KR20210071231A - Long-term stability improved electrolyte composition and redox flow battery apparatus having the electrolyte composition - Google Patents

Abstract

Disclosed is an electrolyte composition applied as a positive electrode electrolyte of a redox flow battery. The electrolyte solution composition includes: an aqueous solvent; an acid salt compound dissolved in a solvent and containing H_2SO_4; an active material compound dissolved in a solvent and containing VOSO_4; and a citric acid reducing agent dissolved in a solvent.

Description

Electrolyte composition with improved long-term stability and redox flow battery device comprising the same {LONG-TERM STABILITY IMPROVED ELECTROLYTE COMPOSITION AND REDOX FLOW BATTERY APPARATUS HAVING THE ELECTROLYTE COMPOSITION}

The present invention relates to an electrolyte composition for a redox flow battery capable of storing electrical energy through oxidation/reduction reaction of an active material, and a redox flow battery device including the same.

A redox flow battery (RFB) is a secondary battery that can store and use energy for a long time by repeating charging and discharging by an electrochemical reversible reaction of an electrolyte. Unlike conventional secondary batteries, this redox flow battery is a system in which an active material dissolved in an electrolyte exchanges electrons to be charged and discharged, and the stack and electrolyte tank, which determine the capacity and output characteristics of the battery, are configured independently of each other. It has the advantage of being free in battery design and having less space restrictions for installation.

Among them, looking at the configuration of the vanadium redox flow battery, which has been in the spotlight recently, the electrode where the cell reaction takes place is composed of a stack similar to a fuel cell together with a separator, and vanadium active materials having different oxidation values are stacked. (stack) It is stored as an anolyte and a catholyte in an external tank.

At this time, in order to increase the durability and energy efficiency according to the charging and discharging of the battery, it is necessary to optimize the components (electrode and separator) and structure of the single cell constituting the stack, but the thermal stability of the electrolyte is also very important.

In the case of a vanadium flow battery, the positive electrode material is recovered to the positive electrode storage tank in the state of VO2+ (V5+) during charging. At this time, the vanadium positive electrode electrolyte is deteriorated, such as a side reaction that easily generates vanadium precipitate at high temperature. The generated positive electrolyte is no longer discharged to the VO2+ state, but is precipitated in the positive electrolyte to obstruct the flow of the electrolyte, or is embedded in the electrode to reduce the efficiency of the vanadium redox flow battery.

One object of the present invention is to provide an electrolyte composition having excellent long-term stability and improving the discharge capacity of a redox flow battery.

Another object of the present invention is to provide a redox flow battery device comprising the electrolyte composition as a positive electrolyte.

The electrolyte composition according to an embodiment of the present invention may be applied as a positive electrolyte of a redox flow battery, and may include an aqueous solvent; an acid salt compound dissolved in the solvent and comprising at least one selected from the group consisting of _{H 2} SO ₄ , HCl, H ₃ PO ₄ and HNO _{3 ;} an active material compound dissolved in the solvent and comprising at least one selected from the group consisting of _{VCl 3} , V ₂ O ₅ , VOSO ₄ , V ₂ O ₃ , V ₂ O ₄ and NH ₄ VO _{3 ;} and a citric acid reducing agent dissolved in the solvent.

In one embodiment, the citric acid reducing agent may be contained in a concentration of 0.07M to 0.20M.

Redox flow battery device according to an embodiment of the present invention is a redox flow battery stack; a first electrolyte tank accommodating the anode electrolyte; a second electrolyte tank accommodating the negative electrolyte; a first pump for circulating the cathode electrolyte so that the cathode electrolyte of the first electrolyte tank is supplied to the cathode electrolyte reaction space of the redox flow battery stack; and a second pump for circulating the negative electrolyte so that the negative electrolyte of the second electrolyte tank is supplied to the negative electrolyte reaction space of the redox flow battery stack, wherein the positive electrolyte includes the electrolyte composition according to claim 1 do.

)이 4가 바나듐 이온(

)환원되지 않아서 방전용량이 감소하는 문제점을 해결할 수 있다.According to the electrolyte composition of the present invention and a redox flow battery device including the same, since the electrolyte composition contains citric acid serving as a reducing agent, it deteriorates due to long-term operation, so that pentavalent vanadium ions (

) is a tetravalent vanadium ion (

) is not reduced, so the problem that the discharge capacity decreases can be solved.

1 is a view for explaining a redox flow battery device according to an embodiment of the present invention.
2 is a graph showing the results of measuring the discharge capacity and the cell resistance according to the molar concentration of citric acid.
3 is a graph showing the result of measuring the discharge capacity according to the charge/discharge cycle.
4A and 4B are graphs showing the results of measuring the discharge capacity and energy efficiency according to the charge/discharge cycle when a positive electrolyte containing 0.15M citric acid is applied.
5A and 5B are graphs showing the results of measuring the discharge capacity and energy efficiency according to the charge/discharge cycle when a positive electrolyte containing 0.075M citric acid is applied.
6 is a graph showing the measurement results of the discharge capacity and the cell resistance according to the mixing time (stirring time) after adding 0.15M of citric acid to the electrolyte.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Since the present invention can have various changes and can have various forms, specific embodiments are illustrated in the drawings and the present invention will be described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements. In the accompanying drawings, the dimensions of the structures are enlarged or reduced than the actual size for clarity of the present invention.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as "comprise", "comprising" or "have" are intended to designate that a feature, number, step, operation, component, or combination thereof described in the specification exists, and is one or the It should be understood that the existence or addition of the above other features or numbers, steps, operations, elements or combinations thereof is not precluded in advance.

Unless defined otherwise, 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 present invention belongs. Terms such as those generally used and defined in the dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and shall not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. .

The electrolyte composition according to an embodiment of the present invention may be applied as a positive electrolyte or a negative electrolyte of a vanadium redox flow battery, and may include a solvent, an acid salt compound, an active material compound, and a reducing agent.

The solvent may include a polar aqueous or organic solvent. In one embodiment, an aqueous solvent, for example, water may be used as the solvent.

The acid salt compound is a compound that can be dissolved in the solvent and dissociated into cations and anions, and not only helps the oxidation/reduction reaction of the active material compound smoothly, but also serves as a counter ion when the oxidation state of the redox pair changes. It can form an ion pair with a redox pair. In an embodiment, the acid salt compound may include at least one selected from the group consisting _{of H 2} SO ₄ , HCl, H ₃ PO ₄ , HNO _{3 , and the like.}

In one embodiment, the solvent may include water, the acid salt compound may include H ₂ SO _{4 In} this case, the H ₂ SO ₄ may be contained in a concentration of about 0.5M to 9M. .

The active material compound may be dissociated into the solvent, and may cause a reversible oxidation/reduction reaction during charging and discharging of the redox flow battery. In one embodiment, the active material compound may include one or more selected from the group consisting _{of VCl 3} , V ₂ O ₅ , VOSO ₄ , V ₂ O ₃ , V ₂ O ₄ , and NH ₄ VO _{3 , preferably} For example, the active material compound may include _{VOSO 4 .} In one embodiment, the active material compound may be included in a concentration of about 0.5M to 8M.

When the electrolyte composition is the positive electrolyte composition of the vanadium redox flow battery, the dissociated active material compound is charged from tetravalent vanadium ions (VO ²⁺ ) to pentavalent vanadium ions (VO ₂ ⁺ ) according to the following Reaction Formula 1 when the switch may be, discharged, it may be five switches 4 from the vanadium ion (VO ₂ ⁺⁾ a vanadium ion (VO ^2+).

[Scheme 1]

The reducing agent may be a 5 a 4 a vanadium ion (VO ₂ ⁺⁾ to promote the reduction reaction of the vanadium ions (VO ^2+). _{In the case of long-term operation of a vanadium redox flow battery, pentavalent vanadium ions (VO 2} ⁺ ) oxidized by charging reaction due to cross-contamination of positive and negative electrolytes caused by long-term operation or deterioration of electrolyte due to exposure to air During this discharge, the tetravalent vanadium ions (VO ²⁺ ) are not reduced, so a problem in which the discharge capacity is reduced may occur. The reducing agent may be in the 5 generated in the discharge reaction of the vanadium ions is 4 (VO ₂ ⁺⁾ to promote the reduction reaction of the vanadium ions (VO ^2+), improving the discharge capacity.

)를 복수개 함유하는 화합물을 포함할 수 있다. 예를 들면, 상기 환원제는 3개의 카르복시기를 포함하고 수용성인 시트릭산(Citric Acid)(

)을 포함할 수 있다. In one embodiment, the reducing agent is a carboxyl group (

) may include a compound containing a plurality of. For example, the reducing agent contains three carboxyl groups and is water-soluble Citric Acid (Citric Acid) (

) may be included.

In one embodiment, the citric acid may be contained in a concentration of about 0.07M to 0.20M, about 0.10M to 0.20M, or about 0.07M to 0.08M. If the concentration of the citric acid is less than 0.07M, the reducing ability of the reducing agent may be low, so that the discharge capacity cannot be improved, and when the concentration of the citric acid exceeds 0.20M, the active material compound is oxidized / It may interfere with the reduction reaction to cause a problem of lowering the discharge capacity.

1 is a view for explaining a redox flow battery device according to an embodiment of the present invention.

1, the redox flow battery device 1000 according to an embodiment of the present invention is a redox flow battery stack 1100, a first electrolyte tank 1200 accommodating a positive electrolyte 1210, a negative electrolyte ( A second electrolyte tank 1300 accommodating 1310 , a first pump 1400 circulating the positive electrolyte 1210 , and a second pump 1500 circulating the negative electrolyte 1310 are included.

The redox flow battery stack 1100 has a structure in which a plurality of unit cells each having a cathode electrolyte reaction space and a cathode electrolyte reaction space divided by an ion exchange membrane 1130 are stacked, and each unit cell is A first electrode 1110 disposed inside the cathode electrolyte reaction space, a second electrode 1120 disposed inside the cathode electrolyte reaction space, and disposed between the first electrode 1110 and the second electrode 1120 , and an ion exchange membrane 1130 dividing the positive electrolyte reaction space and the negative electrolyte space.

The first electrolyte tank 1200 is located outside the redox flow battery stack 1100, can accommodate the positive electrode 1210, and is connected to the positive electrolyte reaction space of the redox flow battery stack 1100 to form a part of the circulation path of the cathode electrolyte 1210 . And the first pump 1400 may supply the positive electrolyte 1210 from the first electrolyte tank 1200 to the positive electrolyte reaction space of the redox flow battery stack 1100, and thus the redox flow battery The positive electrolyte 1210 that has already reacted in the positive electrolyte reaction space of the stack 1100 may be discharged to the first electrolyte tank 1200 .

The second electrolyte tank 1300 is located outside the redox flow battery stack 1100 , can accommodate the negative electrolyte 1310 , and is connected to the negative electrolyte reaction space of the redox flow battery stack 1100 . to form a part of the circulation path of the cathode electrolyte. And the second pump 1500 may supply the negative electrolyte 1310 from the second electrolyte tank 1300 to the negative electrolyte reaction space of the redox flow battery stack 1100, and thus the redox flow battery The negative electrolyte 1310 that has already reacted in the negative electrolyte reaction space of the stack 1100 may be discharged to the second electrolyte tank 1300 .

In this case, the electrolyte composition according to the embodiment of the present invention described above may be used as the positive electrolyte 1210 . Meanwhile, the negative electrolyte 1310 may not contain a reducing agent, unlike the positive electrolyte 1210 .

On the other hand, in the positive electrolyte reaction space and the negative electrolyte reaction space of the redox flow battery stack 1100, the reactions of the following Reaction Formulas 1 and 2 may occur, respectively.

[Scheme 1]

[Scheme 2]

)이 4가 바나듐 이온(

)환원되지 않아서 방전용량이 감소하는 문제점을 해결할 수 있다. According to the electrolyte composition of the present invention and a redox flow battery device including the same, since the electrolyte composition contains citric acid serving as a reducing agent, it deteriorates due to long-term operation, so that pentavalent vanadium ions (

) is a tetravalent vanadium ion (

) is not reduced, so the problem that the discharge capacity decreases can be solved.

Hereinafter, specific embodiments of the present invention will be described in detail. However, the following examples are only some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

[Examples and Comparative Examples]

After dissolving 1.6M of VOSO ₄ and 2.5M of H ₂ SO ₄ in water, 0M, 0.5M, 0.3M, 0.15M, and 0.075M of citric acid were dissolved to form a cathode electrolyte. Then, 1.6M of VOSO ₄ and 2.5M of H ₂ SO ₄ were dissolved in water to form a cathode electrolyte.

After connecting 40 mL of the positive electrolyte and 40 mL of the negative electrolyte to the redox flow battery stack, charge and discharge were performed for 6 cycles according to the experimental conditions shown in Table 1 below, and then charge capacity, discharge capacity, energy efficiency, and cell resistance etc. were measured.

current density charging condition discharge condition Rest CC Mode CC Mode CC Mode 80mA/cm2 1.6 V 2 A 1 V 2 A 5 min

[Experimental example]

2 is a graph showing the results of measuring the discharge capacity and cell resistance according to the molar concentration of citric acid, and Table 2 below shows the measured charge capacity, discharge capacity, energy efficiency, and cell resistance.

reducing agent
Molarity (M) charge
[Ahr] discharge
[Ahr] V.E (%) C.E (%) E.E (%) cell resistance 2nd END 0.5M 0.51 0.42 77.32 82.97 64.14 2.03 2.25 0.3M 0.65 0.56 80.30 85.97 69.03 1.68 1.78 0.15M 1.36 1.31 83.64 92.08 77.01 1.54 1.54 0.075M 1.03 0.98 85.68 94.88 81.29 1.30 1.33

Referring to FIG. 2 and Table 2, when the concentration of citric acid added to the positive electrode electrolyte is 0.3M and 0.5M, when the concentration is 0.15M, 0.075M, charge capacity, discharge capacity (discharge), energy Efficiency (VE, CE, EE) was higher, and cell resistance was lower. Specifically, compared to the case of applying the positive electrode containing 0.5M citric acid, when the positive electrolyte containing 0.075M and 0.15M of citric acid was applied, the discharge capacity was improved by about 151% and about 235%, respectively.

Therefore, the concentration of citric acid added to the positive electrode electrolyte is preferably about 0.070M to 0.20M, preferably 0.13M to 0.17M or 0.070M to 0.080M.

3 is a graph showing the result of measuring the discharge capacity according to the charge/discharge cycle.

Referring to FIG. 3 , when a cathode electrolyte containing 0.15M and 0.75M citric acid is applied, it can be seen that the discharge capacity is relatively excellent, and the discharge capacity is maintained for 6 cycles.

4A and 4B are graphs showing the results of measuring the discharge capacity and energy efficiency according to the charge/discharge cycle when a positive electrolyte containing 0.15M citric acid is applied, and FIGS. 5A and 5B are 0.075M citric acid It is a graph showing the results of measuring the discharge capacity and energy efficiency according to the charge/discharge cycle in the case of applying a cathode electrolyte containing

Referring to FIGS. 4A, 4B, 5A and 5B, when a positive electrolyte containing 0.15M citric acid was applied, the discharge capacity was lowered as the charge/discharge cycle progressed, but the 0.075M sheet When the positive electrolyte containing ric acid was applied, the discharge capacity was rather increased up to 15 cycles, and the discharge capacity was maintained constant after 15 cycles. Specifically, when a cathode electrolyte containing 0.15M of citric acid was applied, a degradation rate of about 30% was observed after 35 cycles, but when a cathode electrolyte containing 0.075M of citric acid was applied, the discharge capacity was constant from 15 cycles. appeared to be maintained.

In addition, when a cathode electrolyte containing 0.15 M citric acid was applied, the energy efficiency slightly increased as the charge/discharge cycle progressed, and when a cathode electrolyte containing 0.075 M citric acid was applied, the energy efficiency was constant. appeared to be maintained.

6 is a graph showing the measurement results of the discharge capacity and the cell resistance according to the mixing time (stirring time) after adding 0.15 M of citric acid to the electrolyte.

Referring to FIG. 6 , when 0.15 M of citric acid was added and mixed for 24 hours, the discharge capacity was the highest and the cell resistance was the lowest. Therefore, it is judged that it is most preferable to mix for about 20 to 28 hours after mixing the reducing agent citric acid.

Table 3 below shows when citric acid was not added to the positive electrolyte and negative electrolyte (Comparative Example 1), when 0.15 M of citric acid was added only to the positive electrolyte (Example), and when 0.15 M of citric acid was added only to the negative electrolyte The charge/discharge capacity, energy efficiency and cell resistance measured in (Comparative Example 2) are shown.

division charge
[Ahr] discharge
[Ahr] V.E (%) C.E (%) E.E (%) cell resistance Results (whether improvement) 2nd END Comparative Example 1 0.41 0.39 83.89 94.03 78.88 1.56 1.59 Bare Example 0.99 0.93 83.13 94.57 78.61 1.60 1.61 Discharge capacity 138%↑ Comparative Example 2 - - 31.29 1.73 0.55 - - -

Referring to Table 3, when 0.15 M of citric acid was added only to the negative electrolyte (Comparative Example 2), there was no increase in discharge capacity compared to the case where citric acid was not added to the positive electrolyte and the negative electrolyte (Comparative Example 1). However, when 0.15 M of citric acid was added only to the positive electrolyte (Example), the discharge capacity increased by about 138%. Therefore, the reducing agent is preferably added to the positive electrolyte. Although the above has been described with reference to the preferred embodiment of the present invention, those skilled in the art can variously modify and change the present invention within the scope without departing from the spirit and scope of the present invention as set forth in the following claims. You will understand that there is

1000: redox flow battery device 1100: redox flow battery stack
1210: positive electrolyte 1200: first electrolyte tank
1310: negative electrolyte 1300: second electrolyte tank
1400: first pump 1500: second pump

Claims (3)

In the electrolyte composition applied as a positive electrolyte of a redox flow battery,
water-based solvents;
an acid salt compound dissolved in the solvent and comprising at least one selected from the group consisting of _{H 2} SO ₄ , HCl, H ₃ PO ₄ and HNO _{3 ;}
an active material compound dissolved in the solvent and comprising at least one selected from the group consisting of _{VCl 3} , V ₂ O ₅ , VOSO ₄ , V ₂ O ₃ , V ₂ O ₄ and NH ₄ VO _{3 ;} and
An electrolyte composition comprising a citric acid reducing agent dissolved in the solvent. According to claim 1,
The citric acid reducing agent, characterized in that contained in a concentration of 0.07M to 0.20M, the electrolyte composition. redox flow battery stack;
a first electrolyte tank accommodating the anode electrolyte;
a second electrolyte tank accommodating the negative electrolyte;
a first pump for circulating the cathode electrolyte so that the cathode electrolyte of the first electrolyte tank is supplied to the cathode electrolyte reaction space of the redox flow battery stack;
and a second pump for circulating the negative electrolyte so that the negative electrolyte of the second electrolyte tank is supplied to the negative electrolyte reaction space of the redox flow battery stack,
The positive electrolyte is characterized in that it comprises the electrolyte composition according to claim 1, a redox flow battery device.

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