating process.

However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

A method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention includes the step of adding an organic reducing agent to a vanadium electrolyte having a pentavalent oxidation state to produce a vanadium electrolyte having a tetravalent oxidation state.

In one embodiment, the organic reducing agent may be ascorbic acid.

In one embodiment, the organic reducing agent may have a concentration of 0.001 M to 1 M.

In one embodiment, an organic reducing agent may be added to the vanadium electrolyte having the pentavalent oxidation number, and then the reaction may be performed at a reaction temperature of 20° C. to 25° C. for 30 minutes to 6 hours.

A vanadium aqueous redox flow battery according to another embodiment of the present invention comprises: a vanadium aqueous redox flow battery positive electrode electrolyte manufactured by a method for manufacturing a vanadium aqueous redox flow battery positive electrode electrolyte according to one embodiment of the present invention; and a negative electrode electrolyte.

According to a method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention, a vanadium electrolyte having a positive oxidation state of pentavalent can be produced in a short period of time into a vanadium electrolyte having a tetravalent oxidation state. Using this, a vanadium electrolyte having a negative electrode V ³⁺ (trivalent) oxidation state and a positive electrode V ⁴⁺ (tetravalent) oxidation state can be produced in a short period of time.

Therefore, the manufacturing process of the electrolyte for a vanadium redox flow battery (VRFB) can be simplified and the cost reduced.

Figure 1 is a drawing for explaining the process of manufacturing a vanadium electrolyte in the form of a conventional negative electrode V ³⁺ (trivalent) and positive electrode V ⁴⁺ (tetravalent) and the charging process.
FIG. 2 is a drawing for explaining a process for manufacturing a vanadium electrolyte in the form of a negative electrode V ³⁺ (trivalent) and a positive electrode V ⁴⁺ (tetravalent) and a charging process according to one embodiment of the present invention.
Figure 3 is a graph showing the 5-valent vanadium conversion concentration according to the reaction time of Example and Comparative Example 1 of the present invention.
Figure 4 is a cyclic voltammetry graph of the electrolytes of Examples 1 and 2 of the present invention.

Hereinafter, embodiments will be described in detail with reference to the attached drawings. However, since various modifications may be made to the embodiments, the scope of the patent application rights is not limited or restricted by these embodiments. It should be understood that all modifications, equivalents, or substitutes to the embodiments are included in the scope of the rights.

The terms used in the examples are for the purpose of description only and should not be construed as limiting. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, the terms "comprises" or "has" and the like are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood to not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments belong. Terms defined in commonly used dictionaries, such as those defined in common dictionaries, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and shall not be interpreted in an idealized or overly formal sense, unless expressly defined in this application.

In addition, when describing with reference to the attached drawings, the same components will be given the same reference numerals regardless of the drawing numbers, and redundant descriptions thereof will be omitted. When describing an embodiment, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the embodiment, the detailed description thereof will be omitted.

Additionally, in describing components of an embodiment, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are only intended to distinguish the components from other components, and the nature, order, or sequence of the components are not limited by these terms.

Components included in one embodiment and components that have common functions will be described using the same names in other embodiments. Unless otherwise stated, descriptions made in one embodiment may be applied to other embodiments, and specific descriptions will be omitted to the extent of overlap.

Hereinafter, the method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery of the present invention will be specifically described with reference to examples and drawings. However, the present invention is not limited to these examples and drawings.

A method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention includes the step of adding an organic reducing agent to a vanadium electrolyte having a pentavalent oxidation state to produce a vanadium electrolyte having a tetravalent oxidation state.

FIG. 2 is a drawing for explaining a process for manufacturing a vanadium electrolyte in the form of a negative electrode V ³⁺ (trivalent) and a positive electrode V ⁴⁺ (tetravalent) and a charging process according to one embodiment of the present invention.

Comparing FIG. 1 and FIG. 2, the method for manufacturing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention does not require a separate extraction and heating process in an external reactor, unlike conventional manufacturing methods.

In the present invention, the vanadium electrolyte may include at least one selected from the group consisting of V ₂ O ₅ , VOSO ₄ , NH ₄ VO ₃ and V ₂ O ₄ .

In one embodiment, the organic reducing agent may be ascorbic acid.

In one embodiment, the organic reducing agent may have a concentration of 0.001 M to 1 M; 0.001 M to 0.01 M; 0.001 M to 0.1 M; 0.001 M to 0.005 M; 0.01 M to 1 M; 0.01 M to 0.01 M; 0.01 M to 0.1 M; 0.01 M to 0.005 M; 0.1 M to 1 M; 0.1 M to 0.01 M; 0.1 M to 0.005 M; 0.3 M to 1 M; 0.3 M to 0.01 M; 0.3 M to 0.005 M; 0.5 M to 1 M; 0.5 M to 0.01 M; or 0.5 M to 0.005 M.

When the concentration of the reducing agent is less than 0.001 M, there is a problem of not sufficiently reducing vanadium ions, and when it is more than 1 M, there is a problem of excess reducing agent remaining.

In one embodiment, after adding an organic reducing agent to the vanadium electrolyte having the pentavalent oxidation number, the reaction may be performed at a reaction temperature of 20° C. to 25° C.; 20° C. to 24° C.; 20° C. to 23° C.; 20° C. to 22° C.; 20° C. to 21° C.; 21° C. to 25° C.; 21° C. to 24° C.; 21° C. to 23° C.; 21° C. to 22° C.; 22° C. to 25° C.; 22° C. to 23° C.; 23° C. to 24° C.; or 24° C. to 25° C.

30 minutes to 6 hours; 30 minutes to 5 hours; 30 minutes to 4 hours; 30 minutes to 3 hours; 30 minutes to 2 hours; 30 minutes to 1 hour; 1 hour to 6 hours; 1 hour to 5 hours; 1 hour to 4 hours; 1 hour to 3 hours; 1 hour to 2 hours; 2 hours to 6 hours; 2 hours to 5 hours; 2 hours to 4 hours; 2 hours to 3 hours; 3 hours to 6 hours; 3 hours to 5 hours; 3 hours to 4 hours; 4 hours to 6 hours; 4 hours to 5 hours; or 5 hours to 6 hours.

In the conventional case, in order to reduce pentavalent vanadium to tetravalent, a heating process is additionally required in addition to an organic reducing agent. However, according to a method for producing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention, by including ascorbic acid as a reducing agent, vanadium pentavalent can be reduced to tetravalent in a short period of time with only 1/10 of the amount of a conventional reducing agent.

A vanadium aqueous redox flow battery according to another embodiment of the present invention comprises: a vanadium aqueous redox flow battery positive electrode electrolyte manufactured by a method for manufacturing a vanadium aqueous redox flow battery positive electrode electrolyte according to one embodiment of the present invention; and a negative electrode electrolyte.

By using the positive electrode electrolyte for a vanadium aqueous redox flow battery manufactured by the method for manufacturing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to one embodiment of the present invention, the redox flow battery can realize excellent performance such as improved energy efficiency, and can have a relatively long electrolyte replacement cycle since the efficiency or performance of the battery does not significantly deteriorate even after long-term use.

The concentration of sulfuric acid (H ₂ SO ₄ ) in each of the positive and negative electrolytes may be 5 M or less, for example, 0.1 M to 5 M.

The above vanadium aqueous redox flow battery may include at least one unit cell including a separator through which ions pass; a pair of electrodes facing each other with the separator as the center; and the positive electrolyte and the negative electrolyte present in the positive electrode cell and the negative electrode cell respectively separated by the separator.

The above redox flow battery may include a module including at least one unit cell.

The above unit cell may further include a pair of flow frames coupled to face each other on both sides of the separator. The flow frame may not only serve as a passage for the electrolyte, but also provide even distribution of the electrolyte between the electrode and the separator so that the electrochemical reaction of the actual battery can occur well. The flow frame may have a thickness of 0.1 mm to 10.0 mm, and may be made of a polymer such as polyethylene, polypropylene, or polyvinyl chloride.

The above unit cell may further include a cell frame formed on the outer surface of the electrode.

The device may include: an anode electrolyte tank in which the anode electrolyte is stored; and an anode electrolyte pump for circulating the anode electrolyte from the anode electrolyte tank to the anode cell of the unit cell during charging and discharging; and an anode electrolyte tank in which the cathode electrolyte is stored; and an anode electrolyte pump for circulating the cathode electrolyte from the cathode electrolyte tank to the cathode cell of the unit cell during charging and discharging.

Hereinafter, the present invention will be described in detail with reference to the following examples and comparative examples. However, the technical idea of the present invention is not limited or restricted thereto.

[Manufacturing example]

Electrolyte manufacturing

The positive and negative electrolytes were prepared by adding 1.6 M of VOSO ₄ (tetravalent) to 3 M of H ₂ SO ₄ solution and stirring for 30 minutes. Both the positive and negative electrolytes used 17 mL of tetravalent.

Unit cell assembly

The electrode used was GFD 4.6 from SGL Carbon, and the separator used was Nafion 117 from Chemours. The electrode area was 2×3 ^cm2 .

The bipolar plate uses carbon and the current collector uses a gold-coated copper plate.

The batteries were tightened in increments of 5 to 30 pound-inch.

System Configuration

The positive and negative electrolyte tanks and the battery were each connected to a pump, and the pump was set to 30 rpm.

Nitrogen was injected for 10 minutes to remove oxygen dissolved in the electrolyte tank.

[Example]

Manufacturing of quaternary electrolyte using ascorbic acid

Charging was performed with a constant current (80 mA cm ^-2 ) up to a specific voltage (1.75 V).

When charging, a trivalent electrolyte is generated for the negative electrode and a pentavalent electrolyte is generated for the positive electrode. At this time, 15 ml of pentavalent electrolyte is taken. After that, 0.08 M (0.2178 g) ascorbic acid is added to 15 ml of 1.6 M pentavalent electrolyte and stored in a sealed container (0<x<20, 0<y<6, 0<z<10).

C ₆ H ₈ O ₆ (aq) + x VO ₂ ⁺ (aq) + y H ⁺ (aq) ↔ x VO ²⁺ (aq) + Hydrocarbon (aq) + y CO ₂ (g) + z H ₂ O ( l)

[Comparative Example 1]

Preparation of tetravalent electrolyte using oxalic acid

It was manufactured using the same manufacturing method as in the example, except that the concentration of 0.8 M oxalic acid (10 times the concentration of ascorbic acid, 1.102 g) was added as a reducing agent.

C ₂ H ₂ O ₄ (aq) + 2VO ₂ ⁺ (aq) + 2H ⁺ (aq) ↔ 2CO ₂ (g)+ 2H ₂ O (l) + 2VO ²⁺ (aq)

[Comparative Example 2]

4. Preparation of electrolyte

VOSO ₄ (4) was added at 1.6 M to each 3 M H ₂ SO ₄ solution.

VOSO ₄ (S) ↔ VO ²⁺ (aq) + SO ₄ ^2- (aq)

[Example]

Conversion concentration comparison

The 5- to 4-valent conversion concentrations of Example 1 and Comparative Example 1 were observed through UV-vis experiments.

Electrochemical evaluation

The reaction current intensities of Examples 1 and 2 and Comparative Examples 1 and 2 were compared using cyclic voltammetry tests.

Charge and discharge evaluation

For Examples 1 and 2, 15 ml each was used as the positive electrode solution, and 15 ml of the trivalent electrolyte was used as the negative electrode solution, and a charge/discharge test was conducted at a constant current (200 mA cm ^-2 ) over a specific voltage range (0.2 V to 1.75 V).

result

Conversion concentration comparison

To confirm the conversion concentration of Example 1 and Comparative Example 1, the change in absorption wavelength was observed through UV-vis.

Figure 3 is a graph showing the 5-valent vanadium conversion concentration according to the reaction time of Example and Comparative Example 1 of the present invention.

Referring to Figure 3, it was found that ascorbic acid was almost completely reacted in about 6 hours at room temperature, and in the case of oxalic acid, the reaction was confirmed to be complete only after 72 hours.

Electrochemical evaluation

In the examples where the reaction was completed, the reaction currents of Comparative Examples 1 and 4, manufactured using a vanadium precursor, were compared and observed through a cyclic voltammetry test.

Figure 4 is a cyclic voltammetry graph of the electrolytes of Examples 1 and 2 of the present invention.

Referring to Fig. 4, the embodiment exhibited an overvoltage of almost the same magnitude as that of Comparative Examples 1 and 2.

Charge and discharge evaluation

The electrolyte prepared with ascorbic acid in the example, the electrolyte prepared with oxalic acid in Comparative Example 1, and the electrolyte prepared with the 4-valent precursor in Comparative Example 2 all showed almost similar charging efficiency, voltage efficiency, and energy efficiency.

Table 1 below shows the charging efficiency, voltage efficiency, and energy efficiency according to Examples 1 and 2 of the present invention.

Example Comparative Example 1 Comparative Example 2 Charging Efficiency (%) 96.3 96.3 96.4 Voltage Efficiency (%) 74.3 72.4 72.6 Energy Efficiency (%) 71.5 69.7 70

In conventional cases, in order to reduce pentavalent vanadium to tetravalent, an additional heating process is required in addition to an organic reducing agent.

However, in the case of the embodiment of the present invention, it can be confirmed that vanadium pentavalent can be reduced to tetravalent in a short period of time with only 1/10 of the amount by simply changing the reducing agent to ascorbic acid.

Through this, the method for manufacturing a positive electrode electrolyte for a vanadium aqueous redox flow battery according to an embodiment of the present invention can increase the volumetric capacity of the battery by resolving the solubility limit of the positive electrode by using oxygen as a positive electrode active material and adding a cobalt complex as a positive electrode electron transfer mediator.

Although the embodiments have been described with limited drawings as described above, those skilled in the art can apply various technical modifications and variations based on the above. For example, even if the described techniques are performed in a different order than the described method, and/or the components of the described system, structure, device, circuit, etc. are combined or combined in a different form than the described method, or are replaced or substituted by other components or equivalents, appropriate results can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are also included in the scope of the claims described below.

Claims (5)

A step of producing a vanadium electrolyte having a tetravalent oxidation number by adding an organic reducing agent to a vanadium electrolyte having a pentavalent oxidation number;
Including,
Method for producing a cathode electrolyte for a vanadium aqueous redox flow battery.
In the first paragraph,
The above organic reducing agent is ascorbic acid.
Method for producing a cathode electrolyte for a vanadium aqueous redox flow battery.
In the first paragraph,
The organic reducing agent has a concentration of 0.001 M to 1 M.
Method for producing a cathode electrolyte for a vanadium aqueous redox flow battery.
In the first paragraph,
After adding an organic reducing agent to the vanadium electrolyte having the above 5 oxidation numbers, the reaction is performed at a reaction temperature of 20°C to 25°C for 30 minutes to 6 hours.
Method for producing a cathode electrolyte for a vanadium aqueous redox flow battery.
A vanadium aqueous redox flow battery cathode electrolyte prepared by the method for preparing a vanadium aqueous redox flow battery cathode electrolyte of claim 1; and
Cathode electrolyte;
Including,
Vanadium aqueous redox flow battery.

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