KR20210150075A - Electrolyte for redox flow battery, redox flow battery using the same and preparing method of active materials for redox flow battery - Google Patents

Abstract

The present invention provides an electrolyte for a redox flow battery including a naphthalene diimide compound represented by chemical formula 1. In chemical formula 1, M is K^+ or Na^+.

Description

Electrolyte for redox flow battery, redox flow battery and active material manufacturing method for redox flow battery

The present invention relates to an electrolyte solution for a redox flow battery, a redox flow battery using the same, and a method for manufacturing an active material for a redox flow battery. More specifically, it relates to an electrolyte for a redox flow battery using the prepared negative potential organic active material and a redox flow battery using the same.

In order to more effectively utilize intrinsically intermittent energy sources such as solar, wind, and hydroelectric power, the development of energy storage technology is very urgent.

Redox flow batteries are large-scale energy storage devices currently being put into practical use for vanadium and zinc-bromine. In the case of a vanadium redox flow battery, substances having oxidation numbers of vanadium II/III and IV/V are dissolved in acidic solutions of anode and cathode, respectively, and confined in a large tank, and then these electrolytes are transferred to the electrode using a pump and electrochemical reaction It has the principle of storing energy through the Dox reaction.

They have a significantly lower energy density than lithium-ion batteries and use large tanks to use a large amount of vanadium.

Redox flow batteries are not related to energy and power density, and they can be converted and stored into electrical energy by interlocking with a new and renewable energy conversion device. have.

A recently commercialized redox flow battery utilizes a vanadium-based redox couple as positive and negative charge carriers, and uses it as an electrolyte. However, vanadium prices are rising, and in order to increase the efficiency of building an energy storage device, development of an organic molecular active material that can replace vanadium to have a higher energy density is very active.

On the other hand, Republic of Korea Patent Publication No. 10-2014986 relates to an organic electrolyte and a redox flow battery containing the same, which has an excellent solubility and uses an electrolyte stable against moisture and heat to provide a battery with high energy density. Disclosed is an electrolyte, but there is no disclosure of a technique for increasing energy density by using a negative potential active material having increased solubility in a neutral electrolyte by replacing vanadium.

The present invention is to solve the above problems, to provide an electrolyte for a redox flow battery by preparing a neutral electrolyte using organic molecules as an organic active material for preparing a negative potential electrolyte.

In particular, a redox flow that can increase energy density by selecting naphthalene diimide, which is chemically stable and has high electron affinity, as an organic active material for negative potential electrolyte, and increases solubility in neutral electrolyte by introducing a substituent An object of the present invention is to provide an electrolyte for a battery.

Another object of the present invention is to provide a redox flow battery with increased energy density by using an electrolyte for a redox flow battery as a negative potential electrolyte.

Another object of the present invention is to provide a method for preparing an active material for a redox flow battery.

The above and other objects of the present invention can all be achieved by the present invention described below.

1. One aspect of the present invention relates to an electrolyte solution for a redox flow battery.

The redox flow battery electrolyte includes a naphthalene diimide compound represented by the following Chemical Formula 1.

[Formula 1]

Here, M is K ⁺ or Na ⁺ .

2. In the first embodiment, the redox flow battery electrolyte further includes a solvent, and the solvent is an aqueous solvent, an organic solvent, or a mixture thereof, and may be neutral.

3. In embodiments 1 or 2, the redox flow battery electrolyte may further include a supporting electrolyte.

4. In the above 1 to 3 embodiments, the naphthalene diimide compound may be an organic active material for a negative potential electrolyte.

5. In the second embodiment, the concentration of the naphthalene diimide compound in the redox flow battery electrolyte may be 0.01 to 10 M.

6. In the second embodiment, the redox flow battery electrolyte may have a voltage difference between the oxidation reaction and the reduction reaction of 0.8 V or less.

7. Another aspect of the present invention is a positive electrode cell comprising a positive electrode and a positive potential electrolyte;

a cathode cell disposed opposite to one side of the anode cell, the cathode cell including a cathode and a negative potential electrolyte; and

a separator disposed between the anode cell and the cathode cell; and

The negative potential electrolyte provides a redox flow battery including a naphthalene diimide compound represented by the following Chemical Formula 1.

[Formula 1]

Here, M is K ⁺ or Na ⁺ .

8. In the 7th embodiment, the positive potential electrolyte may include 4-hydroxy tempo (4-OH-TEMPO).

9. In the 7th or 8th embodiment, the molar concentration ratio of the naphthalene diimide compound and 4-hydroxy tempo (4-OH-TEMPO) may be 1: 2 to 1: 4.

10. In the above 7 to 9 embodiments, the voltage difference between the oxidation reaction and the reduction reaction of the negative potential electrolyte and the positive potential electrolyte may be 1.0 V or more.

11. Another aspect of the present invention provides a method for preparing an active material for a redox flow battery.

The method for preparing an active material for a redox flow battery includes the steps of (a) reacting naphthalene tetracarboxylic dianhydride with glycine to form an intermediate substituted with a glycinyl group; and

(b) reacting the intermediate with a carbonate; includes.

12. In the 11th embodiment, the carbonate may be sodium carbonate or potassium carbonate.

The present invention provides an electrolyte for a redox flow battery with increased energy density and increased stability of the redox reaction.

By substituting a glycinyl group in naphthalene diimide and forming a metal ion pair, an organic active material that is chemically stable and has high electron affinity can be effectively prepared, and the organic active material has increased solubility in a neutral solution. It can be operated in a neutral aqueous electrolyte and can be used as a negative potential electrolyte.

When the organic active material is used as a negative potential electrolyte, it is possible to significantly increase the energy density of the redox flow battery through the sequential movement of two electrons, and to significantly increase stability according to the charge/discharge cycle.

1 is a cyclic voltammetry from 30 mV/s to 500 cycles of an electrolyte containing a _{naphthalene diimide compound (K 2} -BNDI) containing 5 mM potassium ion pair in a 1 M KCl aqueous solution according to an embodiment of the present invention; analysis graph.
2 is a scan rate from 5 to 640 mV/s of an electrolyte containing a _{naphthalene diimide compound (K 2} -BNDI) containing 5 mM potassium ion pair in a 1 M KCl aqueous solution according to an embodiment of the present invention; ) is a cyclic voltammetry analysis graph.
_{Figure 3 is a schematic diagram showing the redox potential when the naphthalene diimide compound (K 2} -BNDI) according to an embodiment of the present invention has an ion pair and when there is no ion pair.
4 is a cyclic voltammetry from 30 mV/s to 500 cycles of an electrolyte containing a _{naphthalene diimide compound (Na 2} -BNDI) containing 5 mM sodium ion pair in a 1 M NaCl aqueous solution according to an embodiment of the present invention. analysis graph.
5 is a scan rate from 5 to 640 mV/s of an electrolyte containing a _{naphthalene diimide compound (Na 2} -BNDI) containing 5 mM sodium ion pair in a 1 M NaCl aqueous solution according to an embodiment of the present invention; ) is a cyclic voltammetry analysis graph.
6 is a schematic diagram of a fixed symmetric cell for evaluating the electrochemical stability of an electrolyte.
7 is a graph showing the results of a constant current test showing the retention capacity (Q) of 225 cycles at 70 mA/g _{of a naphthalene diimide compound (K 2} -BNDI) according to an embodiment of the present invention.
8 is a redox flow battery according to an embodiment of the present invention, 10 mM naphthalene diimide compound (K ₂ -BNDI) as a negative potential electrolyte, 20 mM 4-OH-TEMPO as a positive potential electrolyte and is a graph showing the cyclic voltammetry measured at a scan rate of 40 mV/s.
9 is a redox flow battery according to an embodiment of the present invention, in a flow cell having a flow rate of 15 mL/min and ^{a current density of 5 mA/Cm 2} , 25 mM of a naphthalene diimide compound (K ₂ - BNDI) as a negative-potential electrolyte and 100 mM 4-OH-TEMPO as a positive-potential electrolyte, and the constant current measurement results of charging and discharging in 20 cycles are shown.
10 is a redox flow battery according to an embodiment of the present invention, 10 mM naphthalene diimide compound (K ₂ -BNDI) as a negative potential electrolyte, and 20 mM 4-OH-TEMPO as a positive potential electrolyte, , shows the retention capacity (Q) and coulombic efficiency (CE) according to 100 cycles.
11 is a graph showing a constant current cycle according to a change in current density in a redox flow battery composed _{of 25 mM K 2} -BNDI and 100 mM 4-OH-TEMPO according to an embodiment of the present invention.
Figure 12 and coulombic efficiency (CE), the voltage efficiency (VE) in accordance with K ₂ and LES -BNDI current density in the redox flow cell consisting of 100 mM 4-OH-TEMPO in 25 mM According to one embodiment of the present invention Energy Efficiency (EE) is shown.
13 is a graph showing the coulombic efficiency (CE) and retention capacity for 100 cycles in a redox flow cell composed _{of 25 mM K 2} -BNDI and 100 mM 4-OH-TEMPO, according to an embodiment of the present invention; to be.
Figure 14 according to an embodiment of the 40 mM Na ₂ -BNDI with 160 mM 4-OH-TEMPO redox flow current density changes in the current density from 5 from the battery 20 mA / cm ² according to the present invention consisting of It is a graph showing the constant current cycle.
15 is a graph showing retention capacity and coulombic efficiency for 200 cycles in a redox flow battery composed _{of 40 mM Na 2} -BNDI and 160 mM 4-OH-TEMPO according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. However, the following drawings are provided only to help the understanding of the present invention, and the present invention is not limited by the drawings. In addition, since the shape, size, ratio, angle, number, etc. disclosed in the drawings are exemplary, the present invention is not limited to the illustrated matters.

Like reference numerals refer to like elements throughout. In addition, in describing the present invention, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

When 'including', 'having', 'consisting', etc. mentioned in this specification are used, other parts may be added unless 'only' is used. When a component is expressed in the singular, cases including the plural are included unless otherwise explicitly stated.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

When the positional relationship between two parts is described with ‘on’, ‘on’, ‘on’, ‘beside’, etc., unless ‘directly’ or ‘directly’ is used, between the two parts One or more other portions may be located.

Positional relationships such as 'upper', 'top', 'lower', and 'bottom' are only described based on the drawings, and do not represent absolute positional relationships. That is, the positions of 'upper' and 'lower' or 'upper surface' and 'lower surface' may be changed according to the observed position.

The present invention provides an electrolyte for a redox flow battery with increased energy density by introducing a substituent of two glycinyl groups to naphthalene diimide, an organic active material, to increase solubility in a neutral aqueous solution. .

Specifically, the electrolyte for a redox flow battery according to an aspect of the present invention includes a naphthalene diimide compound represented by the following Chemical Formula 1.

[Formula 1]

Here, M is K ⁺ or Na ⁺ .

The naphthalene diimide (hereinafter 'NDI') may have two electrons in one molecule, and has high electron affinity and thermal and oxidation stability.

In particular, the extended pi-conjugation (π-conjugation) formed on the polycyclic aromatic ring is very stable with minimal change in molecular structure during the reduction reaction.

The NDI has low solubility in water, but solubility increases when substituted with a glycinyl group having an ion pair, and the ion pair is very effective in increasing electron transport.

In the naphthalene diimide compound represented by Formula 1 ^{, when M is K +} , it is _{expressed as K 2} -BNDI, and when it is Na ⁺ , it is expressed as _{Na 2 -BNDI.}

In the redox flow battery electrolyte, the naphthalene diimide compound may be used alone or in a mixture of two.

The redox flow battery electrolyte further includes a solvent, and the solvent is an aqueous solvent, an organic solvent, or a mixture thereof, and the neutral solvent may be neutral as an aqueous, non-aqueous solvent, or a mixture thereof.

Specifically, the solvent is preferably a neutral aqueous system, and in the neutral aqueous system, the solute may be added as an organic active material to form a negative electrolyte.

The redox flow battery electrolyte may further include a supporting electrolyte.

The supporting electrolyte is not particularly limited, but LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCH ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, TEABF ₄ (tetraethylammonium tetrafluoroborate), TBABF ₄ (tetrabuthyl ammonium tetrafluoroborate), NaBF ₄ , NaPF ₆ , trimethyl sulfonyl chloride (trimethyl sulfonylchloride), (NH ₄ ) ₂ SO ₄ Any one or two or more selected from the group consisting of a combination thereof is possible.

The naphthalene diimide compound is an organic active material for a negative potential electrolyte.

The naphthalene diimide compound has a low negative potential, is capable of stable two electron movement, and can be used as a negative potential electrolyte (negolyte) among electrolytes for redox flow batteries.

The concentration of the naphthalene diimide compound in the redox flow battery electrolyte may be 0.01 to 10 M.

It does not form a precipitation in a neutral aqueous solvent within the above range, and may form a negative potential electrolyte.

The redox flow battery electrolyte may have a voltage difference between the oxidation reaction and the reduction reaction of 0.8 V or less.

In the case of the redox flow battery electrolyte, in the case of an aqueous neutral solvent, the voltage difference with respect to the standard electrode is 0.8 or less (-0.8 vs.

Another aspect of the present invention is a positive electrode cell comprising a positive electrode and a positive potential electrolyte; a cathode cell disposed opposite to one side of the anode cell, the cathode cell including a cathode and a negative potential electrolyte; and a separator disposed between the positive electrode cell and the negative electrode cell, wherein the negative potential electrolyte provides a redox flow battery including a naphthalene diimide compound represented by the following Chemical Formula 1.

[Formula 1]

Here, M is K ⁺ or Na ⁺ .

The positive potential electrolyte includes 4-hydroxy tempo (hereinafter '4-OH-TEMPO').

The 4-OH-TEMPO can reversibly transfer one electron to a potential of 0.6 V with respect to the reference electrode (Ag/AgCl), and when used as a positive potential electrolyte in a redox flow battery, increases the stability of the battery cycle can do it

The molar concentration ratio of the naphthalene diimide compound and 4-hydroxy tempo (4-OH-TEMPO) may be 1: 2 to 1: 4.

In the range of the molar concentration ratio, it is possible to maintain stability as the cycle increases.

A voltage difference between the oxidation reaction and the reduction reaction between the negative potential electrolyte and the positive potential electrolyte may be 1.0 V or more.

When the negative potential electrolyte selects the naphthalene diimide compound as a solute, and the positive potential electrolyte selects 4-OH-TEMPO as a solute, the voltage difference may increase the energy density to 1.0 V or more.

More specifically, the voltage may be 1.0 to 1.27 V.

A method for preparing an active material for a redox flow battery according to another aspect of the present invention comprises the steps of (a) reacting glycine with naphthalene tetracarboxylic dianhydride to form an intermediate substituted with a glycinyl group; and (b) reacting the intermediate with a carbonate.

First, glycine is added to naphthalene tetracarboxylic dianhydride to form an intermediate substituted with a glycinyl group.

At this time, the intermediate may be formed by refluxing using acetic acid.

Carbonate was added to the intermediate and reacted to prepare a naphthalene diimide compound containing a metal ion pair.

The naphthalene diimide compound may be used as an organic active material of the negative potential electrolyte.

The carbonate may be sodium carbonate or potassium carbonate.

When the carbonate is sodium carbonate or potassium carbonate, a negative potential electrolyte in which two electrons can move may be formed.

The yield of the active material for the redox flow battery may be 85 to 95%.

When the glycidyl group is substituted with the naphthalene precursor as a starting material, a naphthalene diimide compound can be obtained in high yield.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are only illustrative of the present invention and the scope of the present invention is not limited to the following examples.

Example 1. Preparation of organic active material for negative potential electrolyte

[Scheme 1]

A naphthalene diimide compound was prepared according to Scheme 1.

Glycine was added using Naphthalenetetracarboxylic dianhydride as a precursor and refluxed for 4 hours under acetic acid to form an intermediate substituted with a glycinyl group, and K ₂ CO ₃ ^{containing K +} ions and Na ₂ CO ₃ containing ^{Na +} ions was reacted in a solution at 60 ° C. for 12 hours to prepare _{naphthalene diimide compounds K 2} -BNDI and Na _{2 -BNDI in 90% yield.}

Experimental Example 1. Confirmation of electrochemical properties of naphthalene diamide compound

1 is a cyclic voltammetry from 30 mV/s to 500 cycles of an electrolyte containing a _{naphthalene diimide compound (K 2} -BNDI) containing 5 mM potassium ion pair in a 1 M KCl aqueous solution according to an embodiment of the present invention; analysis graph.

1, using K2-BNDI as a redox couple ([K ₂ -BNDI]/[K ₂ -BNDI] ^1- and [K ₂ -BNDI] ^1- /[K ₂ -BNDI] ^2- ) , two-step single electron transfer with potentials (E1/2) of -0.40 (c1/a1) and -0.67 (c2/a2) with respect to the reference electrode (Ag/AgCl) was confirmed.

In addition, it was confirmed that the two redox reactions were very stable and repeatable even in the cyclic voltammetry scan of 500 cycles.

2 is a scan rate from 5 to 640 mV/s of an electrolyte containing a _{naphthalene diimide compound (K 2} -BNDI) containing 5 mM potassium ion pair in a 1 M KCl aqueous solution according to an embodiment of the present invention; ) is a cyclic voltammetry analysis graph.

Referring to FIG. 2 , it was confirmed that the current density due to the redox reaction increased as the scanning speed increased, and the diffusion according to the redox reaction was controlled. In particular, the fact that the second reduction peak (c2) extends in the negative potential direction as the scanning speed increases indicates a gentle pseudo-reversible reaction of the _{K 2 -BNDI redox couple.}

As a result of measuring the diffusion coefficient, it was calculated to be 3.95 x 10 ^-6 and 1.95 x 10 ^-6 cm ² /s in the first and second reduction reactions, respectively, and in the first reaction, the electron transfer rate was estimated to be about 0.27 cm/s .

In order to confirm the potential change according to the redox reaction, calculations were performed according to the density functional theory using a computer.

_{Figure 3 is a schematic diagram showing the redox potential when the naphthalene diimide compound (K 2} -BNDI) according to an embodiment of the present invention has an ion pair and when there is no ion pair.

Referring to FIG. 3 , it was confirmed that the potential -0.39V of _{K 2 -BNDI in the first reduction reaction was similar to the measured value -0.40.}

In the second reduction reaction, a value of -0.98 V was calculated, which is 310 mV more negative than the actual measured value of -0.67.

Further addition of K+ ions _{forms [K 3} -BNDI] ^1- with a contact ion pair, which explains the discrepancy between the calculated values and the actual measurements.

The addition of K+ ions is related to a free energy charge of -8.0 kcal/mol, and when this energy is included, the redox potential becomes -0.63V, which is consistent with the experimental value.

Binding according to the addition of K+ ions to the reduced [K ₂ -BNDI] ^1- is 17.3 kcal/mol, which is an unfavorable reaction, and it can be seen that the formation of an ion pair is formed after the second reduction reaction. This reaction is diffusion limited and the hydrated K+ ions disperse to form ion pairs in aqueous solvents.

Considering the solvation energy of -70.6 kcal/mol, desolvation can be a factor in reducing the reaction rate in the second reduction reaction, leading to an expansion related to the scanning rate.

The above calculation indicates that monovalent anionic species such as _{[K 2} -BNDI] ^1- and [K ₃ -BNDI] ^1- in aqueous solution are continuously maintained after the first and second reduction reactions in an aqueous solvent _{, [K 2} - BNDI] ^2- phosphorus divalent anionic species were not retained due to addition of counter cations.

4 is a cyclic voltammetry from 30 mV/s to 500 cycles of an electrolyte containing a _{naphthalene diimide compound (Na 2} -BNDI) containing 5 mM sodium ion pair in a 1 M NaCl aqueous solution according to an embodiment of the present invention. analysis graph.

5 is a scan rate from 5 to 640 mV/s of an electrolyte containing a _{naphthalene diimide compound (Na 2} -BNDI) containing 5 mM sodium ion pair in a 1 M NaCl aqueous solution according to an embodiment of the present invention; ) is a cyclic voltammetry analysis graph.

4 and 5, it was confirmed that even when sodium ion pairs are formed, stable and repeatable regeneration is possible through a reversible reduction reaction.

Experimental Example 2. Evaluation of chemical and electrochemical stability of naphthalene diimide compound

The chemical electrochemical stability of K _{2 -BNDI was evaluated.}

6 is a schematic diagram of a fixed symmetric cell for evaluating the electrochemical stability of an electrolyte.

In the cell, _{chemical and electrochemical stability was evaluated using reduced K 2} -BNDI as a counter electrode as a redox couple.

Common active material 5mM [K ₂ -BNDI] is mixed with 1M KCl solvent and placed in the left cell, and the reduced active material 5mM [K ₂ -BNDI] ^2- is mixed with 1M KCl solvent and placed in the right cell to form a symmetrical cell did

7 is a graph showing the results of a constant current test showing the retention capacity (Q) of 225 cycles at 70 mA/g _{of a naphthalene diimide compound (K 2} -BNDI) according to an embodiment of the present invention.

The inset of FIG. 7 shows the change in voltage with respect to the capacitance.

The part indicated by the arrow indicates the shift of the potential in the first reduction reaction.

Referring to FIG. 7 , in the first cycle, potential stagnation of -0.44 and -0.69 with respect to the reference electrode (vs. Ag/AgCl) was confirmed, which is the potential (E _{1/2) according to the cyclic current voltage measurement of Experimental Example 1.} ) was consistent with the results.

As the cycle increased, the potential of the first reduction reaction was decreased, and when the portion indicated by the arrow in the inset was confirmed, it was overlapped with the stagnant graph of the second reduction reaction. This indicates the shift of the negative potential according to the corresponding oxidation reaction.

A decrease in the potential (c1) of the first reduction reaction and an increase in the second potential (c2) were not observed for 500 cycles, and it was confirmed that the time-dependent chemical reaction appeared only under constant current conditions.

When the applied potential was limited according to the first reduction reaction, this reduction of the reduction potential was not observed.

Identification of the voltage of the circuit open to air was confirmed to reduce this tendency in the redox flow cell system.

The electrochemical analysis results showed that during the second reduction reaction, contact ion pairs with ^{K + ions were involved.} Although the ion pair is neutralized after the second reduction reaction, it has been confirmed that K ⁺ _{ions around [K 2} -BNDI] can interfere with the first reduction reaction and cause unusual polarization of the potential, but this characteristic reduction reaction The morphology did not reduce the overall retention capacity of the two electron transport processes.

In addition, the symmetric cell was confirmed to be very stable for 225 cycles over 14 days, and the capacity reduction was only 0.042%/day, _{confirming that [K 2} -BNDI] had very redox stability.

Experimental Example 3. Redox flow battery performance evaluation

Using 4-OH-TEMPO (4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl) as a positive potential electrolyte (posolyte), [K ₂ -BNDI] was used to prepare a redox flow battery. prepared.

In the following, all solvents were 1 M KCl.

8 is a redox flow battery according to an embodiment of the present invention, 10 mM naphthalene diimide compound (K ₂ -BNDI]) as a negative potential electrolyte, 20 mM 4-OH-TEMPO as a positive potential electrolyte This is a graph showing the cyclic voltammetry measured at a scan rate of 40 mV/s.

9 is a redox flow battery according to an embodiment of the present invention, in a flow cell having a flow rate of 15 mL/min and ^{a current density of 5 mA/Cm 2} , 25 mM of a naphthalene diimide compound (K ₂ - BNDI) as a negative-potential electrolyte and 100 mM 4-OH-TEMPO as a positive-potential electrolyte, and the constant current measurement results of charging and discharging in 20 cycles are shown.

10 is a redox flow battery according to an embodiment of the present invention, 10 mM naphthalene diimide compound (K ₂ -BNDI) as a negative potential electrolyte, and 20 mM 4-OH-TEMPO as a positive potential electrolyte, , shows the retention capacity (Q) and coulombic efficiency (CE) according to 100 cycles.

8 to 10, when the 4-OH-TEMPO is selected as the positive potential electrolyte, the movement of a single electron is possible at a potential of +0.6 V with respect to the reference electrode (vs. Ag/AgCl), 1.0 V and It can represent a voltage difference of 1.27V.

It was confirmed that the voltage difference in the redox reaction of the redox flow battery was 1.0V or more.

It was confirmed that the average cell voltage exhibited a higher voltage than that of most conventional water-based organic redox flow batteries.

_{On the other hand, the ideal molarity ratio of K 2} -BNDI to 4-OH-TEMPO is 2:1 based on the number of electrons exchanged.

A decrease in capacity was confirmed in the above ratio, and it was confirmed that the capacity was reduced from 1.13 to 0.12 Ah/L for 100 cycles in a flow cell composed _{of 25 mM [K 2 -BNDI] and 50 mM 4-OH-TEMPO,} This promotes the instability of 4-OH-TEMPO.

In the case of adding an excess of positive potential electrolyte, the negative potential electrolyte can be stabilized, and the molar concentration ratio was increased to 1:4 in the flow cell.

Referring to FIG. 10 , the performance of a flow cell composed of 100 mM 4-OH-TEMPO and 25 mM [K _{2 -BNDI] in 1 M KCl aqueous solution was confirmed.}

It had a 96% coulombic efficiency at a current density of 5 mA/cm ² and 83.2% at an initial capacity of 1.25 Ah/L after 100 cycles, and the initial charge potential stagnant capacity was reduced while the total charge capacity was preserved.

This is due to residual ion pairs as described above.

During the first 20 cycles, mild fluctuations in capacity occur due to electrochemical stabilization reactions.

11 is a graph showing a constant current cycle according to a change in current density in a redox flow battery composed _{of 25 mM K 2} -BNDI and 100 mM 4-OH-TEMPO according to an embodiment of the present invention.

Figure 12 and coulombic efficiency (CE), the voltage efficiency (VE) in accordance with K ₂ and LES -BNDI current density in the redox flow cell consisting of 100 mM 4-OH-TEMPO in 25 mM According to one embodiment of the present invention Energy Efficiency (EE) is shown.

13 is a graph showing the coulombic efficiency (CE) and retention capacity for 100 cycles in a redox flow cell composed _{of 25 mM K 2} -BNDI and 100 mM 4-OH-TEMPO, according to an embodiment of the present invention; to be.

11 to 13 , the polarization curves of the 100% state of charge showed the highest power density at ^{37 mW/cm 2 .} The change in capacity from 5 to 20 mA/cm ² was at 10 mA/cm ² , respectively. At 1.0 Ah/L, 20 mA/cm ² 0.5 Ah/L.

Voltage efficiency (VE) was measured to be 91, 83, 72 and 60% at 5, 10, 15 and 20 mA/cm ² , respectively, and energy efficiency (EE) also showed a similar linear change trend.

13, it was confirmed that the capacity was stable at each current density without a large current change, similar to the 98% coulombic efficiency, and that the negative potential electrolyte composed _{of [K 2 -BNDI] under electrochemical conditions showed high stability during the entire 100 cycles in FIG.} indicated.

Figure 14 according to an embodiment of the 40 mM Na ₂ -BNDI with 160 mM 4-OH-TEMPO redox flow current density changes in the current density from 5 from the battery 20 mA / cm ² according to the present invention consisting of It is a graph showing the constant current cycle.

15 is a graph showing retention capacity and coulombic efficiency for 200 cycles in a redox flow battery composed _{of 40 mM Na 2} -BNDI and 160 mM 4-OH-TEMPO according to an embodiment of the present invention.

14 and 15 , even when a naphthalene diimide compound having a sodium ion pair is used as a negative potential electrolyte, 40 mM Na ₂ -BNDI in an aqueous solution of 1 M NaCl is dissolved to have high solubility, retention capacity and coulombic efficiency It was confirmed that there was an increase during this 200 cycle.

_{Therefore, it was confirmed that K 2} -BNDI and Na ₂ -BNDI formed from naphthalene diimide derivatives with increased solubility can be used as two electron transfer negative potential materials in aqueous neutral aqueous solution, and after charging the two electrons stored in naphthalene diimide It was stabilized by binding to contact cations, and energy efficiency and voltage efficiency reached 86% and 91%, respectively, in a flow cell composed _{of K 2 -BNDI as a negative-potential electrolyte and 4-OH-TEMPO as a positive-potential electrolyte.} , showed a capacity reduction of 0.042%/day in the symmetric cell, confirming that the stability was very high.

Up to now, the present invention has been looked at focusing on examples. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

Claims (12)

An electrolyte for a redox flow battery comprising a naphthalene diimide compound represented by the following Chemical Formula 1:
[Formula 1]

Here, M is K ⁺ or Na ⁺ .
According to claim 1, wherein the redox flow battery electrolyte further comprises a solvent, the solvent is an aqueous solvent, an organic solvent or a mixture thereof, the redox flow battery electrolyte, characterized in that neutral.
The electrolyte for a redox flow battery according to claim 1, wherein the electrolyte for the redox flow battery further comprises a supporting electrolyte.
The electrolyte for a redox flow battery according to claim 1, wherein the naphthalene diimide compound is an organic active material for a negative potential electrolyte.
The redox flow battery electrolyte according to claim 2, wherein the concentration of the naphthalene diimide compound in the redox flow battery electrolyte is 0.01 to 10 M.
The electrolyte for a redox flow battery according to claim 2, wherein the voltage difference between the oxidation reaction and the reduction reaction of the electrolyte for the redox flow battery is 0.8 V or less.
an anode cell comprising an anode and a positive potential electrolyte;
a cathode cell disposed opposite to one side of the anode cell, the cathode cell including a cathode and a negative potential electrolyte; and
a separator disposed between the anode cell and the cathode cell; and
The negative potential electrolyte is a redox flow battery comprising a naphthalene diimide compound represented by the following Chemical Formula 1:
[Formula 1]

Here, M is K ⁺ or Na ⁺ .
The redox flow battery according to claim 7, wherein the positive potential electrolyte comprises 4-hydroxy tempo (4-OH-TEMPO).
The redox flow battery according to claim 8, wherein the molar concentration ratio of the naphthalene diimide compound and 4-hydroxy tempo (4-OH-TEMPO) is 1: 2 to 1: 4.
The redox flow battery according to claim 7, wherein the voltage difference between the oxidation reaction and the reduction reaction between the negative potential electrolyte and the positive potential electrolyte is 1.0 V or more.
(a) reacting glycine with naphthalene tetracarboxylic dianhydride to form an intermediate substituted with a glycinyl group; and
(b) reacting carbonate with the intermediate; redox flow battery active material manufacturing method comprising a.
The method of claim 11, wherein the carbonate is sodium carbonate or potassium carbonate.

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