An amine-bromine dual-electron flow battery electrolyte and its application and flow battery

Abstract

The application discloses an amine bromine two-electron flow battery electrolyte and application and a flow battery, and belongs to the flow battery field. The amino compound with an electron-withdrawing group at the ortho position is used in the electrolyte, and reacts with the bromine charged to the positive valence to form an amine bromine compound, thereby stabilizing the positive valence bromine, and realizing the reversible two-electron transfer reaction of the bromine ion to the amino compound. The amine compound has different solubilities and generates different voltages according to the difference of the substituents, and thus has wide adjustability and applicability, and can be used in an acidic, neutral and weak alkaline flow battery system. The flow battery assembled by using the electrolyte prepared by the reaction has the advantages of low cost and high energy density, and can obtain a long cycle life and high battery efficiency.

Description

TECHNICAL FIELD

[0001] The application relates to a flow battery electrolyte, in particular to an amine bromine two-electron flow battery electrolyte and application thereof and a flow battery, and belongs to the flow battery field. BACKGROUND

[0002] Renewable energy occupies an increasingly important position in modern energy systems, but it still has the problems of discontinuity and instability, which limits its further development. This problem can be effectively alleviated by regulating energy storage technology. Among many energy storage technologies, flow batteries have the advantages of independent design of capacity and power, long cycle life, high safety, etc., and can be used in power generation side grid regulation, user side photovoltaic regulation, etc. It is a very potential energy storage technology. However, the energy density of the current flow battery is generally low, such as the energy density of the all-vanadium flow battery is only 30-40 Wh L -1 , thus resulting in relatively high electrolyte and system cost. The solubility of bromide ion is usually high, and its electrochemical activity is relatively good, so it is a positive active material with development potential. Bromine has rich valence and can theoretically realize multi-electron transfer reaction, but currently bromine only utilizes the single-electron transfer reaction between bromide ion and bromine monomer, and the further loss of electrons is quite unstable, which limits the energy density. SUMMARY

[0003] To solve the above technical problems, the application aims to provide a configuration method of a bromine-based two-electron transfer electrolyte and its application in a flow battery. Based on the single-electron transfer between bromide ion and bromine monomer, the application utilizes the reaction between the further loss of electrons of bromine monomer and the amino group on the amine compound connected with an electron-withdrawing group to form a nitrogen bromoamino compound, realizing two-step two-electron transfer reaction. This reaction expands the reversible valence reaction of bromine from single-electron reaction from minus one valence to zero valence to double-electron reaction from minus one valence to plus one valence, so that the energy density is doubled. And according to the difference of the amino compound, the solubility and voltage can be flexibly adjusted. The flow battery assembled by using the electrolyte with two-electron reaction can realize high energy density, charging and discharging efficiency and stability, and has low cost, and can be applied to distributed energy storage systems with high energy density requirements. To achieve the above purpose, the technical scheme adopted by the application is as follows:

[0004] A flow battery electrolyte, the electrolyte comprising bromide ion, amine compound with amino group adjacent to electron-withdrawing group and supporting electrolyte; when the amine compound with amino group adjacent to electron-withdrawing group itself has an electron-donating group, the electrolyte does not contain supporting electrolyte.

[0005] Further, the bromide ion includes one or more of hydrobromic acid, sodium bromide, potassium bromide, zinc bromide, ammonium bromide, zinc bromide, and other bromide ion-containing salts, and preferably hydrobromic acid and zinc bromide.

[0006] Further, the bromide ion concentration is 0.1-5 mol / L -1 , and preferably 1-2 mol / L -1 .

[0007] Further, the amine compound includes one or more of sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate, sulfamide, succinimide, acetamide, phthalimide, saccharin, sodium pyrrolidone carboxylate, barbituric acid, dicyandiamide, methyl sulfonamide, cyanuric acid, trifluoromethanesulfonamide, and 2-aminopyrimidine, and preferably one or more of sulfamic acid, sodium sulfamate, potassium sulfamate, and ammonium sulfamate.

[0008] Further, the amine compound concentration is 0.1-5 mol / L -1 , and preferably 1-2 mol / L-1.

[0009] The concentration of the amine compound depends on its own solubility. For example, the solubility of sodium sulfamate can reach 8 mol / L -1 .

[0010] Further, the supporting electrolyte includes one or more of sulfuric acid, acetic acid, glycolic acid, bromoacetic acid, potassium chloride, potassium acetate, sodium chloride, sodium acetate, and sodium sulfate, and preferably one or more of sulfuric acid and potassium chloride for use in acidic and neutral environments, respectively. When the amine compound itself can ionize to generate conductive ions, the supporting electrolyte can not be added, such as sodium sulfamate which can be directly used as the supporting electrolyte.

[0011] Further, the supporting electrolyte concentration is 0.1-4 mol / L -1 , and preferably 1-2 mol / L -1 .

[0012] The electrolyte solution is an aqueous solution containing bromide ions, an amine compound with an electron-withdrawing group at the ortho position, and a supporting electrolyte.

[0013] According to another aspect of the present application, the electrolyte solution of the above-mentioned flow battery is applied as a positive electrolyte in a flow battery.

[0014] Further, the active material of the negative electrolyte of the flow battery includes one or more of titanium sulfate, hexafluorotitanic acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate, and preferably one or more of titanium sulfate, cadmium sulfate, and zinc bromide.

[0015] According to another aspect of the present application, a flow battery is provided, which comprises a positive electrode, a negative electrode and a separator for separating the positive and negative electrodes, a positive electrode electrolyte is filled in the positive electrode side cavity, and a negative electrode electrolyte is filled in the negative electrode side cavity; the positive electrode electrolyte comprises at least one of the above-mentioned electrolytes;

[0016] The negative electrode electrolyte active substance is one or two or more of titanium sulfate, hexafluorotitanic acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide and zinc acetate.

[0017] Specifically, the flow battery comprises a metal end plate, a current collector, a liquid flow frame, an active carbon felt or graphite felt as an electrode, a separator for separating the positive and negative electrodes, and a rubber gasket for sealing, a positive electrode graphite felt or carbon felt and a positive electrode electrolyte are filled in the cavity between the positive electrode current collector and the separator, and a negative electrode graphite felt or carbon felt and a negative electrode electrolyte are filled in the cavity between the negative electrode current collector and the separator; the electrolyte is circulated between the cavity and the storage tank by one of a magnetic centrifugal pump or a peristaltic pump, the positive electrode electrolyte can be optionally circulated and sealed in the cavity, serving as a single flow battery.

[0018] Specifically, the metal end plate can be any one of an aluminum alloy plate, a stainless steel plate and other acid-resistant metal plates, and is preferably a stainless steel plate; the current collector can be any one of a graphite plate and a titanium plate, and the positive electrode current collector is preferably a titanium plate; the separator can be any one of a perfluorosulfonic acid membrane, a porous polyolefin membrane, a sulfonated polyether ether ketone membrane and a polybenzimidazole membrane, and is preferably a perfluorosulfonic acid membrane.

[0019] The amine compound with an amino group ortho to an electron-withdrawing group is used in the electrolyte, reacts with bromine charged to a positive valence to form an amine bromide compound, thereby stabilizing the positive valence bromine, and realizing a reversible two-electron transfer reaction of bromine ions to the amine bromide compound. The amine compound has different solubilities and produces different voltages according to different substituents, and thus has wide adjustability and applicability, and can be used in acidic, neutral and weakly alkaline flow battery systems. The flow battery assembled by using the electrolyte prepared by the reaction has the advantages of low cost and high energy density, and can obtain a long cycle life and a high battery efficiency.

[0020] The beneficial effects that can be produced by the present application include:

[0021] The electrolyte provided in the present application has the characteristics of two-electron transfer, and is suitable for a low-cost high-energy-density flow battery system.

[0022] 1) The electrolyte of the flow battery provided in the present application utilizes the characteristic that the amino compound containing an electron-withdrawing group at the ortho position can ionize hydrogen ions to make itself negatively charged, which can stabilize the positive bromine intermediate after further losing electrons from elemental bromine, and thus expand the single-electron transfer reaction between bromide ions and elemental bromine to a double-electron transfer reaction from bromide ions to amine bromide compounds. Thus, the theoretical capacity and theoretical energy density of the battery can be doubled. With 4 mol L -1 of bromide salt, the electron concentration can reach 8 mol L -1 , the battery capacity reaches 214 Ah L -1 , with zinc as the negative electrode, the discharge voltage can reach 1.6 V, and the theoretical energy density can reach 342 Wh L -1 .

[0023] 2) The flow battery assembled using the electrolyte provided in the present application can achieve lower battery polarization and higher voltage efficiency. Compared with the bromine-based flow battery, the resistance of the electrolyte does not increase significantly after adding the amino compound, so the voltage efficiency can be similar to that of the traditional bromine-based flow battery.

[0024] 3) The amine bromide compound formed by the amino compound and the positive bromine in the present application can reduce the positive valence of bromine due to the existence of the conjugated structure, thereby improving its stability. Thus, the flow battery assembled using the electrolyte provided in the present application can achieve higher coulombic efficiency, which can be flat with the traditional bromine-based flow battery after adding a complexing agent without adding a complexing agent, which can reach 98%-99%. And for some amine bromide compounds, their molecular volume is relatively large, so the requirement for the membrane is also relatively low.

[0025] 4) The amino compound used in the present application has wide adjustability and adaptability. In theory, the ortho position of the amino group is an electron-withdrawing group, i.e., it has the ability to bind positive bromine, such as carbonyl and acyl, and the connection of groups at other positions is not limited, so the range of selection is very wide. In addition, according to the different types of amino compounds, they can have different solubilities and exhibit different electrode potentials, and can be suitable for acidic, neutral and weak alkaline environments, so they can match different negative electrodes.

[0026] 5) Some amino compounds used in the present application have the characteristics of being cheap and easy to obtain, so the electrolyte configured has the advantage of low price. For example, aminosulfonic acid is an inorganic solid acid, which is widely used in other fields and is a common chemical raw material.

[0027] 6) The electrolyte used in this application can reduce the generation of bromine element, thereby reducing its corrosiveness, diffusivity and volatility, and there is no need to add bromine complexing agent in the electrolyte, and the requirements for the sealing and materials of the battery are not so strict. Since the reaction of bromine with amino compounds is a two-electron reaction, under the same electron concentration, the amount of bromine used can be half of that of the traditional bromine-based flow battery, thereby reducing its corrosion to materials and harm to the environment. In addition, in a weak alkaline environment, the conversion of bromide ions to bromine element will be difficult to proceed due to the disproportionation of bromine, and instead a one-step two-electron transfer reaction of bromide ions to amine bromide compounds, thereby directly avoiding the generation of bromine element. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Coulomb efficiency plot for Example 1 and Comparative Example 1 battery cycled for 100 cycles.

[0029] Figure 2 Coulomb efficiency plot for Example 1 and Comparative Example 2 battery cycled for 100 cycles.

[0030] Figure 3 Coulomb efficiency plot for Example 1 and Comparative Example 3 battery cycled for 100 cycles.

[0031] Figure 4 Coulomb efficiency plot for Example 1 and Comparative Example 4 battery cycled for 100 cycles.

[0032] Figure 5 Voltage efficiency plot for Example 1 and Comparative Example 5 battery cycled for 100 cycles.

[0033] Figure 6 Coulomb efficiency plot for Example 1 and Comparative Example 6 battery cycled for 100 cycles.

[0034] Figure 7 Charge-discharge curve plot for the flow battery of Example 1. DETAILED DESCRIPTION

[0035] The following examples are further illustrations of the present application and are not intended to limit the scope of the present application. Unless otherwise indicated, the materials used in the examples and comparative examples of the present application were purchased commercially. The battery performance tests used a new wei charge-discharge instrument.

[0036] Example 1

[0037] Assemble the flow battery:

[0038] The positive and negative electrolyte compositions are the same, both composed of 1 mol L -1 of zinc bromide, 2 mol L -1 of sodium sulfamate, 2 mol L -1potassium acetate. The zinc bromide provides both zinc ions for the negative electrode and bromide ions for the positive electrode.

[0039] Assembly of single cell:

[0040] The structure of the single cell includes end plates, graphite plates as current collectors, 6x8 cm carbon felt as positive and negative electrodes, Nafion membrane as a perfluorosulfonic acid separator, liquid flow frame, silica gel pad, end plate, positive and negative electrolyte storage tank and pump, and pipeline.

[0041] Battery test:

[0042] The constant current charge and discharge mode was adopted, the flow rate of the electrolyte was 60 mL min -1 , the charge and discharge current was 40 mA cm -2 , the charge cut-off voltage was 2.0 V, and the discharge cut-off voltage was 0.1 V. The average values of the coulombic efficiency CE, voltage efficiency VE, and energy efficiency EE before 100 cycles of charge and discharge were detected.

[0043] Other examples and comparative examples of assembled flow batteries only differ in the composition of the electrolyte from Example 1, as shown in Table 1.

[0044] Table 1 Composition and performance of batteries of different examples and comparative examples

[0045]

[0046]

[0047] From the battery performance data of Examples 1-5, it can be seen that when the electrolyte contains a suitable negative active material, a bromine source required by the positive electrode, an amino compound containing an electron-withdrawing group, and a supporting electrolyte, the flow battery can obtain higher energy density, coulombic efficiency, voltage efficiency, and energy efficiency.

[0048] As can be seen from Example 1 and Example 2, when the electrolyte required by the positive electrode is unchanged, the negative active material can be selected from a variety of materials, such as Zn 2+ / Zn as the negative electrode pair or Cd 2+ / Cd as the negative electrode pair, both of which can produce high performance. Compared with the Cd 2+ / Cd negative electrode pair, the Zn 2+ / Zn negative electrode pair has a lower standard electrode potential, so the voltage of the battery is higher, and the voltage efficiency and energy efficiency of the battery are also higher.

[0049] As can be seen from Example 1 and Example 3, in the selected range of amino compounds, the batteries can all be opened with higher performance. The amino group ortho to the acetamide is a carbonyl group, and the amino group ortho to the sodium sulfamate is a sulfonic acid group, both of which are electron-withdrawing groups, so they can all combine with bromine to undergo a two-electron transfer reaction, thereby obtaining a higher energy density. Because the electronic structure of each amino compound is different, its ability to combine with bromine is also different, so it exhibits different battery efficiencies.

[0050] As can be seen from Example 1 and Example 4, when the amino compound itself can ionize to conduct ions, without adding a supporting electrolyte, a higher battery efficiency can also be obtained. For example, sodium sulfamate itself can ionize to sodium ions, thus having the effect of conducting ions. Of course, compared to adding a supporting electrolyte, not adding a supporting electrolyte will reduce the conductivity of the solution, and the voltage efficiency of the battery will decrease somewhat.

[0051] As can be seen from Example 1 and Example 5, in the selected range of bromine ion sources, the batteries can all be opened with higher performance. Compared to Example 5, Example 1 uses zinc bromide as the bromine source, and also as the negative active material, so it can save raw materials and reduce some costs.

[0052] Figure 1 The graph of the coulombic efficiency of the batteries of Example 1 and Comparative Example 1 cycled for 100 cycles. As can be seen from the graph, under the same energy density conditions, the coulombic efficiency of the battery of Comparative Example 1, which does not add an amino compound, is only 81%. This is mainly because, without the addition of the selected amino compound, bromine can only reversibly undergo a one-electron reaction, and further charging will charge to hypobromous acid or bromic acid, which has relatively poor reversibility and will undergo side reactions, thus leading to a decrease in coulombic efficiency.

[0053] Figure 2 The graph of the coulombic efficiency of the batteries of Example 1 and Comparative Example 2 cycled for 100 cycles. As can be seen from the graph, although Comparative Example 2 adds glycine as an amino compound, the amino group ortho to glycine is an electron-donating methylene group, which cannot combine with bromine to undergo a reversible two-electron transfer reaction, so it will also lead to a lower coulombic efficiency, similar to Comparative Example 1.

[0054] Figure 3 The graph of the coulombic efficiency of the batteries of Example 1 and Comparative Example 3 cycled for 100 cycles. As can be seen from the graph, although Comparative Example 3 adds ethanolamine as an amino compound, the amino group ortho to ethanol is an electron-donating alcohol hydroxyl group, which cannot combine with bromine to undergo a reversible two-electron transfer reaction, so it will also lead to a lower coulombic efficiency, similar to Comparative Example 2.

[0055] Figure 4Coulomb efficiency plot of Example 1 and Comparative Example 4 battery cycled for 100 cycles. From the plot, it can be seen that in Comparative Example 4, without the addition of bromine source, the Coulomb efficiency is very low. This indicates that the amino compound itself does not have redox activity and needs to be combined with bromine to undergo reversible electron transfer reaction, otherwise only oxygen evolution reaction occurs at the positive electrode, resulting in very low Coulomb efficiency.

[0056] Figure 5 Voltage efficiency plot of Example 1 and Comparative Example 5 battery cycled for 100 cycles. From the plot, it can be seen that in Comparative Example 5, without the addition of supporting electrolyte, and the acetamide itself cannot provide conductive ions, so the conductivity of the solution is low, and thus the voltage efficiency is low.

[0057] Figure 6 Coulomb efficiency plot of Example 1 and Comparative Example 6 battery cycled for 100 cycles. In Comparative Example 6, without the addition of the selected amino compound, only a single electron reaction can occur, so the energy density is half that of the two-electron reaction in Example 1. Moreover, due to the volatilization and diffusion of bromine element in the later charging stage, the Coulomb efficiency of the battery is low.

[0058] Figure 7 Charge-discharge curve plot of the flow battery of Example 1, from which it can be seen that the battery can obtain an energy density of 172 WhL -1 , corresponding to a two-electron transfer reaction of bromine. At this energy density, the battery can still obtain high Coulomb efficiency, voltage efficiency and energy efficiency.

[0059] In summary, using the electrolyte composition of the present application, a two-electron transfer reaction of bromine can be achieved, so that the flow battery can be stably and efficiently operated at a high energy density.

[0060] In addition, the above only describes several embodiments and corresponding comparative examples of the present application, and does not limit the present application in any form. Although the present application is demonstrated as above with preferred embodiments, it is not intended to limit the present application. Any skilled person in the art, without departing from the scope of the technical solution of the present application, can make some changes or modifications to the above-mentioned technical content, which are equivalent to equivalent embodiments, and are within the scope of the technical solution.

Claims

1. A flow battery electrolyte, characterized in that: The electrolyte comprises bromide ions, an amine compound with an electron-withdrawing group at the ortho position of the amino group, and a supporting electrolyte; when the amine compound with an electron-withdrawing group at the ortho position of the amino group itself has an electron-transporting group, the electrolyte does not comprise a supporting electrolyte.

2. The flow battery electrolyte of claim 1, wherein: The bromide ions include one or more of hydrobromic acid, sodium bromide, potassium bromide, zinc bromide, ammonium bromide, zinc bromide, and other bromide ion-containing salts.

3. The flow battery electrolyte of claim 1, wherein: 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.

4. The flow battery electrolyte of claim 1, wherein: The supporting electrolyte includes one or more of sulfuric acid, acetic acid, glycolic acid, bromoacetic acid, potassium chloride, potassium acetate, sodium chloride, sodium acetate, and sodium sulfate.

5. The flow battery electrolyte of claim 1, wherein: The electrolyte is an aqueous solution comprising bromide ions, an amine compound with an electron-withdrawing group at the ortho position of the amino group, and a supporting electrolyte. Wherein, the bromide ion concentration is 0.1-5mol L -1 ; the amine compound concentration is 0.1-5mol L -1 ; the supporting electrolyte concentration is 0.1-4mol L -1 .

6. Use of the flow battery electrolyte of any one of claims 1-5 as a positive electrolyte in a flow battery.

7. The use of claim 6, wherein: The active material of the negative electrolyte of the flow battery includes one or more of titanium sulfate, hexafluorotitanic acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate.

8. A flow battery, characterized in that, The flow battery comprises a positive electrode, a negative electrode, and a separator for separating the positive and negative electrodes, the positive electrode side cavity is filled with a positive electrolyte, and the negative electrode side cavity is filled with a negative electrolyte; the positive electrolyte comprises at least one of the electrolytes of any one of claims 1-5; The active material of the negative electrolyte is one or more of titanium sulfate, hexafluorotitanic acid, titanium bromide, cadmium sulfate, cadmium bromide, cadmium chloride, lead chloride, stannous chloride, zinc bromide, and zinc acetate.

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