Electrolyte for amine-bromine two-electron type redox flow batteries, its use, and redox flow batteries

Abstract

The present invention discloses an electrolyte for an amine-bromine two-electron redox flow battery, its use, and a redox flow battery, which belong to the field of redox flow batteries. The electrolyte uses an amino compound in which the ortho position of the amino is an electron-withdrawing group, and reacts this with positively charged bromine to form an amine bromine compound, thereby stabilizing the positive bromine and realizing a reversible two-electron transfer reaction of bromine ions to the amino compound. Amine compounds have different solubilities and generate different voltages depending on the difference in their substituents, so they have a wide range of adjustability and applicability, and can be used in acidic, neutral, and weakly alkaline redox flow battery systems. A redox flow battery assembled using an electrolyte prepared by this reaction has the advantages of low cost and high energy density, and can achieve a long cycle life and high battery efficiency.

Description

[Technical Field]

[0001] This application relates to an electrolyte for redox flow batteries, specifically an electrolyte for amine-bromine two-electron type redox flow batteries, its use, and redox flow batteries, and belongs to the field of redox flow batteries. [Background technology]

[0002] Renewable energy is becoming increasingly important in modern energy systems, but it still faces problems of discontinuity and instability, which limit its further development. This problem can be effectively mitigated by adjusting energy storage technologies. Among the many energy storage technologies, redox flow batteries are a promising energy storage technology that can be used in scenarios such as grid control on the power generation side and solar power control on the user side, due to their advantages such as uniquely designed capacity and output, long cycle life, and high safety. However, the energy density of current redox flow batteries is generally low; for example, in the case of all-vanadium redox flow batteries, the energy density is only 30-40 Wh L. -1 As a result, the cost of the electrolyte and system becomes relatively high. Bromine ions usually have high solubility and relatively good electrochemical activity, making them a promising cathode active material for development. Bromine has a rich variable valency and can theoretically realize multi-electron transfer reactions, but currently only one-electron transfer reactions between bromine ions and elemental bromine are utilized, and furthermore, the products that lose electrons are very unstable, thus limiting their energy density. [Overview of the project] [Problems that the invention aims to solve]

[0003] The present invention aims to provide a method for preparing a bromine-based two-electron transfer electrolyte and its use in a redox flow battery in order to solve the above technical problems. The present invention utilizes the fact that, based on one-electron transfer between a bromide ion and elemental bromine, elemental bromine further loses electrons and then reacts with an amino acid on an amine compound to which an electron-withdrawing group is linked, forming a nitrobromoamine compound, thereby realizing a two-step two-electron transfer reaction. This reaction expands the reversible valence reaction of bromine, expanding from a one-electron reaction from negative 1-valent to 0-valent to a two-electron reaction from negative 1-valent to positive 1-valent, thereby doubling the energy density. Furthermore, this reaction allows for flexible adjustment of solubility and voltage depending on the type of amino compound. A redox flow battery assembled using such a two-electron reaction electrolyte can achieve high energy density, high charge / discharge efficiency, and high stability, is low-cost, and can be applied to distributed energy storage systems requiring high energy density. To achieve the above objectives, the technical solutions employed by the present invention are as follows. [Means for solving the problem]

[0004] An electrolyte for a redox flow battery comprising a bromide ion, an amine compound in which the ortho position of the amino is an electron-withdrawing group, and a supporting electrolyte, wherein the amine compound in which the ortho position of the amino is an electron-withdrawing group has an electron-conducting group of its own kind, and the electrolyte does not contain a supporting electrolyte. Optionally, the electrolyte comprises a bromide ion, an amine compound in which the ortho position of the amino group is an electron-withdrawing group, and a supporting electrolyte. If the amine compound in which the ortho position of the amino group is an electron-withdrawing group has an electron-conducting group of its own, the electrolyte does not contain a supporting electrolyte.

[0005] Optionally, an amine compound in which the ortho position of the bromide ion or amino is an electron-withdrawing group is used as the active material for the positive electrode, and the amine compound in which the ortho position of the bromide ion or amino is an electron-withdrawing group undergoes oxidation and / or reduction reactions during the cycle of the redox flow battery.

[0006] Optionally, the bromine ions include one or more of hydrobromic acid, sodium bromide, potassium bromide, zinc bromide, ammonium bromide, zinc bromide, and other bromine ion-containing salts, preferably hydrobromic acid and zinc bromide.

[0007] Furthermore, the concentration of the bromine ions is 0 to 5 mol / L -1 , preferably 1 to 2 mol / L -1 .

[0008] The concentration of the bromine ions is 0.1 mol / L -1 , 0.5 mol / L -1 , 1 mol / L -1 , 2 mol / L -1 , 2.5 mol / L -1 , 3 mol / L -1 , 3.5 mol / L -1 , 4 mol / L -1 , 4.5 mol / L -1 , 5 mol / L -1 and is selected from any value or a range of values consisting of any two values among them.

[0009] Furthermore, the amine compound includes one or more of sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate, sulfonamide, succinimide, acetamide, phthalimide, saccharin, sodium pyrrolidone carboxylate, barbituric acid, dicyandiamide, methyl sulfonamide, cyanuric acid, trifluoromethanesulfonamide, and 2-aminopyrimidine, preferably one or more of sulfamic acid, sodium sulfamate, potassium sulfamate, and ammonium sulfamate.

[0010] Furthermore, the concentration of the amine compound is 0 to 5 mol / L -1 , preferably 1 to 2 mol / L -1 .

[0011] The concentration of the amine compound is 0.1 mol / L -1, 0.5 mol L -1 , 1 mol L -1 , 1.2 mol L -1 , 1.4 mol L -1 , 1.6 mol L -1 , 1.8 mol L -1 , 2 mol L -1 , 2.5 mol L -1 , 3 mol L -1 , 3.5 mol L -1 , 4 mol L -1 , 4.5 mol L -1 , 5 mol L -1 It is selected from any value among them or from a range of any two values.

[0012] The concentration of amine compounds depends on their own solubility; for example, the solubility of sodium sulfamate is 8 mol / L. -1 It is possible to reach this.

[0013] Furthermore, the supporting electrolyte comprises one or more of the following: sulfuric acid, acetic acid, hydroxyacetic acid, bromoacetic acid, potassium chloride, potassium acetate, sodium chloride, sodium acetate, and sodium sulfate, preferably one or more of sulfuric acid and potassium chloride, and is used in acidic and neutral environments, respectively. If the amino compound itself can ionize conductive ions, it is not necessary to add a supporting electrolyte separately; for example, sodium sulfamate may function as a supporting electrolyte as is.

[0014] Furthermore, the concentration of the supporting electrolyte is 0-4 mol L. -1 Preferably 1-2 mol L -1 That is the case.

[0015] The concentration of the supporting electrolyte is 0.1 mol L. -1 , 0.5 mol L -1 , 1 mol L -1 , 1.2 mol L -1 , 1.4 mol L -1 , 1.6 mol L -1 , 1.8 mol L-1 , 2 mol L -1 , 2.5 mol L -1 , 3 mol L -1 , 3.5 mol L -1 , 4 mol L -1 It is selected from any value among them or from a range of any two values.

[0016] The electrolyte is an aqueous solution containing bromide ions, an amine compound in which the ortho position of the amino group is an electron-withdrawing group, and a supporting electrolyte.

[0017] According to yet another aspect of the present invention, the use of the above-described redox flow battery electrolyte is provided, applied as the positive electrode electrolyte in a redox flow battery.

[0018] Furthermore, the negative electrode electrolyte of the redox flow battery contains one or more of the following: titanium sulfate, hexafluorotitanium acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate, preferably one or more of the following: titanium sulfate, cadmium sulfate, and zinc bromide.

[0019] According to yet another aspect of the present invention, the invention includes a positive electrode, a negative electrode, and a separator for separating the positive electrode and the negative electrode, wherein a positive electrode electrolyte is filled in the cavity on the positive electrode side, and a negative electrode electrolyte is filled in the cavity on the negative electrode side, and the positive electrode electrolyte comprises at least one of the electrolytes. A redox flow battery is provided in which the negative electrode electrolyte active material is one or more of the following: titanium sulfate, hexafluorotitanium acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate.

[0020] Specifically, the redox flow battery uses metal end plates, a current collector, an electrolyte flow frame, activated carbon felt, or graphite felt as electrodes, and includes a separator to separate the positive and negative electrodes and a rubber gasket for sealing. The cavity between the positive electrode current collector and the separator is filled with positive electrode graphite felt or carbon felt and positive electrode electrolyte, and the cavity between the negative electrode current collector and the separator is filled with negative electrode graphite felt or carbon felt and negative electrode electrolyte. The electrolyte is circulated between the cavity and the tank by either a magnetic centrifugal pump or a peristaltic pump, and the positive electrode electrolyte may be optionally sealed in the cavity without circulation to form a single redox flow battery.

[0021] Specifically, the metal end plate is selected from aluminum alloy plates, stainless steel plates, and other acid-resistant metal plates, preferably stainless steel plates; the current collector is selected from graphite plates and titanium plates, preferably titanium plates for the positive electrode current collector; and the separator is one of a perfluorosulfonic acid film, a porous polyolefin film, a sulfonated polyether ether ketone film, or a polybenzimidazole film, preferably a perfluorosulfonic acid film.

[0022] The electrolyte uses an amino compound in which the ortho position of the amino group is an electron-withdrawing group. This is reacted with positively charged bromine to form an amine-bromine compound, thereby stabilizing the positively charged bromine and enabling a reversible two-electron transfer reaction of the bromine ion to the amino compound. Amine compounds have different solubility and generate different voltages depending on their substituents, giving them broad adjustability and applicability, and they can be used in acidic, neutral, and weakly alkaline redox flow battery systems. Redox flow batteries assembled using the electrolyte prepared by this reaction have the advantages of low cost, high energy density, long cycle life, and high battery efficiency. [Effects of the Invention]

[0023] The beneficial effects of this application are as follows: 1) The electrolyte for redox flow batteries according to this invention utilizes the property of amino compounds having an electron-withdrawing group at the ortho position to ionize hydrogen ions and become negatively charged. This stabilizes the positively charged bromine intermediate product, which is formed when elemental bromine loses further electrons, and expands the one-electron transfer reaction between the original bromine ion and elemental bromine to a two-electron transfer reaction from the bromine ion to the amine-bromine compound. This doubles the theoretical capacity and theoretical energy density of the battery. 4 mol L -1 When converted to bromine salts, the electron concentration is 8 mol L -1 It has reached a capacity of 214 Ah L -1 When zinc is used as the negative electrode, the discharge voltage is 1.6V and the theoretical energy density is 342 Wh L. -1 It reaches. 2) A redox flow battery assembled using the electrolyte for redox flow batteries according to this invention can achieve lower battery polarization and higher voltage efficiency. Compared to bromine-based redox flow batteries, the electrical resistance of the electrolyte does not increase significantly when an amino compound is added, and the same voltage efficiency as conventional bromine-based redox flow batteries can be obtained. 3) In this invention, the amine-bromine compound formed from an amino compound and a positively charged bromine can have its positive valency reduced by the presence of a conjugated structure, thereby improving its stability. Therefore, a redox flow battery assembled using the electrolyte for redox flow batteries according to this invention can achieve a higher Coulombic efficiency, and the Coulombic efficiency without the addition of a complexing agent is equivalent to that of a conventional bromine-based redox flow battery with a complexing agent added, reaching 98% to 99%. Furthermore, for some amine-bromine compounds, the molecular volume is relatively large, so the requirements for the film are also relatively low. 4) The amino compounds used in this application have broad adjustability and applicability. Theoretically, if the ortho position of the amino group is an electron-withdrawing group such as a carbonyl or acyl group, it has the ability to bond with positively charged bromine, but the linkage of groups at other positions is not restricted, so the range of selectable groups is wide. Furthermore, depending on the type of amino compound, the solubility differs, and different electrode potentials can be observed, and it can be applied to acidic, neutral, and weakly alkaline environments, so it can be used with a variety of negative electrodes. 5) Some of the amino compounds used in this invention are inexpensive and readily available, and therefore the prepared electrolyte has the advantage of being low in price. For example, sulfamic acid is an inorganic solid acid that is widely used in other fields and is a common chemical industry raw material. 6) The electrolyte used in this invention can reduce the generation of elemental bromine, thereby lowering its corrosiveness, diffusivity, and volatility. It does not require the addition of a bromine complexing agent to the electrolyte, and the requirements for the battery seal and materials are not so stringent. Since the reaction between bromine and amino compounds is a two-electron reaction, the amount of bromine used in conventional bromine-based redox flow batteries can be reduced by half at the same electron concentration, thereby reducing corrosion to materials and harmful effects on the environment. Furthermore, in a weakly alkaline environment, the conversion from bromine ions to elemental bromine is difficult due to the effect of bromine disproportionation, but instead a one-step two-electron transfer reaction occurs from bromine ions to amine-bromine compounds, directly avoiding the generation of elemental bromine. [Brief explanation of the drawing]

[0024] [Figure 1] This figure shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 1 after 100 cycles. [Figure 2] This figure shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 2 after 100 cycles. [Figure 3] This figure shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 3 after 100 cycles. [Figure 4] This figure shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 4 after 100 cycles. [Figure 5] This figure shows the voltage efficiency of the batteries in Example 1 and Comparative Example 5 after 100 cycles. [Figure 6] This figure shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 6 after 100 cycles. [Figure 7] This is a charge / discharge graph of the redox flow battery in Example 1. [Modes for carrying out the invention]

[0025] The following examples are intended to further illustrate the present application, rather than to limit its scope. Unless otherwise specified, the raw materials used in the examples and comparative examples of this application were purchased commercially. A charging and discharging device from Shin'i Co., Ltd. was used for the battery characteristic testing. [Examples]

[0026] Assembly of a redox flow battery The electrolytes for the positive and negative electrodes have the same composition, both containing 1 mol L. -1 Zinc bromide, 2 mol L -1 Sodium sulfamate, 2 mol L -1 It consists of potassium acetate. Zinc bromide provides both zinc ions used in the negative electrode and bromide ions used in the positive electrode.

[0027] Assembling a single cell The single cell consists of end plates, a graphite plate as a current collector, 6 x 8 cm carbon felt as the positive and negative electrodes, a Nafion film as a perfluorosulfonic acid separator, and is composed of an electrolyte flow frame, silica gel gasket, end plates, positive electrode electrolyte and negative electrode electrolyte storage tanks, a pump, and piping.

[0028] Battery test A constant current charge / discharge mode is employed, and the electrolyte flow rate is 60 mL min. -1 The charge / discharge current is 40 mA cm⁻¹. -2The charge termination voltage is 2.0V and the discharge termination voltage is 0.1V. The average values ​​of Coulomb efficiency CE, voltage efficiency VE, and energy efficiency EE are detected over the first 100 charge-discharge cycles.

[0029] The redox flow batteries assembled in the other examples and comparative examples differed from those in Example 1 only in the electrolyte composition, which is shown in Table 1.

[0030] [Table 1] TIFF0007854259000002.tif75165

[0031] From the characteristic data of the batteries in Examples 1 to 5, it was found that by including an appropriate negative electrode active material, a bromine source necessary for the positive electrode, an electron-withdrawing group-containing amino compound, and a supporting electrolyte in the electrolyte, redox flow batteries can be obtained with high energy density, high Coulomb efficiency, high voltage efficiency, and high energy efficiency.

[0032] From Examples 1 and 2, if the electrolyte required for the positive electrode remains the same, the negative electrode active material can be various, such as Zn. 2+ Even if Zn is used as the negative electrode pair, Cd 2+ Even when using Cd as the negative electrode pair, it can exhibit high performance. 2+ Zn is better than the Cd negative electrode pair. 2+ It was found that the Zn negative electrode pair, due to its lower standard electrode potential, resulted in a higher battery voltage, leading to improved battery voltage efficiency and energy efficiency.

[0033] Examples 1 and 3 showed that within the range of selected amino compounds, the battery can exhibit high performance. The ortho position of the amino group in acetamide is a carbonyl group, and the ortho position of the amino group in sodium sulfamate is a sulfonic acid group. Since both of these are electron-withdrawing groups, they can bind to bromine and undergo a two-electron transfer reaction, thereby obtaining a high energy density. Each amino compound has a different electronic structure and different binding ability to bromine, resulting in different battery efficiencies.

[0034] Examples 1 and 4 show that if the amino compound itself can ionize conductive ions, high battery efficiency can be obtained without adding a supporting electrolyte. For example, sodium sulfamate itself ionizes sodium ions and therefore has an ion-conducting effect. Of course, not adding a supporting electrolyte lowers the conductivity of the solution and slightly reduces the voltage efficiency of the battery compared to adding a supporting electrolyte.

[0035] Examples 1 and 5 showed that within the range of selected bromine ion sources, the battery can exhibit high performance. Compared to Example 5, Example 1 uses zinc bromide as both a bromine source and a negative electrode active material, thus saving raw materials and reducing some costs.

[0036] Figure 1 shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 1 after 100 cycles. As can be seen from the figure, in Comparative Example 1, because no amino compound was added, the Coulomb efficiency of the battery remained at 81% under the same energy density conditions. This is mainly because, without the addition of the selected amino compound, bromine can only undergo a reversible one-electron reaction, and further charging leads to the charging of hypobromous acid or bromate, which have poor reversibility, causing side reactions and reducing the Coulomb efficiency.

[0037] Figure 2 shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 2 after 100 cycles. From the figure, it can be seen that in Comparative Example 2, although glycine is added as an amino compound, the ortho of the amino group of glycine is an electron-donating methylene group and cannot combine with bromine to undergo a reversible two-electron transfer reaction. Therefore, similar to the reaction that occurs in Comparative Example 1, the Coulomb efficiency is reduced.

[0038] Figure 3 shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 3 after 100 cycles. From the figure, it can be seen that in Comparative Example 3, although ethanolamine was added as the amino compound, the ortho amino group of ethanol is an electron-donating alcoholic hydroxyl group and cannot combine with bromine to undergo a reversible two-electron transfer reaction. Therefore, similar to the reaction that occurred in Comparative Example 2, the Coulomb efficiency decreased.

[0039] Figure 4 shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 4 after 100 cycles. From the figure, it can be seen that in Comparative Example 4, the Coulomb efficiency is very low because no bromine source was added. This indicates that the amino compound itself does not have redox activity and needs to combine with bromine to cause a reversible electron transfer reaction; otherwise, the oxygen evolution reaction will only occur at the positive electrode, resulting in extremely low Coulomb efficiency.

[0040] Figure 5 shows the voltage efficiency of the batteries in Example 1 and Comparative Example 5 after 100 cycles. From the figure, it can be seen that in Comparative Example 5, no supporting electrolyte was added, and acetamide itself could not provide conductive ions, resulting in low conductivity of the solution and low voltage efficiency.

[0041] Figure 6 shows the Coulomb efficiency of the batteries in Example 1 and Comparative Example 6 after 100 cycles. In Comparative Example 6, the selected amino compound was not added, and only a one-electron reaction was possible, so the energy density was less than half that of the two-electron reaction in Example 1. In addition, elemental bromine volatilizes and diffuses in the later stages of charging, resulting in a low Coulomb efficiency of the battery.

[0042] Figure 7 shows the charge / discharge graph of the redox flow battery of Example 1. From this figure, it can be seen that the battery has a capacity of 172 Wh L. -1 It was found that an energy density of this magnitude can be obtained, which corresponds to the two-electron transfer reaction of bromine. Even at this energy density, the battery can achieve high Coulomb efficiency, high voltage efficiency, and high energy efficiency.

[0043] In summary, the analysis above indicates that by using the electrolyte composition of the present invention, it is possible to realize the two-electron transfer reaction of bromine, enabling the stable and efficient operation of a redox flow battery at a high energy density.

[0044] Furthermore, the above are merely some embodiments and corresponding comparative examples of the present application and do not limit the present application in any way. Although the present application is shown with better embodiments as described above, these embodiments are not used to limit the present application. Those skilled in the art will know that making some modifications or alterations using the above technical content without departing from the technical solution of the present application is equivalent to equivalent embodiments and all falls within the scope of the technical solution.

Claims

1. An electrolyte for redox flow batteries, It contains a bromide ion, an amine compound in which the ortho position of the amino group is an electron-withdrawing group, and a supporting electrolyte. The amine compound comprises one or more of the following: sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate, sulfonamide, succinimide, acetamide, phthalimide, saccharin, sodium pyrrolidone carboxylate, barbituric acid, dicyanodiamine, methylsulfonamide, cyanuric acid, trifluoromethanesulfonamide, and 2-aminopyrimidine. An electrolyte for a redox flow battery, characterized in that, if the amine compound comprises one or more of sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate, and sodium pyrrolidone carboxylate, the electrolyte does not contain a supporting electrolyte.

2. The electrolyte for a redox flow battery according to claim 1, characterized in that the amine compound having an electron-withdrawing group at the ortho position of the bromide ion and amino is used as the active material for the positive electrode, and the amine compound having an electron-withdrawing group at the ortho position of the bromide ion and amino undergoes oxidation and / or reduction reactions during the cycle of the redox flow battery.

3. The electrolyte for a redox flow battery according to claim 1, characterized in that the bromide ion comprises one or more of hydrobromic acid, sodium bromide, potassium bromide, zinc bromide, ammonium bromide, zinc bromide, and other bromide ion-containing salts.

4. The electrolyte for a redox flow battery according to claim 1, characterized in that the supporting electrolyte contains one or more of sulfuric acid, acetic acid, hydroxyacetic acid, bromoacetic acid, potassium chloride, potassium acetate, sodium chloride, sodium acetate, and sodium sulfate.

5. The electrolyte is an aqueous solution containing bromide ions, an amine compound in which the ortho position of the amino group is an electron-withdrawing group, and a supporting electrolyte. The electrolyte for a redox flow battery according to claim 1, characterized in that the concentration of bromide ions is 0 to 5 mol L-1, the concentration of amine compounds is 0 to 5 mol L-1, and the concentration of supporting electrolyte is 0 to 4 mol L-1.

6. The electrolyte for a redox flow battery according to claim 5, characterized in that the concentration of bromide ions is 1 to 2 mol L-1, the concentration of amine compounds is 1 to 2 mol L-1, and the concentration of supporting electrolyte is 1 to 2 mol L-1.

7. Use of the electrolyte for redox flow batteries according to any one of claims 1 to 6 as a positive electrode electrolyte in a redox flow battery.

8. The use according to claim 7, characterized in that the active material of the negative electrode electrolyte of the redox flow battery contains one or more of the following: titanium sulfate, hexafluorotitanium acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate.

9. The device includes a positive electrode, a negative electrode, and a separator for separating the positive electrode and the negative electrode, wherein the cavity on the positive electrode side is filled with a positive electrode electrolyte, and the cavity on the negative electrode side is filled with a negative electrode electrolyte, and the positive electrode electrolyte includes at least one of the electrolytes described in any one of claims 1 to 6. A redox flow battery characterized in that the negative electrode electrolyte active material is one or more of the following: titanium sulfate, hexafluorotitanium acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate.

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